# XP-39 II - The Groundhog Day Thread



## Shortround6 (Sep 22, 2020)

from an old thread with some edits, edits are in italics.

1, no test report the XP-39 did fly 390mph.
2. reports of continued oil overheating and/or high temperatures causing at least one flight to be cut short.
3, At least one report of high coolant temperatures.
4, reports or accounts of modifications done to oil and radiator ducts. Which did not solve the problem
5, accounts of how the AAC wanted a new drive shaft installed in the plane because of vibration problems or worries if the engine misfired. Until new drive shaft was fitted engine rpm was restricted to either 2600or 2700rpm. The New drive shaft was not fitted until after the plane went to Langley. No full power flights?
6 time available.
a, first flight April 6th, 15/_20_ minutes.
b 2nd flight April 7th cut short due to oil temp
c. 3rd and 4th flights on April 22 total 47 minutes.
d 5th flight April 23, Nose wheel fails after manual lowering of landing gear, 1 hour 40 minutes total flying time in 5 flights.
_E. Taking out the 1st flight and 3rd & 4th flights we have either 33 or 38 minutes to split between flights 2 and 5. While I have not seen how long flight 5 was accounts say they spent at least some time trying to get the landing gear down._ 
_F. for the accounts that claim the XP-39 did 390mph on it's first flight, consider that the flight, depending on who wrote the account was either 15 or 20 minutes. In that short space of time our intrepid test pilot (James Taylor) would have had to take off, get the landing gear up, climb to 20,000ft, perform the speed run, descend (dive?) back down to ground level, lower flaps and landing gear, line up on the run way and land the plane. Taylor would have had to do this in plane that had never been flown before although taxi tests up to 80mph had been performed several months earlier.
G. Birch Mathew's book 'Cobra' says 
"Taylor climbed into the diminutive interceptor, warmed the engine and lifted of uneventfully for a 20 minute flight on 6 April 1939. The only difficulty he experienced was an elevated oil temperature. The next day Taylor demonstrated the airplane for General Hap Arnold. He was forced to cut the flight short because once again oil temperatures shot up causing oil pressure to plummet." 
No mention of a high speed run in this account. _
e. accounts do not say what flying or tests were done in May of 1939. could have been some.
f. Plane is delivered to Langley on June 6th. After arrangements made at the end of April. 
7, Langley claimed that the oil cooling problem was resolved or minimized during initial flight tests by using a higher drag duct than originally fitted.

So, *if *the XP-39 did do 390mph or anywhere near to it it had to be done in May, (_repeating the above _none of the April flights were long enough to get to 20,000ft, do a high speed run and get back down on the ground again.) with a high drag oil cooler duct, a radiator that had problems (like at 350mph the radiator was supposed to have 16,900 cubic ft of air going through but only 10,250 cu ft was needed to cool the engine) and the engine was limited to 90% or less of rated rpm, unless the pilot disobeyed instructions.

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## GregP (Sep 22, 2020)

I still have a book from 1946 that says 390 mph. "U.S.Army Aircraft 1908 - 1946 SC - AEF - AAS - AAC - AAF," by James C. Fahey, published and distributed by SHIPS and AIRCRAFT, P.O. Box 48, Falls Church, Virginia. As you pointed out, Shortround, we do not have flight test data to back it up. But, and here's the rub .... all of the OTHER data I have checked against available period flight test reports matches said tests. That makes me wonder where they got the top speed. We all know it had to come from somewhere; it wasn't just "made up" as fake news.

I like your summary above. I believe that many of us doubt the 390 mph datum is accurate. But, not finding the test data doesn't mean it wasn't generated accurately in a flight test report that has been lost, or at least undiscovered, up to now.

But, let's remember that the P-39Q had a top speed of 385 mph at 8,300 pounds with 1,200 HP. 6.92 pounds per HP. The XP-39 weighed in WITH a turbocharger, at 6,204 pounds and had 1,150 HP. 5.39 pounds per HP. So, the XP-39 is down 50 HP and lighter by 2,100 pounds, which might be a good recipe for another 5 mph due to the power-to-weight ratio alone (22% better). We might not want to believe, but it is entirely possible it DID go 390 mph in some test we have not yet found.

I don't think so and you don't think so, but I suppose we COULD be wrong ... who knows for sure? And that missing test may yet surface at some point. I'll say that I'm with you in thinking it did NOT go 390 mph ... but ... hey, maybe.

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## Mad Dog (Sep 22, 2020)

Shortround6 said:


> ......So, *if *the XP-39 did do 390mph or anywhere near to it it had to be done in May, (_repeating the above _none of the April flights were long enough to get to 20,000ft, do a high speed run and get back down on the ground again.) with a high drag oil cooler duct, a radiator that had problems (like at 350mph the radiator was supposed to have 16,900 cubic ft of air going through but only 10,250 cu ft was needed to cool the engine) and the engine was limited to 90% or less of rated rpm, unless the pilot disobeyed instructions.


Yes, but you're forgetting the XP-39 had no guns, no armour and virtually no equipment for those first few flights. It weighed less than 4000Lbs empty, which is one reason why it climbed to 20,000ft in five minutes. So if Bell had decided to make a carefully planned publicity speed run, twenty minutes might give time for the extra-lightweight prototype to climb to 20,000ft and make the run, and 47 minutes would be plenty. And the XP-39B without the turbo and weighing over 300Lbs more still managed 375mph in the thicker air at 15,000ft. So, no, you have not conclusively proven the XP-39 didn't fly at 390mph.


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## Shortround6 (Sep 23, 2020)

This rather depends on almost suicidal test pilots. 
What other aircraft in all of WW II established record setting climbs to altitude and did high speed runs in the first two hours of testing?

Let alone the first 20 minutes? 

There is no record of the plane making that fantastic climb to 20,000ft. like on what day?

There was no 47 minute flight, two flights in one day equeled 47 minutes. 
The plane was plagued with overheating issues at this time, mostly oil, and they spent 15 days trying to sort that out between flights 2 and 3? and yet we are supposed to believe that they hammered the crap out of the engine on the first flight to set all these marvelous performance records? 

Bell was lying like 2020 politician (pick one from either/any side) back in 1939. The XP-39 was supposed to weigh 5550lbs gross, it didn't, it was weighed at Wright field at 6,104lbs. Unless they added over 500lbs to the useful load that means the Bell was off by 500lbs on the empty weight Bell had admitted before hand that the gross weight had climbed to 5,855lbs before the plane was completed. 

NACA figured that the XP-39 was almost a flying parachute when they got it. The oil cooling problem had NOT been fixed and was causing even more drag than the original set up, the radiator was a disaster, the intercooler was only good for about 25% down to 12% of the cooling needed, and nobody has mentioned the fact that the engine was not allowed to run at full rpm/power on the days in question. 

See Bell's lies to the British about performance and the special aircraft needed to even get to 3% under the contract performance to keep the contract going.

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## overbeck (Sep 23, 2020)

Mad Dog said:


> And the XP-39B without the turbo and weighing over 300Lbs more still managed 375mph in the thicker air at 15,000ft. So, no, you have not conclusively proven the XP-39 didn't fly at 390mph.



If anything this argues against the 390 mph figure. Removing the turbo also deleted the large ducts for intercooler and turbine oil cooler air, which was the main reason for the change. An extra 300 lbs would have a very small effect on top speed. Induced drag doesn't change that much at moderate angles of attack.


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## Mad Dog (Sep 23, 2020)

Shortround6 said:


> ...What other aircraft in all of WW II established record setting climbs to altitude and did high speed runs in the first two hours of testing?....


 Which other manufacturer was as desperate as Bell to get an order to avoid going bust? Which then extends to how desperate a test pilot might be to keep his job that he'd agree to make such a flight. And then you have bravado and just plain guts. During the second flight of the Hawker Typhoon prototype, chief test pilot Philip Lucas noticed the fuselage had started to suffer a structural failure, with a tear large enough to push his hand through opening in one side. Lucas stubbornly refused to bailout, the accepted procedure in such a situation, and saved the prototype. Whilst he was awarded the George Medal for his bravery, he admitted in later years that one possible cause of the failure was some flight manouveres "not in the official test plan".


Shortround6 said:


> ....See Bell's lies to the British about performance and the special aircraft needed to even get to 3% under the contract performance to keep the contract going.


 The British would have rejected the whole order if Bell hadn't have been able to meet the "within 3% of 400mph" requirement. As I already mentioned, the British Direct Purchase Commission to the US weren't exactly the best and brightest, so I'm not surprised they signed some bad contracts. As it was, they were under pressure to buy just about anything. The P-40 snuck under the barrier because they arrived reasonably early and were judged suitable for the Middle East. By the time the P-400s arrived in the UK, we had loads of Spitfire Vs and the Hawker Typhoon was supposed to soon be sweeping the Luftwaffe from the sky. The Bf109F meant nothing without good altitude performance was going to be used as a fighter in the UK. The Desert requirement was already being met by the mediocre but trusted Tomahawk, and a "much-improved" Kittyhawk was being promised by an equally dishonest Curtis, leaving no role for the troublesome P-400s. Not surprisingly, the RAF jumped at the chance to offload the P-400s to the Russians.

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## GregP (Sep 23, 2020)

Good thing you stayed with a boring thread title that doesn't generate comments, huh, Shortround?


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## wuzak (Sep 23, 2020)

Mad Dog said:


> The British would have rejected the whole order if Bell hadn't have been able to meet the "within 3% of 400mph" requirement. As I already mentioned, the British Direct Purchase Commission to the US weren't exactly the best and brightest, so I'm not surprised they signed some bad contracts. As it was, they were under pressure to buy just about anything.



Most of the British order ended up in Russia. And they weren't close to the performance estimates (guarantees), which Bell based on an unarmed and unarmoured prototype.

Why do you think the BPC were "not the best and brightest"? Because they bought P-39s?




Mad Dog said:


> The P-40 snuck under the barrier because they arrived reasonably early and were judged suitable for the Middle East.



The P-40 was ordered because the RAF needed fighters and the P-40 was the only US fighter that had any chance of being available in a short period.

What made the P-40 suitable for the Middle East but not for northern Europe?


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## Mad Dog (Sep 23, 2020)

wuzak said:


> ......Why do you think the BPC were "not the best and brightest"? Because they bought P-39s?....


 Because they didn't say "No, none of this will do." They should have brought a pallet of RR Merlin engines with them and said, "Here, build me something round this, we'd rather wait for something better than order just anything." But they ordered the available P-40. If they had of insisted on the Merlin as the powerplant, we might have had a Merlin-engined P-38 in 1941, which would have been invaluable in every theatre and much more useful than the eventual P-40F/Kittyhawk MkII, and the Mustang MkI would have been a world-beater from the start.



wuzak said:


> ......The P-40 was ordered because the RAF needed fighters and the P-40 was the only US fighter that had any chance of being available in a short period....


 Agreed, but it doesn't say much for the state if the US industry when you consider the US was technically ahead in stressed-metal construction, wing design and turbocharging, that the best they could provide was the Tomahawk. The Mustang was definitely a better effort, but, IIRC, a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109..... After all, the American bombers were very good, probably the best available anywhere until the Mosquito arrived.



wuzak said:


> .....What made the P-40 suitable for the Middle East but not for northern Europe?


 The P-40 had two big advantages over the Hurricane (and Spitfire). Firstly, it had much better range, which was vital for overseas operations. Strangely, the RAF didn't use drop-tanks with the Tomahawks. The other advantage was the Allison V-1710 stood up to Desert conditions better than the RR Merlin. Whilst some of this was down to the down-draught carb inlet, the Allison came with superior air filters, probably because the USAAC expected their aircraft to operate throughout the USA's many and varied environments. And in the Desert theatre in mid-1940, the RAF expected to only be fighting the Italians, and their fighters were inferior to the P-40B/C and had equally poor altitude performance. But in the ETO the fighting was getting to higher and higher altitudes, and the RAF was worried about high-altitude bombers like the Ju86 (which actually proved to be a bit of a flop).


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## Shortround6 (Sep 23, 2020)

Mad Dog said:


> a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109.....



I really love these theories that don't have any real resemblance to the actual time line. 






Sept 9th 1940. There is no engine installed at this time and the exhaust stacks are dummies. 

Just when and where did the NA engineers study this captured 109? 
The French had a captured one in the spring of 1940 that wound up in Britain, British were doing trials with it in Sept of 1940
It is 5400 miles from Los Angeles to London. Not very convenient for a team to go study the 109. 
The British had approved the preliminary design on May 4th 1940. The NA guys must have been very fast workers indeed to incorporate anything from the study of the French 109 which started in March.

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## tomo pauk (Sep 23, 2020)

Mad Dog said:


> Because they didn't say "No, none of this will do." They should have brought a pallet of RR Merlin engines with them and said, "Here, build me something round this, we'd rather wait for something better than order just anything." But they ordered the available P-40. If they had of insisted on the Merlin as the powerplant, we might have had a Merlin-engined P-38 in 1941, which would have been invaluable in every theatre and much more useful than the eventual P-40F/Kittyhawk MkII, and the Mustang MkI would have been a world-beater from the start.



There was no Merlins enough for everyone in 1940-41, especailly once the 2- and 4-engined A/C were being powered with them. Ford, and then Packard deal were made for a reason.



> The Mustang was definitely a better effort, but, IIRC, a lot of the design work on the P-51 was actually done after they spent a lot of time studying a captured ME109..... After all, the American bombers were very good, probably the best available anywhere until the Mosquito arrived.



In other words, Americans studied the draggiest 'new' fighter of 1940 and came out with the streamlined wonder? If someone believes this, I have Brooklyn bridge on sale, real cheap.

Chart of XP-39 doing 340 mh at 20000 ft, as rolled out at Bell: picture

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## GregP (Sep 23, 2020)

Hi Tomo,

I love the chart but am a bit curious about it. I have some observations.

1) It shows the "original airplane" doing 340 mph;
2) The "modified airplane with supercharged engine" doing just over 390 mph;
3) And the "modified airplane with altitude blower engine doing just over 400 mph.

But ...

The "original airplane" DID have a supercharged engine; the 1,150 HP Allisons V-1710-17 (E2). It had a B-5 two-stage turbosupercharger. They never flew an Allison in an airplane that wasn't at least supercharged. So, exactly what is the first curve referring to? Some other powerplant that wasn't supercharged? I can understand the curve with and without the altitude turbosupercharger, but the third curve (the so-called "original airplane") makes me scratch my head and wonder what they were thinking about.

Did the source for this set of curves explain the three curves enough to answer what the first curve was supposed to depict? Just curious, no other agenda here.


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## tomo pauk (Sep 23, 2020)

GregP said:


> Hi Tomo,
> 
> I love the chart but am a bit curious about it. I have some observations.
> 
> ...



'Supercharged engine' = in this case, has turbo to help out the engine-stage supercharger. (for total of 2 stages of supercharging)
'Altitude blower engine' = engine has 'just' the engine-stage supercharger as the only stage of supercharging; the impeller turns faster than on engines that were supposed to have also turbocharger. Eg. 8.77 times the crankshaft speed for the known V-1710-33 engine, vs. 6.44 times the crankshaft speed for the early turbocharged V-1710s.
B-5, or any other turbo of ww2, was 1-stage supercharger - the 2-stage turbochargers were mainly on drawing boards, and on prototype shops/test benches.

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## GregP (Sep 23, 2020)

Thanks, Tomo!

Here's the original XP-39 in 2 configurations, both as the XP-39 with turbocharger (right) and as the "modified" XP-39B.






In the top row, I have it mis-labeled. The pic on the right is the XP-39 and the pic on the left is the same airplane without the turbocharger, but still with the original canopy. All protrusions have been removed, including the exhaust stacks. 

In the second row, this is the same airplane, but you can see the canopy has been lowered and streamlined a bit. In the second row on the right, I'm not too sure, but it looks like the same airplane with dummy exhaust stack (possibly no engine yet). The stacks look kind of "flat" to me.


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## Ivan1GFP (Sep 24, 2020)

Hello All.

There is no doubt that Larry Bell was a bit loose with the facts when advertising the new and wonderful P-39 to the British but there are a few other factors to consider that don't seem to get brought up in these discussions.

The test conditions under which Bell conducted tests and the British did were a bit different.
First of all, for British service, a snow screen was added to the supercharger intake. 
This was an obstruction and caused a noticeable loss in performance.
For later US tests, the backfire screens were removed from the Allison engines. Were they still in place during the British tests?
Many US aircraft at the time used the practice of declaring a partial fuel and ammunition load as "standard" for normal loaded weight.
As an example, even though the P-39D could carry 120 Gallons of Fuel, 100 Gallons was considered the standard load.
Although the .50 cal guns in the nose could carry 270 rounds per gun, seldom did anyone load more than 200..... Except the Soviets.
The wing guns could carry up to 1000 rounds per gun but "standard" was only 300.

In reading through descriptions of the aircraft in the British tests, it seems that they did not get the instructions and loaded their aircraft to capacity.
Also, the substitution of a 20 mm cannon for the 37 mm sounds like a serious weight reduction but it really was not. The aircraft with the 20 mm carried two pieces of "cheek armour" that were not found in the 37 mm aircraft. This was probably also to help maintain proper CG but with everything else and with other equipment substitutions, the British aircraft were heavier.

Another odd thing is that for climb and maximum speed tests, the throttle settings were quite a bit lower than what the engine was capable of.

No doubt there was some additional Larry Bell "Magic" with testing aircraft with no armament or armour or very early versions but there were definitely a few more factors involved.

- Ivan.

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## GregP (Sep 24, 2020)

Hi Tomo,

Just so we're communicating with clarity, the turbo charged version of the XP-39 was a 2-stage system, with the lower-altitude stage being the engine-driven supercharger and the higher-altitude stage being the turbocharger. The turbocharger by itself was one-stage but, when combined with the engine-driven supercharger, resulted in a 2-stage system. Your explanation above makes me think we are essentially saying the same things, but in different words.

Classic mis-communication, probably on my part.

Again, thanks for the charts!


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## Shortround6 (Sep 24, 2020)

To get the "production" Airacobra I to within 4% of the contract speed (it actually did a somewhat better, about 1% low) Bell resorted to a number of 'tricks' like 20 coats of primer sanded between coats. And the finish camouflage coat was lightly sanded to eliminate the seams left by the camouflage templates. 
They also used a wood filler (plastic wood?) around the canopy to smooth the canopy to framework.
Certain panels were made of heavier gauge sheet metal to prevent distortion at high speed.
Improved fasteners/linkage for the landing gear doors to improve fit when closed. 
and others, like no radio mast and fairings over the 

One of my favorites 
the test plane actually had slightly smaller elevators and rudders and slightly larger horizontal stabilizers and vertical fin. Not adopted for any other aircraft.

I don't know if some of these changes did anything or not but some certainly did and the the trick with the paint was totally unusable on a production aircraft. 

The difference in speed between S/N AH 579 (standard ) and S/N AH 571 (modified) was 20mph in top speed. 

Now take a 371mph aircraft that was only a few days old at the factory ramp and fly it in service (or extended tests at a different location) for several weeks and see how the fit/finish deteriorates. 

However, I can think of no other fighter in WW II that was modified to such an extent for an acceptance test, there may have been some?

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## FLYBOYJ (Sep 24, 2020)

Shortround6 said:


> To get the "production" Airacobra I to within 4% of the contract speed (it actually did a somewhat better, about 1% low) Bell resorted to a number of 'tricks' like 20 coats of primer sanded between coats. And the finish camouflage coat was lightly sanded to eliminate the seams left by the camouflage templates.
> They also used a wood filler (plastic wood?) around the canopy to smooth the canopy to framework.
> Certain panels were made of heavier gauge sheet metal to prevent distortion at high speed.
> Improved fasteners/linkage for the landing gear doors to improve fit when closed.
> ...



Sounds like Reno the day before qualifying!

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## ThomasP (Sep 24, 2020)

"...flying parachute..."

Good one.

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## tomo pauk (Sep 25, 2020)

GregP said:


> Hi Tomo,
> 
> Just so we're communicating with clarity, the turbo charged version of the XP-39 was a 2-stage system,



Yes.



> with the lower-altitude stage being the engine-driven supercharger and the higher-altitude stage being the turbocharger.



No.
There was no such thing as 'low altitude stage' nor 'higher-altitude stage'. Both stages were operating when engine was operating - just like on the P-47 and similar US made aircraft with turboed engines. The control system operating the waste gates was controling the speed and thus pressure from turbocharger (lest it would've overboosted the engine up to the point of destroying it) under the rated altitude
Note that both stages were also always operating (when engine was running, obviously) on 2-stage Merlins, Griffons, Jumo 213E or 2-stage V-1710s, even though here both stages were run by engine.
It took both stages operating to achieve pressure ratios of beyond 5:1 (pressure ratio from 1st stage + pressure ratio of 2nd stage), needed for engine operating at thin air at 20000 ft and above.



> The turbocharger by itself was one-stage but, when combined with the engine-driven supercharger, resulted in a 2-stage system.



Yes, again just like on P-43s, or P-47s, or combat-worthy P-38s, or most of B-17s and B-24s we know.


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## Ivan1GFP (Sep 25, 2020)

I was just about to comment on the same thing. The confusion is between two stage and two SPEED superchargers.


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## P-39 Expert (Sep 25, 2020)

Shortround6 said:


> from an old thread with some edits, edits are in italics.
> 
> 1, no test report the XP-39 did fly 390mph.
> 2. reports of continued oil overheating and/or high temperatures causing at least one flight to be cut short.
> ...


Agree with you and doubt the X-P39 ever made 390mph. Was possible on a 20 minute flight if the turbocharged engine actually generated 1150HP at 20000' without any of the temperatures redlining, but again I doubt it actually happened. Probably no calibrated test instruments (like on official govt/military tests), just the airspeed indicator reading then being converted to TAS after the flight. 

The turbocharged XP-39 was a Rube Goldberg contraption that never could have been a combat plane. Historians say deleting the turbocharger was the biggest mistake in the P-39 program, but in reality the AAF made the right decision. It allowed the P-39 to be in production before the war started for the US. The biggest mistakes in the P-39 program were not controlling the weight (easily done) and not installing the two stage V1710-47 or -93 in a standard P-39D/F as early as possible.


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## P-39 Expert (Sep 25, 2020)

Shortround6 said:


> This rather depends on almost suicidal test pilots.
> What other aircraft in all of WW II established record setting climbs to altitude and did high speed runs in the first two hours of testing?
> 
> Let alone the first 20 minutes?
> ...


Larry didn't lie, he promised 400mph from a 6000lb plane. This was before the need for self sealing tanks and armor plate was known. Bell stopped promoting the 400mph figure as the P-400 production contract proceeded and weight gradually grew to 7850lbs.


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## GregP (Sep 25, 2020)

Cme on, Tomo. You are deliberately misunderstanding my post.

The engine-driven supercharger, especially driven at a lower speed, wasn't good for much more than 15,000 feet, if that much. The population of non-turbocharged P-39s proves that without a doubt.

The turbocharger, although running effectively only when the waste gate was closed or partly-closed, was the high-altitude boost part of the system that was added onto the low-altitude engine-driven stage compression. We both know that.

By calling them the low-altitude and high-altitude stages, I very certainly didn't mean that only one stage was used at a time and they changed at some altitude. Noboldy in here thinks that.


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## P-39 Expert (Sep 25, 2020)

Ivan1GFP said:


> Hello All.
> 
> There is no doubt that Larry Bell was a bit loose with the facts when advertising the new and wonderful P-39 to the British but there are a few other factors to consider that don't seem to get brought up in these discussions.
> 
> ...


P-39 weight was always confusing. Actually the early P-39D and the much later P-39Q-1 empty weights were about the same. AHT lists the D at 5523lbs and the Q-1 at 5680lbs but the Q-1 had the additional IFF radio that weighed about 120lbs. Empty weights of all the production P-39 models (D/F/K/L/M/N/Q) were about the same.

Loaded weights varied because of the differences in .30cal ammunition and armor plate, both of which were included in the "load" total and not the empty weight. .30cal ammunition boxes held 1000 rounds per gun but normal load was 300 rounds per gun, a difference of about 200lbs. That's why you sometimes see 7650lbs and 7850lbs quoted al loaded weight. The armor plate varied from about 265lbs on the P-400 to about 195lbs on the later N and Q models. 

The British went a little crazy with armor on the P-400 by armoring the oxygen bottles etc. Compare that 265lbs to the contemporary P-40E with 111lbs of armor plate and glass. Deleting the 100lb nose armor that didn't protect anything and a few small pieces outside of the rear armored glass would get the armor plate/glass to a more reasonable 130lbs while still providing excellent protection.


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## tomo pauk (Sep 25, 2020)

GregP said:


> Cme on, Tomo. You are deliberately misunderstanding my post.
> 
> The engine-driven supercharger, especially driven at a lower speed, wasn't good for much more than 15,000 feet, if that much. The population of non-turbocharged P-39s proves that without a doubt.
> 
> ...



It might be far harder to misunderstand your post if you didn't invent the terms like 'low-altitude stage' or 'high-altitude stage'.


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## P-39 Expert (Sep 25, 2020)

GregP said:


> Cme on, Tomo. You are deliberately misunderstanding my post.
> 
> The engine-driven supercharger, especially driven at a lower speed, wasn't good for much more than 15,000 feet, if that much. The population of non-turbocharged P-39s proves that without a doubt.
> 
> ...


Just because the single stage Allison had a critical altitude of around 15000' didn't mean it stopped running above that altitude. The -85 in the P-39N was rated at 1125hp at 15500' (call it 1150hp @ 15000') but it had a service ceiling of 38500' and would outclimb pretty much everything in 1943 except a Spitfire IX. Service ceiling was about the same as the two stage Hellcat, Corsair and Thunderbolt in 1943.


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## P-39 Expert (Sep 25, 2020)

Mad Dog said:


> Which other manufacturer was as desperate as Bell to get an order to avoid going bust? Which then extends to how desperate a test pilot might be to keep his job that he'd agree to make such a flight. And then you have bravado and just plain guts. During the second flight of the Hawker Typhoon prototype, chief test pilot Philip Lucas noticed the fuselage had started to suffer a structural failure, with a tear large enough to push his hand through opening in one side. Lucas stubbornly refused to bailout, the accepted procedure in such a situation, and saved the prototype. Whilst he was awarded the George Medal for his bravery, he admitted in later years that one possible cause of the failure was some flight manouveres "not in the official test plan".
> The British would have rejected the whole order if Bell hadn't have been able to meet the "within 3% of 400mph" requirement. As I already mentioned, the British Direct Purchase Commission to the US weren't exactly the best and brightest, so I'm not surprised they signed some bad contracts. As it was, they were under pressure to buy just about anything. The P-40 snuck under the barrier because they arrived reasonably early and were judged suitable for the Middle East. By the time the P-400s arrived in the UK, we had loads of Spitfire Vs and the Hawker Typhoon was supposed to soon be sweeping the Luftwaffe from the sky. The Bf109F meant nothing without good altitude performance was going to be used as a fighter in the UK. The Desert requirement was already being met by the mediocre but trusted Tomahawk, and a "much-improved" Kittyhawk was being promised by an equally dishonest Curtis, leaving no role for the troublesome P-400s. Not surprisingly, the RAF jumped at the chance to offload the P-400s to the Russians.


I wouldn't be too hard on the P-400. While it wasn't going to go 400mph (the British made sure of that by adding all that weight) it would have had excellent performance for the time if equipped properly. AHT lists the empty weight as 5523lbs including radio. Load could have easily been reduced to 1520lbs (pilot 160, 20mm+2x.50calMG+ammo 430, armor plate/glass 130, fuel 720 for 120gal, and oil 71) for a loaded weight of 7046lbs. The 20mm cannon only held 60rounds so add another 60 rounds to get to 120 rounds total for only 32lbs more making loaded gross weight 7078lbs. A fully equipped warplane with self sealing fuel tanks, armor plate, cannon and heavy machine gun armament.

The contemporary P-39C was tested in July 1941 weighing 7075lbs with the exact same aerodynamics, engine and propeller (Mike Williams site). Same as the P-400. Compared to the contemporary Spitfire MarkV at 6450lbs:
Top speed P-39C was 379mph at 13000' MarkV 347mph at 13000'
Top speed P-39C 375mph at 20000' MarkV 375mph at 21000'
Climb P-39C 3720feet per minute at 12500' MarkV 3090fpm at 12500' Climb at 3000rpm for P-39C, 2850rpm for MarkV.
Climb P-39C 1900fpm at 25000' MarkV 1820fpm at 25000'
P-39C (P-400) had 20% more fuel than the MarkV.
Armament for the P-400 was a little lighter (1x20mm+2x.50cal vs 2x20mm+4x.30cal) but the P-400 was all centerline fire while MarkV was wing mounted converging fire.

P-400 wouldn't go 400mph but it was darn sure more than a match for the contemporary British Spitfire MarkV.


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## wuzak (Sep 25, 2020)

P-39 Expert said:


> The contemporary P-39C was tested in July 1941 weighing 7075lbs with the exact same aerodynamics, engine and propeller (Mike Williams site). Same as the P-400.






> The Army discovered almost immediately that the P-39C was not combat ready, since it lacked armor and self-sealing tanks.



Bell P-39C Airacobra


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## wuzak (Sep 25, 2020)

It would appear that the first 3 British Airacobras were delivered in P-39C spec, except for the 37mm being replaced by the 20mm.

These arrived in July *1941*, and were the ones tested and found to be wanting.

EDIT: Corrected the year.


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## Shortround6 (Sep 25, 2020)

P-39 Expert said:


> Larry didn't lie, he promised 400mph from a 6000lb plane.



Problem was that the XP-39 showed up at Wright field weighing 6,104lb gross..........................without guns. 
He could not deliver an 6000lb plane with guns.


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## P-39 Expert (Sep 26, 2020)

wuzak said:


> It would appear that the first 3 British Airacobras were delivered in P-39C spec, except for the 37mm being replaced by the 20mm.
> 
> These arrived in July 1943, and were the ones tested and found to be wanting.


Was using the govt/military test of the P-39C because it had the same engine, propeller, weight and drag as a properly equipped P-400 without all the extra weight. P-400 equipped properly had excellent performance for the time.


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## P-39 Expert (Sep 26, 2020)

Shortround6 said:


> Problem was that the XP-39 showed up at Wright field weighing 6,104lb gross..........................without guns.
> He could not deliver an 6000lb plane with guns.


Like I said, Bell didn't promote the P-400 as a 400mph airplane after production weight growth began.


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## Ivan1GFP (Sep 26, 2020)

Hello P-39 Expert,



P-39 Expert said:


> P-39 weight was always confusing. Actually the early P-39D and the much later P-39Q-1 empty weights were about the same. AHT lists the D at 5523lbs and the Q-1 at 5680lbs but the Q-1 had the additional IFF radio that weighed about 120lbs. Empty weights of all the production P-39 models (D/F/K/L/M/N/Q) were about the same.



The airframe of the production P-39 didn't really change all that much. Most of it was a matter of swapping engines and propellers which would change the empty weight a bit. The weight difference between the D and Q is most likely due to engine and propeller differences because later engines were heavier and propellers also got slightly bigger. The IFF radio you mentioned is a bit of a distractor because it would most likely be included in the "load" just as a regular radio and armament would.



P-39 Expert said:


> Loaded weights varied because of the differences in .30cal ammunition and armor plate, both of which were included in the "load" total and not the empty weight. .30cal ammunition boxes held 1000 rounds per gun but normal load was 300 rounds per gun, a difference of about 200lbs. That's why you sometimes see 7650lbs and 7850lbs quoted al loaded weight. The armor plate varied from about 265lbs on the P-400 to about 195lbs on the later N and Q models.



There actually was a lot more differences than that to be found between different models and how each service used them.



P-39 Expert said:


> The British went a little crazy with armor on the P-400 by armoring the oxygen bottles etc. Compare that 265lbs to the contemporary P-40E with 111lbs of armor plate and glass. Deleting the 100lb nose armor that didn't protect anything and a few small pieces outside of the rear armored glass would get the armor plate/glass to a more reasonable 130lbs while still providing excellent protection.



I don't remember how many times you have tried to push this same argument about deleting all the "unnecessary" armour in the nose of the Airacobra.
The problem with this idea is that the Airacobra in most versions ALREADY had a problem with the Center of Gravity migrating too far aft when the ammunition for the nose armament was expended.
Expending the .50 cal ammunition for the cowl guns seemed to cause the most problems and the total weight of all 400 rounds typically carried was only 120 pounds. The 37 mm cannon ammunition weighed 60 pounds but didn't have nearly as long a moment arm.
From pilot reports, aerobatics were not safe when these loads were expended and the CoG migrated aft.

NOW, you are suggesting removing 100 pounds of armour from the extreme nose of the aircraft. That would have an even longer moment arm and also cause CoG to shift aft. Considering how many different weight pieces of armour were fitted in the nose, my belief is that Bell used the armour as permanent ballast for the aircraft to bring the balance into proper range depending on installed equipment.
The extra pieces of cheek armour on the British Airacobras was the same type of thing.
When a 37 mm cannon is removed and replaced by a 20 mm, the missing 100-something pounds needs something to take its place to restore balance.

Some of the other pieces of armour on the Airacobra would not have been necessary on a more conventional design. The big piece of armour protecting the oil tank was in about as bad a place as possible for balance, but without it, the oil tank was exposed to gunfire from aft and not protected by any significant structure. Other pieces of the engine were also exposed but those were the consequences of a rear mounted engine.
The Soviets apparently thought the oil tank armour was so bad that they removed it for most of the spin tests.

There is no doubt the Airacobra carried more armament and armour than it should have for the amount of engine power that was available, but yanking out armour that looked useless wasn't going to help that much. It really needed a redesign which would move the CoG such as that proposed by the P-39E.

- Ivan.

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## Shortround6 (Sep 26, 2020)

I would note that the P-39 retained the fired .50 cal and 37mm casings, while 30 37mm casings may not have made that much difference 400 empty .50 cal casings would go about 840 grains (+/- 25 grains) each so about 48 lbs, weight of the fired primers is negligible (1 lb?) plus the weight of the links, also retained.

My own opinion is that the 100lbs of plate in front of the gear box did protect something, the Center of Gravity.

Further comments on P-39s after the XP-39 & XP-39B will be in a new thread.

P-39C-D & 400


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## Ivan1GFP (Sep 26, 2020)

Shortround6 said:


> I would note that the P-39 retained the fired .50 cal and 37mm casings, while 30 37mm casings may not have made that much difference 400 empty .50 cal casings would go about 840 grains (+/- 25 grains) each so about 48 lbs, weight of the fired primers is negligible (1 lb?) plus the weight of the links, also retained.



Hello Shortround6,

This is interesting because I have heard that also, but have also had a P-39 owner describe the ejection ports for the nose guns. I wonder which is correct.

- Ivan.


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## Shortround6 (Sep 26, 2020)

can't find a picture of the ejection ports on P-39, doesn't mean they don't exist.
But I can find pictures of ejection ports on P-38s.


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## fubar57 (Sep 26, 2020)

First batch of P-39Cs, January 1941. In the foreground is s/n 40-2971. Looks pretty clean though I don't see any armament.





​


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## P-39 Expert (Sep 27, 2020)

Ivan1GFP said:


> Hello Shortround6,
> 
> This is interesting because I have heard that also, but have also had a P-39 owner describe the ejection ports for the nose guns. I wonder which is correct.
> 
> - Ivan.


No ejection ports in the nose of any P-39. Spent shells were removed after each flight.


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## P-39 Expert (Sep 27, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


SCR-535 IFF radio weighed 110lbs-130lbs and was included in the "Load" on P-39D-1/D-2 but included in empty weight of subsequent models K/L/M/N/Q. P-39D/F did not have IFF radio.

The 100lb nose armor plate was unnecessary since it protected the reduction gear which was not armored in any other AAF/Navy planes. P-39 already had armor plate directly in front the pilot mounted on the bulkhead separating the cockpit from the armament bay. 

British clearly specified way too much armor plate/glass for the P-400. Total weight was 265lbs as compared to 111lbs for the contemporary P-40E. 

The nose armor plate was present whether the nose cannon was 37mm or 20mm. The 37mm was 140lbs heavier than the 20mm so Bell obviously had the ability to adjust the COG.

The armor for the oil tank weighed only 29lbs and was absolutely necessary as it protected the oil tank and engine from the rear. 

Regarding the P-39M Bell stated that the nose armor plate was not necessary for balance. The need to adjust weights for the COG was obviously a design necessity since from the beginning the P-39 was designed for larger heavier propellers (both 3 and 4 blade) and the possibility of the mechanical auxiliary stage supercharger located aft of the engine as used on the Allison -47 and -93. 

The only factor that kept the early P-39 from being competitive with the contemporary SpitfireV and Me109F was excessive weight. This was easily corrected by deleting unnecessary armor plate (specified by the British) and the useless .30cal wing guns. The lighter P-39 had self sealing fuel tanks, armor plate/glass and cannon/heavy machine gun armament.


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## glennasher (Sep 27, 2020)

I think the best solution would be to scrap the whole idea of the P-39.

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## P-39 Expert (Sep 27, 2020)

glennasher said:


> I think the best solution would be to scrap the whole idea of the P-39.


Sure, in hindsight the AAF should have pushed development of the P-51 from the beginning. Then we wouldn't have needed the enormously expensive and complicated P-38 and P-47 either. But remember the earliest P-51 to see combat was in England for the British in April 1942 as the Mustang I. It was useless for anything but ground attack and reconnaissance. Top speed was 370mph at 13000' but climb was only 1980fpm at only 11000' and combat ceiling (1000fpm climb) was only 21000'. At that altitude speed had dropped to 357mph. 

Of course in this scenario the two stage Allison V-1710 should have been pushed forward at a faster rate also. The V1710-47 was tested in the XP-39E in April 1942. This engine had the variable speed hydraulic clutch and generated its full 1150HP at 21000'. Simply move the carburetor from the auxiliary stage to its normal position on the engine and critical altitude is up to 25000'. Another three months to get into production and debug any glitches and a two stage P-51 would have been in production in July 1942. Combat by the end of '42. A year later the two stage Packard Merlin P-51 would have been in production. Hindsight is wonderful.

But what to do between Pearl Harbor and the end of 1942? Without the P-39 we would have been stuck with the P-40E. Top speed in the 340mph range at 13000'. Combat ceiling (1000fpm climb) 17000'. Literally could not reach 20000' in clean condition in a combat scenario. No chance against the contemporary Zero, 109 or 190.

Early P-39D/F/P-400 could have easily weighed 7100-7200lbs with performance of 375mph and climb of 2500fpm at 20000' by mid Very competitive/superior to the SpitfireV and Me109F. Armor plate/glass with self sealing fuel tanks and cannon/heavy machine gun armament. Totally wasted by AAF mismanagement.

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## Ivan1GFP (Sep 27, 2020)

Hello P-39 Expert,

Here is a table with armour locations and weights:








P-39 Expert said:


> The 100lb nose armor plate was unnecessary since it protected the reduction gear which was not armored in any other AAF/Navy planes. P-39 already had armor plate directly in front the pilot mounted on the bulkhead separating the cockpit from the armament bay.
> 
> British clearly specified way too much armor plate/glass for the P-400. Total weight was 265lbs as compared to 111lbs for the contemporary P-40E.
> 
> The nose armor plate was present whether the nose cannon was 37mm or 20mm. The 37mm was 140lbs heavier than the 20mm so Bell obviously had the ability to adjust the COG.



Completely agree that the Gearbox Armour was unnecessary for PROTECTION.
As for presence of the armour plate regardless of the 20 mm or 37 mm cannon installation, please observe that the Gearbox Armour varies a bit in weight depending on version. The need for protection certainly would not vary, so it suggests that it was there for balance. Note items 4, and 5 as well. Those pieces would work together to compensate pretty well for the reduced weight of the 20 mm cannon.
This additional armour appears to be the means that Bell compensated for the CoG results of replacing the cannon.

As for whether this quantity of armour was necessary other than for balance, consider that the RAF at the time had actual combat experience with modern aircraft while the US Army did not.



P-39 Expert said:


> The armor for the oil tank weighed only 29lbs and was absolutely necessary as it protected the oil tank and engine from the rear.



The Soviets were easily the most successful operator of the Airacobra. In their testing of spin characteristics of the Airacobra, they chose to remove the oil tank armour from 4 of the 5 test aircraft. They actually retained the wing armament for more of the aircraft. They obviously deleted the wing guns on most of their operational aircraft, but I do not know if the oil tank armour was retained.
The problem wasn't so much the weight of the armour as the location which was very far aft of the CoG.



P-39 Expert said:


> Regarding the P-39M Bell stated that the nose armor plate was not necessary for balance. The need to adjust weights for the COG was obviously a design necessity since from the beginning the P-39 was designed for larger heavier propellers (both 3 and 4 blade) and the possibility of the mechanical auxiliary stage supercharger located aft of the engine as used on the Allison -47 and -93.



It sounds like the P-39M may have had a heavy enough propeller to compensate. I know that some other items of equipment were moved around in later versions to make the aircraft less sensitive to CoG changes when loads were expended.



P-39 Expert said:


> The only factor that kept the early P-39 from being competitive with the contemporary SpitfireV and Me109F was excessive weight. This was easily corrected by deleting unnecessary armor plate (specified by the British) and the useless .30cal wing guns. The lighter P-39 had self sealing fuel tanks, armor plate/glass and cannon/heavy machine gun armament.



There were other issues with the early P-39 that made it generally inferior to the Spitfire V and Me 109F.
The obvious issue is a lack of sufficient altitude performance. Later versions improved on that, but everyone else improved as well.
The other issues are a lack of control harmony. The roll rate of the P-39 was distinctly slow. The elevators were overly sensitive. (This is from NACA Reports and a few pilot accounts.)
Deleting the 30 cal wing guns might have been a good idea but it didn't leave enough gun power remaining.
Now, one might argue that the Soviets did this and they were successful, but the Soviets were generally satisfied with fairly lightly armed fighters with one MG and one Motorcannon. The Soviets also had much faster firing MGs than most other countries did.
The early .50 BMG installed in the cowl of the Airacobra had a particularly low firing rate and synchronizing for firing through the propeller wasn't going to help. The 37 mm gun was powerful but had poor ballistics and with 30 rounds was only good for 12 seconds of use.
For pure air to air use, the armament of the P-39C may have made better sense.

- Ivan.

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## P-39 Expert (Sep 27, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> Here is a table with armour locations and weights:
> View attachment 596327
> ...


Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.

If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.

ONLY reason P-39 altitude performance was insufficient was WEIGHT, and then only on the earlier D/F/K/L models. Reduce the weight and altitude performance improves greatly. Roll rate and control harmonization was just fine. Was Chuck Yeager's favorite plane, until he got the two stage P-51B in 1944.

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## Shortround6 (Sep 27, 2020)

I would note that the Americans used a low pressure oxygen system 400-450psi in the bottles. 
The British used a high pressure system, so far I have not found what pressure they were using. 
When I was a fireman with 2200psi air bottles we considered 400-500psi to be empty. 
Filling bottles (much like scuba tanks) was done in a steel cylinder to hold the bottle in case of mishap.

Perhaps the British high pressure bottles posed a higher risk to the aircraft if punctured?

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## P-39 Expert (Sep 27, 2020)

Shortround6 said:


> I would note that the Americans used a low pressure oxygen system 400-450psi in the bottles.
> The British used a high pressure system, so far I have not found what pressure they were using.
> When I was a fireman with 2200psi air bottles we considered 400-500psi to be empty.
> Filling bottles (much like scuba tanks) was done in a steel cylinder to hold the bottle in case of mishap.
> ...


Valid point, but it ruins my theory that the Brits made the P-400 too heavy to get out of the contract.

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## Ivan1GFP (Sep 27, 2020)

P-39 Expert said:


> Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.



Hello P-39 Expert,

That number of "less than 5000" accounted for over half the total production of the P-39.
The Soviets initially had their issues with the P-39 as well, but they spent the time to iron out the bugs.
The main reason why their pilots liked the Kobra was because it was generally reliable and worked as advertised unlike many of their domestic designs especially early in the war when the first lend-lease aircraft arrived.
Their battles tended to be at very low altitude where the Airacobra was very good and considerably better than than the early Yak and LaGG fighters even when things were working right.
As for being "combat capable" over 8000 Meters (26500 Feet), I wonder what that is in comparison to?
Is it compared to Soviet fighters which may be believable or against German fighters which would be wishful thinking?
You can strip off a couple hundred pounds, but if the engine can't supply enough power, performance is still going to be rather poor.

As for stripping off the .30 cal wing guns, Soviets preferred centrally mounted armament. They stripped off the wing guns from their P-40 Tomahawks as well which only left the two .50 cal cowl guns WITHOUT a motorcannon.



P-39 Expert said:


> If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.



I believe a better way to consider the nose armour on the Airacobra was as "permanent ballast".
Many aircraft have this kind of thing. Removing it may make the aircraft lighter, but also makes it unsafe to fly under certain conditions.
If you really believe that it is possible to remove the Gearbox armour and other "unnecessary" nose armour from the P-400, I suggest you take the chart from the P-39Q manual and see where the CoG would end up with moving around the items you are proposing.
Just keep in mind that the stability becomes unacceptable in the early Airacobra when stores are expended.
This is corroborated by numerous pilot accounts.



P-39 Expert said:


> ONLY reason P-39 altitude performance was insufficient was WEIGHT, and then only on the earlier D/F/K/L models. Reduce the weight and altitude performance improves greatly. Roll rate and control harmonization was just fine. Was Chuck Yeager's favorite plane, until he got the two stage P-51B in 1944.



A better reason for lack of altitude performance for those models was engines that had a critical altitude in the 12,000 - 13,000 Feet range.
NACA report L602 describes the control issues.
Chuck Yeager was an expert pilot and expert pilots can often overcome the idiosyncrasies of an aeroplane.

- Ivan.

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## muskeg13 (Sep 28, 2020)

The Airacobra (P.39) "This was a very inferior fighter aircraft at all times during the war. Its maneuverability, speed, dive and climbing qualities were were poor. It was one of the easiest of the Allied fighters to shoot down."

Galland, Adolf. Generalleutnant. The Luftwaffe Fighter Force: The View from the Cockpit (p. 25). Skyhorse. Kindle Edition. 
The Luftwaffe Fighter Force: The View from the Cockpit (p. 217). Skyhorse. Kindle Edition.

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## wuzak (Sep 28, 2020)

P-39 Expert said:


> Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.
> 
> If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.



I notice that of all the things you state the Soviets took out of the P-39 to improve performance, the nose armour was not one.

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## P-39 Expert (Sep 28, 2020)

wuzak said:


> I notice that of all the things you state the Soviets took out of the P-39 to improve performance, the nose armour was not one.


Correct. But they did remove the IFF radio in the tail cone that weighed 120lbs. That should have been enough to throw the plane totally out of balance. Like I have said before, the P-39 was designed from the beginning to be able to be balanced with different weights both fore and aft.


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## P-39 Expert (Sep 28, 2020)

muskeg13 said:


> The Airacobra (P.39) "This was a very inferior fighter aircraft at all times during the war. Its maneuverability, speed, dive and climbing qualities were were poor. It was one of the easiest of the Allied fighters to shoot down."
> 
> Galland, Adolf. Generalleutnant. The Luftwaffe Fighter Force: The View from the Cockpit (p. 25). Skyhorse. Kindle Edition.
> The Luftwaffe Fighter Force: The View from the Cockpit (p. 217). Skyhorse. Kindle Edition.


He never ran into Alexander Pokryshkin.

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## P-39 Expert (Sep 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> That number of "less than 5000" accounted for over half the total production of the P-39.
> The Soviets initially had their issues with the P-39 as well, but they spent the time to iron out the bugs.
> ...


P-39s were not low altitude planes. Even though the -85 engine's critical altitude was only 15000', service ceiling was 38500'. About the same as contemporary (1943) Corsairs, Hellcats, Thunderbolts, Lightnings and Me109s. Better than FW190 and Typhoon. Would outclimb all those planes up to 25000'.

Earlier P-39s with -39 or -63 engines had good altitude performance (for 1942) if weight was kept down like the Russians did. Unfortunately the AAF did not.


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## Peter Gunn (Sep 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> Here is a table with armour locations and weights:
> View attachment 596327
> ...


Hi Ivan,

Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
1 @ 95.45 lbs
4 @ 35.01 lbs
5 @ 27.60 lbs
---------------
158.06 lbs <-- total weight reduction
=========

If you remove that much weight from the nose from an airplane that we're talking does _not_ eject casings or even links to try to keep the CoG from getting too askew, how will said removal of armor help?

The whole "British added weight to kill the P-39/400" line that some (not you obviously) tout seems a bit disingenuous to say the least. Apparently I've used that word (disingenuous) twice now whilst describing the P-39...

My general feelings, not directed at you Ivan, just as an observation is this:
I've seen mention of other contemporary fighters and their armor schemes mentioned. I think it warrants mentioning that for sake of argument, the Hellcat got what nickname again? I do believe the F6F was somewhat easy to fly if memory serves, the Airacobra... not so much.

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## P-39 Expert (Sep 28, 2020)

Peter Gunn said:


> Hi Ivan,
> 
> Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
> 1 @ 95.45 lbs
> ...


I'm not Ivan but thought I would reply anyway.

The whole "British added weight to kill the P-39/400" is my theory and mine alone as far as I know.

Regarding removing the armor from the nose, #4 and #5 were removed from all the other P-39 models. Removing #1 has always been my idea. 265lbs of armor is way too much for a small fighter as evidenced by the P40E having only 111lbs and the SpitfireV and Me109F having much less also. The Hellcat had only 200lbs of armor plate/glass and it had a 2000HP engine.

P-39 in all forms was an extremely easy airplane to fly. Tricycle landing gear made taxi, takeoff and landing much easier than taildraggers that were blind forward. Would turn inside any plane not made in Japan or named Spitfire, including the Hellcat. Would not tumble unless all nose ammo was expended, and then only on purpose.

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## Ivan1GFP (Sep 28, 2020)

Peter Gunn said:


> Hi Ivan,
> 
> Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
> 1 @ 95.45 lbs
> ...



Hello Peter Gunn,

The Airacobra at least with the 37 mm cannon had the reputation of longitudinal instability when the ammunition in the nose was expended. Apparently this was the situation even though cases and links were retained, so your conclusion regarding the consequences of removing nose armour is the same as mine. The aeroplane is lightened but becomes unsafe to fly.
I know that early models of the P-38 Lightning also had a similar issue. If no ammunition was carried, there needed to be ballast in the nose.



Peter Gunn said:


> The whole "British added weight to kill the P-39/400" line that some (not you obviously) tout seems a bit disingenuous to say the least. Apparently I've used that word (disingenuous) twice now whilst describing the P-39...



As you say, I don't believe it was a matter of intentionally adding weight but more partial versus full ammunition and fuel loads and some added equipment. I also don't believe the switch to a 20 mm cannon was the best idea. The 37 mm already had a short duration of fire (12 seconds). The 20 mm had twice the ammunition load but four times the firing rate so the duration was only 6 seconds.
I believe a bigger problem was that British testing used throttle settings that were lower than what was used in the US and the requirement for snow filters.
For British testing, the Take-Off setting was determined to be 44 inches Hg and 3000 RPM.
For Speed runs, the maximum throttle setting was 42 inches Hg and 3000 RPM.
With a lower throttle setting, the critical altitude should have been increased over what was achieved with US Airacobras, but it was actually the same (13,000 feet) which suggests that there was some kind of intake restriction.
For Climb tests, 2600 RPM and 37 inches Hg was used 
Even the "Take-Off" setting used was only the typical "Military" setting used in US service.
No test used the War Emergency setting which should have been available.
Under these conditions, it isn't a big surprise that the performance achieved was less than impressive.



Peter Gunn said:


> My general feelings, not directed at you Ivan, just as an observation is this:
> I've seen mention of other contemporary fighters and their armor schemes mentioned. I think it warrants mentioning that for sake of argument, the Hellcat got what nickname again? I do believe the F6F was somewhat easy to fly if memory serves, the Airacobra... not so much.



The P-39 was actually very easy to fly. Take-Offs and Landings were particularly easy. Visibility was excellent. Ground handling was excellent except that it had a tendency to overheat with prolonged running on the ground.
Control response was quick though ailerons were a bit heavy.
It developed a reputation for being a "Hot Ship" while P-40s with similar straight line performance didn't have the same reputation.

Regarding Armour, I had hoped to save this discussion for a new thread, but here goes:
Everyone seems to be hung up on the quantity of armour carried by an aircraft on the assumption that more armour means that the aircraft is "tougher" and harder to shoot down.
A year ago, I also was of the same opinion, but since then, I came across a discussion / explanation that made a lot more sense. Redundant structures and surplus structural strength, and designs that locate critical components in protected areas is much more important that the amount of armour carried. Realistically, even aircraft such as the Hellcat, Corsair, or Thunderbolt don't carry armour except to protect critical areas. Most of the airframe is unprotected. Certain aircraft such as the N1K2 Shiden-KAI had a reputation for toughness but actually carried no armour at all. Other aircraft such as the A6M were strong enough under normal conditions but didn't have enough redundant and surplus strength to hold together when major structures were damaged.
Having cockpit armour and self sealing fuel tanks is great but it doesn't make much difference when the whole wing comes off with a few hits.

- Ivan.

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## Ivan1GFP (Sep 28, 2020)

P-39 Expert said:


> P-39s were not low altitude planes. Even though the -85 engine's critical altitude was only 15000', service ceiling was 38500'. About the same as contemporary (1943) Corsairs, Hellcats, Thunderbolts, Lightnings and Me109s. Better than FW190 and Typhoon. Would outclimb all those planes up to 25000'.



Hello P-39 Expert,

I seem to remember that Shortround6 gave a pretty good description of why the P-39 didn't have a lot of use in the ETO for the escort missions that required fighters. As for comparison for altitude performance, it isn't just a matter of being able to reach a decent service ceiling. Even the A6M2 and La 5FN could do that. It is a matter of surplus power and performance when it got to typical altitudes for engagement in the theater.



P-39 Expert said:


> Earlier P-39s with -39 or -63 engines had good altitude performance (for 1942) if weight was kept down like the Russians did. Unfortunately the AAF did not.



The Soviets also did a few things with those early P-39 that were not going to be acceptable in US service. They were typically using throttle settings beyond the War Emergency settings other services used. To them, it was acceptable to have to replace engines after a few flights. The whole aircraft was likely to be lost after a couple months anyway.
The problem with extra high throttle settings is that it only works as long as the supercharger can supply enough boost to allow it. If you read through the report on tests of Koga's A6M2, the P-39 used in those tests tried the same thing with 70 inches Hg at Take-Off. Even with just 52 inches Hg (WEP), the supercharger could not maintain boost past 4500 feet.

The Soviets didn't mind a fighter with ONLY two MG and a Cannon. That was pretty typical of their other fighters though the cannon was bigger than most of theirs.
For the US, that standard of armament was more typical of a tiny lightweight fighter such as the P-77.

- Ivan.

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## P-39 Expert (Sep 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> I seem to remember that Shortround6 gave a pretty good description of why the P-39 didn't have a lot of use in the ETO for the escort missions that required fighters. As for comparison for altitude performance, it isn't just a matter of being able to reach a decent service ceiling. Even the A6M2 and La 5FN could do that. It is a matter of surplus power and performance when it got to typical altitudes for engagement in the theater.
> 
> ...


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## Ivan1GFP (Sep 28, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *Surplus power was pretty good, P-39N would still outclimb a 1943 Thunderbolt at 25000'.*



This really isn't saying very much. The Thunderbolt didn't climb particularly fast at any altitude.



P-39 Expert said:


> *Yes the Soviets burned up their engines quickly by using full power continuously at low altitudes. But above the critical altitude this was a non-issue since that high MP could not be obtained.*



Above the Airacobra's critical altitude generally wasn't where the battles were happening.



P-39 Expert said:


> *The P-39D-1 used in the A6M2 test comparison weighed 7850lbs, one of the heaviest P-39s made. 70"HG was way over takeoff power of 44"HG, so sure it backfired. Even at that weight it climbed with the Zero until 14500' when the 5 minute limit was reached and it had to go to normal power (2600rpm). The 5 minute limit was increased to 15 minutes in mid-42 and at 3000rpm it would have stayed with the Zero on up to service ceiling.*



Do you have evidence that the P-39D-1 used in the test against A6M2 actually was loaded to 7850 pounds?
They didn't actually back off to 44 inches Hg. In one test, they backed off to 52 inches Hg. In another test they ran at 55 inches Hg. These are War Emergency settings or above for the D-1. The A6M2 also had an "Overboost" setting but that was never used.
One of the things that was discovered in these tests was that the A6M2 really wasn't a particularly fast climbing aeroplane. It just had a very good zoom climb and climbed at a very steep angle. Another problem was that the automatic mixture control apparently didn't work in the rebuilt carburetor. The carb originally was designed to prevent negative G flooding but that feature was not restored on this captured A6M2 either.
Note also that the P-39D-1 could not continue these tests past 25,000 feet because it was low on fuel (!)
That DOES say something about lack of range, doesn't it?



P-39 Expert said:


> *Standard for newer AAF and Navy fighters was 4x.50calMGs. P-51A/B/C, FM2 and F8F Bearcat all used 4x.50cal. 20mm cannon and 2x.50cal provided more firepower than 4x.50cal and 37mm and 2x.50cal had even more firepower than that. With centerline fire instead of converging fire from wing guns.*



The single 20 mm cannon and 2 MG does provide greater firepower but only for 6 seconds. After that, you have only two synchronized .50 cal HMG with a rather low ammunition load. One of the main advantages of the 4 gun Wildcats versus 6 gun versions was that the ammunition load and duration of fire was much greater.
For the 37 mm, it would be 12 seconds, but there you also have a cannon whose trajectory isn't remotely close to the .50 cal.
As for "newer" fighters, most of them went to MORE .50 cal guns. With the exception of the P-38, just about everything else used a uniform battery of guns. As for the F8F, although the gun count was lower, the gun used was the M3 which had a higher rate of fire.

Another interesting note regarding acceleration tests against Koga's A6M2 was that the majority of the tests were contrived to show that the US fighters had greater acceleration. This was done by picking a "cruising speed" to start that was usually only about 30-40 MPH below A6M2's maximum level speed. Aircraft don't accelerate quickly when they are near their maximum speed.
I wonder how these drag races would have gone had they started at 120-150 MPH?

- Ivan.

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## Stig1207 (Sep 29, 2020)

P-39 Expert said:


> Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39.



By it self, this does not tell us much in regard to the combat performance of the P-39; aces scores are based on claims and the accuracy of those claims could vary a lot.

Based *alone* on the bomber gunners claims in the ETO, you could reasonly argue that a long range fighter was unnecessary since the losses inflicted on the Jagdwaffe by the gunners were so heavy that the Germans would not be able to withstand that amount of attrition!

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## windhund116 (Sep 29, 2020)

Stig1207 said:


> Based *alone* on the bomber gunners claims in the ETO, you could reasonly argue that a long range fighter was unnecessary since the losses inflicted on the Jagdwaffe by the gunners were so heavy that the Germans would not be able to withstand that amount of attrition!



I have never heard that argument. I thought bomber crew attrition rate, especially 8AF, were high --- when not escorted.


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## GrauGeist (Sep 29, 2020)

With those bombers boxed in so tight and everyone shooting at the same enemy fighter, how many gunners claimed the same aircraft?

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## Stig1207 (Sep 29, 2020)

windhund116 said:


> I have never heard that argument. I thought bomber crew attrition rate, especially 8AF, were high --- when not escorted.



You are correct, but you have misunderstood what I wrote.

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## Stig1207 (Sep 29, 2020)

GrauGeist said:


> With those bombers boxed in so tight and everyone shooting at the same enemy fighter, how many gunners claimed the same aircraft?



Yes, we all know that the bomber gunners overclaimed, that is an undisputed and accepted fact; but let's ignore that for the moment. 

In 1943 the 8th AAF bomber gunners claimed 3253 ea destroyed, according to Caldwell's Day Fighters in Defence of the Reich, and this is when the big raids numbered 200-300 bombers. On the basis of these we could conclude that, if we accepted those claims as factual, that the daylight bomber campaign was succeeding and wearing down the enemy fighter defences rapidly. So instread of fighter escorts we just need more bombers to fly in bigger formations and shooting down even more enemy fighters and at the same time reducing own losses as the enemy is weakened.

Naturally, knowing what really happened the fallacy of above argument is clear, as the Germans weren't losing near as many fighters to the bomber gunners.

Back to the top scoring Soviet aces flying the P-39, how many Axis aircraft did they actually shoot down? After all, the arrival of the P-39 didn't change the overall exchange rate which favoured the Luftwaffe. We can conclude that the Soviet P-39 pilots in all likelihood did better than their American counterparts, we can perhaps also say that they comparatively did better than Soviet pilots flying other fighter types, but imo, we need more concrete numbers of enemy losses to P-39's on the Eastern Front to properly evaluate it's combat performance.

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## P-39 Expert (Sep 29, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


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## Mad Dog (Sep 29, 2020)

Shortround6 said:


> .....Just when and where did the NA engineers study this captured 109?
> The French had a captured one in the spring of 1940......


 The story goes they studied one from the Spanish Civil War, though whether it was a B, C or D model is unclear. There were early Es in Spain in 1939 but I don't think any of those fell into French hands.


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## FLYBOYJ (Sep 29, 2020)

Mad Dog said:


> The story goes they studied one from the Spanish Civil War, though whether it was a B, C or D model is unclear. There were early Es in Spain in 1939 but I don't think any of those fell into French hands.


AFAIK the only -109 captured during the Spanish Civil war was a Bf109 B1. It fell into Republican hands January 1938 and was evaluated by the Soviets and possibly the French. This was documented in the Book "L'Aviation Republicaine Espagnole" by Patrick Laureau. There are several photos of this aircraft in that book.

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## Mad Dog (Sep 29, 2020)

GregP said:


> Thanks, Tomo!
> 
> Here's the original XP-39 in 2 configurations, both as the XP-39 with turbocharger (right) and as the "modified" XP-39B.
> 
> ...


Nice pics! I always liked shiny and polished prototypes in bare aluminium.

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## Mad Dog (Sep 29, 2020)

Shortround6 said:


> ......However, I can think of no other fighter in WW II that was modified to such an extent for an acceptance test, there may have been some?


 All Bell did was game the acceptance criteria set by the BPC. If anyone thinks that doesn't happen every day, even today, then Shortround has a bridge he keeps going on about wanting to sell.


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## tomo pauk (Sep 29, 2020)

Mad Dog said:


> The story goes they studied one from the Spanish Civil War, though whether it was a B, C or D model is unclear. There were early Es in Spain in 1939 but I don't think any of those fell into French hands.



Ah, the 'story goes' source. Those are the best.



Mad Dog said:


> All Bell did was game the acceptance criteria set by the BPC. If anyone thinks that doesn't happen every day, even today, then Shortround has a bridge he keeps going on about wanting to sell.



He does?

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## glennasher (Sep 29, 2020)

I am inclined to believe that the reason the USSR used so many P-39s was because the USAAF didn't want them, and they were sent to the USSR because, while we wanted to help them, we didn't want to help them "too much". Remember that until 1941, the USSR and Germany had that pesky non-aggression pact...............................Yes, we sent them aircraft, but they were not first-line aircraft by any means. I cannot be persuaded that the P-39 was anything but motorized crap.


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## GregP (Sep 29, 2020)

Comparative tests show that below about 16,000 feet, the P-39 was a formidable airplane.

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## Mad Dog (Sep 29, 2020)

glennasher said:


> I am inclined to believe that the reason the USSR used so many P-39s was because the USAAF didn't want them, and they were sent to the USSR because, while we wanted to help them, we didn't want to help them "too much". Remember that until 1941, the USSR and Germany had that pesky non-aggression pact...............................Yes, we sent them aircraft, but they were not first-line aircraft by any means.....


True, we didn't send them Spitfires until later, but then we (stupidly) kept Spitfires only in the UK until 1942, sending old MkIs and MkIIs to training units and sending Hurricane MkIs to the Desert. We didn't send anything to the Soviets until _after_ June 1941, by which time we had already decided to send Tomahawks to the Desert. When we did send Spitfires (Vs and IXs) to the Soviets, they said the P-39 was a better fit for their frontline units. And after Pearl Harbor, the worried Yanks grabbed everything they could from foreign orders, including P-400s and P-66s (<- yeah, that desperate!).


glennasher said:


> ......I cannot be persuaded that the P-39 was anything but motorized crap.


 The P-39 didn't work for the RAF in 1941 because the aircraft still needed development, didn't have the altitude performance demanded of the theatre, and because of Spitfire snobbery. It did (kind of) work for the USAAC in New Guinea, but didn't have the range required to be a real success (unlike the P-38F), and still had issues with altitude. But in Soviets' hands, the P-39 was a big success, because their theatre requirements were different to the West or Pacific, and their own fighter aircraft were - frankly - crap. When you consider that the preferred fighter of the Soviet pilots before the arrival of the P-39 was the I-16, you suddenly understand why they didn't ignore the P-39.

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## wuzak (Sep 29, 2020)

P-39 Expert said:


> Trajectory for the 37mm cannon was actually flat out to 400 yards, which was about the limit for accuracy for any WWII gun. Beyond that distance just meant that the .50calMGs wouldn't be used at the same time.



How does that work?

The 37mm had a significantly lower muzzle velocity than the 0.50" Browning HMG, so if you're hitting a target at 400 yards with the 0.50" HMGs then you would, most likely, be missing it with the 37mm. Not accounting for the trajectory difference, which was enough that the XP-54 had a mechanism and a targeting system designed to compensate.


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## fubar57 (Sep 29, 2020)

View attachment 596594​


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## fubar57 (Sep 29, 2020)



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## GrauGeist (Sep 29, 2020)

Mad Dog said:


> And after Pearl Harbor, the worried Yanks grabbed everything they could from foreign orders, including P-400s and P-66s (<- yeah, that desperate!).


Because the week following 7 December '41, the U.S. was suddenly in a world war with Japan and Germany declaring war.
The U.S. military was still constrained by a cash-strapped budget due to the depression and needed everything they could get their hands on.
Much like Britain in 1940, the U.S. had no idea if there would be an invasion or not and had to build up their aircraft numbers asap.
The 50 P-66s retained by the USAAF were used to bolster numbers at key locations on the west coast until newer types could replace them.
The week following Pearl Harbor, a half-dozen Northrup A-17s arrived at the airfield by where I live (Benton - O85) and remained on patrol duty until they were replaced the following Spring.

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## Shortround6 (Sep 29, 2020)

In 1941 the US was not cash strapped. FDR had called for the 50,000 plane air force in the summer of 1940 and the funding to go with it.
However it takes time to turn that cash into actual factories that are producing much of anything. 

Ford, Studebaker and Buick were all brought into the production plans in 1940 in addition to Packard. This was in addition to large expansions if P&W and Wright and Allison leaning heavily on GM for subcontracting, management and engineering help. Engine production just about tripled from 1940 to 1941 and more than tripled in 1942 over 1941. But the planning/factory building had started in 1940.


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## Ivan1GFP (Sep 30, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *1943 Thunderbolt climbed about the same at 20000' as the Corsair, Hellcat, Fw190 and Zero. Slower below 20000' but better above because of turbocharging. At 25000' Thunderbolt climb was pretty good. *



You keep referring to the "1943 Thunderbolt". What particular model of the Thunderbolt is that?
As for comparisons to the FW 190, I presume you mean the FW 190A which was not noted for great performance at altitude. As for the Zero, if this is the same A6M2 as was tested against the P-39D-1, please note that ITS critical altitude is 13,800 feet or just a bit over a thousand feet higher than the P-39D. It had a pretty good ceiling but not that much altitude performance.



P-39 Expert said:


> *In any air battle the key was getting above your opponent. Normal combat formation for the Soviets was the "flying bookshelves" or "Kuban stairs" with four planes at 5000meters (16500') four more at 6000meters (20000') and the last four at 7000meters (23000') angled up toward the sun. *



This is the ideal case when you have the tactical situation, time and FUEL to implement.
Now think about what happens when the fight starts? Where is it going to be?
Also think about what happened with the P-39D-1 in test against A6M2. Testing could not be conducted above 20,000 feet because the P-39D (with a fuel capacity of 120 gallons) was running out of fuel. (!)
Now think about what the Soviets requested with late model Airacobra; They asked that the fuel capacity be reduced to 87 gallons. 
It sounds to me like they had entirely different tactics in mind.



P-39 Expert said:


> *P-39D-1 Gross weight was 7850#. If it carried 300rounds per gun (instead of 1000) for the .30calMGs then it grossed 7650lbs. Still way too much.
> 
> I don't believe war emergency power was available quite yet if this test was conducted in October 1942. WEP was first available for the Allison in December.*



From the test against A6M2, I do not believe the folks setting up the P-39D-1 had any intention of making this a representative performance comparison. I don't believe 70 inches Hg was ever an approved Emergency Power setting for the P-39D. That factor was actually documented in the testing.
If someone is willing to pull tricks like that, there are plenty of other things that can be done to make the P-39D perform better than it would under combat conditions.



P-39 Expert said:


> *Trajectory for the 37mm cannon was actually flat out to 400 yards, which was about the limit for accuracy for any WWII gun. Beyond that distance just meant that the .50calMGs wouldn't be used at the same time. *



This is not how projectiles fly.
If you play some games with a fairly large target and the concept of "Point Blank Range", you can get all the guns to line up to a fairly reasonable distance.
The problem with this idea is that it only works against a non-maneuvering target. As soon as there is any significant amount of deflection added to the shot, the difference in trajectory becomes pretty important.

By the way, I have already commented more than a few times that I believe the cannons on the early A6M did not have an adequate ammunition supply.

- Ivan.

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## Ivan1GFP (Sep 30, 2020)

Hello All,

Attached is the text of the test between P-39D-1 and A6M2 that was captured in the Aleutians and repaired.




Acceleration Tests:
5000 feet 230 MPH indicated – 248 MPH TAS
10000 feet 220 MPH indicated – 256 MPH TAS
15000 feet 210 MPH indicated – 265 MPH TAS
20000 feet 200 MPH indicated – 288 MPH TAS
25000 feet 180 MPH indicated – 269 MPH TAS

- Ivan.

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## P-39 Expert (Sep 30, 2020)

wuzak said:


> How does that work?
> 
> The 37mm had a significantly lower muzzle velocity than the 0.50" Browning HMG, so if you're hitting a target at 400 yards with the 0.50" HMGs then you would, most likely, be missing it with the 37mm. Not accounting for the trajectory difference, which was enough that the XP-54 had a mechanism and a targeting system designed to compensate.


The 37mm trajectory was about the same as the .50calMGs out to 400 yards. The difference in trajectory was only 23 inches at 400 yards. Past 400 yards the drop in trajectory was greater. 400 yards was about the outside limit for accuracy of airborne guns. Most wing mounted machine guns were sighted to converge at about 300 yards.


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## P-39 Expert (Sep 30, 2020)

Ivan1GFP said:


> Hello All,
> 
> Attached is the text of the test between P-39D-1 and A6M2 that was captured in the Aleutians and repaired.
> View attachment 596607
> ...


My point is that the early P-39s (D/F/K/L) were way to heavy and could have been lightened easily by removing the useless .30calMGs (200-400lbs depending on whether 300 or 1000 rounds per gun was loaded) and the useless nose armor plate (100lbs). This would have improved climb rate to exceed that of the Zero. P-39 was already 40mph faster than the Zero at all altitudes.


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## Ivan1GFP (Sep 30, 2020)

P-39 Expert said:


> My point is that the early P-39s (D/F/K/L) were way to heavy and could have been lightened easily by removing the useless .30calMGs (200-400lbs depending on whether 300 or 1000 rounds per gun was loaded) and the useless nose armor plate (100lbs). This would have improved climb rate to exceed that of the Zero. P-39 was already 40mph faster than the Zero at all altitudes.



Hello P-39 Expert,

We are in partial agreement here.
The early P-39 really was too heavy. The problem though was that there wasn't that much that could be done about it without a significant redesign as was tried in the P-39E.
Removing the Wing Guns probably wasn't a bad idea, but that didn't leave enough armament to suit American requirements. We'll get back to that in a minute.
Unless there was a radical shift in equipment, the nose armour has to stay to make the aeroplane flyable.

FWIW, the early P-39 WASN'T 40 MPH faster than the Zero at all altitudes. The Aleutian A6M2 wasn't a really good representative in terms of actual performance. Keep in mind that it was an aircraft that was crash landed in a bog, flipped and sat partially underwater for a significant amount of time.
One of the pilots commented that it was probably in about 95% condition. Basically, at best, it was a slightly bent bird. I will cover those details in a later post.

If the objective was to improve the P-39, I believe the following would be a reasonable solution:

1. Design new Outer Wing Panels. There is no good reason to use a symmetrical airfoil.
The Wing Tips do have a different airfoil and that actually does serve as "aerodynamic twist" instead of washout but the problem as shown in the NACA report was that the entire rest of the wing stalled at about the same time as shown by tufts attached to the wings.
The new wings should have a more common NACA 23000 series airfoil and a bit of a sweep to put the center of lift further aft to address the CoG problem. At THAT point, perhaps the 100 pound Gearbox armour could be removed.
This is not a new idea. This kind of thing was done on the IL-2 Sturmovik to address the CoG change caused by adding a rear gunner.
This is also a much easier process on the P-39 because the outer wing panels were detachable at the inboard edged of the main landing gear bay and would not greatly affect other aircraft structures.

This may also be an opportunity to increase the wing area slightly and also to improve aileron effectiveness.
Peak roll rate on the P-39 was only around 80 degrees / second which is rather mediocre performance.
Both the NACA report and British testing commented on excessive friction in the aileron linkages which suggest this may be common to the type.

With a redesign of the outer wing panels, it might also be a good idea to move the oil coolers to the roots of the outer panels and free up space in the belly for additional radiator capacity to handle more powerful engines.
Perhaps fuel capacity could also be improved.

2. Replace the 37 mm cannon with a 20 mm Belt Fed weapon. The drum fed HS-404 gun could not carry enough ammunition. Perhaps something similar to the installation in the P-38 might work.
Add back the .30 cal cowl mounted MG from the P-39C if room permits.
This should result in pretty good sustained firepower from guns with similar ballistics.

- Ivan.

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## tomo pauk (Sep 30, 2020)

P-39 was lighter than P-40. What P-39 (and P-40) have had was the lesser engine than what powered current Spitfire/P-51B, Bf 109, P-38, let alone F4U, P-47 or a working Typhoon.

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## P-39 Expert (Sep 30, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> We are in partial agreement here.
> The early P-39 really was too heavy. The problem though was that there wasn't that much that could be done about it without a significant redesign as was tried in the P-39E.
> ...


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## P-39 Expert (Sep 30, 2020)

tomo pauk said:


> P-39 was lighter than P-40. What P-39 (and P-40) have had was the lesser engine than what powered current Spitfire/P-51B, Bf 109, P-38, let alone F4U, P-47 or a working Typhoon.


Yes the P-39 had the Allison engine. 1942 P-39D/F/K/L equipped correctly at 7100lbs would have been a match for the 1942 Spitfire V and Bf109F at all altitudes. P-38F/G, F4U, F6F, Thunderbolt and a workable Typhoon didn't get into combat until very late 1942 or 1943. By that time the P-39N would substantially outclimb all of them at all altitudes at it's normal combat weight of 7650lbs, no weight reduction needed.

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## buffnut453 (Sep 30, 2020)

P-39 Expert said:


> Yes the P-39 had the Allison engine. 1942 P-39D/F/K/L equipped correctly at 7100lbs would have been a match for the 1942 Spitfire V and Bf109F at all altitudes. P-38F/G, F4U, F6F, Thunderbolt and a workable Typhoon didn't get into combat until very late 1942 or 1943. By that time the P-39N would substantially outclimb all of them at all altitudes at it's normal combat weight of 7650lbs, no weight reduction needed.



The problem is that in mid-1942, the Spitfire MkIX was coming on-stream. By all means, compare the P-39D/F/K/L with the MkV but the MkV had been in operational service at least 18 months by 1942...and 18 months was a long time in aircraft development during WW2.

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## tomo pauk (Sep 30, 2020)

P-39 Expert said:


> Yes the P-39 had the Allison engine. 1942 P-39D/F/K/L equipped correctly at 7100lbs would have been a match for the 1942 Spitfire V and Bf109F at all altitudes. P-38F/G, F4U, F6F, Thunderbolt and a workable Typhoon didn't get into combat until very late 1942 or 1943. By that time the P-39N would substantially outclimb all of them at all altitudes at it's normal combat weight of 7650lbs, no weight reduction needed.



Nope.
1942: Bf 109F-4/G2 is both better climber and it is faster than any P-39, even the stripped-down versions. Spitfire V is better climber, and it is faster above 15000 ft. Spitfire IX - no contest.
1943: P-47 is faster above 17000 ft, so is the P-38, F4U, F6F. What is more important, they can either match or better the Axis fighters in speed, especially above 20000 ft (bar F6F vs. German opposition). They all carry better firepower and can offer either superior range or carrier suitability or both vs. what P-39 can offer.

In 1942-43, the non-turbo V-1710 was two years behind curve vs. Merlin, BMW 801 and DB 601/605; same vs. R-2800. Compared with US ww2 that lasted less than 4 years, half of that is huge. Even in 1941, the V-1710 was well behind the curve vs. Merlin or DB 601.

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## P-39 Expert (Sep 30, 2020)

buffnut453 said:


> The problem is that in mid-1942, the Spitfire MkIX was coming on-stream. By all means, compare the P-39D/F/K/L with the MkV but the MkV had been in operational service at least 18 months by 1942...and 18 months was a long time in aircraft development during WW2.


P-39D was in production in early 1941 and we weren't at war until December 1941. 

Spitfire IX was just coming into service in the last half of 1942 with a few operational squadrons and not really into full production until early 1943.

For a real performance boost don't bother with the extensively reworked P-39E, just install the mechanical two stage Allison V1710-47 into any P-39 when it became available in April 1942. At 7650lbs plus the 175lb auxiliary stage supercharger and another 75lbs for a four blade propeller, the two stage P-39 would have weighed 7900lbs instead of 8900lbs for the P-39E or later P-63. Move the carb from the auxiliary stage to the normal location on the engine and increase critical altitude from 21500' to 25000'. That plane would have been a rocket.


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## Ivan1GFP (Sep 30, 2020)

P-39 Expert said:


> *Yes the P-39 was 40mph faster than the A6M2 Zero. Look at the performance graph for the P-39K in Mike Williams' site. 370mph at 16000'. 1942 Zero did 330mph at best. Biggest speed differential was 50mph at 10000' and maintained 40mph differential over 25000'. This for a standard 7650lb P-39 with the early 8.8 supercharger.*



Hello P-39 Expert,

All I can say is that your information is simply incorrect. The Aleutian A6M2 in much less than perfect shape achieved 335 MPH WITHOUT Overboost. In the reports that were distributed, this was corrected down to 332 MPH.
Richard Dunn has a pretty good article supported also by recollections of Saburo Sakai that suggest a more likely maximum speed to be 345 MPH on Overboost. From the combat reports he quotes, the A6M2 seems to be a bit faster than one might expect.
Personally, I believe 340 MPH to be a bit more credible though.
Weight affects climb but really doesn't make that much of a difference in maximum speeds.

- Ivan.


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## P-39 Expert (Sep 30, 2020)

tomo pauk said:


> Nope.
> 1942: Bf 109F-4/G2 is both better climber and it is faster than any P-39, even the stripped-down versions. Spitfire V is better climber, and it is faster above 15000 ft. Spitfire IX - no contest.
> 1943: P-47 is faster above 17000 ft, so is the P-38, F4U, F6F. What is more important, they can either match or better the Axis fighters in speed, especially above 20000 ft (bar F6F vs. German opposition). They all carry better firepower and can offer either superior range or carrier suitability or both vs. what P-39 can offer.
> 
> ...



*Comparing the Allison with the Merlin, BMW801 or DB601 didn't really matter. What was important was the performance of the planes that were powered by those engines. 1942 P-39s were grossly overweight (7650lbs vs 7100lbs) but that could have been easily corrected by removing excess useless armor, .30cal wing guns and in some cases IFF radios. Resulting performance was at least the equal of the Spitfire V and 109F.*

*Two stage Allison -47 was running in the P-39E in April 1942. Problem was the extensively revised E model weighed 8900lbs. Had six .50cal MGs AND a 37mm cannon. And didn't have a 4 blade propeller. Put the -47 into a regular P-39, add a 4 blade propeller and you had a 7900lb rocket.*


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## Ivan1GFP (Sep 30, 2020)

P-39 Expert said:


> *How long will it take to design a new wing and get it into production? A year? P-39 wing was just fine. COG was adequate. Remove the useless equipment to increase the climb/ceiling. Could have been done in 2-3 hours at any combat base. Roll was adequate and the standard P-39 would out turn any plane not made in Japan or named Spitfire.*



Hello P-39 Expert,

However long it would have taken to design a new wing, this was a basic design flaw in the P-39 that was a serious limitation. The symmetrical airfoil had a pretty low coefficient of lift relative to more modern airfoils.
The wing retained good lateral control because the tips did not stall with the rest of the wing, but the rest of the wing tended to stall all at once. (from NACA Report)
If the aircraft had any directional misalignment during the stall, the stall was asymmetrical and the aircraft would flip.
This was described in NACA testing.
Even with equipment shifts to attempt CoG corrections, the problem appears to be a significant rear weight bias and there are not that many places equipment can be moved with such a small airframe.
The CoG may have been fine with the aircraft loaded but was not so fine when loads were expended. Both conditions need to be addressed.

As for taking a year to design a replacement wing, that is a pretty sad commentary. The Soviets managed to do this kind of a thing much quicker.

Roll at a MAXIMUM of 80 degrees per second was hardly adequate. Whether or not a new wing is involved, this should have been improved.

As for turn rates, the Hurricane typically also turns better than the Spitfire.....
I suspect some of the Soviet fighters did better as well.

- Ivan.

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## P-39 Expert (Sep 30, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> However long it would have taken to design a new wing, this was a basic design flaw in the P-39 that was a serious limitation. The symmetrical airfoil had a pretty low coefficient of lift relative to more modern airfoils.
> The wing retained good lateral control because the tips did not stall with the rest of the wing, but the rest of the wing tended to stall all at once. (from NACA Report)
> ...


Pretty much every source says the P-39 had good stall characteristics. No plane will fly with a significant rear weight bias. Expending the nose ammo had no effect in normal flight maneuvers or anytime during landing.


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## tomo pauk (Sep 30, 2020)

P-39 Expert said:


> *Beg to disagree. At 7100lbs the 1942 P-39 outclimbs the SpitfireV and 109F at all altitudes. Check the P-39C in Mike Williams' site but use 3000rpm for climb. I'm aware that the P-39C was not combat capable but it did weigh 7100lbs and had the same engine, propeller and drag as a P-39D/F at 7100lbs.*
> 
> *The 1943 P-39N would do over 380mph at 20000' but more importantly it would substantially outclimb the P-38F/G, F4U, F6F, Thunderbolt, Zero and FW190. By about 600feet per minute at 20000'. The ability to get above your opponent trumps speed since you are diving on them. Range with 120 gallons internal was about the same as a Thunderbolt, F4U or F6F under the same conditions and better than FW190. P-39 firepower was at least adequate.*
> 
> ...



I'm not sure there is point anymore to discuss P-39 with you here.

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## P-39 Expert (Sep 30, 2020)

tomo pauk said:


> I'm not sure there is point anymore to discuss P-39 with you here.


You don't believe my numbers?


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## fubar57 (Sep 30, 2020)

Wiki but still...

Soon after entering service, pilots began to report that "during flights of the P-39 in certain maneuvers, it tumbled end over end." Most of these events happened after the aircraft was stalled in a nose high attitude with considerable power applied. Concerned, Bell initiated a test program. Bell pilots made 86 separate efforts to reproduce the reported tumbling characteristics. In no case were they able to tumble the aircraft. In his autobiography veteran test and airshow pilot R.A. "Bob" Hoover provides an account of tumbling a P-39. He goes on to say that in hindsight, he was actually performing a _Lomcovak_, a now-common airshow maneuver, which he was also able to do in a Curtiss P-40.[36] [N 6] An informal study of the P-39's spinning characteristics was conducted in the NASA Langley Research Center 20-foot Free-Spinning Tunnel during the 1970s. A study of old reports showed that during earlier spin testing in the facility, the aircraft had never tumbled. However, it was noted that all testing had been done with a simulated full ammunition load, which drew the aircraft's center of gravity forward. After finding the original spin test model of the P-39 in storage, the new study first replicated the earlier testing, with consistent results. Then, the model was re-ballasted to simulate a condition of no ammunition load, which moved the aircraft's center of gravity aft. Under these conditions, the model was found to often tumble when thrown into the tunnel 

As soon as I can find it again, an article mentions that Soviet pilots showed an unbelieving U.S. official how the -39 tumbles after expending forward ammo


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## fubar57 (Sep 30, 2020)

From this site...The P-39 Airacobra - Warfare History Network

".....At the same time, the plane was considered underpowered with its 1,200 horsepower Allison V-1710 engine, although it could do 376 miles per hour at 15,000 feet. Also, it lacked a supercharger that limited its effectiveness above 17,000 feet. Worse, the P-39 had a reputation for tumbling out of control when operated by inexperienced pilots....


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## tomo pauk (Oct 1, 2020)

fubar57 said:


> From this site...The P-39 Airacobra - Warfare History Network
> 
> ".....At the same time, the plane was considered underpowered with its 1,200 horsepower Allison V-1710 engine, although it could do 376 miles per hour at 15,000 feet. Also, it lacked a supercharger that limited its effectiveness above 17,000 feet. Worse, the P-39 had a reputation for tumbling out of control when operated by inexperienced pilots....



P-39 was always powered by a supercharged engine.

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## Peter Gunn (Oct 1, 2020)

Wish I could remember the book/author but bear with me. When my oldest son was in the summer symphony program (violin) I used to walk across the street to the Sarasota library. They had an "old" section that was massive to say the least, you could spend days in there. Regardless, I found a book written I believe in the 1950's by a German test pilot. It was very interesting to get his take on "our" aircraft.

I remember him not overly liking the B-24 but was astounded by the performance of the P-51B with what he considered a rather low powered Merlin. Not sure why he used that term but I believe he had also just flown a captured Thunderbolt, so perhaps that had some bearing on his judgement. He couldn't believe the speed he got out of the Mustang.

When he mentions the P-39 well, he was impressed with the tricycle landing gear and I think he did compliment it on being an airplane he didn't mind flying but as a combat plane he pretty much gave it a zero. I believe he had stability problems, probably stemming from the lack of ammo/ballast issues discussed above, and was decidedly NOT impressed with the speed or rate of climb. He did say, if memory serves, that it was doubtful he was getting the full performance out of the plane but even making allowances for that he still wasn't to high on it as a combat aircraft.

With that last sentence in mind, I believe one should be careful about comparing ANY allied aircraft with the Aleutian A6M2.


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## Ivan1GFP (Oct 1, 2020)

P-39 Expert said:


> Pretty much every source says the P-39 had good stall characteristics. No plane will fly with a significant rear weight bias. Expending the nose ammo had no effect in normal flight maneuvers or anytime during landing.



Hello P-39 Expert,

I didn't say the P-39 had particularly bad stall characteristics. You really need to read NACA Report L602.
What I stated was that the maximum coefficient of lift was lower than for the more common 23000 series airfoil as used in the wing tips. Stalls came without warning and were abrupt.
As for "No plane will fly with a significant rear weight bias.", that statement is not entirely true but a detailed discussion is way beyond the scope of this thread.
Consider though that if a disposable load in the nose of the plane can compensate enough for the rear weight bias, then the aeroplane should behave normally.
When that disposable load is expended, things may get ugly.

Your statement that expending the nose ammunition had no effect in normal flight maneuvers is directly contradicted by many pilot accounts.

- Ivan.


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## Ivan1GFP (Oct 1, 2020)

Peter Gunn said:


> Wish I could remember the book/author but bear with me. When my oldest son was in the summer symphony program (violin) I used to walk across the street to the Sarasota library. They had an "old" section that was massive to say the least, you could spend days in there. Regardless, I found a book written I believe in the 1950's by a German test pilot. It was very interesting to get his take on "our" aircraft.



Hello Peter Gunn,

Could this be the book you are remembering?
It might not be the same edition or cover.

- Ivan.


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## Peter Gunn (Oct 1, 2020)

Ivan1GFP said:


> Hello Peter Gunn,
> 
> Could this be the book you are remembering?
> It might not be the same edition or cover.
> ...


Quite possibly, thanks, I'll look it up and try to snag a copy.


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## Ivan1GFP (Oct 1, 2020)

Peter Gunn said:


> With that last sentence in mind, I believe one should be careful about comparing ANY allied aircraft with the Aleutian A6M2.



It is quite interesting that even though this A6M2 was pretty beat up and bent before repairs, it still had no aborts or malfunctions during the testing. The same could not be said about some of the US aircraft in the test report (IIS 85).
They were a bit lucky that this was a fairly new aircraft and had not seen much service before the crash.
Here is a list of the repairs that were done just so folks can get a feel for how "intact" the A6M2 actually was:


*A 15 August 1942 memo from the Commanding Officer of the U.S. Naval Air Station, San Diego, to the Chief of the Bureau of Aeronautics, listed repairs that Zero 4593 needed to make it airworthy. The following is a text of that memo, start:

1. Subject airplane can be put into flying condition in six weeks, provided no unexpected trouble is encountered. It will be necessary to manufacture numerous replacement parts, particularly bolts, machine screws, etc., as they appear to be metric. Work has commenced and will be expedited by day and night shifts, seven days a week.

2. The engine appears to be in good general condition. The bottom front cylinder was dented, apparently by the bullet, which severed the forward sump oil line. The Station will straighten and re-hone this cylinder, and it is believed that it will be in satisfactory condition. The carburetor and possibly other engine accessories are in bad shape internally from corrosion, and will need considerable reconditioning. No undue difficulty in accomplishing this is anticipated.

Structural Repairs Necessary to Fuselage and Wings:
1. Rebuild fin.
2. Repair both elevators.
3. Repair rudder.
4. Rear section of fuselage out of line and bulkheads buckled necessitating considerable repair.
5. Repair fuselage belt frame at stations 9 and 11.
6. Replace top fuselage skin and stringers
7. Rebuild sliding cockpit enclosure
8. Repair seat
9. Straighten fuselage adjacent to cockpit both sides at stations 2-5.
10. Repair fuselage skin at station 4.
11. Repair fuselage at top forward of pilot at station 1.
12. Rebuilt entire engine cowling
13. Repair cowl flaps.
14. Rebuild both sides of landing gear (both main attaching fittings sheared off).
15. Rebuild left landing flap.
16. Replace all ribs on right landing flap.
17. Cut and splice main left wing beam at landing gear attachment.
18. Rebuild one wing tip.
19. Repair left bottom wing skin at station 2.
20. Repair bullet holes in left wing at station 0.
21. Repair leading edge skin on right wing at stations 1.4 and 2.
22. Remake gun cover in right wing between stations 2 and 2.25
23. Patch right wing leading edge skin at station 3.
24. Patch skin and splice main wing bulkhead at station 3.7.
25. Manufacture two aileron fittings which have been sawed off.
26. Replace pilot tube located on left wing.
27. Manufacture various nuts, bolts, etc. which are missing and patch various small holes in skin.
28. Check all wiring. It may be necessary to replace fifty percent of wiring in ship.
29. Test oil and gas tanks. Overhaul is probably necessary.
30. Re-rig all surfaces and other controls.

Necessary Engine Repairs:
1. Straighten and repair nine push rods.
2. Repair one cylinder.
3. Rewire and overhaul harness.
4. Replace two missing spark plugs with LS321 plugs.
5. Completely overhaul carburetor (badly corroded - all springs and some other parts to be replaced)
6. Recondition magnetos (badly corroded).

Instruments:
1. Overhaul all instruments, hydraulic units.
2. If necessary, replace instruments and other small units with Navy standard articles.

End.*

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## Shortround6 (Oct 1, 2020)

*Two stage Allison -47 was running in the P-39E in April 1942. Problem was the extensively revised E model weighed 8900lbs. Had six .50cal MGs AND a 37mm cannon. And didn't have a 4 blade propeller.* 


Let's see. 
_Two stage Allison -47 was running in the P-39E in April 1942._
Yep, true, sort of, an Allison -47 was running in the P-39E in APril of 1942, but in what configuration? 
There were 3+ Allison -47 built. over 4000 on order at one point but either canceled or changed to other versions. 
The -47 was eventually turned into the -93. 
The -47 was initially built with an auxiliary supercharger using the same diameter impeller as the engine supercharger and fixed speed (single) drive. This was while still on test bench. 
The drive system was modified a number of times to finally get to the configuration used in the P-63, hydraulic coupling with variable speed. 
The -47 was rated at 1150hp at 21,000ft at some point (not April of 1942, they had not finalized the drive system yet, they decided to use the automatic hydraulic coupling in July of 1942) engine weighed 1525lbs in Feb of 1942. 
The developed -93 engine was designed in the fall of 1942, not fully prepared for model testing until May of 1943. 
Yep, lets use a near vaporware engine.


_Had six .50cal MGs AND a 37mm cannon_

No, it didn't. That armament was proposed by Larry Bell in a letter to General Echols in the spring of 1942 when they were asking for funding for a 3rd XP-39E to be built after the first one crashed. He also proposed a low altitude version of the engine with 1500hp at 3000ft. to power this version which Larry Bell envisioned as an attack plane for use against invasion forces attacking the United States. WEP ratings had not been approved for US engines at this point. 

Please find any photo or drawing of an XP-39E with _any_ wing guns, even the .30 cal ones. 

need for 4 bladed propeller to handle 1325hp for take-off and 1150hp at 21,000ft seems a little iffy. Need for a 4 blade propeller won't show up until some time in 1943.

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## Peter Gunn (Oct 1, 2020)

Hi Ivan,

Excellent info, gives a whole new meaning to the words "almost intact" when reading the "to do" list. That it was rebuilt was a testament to both its initial design and high manufacturing standards but also the the Navy guys at the San Diego Naval Air Station. To fly after all that and not have any aborts or malfunctions really says something about the aircraft.

P.S. I snagged a copy of "Luftwaffe Test Pilot" off Amazon for twelve bucks, should be here next week. I'll be interested to see how good my memory is, I'll make any corrections to my post (if it matters) if I find I was wrong. Many thanks again.

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## Peter Gunn (Oct 1, 2020)

Ivan1GFP said:


> It is quite interesting that even though this A6M2 was pretty beat up and bent before repairs, it still had no aborts or malfunctions during the testing. The same could not be said about some of the US aircraft in the test report (IIS 85).
> They were a bit lucky that this was a fairly new aircraft and had not seen much service before the crash.
> Here is a list of the repairs that were done just so folks can get a feel for how "intact" the A6M2 actually was:
> 
> ...


Ach... double post, see post #104, apologies.


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## XBe02Drvr (Oct 1, 2020)

fubar57 said:


> it lacked a supercharger that limited its effectiveness above 17,000 feet.





tomo pauk said:


> P-39 was always powered by a supercharged engine.


I think George made a typo, omitting the words "two stage" ahead of supercharger.


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## tomo pauk (Oct 1, 2020)

XBe02Drvr said:


> I think George made a typo, omitting the words "two stage" ahead of supercharger.



Nope - the article is wrong. 
Plus, there was a lot of aircraft that were effective way past 17000 ft despite having just 1 stage of supercharging.

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## P-39 Expert (Oct 1, 2020)

Shortround6 said:


> *Two stage Allison -47 was running in the P-39E in April 1942. Problem was the extensively revised E model weighed 8900lbs. Had six .50cal MGs AND a 37mm cannon. And didn't have a 4 blade propeller.*
> 
> 
> Let's see.
> ...


Did weigh 8900lbs though, right? Wonder how it would have performed in a regular P-39 at 7900lbs?

Needed the 4 blade prop for high altitude thin air.

-93 was in production in April 1943.

Was the same engine as any 1325HP V-1710 with 8.1 supercharger gears. Only thing new was just the mechanical first stage. Just an impeller in a diffuser with a hydraulic coupling turned by a shaft from the starter. Pretty simple, just took forever.


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## P-39 Expert (Oct 1, 2020)

fubar57 said:


> From this site...The P-39 Airacobra - Warfare History Network
> 
> ".....At the same time, the plane was considered underpowered with its 1,200 horsepower Allison V-1710 engine, although it could do 376 miles per hour at 15,000 feet. Also, it lacked a supercharger that limited its effectiveness above 17,000 feet. Worse, the P-39 had a reputation for tumbling out of control when operated by inexperienced pilots....


Was a little faster than 376mph at 15000'. Would outclimb anything in 1943 except a Spitfire IX.


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## Ivan1GFP (Oct 1, 2020)

P-39 Expert said:


> Was a little faster than 376mph at 15000'. Would outclimb anything in 1943 except a Spitfire IX.



Hello P-39 Expert,

I take it you must not have seen the testing of Faber's FW 190A-3 or USN testing of a FW 190A-5/U4.
I believe the A-3 was almost a year earlier and the A-5/U4 had a higher rate of climb AND better speed without running Emergency power.
The early Me 109G was also a bit faster and had comparable climb rates but I am not sure when their engines were cleared to run full manifold pressure.

- Ivan.


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## Shortround6 (Oct 1, 2020)

P-39 Expert said:


> Just an impeller in a diffuser with a hydraulic coupling turned by a shaft from the starter. Pretty simple, just took forever.


 Yeah, real simple. 
It just took Allison two stages, a hydraulic coupling (with variable speed) to do what R R did with one stage on a Merlin 46. And RR did it well before March of 1942. 

Getting airflow to match between two compressors wasn't quite so easy. 
That shaft from the starter and the hydraulic coupling (torque converter) had to handle 225 hp at a minimum. 
and at part throttle or less than full rated height about 25% of the power used drive the auxiliary compressor went to heating up the oil in the hydraulic coupling. At full boost the loss was only 4%. But the oil cooler for the Auxiliary stage had to get rid of around 45hp worth of heat at lower altitudes. 
Working out the increased cooling loads for radiators and oil coolers might not have been that simple. As in the engine needs to make an extra 225hp in the cylinders above what was needed for the same power to the prop in a single stage engine. Now if you are flying in thinner air you need even bigger radiators/oil coolers or improved ducts. 

Concepts can be simple, getting them to work under varying conditions sometimes isn't simple. 

BTW the -47 engine was originally envisioned with an inter-cooler. As was the -93 engine.

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## SaparotRob (Oct 1, 2020)

Ivan1GFP said:


> It is quite interesting that even though this A6M2 was pretty beat up and bent before repairs, it still had no aborts or malfunctions during the testing. The same could not be said about some of the US aircraft in the test report (IIS 85).
> They were a bit lucky that this was a fairly new aircraft and had not seen much service before the crash.
> Here is a list of the repairs that were done just so folks can get a feel for how "intact" the A6M2 actually was:
> 
> ...


Very informative. After having read about the capture of an intact Zero in probably every book about the Battle of Midway, it doesn’t look quite so intact.

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## XBe02Drvr (Oct 2, 2020)

SaparotRob said:


> Very informative. After having read about the capture of an intact Zero in probably every book about the Battle of Midway, it doesn’t look quite so intact.


Yes, but...it's a tribute to the genius of Horikoshi Jiro that the basic airplane was so simple, straightforward, and non-critical that foreigners accustomed to different hardware, structural materials and design practices, and no usable documentation could repair it, rig it, and flight test it with no manufacturer support. And in a manner that delivered bulletproof reliability.
When a twin row radial suffers a prop strike/sudden stop, an awful lot of rotating mass comes to an abrupt halt, deforming internal parts, which under normal circumstances would be replaced. If you have no spares, no drawings, and no table of limits, reconstituting said parts entails a lot of "by guess and by golly" and infinite opportunities for getting it wrong. Ask our Allison Man, Greg P, how critical these things are in rebuilding an engine, especially one with unfamiliar tolerances, an unfamiliar measurement system, unfamiliar design practices, and no documentation.

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## BiffF15 (Oct 2, 2020)

XBe02Drvr said:


> Yes, but...it's a tribute to the genius of Horikoshi Jiro that the basic airplane was so simple, straightforward, and non-critical that foreigners accustomed to different hardware, structural materials and design practices, and no usable documentation could repair it, rig it, and flight test it with no manufacturer support. And in a manner that delivered bulletproof reliability.
> When a twin row radial suffers a prop strike/sudden stop, an awful lot of rotating mass comes to an abrupt halt, deforming internal parts, which under normal circumstances would be replaced. If you have no spares, no drawings, and no table of limits, reconstituting said parts entails a lot of "by guess and by golly" and infinite opportunities for getting it wrong. Ask our Allison Man, Greg P, how critical these things are in rebuilding an engine, especially one with unfamiliar tolerances, an unfamiliar measurement system, unfamiliar design practices, and no documentation.



Wes,

I was wondering about the prop strike until I looked at the pictures. It appears either the motor was rotating very slowly or had stoped. In the previous shots you can see he basically came down in a marsh and the props appear to have no noticeable damage. The amazing thing to me, along the lines or repairing another countries goods, is that the landing gear were ripped out / off and they were able to fix that. Mechanically skilled at repair is an obvious understatement.

Cheers,
Biff

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## Peter Gunn (Oct 2, 2020)

I must admit, back when I was in middle school in the 19XX's, I remember reading (probably Caiden) about this "Intact Zero" in the Aleutians that was the DIRECT reason the Hellcat was designed and built. Some numb-nuts writer was actually attributing the whole F6F program (beginning to end) as a response to the Zero. I don't remember how long it was (almost a year I think) before I found out that was not the case, at the time I just knew is was true, but then you keep learning new info everyday, especially here.

So as Tommy Lee Jones said in Men in Black, "Imagine what you'll _KNOW_... tomorrow.".

So I hereby christen this forum... "Tomorrowland".

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## XBe02Drvr (Oct 2, 2020)

BiffF15 said:


> I was wondering about the prop strike until I looked at the pictures. It appears either the motor was rotating very slowly or had stoped. In the previous shots you can see he basically came down in a marsh and the props appear to have no noticeable damage.


Quite likely he was at flight idle or slightly above, as he was trying to make a smooth landing in a grassy field of unknown roughness. I have a book about this Zero with pictures in which the third propeller blade is visible, and it clearly took a hit, stopping the engine from maybe 900-1000 RPM in 1/3 revolution to a dead stop. Yes, the con rods were bent, according to the report of the repairs, not unusual for a reduction geared twin row radial. Two master rods, twelve connecting rods, fourteen pistons, a supercharger disk, a planetary gearset, and a propeller, all slammed to a stop at once in less than half a revolution, something's going to give.

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## Ivan1GFP (Oct 2, 2020)

Hello XBe02Drvr, BiffF15,

BiffF15 is correct about the engine not running at the time of the landing.
Anti-aircraft fire over Dutch Harbor had cut an oil line and Koga had flown his crippled bird to a previously scouted site to put it down. From the air, it looked like an open field with high grass.
The plan for pilots in his situation was to put the aircraft down on this island, destroy the plane and then make it to the beach where he could signal for a pre-arranged pickup of downed pilots by submarine.

When Koga touched down, he found a marsh instead of a grassy field, his landing gear dug in, got ripped off and flipped the plane pretty violently. The canopy was crushed, he ended up with a broken neck and his head under water.

As the great philosopher Gomer Pyle would say: "Sur-prise! Sur-prise! Sur-prise!".

His two wingmen had standing orders not to leave a more or less intact aircraft and had plenty of ammunition but chose not to shoot the plane because they thought Koga might still be alive.
The wreck stayed there for a couple months until it was spotted from a passing PBY.

As for being able to recreate the landing gear mechanism, this probably wasn't quite as difficult as it would seem today because there were other crashed A6M2, notably at Pearl Harbor, that had been studied. Hirano's A6M2 was not even close to repairable, but from photographs, it appears that the canopy was intact enough to serve as a template if not to supply parts.
The thing that makes me wonder is that I would have expected force that is violent enough to rip off landing gear might also seriously deform the wing structure.

- Ivan.

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## P-39 Expert (Oct 2, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> I take it you must not have seen the testing of Faber's FW 190A-3 or USN testing of a FW 190A-5/U4.
> I believe the A-3 was almost a year earlier and the A-5/U4 had a higher rate of climb AND better speed without running Emergency power.
> ...


The climb numbers for Faber's 190A-3 as tested by the British have always been an outlier. No other 190A approached that level of climb. Interesting that the British could only get 375mph at 18000' out of it.

Regarding the Navy test of the 190A-5 it climbed about the same as the Hellcat and Corsair. Attached climb graphs of the 190A-6 and the Hellcat show that the P-39N outclimbed both substantially at all altitudes.


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## Ivan1GFP (Oct 2, 2020)

P-39 Expert said:


> The climb numbers for Faber's 190A-3 as tested by the British have always been an outlier. No other 190A approached that level of climb. Interesting that the British could only get 375mph at 18000' out of it.



Hello P-39 Expert,

Why would you consider this an outlier? The 190A-3 had an engine of approximately the same power as later versions but was one of the lightest versions built. Why is it a wonder that it should climb very well? The only issues with this testing were that the plugs were probably not in the best of shape and the engine was de-rated but the British did not run it in that manner.



P-39 Expert said:


> Regarding the Navy test of the 190A-5 it climbed about the same as the Hellcat and Corsair. Attached climb graphs of the 190A-6 and the Hellcat show that the P-39N outclimbed both substantially at all altitudes.



I was referring to the FW 190A-5/U4 that was captured and tested by the USN. It was a ground attack version and did not carry the two outboard cannon. Even so, it carried enough armament with 2 x 20 mm and 2 x 7.92 mm guns to be pretty dangerous. It weighed substantially less than the typical fighter versions and climbed better.
....and no, it did NOT climb the same as the Hellcat and Corsair. That is pretty good performance for a captured bird that isn't even running emergency power.

Why are you so convinced that the Airacobra was a miracle aeroplane?
Either one of these FW 190s was running in the neighbourhood of 1700 - 1750 HP at Sea Level and 1450 - 1550 HP at 20,000 feet. The Airacobra had a nice slick airframe but that doesn't make that much difference at best climb speeds and its airfoil had a relatively low coefficient of lift.
The only place where any of the Airacobra could possibly have comparable power is very near the ground and running manifold pressures well beyond War Emergency.
FW 190A-3 loaded weight is 3855 Kg or 8500 pounds.
FW 190A-5/U4 was ballasted to 8690 pounds for testing which was about 400 pounds less than the typical A-5 fighter with full armament. The A-6 fighter would weigh about 175 pounds even more than that.

- Ivan.

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## Milosh (Oct 2, 2020)

Also Faber's 190 was using Brit fuel which was different from the German C3 fuel.


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## P-39 Expert (Oct 2, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> Why would you consider this an outlier? The 190A-3 had an engine of approximately the same power as later versions but was one of the lightest versions built. Why is it a wonder that it should climb very well? The only issues with this testing were that the plugs were probably not in the best of shape and the engine was de-rated but the British did not run it in that manner.
> 
> ...


Go to Mike Williams site and look at the official government/military tests. It didn't matter how much horsepower an engine developed, what mattered was how the airplane performed.


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## Shortround6 (Oct 2, 2020)

lift of the wing actually doesn't have a whole lot to do with climb. This is counter intuitive but I believe it is true. 

Best climb is achieved at the point where the induced drag curve crosses the profile drag curve.

Like this.





with the plane flying at the minimum drag speed the rest of the engines power can be used for climbing. This assumes that the minimum drag speed has a comfortable margin above the minimum control speed. 

Lift goes up with square of the speed, which is why the induced drag (or drag from creating lift) goes down so quickly, at least to a certain point. However the profile or parasitic drag also goes up the square of the speed so trying to fly faster to create more lift to increase climb doesn't work very well. You have less power left to actually do the work of lifting the plane. 

You can estimate climb to some extent if you have (or can reasonable guess) the power needed to fly at the minimum drag speed and figure the power to weight ratio of the plane using the excess power available. 


Any of our members who know more about aeronautics ( a bunch of them) are free to correct me on this. 

However we can also make the same mistakes than many designers of the 30s made. Those inaccurate estimates of drag and/or induced drag that often under estameted the power needed to fly at minimum speed (prop efficiency can also screw things up).

When you have planes that outperform similar aircraft by a large margin you really have to start looking for the answer. Not always easy to find and make sure you are comparing the same things.
The US was one of the few countries that used military power for the first 5 minutes of a climb, Both Britain and Germany used a much longer time period rating. The US also, at some point during the war on certain aircraft ran take-off power for 5 minutes and then some WEP rating for the rest of the climb unless the engine overheated. 
Sometimes a Non US test did use full power for a climb but it is almost always noted.
British tests for the Spitfire for instance used 2600rpm for the early Spitfire with Merlin III engines, later Spitfires used 2850rpm for the climb. Later on some spits were allowed to use 3000rpm at the higher altitudes where the supercharger could not provide full pressure. But finding a test for a Spitfire where they used 3000rpm and full boost from the ground to 25,000 ft or more is going to be a very rare test. 

The P-39N in those tests seems to outperform, and by a large margin, the P-39s that came before it and the P-39 that came after it (the Q). 
It was also running over the allowable temperature limits.


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## XBe02Drvr (Oct 2, 2020)

Ivan1GFP said:


> BiffF15 is correct about the engine not running at the time of the landing.
> Anti-aircraft fire over Dutch Harbor had cut an oil line and Koga had flown his crippled bird to a previously scouted site to put it down.



You must have the same book I do. Mine's packed away for moving, but from memory, I believe Koga still had engine power available, as the oil wasn't lost catastrophically, and he didn't have to push it very hard to reach his emergency field. His wingmen made no mention of a dead stick landing. On teardown the bearings were burned but not seized. The pistons were seized, but that was attributed to post-crash corrosion.



Ivan1GFP said:


> I would have expected force that is violent enough to rip off landing gear might also seriously deform the wing structure.


Good point. On an American aircraft (other than Grumman) it probably would. US landing gear trunnions tend to be hell for stout, but Horikoshi was a master of lightweight construction, and likely created a design that was strong for vertical loads, but less so for sheer. Also, his one-piece integral wing design didn't have the weak points of detach fittings for the wing panels. "Sheet metal forensics" can generally determine if a fabricated structure of complex shape, such as a wing, has been deformed. The trauma usually wrinkles skins and pops rivets. We did a little of that in mech school.
What I wonder is why didn't Koga make a gear up belly landing? He probably would have walked away, the plane burned, and Naval Intelligence frustrated.

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## XBe02Drvr (Oct 2, 2020)

Shortround6 said:


> lift of the wing actually doesn't have a whole lot to do with climb. This is counter intuitive but I believe it is true.


Spot on! People get over fixated on Coefficient of Lift and Total Lift because they're simple single-value functions and sound impressive. What really matters in most all aircraft performance regimes is Lift/Drag. As Shortround points out, best climb occurs at or very near the best Lift/Drag ratio, tempered slightly by powerplant concerns such as prop efficiency or tailpipe deflection angle. This is where thrust available exceeds thrust required by the greatest amount, and thrust required is, of course, tied to L/D. The excess thrust can be converted to linear acceleration in the horizontal plane, or by maintaining airspeed constant, find an upward inclined plane that achieves the maximum defeat of gravity by that excess thrust.

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## Shortround6 (Oct 2, 2020)

Even into the early 30s there were people who should have known better (like editors of aviation magazines) who thought that biplanes would outclimb monoplanes because they had more _LIFT_. This totally ignored the higher drag of the biplane and given equal engines the resulting lower surplus power/thrust at a given speed that could be used for climb. 

It is possible to muck things up if you go too far though. The clipped with P-63s used in post war air racing might not have climbed very well, they sure couldn't turn very well. 




But that may be a case of needing either a high angle of attack (high drag) to generate lift or needed to fly faster (higher drag) to generate the needed lift. 
According to at least one pilot, whatever they gained on the straightaway they lost in the turns having to take a wider (longer) track around the pylons.

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## FLYBOYJ (Oct 2, 2020)

XBe02Drvr said:


> What I wonder is why didn't Koga make a gear up belly landing? He probably would have walked away, the plane burned, and Naval Intelligence frustrated.


In the series "Air War" by David Jablonski, it was mentioned the area Koga chose was a predetermined emergency landing site and it was thought the surface would be acceptable for an emergency landing, it turned out to be soft muddy tundra. Lt. Michio Kobayashi who was flying a Kate actually scouted the landing spot and witnessed the crash. It was also mentioned that he was leaking fuel. Photo from wiki






Some more on this...

The Akutan Zero – the first intact to be captured by the US in 1942 and the last flight of Tadayoshi Koga – WW2Wrecks.com

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## fastmongrel (Oct 3, 2020)

Milosh said:


> Also Faber's 190 was using Brit fuel which was different from the German C3 fuel.



The fuel remaining in the tanks would have been removed for analysis. I wonder if there was any facility to replicate the C3 fuel so that tests would be more realistic.

A minor point but at this time there was no British fuel all production of Petroleum products had been standardised. Unless the RAF had a secret refinery tucked away somewhere.


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## Milosh (Oct 3, 2020)

Wasn't Brit fuel (avgas) for the Merlins 100 PN?


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## P-39 Expert (Oct 3, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> Why would you consider this an outlier? The 190A-3 had an engine of approximately the same power as later versions but was one of the lightest versions built. Why is it a wonder that it should climb very well? The only issues with this testing were that the plugs were probably not in the best of shape and the engine was de-rated but the British did not run it in that manner.
> 
> ...


Couple more things. I'm not convinced that the Airacobra was a miracle airplane. Just that it was a much better plane than we all have been lead to believe for the last 75 years. All the reference books, every single one listed the performance figures for the P-39 well below the figures and graphs in wwiiaircraftperformance.org (Mike Williams site). Those were the official military tests. William Green, America's Hundred Thousand, all the reference books were pretty accurate except for the P-39. The information on Mike Williams site for the P-39 were released in 2012. Makes me wonder if his information had been somehow lost for the past 75 years. My whole contention is that the P-39 in most all its models was a better performing plane than previously published books indicate. This also helps explain why the Soviets were so successful with it.

And the FW190 did climb about the same as the Hellcat and Corsair. Look at the climb graphs in my post #118. At 20000' the 190 climbed at about 2000feet per minute, about the same as the 1943 Hellcat, Corsair, Thunderbolt, Lightning F/G, Typhoon and Zero. All in the 1800-2200fpm range.

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## P-39 Expert (Oct 3, 2020)

Shortround6 said:


> Yeah, real simple.
> It just took Allison two stages, a hydraulic coupling (with variable speed) to do what R R did with one stage on a Merlin 46. And RR did it well before March of 1942.
> 
> Getting airflow to match between two compressors wasn't quite so easy.
> ...


That Merlin 46 graph is with ram air. Allison figures a without ram air.

The -93 engine as eventually installed in the P-63 (and XP-39E) didn't have an intercooler.


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## fastmongrel (Oct 3, 2020)

Milosh said:


> Wasn't Brit fuel (avgas) for the Merlins 100 PN?



I am not sure of the exact fuel used at the time. My point was that there was no British fuel the same as there was no US fuel it was as far as possible a universal Allied fuel.


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## P-39 Expert (Oct 3, 2020)

Shortround6 said:


> lift of the wing actually doesn't have a whole lot to do with climb. This is counter intuitive but I believe it is true.
> 
> Best climb is achieved at the point where the induced drag curve crosses the profile drag curve.
> 
> ...


The AAF increased the time limit for military power from 5 minutes to 15 minutes for the Allison V-1710 (and P&W R-2800) in mid year 1942. About the same time they finally discarded the unnecessary and performance robbing backfire screens. Prior to that the 5 minute limit required reduction to normal power (2600rpm for the Allison, 2550 for P&W) during climb tests which greatly reduced the tested climb rate. The simple use of combat power for 15 minutes increased the tested climb rates dramatically, especially at the higher altitudes reached after 5 minutes. If you look at the tests, all of them reduced power after 5 minutes before 6/30/1942, and used full power at all altitudes after that date.

Rolls Royse (and the RAF) chose to rate the Merlins at 2850rpm for climb, which was barely under their 3000rpm combat rating. That's what they felt their engines could reliably bear under climb conditions. Different countries, different companies, slightly different ratings.

The N model had a few advantages that other P-39 models didn't. Tests of the D/F/K/L models were done before the 15 minute limit so their climb figures were lower after the 5 minute limit was reached and power was reduced to 2600rpm. The M/N/Q models had the benefit of 3000rpm for the full 15 minutes and the more powerful -85 engine. The M as tested had the 2:1 reduction gear and sway braces attached to the drop tank shackle. The N had the 2.36:1 reduction gear and no sway braces. And possibly the larger 11'7" propeller but we don't know that for sure. The Q had the obvious underwing .50calMG pods that cost 14mph in speed and who knows how much climb. All for an additional 130lbs in weight and an increase in firepower of about 2/3rds of one .50calMG. 

Most all the AAF WWII fighters with Allison engines ran a little hot during combat power. Except the P-40.


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## XBe02Drvr (Oct 3, 2020)

Shortround6 said:


> Even into the early 30s there were people who should have known better (like editors of aviation magazines) who thought that biplanes would outclimb monoplanes because they had more _LIFT_.


Clearly they had never flown gliders.



Shortround6 said:


> According to at least one pilot, whatever they gained on the straightaway they lost in the turns


_Shelby Cobra and 427 Corvette Lose to Austin Cooper S ! _(Old school Mini-Cooper bored out to 1.5L)
I saw it happen at le Circuit Mont Tremblant in 1968 at an SCCA regional. Admittedly, a rather tight course: the winning average speed at the Canadian GP later that year was barely 100 MPH. Saw that too. Monaco without the buildings and waterfront.


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## fastmongrel (Oct 3, 2020)

XBe02Drvr said:


> Clearly they had never flown gliders.
> 
> 
> _Shelby Cobra and 427 Corvette Lose to Austin Cooper S ! _(Old school Mini-Cooper bored out to 1.5L)
> I saw it happen at le Circuit Mont Tremblant in 1968 at an SCCA regional. Admittedly, a rather tight course: the winning average speed at the Canadian GP later that year was barely 100 MPH. Saw that too. Monaco without the buildings and waterfront.



Have a read about Stirling Moss winning at Monaco 1961 in a Lotus Climax which only had 145hp against the two Ferrari cars which had over 200hp.


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## XBe02Drvr (Oct 3, 2020)

FLYBOYJ said:


> In the series "Air War" by David Jablonski, it was mentioned the area Koga chose was a predetermined emergency landing site and it was thought the surface would be acceptable for an emergency landing, it turned out to be soft muddy tundra. Lt. Michio Kobayashi who was flying a Kate actually scouted the landing spot and witnessed the crash. It was also mentioned that he was leaking fuel. Photo from wiki
> 
> View attachment 596929
> 
> ...


I have Reardon's book on the Akutan Zero, but it's packed away in storage. Good excuse to dig it out and read it again. Fascinating read.


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## XBe02Drvr (Oct 3, 2020)

fastmongrel said:


> Have a read about Stirling Moss winning at Monaco 1961 in a Lotus Climax which only had 145hp against the two Ferrari cars which had over 200hp.


Pretty amazing what they were able to do with the old 1.5L F1 with no turbos allowed. But apparently the fans didn't find it "interesting enough" and there was agitation for more performance. Quantum leap when it went to 3L in the mid 60s.
Back to P39s. Do I detect the sickly aroma of an expired equine carcass? My toes are bruised and bleeding; how about yours?

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## Ivan1GFP (Oct 3, 2020)

P-39 Expert said:


> Couple more things. I'm not convinced that the Airacobra was a miracle airplane. Just that it was a much better plane than we all have been lead to believe for the last 75 years. All the reference books, every single one listed the performance figures for the P-39 well below the figures and graphs in wwiiaircraftperformance.org (Mike Williams site). Those were the official military tests. William Green, America's Hundred Thousand, all the reference books were pretty accurate except for the P-39. The information on Mike Williams site for the P-39 were released in 2012. Makes me wonder if his information had been somehow lost for the past 75 years. My whole contention is that the P-39 in most all its models was a better performing plane than previously published books indicate. This also helps explain why the Soviets were so successful with it.



Hello P-39 Expert,

For the most part, I agree with your statements above. The problem though is that I am finding that very often you have a tendency to cherry pick tests under one test and load condition and use them as a general conclusion under all conditions. The early P-39 with the -35 and -63 engines are a good example. They were cool little screamers at low altitude, but those engines didn't have enough performance at altitude. The climb test at each altitude against the Aleutian A6M2 proved that despite attempts by the pilot to play with boost settings, he couldn't make up the difference past about 12,500 feet even though the testing was arranged to make US fighters look as good as possible against a beat up A6M2.

The point is that the Airacobra isn't the horrible fighter that some people think. It had its strong points, but it also had some serious limitations inherent in its design that were impossible to correct without a serious re-design.

FWIW, the data from AHT isn't necessarily inaccurate. There are just plenty of typos and the data may not always be complete. The roll rates quoted for P-39 actually are in pretty good agreement with those in NACA testing.
Your ideas for armament reduction may have its merits but it obviously wasn't acceptable to US Army. I don't know that my idea of reverting back to P-39C armament would have been acceptable either.



P-39 Expert said:


> And the FW190 did climb about the same as the Hellcat and Corsair. Look at the climb graphs in my post #118. At 20000' the 190 climbed at about 2000feet per minute, about the same as the 1943 Hellcat, Corsair, Thunderbolt, Lightning F/G, Typhoon and Zero. All in the 1800-2200fpm range.



Your charts are showing a different model FW 190. Take the same aeroplane and delete about 550 pounds of equipment from it and see how it behaves. This equipment deletion isn't a "custom" modification or speculation; it was simply not found on the ground attack FW 190A-5/U4. They were serious load lifters but also pretty respectable hotrods when the ordnance was gone. The problems though were a difference in engine tuning and also non-pressurized ignitions which is probably why they could not get the test aeroplane to fly above 34,500 feet.

- Ivan.


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## Ivan1GFP (Oct 3, 2020)

XBe02Drvr said:


> I have Reardon's book on the Akutan Zero, but it's packed away in storage. Good excuse to dig it out and read it again. Fascinating read.



Hello XBe02Drvr,

Good book, but a bit lacking in technical details from the various test reports. My copy is on the shelf but for some reason it is disintegrating at the binding.

One point I forgot to mention about the repair work is that one prop blade needed straightened and reconditioned and it is not mentioned in the repair items.

One morning many years ago, I was at Fort Meade with a friend of mine very early in the morning. I watched the local Porsche club set up cones for an autocross event in a parking lot. When the competitions were run, I was a bit surprised when the 914s were winning everything. Some of the faster drivers simply laid on the gas and drifted through every turn. None of the other cars could do the same. One of the other cars, a 944 or 928 picked up a little too much speed and almost ran off the parking lot and down a rather long embankment.

- Ivan.


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## P-39 Expert (Oct 3, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> For the most part, I agree with your statements above. The problem though is that I am finding that very often you have a tendency to cherry pick tests under one test and load condition and use them as a general conclusion under all conditions. The early P-39 with the -35 and -63 engines are a good example. They were cool little screamers at low altitude, but those engines didn't have enough performance at altitude. The climb test at each altitude against the Aleutian A6M2 proved that despite attempts by the pilot to play with boost settings, he couldn't make up the difference past about 12,500 feet even though the testing was arranged to make US fighters look as good as possible against a beat up A6M2.
> 
> ...


The P-39D-1 was the heaviest of the early P-39s at 7850lbs. My whole point is that the weight could be easily reduced AT FORWARD BASES by removing some equipment that wasn't needed. The weight reduction was primarily to increase climb rate and ceiling AT ALL ALTITUDES. The P-39 was already 40mph faster at all altitudes than the 1942 Zero. Just using combat power in climb would make the early P-39s equal to the Zero, and the weight reduction would increase climb rate to well above the Zero. With climb AND speed greater than the Zero the air battles would have been very different.

Regarding the FW190A, look at the climb charts for each model -3 through -8. They are all about the same. Much lower than Faber's 190A-3 as tested by the British.


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## XBe02Drvr (Oct 3, 2020)

Ivan1GFP said:


> When the competitions were run, I was a bit surprised when the 914s were winning everything. Some of the faster drivers simply laid on the gas and drifted through every turn. None of the other cars could do the same.


It's that mid-engine design with optimum weight distribution. Works a lot better for a Porsche 914 than a Bell P39.

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## XBe02Drvr (Oct 3, 2020)

Ivan1GFP said:


> One point I forgot to mention about the repair work is that one prop blade needed straightened and reconditioned and it is not mentioned in the repair items.


That's the one that sudden-stopped the engine.


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## SaparotRob (Oct 3, 2020)

I read Samauri by Saburo Sakai many years ago. He wrote, IIRC, having spotted a P-39 he came up above and behind it. He followed it noting its cruise speed and the altitude. I think he wrote 200 knots. I can’t remember the altitude. He then shot it down. Of course Sakai Saburo was flying a Zero but which model I can’t recall.

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## XBe02Drvr (Oct 3, 2020)

SaparotRob said:


> I read Samauri by Saburo Sakai many years ago. He wrote, IIRC, having spotted a P-39 he came up above and behind it. He followed it noting its cruise speed and the altitude. I think he wrote 200 knots. I can’t remember the altitude. He then shot it down. Of course Sakai Saburo was flying a Zero but which model I can’t recall.


I read that years ago also, and given the timing of this event, when IJNAF vs USAAF/RAAF were trading raids back and forth Port Moresby-Lae, likely it was an A6M2.
IIRC, he followed the P39, inspected it closely, marvelled that the pilot seemed to never look in his mirror, then turned off his machine guns, just touched the trigger, and shot it down with four cannon shells, the shortest burst he could fire.

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## buffnut453 (Oct 3, 2020)

P-39 Expert said:


> My whole point is that the weight could be easily reduced AT FORWARD BASES by removing some equipment that wasn't needed. The weight reduction was primarily to increase climb rate and ceiling AT ALL ALTITUDES.



But the simple fact is that the people operating the P-39 didn't do that. Removing unnecessary weight is hardly rocket science, providing it can be done without upsetting the aircraft's CofG. If it was so simple to accomplish and if it would achieve such beneficial results, why wasn't it done? There must be a reason why such an obvious improvement was not implemented.

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## P-39 Expert (Oct 3, 2020)

buffnut453 said:


> But the simple fact is that the people operating the P-39 didn't do that. Removing unnecessary weight is hardly rocket science, providing it can be done without upsetting the aircraft's CofG. If it was so simple to accomplish and if it would achieve such beneficial results, why wasn't it done? There must be a reason why such an obvious improvement was not implemented.


Depends on when that happened, but remember in mid '42 the AAF had no combat experience outside of a couple of guys who got off the ground at Pearl Harbor. Nobody really knew what they were doing. 

The extra weight and the 110gal drop tank meant the P-39 had trouble getting over 17-18000'. Too bad for the guys that were there, made their lives very difficult.


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## buffnut453 (Oct 3, 2020)

P-39 Expert said:


> Depends on when that happened, but remember in mid '42 the AAF had no combat experience outside of a couple of guys who got off the ground at Pearl Harbor. Nobody really knew what they were doing.



True enough, but the RAAF Buffalo pilots were ripping "unnecessary" weight out of their aircraft after just 3 weeks fighting the Japanese - and none of those Aussies had combat experience prior to 8 Dec 41. From May-August 1942, air combat between USAAF P-39s and Zeros was commonplace. That's 4 months...plenty of time to identify the need for improvement. 

Again, I have to ask why the boots on the ground (or in the cockpit) didn't do something to improve the performance if it was as easy and as impactful as you suggest? Is it possible that the theoretical performance improvements you're proposing weren't achievable in practice?

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## Elmas (Oct 3, 2020)

If I remember well, the Zero had a propeller built under an Hamilton Standard license.
So, probably it wasn't too difficult to repair it.
From memory, I may be wrong.


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## XBe02Drvr (Oct 3, 2020)

Elmas said:


> If I remember well, the Zero had a propeller built under an Hamilton Standard license.
> So, probably it wasn't too difficult to repair it.
> From memory, I may be wrong.


You're not wrong. I've read that from several sources. I believe the only changes were to substitute metric hardware.


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## XBe02Drvr (Oct 3, 2020)

buffnut453 said:


> Again, I have to ask why the boots on the ground (or in the cockpit) didn't do something to improve the performance if it was as easy and as impactful as you suggest? Is it possible that the theoretical performance improvements you're proposing weren't achievable in practice?


I suspect it might have something to do with the local chain of command and how willing they'd be to tolerate "unauthorized" modifications to the aircraft. Feeling vulnerable to criticism due to the less-than-stellar performance of their fighters, they'd be afraid that the poor performance record would get blamed on those modifications. Basic careerthink.
If you look at the P39D carefully, it should become obvious that it wasn't slated to be a stellar tropical fighter. Too much airplane sitting on too little wing with a less than optimum airfoil, and equipped with a low altitude engine whose unorthodox location made the plane prone to squirrelly handling under some combat conditions, just isn't the optimum setup for fighting in the high teens and low twenties in the high temperatures and density altitudes of New Guinea. Even though the performance charts supposedly give it a significant ultimate level flight speed advantage over the Zero, the thin air at those altitudes would likely limit its maneuverability and its acceleration enough to give the Zero a good shot at it before it can pull out of range. There's just so little excess power for climbing, accelerating, or turning.
I don't know how many of you have tried to coax a tired airplane with optimistically rated engines up to its performance chart altitudes and speeds, but I can tell you from frequent experience, it's a frustrating exercise. It wallows like a half flooded lifeboat and acts sluggish like it was approaching a stall, which it is, and steadfastly refuses to get on the step. A Be1900 with both engines in need of hot section overhauls in the first hot days of spring after a winter of eating sand in beta on slippery airport surfaces, is a classic example. You can't make flight planned speeds at flight planned altitudes and are constantly exceeding flight planned fuel burns, necessitating more frequent fueling than the schedule allows. The hurrier you go, the behinder you get.

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## buffnut453 (Oct 3, 2020)

XBe02Drvr said:


> I suspect it might have something to do with the local chain of command and how willing they'd be to tolerate "unauthorized" modifications to the aircraft.



Don't disagree. However, during WW2 it's usually the Brits who get painted as the rule-bound bureaucrats while the American free-spirit-thinkers just did what was needed to get the job done. Given the very rough field conditions at Guadalcanal, I have a really hard time believing that stuff-shirtedness would last very long. 

Maintenance rules were being broken all the time on Guadalcanal as wrecks were cannibalized for spares. The prospect of greatly improving the performance of the key USAAF fighter in the region by "simply" removing some unnecessary armour plate and the "useless" wing guns strikes me as small beans compared to some of the hybrid airframes that are seen in photos. The book "Lightning Strikes" by Donald A. Davis describes one of the hybrid airframes at Cactus:

*“Since there were so few P-400’s in service, every cannibalized part could keep another plane flying. The favorite P-400 on the island was a battered craft that had skidded to a halt one day after landing on its belly because its wheels collapsed. It came to a rest with a wing crumpled and the propeller bent, making it an open source for spare parts. However, the need for flyable aircraft was so great that mechanics nursed it back to health. One wing was U.S. Army olive green and the other was British camouflage. Instruments were plugged into gapping holes in the cockpit panel. The three-bladed propeller contained two blades from one wrecked plane and one blade form another; it was balanced by pouring lead in until it spun almost correctly. The aircraft took on a strange personality all its own and would outlast every other plane in the squadron. It was proudly christened The Resurrection.”* 

Given that mish-mash of parts and missing components, the prospect of taking out armour plate and a couple of wing guns really is trivial.

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## XBe02Drvr (Oct 3, 2020)

buffnut453 said:


> Given the very rough field conditions at Guadalcanal, I have a really hard time believing that stuff-shirtedness would last very long.


Guadalcanal was a "generation" of war experience later and an even more desperate situation with a longer and more tenuous supply chain than early days in New Guinea, with the IJNAF by day and Tokyo Express by night. And don't forget "Maytag Charlie"!
And the P400s with their non US standard setups were in an even more desperate spares situation. Any tendency toward formality would be long gone by then, especially with Gen Vandegrift around.



buffnut453 said:


> Instruments were plugged into gapping holes in the cockpit panel.


We used to have an Albany based competitor on the SLK-ALB-LGA run who ran ancient beatup Be99s that fit the above description and would have made "The Resurrection" look like a virgin. Great source of pilot recruits, as our company actually paid a living wage, and these guys came to us deep in debt, but well experienced in emergency procedures. Despite being headquartered right next to the FAA FSDO, who received constant complaints about them, their owner's political clout rendered them untouchable until a change of administration in NY state government and the end of the Reagan administration deprived him of his influential connections. Then they lost their certificate.

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## SaparotRob (Oct 3, 2020)

XBe02Drvr said:


> Guadalcanal was a "generation" of war experience later and an even more desperate situation with a longer and more tenuous supply chain than early days in New Guinea, with the IJNAF by day and Tokyo Express by night. And don't forget "Maytag Charlie"!
> And the P400s with their non US standard setups were in an even more desperate spares situation. Any tendency toward formality would be long gone by then, especially with Gen Vandegrift around.
> 
> 
> We used to have an Albany based competitor on the SLK-ALB-LGA run who ran ancient beatup Be99s that fit the above description and would have made "The Resurrection" look like a virgin. Great source of pilot recruits, as our company actually paid a living wage, and these guys came to us deep in debt, but well experienced in emergency procedures. Despite being headquartered right next to the FAA FSDO, who received constant complaints about them, their owner's political clout rendered them untouchable until a change of administration in NY state government and the end of the Reagan administration deprived him of his influential connections. Then they lost their certificate.


That’s quite an item for job application. “Experienced in aircraft catastrophes because I worked for a corrupt air carrier.”

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## XBe02Drvr (Oct 3, 2020)

SaparotRob said:


> That’s quite an item for job application. “Experienced in aircraft catastrophes because I worked for a corrupt air carrier.”


We stole quite a few pilots from ragtag marginal commuter carriers. It was the boomtown expansion of the regional airline industry in the 1980s, stepping in to serve the smaller places the majors were allowed to abandon under deregulation. It attracted all kinds of slick operators trying to build an empire on other people's money, often with limited understanding of the nuts and bolts of aviation business. It was the Reagan era, entrepreneurship was king, the rules were often more winked at then obeyed, and the carnage was horrendous by today's standards. Shoddy operators like Frank Lorenzo, Carl Icahn, and Allyn Caruso were the darlings of the entrepreneur worshipping set as they amassed fortunes and power off the backs of their creditors, their employees, and the diminished safety of the flying public.
OTOH, they gave pilot jobs to unlikely specimens of airline pilotage like me, who wouldn't have a snowball's chance you know where of getting hired by a major airline. (Not military trained, too tall, too skinny, too unattractive, wearing *THICK *glasses, history of eye disease and other chronic conditions, and a little shy on multi engine time.) I just didn't fit the desired profile. Oddly enough a lot of the "less desirables" who got hired by commuter airlines that survived the consolidation wars and were absorbed into the major airline networks wound up retiring as senior captains at American or United or Delta, including some of the folks I flew with at Brockway, who went over to Business Express after we went Chapter 11, then 7, thanks to Carl Icahn.


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## XBe02Drvr (Oct 3, 2020)

buffnut453 said:


> during WW2 it's usually the Brits who get painted as the rule-bound bureaucrats while the American free-spirit-thinkers just did what was needed to get the job done.


And where was USAAF's SW Pacific base of operations, command and control? In RAAF territory with plenty of RAF bureaucrats right at hand. "When in Rome, do as...etc, etc."


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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> And where was USAAF's SW Pacific base of operations, command and control? In RAAF territory with plenty of RAF bureaucrats right at hand. "When in Rome, do as...etc, etc."



Oh come off it. Are you really suggesting that it's the Brit's fault that Americans didn't take steps to improve their own aircraft? Really??? That's too much. Has ANY American listened to a Brit since 1775?


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## Ivan1GFP (Oct 4, 2020)

XBe02Drvr said:


> That's the one that sudden-stopped the engine.



Hello XBe02Drvr,

You might be right, but I suspect that more likely it was the one that ended up stuck in the mud for a couple months when the plane flipped over. That blade sticks out pretty far and the flip was violent enough to destroy the canopy and buckle the fuselage at the cockpit. I still can't quite figure out how exactly the plane wiped off both main gear, scraped up the belly and flipped without that much damage to the underside of the cowl or the other two prop blades.

- Ivan.


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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> Guadalcanal was a "generation" of war experience later and an even more desperate situation with a longer and more tenuous supply chain than early days in New Guinea, with the IJNAF by day and Tokyo Express by night.



First combat for the 39th took place on 30 Apr 1942 so hardly a 'generation' of war experience. Regardless, even if we include the experience of getting P-39s operational in New Guinea as 'war experience' it still doesn't change my question, in fact it makes it even more relevant.

Inexperienced Aussies operating in Singapore under RAF command could strip weight out of their Buffalos, including changing 50cals for 303s in the wings, after just 3 weeks of combat. Why, then, didn't any USAAF units do a similar thing with their P-39s and P-400s? 

The "they were inexperienced" excuse doesn't make sense, nor does it tally with the innovation demonstrated at Guadalcanal, first erecting P-400s without manuals and then keeping them flying despite the incredibly long and at-risk supply chain.

Of note, "Buzz" Wagner (CO of the 39th) recommended around 8 changes to the P-39 including ADDING armour to protect the engine, and improving reliability of the wing-mounted 30 cals. Again, if the "useless" wing guns weren't reliable, why not just take them out?

It seems to me that someone would at least TRY to reduce the weight of the under-performing P-39s if they thought it would do any good. One logical conclusion is that they didn't think it would help much. 

I'm open to other suggestions but they need to be realistic and relevant.

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## P-39 Expert (Oct 4, 2020)

buffnut453 said:


> First combat for the 39th took place on 30 Apr 1942 so hardly a 'generation' of war experience. Regardless, even if we include the experience of getting P-39s operational in New Guinea as 'war experience' it still doesn't change my question, in fact it makes it even more relevant.
> 
> Inexperienced Aussies operating in Singapore under RAF command could strip weight out of their Buffalos, including changing 50cals for 303s in the wings, after just 3 weeks of combat. Why, then, didn't any USAAF units do a similar thing with their P-39s and P-400s?
> 
> ...


Armor behind the engine was included in the armor totals. Thinking it wouldn't help much and not knowing how much it would help are two different things.


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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> Armor behind the engine was included in the armor totals. Thinking it wouldn't help much and not knowing how much it would help are two different things.



So you do what every good to tinkerer does and try an experiment. That's what the Aussies did. They took one Buffalo, stripped out the excess weight, replaced the wing 50 cals with 30 cals, replaced the 50 cal fairing bumps with smooth sheet, and then they flew a trial against a standard Buffalo. The results were good enough that, reportedly, they made the change to all the squadron's aircraft (although none of the other Buffalo squadron's followed suit).

None of the above was challenging and it gave a good enough demonstration of the performance improvement. You still need to find a worthwhile excuse for why at least one USAAF P-39/400 squadron didn't attempt something similar.

As to the armour for the engine, I never said there wasn't any. I said Wagner asked for more of it.

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## buffnut453 (Oct 4, 2020)

While I'm on a roll here, also remember a few weeks ago the discussion of how Americans were so much better equipped for WW2 because they all had Model Ts and knew how to tinker with engines? Now, apparently, it was beyond the ken of those same Americans to realise that removing unnecessary weight from an aircraft would improve its performance...and that they couldn't work out how to demonstrate those benefits objectively.

C'mon fellas...pick one side of an argument and stick with it, please. 😃

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## Elmas (Oct 4, 2020)

buffnut453 said:


> Don't disagree. However, during WW2 it's usually the Brits who get painted as the rule-bound bureaucrats while the American free-spirit-thinkers just did what was needed to get the job done. Given the very rough field conditions at Guadalcanal, I have a really hard time believing that stuff-shirtedness would last very long.
> 
> Maintenance rules were being broken all the time on Guadalcanal as wrecks were cannibalized for spares. The prospect of greatly improving the performance of the key USAAF fighter in the region by "simply" removing some unnecessary armour plate and the "useless" wing guns strikes me as small beans compared to some of the hybrid airframes that are seen in photos. The book "Lightning Strikes" by Donald A. Davis describes one of the hybrid airframes at Cactus:
> 
> ...



It wasn't done just in Guadalcanal...


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## Ivan1GFP (Oct 4, 2020)

P-39 Expert said:


> The P-39D-1 was the heaviest of the early P-39s at 7850lbs. My whole point is that the weight could be easily reduced AT FORWARD BASES by removing some equipment that wasn't needed. The weight reduction was primarily to increase climb rate and ceiling AT ALL ALTITUDES. The P-39 was already 40mph faster at all altitudes than the 1942 Zero. Just using combat power in climb would make the early P-39s equal to the Zero, and the weight reduction would increase climb rate to well above the Zero. With climb AND speed greater than the Zero the air battles would have been very different.



Hello P-39 Expert,

Despite evidence to the contrary, you refuse to accept that the early P-39 really DIDN'T have a 40 MPH speed advantage over the A6M2. The problem also is that very often actual maximum speed is meaningless because of how long it takes to get there. The A6M in most models had extremely good low and medium speed acceleration which is why the tests against the Aleutian A6M2 didn't start there. If the P-39 takes the time to fly straight and level to accelerate to the point where it can pull away from the A6M2, it has spent far too long in gun range.

The testing described in IIS 85 showed that even at the P-39D's dritical altitude at which its engine has the greatest advantage, the A6M2 had gained the advantage in climb rate. Power would fall off pretty quickly after that.
The A6M2 only had a critical altitude about 1000-1500 feet high but for some reason was able to maintain its climb rate much better.

Now keep in mind that even though the A6M2 had better climb performance, the Japanese themselves recognized that it was at a disadvantage in combat at higher altitudes which is why later models of A6M switched to a two-speed supercharger.



P-39 Expert said:


> The extra weight and the 110gal drop tank meant the P-39 had trouble getting over 17-18000'. Too bad for the guys that were there, made their lives very difficult.



The problem is that without the drop tank, the P-39 didn't have the endurance to do anything useful or even get to where the fight was.



P-39 Expert said:


> Regarding the FW190A, look at the climb charts for each model -3 through -8. They are all about the same. Much lower than Faber's 190A-3 as tested by the British.



That is probably because the typical testing of climb performance was at 1.35 ATA and 2450 RPM while Faber's A-3 was tested at 1.42 ATA and probably 2700 RPM.
By the way, which chart shows tests of the Ground Attack version I was referring to?
If your charts show nearly the same climb performance for the FW 190A-3 through FW 190A-8, there is something seriously wrong. The late models weighed over 1200 pounds more than the early ones and were not nearly as slick because of changes in armament.

- Ivan.

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## P-39 Expert (Oct 4, 2020)

buffnut453 said:


> So you do what every good to tinkerer does and try an experiment. That's what the Aussies did. They took one Buffalo, stripped out the excess weight, replaced the wing 50 cals with 30 cals, replaced the 50 cal fairing bumps with smooth sheet, and then they flew a trial against a standard Buffalo. The results were good enough that, reportedly, they made the change to all the squadron's aircraft (although none of the other Buffalo squadron's followed suit).
> 
> None of the above was challenging and it gave a good enough demonstration of the performance improvement. You still need to find a worthwhile excuse for why at least one USAAF P-39/400 squadron didn't attempt something similar.
> 
> As to the armour for the engine, I never said there wasn't any. I said Wagner asked for more of it.


So substituting two .30calMGs for two .50calMGs saved, what, 100lbs? And that improved performance enough to modify the whole squadron? And removing 300+lbs wouldn't help a P-39? I have no excuse for why the weight wasn't reduced on P-39s. But I am sure it would have helped tremendously.


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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> So substituting two .30calMGs for two .50calMGs saved, what, 100lbs? And that improved performance enough to modify the whole squadron? And removing 300+lbs wouldn't help a P-39? I have no excuse for why the weight wasn't reduced on P-39s. But I am sure it would have helped tremendously.



Sorry, but you have to explain why it wasn't done and why Wagner was asking for more armour not less. Frankly, I trust the experience of the operators at the time. If the improvements you cite would have improved performance to the extent you propose, I have to believe it would have been attempted.

The other option is that the theoretical benefits you keep pushing based on performance diagrams weren't achievable in the real world, and the men who were there at the time knew they were already wringing out the maximum performance from their aircraft.

My company prides itself on solving hard problems in the public interest. Typically, if there's an easy solution to a hard problem, then we don't get involved because it's already been tried. I think that principle applies in the case of the P-39. If it could have been substantively improved in the field, it would have been. I'm afraid no amount of theoretical chart analysis will change that.

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## Ivan1GFP (Oct 4, 2020)

buffnut453 said:


> While I'm on a roll here, also remember a few weeks ago the discussion of how Americans were so much better equipped for WW2 because they all had Model Ts and knew how to tinker with engines? Now, apparently, it was beyond the ken of those same Americans to realise that removing unnecessary weight from an aircraft would improve its performance...and that they couldn't work out how to demonstrate those benefits objectively.
> 
> C'mon fellas...pick one side of an argument and stick with it, please. 😃



Hello buffnut453,

I would say there is a vast difference between messing with a car in which screwing up just means you pull it over on the side of the road and finding out you screwed up in an aeroplane while flying at 10,000 feet.

I once watched a family living next to me spend over a month pulling out an old V-6 from a sputtering and battered old Buick Regal and order a Chevy 350 crate motor to replace it. They eventually got it installed. It sounded pretty good and could chirp the tires nicely.
A couple weeks later, the car disappeared. They didn't seem to want to talk about what happened so I didn't ask.

I remember watching as my Dad tried to explain to their dad why their lawn mower would not start. From that conversation, I gathered that the general level of technical knowledge and analytical ability in that bunch wasn't really that high but it never stopped them from working on their own cars.
A lot of people may work on cars, but that doesn't mean everyone is good at it.

- Ivan.


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## P-39 Expert (Oct 4, 2020)

buffnut453 said:


> Sorry, but you have to explain why it wasn't done and why Wagner was asking for more armour not less. Frankly, I trust the experience of the operators at the time. If the improvements you cite would have improved performance to the extent you propose, I have to believe it would have been attempted.
> 
> The other option is that the theoretical benefits you keep pushing based on performance diagrams weren't achievable in the real world, and the men who were there at the time knew they were already wringing out the maximum performance from their aircraft.
> 
> My company prides itself on solving hard problems in the public interest. Typically, if there's an easy solution to a hard problem, then we don't get involved because it's already been tried. I think that principle applies in the case of the P-39. If it could have been substantively improved in the field, it would have been. I'm afraid no amount of theoretical chart analysis will change that.


In May of 1942 Larry Bell sent the AAF a list of weight reduction items that would have saved 1000lbs. None were implemented by the AAF.


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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> In May of 1942 Larry Bell sent the AAF a list of weight reduction items that would have saved 1000lbs. None were implemented by the AAF.



Again, stick to one side of the argument please. This observation is at the AAF level yet previously you said that all the changes you propose could have been done by squadrons in the field. AAF policy had little meaning at Guadalcanal.

You cited Wagner's combat record as evidence of the P-39s qualities and yet that same Wagner wanted more armour protection AND he wanted the 30 cals in the wings. He never said "stop putting useless 40 cals in the wings", he just wanted the guns to work. 

You're the one who keeps adding the adjective "useless" to the wing 30 cals and yet Wagner still wanted them. If he didn't, he'd have said so. Therefore, the operational squadron boss didn't find them useless.

You really have to come up with some explanation for why your "simple" changes weren't implemented. The actual reason, I suspect, is that the operational pilots wanted every item that they flew with, and none of it was "useless" from their perspective.

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## buffnut453 (Oct 4, 2020)

Ivan1GFP said:


> Hello buffnut453,
> 
> I would say there is a vast difference between messing with a car in which screwing up just means you pull it over on the side of the road and finding out you screwed up in an aeroplane while flying at 10,000 feet.
> 
> ...



Ivan,

I wasn't the one pushing that idea, in fact I find it vaguely ridiculous. Other forum members were suggesting that American youth grew up with an inmate ability to resolve mechanical problems because every farmer had a beat-up Model T. It's an attempt to demonstrate American exceptionalism compared to other nations in an area where, frankly, it didn't exist.


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## XBe02Drvr (Oct 4, 2020)

buffnut453 said:


> Oh come off it. Are you really suggesting that it's the Brits fault that Americans didn't take steps to improve their own aircraft? Really??? That's too much. Has ANY American listened to a Brit since 1775?


No, I'm suggesting the cultural climate of the USAAF's hosts might have had an inhibiting effect on the more innovative impulses of the American squadrons. Not blaming the British, just acknowledging their potential influence. The farther they get from HQ and the big brass, the less inhibited the innovators become.

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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> No, I'm suggesting the cultural climate of the USAAF's hosts might have had an inhibiting effect on the more innovative impulses of the American squadrons. Not blaming the British, just acknowledging their potential influence. The farther they get from HQ and the big brass, the less inhibited the innovators become.



I still don't buy it. US-Brit relations may have been relevant at the operational level but not at the squadron level.


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## XBe02Drvr (Oct 4, 2020)

Ivan1GFP said:


> Hello XBe02Drvr,
> 
> You might be right, but I suspect that more likely it was the one that ended up stuck in the mud for a couple months when the plane flipped over. That blade sticks out pretty far and the flip was violent enough to destroy the canopy and buckle the fuselage at the cockpit. I still can't quite figure out how exactly the plane wiped off both main gear, scraped up the belly and flipped without that much damage to the underside of the cowl or the other two prop blades.
> 
> - Ivan.


Visualize Koga's approach. He's touching down in tall grass with an unknown surface below. Because of his flat viewing angle, he's not going to catch the gleam of the water below. The slowest, softest touchdown with a taildragger is accomplished with an exaggerated three point landing, likely tailwheel first, and the engine ticking over a little above idle to aid in controllability. This was a one shot attempt, as his engine was practically out of oil and not likely to survive a go around.
As his tailwheel starts to drag in the tundra, the mains splash down, dig in hard, and flip the plane violently ass over teakettle onto its prop spinner then onto its back, capturing one prop blade underneath and sudden-stopping the engine. The main gear struts probably didn't come completely unglued until after the somersault impetus was well underway. I remember reading that one of the recovery party remarked that the landing gear struts were lying in rather odd locations, given the imagined gyrations of the aircraft.
Take a model of a Zero or other low wing taildragger and "hand fly" it through a couple table top three point landings, noting the angles at which the landing gears contact the surface. I think it will become self evident.


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## XBe02Drvr (Oct 4, 2020)

buffnut453 said:


> One logical conclusion is that they didn't think it would help much.


Valid point, and I think, a likely answer. I tend to think that in extreme situations the guys on the flight line tend towards doing what needs to be done, while the chain of command is apt to lean on "by the book". The more remote the flight line is from the chain of command, the more likely are experimentation and innovation to flourish.


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## Shortround6 (Oct 4, 2020)

P-39 Expert said:


> So substituting two .30calMGs for two .50calMGs saved, what, 100lbs? And that improved performance enough to modify the whole squadron? And removing 300+lbs wouldn't help a P-39? I have no excuse for why the weight wasn't reduced on P-39s. But I am sure it would have helped tremendously.


Changing the .50s for .30s would save only about 100lbs, you are correct on that. but guns without ammo are pretty worthless. You can carry 500 rounds of .303 for the same weight as 100 rounds of .50 cal ammo. I don't know what that squadron was using for an ammo load for the .50s per gun nor do I know what they used for the .303s but obviously there is another 60-100lbs of weight loss just in ammo. I don't know if they took anything else out. 

Then we have the 37mm problem, it wasn't very reliable at first, yes it got fixed, but when? Taking out the .30s in early/mid 1942_ if _the 37mm wasn't fixed yet might not have been a good idea? Apparently many of the US gun installations were not trouble free in early 1942. 

the 'worthless' wing 30s were about 3 times the firepower of the cowl guns in the A6M2. Perhaps the Japanese should have pulled those guns to improve performance?


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## XBe02Drvr (Oct 4, 2020)

buffnut453 said:


> apparently, it was beyond the ken of those same Americans to realise that removing unnecessary weight from an aircraft would improve its performance...and that they couldn't work out how to demonstrate those benefits objectively.
> 
> C'mon fellas...pick one side of an argument and stick with it, please. 😃


Colonel REMF: "Lieutenant, what are you doing to that aircraft? Who authorized it?"
Lieutenant Nonothing: "Sir, my crew chief and I are conducting an experiment, Sir. Removing useless weight to improve performance, Sir! Our squadron maintenance officer said he thought these planes are overweight and causing our heavy losses in combat, Sir."
Colonel: "Lieutenant, every item in that aircraft is ESSENTIAL! Otherwise the Air Corps wouldn't have put it there! Now put all that stuff back in where it belongs, and don't make any changes unless IAW the P39 Maintenance Tech Order, DO YOU READ ME, LIEUTENANT?"
Lieutenant: "Yes Sir!"

A bit exaggerated, but indicative of an attitude that might explain the lack of initiative in "fixing" the P39.

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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> Colonel REMF: "Lieutenant, what are you doing to that aircraft? Who authorized it?"
> Lieutenant Nonothing: "Sir, my crew chief and I are conducting an experiment, Sir. Removing useless weight to improve performance, Sir! Our squadron maintenance officer said he thought these planes are overweight and causing our heavy losses in combat, Sir."
> Colonel: "Lieutenant, every item in that aircraft is ESSENTIAL! Otherwise the Air Corps wouldn't have put it there! Now put all that stuff back in where it belongs, and don't make any changes unless IAW the P39 Maintenance Tech Order, DO YOU READ ME, LIEUTENANT?"
> Lieutenant: "Yes Sir!"
> ...



Believe me, I'm fully conversant in the ways military intransigence can rear it's ugly head. However, I'm pretty certain there weren't many REMF O-6s in either PNG or Guadalcanal. 

Also, I'm going to stress (again) Wagner's critique of the P-39. He wanted more armour to protect the engine and wing 30 cals that worked. Therefore, he clearly didn't think there was excess "useless" weight to be removed. Also he was an O-5 in charge of a squadron...and I don't see him listening to any O-6 REMF (i.e. "It's my squadron and I'll do what I want with it. You aren't in my chop chain, sir, so you can go and do u speakable things to yourself...with all due respect, sir.").

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## Milosh (Oct 4, 2020)

fastmongrel said:


> I am not sure of the exact fuel used at the time. My point was that there was no British fuel the same as there was no US fuel it was as far as possible a universal Allied fuel.


There might have been a standard spec but part of the problem with the P-38 at one time, iirc, was the use of 'Brit' avgas. When American avgas was used the problem disappeared. Anyways, the fuel used in Faber's 190 was drawn from a 'Brit' fuel tank.


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## buffnut453 (Oct 4, 2020)

Shortround6 said:


> Changing the .50s for .30s would save only about 100lbs, you are correct on that. but guns without ammo are pretty worthless. You can carry 500 rounds of .303 for the same weight as 100 rounds of .50 cal ammo. I don't know what that squadron was using for an ammo load for the .50s per gun nor do I know what they used for the .303s but obviously there is another 60-100lbs of weight loss just in ammo. I don't know if they took anything else out.



In addition to swapping out the wing guns, the Aussies also reduced ammo load, removed the radio mast, the signal flare system (this was not a hand-held Very pistol but, rather, a substantial metal tube located in the rear fuselage), cockpit heater and ducting, and a few other items I can't recall off the top of my head.

I didn't want to specify everything previoualy because the exact details aren't germane to the general question of why USAAF squadron's didn't attempt something similar.


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## P-39 Expert (Oct 4, 2020)

Shortround6 said:


> Changing the .50s for .30s would save only about 100lbs, you are correct on that. but guns without ammo are pretty worthless. You can carry 500 rounds of .303 for the same weight as 100 rounds of .50 cal ammo. I don't know what that squadron was using for an ammo load for the .50s per gun nor do I know what they used for the .303s but obviously there is another 60-100lbs of weight loss just in ammo. I don't know if they took anything else out.
> 
> Then we have the 37mm problem, it wasn't very reliable at first, yes it got fixed, but when? Taking out the .30s in early/mid 1942_ if _the 37mm wasn't fixed yet might not have been a good idea? Apparently many of the US gun installations were not trouble free in early 1942.
> 
> the 'worthless' wing 30s were about 3 times the firepower of the cowl guns in the A6M2. Perhaps the Japanese should have pulled those guns to improve performance?


Four .30calMGs with two synchronized is not much armament for a modern fighter. 

I was assuming the ammo load weight for both the .30s and .50s was approximately the same.


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## P-39 Expert (Oct 4, 2020)

XBe02Drvr said:


> Colonel REMF: "Lieutenant, what are you doing to that aircraft? Who authorized it?"
> Lieutenant Nonothing: "Sir, my crew chief and I are conducting an experiment, Sir. Removing useless weight to improve performance, Sir! Our squadron maintenance officer said he thought these planes are overweight and causing our heavy losses in combat, Sir."
> Colonel: "Lieutenant, every item in that aircraft is ESSENTIAL! Otherwise the Air Corps wouldn't have put it there! Now put all that stuff back in where it belongs, and don't make any changes unless IAW the P39 Maintenance Tech Order, DO YOU READ ME, LIEUTENANT?"
> Lieutenant: "Yes Sir!"
> ...


Agree, especially at this very early stage in the war for the AAF.


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## P-39 Expert (Oct 4, 2020)

buffnut453 said:


> Again, stick to one side of the argument please. This observation is at the AAF level yet previously you said that all the changes you propose could have been done by squadrons in the field. AAF policy had little meaning at Guadalcanal.
> 
> You cited Wagner's combat record as evidence of the P-39s qualities and yet that same Wagner wanted more armour protection AND he wanted the 30 cals in the wings. He never said "stop putting useless 40 cals in the wings", he just wanted the guns to work.
> 
> ...


I have only one side of any P-39 argument: the early D/F/K/L models with the 8.8 supercharged engines were way overweight at 7650-7850lbs. Removing some useless or redundant equipment would have improved their climb rate/ceiling substantially and allowed them to dominate the early A6M2 Zero. Speed advantage+climb advantage+dive advantage.

And Wagner's assessment was after only the first week of combat. If the P-39s were lighter and could get above the Zeros he wouldn't have needed any extra engine armor.


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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> And Wagner's assessment was after only the first week of combat. If the P-39s were lighter and could get above the Zeros he wouldn't have needed any extra engine armor.



So you know better than the guy who was there and who was a credited ace to boot?

I'm lost for words.

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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> Four .30calMGs with two synchronized is not much armament for a modern fighter.
> 
> I was assuming the ammo load weight for both the .30s and .50s was approximately the same.



It wasn't 4x30 cals. They only swapped out the wing guns (because the wing 50cals were unreliable). The nose 50cals were retained. 

They clearly thought the mix of 2x50s and 2x303s was sufficient for the adversary they were facing.


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## Ivan1GFP (Oct 4, 2020)

buffnut453 said:


> Ivan,
> 
> I wasn't the one pushing that idea, in fact I find it vaguely ridiculous. Other forum members were suggesting that American youth grew up with an inmate ability to resolve mechanical problems because every farmer had a beat-up Model T. It's an attempt to demonstrate American exceptionalism compared to other nations in an area where, frankly, it didn't exist.



Hello buffnut453,

I am not saying that the idea doesn't have SOME merit. What I am saying is that having experience working on tractors and cars and farm equipment in general may not necessarily translate to aeroplanes. Also, given the same opportunities, some people actually figure out what they are doing and some don't, but if more people are given the opportunity and necessity to experiment, some are bound to learn.

BTW, I know it is a typo, but your "inmate ability" had me laughing...... There is probably an element of truth to it though.

- Ivan.

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## Ivan1GFP (Oct 4, 2020)

XBe02Drvr said:


> Visualize Koga's approach. He's touching down in tall grass with an unknown surface below. Because of his flat viewing angle, he's not going to catch the gleam of the water below. The slowest, softest touchdown with a taildragger is accomplished with an exaggerated three point landing, likely tailwheel first, and the engine ticking over a little above idle to aid in controllability. This was a one shot attempt, as his engine was practically out of oil and not likely to survive a go around.
> As his tailwheel starts to drag in the tundra, the mains splash down, dig in hard, and flip the plane violently ass over teakettle onto its prop spinner then onto its back, capturing one prop blade underneath and sudden-stopping the engine. The main gear struts probably didn't come completely unglued until after the somersault impetus was well underway. I remember reading that one of the recovery party remarked that the landing gear struts were lying in rather odd locations, given the imagined gyrations of the aircraft.
> Take a model of a Zero or other low wing taildragger and "hand fly" it through a couple table top three point landings, noting the angles at which the landing gears contact the surface. I think it will become self evident.



Hello XBe02Drvr,

Sounds like a plausible decision for a pilot in Koga's situation.... but for a few problems.
Go through the list of repairs again. Note the extensive damage to cowl and forward fuselage ahead of cockpit.
How is it possible with an engine idling to plant the spinner and flip the plane and plant one propeller blade vertically into the mud when the plane flipped and then only have one damaged propeller blade?
I don't believe the engine was turning any more when he touched down.

- Ivan.


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## glennasher (Oct 4, 2020)

XBe02Drvr said:


> Back to P39s. Do I detect the sickly aroma of an expired equine carcass? My toes are bruised and bleeding; how about yours?



The aroma has long passed on, all that's left is the hide and bones.


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## XBe02Drvr (Oct 4, 2020)

M


Ivan1GFP said:


> Note the extensive damage to cowl and forward fuselage ahead of cockpit.


In the words of forensic pathologists, "blunt force trauma". Once it stubbed its toe in the tundra, it would have bashed its nose in the mud as it flipped onto its back.



Ivan1GFP said:


> I don't believe the engine was turning any more when he touched down.


Then how do you account for the need to straighten twelve connecting rods? On a radial with that much rotating mass that's generally indicative of a sudden stop. The master rod in each cylinder row is massive and generally doesn't bend. Have you ever been inside one of these beasts?
Single engine planes generally don't have full feathering propellers, so even if the engine had quit running or was shut down it would still be windmilling. The bearings showed overheating but not seizure. Stopping a windmilling prop in flight requires holding the plane right on the edge of a stall for an extended period while engine compression slowly overcomes the aerodynamic windmilling effect, and is unachievable in some planes. A stationary prop significantly improves glide ratio, but is only useful when there's enough altitude to compensate for the loss due to the high sink rate while trying to get the prop stopped.

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## FLYBOYJ (Oct 4, 2020)

P-39 Expert said:


> *If* the P-39s were lighter and could get above the Zeros he wouldn't have needed any extra engine armor.



All I hear is "IF, IF, IF."

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## XBe02Drvr (Oct 4, 2020)

(buffnut453)
Ivan,

I wasn't the one pushing that idea, in fact I find it vaguely ridiculous. Other forum members were suggesting that American youth grew up with an inmate ability to resolve mechanical problems because every farmer had a beat-up Model T. It's an attempt to demonstrate American exceptionalism compared to other nations in an area where, frankly, it didn't exist.




Ivan1GFP said:


> Hello buffnut453,
> 
> I am not saying that the idea doesn't have SOME merit. What I am saying is that having experience working on tractors and cars and farm equipment in general may not necessarily translate to aeroplanes. Also, given the same opportunities, some people actually figure out what they are doing and some don't, but if more people are given the opportunity and necessity to experiment, some are bound to learn.


I'm not claiming American technology was innately superior, certainly not to British or German, where we were a distant third or perhaps not on the podium at all, nor was I claiming tractor tinkerers would make instant aircraft maintenance technicians.
What I was saying is that given the size of our population and the degree of mechanical penetration of our society, we could summon a greater cumulative mass of hands-on knuckle- busting, greasy hands, and behind-the-wheel experience than any other nation on earth. Though I dislike the term "American Exceptionalism", if that is what it is, so be it.

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## P-39 Expert (Oct 4, 2020)

buffnut453 said:


> So you know better than the guy who was there and who was a credited ace to boot?
> 
> I'm lost for words.


Are you arguing that less weight doesn't improve climb and ceiling? 

Wagner had a little experience in the Philippines but his pilots had literally no combat experience and the vast majority were just out of flying school. He wrote three reports within the first 15 days of combat. He criticized altitude performance, the .30calMGs and the weak nose gear on the rough airfields. Altitude performance would have been improved by the deletion of the .30calMGs and other redundant equipment. And the AAF learned that paved or steel plank runways were necessary for the forward operation of all AAF planes.


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## FLYBOYJ (Oct 4, 2020)



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## buffnut453 (Oct 4, 2020)

P-39 Expert said:


> Are you arguing that less weight doesn't improve climb and ceiling?



I'm not arguing that less weight doesn't improve climb or ceiling. Clearly you're not reading what I'm writing...or you're deliberately misunderstanding it because you don't like the case I'm making.

I'm questioning whether the weight was necessary or not. You have consistently stated that the wing 30 cals and some amount of armour plate were unnecessary. That view is entirely contradicted by the man on the spot, Boyd Wagner, who clearly thought the 30 cals were necessary and he also asked for more armour plate for the engine. In short, the things you claim as unnecessary were deemed by the commander on-the-spot to be necessary.



P-39 Expert said:


> Wagner had a little experience in the Philippines but his pilots had literally no combat experience and the vast majority were just out of flying school.



And you've assiduously ignored the RAAF example of 453 Sqn which reduced the weight of their Buffalos. None of those pilots, with the exception of the Squadron CO, had ANY combat experience prior to 8 Dec 41 and yet they made the weight reduction modifications around Christmas time 1941.

Again, if inexperienced Aussies could do it with the Buffalo, why didn't USAAF squadrons make similar changes with the P-39 when they were in combat for several months? The only logical explanation is that the people on the spot in PNG and Guadalcanal thought that the "extra weight" of wing 30 cals and armour plate was NECESSARY and not "useless."

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## Ivan1GFP (Oct 4, 2020)

XBe02Drvr said:


> In the words of forensic pathologists, "blunt force trauma". Once it stubbed its toe in the tundra, it would have bashed its nose in the mud as it flipped onto its back.



Hello XBe02Drvr,

Can you show exactly how an upright aeroplane plants one prop blade, flips upside down and then ends up with the SAME prop blade dug into the ground??? I am having a very hard time figuring out the gyrations needed to make that happen.



XBe02Drvr said:


> Then how do you account for the need to straighten twelve connecting rods? On a radial with that much rotating mass that's generally indicative of a sudden stop. The master rod in each cylinder row is massive and generally doesn't bend. Have you ever been inside one of these beasts?
> Single engine planes generally don't have full feathering propellers, so even if the engine had quit running or was shut down it would still be windmilling. The bearings showed overheating but not seizure. Stopping a windmilling prop in flight requires holding the plane right on the edge of a stall for an extended period while engine compression slowly overcomes the aerodynamic windmilling effect, and is unachievable in some planes. A stationary prop significantly improves glide ratio, but is only useful when there's enough altitude to compensate for the loss due to the high sink rate while trying to get the prop stopped.



I am not sure how the engine would stop either with significant forward speed. The only thing I can think of is that it seized because of a lack of oil when he was very slow before he touched down.
You mentioned overheated bearings. Do you have a more thorough repair list?

There were no bent connecting rods in the repair list I have. There were 9 bent push rods. Yes, I have seen the inside of a radial engine but I believe it was a R-2800 in a museum. Seen plenty of torn down auto engines and even helped rebuild a few. FWIW, I believe the Me 109 typically had full feathering props.

- Ivan.


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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> I'm not claiming American technology was innately superior, certainly not to British or German, where we were a distant third or perhaps not on the podium at all, nor was I claiming tractor tinkerers would make instant aircraft maintenance technicians.
> What I was saying is that given the size of our population and the degree of mechanical penetration of our society, we could summon a greater cumulative mass of hands-on knuckle- busting, greasy hands, and behind-the-wheel experience than any other nation on earth. Though I dislike the term "American Exceptionalism", if that is what it is, so be it.



In response to the question "Pre WW2 how many people had even driven a car let alone knew how they worked?" you wrote:

_In the US and to a lesser extent, Canada, Australia and Germany, *many.* In the rest of the world, not so many. The US generation that fought WWII grew up between wars driving and tinkering on cars, trucks, tractors, and for some, even airplanes...You could call it "mechanical advantage". Even destitute poor folk like the Joads in Grapes of Wrath could find a way to acquire an ancient Model T Ford (converted to a pickup truck) in which to make their exodus to California, stopping along the way to grind the valves and fashion new head gaskets out of scrounged materials. This fostered a level of mechanical and operational experience and ingenuity on a broad scale that manifested itself in Construction Battalions, engine rooms, aircraft and tank maintenance shops, and a ready adaptability to aerial, mechanized, and naval warfare on a scale unmatched in the world._

It seems pretty clear to me that you were assuming a level of technical competence in certain countries based on ability to operate/maintain a car, the corollary being that other countries (including the UK) lacked that expertise. As I pointed out in the other thread, in 1940 the UK had the most mechanized army in the world. You don't get to that scale of capability if "not so many" people knew about machinery. 

I believe the only significant difference was in the sizes of populations, not in the degree or extent of mechanical expertise. Circa 1940, the US had a population of 132 million while the UK had just 48 million so, unsurprisingly, the US was able to generate more mechanics. It could also generate more farmers, more mule drivers, more underwater basket-weavers, and any other number of professions.

If population size is a sign of exceptionalism, then India and the China had us beat decades ago.


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## SaparotRob (Oct 4, 2020)

XBe02Drvr and I weren’t inferring American Exceptionalism in the thread about “Exceptional CGI and the Battle of Midway” (or something like that - great thread Admiral!). We were discussing the loss of mechanically trained aircrews. 
The United States, Britain and Germany all had a greater percentage of their populaces involved with machinery IMO. “Righty tighty, lefty loosey” has been ingrained into us since childhood. The draftees in Japan at that time were far less exposed machinery. Therefore, the loss of technically trained maintenance crews was a loss out of proportion for the IJN. 
I’ve seen traditional rice farming up close and personal (from my hammock whilst smoking a maduro and quaffing a Coca-Cola). No technical experience required.


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## XBe02Drvr (Oct 4, 2020)

Ivan1GFP said:


> There were no bent connecting rods in the repair list I have. There were 9 bent push rods.


MEA CULPA, MEA MAXIMA CULPA! My apologies. I rechecked the repair list, and you're right, it *was* pushrods, not conrods. Disregard all my previous conjecture about sudden stops. You're probably also correct about the increasing internal friction likely bringing the prop to a stop during the flare to landing. Large aircooled engines have their piston rings riding on a thicker oil film on the cylinder walls than the more temperature-stable liquid cooled variety. That's why they consume so much oil, and why the internal friction rises more rapidly with oil depletion. No "STP to the rescue" here.
Ptewy! Crow tastes awful! Even barbecued! Even Cajun style!

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## FLYBOYJ (Oct 4, 2020)

buffnut453 said:


> The only logical explanation is that the people on the spot in PNG and Guadalcanal thought that the "extra weight" of wing 30 cals and* armour plate was NECESSARY and not "useless."*



Quoting the report from Buzz Wagner - _"*Lack of armor plate rear protection for the engine and the resultant high vulnerability are the greatest disadvantages of the P-39 type airplane.* All P-39s shot down were hit in the engine and the coolant system."_

If anything Wager felt the P-39 needed MORE armor, not less.


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## buffnut453 (Oct 4, 2020)

XBe02Drvr said:


> Crow tastes awful! Even barbecued! Even Cajun style!



Doesn't it just taste like chicken?

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## SaparotRob (Oct 4, 2020)

buffnut453 said:


> Doesn't it just taste like chicken?


From personal experience I can tell you NO.

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## XBe02Drvr (Oct 4, 2020)

buffnut453 said:


> Doesn't it just taste like chicken?


More like "bean porridge in the pot, nine days old"! Eye of newt and toe of frog for garnish.


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## SaparotRob (Oct 4, 2020)

XBe02Drvr said:


> More like "bean porridge in the pot, nine days old"! Eye of newt and toe of frog for garnish.


That’s how mom made it.


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## XBe02Drvr (Oct 4, 2020)

buffnut453 said:


> I believe the only significant difference was in the sizes of populations, not in the degree or extent of mechanical expertise. Circa 1940, the US had a population of 132 million while the UK had just 48 million


This is where we disagree. I'm convinced that it's an equation in two variables: size of population, and degree of mechanization of that population. Admittedly, nobody worldwide was overly prosperous during the 1930s, but the US, not as depleted and run down by the great world war as the rest of the industrial world, had experienced a booming and prosperous "roaring twenties". Cars, trucks, tractors, motorcycles and even motorboats spread through the population to an unprecedented degree, promoting familiarity with mechanical things on a broad scale. Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
In answer to the question:


buffnut453 said:


> "Pre WW2 how many people had even driven a car let alone knew how they worked?"


 the answer is "a significant majority of the population".

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## fubar57 (Oct 4, 2020)

FLYBOYJ said:


> View attachment 597124


Thank you Joe. That saved me an awful lot of searching

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## Graeme (Oct 4, 2020)

XBe02Drvr said:


> is "a significant majority of the population".



*"Circa 1940, the US had a population of 132 million while the UK had just 48 million."*

Certainly a greater ratio of cars to people in the USA in 1940.
26.5 million on the roads for the USA.
1.34 for Great Britain.

1940 British and European Car Spotters Guide


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## Shortround6 (Oct 4, 2020)

I don't have it to hand but I believe a book by James Dunnigan 

Jim Dunnigan - Wikipedia

went over the american advantage in one chapter. It may have been _How to Make War_

The US did have a much higher per capita ownership of cars/trucks and radios than any other nation in the world. This means that out of every 100 (or 1000) recruits brought into the service (army, air force, navy) the US had a higher percentage of drivers and low grade mechanics than any other country. It certainly does not mean that every US recruit could drive or change a spark plug or change a radio tube in a radio. 

I think you will find that while the British Army was the first to be fully motorized (no more horses except in ceremonial units) The car ownership in the UK by private citizens was significantly lower than in the US. Germany, for all it's propaganda, was even lower. 

for the US car ownership between 1927 and 1940 varied from 192 (in 1933) to 245 per 1000 people. 

Fact #962: January 30, 2017 Vehicles per Capita: Other Regions/Countries Compared to the United States

as for farm tractors





so by 1940 the US had 1.5 million tractors in use on farms. Yes the US was much larger in population than most other countries, but many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort. 

Not saying that other countries had no exposure, just less as percentage of population. This does not make american troops smarter, just better educated or experienced with some mechanical equipment.

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## GrauGeist (Oct 4, 2020)

And American kids loved their "Jalopies" - Bill Overstreet even had whitewalls on his P-51

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## Shortround6 (Oct 4, 2020)

It would seem as of the date of Wagner's letter/report (May 1942) none of the P-39s weapons systems was near a desired standard of reliability and/or serviceability. 
The 37mm was not reliable and difficult to cock/reload in the air. 
The .50 cal guns had problems with the firing solenoids. 
The .30 cal guns were difficult to cock/reload in the air. 

This may have influenced the pilots into keeping whatever guns they had on the theory that out of three different guns systems, something might go off (and continue to go off) when the trigger was pulled. 
later P-39s may have gotten much better. However the question for 1942 is when did each gun system actually get better. 
If you lose one .30 out of four your total firepower doesn't take much of a hit, Losing the 37mm or a .50 makes a more significant difference.

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## FLYBOYJ (Oct 4, 2020)

It also seems, based on Wagner's report, that his 8th PG pilots were dogfighting with the Zeros they encountered (although head on attacks were mentioned) and boom and zoom tactics were yet to be adopted.

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## Ivan1GFP (Oct 5, 2020)

XBe02Drvr said:


> .....Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
> In answer to the question:
> the answer is "a significant majority of the population".



Hello XBe02Drvr,

The same thing happened again more recently in history though not in the United States.
Does anyone remember what it looked like in Cuba when Americans started visiting again a few years ago?
Many of the cars on the roads were from the 1950's. That was the last time the Cubans could import American cars and there weren't any more coming after that. When you can't get replacements, you learn to keep the ones you have running. It was a beautiful sight for the antique car buff.
Of course there were also a bunch of hulks sitting on the side of the road in various places.

- Ivan.

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## XBe02Drvr (Oct 5, 2020)

FLYBOYJ said:


> It also seems, based on Wagner's report, that his 8th PG pilots were dogfighting with the Zeros they encountered (although head on attacks were mentioned) and boom and zoom tactics were yet to be adopted.


It's awfully hard to boom and zoom when you can't get above your enemy. Not enough warning time plus a lackluster rate of climb makes for unpleasant interception geometry. And booming and zooming an opponent with the acceleration and initial climb rate of a Zero in your lead sled can be an unhealthy practice.

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## P-39 Expert (Oct 5, 2020)

FLYBOYJ said:


> View attachment 597124


Two missions, right? One under 1000' and the other at 23000'. The performance above 18000' is probably with drop tank, this is what the performance charts in wwiiaircraftperformance.org show.


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## P-39 Expert (Oct 5, 2020)

buffnut453 said:


> I'm not arguing that less weight doesn't improve climb or ceiling. Clearly you're not reading what I'm writing...or you're deliberately misunderstanding it because you don't like the case I'm making.
> 
> I'm questioning whether the weight was necessary or not. You have consistently stated that the wing 30 cals and some amount of armour plate were unnecessary. That view is entirely contradicted by the man on the spot, Boyd Wagner, who clearly thought the 30 cals were necessary and he also asked for more armour plate for the engine. In short, the things you claim as unnecessary were deemed by the commander on-the-spot to be necessary.
> 
> ...


In a later report Wagner criticized the reliability of the .30s. 

P-39 was a liquid cooled plane, most vulnerable spot on any liquid cooled engine is the coolant radiators. Hard to armor coolant radiators. Nose armor is what should have been deleted. Almost half the weight of the total armor plate/glass protecting the propeller reduction gear that was not armored on the P-38, P-40, P-47 or P-51. 

Again, removing just these two items (nose armor and .30calMGs) would have saved 300lbs, increased climb rate by 360feet/minute and combat ceiling to 29000' (at 3000rpm). That climb increase would have made the early P-39s climb faster than the early Zeros. Speed advantage and climb advantage. P-39 could then attack from above.

Again, I have no idea why the AAF chose to retain these items. Russians immediately removed the .30s on virtually all their P-39s and had great success against the Luftwaffe.


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## nuuumannn (Oct 5, 2020)

GrauGeist said:


> Bill Overstreet even had whitewalls on his P-51



Whitewall tyre (tire!) P-51s look awesome!


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## XBe02Drvr (Oct 5, 2020)

Shortround6 said:


> US car ownership between 1927 and 1940 varied from 192 (in 1933) to 245 per 1000 people.


In 1940 the average US family consisted of 3.76 people,* meaning 1000 people consisted of 265.9 families, who owned 245 cars that year.
I'd say that was a pretty high exposure rate to automotive technology. This may be off by a little, since the cars/1,000 number probably includes corporate and public sector fleet cars, taxicabs, etc. IE:Total passenger car production.
*US Census figures


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## buffnut453 (Oct 5, 2020)

XBe02Drvr said:


> This is where we disagree. I'm convinced that it's an equation in two variables: size of population, and degree of mechanization of that population. Admittedly, nobody worldwide was overly prosperous during the 1930s, but the US, not as depleted and run down by the great world war as the rest of the industrial world, had experienced a booming and prosperous "roaring twenties". Cars, trucks, tractors, motorcycles and even motorboats spread through the population to an unprecedented degree, promoting familiarity with mechanical things on a broad scale. Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
> In answer to the question:
> the answer is "a significant majority of the population".





Graeme said:


> *"Circa 1940, the US had a population of 132 million while the UK had just 48 million."*
> 
> Certainly a greater ratio of cars to people in the USA in 1940.
> 26.5 million on the roads for the USA.
> ...





Shortround6 said:


> I don't have it to hand but I believe a book by James Dunnigan
> 
> Jim Dunnigan - Wikipedia
> 
> ...




Thanks for the responses, gents. I'm replying-to-all to save time and coalesce my response into a couple of key thoughts that apply to all.

There are 2 fundamental flaws in the proposed concept of US mechanical superiority. The first is that other countries had a similar proportion of working-age men engaged in agriculture compared to more technical industries (e.g. Shortround's comment about "many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort."). The second, and far more significant, is the creation of a false dichotomy where car ownership/awareness of the internal combustion engine is directly correlated with technical awareness/proficiency. 

In the 1930s, the UK had a greater proportion of men engaged in industry rather than agriculture compared to the US (figures for 1940 agriculture/industry: US - 18.5/23.4; UK 10%/36%) (Sources: US , UK). Almost all that industrial output required mechanics of some sort or other, whether maintaining pit engines, factory steam plants, machinery or whatever (e.g. one of my cousins who died in WW1 worked in a brewery but his job was maintaining a steam engine). 

Even in rural areas, lower tractor ownership did not equate to a lack of technical expertise. The internal combustion engine was not the only means of providing automotive power, particularly in rural areas. In the UK, a great many farms were still using steam traction engines well into the 1930s. Many of these engines were decades old and required replacement parts to be hand-made/fettled by the owner or the local blacksmith (maybe that's where the workforce came from to hand-make all those Merlin engines?  ).

I come from a working-class industrial town and there were literally hundreds of mechanical firms supporting the town; everything from metal forging to glassmaking to toolmaking and machining. Almost the entire town built, operated or maintained mechanical systems of one sort or another. To suggest that, somehow, these men were technically bereft because they couldn't drive and hadn't operated an internal combustion engine is ludicrous. To cite a personal example, my family only got its first car in the early 1950s. However, my three uncles collectively built the car from multiple boxes of bits. My family was dirt-poor working class but my uncles were all sufficiently technically-minded to build a car from components, and two of them had been driving for well over a decade when they made the car...but they'd never owned a car before.

My fundamental gripe is the over-emphasis of car ownership on the penetration of technology within society. America had certain factors which promoted the internal combustion engine. However, the absence of those factors did not make other populations any less technically savvy/aware, percentage-wise across the workforce.

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## XBe02Drvr (Oct 5, 2020)

P-39 Expert said:


> Nose armor is what should have been deleted. Almost half the weight of the total armor plate/glass protecting the propeller reduction gear that was not armored on the P-38, P-40, P-47 or P-51.


There you go again, removing weight from the front of the plane, despite being told repeatedly by virtually everyone here that's not an acceptable solution for weight and balance reasons. You could probably get away with it by loading all your nose mounted guns to their maximum capacity, then disconnecting the firing circuits so they can't further lighten the nose. Any way you slice it, you've got to have that weight up there, unless you can relocate some heavy items from behind the engine to the nose compartment, or delete them completely.
This isn't rocket science. The folks who built, maintained, and flew this bird knew this stuff. If there were feasible ways of fixing this issue that didn't trample on USAAF's fetishes they would have thought of them long before your time. The Russians, not slaved to the same fetishes, did exactly that. And it served them well.

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## XBe02Drvr (Oct 5, 2020)

buffnut453 said:


> In the 1930s, the UK had a greater proportion of men engaged in industry rather than agriculture compared to the US (figures for 1940 agriculture/industry: US - 18.5/23.4; UK 10%/36%)


Very interesting. What doesn't show here is that with it's vastly greater land under cultivation, and its relatively cheaper cost (in real terms) of farm machinery, US agriculture was significantly more mechanized in terms of machines/farm worker and raw numbers of agricultural machinery than any other nation. So ratios of agricultural/industrial employment aren't necessarily clear cut indicators of likely technical familiarity and experience.
I've taught two Iranians, an Iraqi, and a rural Kenyan to fly, none of whom had much experience with machinery of any kind until adulthood and arrival in the US. Smart guys all, but not technically minded. Visualizing mechanical relationships, understanding airflow, and comprehending such basic physics as gas behavior or gyroscopic properties was a real challenge, despite their well schooled English.


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## buffnut453 (Oct 5, 2020)

XBe02Drvr said:


> Very interesting. What doesn't show here is that with it's vastly greater land under cultivation, and its relatively cheaper cost (in real terms) of farm machinery, US agriculture was significantly more mechanized in terms of machines/farm worker and raw numbers of agricultural machinery than any other nation. So ratios of agricultural/industrial employment aren't necessarily clear cut indicators of likely technical familiarity and experience.



I entirely agree, but then that's rather my point. Different countries had different factors that drove automation and technology in different directions, or which had differing scales of impact on different industries.

Take the fishing industry, for example. As a proportion of US employment, it was probably quite small. Comparatively, the fishing industry in Britain was much more significant, given it is a small island nation with a smaller population. Now consider the thousands of coastal fishing villages in the UK, each with it's fleet of boats. By the 1930s, these were mostly powered vessels which the crew knee how to maintain. Again, it's not automotive or a tractor...but it required technical and machinery understanding that impacted the UK much more than the equivalent industry in the US.


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## Shortround6 (Oct 5, 2020)

P-39 Expert said:


> Again, removing just these two items (nose armor and .30calMGs) would have saved 300lbs, increased climb rate by 360feet/minute and combat ceiling to 29000' (at 3000rpm). That climb increase would have made the early P-39s climb faster than the early Zeros. Speed advantage and climb advantage. P-39 could then attack from above.



again, nose armor weight and balance/CG issues. 

All three guns systems had issues in May of 1942. 
Yanking the .30s may not have been good idea. Not all of the 30s are going to crap out at the same time. 

Russians noted the 37mm (at least early ones) were unreliable. They got better later. 
The "fix" for the .50 cal may have been relatively easy. Wagner says the firing solenoids weren't powerful enough. New (improved) solenoids could be fitted to existing guns. Please note that the recharging of the .50 cal guns was still a manual affair. 




the .50 gun receivers are coming back into the cockpit. the red flags are attached to the cocking/recharging handles. the cylinders sticking back with the slot are the firing solenoids. 




P-39 Expert said:


> Again, I have no idea why the AAF chose to retain these items. Russians immediately removed the .30s on virtually all their P-39s and had great success against the Luftwaffe.



You are rearward projecting. Russians pulled .30 cal guns in late 1942 or in 1943 on later P-39s. How many fixes/modifications to the 37mm and .50 cal guns had been done? 
Russians were used to light armament and had often resorted to using less than the designed armament to improve performance. 
I don't know what the russians got for a rate of fire out the .50s in most of their planes. The British were getting under 500rpm out of the .50s in the AIrcobra I (P-400 and 212 to Russia) 
which is about the only commonly known number. 
If the 37 packs it in and you have no wing guns you have about 15 rps of .50 cal, assuming they stay working. 

Again relaibilty of the gun installations in the spring/summer of 1942 may have been lower than at later times. Making the extra .30 cal guns more important.


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## P-39 Expert (Oct 5, 2020)

XBe02Drvr said:


> There you go again, removing weight from the front of the plane, despite being told repeatedly by virtually everyone here that's not an acceptable solution for weight and balance reasons. You could probably get away with it by loading all your nose mounted guns to their maximum capacity, then disconnecting the firing circuits so they can't further lighten the nose. Any way you slice it, you've got to have that weight up there, unless you can relocate some heavy items from behind the engine to the nose compartment, or delete them completely.
> This isn't rocket science. The folks who built, maintained, and flew this bird knew this stuff. If there were feasible ways of fixing this issue that didn't trample on USAAF's fetishes they would have thought of them long before your time. The Russians, not slaved to the same fetishes, did exactly that. And it served them well.


Bell said in writing that the nose armor plate was not needed for ballast/balance on the P-39M. The M was an early model with the same weight and weight distribution as previous and later models. They were able to balance the plane with larger (heavier) propellers and different nose cannons that differed in weight by 140lbs. Bell designed the P-39 to take larger (heavier) three blade and four blade propellers and an auxiliary stage supercharger behind the engine that weighed 175lbs. They certainly were able to maintain proper balance with any or all of these items installed. The nose armor certainly could have been deleted and balance maintained.

If you remove the 100lb nose armor you don't need to relocate an item from behind the engine to the nose compartment. That would make the nose heavier than the tail. You could delete the item behind the engine to balance the plane, or move it to the center of gravity right behind the pilot above the engine. The IFF radio in the tail cone could have been deleted (some other planes didn't have it) or moved up right behind the pilot. If deleted you just saved another 130lbs. The Soviets deleted this radio (and the .30MGs) and reduced the weight of their P-39s by about 330lbs. They kept the nose armor and didn't have any CG problems.


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## Shortround6 (Oct 5, 2020)

Planes fly better if they are slightly nose heavy compared to slightly tail heavy. Neither is ideal but nose heavy but nose heavy doesn't bring out the problems quite as quickly. 

The P-39 was NOT designed to have auxiliary supercharger behind the engine. Where is this story coming from? 

You had the XP-39 with turbo UNDER the engine. 
XP-39B with turbo taken out and radiators/oil coolers under the engine. 
Same airframe rebuilt.
YP-39s and P-39Cs with the same layout out as the XP-39B

When/where was the P-39 with an auxiliary supercharger behind the engine? 

The XP-39E was designed to use the Continental ?-1430 engine which was much longer than the Allison, fuselage was almost 2 feet longer than standard P-39. This gave plenty of room for the Allison with the auxiliary supercharger behind it. Bell never tried to stick a two stage Allison in a normal P-39 airframe, if I am wrong please provide photo's. drawings, or memo, letter of it being done. Not somebody just suggesting it.


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## Peter Gunn (Oct 5, 2020)

XBe02Drvr said:


> *SNIP*
> 
> OTOH, they gave pilot jobs to unlikely specimens of airline pilotage like me, who wouldn't have a snowball's chance you know where of getting hired by a major airline. (Not military trained, too tall, too skinny, too unattractive, wearing *THICK *glasses, history of eye disease and other chronic conditions, and a little shy on multi engine time.) I just didn't fit the desired profile.
> 
> *SNIP*



*And here I had you pictured like this:*







*So I guess this would be closer?*

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## FLYBOYJ (Oct 5, 2020)

P-39 Expert said:


> Two missions, right? One under 1000' and the other at 23000'. The performance above 18000' is probably with drop tank, this is what the performance charts in wwiiaircraftperformance.org show.


Yep - two missions that confirmed the P-39s shortcomings for months to come. You can't "what if" history away, although he did have some complements for the P-39. Should we ignore those based on 2 missions?

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## FLYBOYJ (Oct 5, 2020)

XBe02Drvr said:


> It's awfully hard to boom and zoom when you can't get above your enemy. Not enough warning time plus a lackluster rate of climb makes for unpleasant interception geometry. And booming and zooming an opponent with the acceleration and initial climb rate of a Zero in your lead sled can be an unhealthy practice.


Exactly!

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## P-39 Expert (Oct 5, 2020)

Shortround6 said:


> again, nose armor weight and balance/CG issues.
> 
> All three guns systems had issues in May of 1942.
> Yanking the .30s may not have been good idea. Not all of the 30s are going to crap out at the same time.
> ...


I believe the Russians pulled the .30s from the very first P-400s that the Brits gave them. And the IFF radio in the tail cone. Saved about 330lbs. Made them competitive with German planes.

I've always figured a little less than 500rpm out of the synchronized .50s. Works out to about 1 and a half .50s of centerline fire and about 25 seconds firing time. Not optimal but still capable of shooting down another plane. 

Not to be picky but those aren't red flags hanging from the .50s charging handles, they ARE the charging handles.  The other red handles below are for the drop tank/bomb release, recharging/reloading the 37mm cannon and charging the wing .30s. Charging the .50s was said to be quite a challenge for a 140lb pilot. Fix was for the ground crew to charge them before the flight. Everything was manual, charging the guns, dropping the tanks/bombs, controlling the coolant and oil temperatures etc.

The 37mm cannon fix was to duct more warm air from the cockpit to the gun bay to keep it from freezing at altitude. Most all new airplanes had glitches that had to be corrected.


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## fubar57 (Oct 5, 2020)

P-39 Expert said:


> In a later report Wagner criticized the reliability of the .30s.
> 
> 
> P-39 Expert said:
> ...



Could you provide these documents with references please


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## P-39 Expert (Oct 5, 2020)

FLYBOYJ said:


> Yep - two missions that confirmed the P-39s shortcomings for months to come. You can't "what if" history away, although he did have some complements for the P-39. Should we ignore those based on 2 missions?


No, we should have lightened the plane by removing redundant or unnecessary items to make it climb faster and higher. It was already faster than the Zero. It's either remain way too heavy (as compared to other fighters) and skulk around under 20000' or get lean and climb up to and above where the Japanese are. Just like what the Russians did.


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## FLYBOYJ (Oct 5, 2020)

P-39 Expert said:


> No, we should have lightened the plane by removing redundant or unnecessary items to make it climb faster and higher. It was already faster than the Zero. It's either remain way too heavy (as compared to other fighters) and skulk around under 20000' or get lean and climb up to and above where the Japanese are. Just like what the Russians did.


"we should have"

The P-38 "should have" had Merlins.
The F4U "should have" been carrier qualified earlier.
The SB2C "should have" been in service a year earlier.
The P-38K "should have" been put into production.

Even with your wishful thinking the P-39 would not have been able to prevail as a front line fighter in the SWP, especially with the P-38 coming on line.


P-39 Expert said:


> Again, removing just these two items (nose armor and .30calMGs) would have saved 300lbs, *increased climb rate by 360feet/minute and combat ceiling to 29000'* (at 3000rpm). That climb increase would have made the early P-39s climb faster than the early Zeros. Speed advantage and climb advantage. P-39 could then attack from above.


How did you come up with that number?


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## Elmas (Oct 5, 2020)

MODE O.T. ON






The newspaper, which was the main press journal of the Italian Communist Party, says:
*Eternal glory to the man who most of all did
for the liberation and progress of humanity*
and​






*Stalin's work is immortal!
Long live his invincible cause!*​
Not only I had the dubious privilege of being born and live in the Nation that had the largest Communist Party in the Western world, but also in the Nation with the largest Communist Party in the world after the Soviet Union. 

Almost one in three Italians voted until 1989 for the Communist Party and, considering that there were over thirty million voters in Italy, this meant more than ten million Communist votes.

I imagine that it is very difficult for an American or a British to understand how the propaganda of such a strong Communist Party was: everything had been invented in the Soviet Union, from radio to condensed milk and the Party newspaper every day gave the news of some amazing discovery made by some Soviet scientist. The Italians were divided in two: those who believed in it and who would have been ready to swear on what "L’Unità” said, and those who had been vaccinated and instead did not believe a single word of it. In 1989 we saw who History proved right.

Every single statement, or even word, in those times, made by a Communist or a Soviet Military, had to be strictly reviewed by a political staff: so when I read in this Forum that certain statements made by Military of the then Soviet Union are taken as historical truth, I can't help but smile.

MODE O.T. OFF

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## GrauGeist (Oct 5, 2020)

nuuumannn said:


> Whitewall tyre (tire!) P-51s look awesome!


And his Mustang's wheels were bright red, too!

In regards to technical aptitude by various populations, we have to consider the circumstances of each population leading up to the late 30's.
In the urban areas (pick any nation), people didn't need technical savvy to go about their daily lives - they could walk to their destination, catch a tram, trolley, bus or train.
However, outside of urban areas is where things change. Prior to WWII, a great deal of populations still lived in the countryside and were farmers, fishermen, ranchers, loggers, miners and so on.
In the case of the U.S., mass production of cars, tractors, trucks and evennutility engines coupled with readily available (and inexpensive) fuel saw widespread use where many other nation's were still using teams as a primary means.
Americans could even order a Ford or Allstate (ford licensed) car through the Sears catalogue - which was delivered in a crate and required assembly (and you thought IKEA was the first!). Additionally, these car kits could be modified to operate saw mills, irrigation pumps and so on (the car would be partially assembled, raised off the ground and a leather belt ran the apperatus from a special "wheel" mounted to the rear axle).
So in the end, it wasn't that Americans were smarter than Soviets, British, Germans or anyone else, it's the abundance of available machines that put them in that position.

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## buffnut453 (Oct 5, 2020)

GrauGeist said:


> And his Mustang's wheels were bright red, too!
> 
> In regards to technical aptitude by various populations, we have to consider the circumstances of each population leading up to the late 30's.
> In the urban areas (pick any nation), people didn't need technical savvy to go about their daily lives - they could walk to their destination, catch a tram, trolley, bus or train.
> ...



You state that "Prior to WWII, a great deal of populations still lived in the countryside and were farmers, fishermen, ranchers, loggers, miners and so on." That may have been true in the US but it was NOT true in the UK. Most population lived in cities and large towns, and had done since the mid-1800s. Only around 10 percent of British workers were involved in agriculture in 1939.

The urban areas were heavily industrialised. People may not have needed a car to get to work but they used and maintained machinery in every factory. To suggest that owning a car was somehow superior to being a trained technician maintaining milling machines, steam hammers, cotton mills, or any other number of the thousands of machines that came about in the 200 years following the industrial revolution is ridiculous.

It's precisely this sort of Tom Sawyer/Huck Finn-goes-to-war myth that drives me bonkers. If the greater part of a country's workforce is urbanised and working in manufacturing (as it was in the UK), are they less technically savvy than a farmer with a Model T? Almost all manufacturing in the 1930s still required human skill and ingenuity...but, of course, that doesn't fit the American mythology and so it gets ignored.


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## P-39 Expert (Oct 5, 2020)

fubar57 said:


> Could you provide these documents with references please


Not that I'm writing a doctoral thesis, but that is from Vees for Victory, book about the Allison V-1710.


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## P-39 Expert (Oct 5, 2020)

FLYBOYJ said:


> "we should have"
> 
> The P-38 "should have" had Merlins.
> The F4U "should have" been carrier qualified earlier.
> ...


The Merlin P-38 would have taken how long to bring to production? A year maybe?
The F4U probably should have.
The SB2C I have no idea, but the Navy kept changing their requirements.
P-38K would have taken how long to bring to production, and how many P-38J/L would have been delayed/cancelled?

Lighter P-39 would have taken about 3 hours of maintenance crew's time at a combat base. Remove the wing .30s and their mounts, chargers, heaters and ammo boxes, and the nose armor plate. While you're at it remove the IFF radio and save another 130lbs. Still have the voice radio.

The 1.2feet/minute climb per pound of weight saved comes from wwiiaircraftperformance.org. Compare the climb rates of the P-39D and the P-39C at their different weights. C climbed 1000fpm faster than the D and weighed 836lbs less, making each pound of weight improve climb by 1.2fpm. I know the C model did not have self sealing tanks and armor plate but it had the exact same engine, propeller and aerodynamics as the D model. Only difference in performance was the weight.


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## Ivan1GFP (Oct 5, 2020)

XBe02Drvr said:


> It's awfully hard to boom and zoom when you can't get above your enemy. Not enough warning time plus a lackluster rate of climb makes for unpleasant interception geometry. And booming and zooming an opponent with the acceleration and initial climb rate of a Zero in your lead sled can be an unhealthy practice.



Hello XBe02Drvr,

From the first combat report with P-39Ds, The Zeros encountered were reported as having larger cowls.
That factor is quite noteworthy. If ever there was a "lead sled" version of the A6M fighter, they had just encountered it.
The reasoning is this:
The report only notes a cowl change and not a clipped and squared wing which meant that it was not the A6M3 Model 32 (AKA "Hap" / "Hamp"). It would have been the later A6M3 Model 22 which was one of the heaviest versions because of increased fuel capacity until the very late war versions got even heavier.
At low altitude, power is slightly greater. (Surprisingly little.) but the combination of significantly more weight and different propeller pitch ranges probably made this a little less quick in acceleration and definitely less maneuverable.

The Japanese note in their manual that at medium altitudes and below, the Mark I fighter (A6M2) is superior to the Mark II (A6M3 / A6M5) but above 8000 Meters, the performance of the Mark II becomes progressively better.
Maximum speed under "Normal Power" was substantially better in Mark II but actual maximum speed for the type is very hard to pin down. Sources don't seem to agree. My best guess is that the difference was no more than a 5 MPH advantage for the A6M3.

Neither combat described was above 8000 Meters.

From a performance standpoint, the P-39F is identical to the P-39D with the same V-1710-35 but just with an Aeroproducts propeller with slightly different pitch ranges.

- Ivan.

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## P-39 Expert (Oct 5, 2020)

Ivan1GFP said:


> Hello XBe02Drvr,
> 
> From the first combat report with P-39Ds, The Zeros encountered were reported as having larger cowls.
> That factor is quite noteworthy. If ever there was a "lead sled" version of the A6M fighter, they had just encountered it.
> ...


A6M3 was not available until October 1942, this was in May.


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## Ivan1GFP (Oct 5, 2020)

P-39 Expert said:


> A6M3 was not available until October 1942, this was in May.



Hello P-39 Expert,

I am just going by what the combat report says. I presume the pilots were reporting accurately.
The Japanese had a habit of fielding prototypes before the production models were finalized, so perhaps that is what happened here. I am a bit suspicious of that theory because the prototypes were not usually available in great numbers.

- Ivan.


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## P-39 Expert (Oct 5, 2020)

Shortround6 said:


> Planes fly better if they are slightly nose heavy compared to slightly tail heavy. Neither is ideal but nose heavy but nose heavy doesn't bring out the problems quite as quickly.
> 
> The P-39 was NOT designed to have auxiliary supercharger behind the engine. Where is this story coming from?
> 
> ...


As we have discussed before, the engine compartment of the P-39 without the auxiliary stage supercharger was exactly the same size as the engine compartment of the later P-63 with the auxiliary stage supercharger. Exactly the same distance from the front of the engine section to the bulkhead at the rear. See the attached drawings. Now that is either an amazing coincidence or the P-39 was designed from the beginning to accommodate the auxiliary stage supercharger. All the Allisons had long lead/development periods. Bell knew that a two stage engine was coming, just like they new the -63 and the -85 were coming. Just like they knew larger, heavier propellers were coming. All designed in from the beginning.

That story about the P-39E being two feet longer is correct, but it was the tail cone section that was lengthened, not the engine compartment. That was the same as any P-39. Just another story handed down for the last 75 years that is taken as fact, like the Russians used the P-39 for ground attack, the 37mm cannon had a looping trajectory, the Allison didn't have a supercharger etc. Almost all of them wrong.

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## Ivan1GFP (Oct 5, 2020)

P-39 Expert said:


> Bell said in writing that the nose armor plate was not needed for ballast/balance on the P-39M. The M was an early model with the same weight and weight distribution as previous and later models. They were able to balance the plane with larger (heavier) propellers and different nose cannons that differed in weight by 140lbs.



Hello P-39 Expert,

The P-39M was one of the Mid Production versions, about the same as the P-39N.
The engine was the V-1710-83 with significantly better altitude performance than the earlier models with the V-1710-35 and V-1710-63. It carried a bigger propeller (11 feet 1 inch) with different reduction gearing because the engine had the altitude performance to use it. Earlier models had a 10 feet 4 1/2 inch propeller.

What could be done with this engine is not indicative of what would work with earlier engines.

What change in nose cannons made a difference of 140 pounds?

- Ivan.


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## Elmas (Oct 5, 2020)

GrauGeist said:


> And his Mustang's wheels were bright red, too!
> 
> In regards to technical aptitude by various populations, we have to consider the circumstances of each population leading up to the late 30's.
> In the urban areas (pick any nation), people didn't need technical savvy to go about their daily lives - they could walk to their destination, catch a tram, trolley, bus or train.
> ...





buffnut453 said:


> Sorry but that's utter tosh. You state that "Prior to WWII, a great deal of populations still lived in the countryside and were farmers, fishermen, ranchers, loggers, miners and so on." That may have been true in the US but it was NOT true in Europe. Most population lived in cities and large towns, and had done since the mid-1800s.
> 
> The urban areas were heavily industrialised. People may not have needed a car to get to work but they used and maintained machinery in every factory. To suggest that owning a car was somehow superior to being a trained technician maintaining milling machines, steam hammers, cotton mills, or any other number of the thousands of machines that came about in the 200 years following the industrial revolution is ridiculous.
> 
> It's precisely this sort of Tom Sawyer/Huck Finn-goes-to-war myth that drives me bonkers. If the greater part of a country's workforce is urbanised and working in manufacturing (as it was in the UK), are they less technically savvy than a farmer with a Model T? Almost all manufacturing in the 1930s still required human skill and ingenuity...but, of course, that doesn't fit the American mythology and so it gets ignored.



It has to be said that in Italy, expecially in the South, until 1960, practically all the farming was done with carts like these.




I remember perfectly well, when I was a young lad, the clinging of the bells of the oxen going to work at sunrise, when I spent my summer holidays in a tiny village of the inner part of Sardinia, and also remember that in Sicily, same period, fishermen went to sea by oar and sail. (Not joking...)

For the average Italian, outside public transport, until early-mid 50s, when Piaggio started the production of the famous "Vespa"





the only private transport available was the bicycle, and to have a car privately owned by practically every family we had to wait until early 60s, with the Fiat 600.






That, of course, does not mean that Italians could not master mechanics





but numbers were not at all comparable with those of U.S.

Wehrmacht used mainly horse drawn carts in the lands of Russia but, for propaganda purposes, just trucks appeared in the photos officially released.

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## buffnut453 (Oct 5, 2020)

Elmas said:


> It has to be said that in Italy, expecially in the South, until 1960, practically all the farming was done with carts like these.
> View attachment 597220
> 
> I remember perfectly well, when I was a young lad, the clinging of the bells of the oxen going to work at sunrise, when I spent my summer holidays in a tiny village of the inner part of Sardinia, and also remember that in Sicily, same period, fishermen went to sea by oar and sail. (Not joking...)
> ...



My point is that applying the American situation to other countries is inappropriate. Equally, applying the situation in the UK to that in Italy is equally futile. The industrial revolution occurred at different times at different regions. Equally, levels of technical awareness varied greatly...but to suggest the US had greater technical savvy because farmers had Model Ts is taking things much too far (IMHO).


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## Ivan1GFP (Oct 5, 2020)

buffnut453 said:


> My point is that applying the American situation to other countries is inappropriate. Equally, applying the situation in the UK to that in Italy is equally futile. The industrial revolution occurred at different times at different regions. Equally, levels of technical awareness varied greatly...but to suggest the US had greater technical savvy because farmers had Model Ts is taking things much too far (IMHO).



Hello buffnut453,

You have a point. Ford Model Ts are crap. Much more likely they were Model As or something later.

- Ivan.


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## SaparotRob (Oct 5, 2020)

buffnut453 said:


> My point is that applying the American situation to other countries is inappropriate. Equally, applying the situation in the UK to that in Italy is equally futile. The industrial revolution occurred at different times at different regions. Equally, levels of technical awareness varied greatly...but to suggest the US had greater technical savvy because farmers had Model Ts is taking things much too far (IMHO).


I don’t think XBe02Drvr was saying Americans were/are more technically savvy (I know I wasn’t), but that Americans were more habituated with rudimentary tech than most other nations as a whole.

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## BiffF15 (Oct 5, 2020)

Elmas said:


> MODE O.T. ON
> 
> View attachment 597215
> 
> ...



Cheers,
Biff


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## P-39 Expert (Oct 5, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> The P-39M was one of the Mid Production versions, about the same as the P-39N.
> The engine was the V-1710-83 with significantly better altitude performance than the earlier models with the V-1710-35 and V-1710-63. It carried a bigger propeller (11 feet 1 inch) with different reduction gearing because the engine had the altitude performance to use it. Earlier models had a 10 feet 4 1/2 inch propeller.
> ...


The M was an earlier model, 7000 more N/Q models would still be produced out of 9500 total.

The larger propeller was introduced with the 167th N model. Reduction gear was the same 2:1 as the D-2/K/L that used the -63 engine.

The 37mm cannon weighed 300lbs with ammo, the 20mm 160lbs with ammo. Difference 140lbs.


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## buffnut453 (Oct 5, 2020)

SaparotRob said:


> I don’t think XBe02Drvr was saying Americans were/are more technically savvy (I know I wasn’t), but that Americans were more habituated with rudimentary tech than most other nations as a whole.



My use of the term tech savvy reflected exactly what you stated more elegantly as "more habituated with rudimentary tech.". I just couldn't be bothered typing long words like habituated and rudimentary with my fumble-thumbs. 😁

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## Ivan1GFP (Oct 5, 2020)

Hello P-39 Expert,



P-39 Expert said:


> The M was an earlier model, 7000 more N/Q models would still be produced out of 9500 total.



It depends on how you want to group things. Most books I have count the L through N models as the "Mid Production" series. There were about 240 M models produced and about 2000 N models produced.



P-39 Expert said:


> The larger propeller was introduced with the 167th N model. Reduction gear was the same 2:1 as the D-2/K/L that used the -63 engine.



This is still different from the 1.8:1 reduction gear originally used on the P-39C/D/F series. The propeller on the M was 11 feet 1 inch diameter. The N model changed the reduction gear ratio to 2.23:1 and used either a 11 feet 4 inch or 11 feet 7 inch propeller. The Q used a 11 feet 7 inch propeller.
The early series propellers on -35 and -63 engines were almost always 10 feet 4 1/2 inch regardless of whether they were Curtiss Electric or Aeroproducts manufacture.



P-39 Expert said:


> The 37mm cannon weighed 300lbs with ammo, the 20mm 160lbs with ammo. Difference 140lbs.



This is a cool little bait and switch you are trying to pull here. There were plenty of P-39 models armed with the 37 mm cannon before the M model came along, notably the C, D, F, J, K and L.
To say the M had cannons weighing 140 pounds more is a pretty poor argument when the majority of US service models already carried the same gun as the M.

- Ivan.

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## SaparotRob (Oct 5, 2020)

buffnut453 said:


> My use of the term tech savvy reflected exactly what you stated more elegantly as "more habituated with rudimentary tech.". I just couldn't be bothered typing long words like habituated and rudimentary with my fumble-thumbs. 😁


A full tenured professor at Brooklyn College said I was the best B.S. artist he ever met.

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## SaparotRob (Oct 5, 2020)

But no better than a B.S. artist from any other nation.

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## gordonm1 (Oct 5, 2020)

I've read here the P40 was lengthened for the higher powered engines/speed giving more torque. I'm not sure how this played out with the P39? No changes?

Also any comparison on what actual metals were used on each plane? Duralum or something? steel?


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## FLYBOYJ (Oct 5, 2020)

P-39 Expert said:


> Lighter P-39 would have taken about 3 hours of maintenance crew's time at a combat base. Remove the wing .30s and their mounts, chargers, heaters and ammo boxes, and the nose armor plate. While you're at it remove the IFF radio and save another 130lbs. Still have the voice radio.


 Having worked on many aircraft (to include warbirds) I can somewhat agree with your field removal of some the equipment to save weight, 3 hours of maintenance is a bit skewed unless you're going to just hack the items mentioned out, not plug rivet holes and possibly leave wire bundles.


P-39 Expert said:


> The 1.2feet/minute climb per pound of weight saved comes from wwiiaircraftperformance.org. Compare the climb rates of the P-39D and the P-39C at their different weights. C climbed 1000fpm faster than the D and weighed 836lbs less, making each pound of weight improve climb by 1.2fpm. I know the C model did not have self sealing tanks and armor plate but it had the exact same engine, propeller and aerodynamics as the D model. Only difference in performance was the weight.


Your linear calculation does not address weight and balance of the items removed. If you're lucky enough to make the aircraft slightly tail heavy, it will fly faster but be more unstable, something already plaguing the P-39. You're comparing the C and D models and by your own post, no armor and no self sealing tanks. So you're making your point with performance numbers from an aircraft that was really not capable of entering combat????


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## FLYBOYJ (Oct 5, 2020)

gordonm1 said:


> Also any comparison on what actual metals were used on each plane? Duralum or something? steel?


 I think you will find both aircraft were constructed of similar material (24T, mild steel where required)


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## MiTasol (Oct 5, 2020)

Shortround6 said:


> the .50 gun receivers are coming back into the cockpit. the red flags are attached to the cocking/recharging handles. *the cylinders sticking back with the slot are the firing solenoids.*



Sorry Shortround but that is not correct. The cylinders sticking back with the slot are actually the buffers (shock absorbers)





The American 30 cal, 50 cal and 20mm solenoids look like this and mount on the side of the gun.





These pictures show them mounted on the P-39 wing guns.




The Brit .303 solenoids look like this and mount on the bottom of the gun

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## MiTasol (Oct 5, 2020)

Shortround6 said:


> the *red flags* are attached to the cocking/recharging handles.



The "red flags" are, in fact, the cocking handles.

Again from the manual





Note items 20 and 60

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## wuzak (Oct 5, 2020)

Ivan1GFP said:


> It depends on how you want to group things. Most books I have count the L through N models as the "Mid Production" series. There were about 240 M models produced and about 2000 N models produced.



Only the N and Q models followed the M. That would suggest the M was a later production version!

The Q was in production 8 or 9 months after the M.


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## MiTasol (Oct 5, 2020)

P-39 Expert said:


> Bell said in writing that the nose armor plate was not needed for ballast/balance on the P-39M. The M was an early model with the same weight and weight distribution as previous and later models. They were able to balance the plane with larger (heavier) propellers and different nose cannons that differed in weight by 140lbs. Bell designed the P-39 to take larger (heavier) three blade and four blade propellers and an auxiliary stage supercharger behind the engine that weighed 175lbs. They certainly were able to maintain proper balance with any or all of these items installed. The nose armor certainly could have been deleted and balance maintained.
> 
> If you remove the 100lb nose armor you don't need to relocate an item from behind the engine to the nose compartment. That would make the nose heavier than the tail. You could delete the item behind the engine to balance the plane, or move it to the center of gravity right behind the pilot above the engine. The IFF radio in the tail cone could have been deleted (some other planes didn't have it) or moved up right behind the pilot. If deleted you just saved another 130lbs. The Soviets deleted this radio (and the .30MGs) and reduced the weight of their P-39s by about 330lbs. They kept the nose armor and didn't have any CG problems.



You have obviously never done weight and balance on a real aircraft, or actually worked on a P-39, or you would know that much of what you wrote above is not correct. Worse still, as many of the pilots on the forum will tell you, a stall caused by aft CG on many aircraft is stable meaning you cannot regain control. Regardless of power or control inputs the aircraft remains stalled and drops like a brick with almost zero forward speed. I have gone to two funerals caused by this mistake. Both pilots had carefully calculated there gross weight CG but forgot to check their low fuel, low speed, gear down CG.

You will note in your own writing that the Soviets removed the IFF to compensate for the removal of the 30 cals. There is nothing else heavy back there to remove except the oil tank and that is aft of the fuselage joint line. There is a tie down kit but that weighs about 5 or 6 lbs so is not going to help. Yes you could move the oil tank (and coolant tank) into the wing leading edge like the Hurricane did but that introduces all sorts of other problems. And you can remove the radios from above the engine (they and the engine are actually aft of the CG which is just above 2 = fuel, 9 = guns and 10 = wing ammo in the diagram the below and all forward of the CG) but where would you fit them?
\





On any aircraft if you remove 100lb from the very front of the aircraft you must compensate by removing weight from the rear.
If the weight you remove aft of the cg is only 50 lb then it must come from twice the distance from the CG that the removed weight was. etc etc etc

I have never seen anything from Bell saying the designed the P-39 to take the ASB used on the P-63. The coolant tank takes up all that space behind the engine on a P-39 and there is also structure there, including the fuselage bolt line, that would prevent an ASB being fitted. Find a flying example near you and go visit it as soon as restrictions allow. The lack of free space in that powerplant will surprise you and clearly show that there is no way it could fit an ASB.

They did design it with a turbo but that went under the engine.





This diagram shows the engine and supercharger outline but does not show the starter or generator or any of the mass of plumbing and "small" parts that extend from the rear of the engine. The oil tank is aft of the bolt line but the bulkhead is shaped to allow part of it to extend into the engine bay. There is no way an ASB would fit there.

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## Shortround6 (Oct 5, 2020)

MiTasol
l

Thank you for the correction and the photos/pages.


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## XBe02Drvr (Oct 5, 2020)

Shortround6 said:


> MiTasol
> l
> 
> Thank you for the correction and the photos/pages.


I was writing a similar treatise on weight and balance, but MiTasol's was way better.
Thanks, MiTasol !


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## Ivan1GFP (Oct 5, 2020)

wuzak said:


> Only the N and Q models followed the M. That would suggest the M was a later production version!
> 
> The Q was in production 8 or 9 months after the M.



Hello Wuzak,

Your timing is probably correct, but there are other factors.
1800 P-39G models were originally ordered. None were actually built.
Instead, the contract for the G models was distributed in small batches into the K, L, M, and N (large batch) which don't differ much except in fairly minor detail and so are considered the same mid production series.

As for Letter designations in the P-39, in other fighters such as the P-47D, the degree of change between one Letter designation in the P-39 and the next was often less than that from one production block and the next in other fighters.
Look at how many versions were simply because the propeller was from a different manufacturer.

- Ivan.


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## windhund116 (Oct 6, 2020)

Thought some may like this photo. Lineup of some USAAF fighters used in SWPA action.

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## SaparotRob (Oct 6, 2020)

Is there a date on that photo?


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## windhund116 (Oct 6, 2020)

No date on photo. Would be 1942-43, because of type of USAAF roundels?


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## Stig1207 (Oct 6, 2020)

FLYBOYJ said:


> View attachment 597124



Currently reading this P-39/P-400 Airacobra vs A6M2/3 Zero-sen: New Guinea 1942 and Wagner's report is an interesting assessment, based on his and his pilots perpective.

According to Claringbold one Zero was lost and the pilot FPO2c Hideo Izumi was killed. 
Four P-39's were lost, with one pilot MIA, but not mentioned in the report?! The cause of loss given for the other 3 P-39's also differ from the report.
41-6930
41-7128
41-7186
41-6982

The combat the following day I have to re-check in the book but I think it is related differently; there is a Zero shot down, but I don't think a P-39 is lost?


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## GrauGeist (Oct 6, 2020)

The P-39 in the foreground is a P-39N-1, the Mustang is an A-36A, the P-40K-15-CU - the P-47 and P-38 I can't make out.

And Lo and Behold, that is a P-36A in the background, upper left!

That P-39 was used in USAAF evaluations, by the way.

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## MiTasol (Oct 6, 2020)

Ivan1GFP said:


> From the first combat report with P-39Ds, The Zeros encountered were reported as having larger cowls.
> That factor is quite noteworthy.



Given that the US pilots of the day often called every Japanese fighter a Zero that could also mean the previous _Zeros_ those pilots encountered were Ki-43s

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## MiTasol (Oct 6, 2020)

P-39 Expert said:


> As we have discussed before, the engine compartment of the P-39 without the auxiliary stage supercharger was exactly the same size as the engine compartment of the later P-63 with the auxiliary stage supercharger. Exactly the same distance from the front of the engine section to the bulkhead at the rear. See the attached drawings. Now that is either an amazing coincidence or the P-39 was designed from the beginning to accommodate the auxiliary stage supercharger.



Tomorrow I will demolish this claim. I was hoping to do it today but the material I need to do so is not at hand. The civil P-63 Pinball that I worked on in 72 had no ASB but the space where it fitted was very obvious and much of it was AFT of the split line. On the P-39 part of the oil tank intrudes forward of the split line. As such it is absolutely impossible to fit the ASB in a P-39. The rear fuselage extension on the P-39E would almost certainly have been the same concept as on the P-63 with the oil tank moved aft to make room for the ASB.


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## MiTasol (Oct 6, 2020)

Elmas said:


> It has to be said that in Italy, expecially in the South, until 1960, practically all the farming was done with carts like these.
> 
> I remember perfectly well, when I was a young lad, the clinging of the bells of the oxen going to work at sunrise, when I spent my summer holidays in a tiny village of the inner part of Sardinia, and also remember that in Sicily, same period, fishermen went to sea by oar and sail. (Not joking...)
> 
> ...



AND Italy had some very fast and technically advanced Schneider Trophy aircraft, winning four times. America only won twice.

PS I have fond memories of a (smaller) Fiat 500 Bambino with ejector doors just like the one in your photo. It was not as fast as a mini but it could go places that no mini could ever dream of getting to. Plus it had wind up windows and self adjusting brakes etc that the mini lacked. A truly fun vehicle.


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## Ivan1GFP (Oct 6, 2020)

MiTasol said:


> Given that the US pilots of the day often called every Japanese fighter a Zero that could also mean the previous _Zeros_ those pilots encountered were Ki-43s



Hello MiTasol,

You could be correct, but there are a couple problems with this theory.
There are considerable shape differences between the Ki 43 and the A6M2 which were not noted.
The cowl size isn't particularly different between Ki 43 and A6M2.
There is no comment that they "new Zeros" now have cannon in their wings which probably would have been a pretty significant change.

I certainly wasn't there, so I am guessing as well.

- Ivan.


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## Peter Gunn (Oct 6, 2020)

I guess the question then would be were there any Ki-43s based within the area where the combat took place that could have tangled with the Airacobras?

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## Elmas (Oct 6, 2020)

MiTasol said:


> AND Italy had some very fast and technically advanced Schneider Trophy aircraft, winning four times. America only won twice.
> 
> PS I have fond memories of a (smaller) Fiat 500 Bambino with ejector doors just like the one in your photo. It was not as fast as a mini but it could go places that no mini could ever dream of getting to. Plus it had wind up windows and self adjusting brakes etc that the mini lacked. A truly fun vehicle.



A Collegue, after his graduation, wento to work for Abarth.
Abarth used to modify Fiat cars for competitions
He told me that one time they installed on a Fiat 500 an overcompressed engine of 1500 cc and went to try she on the roads.
The most funny thing was the glimpse of other drivers when they were overtaken at more than 170 km/h, he told me....

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## Shortround6 (Oct 6, 2020)

I think we are letting national pride intrude on the discussion of how mechanically adept the Americans were.

It is not a question of how good a small group of engineers or designers were.

It is a question of how many troops (a percentage of total troops) had driven or worked on motor vehicles (or boats or industrial machinery).

What this means to an army (any army) is how much training is required to turn recruits into drivers or mechanics/fitters.
The army is going to put the troops selected for those jobs through some sort of training course and not just turn them loose.
How many hours or weeks should the course/s be given the average level of knowledge the troops bring from civilian life?
In case of casualties (or sickness) what does the 'reserve' of troops who did not go through the "school" look like.
This assumes the army is bright enough to steer people to the right jobs given their civilian experience. My father went to an civilian aviation school for 9 moths before WW II, he worked for Sikorsky on the VS-44 flying boat and then worked for Chance Vought building Corsairs. When He went into the Marines (only large scale user of the Corsair at the time) the Marines, in their infinite wisdom, sent him to school to be a signalman/radio operator. 

My mothers father joined the army in WW I and wound up in Texas in the air corp as a machine gun instructor. Not on how to shoot them but on how to strip them and maintain them. I doubt he had ever seen a machine gun before. Between the wars he worked as a watch and clock repairman, gunsmith and machinist, during WW II he worked in a four man shop making parts for gyroscopes on old machinery driven by overhead belts. He was extremely mechanically adept. But his mechanical 'experience' training in 1917 was?????? 

Some people are naturally mechanically inclined. Even if from a primarily primitive agricultural area (and there some in the US) some people are going to catch on quicker. SOme people who have driven even a model T for years were never going to catch on (flat tire? call auto club.....or brother/cousin).

The American advantage was not that they were smarter or more mechanical adept 'naturally' but that they had much more experience driving/maintaining cars and machinery_ on average
per 1000 recruits. _than other armies.
How good you were rebuilding a turret lathe in civilian life gives you some advantage in working on truck/tank but perhaps not as much as a guy who worked in a gas station and had seen any number of minor problems.

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## Ivan1GFP (Oct 6, 2020)

Peter Gunn said:


> I guess the question then would be were there any Ki-43s based within the area where the combat took place that could have tangled with the Airacobras?



Hello Peter Gunn,

The entire area of operations in New Guinea had both sides very close on a large land mass. The presence of Japanese Army units would have meant the presence of Ki 43 and other Army types.
These attacks were on the Japanese Navy airbase at Lae.
On the attached map linked, look toward the East at the Northern coast.
Look for the arrow marked Jun 1943.
It is amazing how little actual distance separated the two sides though a mountain range in between helped a bit.

- Ivan.

https://history.army.mil/books/AMH/Map23-43.jpg

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## SaparotRob (Oct 6, 2020)

windhund116 said:


> No date on photo. Would be 1942-43, because of type of USAAF roundels?


I was wondering because I think that is a P-36 at the top of the picture. I’ve never seen all those aircraft in the same picture.

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## GrauGeist (Oct 6, 2020)

SaparotRob said:


> I was wondering because I think that is a P-36 at the top of the picture. I’ve never seen all those aircraft in the same picture.


As I mentioned earlier, that is a P-36A and the other aircraft have either 41- or early production 42- serials plus the national insignia no longer has the "meatball" so this photo could be perhaps June of 1942.

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## SaparotRob (Oct 6, 2020)

Elmas said:


> A Collegue, after his graduation, wento to work for Abarth.
> Abarth used to modify Fiat cars for competitions
> He told me that one time they installed on a Fiat 500 an overcompressed engine of 1500 cc and went to try she on the roads.
> The most funny thing was the glimpse of other drivers when they were overtaken at more than 170 km/h, he told me....
> View attachment 597278


We need a “COOL” icon.

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## buffnut453 (Oct 6, 2020)

Ivan1GFP said:


> Hello MiTasol,
> 
> You could be correct, but there are a couple problems with this theory.
> There are considerable shape differences between the Ki 43 and the A6M2 which were not noted.
> ...



The Allies didn't recognize the Ki-43 as a distinct type until 1943. Prior to that point, all single-engine Japanese fighters with retractable undercarriage were Zeros, with the variation for the A6M3 identified when it entered service because of its clipped wingtips (and, of course, the Allied reporting names that were associated).

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## windhund116 (Oct 6, 2020)

SaparotRob said:


> I was wondering because I think that is a P-36 at the top of the picture. I’ve never seen all those aircraft in the same picture.



Sorry, I have no history behind that photo.


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## windhund116 (Oct 6, 2020)

Ivan1GFP said:


> Hello Peter Gunn,
> 
> The entire area of operations in New Guinea had both sides very close on a large land mass. The presence of Japanese Army units would have meant the presence of Ki 43 and other Army types.
> These attacks were on the Japanese Navy airbase at Lae.
> ...



Elements of the 26th Sentai flew Ki-43 out of New Guinea. Late 1942-43. The unit was decimated. So, they could have fought P-39s stationed at Port Moresby. From _Fighters of Japanese Imperial Army. 1939-1945_. Eduardo Cea. AF Editions. Pages 48-49.

In case anyone finds a photo the tail fin had "26" as stylized Kanji for "2" with Western "6" backwards and leaning.

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## P-39 Expert (Oct 6, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


Expand above.


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## P-39 Expert (Oct 6, 2020)

MiTasol said:


> Tomorrow I will demolish this claim. I was hoping to do it today but the material I need to do so is not at hand. The civil P-63 Pinball that I worked on in 72 had no ASB but the space where it fitted was very obvious and much of it was AFT of the split line. On the P-39 part of the oil tank intrudes forward of the split line. As such it is absolutely impossible to fit the ASB in a P-39. The rear fuselage extension on the P-39E would almost certainly have been the same concept as on the P-63 with the oil tank moved aft to make room for the ASB.


I'm not sure what you mean by the term "split line?"

Look at the drawings of the P-39 and P-63 fuselages in my post #236. The distances are marked in inches. The engine compartments are exactly the same length. The bulkhead at the rear point of the triangle aft of the engine separates the engine compartment from the oil tank which was fully aft of that bulkhead. 

The space for the aux. stage is exactly the same size on the P-63 as all P-39s including the E model that was the first to take the -47 engine with the aux. stage supercharger. Room for the aux. stage was created by moving the coolant tank from behind the engine to above the engine just behind the pilot. Coolant tank shape was changed to be flatter to fit in the new space. The aux. stage was then installed in the space formerly occupied by the coolant tank. The oil tank was aft of the aux. stage and aft of the bulkhead separating the engine compartment from the tail cone. Oil tank was in the same position on all P-39s and P-63s.


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## P-39 Expert (Oct 6, 2020)

FLYBOYJ said:


> Having worked on many aircraft (to include warbirds) I can somewhat agree with your field removal of some the equipment to save weight, 3 hours of maintenance is a bit skewed unless you're going to just hack the items mentioned out, not plug rivet holes and possibly leave wire bundles.
> 
> Your linear calculation does not address weight and balance of the items removed. If you're lucky enough to make the aircraft slightly tail heavy, it will fly faster but be more unstable, something already plaguing the P-39. You're comparing the C and D models and by your own post, no armor and no self sealing tanks. So you're making your point with performance numbers from an aircraft that was really not capable of entering combat????


As I said before, for climb comparison purposes, the C and D as tested were identical. They had the same engine, propeller and aerodynamic shape. Only difference was weight. Didn't matter that the C model had no self sealing tanks or armor. What was proven was that a C model climbed 1000fpm faster than a D and was 836lbs lighter. This means that for every pound of weight saved the rate of climb increases by 1.2fpm. In other words, if you reduce the weight of a P-39 by 300lbs the rate of climb increases by 360fpm.

Yes the plane had to be in balance after the items were removed. Bell proved they could do that even with varying weights for propellers, nose cannons, aux. stage superchargers, rear armor plate and radio equipment in the tail. The plane was balanced on all those different forms.


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## P-39 Expert (Oct 6, 2020)

GrauGeist said:


> As I mentioned earlier, that is a P-36A and the other aircraft have either 41- or early production 42- serials plus the national insignia no longer has the "meatball" so this photo could be perhaps June of 1942.


Correct. And the "Arnold Wings", those rectangles on either side of the roundel originated in June 1943. So the photo was sometime after the meatball was removed and the wings were added.


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## P-39 Expert (Oct 6, 2020)

MiTasol said:


> You have obviously never done weight and balance on a real aircraft, or actually worked on a P-39, or you would know that much of what you wrote above is not correct. Worse still, as many of the pilots on the forum will tell you, a stall caused by aft CG on many aircraft is stable meaning you cannot regain control. Regardless of power or control inputs the aircraft remains stalled and drops like a brick with almost zero forward speed. I have gone to two funerals caused by this mistake. Both pilots had carefully calculated there gross weight CG but forgot to check their low fuel, low speed, gear down CG.
> 
> You will note in your own writing that the Soviets removed the IFF to compensate for the removal of the 30 cals. There is nothing else heavy back there to remove except the oil tank and that is aft of the fuselage joint line. There is a tie down kit but that weighs about 5 or 6 lbs so is not going to help. Yes you could move the oil tank (and coolant tank) into the wing leading edge like the Hurricane did but that introduces all sorts of other problems. And you can remove the radios from above the engine (they and the engine are actually aft of the CG which is just above 2 = fuel, 9 = guns and 10 = wing ammo in the diagram the below and all forward of the CG) but where would you fit them?
> \
> ...


*Please expand the above for more comments and drawings.*

*The aux. stage supercharger occupied the same space as the coolant tank. On the P-63 (and the XP-39E) the coolant tank was moved forward to above the engine just aft of the pilot and flattened somewhat in shape to fit. In this diagram there is a bulkhead between the oil tank and the coolant tank, and the oil tank is clearly completely behind that bulkhead, as it was on the P-63. The area occupied by the coolant tank on the P-39 was exactly the same size as the area occupied by the aux. stage supercharger on the P-63. *

*The IFF radio is the black rectangle in the tail. It is actually farther away from the CG than the nose armor. Remove the 100lb nose armor and the IFF radio and the P-39 is balanced. Or just move the IFF radio up above the engine behind the pilot nearly on the CG and accomplish the same thing.*


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## buffnut453 (Oct 6, 2020)

Shortround6 said:


> I think we are letting national pride intrude on the discussion of how mechanically adept the Americans were.



Not from me. I am, after all, American. I'm as patriotic as the next man. I just want to do so with clear-eyed comprehension, cognizant of the widest-possible breadth of facts rather than a nationalistic agenda that perpetuates myths based on false assumptions. 




Shortround6 said:


> It is not a question of how good a small group of engineers or designers were.



Entirely agree. However, there persists this perception that countries other than America all had a "small group of engineers". 




Shortround6 said:


> It is a question of how many troops (a percentage of total troops) had driven or worked on motor vehicles (or boats or industrial machinery).
> 
> What this means to an army (any army) is how much training is required to turn recruits into drivers or mechanics/fitters.
> The army is going to put the troops selected for those jobs through some sort of training course and not just turn them loose.
> How many hours or weeks should the course/s be given the average level of knowledge the troops bring from civilian life?



That's a nice idea but it doesn't work in reality. You can't guarantee that every entrant has the same basic level of experience, nor can you tailor courses to suit the needs of an individual class (one class might be packed with motor mechanics while the next is filled with clerks). There's also the risk that new recruits may have learned bad habits in their prior experience. Regardless of incoming skills, you have to start from square one and give every recruit the same training with an assumed zero level of starting knowledge. Certainly, that means some highly-skilled recruits will be bored out of their tiny minds but the training has to be of sufficient duration and tempo that a student with no prior knowledge can reasonably be expected to graduate. It's exactly the same today. I've run military training courses for many years and you have to assume zero knowledge to ensure they've all been training the "right way". 




Shortround6 said:


> The American advantage was not that they were smarter or more mechanical adept 'naturally' but that they had much more experience driving/maintaining cars and machinery_ on average
> per 1000 recruits. _than other armies.
> How good you were rebuilding a turret lathe in civilian life gives you some advantage in working on truck/tank but perhaps not as much as a guy who worked in a gas station and had seen any number of minor problems.



Ok...let's take a look at things from the other end of the telescope. The 1930s didn't happen in isolation: they built on existing structures from the preceding decades. The US was largely unaffected by the Great War while the European nations were impacted massively. Again, I'll focus on the UK because it's the nation I know best. 

In 1918, the British Army operated enough vehicles powered by internal combustion engines to provide one vehicle per 350 of the British population (and that doesn't include the vehicles operated by the Royal Navy or the Royal Air Force). The vast majority of those vehicles were trucks, ambulances and motorbikes which weren't scrapped at the end of the Great War; they were demobilized and put to civilian use. In personnel terms, the Army Service Corps had 314 Motor Transport Companies, each of around 400 personnel...and that was just the establishment, not including those in training, or those who had been demobbed but still capable of working. 

The Royal Engineers had a personnel strength in 1918 of almost 300,000 men. Not all of them were technical but a great many were. There were Electrical and Mechanical Companies who maintained generators, pumps and plumbed electric lines in the trenches. There were Signals Companies attached to each Division (and the British Army had 70+ Divisions by the end of the War) to operate and maintain wireless, telegraph and other communication systems in the field. There were also Railway Companies, Light Railway Companies, Tramways Companies, and Transportation Works Companies (for maintaining vehicles...in addition to those belonging to the ASC which owned the MT Companies).

In 1918, the Royal Air Force was the largest air arm the world had ever seen, operating 22,000 aircraft--all powered by internal combustion engines--with a force of around 300,000 personnel, the vast majority of whom had a technical background. The RAF also made extensive use of motor vehicles which were critical to help the RAF keep pace with the rapid advances made in 1918 (my cousin served on 11 Sqn and moved airfields 4 times in 6 weeks towards the end of the war. These were not short trips and all personnel and equipment were moved in trucks. As the most technologically advanced service, the RAF had also adopted wireless for communicating within aircraft formations and from aircraft to ground forces for CAS coordination. All of this technology and innovation came was enabled because of the technical proficiency of the personnel. 

On the Home Front, the entire national production switched over to making war materiel. Factories were repurposed and many jobs previously held by men were being taken by women who drove motorbikes, trucks, ambulances, and cars. They maintained and operated machinery, including precision work, gaining skills and proving their abilities so that the 1918 push for women's suffrage became an irresistible force. Britain had the largest rail network per capita in the world. If the US had cars, the UK had railways and, while rail is a mass transit system in which passengers are scarcely aware of the machine they're using, the industry itself employed literally hundreds of thousands of men who understood machinery and were mechanically-minded. 

I've already mentioned the interwar fishing fleet and the many thousands of local fishermen who operated their own powered trawlers (again, internal combustion engines during this timeframe). None of the above has even touched the massive proportion of the British workforce engaged in maritime shipping. Yes, many were dockhands. But there were countless machinists, engineers and other technical staff, ontop of those employed in shipyards. 

When the Great War ended, the UK Government's biggest focus was finding "jobs for heroes." It seems likely that well over 1.5 million former soldiers and airmen (not including Navy or Merchant Marine personnel) came home from war with technical skills, a great many related to internal combustion engines, electric power, wireless and telecommunications. That's 10% of the entire male workforce, not including the men who never wore uniform but also had the same or similar technical skills, nor does it include the hundreds of thousands of women who learned to drive and maintain machinery during WW1. Given the logistical demands of the Great War, it's not unreasonable to assume that at least another 1.5 million Home Front citizens developed similar technical skills directly as a result of the War. 

These demobbed soldiers didn't just go back to pitchforking hay into the back of horse-drawn wagons. They went back to the cities (where most of them came from, anyhow) and into major growth industries related to automation and technology. Electricity and telephones were just being rolled out to the wealthy in 1913. After the war, there was an explosion in the use of these new technologies, with consequent increasing demand for generators (and staff to operate them), both as primary power sources and to provide back-ups. The demobbed trucks flooded the haulage market to the extent that use of horses went into rapid terminal decline in urban areas. The vast increase in road haulage also put the rail network under stress, and by the 1930s large sections were already being closed because they were no longer profitable. 

These Great War veterans were the backbone of British industry in the 1930s....and yet you're telling me that, because they didn't own a car, they weren't as well-versed in things mechanical as their American counterparts? 

Britain's servicemen in WW2 were the sons of these WW1 veterans and, like their fathers, the VAST majority came from industrialized, urban areas. They came from families where working with machinery was just second nature. It's what they grew up doing. My uncle served in the RAF as an engine fitter. As previously related, he didn't own a car until the 1950s...but he knew how to strip down an engine before he even joined up. 

As stated earlier, the biggest flaw in the "American farmer-mechanic" myth is the assumption that other countries had similar demographics. The vast differences in the degree of urbanization between the US and the UK alone should make people question the assumption, before we consider the disparate proportions of the respective workforces relative to agriculture and manufacturing. 

I am immensely proud of America's accomplishments during WW2. The spin-up was remarkable and turned our nation into the world's first Super Power. However, we do ourselves no favors if we denigrate other countries, particularly our Allies, by pushing cosy narratives that promote perceived superiority where none exists.

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## FLYBOYJ (Oct 6, 2020)

P-39 Expert said:


> This means that for every pound of weight saved the rate of climb increases by 1.2fpm. In other words, if you reduce the weight of a P-39 by 300lbs the rate of climb increases by 360fpm.


 And again, that is a linear calculation based on that one aircraft. You cannot guarantee that for all P-39s especially if you were to remove that weight in the field. Removing weight in the nose may require ballast in the tail and again this depends where the Mean Aerodynamic Chord falls to give the best flying qualities (whether you're looking for speed or maneuverability). Yes, the weight removal will give you the performance, but there's a limit on what you can do in the field.


P-39 Expert said:


> Yes the plane had to be in balance after the items were removed. Bell proved they could do that even with varying weights for propellers, nose cannons, aux. stage superchargers, rear armor plate and radio equipment in the tail. The plane was balanced on all those different forms.


This was a very "doable" exercise at the factory but as this discussion started out about doing this in the field to a production airframe, you're looking at 2 different scenarios that will not yield the same results and could actually be dangerous. As stated many times, the P-39 had a vertical and horizontal C/G which is not very common for fixed wing aircraft. In the field you can remove weight but may have to add ballast to remain within C/G limits, and even then I don't think the P-39 is an aircraft you really want to be tail heavy.

I'd like to see this play out on an actual weight and balance chart and it the end see where everything falls into place with a "production" equipment list.

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## Milosh (Oct 6, 2020)

> I'd like to see this play out on an actual weight and balance chart and it the end see where everything falls into place with a "production" equipment list.

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## FLYBOYJ (Oct 6, 2020)

P-39 Expert said:


> *The IFF radio is the black rectangle in the tail. It is actually farther away from the CG than the nose armor. Remove the 100lb nose armor and the IFF radio and the P-39 is balanced. Or just move the IFF radio up above the engine behind the pilot nearly on the CG and accomplish the same thing.*



You don't know that until you know the arm and moment!!!! And you also have to calculate that in vertical datum!

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## FLYBOYJ (Oct 6, 2020)

So let's start here...

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## Shortround6 (Oct 6, 2020)

buffnut453 said:


> Not from me. I am, after all, American. I'm as patriotic as the next man. I just want to do so with clear-eyed comprehension, cognizant of the widest-possible breadth of facts rather than a nationalistic agenda that perpetuates myths based on false assumptions.



The number of cars per 1000 people is not a false assumption, it is a fact. However it is just one fact out of many.



buffnut453 said:


> Entirely agree. However, there persists this perception that countries other than America all had a "small group of engineers".



Well, considering that the US had over 2 1/2 times the population of the UK in 1939/40 (and much larger than Germany and almost 3 times the population of Italy, any industrialized country had a small number of engineers compared to the US. Not saying the US engineers were smarter, just that there were more of them.

Do we really want to get into nitpicking the size of fishing fleets? Just look at US population and the size of the US coast.
Now for the US considering the size of it's population the _percentage_ of men with fishing boat experience would be less than the UK, even if the total number was higher.

Same for railroads. US went into WW II (2 years late) with 41,000 locomotives, 2 million freight cars and 230,000 miles of track.

Factory workers?
From Wiki " In 1937 the UK produced 379,310 passenger cars and 113,946 commercial vehicles"
In 1937 production numbers for the top_ eight_ US makers were
Ford........................942,005
Chevrolet.............815,375
Plymouth.............566,128
Dodge...................295,047
Pontiac.................236,189
Buick.....................220,346
Oldsmobile........200,886
Packard...............122,593

trucks/commercial vehicles not included nor the rest of US production.

For Germany in 1937 they built 267,910 cars, 79,16 trucks and 171,239 motorcycles which helps to point out the misconception that Germany was highly motorized.
Italy, France and Japan were even further behind.




buffnut453 said:


> These Great War veterans were the backbone of British industry in the 1930s....and yet you're telling me that, because they didn't own a car, they weren't as well-versed in things mechanical as their American counterparts?



car ownership may have nothing to do with or it may have something to do with it. The _chances_ of an american being well versed (or at least somewhat versed) is better but certainly not an absolute.
Story from grandfather when he was working in the clock/watch shop. Man comes in and asks the best way to clean the works of an old clock (most of which used brass works, gears, shafts and frame). My Grandfather tells him to take the works out of the case and boil it in a pot of water to get rid of the accumulated grease/oil and dirt. Man says thanks and leaves.
The Man comes back a couple of days later spitting mad that my grandfathers advice had ruined his clock. Come to find out the man had a clock with the works made of *wood.*
Wooden gears, shafts and frame and he had gone ahead and boiled it in a pot of water.
Some people should not be let loose near mechanical devices even if they can drive a car

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## wuzak (Oct 6, 2020)

P-39 Expert said:


> *The IFF radio is the black rectangle in the tail. It is actually farther away from the CG than the nose armor. Remove the 100lb nose armor and the IFF radio and the P-39 is balanced. Or just move the IFF radio up above the engine behind the pilot nearly on the CG and accomplish the same thing.*





FLYBOYJ said:


> You don't know that until you know the arm and moment!!!! And you also have to calculate that in vertical datum!



Isn't the IFF something you probably want to keep, except in Russian service?

Also, many items have been identified as being removed by the Russians. The nose armour is not one of them.

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## Ivan1GFP (Oct 6, 2020)

buffnut453 said:


> The Allies didn't recognize the Ki-43 as a distinct type until 1943. Prior to that point, all single-engine Japanese fighters with retractable undercarriage were Zeros, with the variation for the A6M3 identified when it entered service because of its clipped wingtips (and, of course, the Allied reporting names that were associated).



Hello buffnut453,

I am not disputing that fact. I am just wondering that if the pilots were noting a difference in the cowl size and nothing else, then perhaps there was nothing else to note and there are a LOT more detail differences between the Ki 43 and A6M.
Some of those differences are a lot more obvious than the size of the engine cowl such as the presence or absence of wing guns.

It is sort of like telling me that this is a different woman because the colour of her eyes is different but not pointing out that she is also six inches taller and 50 pounds heavier.

- Ivan.


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## Ivan1GFP (Oct 7, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *You are correct on the reduction gear, but the 2:1 was also used on the D-2 with the -63 engine. I really can't be sure about the M propeller, some sources say the Curtiss prop was used, some say the Aeroproducts prop was used. I haven't read anywhere that either prop was larger then the 10'4" prop used on the earlier models.*



The P-39K also used a 2:1 reduction with a -63 engine.
Detail & Scale 63 states that an Aeroproducts propeller of 11 feet 1 inch was used on the P-39M. I don't know if other sources give greater detail on the specifics about the propeller. I was gathering information on P-39 when I started working on a project a couple years ago. I got a bit stuck because I could not find a really good fuselage drawing.

Regarding P-39M propeller diameters, what you just stated directly contradicts your earlier statement which I have reproduced below. You need to make up your mind which story you are going with.



P-39 Expert said:


> Bell said in writing that the nose armor plate was not needed for ballast/balance on the P-39M. The M was an early model with the same weight and weight distribution as previous and later models. They were able to balance the plane with larger (heavier) propellers and different nose cannons that differed in weight by 140lbs. Bell designed the P-39 to take larger (heavier) three blade and four blade propellers and an auxiliary stage supercharger behind the engine that weighed 175lbs. They certainly were able to maintain proper balance with any or all of these items installed. The nose armor certainly could have been deleted and balance maintained.





P-39 Expert said:


> *Guess I wasn't clear, didn't mean to imply that the 20mm was used in the M. The 20mm was used in the P-400 and the D-1. Point I was making was that the 140lb weight difference was compensated for by Bell to make prior and subsequent P-39 models balanced. Why would you say that I am trying to bait and switch?*



Your two statements above which I have quoted simply do not agree.
You state that the P-39M didn't need the nose armour because a larger (heavier) propeller and cannon that weighed 140 pounds more could make up the difference.
The problem is 140 pounds more than WHAT?
ALL of the preceding models of the P-39 back to the P-39F (F, J, K, L) carried the same 37 mm cannon with only minor differences in weight as the P-39M did.

- Ivan.

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## buffnut453 (Oct 7, 2020)

Ivan1GFP said:


> Hello buffnut453,
> 
> I am not disputing that fact. I am just wondering that if the pilots were noting a difference in the cowl size and nothing else, then perhaps there was nothing else to note and there are a LOT more detail differences between the Ki 43 and A6M.
> Some of those differences are a lot more obvious than the size of the engine cowl such as the presence or absence of wing guns.
> ...



Entirely agree. I'm always dubious of aircraft descriptions derived from the heat of combat. I think it highly unlikely that anyone could objectively determine different cowling opening diameters. I suspect it was just the impression the pilot(s) perceived in the split second they saw it...and that perception could be entirely skewed by stress.

If pilots were so good at aircraft recognition, we wouldn't have Hurricanes being mistaken for Spitfires, Me 109s for He113s, or even noting Me109s over Malaya in 1941!

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## GrauGeist (Oct 7, 2020)

buffnut453 said:


> The Allies didn't recognize the Ki-43 as a distinct type until 1943. Prior to that point, all single-engine Japanese fighters with retractable undercarriage were Zeros, with the variation for the A6M3 identified when it entered service because of its clipped wingtips (and, of course, the Allied reporting names that were associated).


From a screenshot of a USAAF identification chart from *1942*.
Please note in the upper left corner the two fighters: "Zeke" and "Oscar".
In the heat of battle, you have a split second to realize you're being bounced by an enemy fighter.
Do you:
A) stop to be sure of the aircraft type
B) wait to see if it has any particular identifying features
C) shoot it down and try and figure out what it was later in the action report.

A and B will get you killed.
C is what happened most often and due to the strong similarity between the two, confusion is very understandable.

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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> Please expand the above for more comments and drawings.
> 
> *The aux. stage supercharger occupied the same space as the coolant tank.* On the P-63 (and the XP-39E) the coolant tank was moved forward to above the engine just aft of the pilot and flattened somewhat in shape to fit. In this diagram there is a bulkhead between the oil tank and the coolant tank, and *the oil tank is clearly completely behind that bulkhead, as it was on the P-63.* * The area occupied by the coolant tank on the P-39 was exactly the same size as the area occupied by the aux. stage supercharger on the P-63.*



Now let us put those three errors you keep making *permanently* to bed.

The aux. stage supercharger occupied the same space as the coolant tank.
the (P-39) oil tank is clearly completely behind that bulkhead, as it was on the P-63.
The area occupied by the coolant tank on the P-39 was exactly the same size as the area occupied by the aux. stage supercharger on the P-63.
*P-39 rear fuselage. *I cannot find my -2, -3 &- 4 for the P-39 aircraft so the first drawing is a P-39 rear fuselage from an on line IPL (-4) that is missing 90% of its pages. *Note that the oil tank extends forward from the bulkhead *and is partially restrained by curved strap across the front of the bulkhead.






The following diagrams are from the _Airacobra Design Analysis_ in the May 43 edition of _Aviation_ magazine and clearly show the shape of the P-39 rear fuselage front bulkhead and the cutout that the oil tank extends through and that the oil tank is mounted hard forward in the rear fuselage. Furthermore is mounted at an angle causing a significant volume of it to extend forward into the engine bay.










*P-63 rear fuselage* from SRM (-3) and IPL (-4). Note that all three illustrations show the oil tank spherical support is mounted back from the bulkhead, and the oil tank is mounted *behind* the bulkhead to allow space for the ASB. NOte also the cutout in the P-63 bulkhead is somewhat larger than the cutout in the P-39 bulkhead.
















From the above it is abundantly clear that the only way to fit and ASB in a P-39 is to delete the oil tank and carve a large hole in the rear fuselage front bulkhead. Either and both of these changes would render the aircraft inoperative.

*QED* Allison engines with ASBs attached cannot be installed in any production P-39 airframes because

The aux. stage supercharger occupied* a larger* space as than the coolant tank.
the (P-39) oil tank is clearly *not* completely behind that bulkhead, as it was on the P-63.
The area occupied by the coolant tank on the P-39 was *not* exactly the same size as the area occupied by the aux. stage supercharger on the P-63.

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## windhund116 (Oct 7, 2020)

GrauGeist said:


> From a screenshot of a USAAF identification chart from *1942*.
> Please note in the upper left corner the two fighters: "Zeke" and "Oscar".
> In the heat of battle, you have a split second to realize you're being bounced by an enemy fighter.
> Do you:
> ...



Correct. It's like trying to ID what pistol a robber has, at 50 yards, while running your @ss off.  The only thing I noticed is a lot of Nakajima made fighter planes have straight leading edges. Whereas the Zero has a tapered leading edge. The Oscar has a more slender fuselage. But, at 300MPH turning 3Gs, at 1000 yards... good luck with a positive ID.

I believe that by this time of the the SWPA action (late 1942-43) both Imperial Navy and Army fighters used the same loose finger-four formation. Similar layered attack strategies. So, it would be hard to tell from a distance, just looking at the formations --- whether it was IJNAF or IJAAF.


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## Elmas (Oct 7, 2020)

buffnut453 said:


> Entirely agree. I'm always dubious of aircraft descriptions derived from the heat of combat. I think it highly unlikely that anyone could objectively determine different cowling opening diameters. I suspect it was just the impression the pilot(s) perceived in the split second they saw it...and that perception could be entirely skewed by stress.
> 
> If pilots were so good at aircraft recognition, we wouldn't have Hurricanes being mistaken for Spitfires, Me 109s for He113s, or even noting Me109s over Malaya in 1941!



Or Ki-61 mistaken for Macchi 202...


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## Milosh (Oct 7, 2020)

Germans said they shot down, or were shot down by Spitfires but were actually Hurricanes. Course this could have been German fighter pilot snobbery.

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## P-39 Expert (Oct 7, 2020)

FLYBOYJ said:


> So let's start here...
> 
> View attachment 597318


Delete No. 12. This chart is for the P-39Q, this item weighed 100lbs on most earlier models.
Move the IFF radio from the tail cone forward to just aft of No. 18. IFF radio not shown on this drawing, weighed approximately 120lbs, located about midway between No. 17 and the leading edge of the horizontal stabilizer. Or delete the IFF radio altogether and save another 120lbs, as the Russians did.


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## buffnut453 (Oct 7, 2020)

GrauGeist said:


> From a screenshot of a USAAF identification chart from *1942*.
> Please note in the upper left corner the two fighters: "Zeke" and "Oscar".
> In the heat of battle, you have a split second to realize you're being bounced by an enemy fighter.
> Do you:
> ...



Agree with your comments about split second decisions. That's exactly why I don't trust pilot reports. It's not a criticism of the pilots, just a reflection of the operational environment.

BTW, that recognition chart is NOT from 1942. The Rex floatplane wasn't introduced until 1943. In fact the presence of the Norm puts it well into 1944. The only operational deployment for Norms took place 1 June thru 12 August 1944. First encounter with US forces was 15 June when 2 were destroyed by a US Navy task force.

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## P-39 Expert (Oct 7, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


My statements agree exactly. I stated that the nose armor was not needed on the P-39M and that the M was an early model with similar weight and weight distribution as earlier and later models. All the P-39 models were balanced whether they had the heavier 37mm cannon or the lighter by 140lbs 20mm cannon.

Then I said that Bell was able to balance *the plane* with varying weights for different components located fore and aft of the CG. When I said *the plane *I was referring to all the P-39 models that had different components. I can see how this could have been misinterpreted. 

Let me be absolutely clear: P-39s (and P-400s) had different propellers, nose armor, nose cannons, radios (in different locations) etc that had different weights. Bell was able to balance all the different models with all these different components. The nose armor could have been deleted and the plane could have been balanced.


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## P-39 Expert (Oct 7, 2020)

MiTasol said:


> Now let us put those three errors you keep making *permanently* to bed.
> 
> The aux. stage supercharger occupied the same space as the coolant tank.
> the (P-39) oil tank is clearly completely behind that bulkhead, as it was on the P-63.
> ...


When I said the aux. stage blower occupied the same space as the coolant tank, I meant that it occupied the same general location. Not that it was exactly the same size. It was larger than the coolant tank, but did fit in the location occupied by the coolant tank.

The P-39 oil tank is completely behind the bulkhead. It's base sat in the same type of cradle as the P-63, behind the bulkhead.

The aux. stage blower was installed in the XP-39E. The engine compartment was not enlarged to accommodate the aux. stage, it was the same length as the other P-39s and the P-63 as evidenced by the drawings in my post #236. The E model was longer because the tail section was longer, not the engine section as reported by other sources.


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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> Delete No. 12. This chart is for the P-39Q, this item weighed 100lbs on most earlier models.
> Move the IFF radio from the tail cone forward to just aft of No. 18. IFF radio not shown on this drawing, weighed approximately 120lbs, located about midway between No. 17 and the leading edge of the horizontal stabilizer. Or delete the IFF radio altogether and save another 120lbs, as the Russians did.


How far do you move the IFF? You need an exact distance in inches to know how its going to effect the c/g. It's not that simple, but please go on.

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## fastmongrel (Oct 7, 2020)

Shortround6 said:


> Same for railroads. US went into WW II (2 years late) with 41,000 locomotives, 2 million freight cars and 230,000 miles of track.



An example of how things were similar but different. The UK at the same time had 29,000 locomotives, 0.75 million freight vehicles and 19,000 route miles 50,000 total miles of track. 1.2 billion passenger journeys and 92 million parcels. Clapham junction was (and still is I think) the busiest station in the world with a train movement every 5 seconds at peak times.

so much smaller but more intensively used. Mind you most British locomotives would have fitted into the tender of a UP behemoth with room to spare.


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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> My statements agree exactly. I stated that the nose armor was not needed on the P-39M and that the M was an early model with similar weight and weight distribution as earlier and later models. All the P-39 models were balanced whether they had the heavier 37mm cannon or the lighter by 140lbs 20mm cannon.
> 
> Then I said that Bell was able to balance *the plane* with varying weights for different components located fore and aft of the CG. When I said *the plane *I was referring to all the P-39 models that had different components. I can see how this could have been misinterpreted.
> 
> Let me be absolutely clear: P-39s (and P-400s) had different propellers, nose armor, nose cannons, radios (in different locations) etc that had different weights. Bell was able to balance all the different models with all these different components. The nose armor could have been deleted and the plane could have been balanced.



And the weight and balance charts that show this? As a teacher once told me, "show me the math!"

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## DerAdlerIstGelandet (Oct 7, 2020)

FLYBOYJ said:


> How far do you move the IFF? You need an exact distance in inches to know how its going to effect the c/g. It's not that simple, but please go on.



I get the feeling that some people believe W&B and CG is a simple task, when there really is a science to it. You cannot simply take weight away from somewhere, and add some weight here. When I was on 2nd shift working as an A&P I had to work with QC quite a bit doing them after modifications had been performed. I always enjoyed it.

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## Elmas (Oct 7, 2020)

Shortround6 said:


> The number of cars per 1000 people is not a false assumption, it is a fact. However it is just one fact out of many.
> _Omissis_
> Italy, France and Japan were even further behind.
> _Omissis_



When at the end of May 1940 Italy was on the verge to declare war to G.B. and France, Italo Balbo was desperate, as in Italy public opinion clearly knew that U.S. would have not remained idle in supporting the British:
_"The Duce has never seen the size of the phone book of New York!"_ he repetedly told his staff.
Probably the phone book of Rome in 1939 was some one hundred pages, that of N.Y. a couple of thousand if not more...


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## Peter Gunn (Oct 7, 2020)

Gentlemen,

I believe you _ALL_ are going about this issue of lightening the P-39 to get a better climb rate out of it the wrong way. I mean, I have no training in aerodynamics or engineering but ye gods and little fishes but you guys are dense. The answer is soooo simple:







*I mean... DUH!*

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## FLYBOYJ (Oct 7, 2020)

DerAdlerIstGelandet said:


> I get the feeling that some people believe W&B and CG is a simple task, when there really is a science to it. You cannot simply take weight away from somewhere, and add some weight here. When I was on 2nd shift working as an A&P I had to work with QC quite a bit doing them after modifications had been performed. I always enjoyed it.


I pulled some other charts from what I can find on the internet. It seems that the P-39N used a %of MAC for it's CG envelope, the P-39Q uses inches aft of a datum line which I believe is at the nose of the aircraft. I see similarities between both models and can probably "interpulate" a C/G range. I have more info but let's see what our friend comes up with.


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## wuzak (Oct 7, 2020)

FLYBOYJ said:


> I pulled some other charts from what I can find on the internet. It seems that the P-39N used a %of MAC for it's CG envelope, the P-39Q uses inches aft of a datum line which I believe is at the nose of the aircraft. I see similarities between both models and can probably "interpulate" a C/G range. I have more info but let's see what our friend comes up with.



I still want to know why the Russians didn't remove the nose armour after they removed the IFF.

And I still believe the IFF was kinda important for operators other than Russia!


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## FLYBOYJ (Oct 7, 2020)

wuzak said:


> I still want to know why the Russians didn't remove the nose armour after they removed the IFF.
> 
> And I still believe the IFF was kinda important for operators other than Russia!


Hard to say but from I got from the P-39D W&B chart, the CG range was between 23 and 31 % of MAC. The Chart shows 3 loading configurations operating between 28.9 and 29.5 % of MAC which is not only a tight envelope but shows the aircraft tail heavy. My guess would be to make the aircraft more nose heavy.


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## P-39 Expert (Oct 7, 2020)

FLYBOYJ said:


> Hard to say but from I got from the P-39D W&B chart, the CG range was between 23 and 31 % of MAC. The Chart shows 3 loading configurations operating between 28.9 and 29.5 % of MAC which is not only a tight envelope but shows the aircraft tail heavy. My guess would be to make the aircraft more nose heavy.


CG location is shown on the drawing you furnished in post #286.


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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> CG location is shown on the drawing you furnished in post #286.



Yes it is shown - So tell us, what's the value? You don't calculate W&B on a pictorial image with no value.


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## P-39 Expert (Oct 7, 2020)

wuzak said:


> I still want to know why the Russians didn't remove the nose armour after they removed the IFF.
> 
> And I still believe the IFF was kinda important for operators other than Russia!


Yes the Russians removed the IFF radio that weighed about 120lbs from the tail section and didn't remove the 100lb nose armor. According to some folks on here the plane should have immediately fallen out of the sky.

Why would the IFF radio be important to the AAF and not the Russians? I don't know.


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## pinsog (Oct 7, 2020)

fastmongrel said:


> An example of how things were similar but different. The UK at the same time had 29,000 locomotives, 0.75 million freight vehicles and 19,000 route miles 50,000 total miles of track. 1.2 billion passenger journeys and 92 million parcels. Clapham junction was (and still is I think) the busiest station in the world with a train movement every 5 seconds at peak times.
> 
> so much smaller but more intensively used. Mind you most British locomotives would have fitted into the tender of a UP behemoth with room to spare.


I read somewhere that German spies in the US reported back to Germany on the size of American locomotives like the Union Pacific Big Boy and the Germans simply thought they were lying.

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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> Yes the Russians removed the IFF radio that weighed about 120lbs from the tail section and didn't remove the 100lb nose armor. According to some folks on here the plane should have immediately fallen out of the sky.


It possibly can, but again the c/g calculation will show if this is possible.


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## Ivan1GFP (Oct 7, 2020)

FLYBOYJ said:


> Yes it is shown - So tell us, what's the value? You don't calculate W&B on a pictorial image with no value.



Hello FLYBOYJ,

I did these calculations off the P-39Q chart a couple years ago when I was working on a design project for the P-39.
These numbers might be helpful in interpreting the values from the P-39Q chart:

The Leading Edge of MAC is at Fuselage Station 111.56 inch.
(LE Wing Root to LE MAC is 5.41 inch.)
MAC is 80.64 inch.
CoG at Basic Weight + 200 pound Pilot is at Station 135.88 inch.
That would make it 30.16% MAC.

I specified the pilot weight because it makes a significant difference and it ain't goin' nowhere without the pilot.

- Ivan.

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## FLYBOYJ (Oct 7, 2020)

Ivan1GFP said:


> Hello FLYBOYJ,
> 
> I did these calculations off the P-39Q chart a couple years ago when I was working on a design project for the P-39.
> These numbers might be helpful in interpreting the values from the P-39Q chart:
> ...



Excellent Ivan!!!

My calculations are about the same. I'm going to assume that the P-39Q carries the same CG range of 23.0 to 31.0% of MACas the P-39N. Assuming 23.0% of MAC = at station 111.56, 31.0% of MAC should be 140.98?


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## FLYBOYJ (Oct 7, 2020)

FLYBOYJ said:


> Excellent Ivan!!!
> 
> My calculations are about the same. I'm going to assume that the P-39Q carries the same CG range of 23.0 to 31.0% of MACas the P-39N. Assuming 23.0% of MAC = at station 111.56, 31.0% of MAC should be 140.98?



P-39 Expert - If you understand any of this feel free to chime in.


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## Ivan1GFP (Oct 7, 2020)

FLYBOYJ said:


> Excellent Ivan!!!
> 
> My calculations are about the same. I'm going to assume that the P-39Q carries the same CG range of 23.0 to 31.0% of MACas the P-39N. Assuming 23.0% of MAC = at station 111.56, 31.0% of MAC should be 140.98?



Hello FLYBOYJ,

Station 111.56 is Leading Edge of MAC, so it would be 0% MAC.
Here is how I arrived at %MAC:

Station in inches - Station of LE MAC / Length of MAC
so
140.98 - 111.56 = 29.42 inch
divided by 80.64 = 36.48% MAC

31% MAC would be 24.9984 inch so it would be
24.9984 + 111.56 = 136.5584 inch.

- Ivan.

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## FLYBOYJ (Oct 7, 2020)

Ivan1GFP said:


> Hello FLYBOYJ,
> 
> Station 111.56 is Leading Edge of MAC, so it would be 0% MAC.
> Here is how I arrived at %MAC:
> ...



Going back to check my math.

So the T/E of MAC would be Sta 192.2 (111.56+80.64)

So the most aft CG 31% of MAC is at 136.5584

so 23% of MAC would be 125.63~? (a rough calculation, I'm in a meeting)


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## Ivan1GFP (Oct 7, 2020)

FLYBOYJ said:


> Going back to check my math.
> 
> So the T/E of MAC would be Sta 192.2 (111.56+80.64)
> 
> ...



23% MAC would be 130.1072 inch 
80.64 inch * 0.23 = 18.5472 inch from LE MAC
18.5472 + 111.56 LE MAC = 130.1072 inch

My Daughter would be screaming at me for significant figures right about now!

- Ivan.


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## Peter Gunn (Oct 7, 2020)

Got my "Luftwaffe Test Pilot" from Amazon yesterday, good stuff. there is a section on the P-39, some quick quotes from the German test pilot Hans-Werner Lerche:

_"From the performance point of view the Airacobra with its 1200hp Allison engine was not of much interest to us, but we were rather intrigued by the construction of this fighter ... and the 37mm cannon."_

_"I would like to add that in the concluding report about the airframe and the flying characteristics of the Airacobra there was nothing really exciting to be mentioned."_

The section on the Airacobra states they had the correct captured Allied fuel (not sure if he's totally correct there but benefit of the doubt) and he does make the statement _"The Airacobra carried a comparatively large amount of fuel for a fighter..."_

Also, _"The Airacobra did not have the reputation of being exactly a terrific aircraft..."_

He does say he was impressed by the design and workmanship of the aircraft and compliments the tricycle landing gear and good instrumentation and thought the red pins on the fuselage and wings to show the landing gear down and locked rather ingenious.

In the back of the book he has a chart of all the planes he flew and the performance figures he got out of them.

For the *P-39D:
Weight:* 7845 lbs
*Speed:* 335 mph @ 5,000 feet
*Climb:* 1 min 54 sec to 5,000 feet

His claims for the *P-51B* WITHOUT correct fuel, or a bit of a mixture with German fuel:
*Weight:* 11,200 lb
*Speed:* 440 mph @ 30,000 feet
*Climb:* 1 min 48 sec to 10,000 feet

I thought it might be interesting to see what the "Other side" had to say about it. I only included the Mustang numbers because reasons.

Did you really expect *ME* to *NOT* to post Mustang info at the drop of a hat?

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## davparlr (Oct 7, 2020)

Graeme said:


> *"Circa 1940, the US had a population of 132 million while the UK had just 48 million."*
> 
> Certainly a greater ratio of cars to people in the USA in 1940.
> 26.5 million on the roads for the USA.
> ...



Between 1921 and 1935 over 36 million cars had been produced in the USA, and that includes 6 years of the Great Depression. In 1935, there were about 34 million household consisting of an average of about 4 people per household. It is not unreasonable to assume that, in 1935, a significant number of American households had an automobile, all of which, I'm sure, required a significant amount of maintenance in some form or other.


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## FLYBOYJ (Oct 7, 2020)

Ivan1GFP said:


> 23% MAC would be 130.1072 inch
> 80.64 inch * 0.23 = 18.5472 inch from LE MAC
> 18.5472 + 111.56 LE MAC = 130.1072 inch
> 
> ...


LOL - that makes more sense


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## XBe02Drvr (Oct 7, 2020)

FLYBOYJ said:


> P-39 Expert - If you understand any of this feel free to chime in.


I don't think he's caught on yet that CG is not a fixed location. Most of my flying students were reluctant to wrap their heads around that idea, even after reading the W&B chapter in the student pilot manual.

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## XBe02Drvr (Oct 7, 2020)

P-39 Expert said:


> Why would the IFF radio be important to the AAF and not the Russians? I don't know.


Russian radar may have been a little more primitive than in the West, and may have lacked the IFF transmitter and receiver.

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## Elmas (Oct 7, 2020)

Sorry for my quick translation, made from a page or two found on the internet, the whole book is on the way to my bookshelf. For those who want to know more the book is Italian and English.
_The P39 Aircobra in service in the ICAF: a robust but dangerous aircraft_
Extract from
Marco Mattioli - P39 Airacobra in Italian Service - IBN Editore






On 22 June 1944, ten. col. Fanali, Magg. Martinoli and ten. Alessandro Mettimano transported the three P-39s to Campo Vesuvio for the training of the pilots of the 12th Grp. On 24 June, another flight department of the 4th Stm, the 9th Grp, gave its MC.205s to the 21st Grp of the 51st Stm. On 7 July 1944 the Command of the 4th Stm moved from Nuova to Campo Vesuvio, followed by the 10th Grp Caccia, which from the Nuova base reached the Vesuvian runway, after having delivered its MC.205s to the 155th Grp of the 51st Stm on July 9th. On July 18, 1944 the 9th Grp of the 4th Stm moved from Lecce to Campo Vesuvio, completing the deployment of the Stormo on that base. In three months of intense training on the P-39N, 77 pilots of the 4th STM carried out 1,702 flights for 1,000 flight hours: there were eleven accidents, all caused by the bad characteristics of the airport or by sudden engine failures, which caused three pilots dead and several others injured, including two serious ones. The first of the three pilots who died was s. ten. Armando Moresi, who crashed on July 20, 1944, while carrying out a training flight paired with the ten. Giorgio Bentolaso: Moresi was an excellent aerobatic pilot, and he had tried to loop with his Airacobra, losing control; the Italian pilot, instead of launching himself, had tried to bring the P-39 to the ground. The death of Moresi convinced ten. Bortolaso to refrain from superfluous acrobatics. Bertolaso, recalls that when P39s were delivered to the pilots of the 4th STM, the American chief pilot, a major whose name he does not remember, made only one recommendation to the Italians: "P-39 is a wonderful aircraft , but don't do stunts; I flew more than 500 hours with him, but if I am still alive I owe it to the fact that I never let myself be tempted by aerobatics. "For many of the Italian pilots, convinced that a good fighter pilot must also be a good aerobatic pilot, these sensible words sounded like a challenge, and for this reason some of them lost their lives. The P-39 was an aircraft designed for ground assault, but not for flying stunts; in this regard, ten. Bertolaso (now General) still remembers: "the stabilizer of the Airacobra was very low, more or less at the same level as the wing; because of the way the weights were arranged, it was very close to him. When you pulled a lot, the stabilizer went into the shadow of the wing, and stalled before the wing itself, so the aircraft began to rotate through its transverse axis, and there was no maneuver capable of taking it out of this aerodynamic situation ( as demonstrated by the Moresi accident). Someone, we don't know how, happened to get out, but most of them were saved by parachute ”. Ten. Bertolaso recalls that another inconvenience that made the "Cobra" unsuitable for acrobatic flight was the engine: "While our engines and those of the Macchi 202 and 205, the Daimler Benz DB6O1 and DB605, were fueled by injection, with a hydraulically driven compressor, the Cobra's Allison V-1710 had a carburettor with a mechanically driven compressor. This fundamental difference meant that the Daimter Benz had a greater elasticity of operation and stability of the mixture. The Allison, on the other hand, with its carburetor, during the acrobatic maneuvers and especially in the sustained reverse, suffered from considerable impoverishment of the mixture, which often caused considerable backfires - the famous spitting of the engine - which for the complex compressor represented a very violent shock. Its gears broke, and the pieces were swallowed by the engine, smashing you heads. I personally had this terrible experience, during a very low-altitude tonneau: I had a flash back and all hell broke loose. Fortunately the engine, albeit with some broken pistons, smoking and trumpeting, brought me in sight of the field, but I had to land with the cart retracted, because I didn't have time to extract it. In normal conditions, the engine was very good ”. The other two pilots of the 40 Strm. fallen in air accidents were the sergeant major Teresio Martinoli, ace of the axes of the Regia Aeronautica in the Second World War with 22 victories, crashed during take-off on 25 August 1944, and decorated with the Gold Medal for Military Valor (MOVM), and S.ten. Guerniero Silvestrini, who crashed due to engine failure during take-off on 27 September 1944, and was killed by the explosion of the auxiliary tank which hit the ground. According to the ten. Bertotaso, who witnessed the death of Silvestrini, the accident occurred due to a strong overheating of the engine, due to the fact that before take off, Silvestrini remained stationary for too long with the engine running at the bottom of the runway. Among the injured pilots were Mar. Martelli (21 July), ten. Clauser (August 3), Ser. Novetto and ten. Rizzitelli (7 September), s. ten. Stoppani (9 September) and ten. Zanioto (September 14). The accident that occurred on ten Rizzitelli was singular: the engine of his P-39 crashed due to the volcanic dust, but Rizzitelli managed to land without landing gear at very high speed; in the collision, the Airacobra lost its entire nose and the pilot lost his shoes, remaining unharmed and barefoot.

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## SaparotRob (Oct 7, 2020)

FLYBOYJ said:


> I pulled some other charts from what I can find on the internet. It seems that the P-39N used a %of MAC for it's CG envelope, the P-39Q uses inches aft of a datum line which I believe is at the nose of the aircraft. I see similarities between both models and can probably "interpulate" a C/G range. I have more info but let's see what our friend comes up with.


Please tell me what is “MAC”?

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## BiffF15 (Oct 7, 2020)

SaparotRob said:


> Please tell me what is “MAC”?



Mean_Aerodynamic_Chord_(MAC)

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## Elmas (Oct 7, 2020)



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## FLYBOYJ (Oct 7, 2020)

So based on Ivan's calculations (Thanks again Ivan, I know your math is better than mine!!) we have the "station" C/G range of 130.1072 - 136.5584. The MAC range is 23 - 31%. 

The weight and balance chart shown in the P-39N manual has 3 loading configurations (Max Fuel, Bomber and Normal load) at 29.%, 28.8% and 28.9% MAC. From what I see if you load your aircraft in any of those configurations you're good to go. 

Now in the P-39Q flight manual I've seen, the same representation is made in inches from a datum point (which seems to be the tip of the nose). C/G data is omitted. ???












So if we use this information and go back to the original chart we can start removing items and see where they align within the W&B envelope. Mind you this is only for the horizontal C/G, I haven't even touch on the Vertical C/G.


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## SaparotRob (Oct 7, 2020)

BiffF15 said:


> Mean_Aerodynamic_Chord_(MAC)


Thanks, I can Wikipedia the definition now.

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## FLYBOYJ (Oct 7, 2020)

SaparotRob said:


> Thanks, I can Wikipedia the definition now.



Some manufacturers calculate weight and balance based on % of MAC, others use fuselage stations and the distance from a datum point.

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## XBe02Drvr (Oct 7, 2020)

FLYBOYJ said:


> based on Ivan's calculations (Thanks again Ivan, I know your math is better than mine!!) we have the "station" C/G range of 130.1072 - 136.5584.


So, with a CG range of roughly 6.5 inches we have all three common loading examples clustered within 1 inch of the aft CG LIMIT, before ammunition is expended or fuel burned? This plane needs a helium generator back by the IFF that operates whenever the nose guns are fired to keep it out of Lomcevak Land! Easy, just wire it into the gun camera circuit.
"Don't give me a P39!"

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## SaparotRob (Oct 7, 2020)

It’ll tumble and roll. It’ll dig a deep hole.

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## FLYBOYJ (Oct 7, 2020)

XBe02Drvr said:


> So, with a CG range of roughly 6.5 inches we have all three common loading examples clustered within 1 inch of the aft CG LIMIT, before ammunition is expended or fuel burned? This plane needs a helium generator back by the IFF that operates whenever the nose guns are fired to keep it out of Lomcevak Land! Easy, just wire it into the gun camera circuit.
> "Don't give me a P39!"


Here's one chart for a P-39N


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## P-39 Expert (Oct 7, 2020)

Thank you for all the comments about what I understand and don't understand. I understand mean aerodynamic chord and CG being within certain limits of distance from the wing leading edge.

I also understand that the CG is also a fixed point on the plane, and that if an item is removed from one point on the horizontal axis of the plane then an adjustment must be made on another part of the plane in order to maintain CG. If the nose armor is removed then corresponding weight from the rear of the plane must be removed or moved to the CG. Or a different item must be substituted where the nose armor was. It's called balance.

I also understand, as should you, that the manufacturer was able to maintain the CG within acceptable limits when items of different weights were substituted or removed. Such as larger (heavier) propellers or different (lighter) cannons were substituted in the nose, or different radios were substituted or removed from the tail. Balance was maintained by the manufacturer through all these different equipment changes. Bell stated that the P-39M did not need the nose armor as ballast. And the Russians removed the IFF radio that weighed 120lbs from the tail cone of the plane yet did not remove anything from the nose to maintain balance. According to you all the Russian P-39s should not have been able to fly.

All of you are making much more of this than actually happened. The P-39 was by all accounts easy to operate, safer than most and capable of performing all combat maneuvers. It had good stalling characteristics, acceptable spin characteristics (which could only happen after a stall) and would not tumble when ballasted properly. Most all other fighter planes had some unfortunate characteristics. Such is the nature of high performance airplanes.


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## Milosh (Oct 7, 2020)

Not sure if this will help, CG and Balance calculator.
Aircraft Center of Gravity Calculator


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## DerAdlerIstGelandet (Oct 7, 2020)

Except CG is not a fixed point. It changes based on the distribution of weight in the aircraft. It changes in flight as the fuel is depleted.

i suggest reading...

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/12_phak_ch10.pdf

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## P-39 Expert (Oct 7, 2020)

XBe02Drvr said:


> Russian radar may have been a little more primitive than in the West, and may have lacked the IFF transmitter and receiver.


It wasn't Russian radar, it was American radar supplied to the Russians under lend-lease. We supplied them with tactical radar sets beginning in April 1943. This allowed them to detect and intercept German attacks without flying standing patrols. I have read that they removed their IFF sets because they operated on different wavelengths than their own radio equipment, but I don't know that for sure. The IFF sets in the planes transmitted a signal for 15 seconds out of every minute and supposedly notified ground stations that the plane was friendly. Maybe we didn't supply them with the IFF receivers, I don't know. But they did remove the IFF transmitters from their planes.


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## P-39 Expert (Oct 7, 2020)

DerAdlerIstGelandet said:


> Except CG is not a fixed point. It changes based on the distribution of weight in the aircraft. It changes in flight as the fuel is depleted.
> 
> i suggest reading...
> 
> https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/12_phak_ch10.pdf


Not if the fuel is on the center of gravity as it should be.


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## Milosh (Oct 7, 2020)

So what happens in a climb, or dive, in a partially filled tank?

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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> The P-39 oil tank is completely behind the bulkhead. It's base sat in the same type of cradle as the P-63, behind the bulkhead.



Yes it fits in a cradle similar to the P-63 but the tank is mounted at an angle and protrudes thru the bolted bulkhead at stn 228.5 as shown in the first diagram in post 293.
Seeing that you will not believe someone who has worked on these aircraft maybe you will believe the Bell Aircraft Company, though I am beginning to doubt even they can convince you.







As shown in post 293 the P-63 oil tank is mounted vertically some six to eight inches behind the bulkhead and the bulkhead has a far larger cutout.







P-39 Expert said:


> The aux. stage blower was installed in the XP-39E.
> The engine compartment was not enlarged to accommodate the aux. stage, it was the same length as the other P-39s and the P-63
> as evidenced by the drawings in my post #236.



1. Yes, one out of three is correct

2. Yes and no.
Yes, the engine bay* in the forward fuselage* was not extended
No because the rear fuselage bulkhead was changed to allow the total engine bay to extend into the rear fuselage, unlike on all other P-39s, like on the P-63, and the angled oil tank was moved rearwards and positioned vertically, and the coolant tank relocated, to provide the space required to install the ASB.
The only way to fit the ASB in the P-39E was to extend the rear fuselage so that the ASB can extend through it like on the P-63 as shown above.

3. Station and skin panel drawings do not show any internals so are totally irrelevant to this discussion.



P-39 Expert said:


> The E model was longer because the tail section was longer, not the engine section as reported by other sources.



Yes and no. See above. The rear fuselage was longer in part because the engine bay was extended into the rear fuselage and the oil tank was moved aft and mounted vertically, and coolant tank relocated, to provide room for the ASB.


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## buffnut453 (Oct 7, 2020)

P-39 Expert said:


> Not if the fuel is on the center of gravity as it should be.



Or ammunition, or oil, or signal flares, or oxygen, or bombs...you can't put every consumable item "on the center of gravity". This is getting ludicrous.

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## DerAdlerIstGelandet (Oct 7, 2020)

P-39 Expert said:


> Not if the fuel is on the center of gravity as it should be.



CG shifts both longitudinally and laterally. Also, do you plan on moving the fuel tanks every time you remove components, equipment, etc., so that is always at the CG? What about oil? What about any other expendable item in the aircraft?

Read this...

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/faa-h-8083-1.pdf

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## DerAdlerIstGelandet (Oct 7, 2020)

buffnut453 said:


> Or ammunition, or oil, or signal flares, or oxygen, or bombs...you can't put every consumable item "on the center of gravity". This is getting ludicrous.



Ding, ding, ding. Someone gets it!


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## buffnut453 (Oct 7, 2020)

DerAdlerIstGelandet said:


> Ding, ding, ding. Someone gets it!



I had a vision of a fuel tank that looked like a very tall, very slender test tube so that it could persistently sit directly on the CofG. Alas, that would only work for straight-and-level flight.

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## DerAdlerIstGelandet (Oct 7, 2020)

There is a reason every time I go flying in my lil Piper Cherokee (Yeah I know its not a hot rod warbird, but weight & balance is still crucial for it too) that I do a W&B for before takeoff, and one for landing. I have to compute the amount if fuel and oil, how much each weighs, where my baggage (if any) are located, and how much it weighs, and the weight of my passengers. I have to do two because during the flight I will use up fuel. Therefore the CG shifts during the flight.


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## P-39 Expert (Oct 7, 2020)

MiTasol said:


> Yes it fits in a cradle similar to the P-63 but the tank is mounted at an angle and protrudes thru the bolted bulkhead at stn 228.5 as shown in the first diagram in post 293.
> Seeing that you will not believe someone who has worked on these aircraft maybe you will believe the Bell Aircraft Company, though I am beginning to doubt even they can convince you.
> 
> View attachment 597411
> ...


I stand corrected, the oil tank did protrude slightly into the engine bay.

But I am correct in that the engine bay was not extended on the P-63, it was exactly the same size as the P-39, including the XP-39E. Please look at the drawings in my post #236 of the P-39 and the P-63. Those numbers above the fuselage are inches from the tip of the nose. On the P-39 the engine bay starts at station 138.25 and ends at station 228.5 meaning the length of the engine bay was 90.25". On the P-63 drawing the engine bay starts at station 141.25 and ends at station 231.50 for a difference of 90.25". The engine bay was 90.25" exactly for both the P-39 and P-63. The tail cone was lengthened but not the engine bay. The aux. stage supercharger would fit in the P-39 just like it would in the P-63. 

Maybe the P-39 oil tank would need to be adjusted to stand vertically instead of at that angle, but the engine bay was not lengthened, it was the exact same size. Exactly.


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## MiTasol (Oct 7, 2020)

DerAdlerIstGelandet said:


> I get the feeling that some people believe W&B and CG is a simple task, when there really is a science to it. You cannot simply take weight away from somewhere, and add some weight here. When I was on 2nd shift working as an A&P I had to work with QC quite a bit doing them after modifications had been performed. I always enjoyed it.


And then there are the structural modifications that must be made to move something.

At 9g a 150lb radio "weighs" 1350lb so the structure where it is being moved to needs to reflect that. 

Further there is the structure that originally held the radio. Can all or part of it safely be removed? If it is left in will it produce other problems like too much rigidity in the area which will cause cracking nearby? This is not an insignificant issue as shown on the Lockheed L-188 which was too strong in one area. This resulted in the wings separating from the aircraft in flight and killed a lot of passengers and crew before the LEAP mods which changed the engine mounts to reduce a specific vibration, caused by whirl mode, and removed a lot of structure in the wing to fuselage joint area.

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## DerAdlerIstGelandet (Oct 7, 2020)

MiTasol said:


> And then there are the structural modifications that must be made to move something.
> 
> At 9g a 150lb radio "weighs" 1350lb so the structure where it is being moved to needs to reflect that.
> 
> Further there is the structure that originally held the radio. Can all or part of it safely be removed? If it is left in will it produce other problems like too much rigidity in the area which will cause cracking nearby? This is not an insignificant issue as shown on the Lockheed L-188 which was too strong in one area. This resulted in the wings separating from the aircraft in flight and killed a lot of passengers and crew before the LEAP mods which changed the engine mounts to reduce a specific vibration, caused by whirl mode, and removed a lot of structure in the wing to fuselage joint area.



That is something I deal with every day in my job, which deals with the engineering and design of retrofit and modifications. I am an aircraft mechanic by training, and not an engineer, but I basically work in the engineering support for this. I know longer turn wrenches. Structural testing and weight and balance are things we deal with every day.


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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> I also understand that the CG is also a fixed point on the plane


Right there you're wrong - the C/G will move (as shown) depending on weight, arm and moment


P-39 Expert said:


> I also understand, as should you, that the manufacturer was able to maintain the CG within acceptable limits when items of different weights were substituted or removed.


Absolutely


P-39 Expert said:


> Such as larger (heavier) propellers or different (lighter) cannons were substituted in the nose, or different radios were substituted or removed from the tail. Balance was maintained by the manufacturer through all these different equipment changes. Bell stated that the P-39M did not need the nose armor as ballast. And the Russians removed the IFF radio that weighed 120lbs from the tail cone of the plane yet did not remove anything from the nose to maintain balance. According to you all the Russian P-39s should not have been able to fly.


Of course different equipment will change weights and C/G limits but are you trying to say that Bell would pick out a "heavier" propeller or cannon of the same make/ model to adjust for weight and balance requirements on a specific production model? And again you're making the statement " According to you all the Russian P-39s should not have been able to fly." All I'm saying is "Show me the math" to prove your point! I actually think removing 120 lbs from the tail would have made the plane fly better, but that's just an opinion - I'd have to do the math 



P-39 Expert said:


> All of you are making much more of this than actually happened.


No - we're actually trying to get you to prove your point based on the data shown.



P-39 Expert said:


> The P-39 was by all accounts easy to operate, safer than most and capable of performing all combat maneuvers. It had good stalling characteristics, acceptable spin characteristics (which could only happen after a stall) and would not tumble when ballasted properly. Most all other fighter planes had some unfortunate characteristics. Such is the nature of high performance airplanes.


Agree, providing the aircraft stays between 23 - 31% MAC (which is a little over 6 inches) during all flight regimes in it's factory condition.

Now do you want to do more math?


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## MiTasol (Oct 7, 2020)

XBe02Drvr said:


> I don't think he's caught on yet that CG is not a fixed location. Most of my flying students were reluctant to wrap their heads around that idea, even after reading the W&B chapter in the student pilot manual.



Agreed so maybe he should study a basic introduction like https://skybrary.aero/bookshelf/books/879.pdf

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## FLYBOYJ (Oct 7, 2020)

P-39 Expert said:


> Not if the fuel is on the center of gravity as it should be.


Look - it's evident you never weighed a real aircraft. This has nothing to do with fuel being on the center of gravity!


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## ThomasP (Oct 7, 2020)

Question - what IFF set are talking about here? The only Allied electronic IFF bare units used (before the very end of the war) topped out at around 36 lbs plus a few pounds for wiring and such (most of the installation weights I have seen were around 40 lbs total). Where does the 120-130 lbs value come from?


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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> Yes the Russians removed the IFF radio that weighed about 120lbs from the tail section and didn't remove the 100lb nose armor. According to some folks on here the plane should have immediately fallen out of the sky.



Removing the IFF, but not the armour, as done in Russia, would prevent the CG moving as far aft once all the ammo was expended meaning the aircraft would be more stable and handle better with zero ammo and almost zero fuel.



P-39 Expert said:


> Why would the IFF radio be important to the AAF and not the Russians? I don't know.



IFF means Identification Friend or Foe and the allied radar was able to interpret the IFF signals to tell if you were friendly and therefore the allied aircraft and antiaircraft guns would not shoot you down.


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## MiTasol (Oct 7, 2020)

ThomasP said:


> Question - what IFF set are talking about here? The only Allied electronic IFF bare units used (before the very end of the war) topped out at around 36 lbs plus a few pounds for wiring and such (most of the installation weights I have seen were around 40 lbs total). Where does the 120-130 lbs value come from?



You are right. The AAF SCR595 and USN ABK IFF units were both 32.5lb for the main box excluding mounting tray and a few pounds for the wiring and cockpit control box. I should have picked up on that earlier

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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> Thank you for all the comments about what I understand and don't understand. I understand mean aerodynamic chord and CG being within certain limits of distance from the wing leading edge.
> 
> *I also understand that the CG is also a fixed point on the plane*



*NO IT IS NOT*

*Go and read the posts about CG again and again and again until you get the message that the CG moves in flight with changes of fuel, oil and disposable load like ammunition and bombs.*

*On the P-40 and P-51 it moves considerably forward as fuselage tank fuel is burned and on the P-39 it moves considerably aft as the fuselage ammunition is used. On the P-39 it also moves slightly aft as the fuel and wing ammunition are expended. The only thing that moves the P-39 CG forward in flight is oil consumption and that is a minor change as so little is used relatively.*

[My apologies to all the other forum members for shouting.]

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## windhund116 (Oct 7, 2020)

Elmas said:


> View attachment 597402



Didn't they call a P400, "A P39 with a Zero on its tail?"

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## fubar57 (Oct 7, 2020)

*That's OK, I'm hard of hearing*

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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> Not if the fuel is on the center of gravity as it should be.



On most aircraft the wing fuel is NEAR the CG. On the P-39 it is slightly forward of the CG

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## MiTasol (Oct 7, 2020)

P-39 Expert said:


> I stand corrected, the oil tank did protrude slightly into the engine bay.
> 
> But I am correct in that the engine bay was not extended on the P-63, it was exactly the same size as the P-39, including the XP-39E. Please look at the drawings in my post #236 of the P-39 and the P-63. Those numbers above the fuselage are inches from the tip of the nose. On the P-39 the engine bay starts at station 138.25 and ends at station 228.5 meaning the length of the engine bay was 90.25". On the P-63 drawing the engine bay starts at station 141.25 and ends at station 231.50 for a difference of 90.25". The engine bay was 90.25" exactly for both the P-39 and P-63. The tail cone was lengthened but not the engine bay. The aux. stage supercharger would fit in the P-39 just like it would in the P-63.
> 
> Maybe the P-39 oil tank would need to be adjusted to stand vertically instead of at that angle, but the engine bay was not lengthened, it was the exact same size. Exactly.



There are none so blind as those that will not see.

Ask yourself these questions

Why did they move the oil tank aft and cut a far larger hole in the rear fuselage front bulkhead on the P-63? That much bigger hole requires heavier material and significant additional structure to replace the original bulkhead and that means that bulkhead is heavier and that in turn means the aft CG is made very slightly worse.

Why was it necessary that they create this large volume of space behind the engine, *in the rear fuselage*, that can only be accessed through the engine bay in the forward fuselage. Apart from inspection panels there is no other access unless you remove the oil tank. That makes this totally dead space unless it is filled with something that extends aft from the forward fuselage engine bay.

Was it to fix the aft CG problem? No because it will actually make the aft CG problem worse.

Was it to install the coolant tank? Obviously not as that was moved to behind the pilot.

Was it to look pretty? Obviously not.

Was it because it seemed like a good idea at the time? Obviously not.

Was it to install helium to fix the aft CG problem? Obviously not.

Was it to fill with horse feathers? Obviously not.

So what does that leave? To extend the engine bay in order to make room for the ASB.


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## FLYBOYJ (Oct 7, 2020)

MiTasol said:


> * on the P-39 it moves considerably aft as the fuselage ammunition is used. On the P-39 it also moves slightly aft as the fuel and wing ammunition are expended. *



Ouch, my ears! LOL!

Hi MiTasol -

Based on the loading chart for the P-39Q and the numbers calculated by Ivan earlier, I came up with a few items...

At 7075 pounds, wheels up, the CG arm is 134.22. Within the envelope but very aft.

First, the wheels up and wheels down moment numbers on the chart are wrong, off by a smidge.

But if we use the CG range of 130.1072 - 136.5584 you'll find that if you use half fuel and expend all ammo, you're right at the aft CG (I came up with 136.58) Funny that when I did the same calculation with 1/4 tanks I came up with similar CG numbers.

If anyone wants to see my math, I can scan my calculations.


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## MiTasol (Oct 7, 2020)

I agree Flyboy J that the CG does not change much with fuel consumption, unlike many other fighters, though I would have expected a smidge of a change. Maybe if you do the numbers on the earlier models with the greater fuel tankage it may be more significant, though I doubt it. Likewise wing ammo is not going to move the CG much but the nose ammo certainly does affect the CG and if you remove the gearbox armour,* as is consistently suggested*, you will find the aircraft is past the aft limit. The Q model had lighter front armour but other changes added weight forward, like the bigger heavier 50 cal blast tubes and the wing gun installation, to allow this.

Maybe it is worth doing those calcs?


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## FLYBOYJ (Oct 7, 2020)

MiTasol said:


> I agree Flyboy J that the CG does not change much with fuel consumption, unlike many other fighters, though I would have expected a smidge of a change. Maybe if you do the numbers on the earlier models with the greater fuel tankage it may be more significant, though I doubt it. Likewise wing ammo is not going to move the CG much but the nose ammo certainly does affect the CG and if you remove the gearbox armour you will find the aircraft is past the aft limit.
> 
> Maybe it is worth doing that calc?



I'm going off for dinner, I'll do the math in a bit!


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## Shortround6 (Oct 7, 2020)

P-39 Expert said:


> According to you all the Russian P-39s should not have been able to fly.



There is a difference between exceeding he CG _*limits *_to the front and exceeding them to rear. Correction by real pilots welcome.

If the CG moves forward the plane becomes harder to control as the control surfaces become less effective. Primarily in pitch??? 
More control input (control surface deflection) is needed to get the same result. You also need more up trim or elevator deflection to fly level. 

If the CG moves rearward the plane becomes harder to control as the control surfaces become more effective (in pitch?) and at times the plane may decide to change it's AoA (pitch) just about on it's own. 

Think of a paper airplane with a paperclip on it's nose, now move the paperclip to the tail and see what happens. A bit extreme but a pilot should be able to handle a plane with the CG a few inches forward of the limit even if the combination losses speed and agility. According to one site with the CG too far forward makes a plane hard to flare for landing.

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## MiTasol (Oct 7, 2020)

This manual page shows how little spare room there was between the ASB and oil tank on the P-63.


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## DerAdlerIstGelandet (Oct 7, 2020)

Shortround6 said:


> There is a difference between exceeding he CG _*limits *_to the front and exceeding them to rear. Correction by real pilots welcome.
> 
> If the CG moves forward the plane becomes harder to control as the control surfaces become less effective. Primarily in pitch???
> More control input (control surface deflection) is needed to get the same result. You also need more up trim or elevator deflection to fly level.
> ...



Correct. An out of CG tail heavy aircraft is worse than an out of CG nose heavy aircraft (none is desirable). Nose heavy will have stability issues and be difficult to raise the nose. Especially during takeoff and landing. It can be difficult to flare and land. Tail heavy, on the other hand, make it difficult to recover from a stall (See United 1900 Crash). Also tail heavy can cause very light control surfaces making It easier to over stress the aircraft.

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## FLYBOYJ (Oct 7, 2020)

MiTasol said:


> I agree Flyboy J that the CG does not change much with fuel consumption, unlike many other fighters, though I would have expected a smidge of a change. Maybe if you do the numbers on the earlier models with the greater fuel tankage it may be more significant, though I doubt it. Likewise wing ammo is not going to move the CG much but the nose ammo certainly does affect the CG and if you remove the gearbox armour,* as is consistently suggested*, you will find the aircraft is past the aft limit. The Q model had lighter front armour but other changes added weight forward, like the bigger heavier 50 cal blast tubes and the wing gun installation, to allow this.
> 
> Maybe it is worth doing those calcs?



OK - dinner is down along with a couple of beers!

So I recalculated and removed the gear box armor (70.7 pounds) and "Armor Plate FUME" (27 pounds) which appears to be over the nose 50s. I came up with a weight of 6841.3 with all ammo expended, half fuel left and a moment of 975294.7 which equates to a CG arm of 142.55, way out of the the earlier calculated envelope.

"Better start removing some weight from the tail"!

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## MiTasol (Oct 7, 2020)

Shortround6 said:


> There is a difference between exceeding he CG _*limits *_to the front and exceeding them to rear. Correction by real pilots welcome.
> 
> If the CG moves forward the plane becomes harder to control as the control surfaces become less effective. Primarily in pitch???
> More control input (control surface deflection) is needed to get the same result. You also need more up trim or elevator deflection to fly level.
> ...



A good summary. Also think about how the centre of gravity sits in relation to a theoretical pivot point about which the aircraft rotates in all directions. Having a CG above the pivot is inherently unstable. Having it below is inherently stable and the stability increases as the CG moves lower which is why the vertical component of CG matters. In a low wing aircraft the CG moves up as wing fuel is burned off.

Now think of the forces that need to be applied by the elevators as the CG moves forward and aft from this pivot point. If the tail drops with the CG forward of the pivot, the force required to bring it back to horizontal is much less than if the CG moves the same distance behind the pivot point. Simple basic maths.

Now add to this the effect of airflow on the elevators. High set elevators are out of the wing wash (the turbulent air behind a wing) so are fully effective for higher angles of attack. Very low elevators are always out of the wing wash so again remain effective. Mid set elevators, like on the P-39, will be in unstable air when the tail is low and that reduces the effectiveness of the elevators.

Now add aft cg requiring higher elevator effectiveness with the elevators being in the wing wash and you have a major reduction in nose down pitch control. This situation demonstrates why there are defined front and rear limits to CG travel, and why aft CG is more critical than forward CG on the vast majority of aircraft.

It is not exclusive to the P-39 but does demonstrate why CG is important on all aircraft (except balloons).

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## fubar57 (Oct 7, 2020)

FLYBOYJ said:


> "Better start removing some weight from the tail"!

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## FLYBOYJ (Oct 7, 2020)

God I'm getting old! I'm doing weight and balance calculations just for fun!

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## ThomasP (Oct 7, 2020)

You are not old, you just have no life. (You We have plenty of company.)

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## FLYBOYJ (Oct 7, 2020)

ThomasP said:


> You are not old, you just have no life. (You We have plenty of company.)

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## BiffF15 (Oct 7, 2020)

Shortround6 said:


> *There is a difference between exceeding he CG limits to the front and exceeding them to rear*. Correction by real pilots welcome.
> 
> *Exceeding out of the front is NO WHERE near the penalty / danger that exceeding it out of the aft limit.*
> 
> ...



*Yes, and in transport aircraft this may be noticed by where your trim is during the approach. This can be dangerous in transport category aircraft when the pilot leaves the autopilot on until just before landing and can be surprised when turning it off and feeling how heavy / sluggish the nose is. He / she may not flare enough to prevent a hard or worse landing.*

Shortround6 pardon me for being lazy and cribbing your entire post. You are correct in all your comments / assumptions above. Highlights are for emphasis.

While I have not flown an airplane out of CG I have flown them with forward and aft balances (inside the allowable window). In an Eagle (or any plane) with a nose heavy CG (forward) you will burn airspeed faster doing a hard / break turn (max performance). An identical plane with its CG sitting on the aft limit will burn less energy / airspeed and generate nose movement faster due to the horizontal tail being more effective doing the same max performance turn. Nose heavy aircraft (forward CG) will feel sluggish compared to it's twin with it's CG on the aft limit. I have flown the F15 this way and it's preferred. The F15B was especially "squirrelly" on it's aft stop (longer canopy affected airflow over the tail to a greater extent. I would actually prefer the B as I felt I could get a little more performance out of it.

The F16 is actually tail heavy (but inside it's CG window I assume as it flies like this consistently). The result is that in a hard / max performance turn it will hold energy / airspeed longer. The reality is its horizontal tail moves less to get the corresponding movement out of the nose, and therefor creates less drag. The plane WILL NOT FLY WITHOUT AN OPERABLE FBW SYSTEM. The aircraft is dynamically unstable. The F15 is dynamically stable (very much so). We lost an F16 when it had a midair over the Pacific with a tanker. Its radome was knocked off, and that contains it's AOA sensors. Without those it doesn't fly regardless of how well everything else is working.

P39E I haven't flown the Cobra, or any other WW2 aircraft, nor can I do the W&B calculations like FlyboyJ, Ivan or DerAdler, or read diagrams like MiTasol. However, I can tell you that flying a nose heavy plane is at it's forward limits is much safer than flying one at or aft of it's aft limit. The P39 looks like it operated near or at it's aft limits in normal ops, but low on fuel / oil / ammo and doing hard pulls looks like a recipe for disaster. My second or third flight in the Eagle we went to the airspace and did tail slides. Straight up and until you ran out of airspeed, then flop over, recover and do it again. The bet was to see who could tail slide the furtherest. F16 guys will NOT do that, ever even with FBW. The don't have enough control to easily get out of it. Needless to say when I fought them I knew that, however the point to glean is an aircraft with too heavy of a tail can be at a minimum a handful, or worse.

Cheers,
Biff

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## Shortround6 (Oct 7, 2020)

No worries Biff, crib away.


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## Ivan1GFP (Oct 7, 2020)

FLYBOYJ said:


> So based on Ivan's calculations (Thanks again Ivan, I know your math is better than mine!!) we have the "station" C/G range of 130.1072 - 136.5584. The MAC range is 23 - 31%.
> 
> The weight and balance chart shown in the P-39N manual has 3 loading configurations (Max Fuel, Bomber and Normal load) at 29.%, 28.8% and 28.9% MAC. From what I see if you load your aircraft in any of those configurations you're good to go.
> 
> ...



Hello FLYBOYJ,

Thanks again, but be very wary of what exactly I was stating and how I got those numbers.
The Percent MAC calculation is most likely correct for every production Airacobra version.
The allowable CoG range of 23-31% is probably the same for all versions.
I don't believe their wings or tail changed from the aerodynamic standpoint though late versions had some structural improvements.

The Weight and Balance Table for P-39Q was used as the basis for calculating the CoG at Basic Weight and Pilot by using the Moments for Loaded Weight and Deducting the Moment for each disposable load using a spreadsheet. This was done for the Wheels-Up condition because in my opinion, it is the more important. The Wheels-Down would tend to move CoG forward and down and improve stability.
Note that FOR THIS SPECIFIC MODEL of P-39Q, with a 200 pound Pilot and no disposable loads (Basic Weight), it is still within the allowable CoG range.

I am pretty certain you already know this but others here may not:
Although this is presumably accurate for the P-39Q, I am quite convinced that earlier models of Airacobra had enough equipment differences to put the CoG with Basic Weight and Pilot at least 2-3 inches further AFT which would make them fall outside the allowable CoG range under certain load conditions.

As for CoG being moved a bit forward, The test P-39D-1 was loaded to have CoG at 25.1% MAC in NACA Memorandum Report L602. Even then, the Elevators were sufficiently powerful to lift the nose of the aircraft at 60 MPH while taxying before the aircraft had reached flying speed.

The Soviets probably also figured this part out. I saw it mentioned in a forum discussion but have not been able to confirm elsewhere that the Soviets also tended to load more ammunition for the .50 cals in the nose than was common in US service. The number stated was 270 rounds per gun.
The aircraft manual confirms that this number is possible.
Some US tests show 250 rounds per gun being loaded for flight testing.

As I mentioned in prior posts, for Spin tests, the Soviets removed the Oil Tank armour for 4 of the 5 test aircraft though I do not know if they did this for their service aircraft.

Seems like they really wanted the CoG forward which may be why they didn't run into as many problems.

- Ivan.

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## wuzak (Oct 7, 2020)

So after all that, the conclusion must be that removing the nose armour would be a bad thing for CoG and stability?


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## Shortround6 (Oct 7, 2020)

One wonders if the Russians pulled the wing .30 cal guns to improve climb *OR* to improve roll response. The P-39D was not a particularly good roller, at least until the IAS was near 340mph. And it wasn't that the P-39 got "better" it was that most of the other aircraft got worse quicker and the gap was much reduced.


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## FLYBOYJ (Oct 7, 2020)

Ivan1GFP said:


> Hello FLYBOYJ,
> 
> Thanks again, but be very wary of what exactly I was stating and how I got those numbers.
> The Percent MAC calculation is most likely correct for every production Airacobra version.
> ...


Hi Ivan - and thanks for this very interesting exercise! No, totally agree that these numbers aren't exact or finite for every P-39 but I think the point was well made that before you start talking about moving things about an airframe you really need to understand weight and balance, especially on an aircraft like this. There is no doubt the Soviets made their aircraft lighter and probably nose heavier, but the process was not as simplistic as originally presented. I suspect the aft CG measurement of 136.5584 might be off but not that much. I also agree with your comments about earlier P-39s operating outside CG limits as well when put in certain operating situations, corrected on later aircraft (P-39Q). Regardless I think in US and western service, the P-39 carried an aft CG that could be potentially dangerous given certain conditions. I flew an aircraft that was tail heavy, and although it was a GA aircraft, I didn't like the way it felt close to stall speeds and when flaring to land.

"Seems like they really wanted the CoG forward which may be why they didn't run into as many problems." Agree 100%

Now shall we calculate the vertical CG?


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## FLYBOYJ (Oct 7, 2020)

wuzak said:


> So after all that, the conclusion must be that removing the nose armour would be a bad thing for CoG and stability?



YES! And just to arbitrarily pick a piece of equipment of the same weight and saying that would counter the weight in the nose doesn't cut it unless you understand W&B calculations. The initial comment was made to remove the armor around the gearbox. I calculated the removal of that armor and some additional armor I believe located by the nose guns. I think if I left that armor in, you can still find a potential out of limit CG when all the ammo was depleted and fuel fell below a certain level. Even though our calculations were an "accurate wag" it still shows that the P-39 stock operated at an aft CG during most if not all operations.

CORRECTED! Removed statement about ballast!


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## Ivan1GFP (Oct 7, 2020)

Shortround6 said:


> One wonders if the Russians pulled the wing .30 cal guns to improve climb *OR* to improve roll response. The P-39D was not a particularly good roller, at least until the IAS was near 340mph. And it wasn't that the P-39 got "better" it was that most of the other aircraft got worse quicker and the gap was much reduced.



Hello Shortround6,

Please remember that the Soviets also pulled the wing guns out of the P-40 Tomahawks and left only the two cowl .50 cal MG. The Tomahawk didn't have a particularly bad roll rate. They just didn't seem to like wing armament and didn't mind lightly armed fighters.

- Ivan.


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## wuzak (Oct 7, 2020)

FLYBOYJ said:


> IMO, without adding some rear ballast, YES!



Adding rear ballast after removing forward ballast?


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## XBe02Drvr (Oct 8, 2020)

DerAdlerIstGelandet said:


> Tail heavy, on the other hand, make it difficult to recover from a stall (See United 1900 Crash). Also tail heavy can cause very light control surfaces making It easier to over stress the aircraft.


Step away for a couple hours and miss all kinds of interesting stuff! I did a little research on tail heavy 1900 crashes and couldn't find one by United Express. The two shining examples I found were Ryan Air in Homer AK, and US Air Express in Charlotte NC, both classic out-of-CG-aft loss of control situations. In an earlier thread I detailed my own experience with a badly out of limits aft Be1900, which I won't reiterate here. Suffice it to say, the 1900 had an exceptionally wide CG range, but due to it's long cabin and relatively narrow chord, was often flown at or very near both forward and aft CG limits at various times, giving crews plenty of experience over the entire CG range. Our adventure happened very shortly after the Homer AK crash, so when we got into the air and realized we had a real squirrel on our hands, we made a point of flying real gingerly and quickly but smoothly correcting every bob and weave.
It was my leg to fly, and I've got to hand it to my captain, he let me fly it, but kept a close watch on my progress. He pulled out my W&B and checked my figures again and confirmed we were near the aft limit, but not over it, then said it wasn't unusual to act a bit squirrelly at the aft limit. More than squirrelly, it wanted to go everywhere but straight and level. More like herding it than driving it, and very tiring. When we got to BTV we agreed we should land fast with only one notch of flaps, since full flaps had been the undoing of the Ryan aircraft. At the gates a couple hefty baggage smashers hopped up into the aft compartment to throw down the bags, and the old girl promptly sat down on her tail.
Turns out we were hauling 400 pounds of undocumented Piedmont Comat hiding under the passenger baggage. If the Ryan crew and passengers hadn't paid with their lives for the lesson, it could have been us.

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## DerAdlerIstGelandet (Oct 8, 2020)

XBe02Drvr said:


> Step away for a couple hours and miss all kinds of interesting stuff! I did a little research on tail heavy 1900 crashes and couldn't find one by United Express. The two shining examples I found were Ryan Air in Homer AK, and US Air Express in Charlotte NC, both classic out-of-CG-aft loss of control situations. In an earlier thread I detailed my own experience with a badly out of limits aft Be1900, which I won't reiterate here. Suffice it to say, the 1900 had an exceptionally wide CG range, but due to it's long cabin and relatively narrow chord, was often flown at or very near both forward and aft CG limits at various times, giving crews plenty of experience over the entire CG range. Our adventure happened very shortly after the Homer AK crash, so when we got into the air and realized we had a real squirrel on our hands, we made a point of flying real gingerly and quickly but smoothly correcting every bob and weave.
> It was my leg to fly, and I've got to hand it to my captain, he let me fly it, but kept a close watch on my progress. He pulled out my W&B and checked my figures again and confirmed we were near the aft limit, but not over it, then said it wasn't unusual to act a bit squirrelly at the aft limit. More than squirrelly, it wanted to go everywhere but straight and level. More like herding it than driving it, and very tiring. When we got to BTV we agreed we should land fast with only one notch of flaps, since full flaps had been the undoing of the Ryan aircraft. At the gates a couple hefty baggage smashers hopped up into the aft compartment to throw down the bags, and the old girl promptly sat down on her tail.
> Turns out we were hauling 400 pounds of undocumented Piedmont Comat hiding under the passenger baggage. If the Ryan crew and passengers hadn't paid with their lives for the lesson, it could have been us.



You are correct, I meant US Air Express not United. My apologies. There was more to it than the out of CG. Improper maintenance ultimately doomed it. Always set your control cable tensions correctly. She went right into a hangar though and killed all 20 on board, and one on the ground.

The 1900 as you know very well was notoriously tail heavy. If we did not use a tail stand when doing maintenance on them, they would tip right over.


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## XBe02Drvr (Oct 8, 2020)

DerAdlerIstGelandet said:


> The 1900 as you know very well was notoriously tail heavy. If we did not use a tail stand when doing maintenance on them, they would tip right over.


And yet with two big guys in the cockpit, with their overnight bags in nose baggage, full fuel and no pax, she was at the forward CG limit.

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## SaparotRob (Oct 8, 2020)

You guys should keep going with this. Eighty years later you’ll finally get the P-39 right! Anybody have Mr. Bell’s phone number?

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## P-39 Expert (Oct 8, 2020)

MiTasol said:


> There are none so blind as those that will not see.
> 
> Ask yourself these questions
> 
> ...


The engine bay was 90.25" long in both the P-39 and P-63. The aux. stage did not extend past the aft end of the engine bay, there was a bulkhead there.


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## P-39 Expert (Oct 8, 2020)

MiTasol said:


> This manual page shows how little spare room there was between the ASB and oil tank on the P-63.
> View attachment 597432


That's because the ASB was in the engine bay, the oil tank was not, and they were separated by a bulkhead. Engine bay was the same length as on the P-39, 90.25".


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## P-39 Expert (Oct 8, 2020)

ThomasP said:


> Question - what IFF set are talking about here? The only Allied electronic IFF bare units used (before the very end of the war) topped out at around 36 lbs plus a few pounds for wiring and such (most of the installation weights I have seen were around 40 lbs total). Where does the 120-130 lbs value come from?


America's Hundred Thousand lists the weight of the IFF radio on the P-39D-2 as 130lbs, and on the P-400 as 110lbs.


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## P-39 Expert (Oct 8, 2020)

How many times do I need to say this: Bell stated that the nose armor was not needed for ballast on the P-39M. Quoted from Vees for Victory, which most of us recognize as the best reference for the Allison V-1710.

How does that work in your CG calculations?


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## MiTasol (Oct 8, 2020)

P-39 Expert said:


> That's because the ASB was in the engine bay, the oil tank was not, and they were separated by a bulkhead. Engine bay was the same length as on the P-39, 90.25".



*What bulkhead?* 
Show it to me in any photo or manual page or show it with an arrow in the manual diagrams I provided in post 293. Those diagrams from the manuals do not lie.

Note this is the P-63 I worked on taken immediately after we unloaded it from the truck so I do know what is in that engine bay and I do know how long it is. It is one of my few photos that survived the 2013 floods.





Yes there is 90.25 inches in the forward fuselage but that freaking big hole in the rear fuselage between the forward fuselage and the oil tank is not for storing fairy floss. It is part of the total engine bay

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## MiTasol (Oct 8, 2020)

P-39 Expert said:


> America's Hundred Thousand lists the weight of the IFF radio on the P-39D-2 as 130lbs, and on the P-400 as 110lbs.



That is interesting. Both were fitted with the SCR-595 if my memory is correct (the Brits called it the R3003 or some such thing) and here is the manual section showing the weight of the radio (32.5lb including mounting) and all its additional components. Maybe they were including the tray in the rear fuselage that the mounting sits on and its support beams but I still cannot see 110 lbs let alone 130.


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## MiTasol (Oct 8, 2020)

P-39 Expert said:


> The engine bay was 90.25" long in both the P-39 and P-63. The aux. stage did not extend past the aft end of the engine bay, there was a bulkhead there.



What freaking bulkhead - show me some proof.


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## wuzak (Oct 8, 2020)

P-39 Expert said:


> America's Hundred Thousand lists the weight of the IFF radio on the P-39D-2 as 130lbs, and on the P-400 as 110lbs.



Table 26 has a line item "Miscellaneous Equipment (Radio)" 129.2lb for the P-39D-2 and 109.9lb for the P-400. It doesn't mention IFF.

Under the electrical system section in the table, "Communication" lists 62.0lb, 80.2lb and 35.0lb for the P-39D, P-39D-2 and P-400 respectively.

In the systems description section for communication, navigation and identification systems three radio systems are described as being typical equipment: 

SCR-535A radio recognition set with detonator and crash inertia switch (that's be the IFF).

SCR-522A command radio set

SCR-274N radio.


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## wuzak (Oct 8, 2020)

Here is a picture of a P-39 engine bay, looking rearwards




P-39 engine bay by Errol Cavit, on Flickr

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## MiTasol (Oct 8, 2020)

wuzak said:


> Here is a picture of a P-39 engine bay, looking rearwards
> 
> View attachment 597503
> P-39 engine bay by Errol Cavit, on Flickr



Yep, nice rebuild - the structure at the upper rear is to support the coolant tank


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## MiTasol (Oct 8, 2020)

From P-63 manual - notice the lack of coolant tank support structure.

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## MiTasol (Oct 8, 2020)

This photo from the manual shows the removal of the rear fuselage attach bolts (fuselage splice bolts).
The hole the guys arm is going through is the hole the oil tank fits in.
You will note the total absence of any bulkhead at the end of the engine bay. That is to allow part of the ASB to be installed into the rear fuselage.


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## FLYBOYJ (Oct 8, 2020)

wuzak said:


> Adding rear ballast after removing forward ballast?


Actually my bad, no ballast!


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## FLYBOYJ (Oct 8, 2020)

P-39 Expert said:


> How many times do I need to say this: Bell stated that the nose armor was not needed for ballast on the P-39M. Quoted from Vees for Victory, which most of us recognize as the best reference for the Allison V-1710.
> 
> *How does that work in your CG calculations?*



Go back and READ our calculations (Post 368). In our example using numbers from the P-39Q loading chart, IT PUTS THE AIRCRAFT OUT OF CG!! It's probably the same for the P-39M as well.


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## MiTasol (Oct 8, 2020)

wuzak said:


> Table 26 has a line item "Miscellaneous Equipment (Radio)" 129.2lb for the P-39D-2 and 109.9lb for the P-400. It doesn't mention IFF.
> 
> Under the electrical system section in the table, "Communication" lists 62.0lb, 80.2lb and 35.0lb for the P-39D, P-39D-2 and P-400 respectively.
> 
> ...



Thanks Wuzak
I do not have an SCR-535 manual so I cannot provide a weight breakdown for that. If my memory is correct, and I avoided learning about boat anchors (radios) as much as I could so may well be wrong, all the IFF boxes fitted on the same racks and weighed about the same. Certainly this applied to the SCR-595 and SCR-695.

However the claim that the IFF alone weighed over 100 lb is now shot to hell by both the SCR-595 manual and your sources.


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## MiTasol (Oct 8, 2020)

FLYBOYJ said:


> Go back and READ our calculations (Post 368). In our example using numbers from the P-39Q loading chart, IT PUTS THE AIRCRAFT OUT OF CG!! It's probably the same for the P-39M as well.


Does anyone have charts for the M model. The Q had the external 50 cals and I think they actually bought the CG forward a tad meaning the M would be affected more by the removal of armour as it probably had the heavier early armour. Vs for Victory is a great book but it is not infallible. I have never seen an error in it but then again I have never seen the quoted Bell statement that the M could safely delete the nose armour.

Some sources (such as Instructions of Red Army Air Force Commission No. 4 on Winterized P-39M Airplanes, No. 6, 29-Jan-1943) say the P-39M was fitted with BFGoodrich deicer boots on the wings and tail. That would make the aircraft basic weight greater which may be a factor although I would have expected the tail boots total moment to be vastly greater than the counterbalancing wing boots. The Russians removed said deicer boots.


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## FLYBOYJ (Oct 8, 2020)

MiTasol said:


> *Does anyone have charts for the M model*. The Q had the external 50 cals and I think they actually bought the CG forward a tad meaning the M would be affected more by the removal of armour as it probably had the heavier early armour. Vs for Victory is a great book but it is not infallible. I have never seen an error in it but then again I have never seen the quoted Bell statement that the M could safely delete the nose armour.
> 
> Some sources (such as Instructions of Red Army Air Force Commission No. 4 on Winterized P-39M Airplanes, No. 6, 29-Jan-1943) say the P-39M was fitted with BFGoodrich deicer boots on the wings and tail. That would make the aircraft basic weight greater which may be a factor although I would have expected the tail boots total moment to be vastly greater than the counterbalancing wing boots. The Russians removed said deicer boots.



That's the issue - that one loading chart that shows the horizontal and vertical GC locations in inches was in the P-39Q manual. If *ANYONE * comes up with a similar chart or data from a different model, I'll be glad to run the numbers (and show the math). However, I don’t think there’s going to be much of a difference.


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## DerAdlerIstGelandet (Oct 8, 2020)

This is a very informative thread, and yet it is quite amusing.

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## Ivan1GFP (Oct 8, 2020)

P-39 Expert said:


> How many times do I need to say this: Bell stated that the nose armor was not needed for ballast on the P-39M. Quoted from Vees for Victory, which most of us recognize as the best reference for the Allison V-1710.
> 
> How does that work in your CG calculations?



Hello P-39 Expert,

IF the fixed equipment were all the same as the prior P-39L, there is still a matter of a propeller that is now 11 feet 1 inch diameter on the M while prior propellers were only 10 feet 4 1/2 inches. That would count for a bit of extra weight in the nose. The Gear Box Armour was 71 pounds in the L and M, so perhaps the difference in propeller weight made up enough of the difference to keep the CoG within proper range under most conditions.
This is not to say that under certain load conditions that the CoG will NOT be in the safe range on the M without its Gear Box Armour.
Please note however that the armour was still retained for the type which meant that the Army didn't buy the idea.

- Ivan.


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## P-39 Expert (Oct 8, 2020)

MiTasol said:


> From P-63 manual - notice the lack of coolant tank support structure.
> View attachment 597520


Please expand the above drawing. This drawing explains exactly what I have been saying. The engine bay is 90.25" long. It extends from the aft edge of the cabin assembly to the bulkhead (with the hole in it) just in front of the oil tank. The entire engine and aux stage supercharger including carburetor are contained in that engine bay. It does not extend past the oil tank bulkhead.

The engine bay is exactly the same length on the P-39 as it is on this P-63. The aux. stage would fit in the P-39 engine bay after the coolant tank had been moved up to the top front edge of the engine as it is in this diagram. The XP39-E did not have a lengthened engine bay (as was often stated in reference books), it had a lengthened tail cone aft of the engine bay.


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## P-39 Expert (Oct 8, 2020)

wuzak said:


> Table 26 has a line item "Miscellaneous Equipment (Radio)" 129.2lb for the P-39D-2 and 109.9lb for the P-400. It doesn't mention IFF.
> 
> Under the electrical system section in the table, "Communication" lists 62.0lb, 80.2lb and 35.0lb for the P-39D, P-39D-2 and P-400 respectively.
> 
> ...


The 522A and the 274N would not be used together, they perform the same function. P-39s after the D/F models had either the 522 or the 274, but not both. And the 535A.


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## P-39 Expert (Oct 8, 2020)

FLYBOYJ said:


> OK - dinner is down along with a couple of beers!
> 
> So I recalculated and removed the gear box armor (70.7 pounds) and "Armor Plate FUME" (27 pounds) which appears to be over the nose 50s. I came up with a weight of 6841.3 with all ammo expended, half fuel left and a moment of 975294.7 which equates to a CG arm of 142.55, way out of the the earlier calculated envelope.
> 
> "Better start removing some weight from the tail"!


Exactly as I have said all along, radios from the tail would need to be moved forward above the engine just aft of the cockpit. Or removed altogether. Bell managed to keep the plane in balance with a variety of propeller, armor, armament, radio etc variations.


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## P-39 Expert (Oct 8, 2020)

FLYBOYJ said:


> Here's one chart for a P-39N
> 
> View attachment 597407



Did you get that from a pilot's manual? If so, could you post that also? Thanks.


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## GregP (Oct 8, 2020)

Does anybody know the moment arm for external centerline tanks?


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## davparlr (Oct 8, 2020)

A few comments on P-39.
The P-39 appears to be optimized for the technology of the moment, with limited growth space, ala F-16, which had 2 sqft growth space when I did avionic installation work for the Nothrop AMRAAM proposal. With limited growth bound by size and critical Cg requirements, building a really capable fighter was difficult. They probably should have started off with a longer fuselage ala P-63, increasing the nose length and moving the pilot/engine forward moving the natural Cg forward allowing more flexibility in stability and equipment layout. This would have allowed the room for turbo or fuel or maybe both. Of course, slightly more weight, bigger wings needed?, more power?, on and on. It was quite fast compared to the P-40, F4F,and the Zero, so it had some airspeed to trade off against a bigger wing. The turbo would certainly improve performance at higher altitude. I kinda guess that they should have started off with a lightened P-63ish design.

Second, a few months ago, I read The First Team and the Guadalcanal Campaign and there was not too much derogatory comments about the P-39 except the limited high altitude ability. I it did provide quite capable close air support for the Marines. Also, General Kenney did not complain much about the plane and wanted more of them, of course, he was desperate for aircraft and really wanted P-38s.

Finally, degrading the P-39 performance in the Pacific was possibly the capability or lack thereof of the pilots. The army had a 100 new pilots fresh out of flight training enroute to the Philippines when war broke out and these were then diverted to Australia. I suspect these very inexperienced pilots had a tough time against Japans best. 

I was much confused by the data on the P-39. While it has been ragged on as a second class fighter the flight test data in comparison with contemporary fighters, the P-40E and the F4F-4, and the Zero, the P-39 was significantly faster than the P-40E up to about 19k, significantly faster than the F4F-4 up to 25k (50 mph at 15k), and faster than the Zero up to 25k. In climb, the P-39 is equal to or better than both the P-40E and the F4F-4 up to 25k. The Zero is much better than the American planes in climb rate at all altitudes. So, below 15k the P-39 is quite a bit faster than both American fighters and the Zero, and below 10k, the Zero has only about 300 ft/min advantage in climb over the P-39. So, it is a low altitude fighter, but could certainly be formidable there in the hands of a capable pilot.

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## FLYBOYJ (Oct 8, 2020)

P-39 Expert said:


> Exactly as I have said all along, radios from the tail would need to be moved forward above the engine just aft of the cockpit. Or removed altogether. Bell managed to keep the plane in balance with a variety of propeller, armor, armament, radio etc variations.



The point is HOW MUCH do you move it and where and this becomes more critical if you're attempting to do this in the field. And again, are these W&B "variations" for specific aircraft or for an entire production run of a specific model or configuration?



P-39 Expert said:


> Did you get that from a pilot's manual? If so, could you post that also? Thanks.

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## fubar57 (Oct 8, 2020)

Thanks Joe

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## FLYBOYJ (Oct 8, 2020)

davparlr said:


> A few comments on P-39.
> The P-39 appears to be optimized for the technology of the moment, with limited growth space, ala F-16, which had 2 sqft growth space when I did avionic installation work for the Nothrop AMRAAM proposal. With limited growth bound by size and critical Cg requirements, building a really capable fighter was difficult. They probably should have started off with a longer fuselage ala P-63, increasing the nose length and moving the pilot/engine forward moving the natural Cg forward allowing more flexibility in stability and equipment layout. This would have allowed the room for turbo or fuel or maybe both. Of course, slightly more weight, bigger wings needed?, more power?, on and on. It was quite fast compared to the P-40, F4F,and the Zero, so it had some airspeed to trade off against a bigger wing. The turbo would certainly improve performance at higher altitude. I kinda guess that they should have started off with a lightened P-63ish design.
> 
> Second, a few months ago, I read The First Team and the Guadalcanal Campaign and there was not too much derogatory comments about the P-39 except the limited high altitude ability. I it did provide quite capable close air support for the Marines. Also, General Kenney did not complain much about the plane and wanted more of them, of course, he was desperate for aircraft and really wanted P-38s.
> ...



Dave - a lot of good points! We keep hearing what a dog the P-39 was but it did hold it's own in the SWP, personally I think much of the "P-39 bad press" was due to the P-38 coming on board and the results such units like the 39th FS had after they transitioned. Just my opinion.

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## P-39 Expert (Oct 8, 2020)

FLYBOYJ said:


> The point is HOW MUCH do you move it and where and this becomes more critical if you're attempting to do this in the field. And again, are these W&B "variations" for specific aircraft or for an entire production run of a specific model or configuration?


Many thanks.

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## P-39 Expert (Oct 8, 2020)

davparlr said:


> A few comments on P-39.
> The P-39 appears to be optimized for the technology of the moment, with limited growth space, ala F-16, which had 2 sqft growth space when I did avionic installation work for the Nothrop AMRAAM proposal. With limited growth bound by size and critical Cg requirements, building a really capable fighter was difficult. They probably should have started off with a longer fuselage ala P-63, increasing the nose length and moving the pilot/engine forward moving the natural Cg forward allowing more flexibility in stability and equipment layout. This would have allowed the room for turbo or fuel or maybe both. Of course, slightly more weight, bigger wings needed?, more power?, on and on. It was quite fast compared to the P-40, F4F,and the Zero, so it had some airspeed to trade off against a bigger wing. The turbo would certainly improve performance at higher altitude. I kinda guess that they should have started off with a lightened P-63ish design.
> 
> *Please remember the Allison only had 1150hp. Uprated engine or auxiliary stage supercharger wasn't available until 1943. Had to keep it small to have any performance at all.*
> ...




Good analysis, thanks for posting. Please expand above for more comments.

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## SaparotRob (Oct 8, 2020)

Just wondering if a small nitrous oxide system could have been installed. It worked on my friend’s old Mercury Cougar.


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## davparlr (Oct 8, 2020)

SaparotRob said:


> Just wondering if a small nitrous oxide system could have been installed. It worked on my friend’s old Mercury Cougar.


Good question. I know that the Germans used it in some of their advanced fighters in late '44. Haven't heard it pop up any where else. I suspect there are plenty of people on board that can answer your questions.


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## Milosh (Oct 8, 2020)

Iirc some Mosquitoes had NOX installed.


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## ThomasP (Oct 8, 2020)

Hey P-39 Expert,

As far as I can find, the standard electronics fit - TR.1133 (71 lbs) or TR.1143 (84 lbs), plus R.3003 IFF (30 lbs) - of the mid-war UK aircraft, or about 120-130 lbs including the other removable bits and pieces. I think this would have been the total weight of electronics in the P-400 as installed for the UK. If carrying the R.1147 DF receiver it would have another 19-23 lbs. As far as I know the USAF used the American made equivalents at the time (as mentioned by wuzak above).

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## pinsog (Oct 8, 2020)

SaparotRob said:


> Just wondering if a small nitrous oxide system could have been installed. It worked on my friend’s old Mercury Cougar.


I was waiting for Shortround to respond to this but he hasn’t. I believe he will say that manufacturing nitrous oxide and transporting it to a remote location is extremely problematic. The supply would be used quickly and I believe that even though it is in a pressurized container, somehow it leaks out or dissipates on its own if not used quickly. So while nitrous might work well on a Spitfire based in England or on a P40 in Hawaii, trying to use it at Guadalcanal or Alaska or some other remote location would not really be feasible.

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## P-39 Expert (Oct 8, 2020)

FLYBOYJ said:


> The point is HOW MUCH do you move it and where and this becomes more critical if you're attempting to do this in the field. And again, are these W&B "variations" for specific aircraft or for an entire production run of a specific model or configuration?


How do you get these?


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## GregP (Oct 8, 2020)

here is my spreadsheet on the P-39 weight and balance. I am missing the moment arm for centerline external tanks and I also don't have the upper and lower limit for the vertical CG, but it is calculated. The sheet is protected, but without a password.

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## FLYBOYJ (Oct 8, 2020)

P-39 Expert said:


> How do you get these?



They should be on blue prints, equipment lists or weight and balance charts (like the one shown for the P-39Q). This information varied in it's presentation between manufacturers.


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## FLYBOYJ (Oct 8, 2020)

GregP said:


> here is my spreadsheet on the P-39 weight and balance. I am missing the moment arm for cernerline external tanks and I also don't have the upper and lower limit for the vertical CG, but it is calculated. The sheet is protected, but without a password.


Dude - YOU ROCK! That looks fantastic!!!! I'm on my way to dinner, I'll play around with it later on.

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## Ivan1GFP (Oct 8, 2020)

P-39 Expert said:


> *1942 P-39 data has always been biased. 750lbs lighter than the P-40E with the same engine and propeller it had to be faster and climb much better at all altitudes. Reduce the weight like the Russians did and it would climb with a Zero.*



Hello P-39 Expert,

You are actually incorrect. While the engine on the P-39C/D/D-1/F was pretty comparable to that of the P-40E, the propeller was quite different.
Those P-39 used a 10 feet 4 1/2 inch propeller with a 1.8:1 reduction
The P-40E used a 11 feet 0 inch propeller with a 2:1 reduction

The power coefficient of the P-40E engine / propeller would suggest that it would be better suited (than the P-39) to higher altitudes..... Not that its supercharger was any better suited.

Another thing I have always wondered about is how effective the carb intake was on the P-39 for optimum ram effect. It looks like it would be sitting in a low pressure area. On the P-40, it is sitting at the nose in a high pressure area.

- Ivan.


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## FLYBOYJ (Oct 8, 2020)

GregP said:


> here is my spreadsheet on the P-39 weight and balance. I am missing the moment arm for cernerline external tanks and I also don't have the upper and lower limit for the vertical CG, but it is calculated. The sheet is protected, but without a password.


Thanks again Greg for putting that together. It clearly shows that if you remove the GB armor, expend all ammo and run the fuel down to half tanks you'll go out of CG. I've tried it a few different ways (removing the wing guns) and it still comes out the same.


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## Shortround6 (Oct 8, 2020)

Ivan1GFP said:


> Another thing I have always wondered about is how effective the carb intake was on the P-39 for optimum ram effect. It looks like it would be sitting in a low pressure area. On the P-40, it is sitting at the nose in a high pressure area.



The P-40 always seems to have a higher critical altitude with equivalent engines.


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## davparlr (Oct 8, 2020)

P-39 Expert said:


> Good analysis, thanks for posting. Please expand above for more comments.





> Please remember the Allison only had 1150hp. Uprated engine or auxiliary stage supercharger wasn't available until 1943. Had to keep it small to have any performance at all.



Yes, but better performing engines and better fuel was on the way. If there is no design capable of upgrading, it quickly becomes, not needed. However I do think the P-38 turbo was available, theoretically.



> This was huge. Best pilots in the world vs 100 guys fresh out of flight school. Hellcat (and even Lightning) were great planes but they never faced the Japanese first team.



Yes, I think the Japanese lost a lot of their hard to replace experienced airmen in the Guadalcanal and Solomon Sea battles facing these three American fighters and some Brit fighters. The young AAF pilots had to come up to speed quickly to live.



> 1942 P-39 data has always been biased. 750lbs lighter than the P-40E with the same engine and propeller it had to be faster and climb much better at all altitudes. Reduce the weight like the Russians did and it would climb with a Zero



Possibly below 10k as the P-39 was only about 300 ft/min less than the Zero but above 10k I don't think that much weight could be removed. At 15k the Zero could climb about 1200 ft/min faster.



> Another thing I have always wondered about is how effective the carb intake was on the P-39 for optimum ram effect. It looks like it would be sitting in a low pressure area. On the P-40, it is sitting at the nose in a high pressure area.



I think below the fuselage, like the P-51coolent intake, would be a better place in higher pressure air and less turbulence.


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## MiTasol (Oct 8, 2020)

P-39 Expert said:


> Please expand the above drawing. This drawing explains exactly what I have been saying. The engine bay is 90.25" long. It extends from the aft edge of the cabin assembly to the bulkhead (with the hole in it) just in front of the oil tank. The entire engine and aux stage supercharger including carburetor are contained in that engine bay. It does not extend past the oil tank bulkhead.
> 
> The engine bay is exactly the same length on the P-39 as it is on this P-63. The aux. stage would fit in the P-39 engine bay after the coolant tank had been moved up to the top front edge of the engine as it is in this diagram. The XP39-E did not have a lengthened engine bay (as was often stated in reference books), it had a lengthened tail cone aft of the engine bay.


The P-39 has a lot of structure between the keel beams as shown in the photo Wuzak posted.

The P-63 has a lot of fresh air and one single cross member in the same area


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## MiTasol (Oct 8, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> You are actually incorrect. While the engine on the P-39C/D/D-1/F was pretty comparable to that of the P-40E, the propeller was quite different.
> Those P-39 used a 10 feet 4 1/2 inch propeller with a 1.8:1 reduction
> ...



Gidday Ivan, naturally you are correct and the reasons are so blindingly obvious to anyone who thinks.

For beginners it is totally impossible to fit a cannon thru a P-40 propeller hub because the pitch change motor is front and centre on the prop.

The P-40 blades are alloy. Some P-39 blades were alloy but many were hollow steel, another difference.








A further, very minor, factor is that the hub diameter on the P-39 props, both CE and AP, is far larger than the P-40 hub, as shown in the above diagrams, in order to accommodate the cannon down the shaft. This means the blades are a smaller percentage of the propeller diameter and the transition from circular profile to aerofoil is further from the prop centreline.

Being a smaller diameter that further reduces the percentage of the blade available to create thrust.

Can we call this another myth busted?

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## MiTasol (Oct 9, 2020)

P-39 Expert said:


> *Please expand the above drawing. * This drawing explains exactly what I have been saying. The engine bay is 90.25" long. It extends from the aft edge of the cabin assembly to the bulkhead (with the hole in it) just in front of the oil tank. The entire engine and aux stage supercharger including carburetor are contained in that engine bay. It does not extend past the oil tank bulkhead.
> 
> The engine bay is exactly the same length on the P-39 as it is on this P-63. The aux. stage would fit in the P-39 engine bay after the coolant tank had been moved up to the top front edge of the engine as it is in this diagram. The XP39-E did not have a lengthened engine bay (as was often stated in reference books), it had a lengthened tail cone aft of the engine bay.



The P-39 has a lot of structure to support the coolant tank and provide rigidity between the keel beams as shown in the photo Wuzak posted. In particular that bulkhead with the flanged lightening hole (visible behind the coolant tank support) between the two keel units adds a massive amount of rigidity to the structure as does that curved plate connecting both keel units.




The P-63 has a lot of fresh air and one single cross member in the same area in the forward fuselage and significantly less structure in the rear fuselage than the P-39 where the two fuselage halves join.

Front fuselage




Looking at this diagram below we again see that there is no bulkhead between the front and rear fuselage as you can see clear through into the forward fuselage. You will note that the oil return line (yellow) is totally hidden behind the metal part of the rear fuselage bulkhead (the edge being just to the right of the orange line. Have you ever wondered why they hid that pipe there when it would be so much more accessible for maintenance if it was inside the area that you say holds nothing but glider fuel. Now ask yourself why do they need to keep that area totally free of everything except glider fuel? Now tell my what your answer is.
Mine is the ASB partially occupies that area.






P-39 Expert said:


> Please expand the above drawing. This drawing explains exactly what I have been saying. The engine bay is 90.25" long. It extends from the aft edge of the cabin assembly to the bulkhead (with the hole in it) just in front of the oil tank. The entire engine and aux stage supercharger including carburetor are contained in that engine bay. * It does not extend past the oil tank bulkhead.*
> 
> The engine bay is exactly the same length on the P-39 as it is on this P-63. The aux. stage would fit in the P-39 engine bay after the coolant tank had been moved up to the top front edge of the engine as it is in this diagram. The XP39-E did not have a lengthened engine bay (as was often stated in reference books), it had a lengthened tail cone aft of the engine bay.



Maybe it is time to go back to the basics that any airframe driver (pilot) and spanner wrencher (aircraft maintenance technician) learns about day one. Everything contained *within the single area* bounded by the cowlings and aircraft structure/skin is the engine bay or engine compartment. On the P-63 that includes everything from the firewall behind the pilot on the P-39/63 to the next full bulkhead. On the P-39 that is the bulkhead that the oil tank protrudes through. On the P-63 that is the bulkhead behind the oil tank. So you are right - it only extends as far as the oil tank bulkhead at station 253. 
You will be pleased to know both aircraft are very questionable on these limits because there is no effective firewall at the back of the engine bay so one could also be technically accurate claiming the whole of the rear fuselage as engine bay. To say however that the engine bay ends at the fuselage joint line is a complete fallacy. The engine bay extends to the back of the oil tank.
To suggest that the designers went to all the trouble to move the tank as far back as they did, instead of just mounting it vertically behind the joint line bulkhead, for any reason except the engine installation needs that room for the back of the ASB and the associated plumbing, wiring and controls is equally fallacious.


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## MiTasol (Oct 9, 2020)

FLYBOYJ said:


> The point is HOW MUCH do you move it and where and this becomes more critical if you're attempting to do this in the field. And again, are these W&B "variations" for specific aircraft or for an entire production run of a specific model or configuration?



There is actually some guidance on that in the P-39N-0 and N-1 manual. One of the primary differences, maybe the only primary difference, is which prop is fitted.

The manual includes a section on changing from the CE prop to the Aeroprop and that includes changing the gearbox armour plate. I do not know how much of that is because the Aeroprop has fittings that must pass through the armour and how much is for weight and balance but given the difference in prop weights I suspect both.


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## FLYBOYJ (Oct 9, 2020)

MiTasol said:


> There is actually some guidance on that in the P-39N-0 and N-1 manual. One of the primary differences, maybe the only primary difference, is which prop is fitted.
> 
> The manual includes a section on changing from the CE prop to the Aeroprop and that includes changing the gearbox armour plate. I do not know how much of that is because the Aeroprop has fittings that must pass through the armour and how much is for weight and balance but given the difference in prop weights I suspect both.



Manual? Flight or maintenance?


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## P-39 Expert (Oct 9, 2020)

FLYBOYJ said:


> They should be on blue prints, equipment lists or weight and balance charts (like the one shown for the P-39Q). This information varied in it's presentation between manufacturers.


N
I meant how do you get these pilot manuals?


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## FLYBOYJ (Oct 9, 2020)

P-39 Expert said:


> N
> I meant how do you get these pilot manuals?


Found them on line, I think one of them was on here in the manuals area


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## Elmas (Oct 9, 2020)

*JOCULAR MODE: ON*

Once that with Varignon's theorem, that states that the torque of a resultant of two concurrent forces about any point is equal to the algebraic sum of the torques of its components about the same point ( in other words, "If many concurrent forces are acting on a body, then the algebraic sum of torques of all the forces about a point in the plane of the forces is equal to the torque of their resultant about the same point), in brief



we have investigated the Moments of First Order, and so we have found the C.G of the “said” airplane.

Let’s now investigate the Moments of Second Order namely the Moment of Inertia, otherwise known as the mass moment of inertia, angular mass or rotational inertia.
That is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis: it depends on the body's masses and the square of the distance of each mass from the axis chosen, with larger moments requiring more torque to change the body's rate of rotation.

In brief:





All this stated, a very rich man, but a very queer character




orders his Chief Pilot




to take an airplane out of his fleet to bring his guest to his private Caribbean Island.





Chief Pilot Pussy Galore choses an B-737/800 and 198 passengers ( mostly blondes) and their luggage are brought to the Island.





While Mr Goldfinger and his guests have jolly good time, he orders his Chief Pilot to smuggle in a nearby Country some of his gold, and also orders that all the gold ingost are to be hidden in the fore and aft toilets (he tipped the Customs, so they won’t inspect there) and to fully load with gold the airplane. The volume of gold of the equivalent weight of the passengers is not that big, the gold can be stored in the toilets very easily.






Captain Galore is a very good Pilot (but she's not an aeronautical engineer…) so she divides the gold ingots between fore and aft toilets so that the C.G. (by Varignon’s Theorem!) is exactly as it should be.
Now:
The weight of the airplane is within limits allowed.
C.G. is at the proper place.
Question:
Pussy Galore, on the return trip with the airplane laden of gold ingots will notice some “slight” differences in the “behaviour” of her B-737/800 or she will notice anything different?”



*MODE JOCULAR: OFF*

P.S. not taking into consideration structural problems, of course: fuselage will likely split in two but even before the floor of the toilets won’t resist…

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## Ivan1GFP (Oct 9, 2020)

The Original


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## P-39 Expert (Oct 9, 2020)

FLYBOYJ said:


> Found them on line, I think one of them was on here in the manuals area


Where do you search onlne? Just asking, so I don't have to waste anymore of your time.


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## P-39 Expert (Oct 9, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> You are actually incorrect. While the engine on the P-39C/D/D-1/F was pretty comparable to that of the P-40E, the propeller was quite different.
> Those P-39 used a 10 feet 4 1/2 inch propeller with a 1.8:1 reduction
> ...


You are correct on the propeller.


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## P-39 Expert (Oct 9, 2020)

Shortround6 said:


> The P-40 always seems to have a higher critical altitude with equivalent engines.


How is that possible?


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## fubar57 (Oct 9, 2020)

They are here....Manual Index - American along with other countries here...Other Mechanical Systems Tech.

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## pinsog (Oct 9, 2020)

P-39 Expert said:


> How is that possible?


The air intake on a P40 was at the front of the plane and it benefited from ram at high speed. The air intake on a P39 was blocked by the canopy in a low pressure area so it didn’t get the benefit of ram air like the P40 did.


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## P-39 Expert (Oct 9, 2020)

fubar57 said:


> They are here....Manual Index - American along with other countries here...Other Mechanical Systems Tech.


Thanks.


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## GregP (Oct 9, 2020)

Thanks FlyboyJ.

As a retired electrical engineer, I have done a LOT of Excel, so doing weight and balances is right up my alley.

Cheers.

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## P-39 Expert (Oct 9, 2020)

davparlr said:


> Yes, but better performing engines and better fuel was on the way. If there is no design capable of upgrading, it quickly becomes, not needed. However I do think the P-38 turbo was available, theoretically.
> 
> *Right, the -85 engine with a greater critical altitude would be available in Nov 1942 for the P-39N, big performance increase. *
> 
> ...



Expand above.


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## P-39 Expert (Oct 9, 2020)

MiTasol said:


> The P-39 has a lot of structure to support the coolant tank and provide rigidity between the keel beams as shown in the photo Wuzak posted. In particular that bulkhead with the flanged lightening hole (visible behind the coolant tank support) between the two keel units adds a massive amount of rigidity to the structure as does that curved plate connecting both keel units.
> View attachment 597569
> 
> The P-63 has a lot of fresh air and one single cross member in the same area in the forward fuselage and significantly less structure in the rear fuselage than the P-39 where the two fuselage halves join.
> ...



Please expand above.


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## Ivan1GFP (Oct 9, 2020)

Hello P-39 Expert,

There are lots of places online that people have posted aircraft manuals.
If you visit some of the flight simulator forums, especially those in which people get a bit argumentative over detail, you will often find that someone has linked to a manual or test report to try to back up their opinion.
I have also done pretty well lurking in some Russian language forums but of course most of the manuals there tend to be about Russian subjects though not always and not always about aircraft.
Scribd is another good place that has a few manuals and test reports but finding things is difficult and much is restricted unless you have a subscription which I do not.

- Ivan.

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## P-39 Expert (Oct 9, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> There are lots of places online that people have posted aircraft manuals.
> If you visit some of the flight simulator forums, especially those in which people get a bit argumentative over detail, you will often find that someone has linked to a manual or test report to try to back up their opinion.
> ...


Thanks.


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## FLYBOYJ (Oct 9, 2020)

P-39 Expert said:


> Where do you search onlne? Just asking, so I don't have to waste anymore of your time.


No waste of time. I searched P-39 flight manual and it gave me a few different models.

https://airandspace.si.edu/webimages/collections/full/Pilot's flight manual for P-39 Airacobra.pdf

P-39 Airacobra Pilots Flight Operating Instructions

http://www.wwiiaircraftperformance.org/P-39/P-39Q-1_Operating_Instructions.pdf

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## Husky (Oct 9, 2020)

Ahhh, CG. Some aircraft with so limited CG range; mostly on the longitude axis, but as well the lateral axis. Can be a tough nut. My first thought; don't design an aircraft with such a limited CG range....leads to so much restrictions and growth. Unless that aircraft has a very quite specific purpose of operation and is intended to go no other.

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## Ivan1GFP (Oct 9, 2020)

Husky said:


> Ahhh, CG. Some aircraft with so limited CG range; mostly on the longitude axis, but as well the lateral axis. Can be a tough nut. My first thought; don't design an aircraft with such a limited CG range....leads to so much restrictions and growth. Unless that aircraft has a very quite specific purpose of operation and is intended to go no other.



Hello Husky,

I don't believe the problem was that the CoG range was particularly narrow.
23% - 31% MAC isn't that bad.
I believe there were two major problems. One was that very large disposable loads were very far from the longitudinal CoG.
The second problem was that the center of lift of the wing was too far forward in relation to the typical fixed loads in the aircraft which meant that although the aircraft could be brought within the allowable CoG range when fully loaded, it would get too close or even past the aft CoG limit when loads were expended.

- Ivan.


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## P-39 Expert (Oct 9, 2020)

You guys are working this CG thing to death. A few more days of this and the plane won't fly at all.

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## fubar57 (Oct 9, 2020)

Some people make certain claims that would unbalance things..................

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## FLYBOYJ (Oct 9, 2020)

Ivan1GFP said:


> Hello Husky,
> 
> I don't believe the problem was that the CoG range was particularly narrow.
> 23% - 31% MAC isn't that bad.
> ...


Hi Ivan - agree to a point but if you look at the loading charts most of the time it seems the aircraft was never forward than 28.8%, tail heavy through all operations, but I guess we're sought of saying the same thing.





P-39 Expert said:


> You guys are working this CG thing to death. A few more days of this and the plane won't fly at all.



*A few more days of this and maybe you'll learn something!*

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## ThomasP (Oct 9, 2020)

At the risk of further unbalance.

First, a video of a restored P-39 giving a good idea of the area/length taken up by the single-stage engine/supercharger:

""
at 29 & 40 sec

I ran across a reference to the engine fit for the P-63.

Apparently, the P-63 was originally intended to be powered by the Continental V-1430 engine (as was the P-39E). However, since the V-1430 did not become available, the Allison V-1710-93 was fitted instead.

Also, I ran a cross a reference that the P-39D-1 (as originally ordered by the British) was fitted with a different oil tank that was smaller, and was held vertically slightly further to the rear. This was in order to allow room for some sort of equipment in the lower-rear of the engine compartment (I do not know what equipment, but it may have been the obligatory 2x emergency landing flares). I can not guarantee the accuracy of this. I do not know if the P-400s were the same? Maybe someone can find an image of the P-39D-1/P-400 rear engine compartment, minus the engine but with additional equipment?

Then I looked at some photos of a production model P-63 being serviced and noticed these images of the auxiliary stage SC and engine compartment:












And then I looked around some more and found this image in a P-63 e&m manual:





The rectangular item with rounded corners in pics#2&3 is the protective cover for the auxiliary SC air intake.

I will leave you gentlemen to decide what, if anything, the above proves/disproves.

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## MiTasol (Oct 9, 2020)

P-39 Expert said:


> Where do you search onlne? Just asking, so I don't have to waste anymore of your time.



There are multiple sites that will sell you a download or a CD of P-39 and/or P-63 material.
I would avoid _Mach-1 manuals_ and _military-aircraft-photos_ and any other group that watermark their documents as the watermark often obscures the information you are looking for.





I can understand why they do that (the same reason I watermark all manuals I post to this site but the manuals I post are free and I want them to remain that way.

There are also outfits out there that will sell you a cd of aircraft blueprints and you will find that it only contains an index and a few blueprints - you then need to pay for several or many other CDs. I have no personal experience with these sites but a friend has just spent 90 pounds for what is advertised as a complete set of another types blueprints only to find that he must pay another 450 pounds to get the full set.

For a modest monthly fee WWII Era Military Blueprints & Manuals | AirCorps Library is good value though they do not have much on the P-63. They do have a set of P-39 blueprints and a selection of manuals that are a recent addition and so most drawings are only listed by part number. If you access a drawing that has no description please identify the content from the title box in the lower right hand corner. That makes it easier for you and others to search for the same thing later as you can then do a keyword search. For some drawings there are multiple pages and the title box is on the last page. They also have engine and prop manuals.

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## MiTasol (Oct 9, 2020)

ThomasP said:


> At the risk of further unbalance.
> 
> First, a video of a restored P-39 giving a good idea of the area/length taken up by the single-stage engine/supercharger:
> 
> ...




Excellent material, thank you Thomas.

I have to concede that it appears from those photos that the ASB is totally installed forward of the fuselage joint line *making P39 expert correct.* There only remains the question - why did Bell create all that waste space if not for the ASB. I shall continue looking and report further *if* I can solve that question. Maybe so the engine can be shifted rearwards during removal so that the stub shaft clears the roll over truss. Only a WAG as I know the P-39 engine can move rearwards, or be tilted, during removal.

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## ThomasP (Oct 9, 2020)

Hey MiTasol,

I was wondering if the excess length was for the Continental V-1430 engine installation. I do not have any good references for the arrangement/dimensions/weights for this engine as it was planned for the P-39E/P-63. If it was a significantly lighter installation I suspect the center of the engine's mass would have to be farther to the rear to maintain CG . . . maybe that is why? Just a WAG.


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## MiTasol (Oct 9, 2020)

That is certainly a reasonable assumption and may well be the total answer. I know someone on this forum wrote a book on that engine and that may complete the puzzle. Unfortunately that engine never did anything for me so I did not keep the author or book title in my tired old memory.


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## Tkdog (Oct 10, 2020)

buffnut453 said:


> Thanks for the responses, gents. I'm replying-to-all to save time and coalesce my response into a couple of key thoughts that apply to all.
> 
> There are 2 fundamental flaws in the proposed concept of US mechanical superiority. The first is that other countries had a similar proportion of working-age men engaged in agriculture compared to more technical industries (e.g. Shortround's comment about "many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort."). The second, and far more significant, is the creation of a false dichotomy where car ownership/awareness of the internal combustion engine is directly correlated with technical awareness/proficiency.
> 
> ...



I’m afraid that it is difficult for the average American to separate car ownership from their emotional makeup. We are a fragile people, especially these days.

but you are correct. The average GI of the time did not possess more technical knowledge that any of their colleagues across the developed world.

A friend of mine made chief on a LST in the pacific because he was the only enlisted guy who could read the electrical drawings. He says he happened to learn how from an eccentric high school teacher.

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## P-39 Expert (Oct 10, 2020)

MiTasol said:


> Excellent material, thank you Thomas.
> 
> I have to concede that it appears from those photos that the ASB is totally installed forward of the fuselage joint line *making P39 expert correct.* There only remains the question - why did Bell create all that waste space if not for the ASB. I shall continue looking and report further *if* I can solve that question. Maybe so the engine can be shifted rearwards during removal so that the stub shaft clears the roll over truss. Only a WAG as I know the P-39 engine can move rearwards, or be tilted, during removal.


I can't prove this but I believe that Bell designed the P-39 from the beginning to accommodate an ASB, as well as larger, heavier 4 blade propellers. Otherwise it's just an amazing coincidence that the engine bays were exactly the same size. All the manufacturers knew that Allison was developing engines with more horsepower, different supercharger gears, auxiliary stage superchargers, etc. The ASB had been in development since 1940.


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## buffnut453 (Oct 10, 2020)

Saw this news item today:

Luton Airport: Too many passengers at front of plane caused take-off issue

CofG issues can still bite, even in the modern era of air travel.

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## Ivan1GFP (Oct 10, 2020)

Excessively forward CoG can get you killed almost as easily.
That is how Wiley Post and his passenger the singing cowboy Will Rogers died.

- Ivan.

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## XBe02Drvr (Oct 10, 2020)

buffnut453 said:


> Saw this news item today:
> 
> Luton Airport: Too many passengers at front of plane caused take-off issue
> 
> CofG issues can still bite, even in the modern era of air travel.



That's exactly the sort of communications error that resulted in us flying BOS->BTV with 400 pounds of undocumented cargo in aft baggage and out of CG aft by nearly 3 inches. The captain and I were issued emergency revocations of our certificates on the spot by an FAA inspector, a new hire in training, who didn't know he lacked that authority. We got an unscheduled day off while the Feds got to the bottom of the issue and cooler heads prevailed.

PS: The captain and I both got an aircraft accident on our records, scotching any chance of a major airline career. Even though we were on the ground and parked, there were passengers present, one of whom scraped her elbow on the airstair door (injury) and a flight control surface (the tail skeg) was damaged, which by definition, elevated the damage from "minor" to "substantial".

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## pinsog (Oct 10, 2020)

ThomasP said:


> Hey MiTasol,
> 
> I was wondering if the excess length was for the Continental V-1430 engine inastallation. I do not have any good references for the arrangement/dimensions/weights for this engine as it was planned for the P-39E/P-63. If it was a significantly lighter installation I suspect the center of the engine's mass would have to be farther to the rear to maintain CG . . . maybe that is why? Just a WAG.


The XP39 was shorter and was lengthened/stretched for the production P39. Perhaps that space is just a space that occurred when they stretched it?

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## buffnut453 (Oct 10, 2020)

P-39 Expert said:


> I can't prove this but I believe that Bell designed the P-39 from the beginning to accommodate an ASB, as well as larger, heavier 4 blade propellers. Otherwise it's just an amazing coincidence that the engine bays were exactly the same size. All the manufacturers knew that Allison was developing engines with more horsepower, different supercharger gears, auxiliary stage superchargers, etc. The ASB had been in development since 1940.



Unless Bell had a time machine or a crystal ball, there's no way that the P-39 could have been designed from the beginning to accommodate an ASB. 

XP-39-BE
Bell Model 11, one prototype _38–326_ first flown *6 April 1938*. Powered by an Allison V-1710-17 (E2) engine (1,150 hp/858 kW), the aircraft was fitted with a General Electric B-5 turbosupercharger, creating a two stage supercharging system similar to the P-38 (engine-mounted mechanical supercharger, remote exhaust-driven turbo-supercharger as a second stage for high-altitude). Provision was made for two .50 in (12.7 mm) machine guns in the forward fuselage and one 25 mm (.98 in) cannon but aircraft remained unarmed. Later converted to XP-39B.

XP-39B
One conversion first flown *25 November 1939*. Streamlined XP-39 based on NACA wind tunnel testing resulting in revised canopy and wheel door shape, oil cooler/ engine coolant radiator intakes moved from right fuselage to wing roots, *fuselage increased length (by 1 ft 1 in, to 29 ft 9 in) and decreased wingspan (by 1 ft 10 in, to 34 ft). *The turbosupercharger was removed, and the single-stage, single speed, supercharged Allison V-1710-37 (E5) engine (1,090 hp/813 kW) was left in place. The carburetor air intake was moved behind canopy, just above the carburetor.


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## tomo pauk (Oct 10, 2020)

buffnut453 said:


> ...
> 
> XP-39-BE
> Bell Model 11, one prototype _38–326_ first flown *6 April 1938*. Powered by an Allison V-1710-17 (E2) engine (1,150 hp/858 kW), the aircraft was fitted with a General Electric B-5 turbosupercharger, creating a two stage supercharging system similar to the P-38 (engine-mounted mechanical supercharger, remote exhaust-driven turbo-supercharger *as a second stage for high-altitude*).
> ...



(my bold)
Turbo-supercharger was the 1st stage, working whenever the engine was working (regardless the altitude).


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## P-39 Expert (Oct 10, 2020)

buffnut453 said:


> Unless Bell had a time machine or a crystal ball, there's no way that the P-39 could have been designed from the beginning to accommodate an ASB.
> 
> XP-39-BE
> Bell Model 11, one prototype _38–326_ first flown *6 April 1938*. Powered by an Allison V-1710-17 (E2) engine (1,150 hp/858 kW), the aircraft was fitted with a General Electric B-5 turbosupercharger, creating a two stage supercharging system similar to the P-38 (engine-mounted mechanical supercharger, remote exhaust-driven turbo-supercharger as a second stage for high-altitude). Provision was made for two .50 in (12.7 mm) machine guns in the forward fuselage and one 25 mm (.98 in) cannon but aircraft remained unarmed. Later converted to XP-39B.
> ...


First flight of the XP-39 was 6 April 1939.

Development work on the auxiliary stage dates from 1938.


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## wuzak (Oct 10, 2020)

P-39 Expert said:


> First flight of the XP-39 was 6 April 1939.
> 
> Development work on the auxiliary stage dates from 1938.



One wonders why Bell, having designed the XP-39 around the 2 stage Allison that did not exist during design work, would have bothered with the turbocharger installation?


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## P-39 Expert (Oct 10, 2020)

wuzak said:


> One wonders why Bell, having designed the XP-39 around the 2 stage Allison that did not exist during design work, would have bothered with the turbocharger installation?


Turbo specified by the AAF.

Wasn't designed around the aux. stage, just allowed for.


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## Shortround6 (Oct 10, 2020)

P-39 Expert said:


> Wasn't designed around the aux. stage, just allowed for.




Allowed for how?

In 1938-40 Allison didn't know how big the aux stage should be and they sure hadn't decided on how to drive it. 

About all Allison could tell Bell (or any other company was that they were thinking about/developing a two stage system. 
They didn't make any components even for a ground test rig until 1940. 

The aircraft companies needed to know more than just the length of the engine, they needed to know how wide and tall the aux supercharger was going to be, how much it weighed, 
They needed to know the cooling requirements of the engine, both water/glycol and oil, which are different and larger than a single stage engine. 

How much "preliminary" information was put out I don't know but it seems to be a very large stretch that Bell both allowed room for the two stage engine and then never tried to put one into the P-39 when the two stage engine did become available (in 1942)


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## MiTasol (Oct 10, 2020)

First flight dates are totally immaterial to when design of the ASB was commenced and at that stage the length of the ASB would be only guesswork as there were multiple models and configurations of ASB built so early on it would purely be guesswork on the length of a engine with ASB.

Look at http://www.enginehistory.org/Piston/Allison/AllisonImages/V-1710-G(02).jpg and Google Image Result for http://www.enginehistory.org/Piston/Allison/AllisonImages/V-1710-F32.jpg and




for just three of the many other versions.

The first significant date was the date the design started and the second was the date the first metal was cut. After that you are in modification (next model) territory.


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## P-39 Expert (Oct 10, 2020)

Shortround6 said:


> Allowed for how?
> 
> In 1938-40 Allison didn't know how big the aux stage should be and they sure hadn't decided on how to drive it.
> 
> ...


They put one in the XP-39E and flew it in April 1942. Unfortunately they also put a new wing and tail on it and in their own inimitable AAF style they made it weigh 8900lbs. It was decently fast up to 25000', but would barely outclimb a regular P-39D. It never got the four blade propeller it needed.

If they had just put that aux. stage into a regular P-39D it would have only weighed 7900lbs including 4 blade propeller. At 1000lbs less than the E it would have been a rocket.


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## fubar57 (Oct 10, 2020)

But their engineers were stupid?


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## Shortround6 (Oct 10, 2020)

fubar57 said:


> But their engineers were stupid?



Must have been,
After building 3 P-39Es they still forgot about the secret drawer where the two stage Allison fits into the P-39D plans/drawings were kept (or they spilled coffee on them) and they went and designed the P-63.


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## fubar57 (Oct 10, 2020)

If only they were as SMRT as forum members


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## P-39 Expert (Oct 10, 2020)

fubar57 said:


> But their engineers were stupid?


No, the AAF just insisted on six .50calMGs AND a 37mm cannon, a much larger wing etc. until they got it up to 8900lbs.

Just put the damn thing into a regular P-39.


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## wuzak (Oct 10, 2020)

P-39 Expert said:


> Turbo specified by the AAF.
> 
> Wasn't designed around the aux. stage, just allowed for.



Bell designed the XP-39 around the turbo the USAAC specified, but allowed for an auxiliary stage version of the engine that the USAAC did not want nor specify as a possibility, that was barely an inkling of an idea at Allison who, btw, were not very quick with their development at that stage?


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## Shortround6 (Oct 10, 2020)

No, the six .50 cal guns were Larry Bell's idea when he realized the P-38E was never going to be an interceptor. He was trying to pitch it as a ground attack plane.


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## wuzak (Oct 10, 2020)

P-39 Expert said:


> No, the AAF just insisted on six .50calMGs AND a 37mm cannon, a much larger wing etc. until they got it up to 8900lbs.
> 
> Just put the damn thing into a regular P-39.






> The XP-39E bore the same armament as the P-39D but featured a new wing with square-cut tips.



Bell XP-39E Airacobra.




> The P-39D differed from the P-39C primarily in having a heavier armament. It had four wing-mounted 0.30-inch machine guns with 1000 rpg, two fuselage-mounted 0.50-inch machine guns with 200 rounds per gun, plus the 37-mm cannon (with increased ammunition capacity of 30 rounds).


Bell P-39D Airacobra


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## Shortround6 (Oct 10, 2020)

What is more than a bit strange about this saga of the P-39 holding the two stage engine is that the original XP-39 had a lot trouble with the intercooler (proper airflow for cooling).

Allison was planning on using an intercooler with the two stage engine, Perhaps Bell was too for the P-76 and P-63, but the subcontractor never delivered a suitable intercooler matrix forcing Bell to use large amount of water injection for the two stage engine. Did simplify the air scoop problem though. 

Without a good intercooler high altitude performance is going to crap or short lived until the ADD fluid runs out.


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## Ivan1GFP (Oct 11, 2020)

P-39 Expert said:


> They put one in the XP-39E and flew it in April 1942. Unfortunately they also put a new wing and tail on it and in their own inimitable AAF style they made it weigh 8900lbs. It was decently fast up to 25000', but would barely outclimb a regular P-39D. It never got the four blade propeller it needed.
> 
> If they had just put that aux. stage into a regular P-39D it would have only weighed 7900lbs including 4 blade propeller. At 1000lbs less than the E it would have been a rocket.



Hello P-39 Expert,

ASSUMING that the Aux Stage Supercharger actually fit into the engine compartment, there are still a bunch of problems that need to be addressed.

First of all, regarding "it would have been a rocket", the benefit of the second stage is mostly increased altitude performance.
Low level performance would not have changed much especially with the increased weight.
The increased altitude capability also brings a greater requirement for cooling capacity which was somewhat lacking even with the engines that were already installed in the P-39.
The new ASB also sits at the aft end of the engine and would make a aft CoG problem even worse. Perhaps this could be counterbalanced by a significantly heavier 4 blade propeller, but would any steps be taken to bring the CoG in empty condition further forward to address handling problems?
The new P-39 Rocket would still have a relatively low internal fuel capacity. What mission would it be suited for?

- Ivan.


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## ThomasP (Oct 11, 2020)

Hey Ivan1GFP,

Fuel problem solved:






P-39 with a 350 USgal LRFT.


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## MiTasol (Oct 11, 2020)

With that fin area it will fly VERY straight after the tank is dropped.


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## XBe02Drvr (Oct 11, 2020)

ThomasP said:


> Hey Ivan1GFP,
> 
> Fuel problem solved:
> View attachment 597820
> ...


Where's that midwife? Contractions have started already!

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## P-39 Expert (Oct 11, 2020)

Shortround6 said:


> No, the six .50 cal guns were Larry Bell's idea when he realized the P-38E was never going to be an interceptor. He was trying to pitch it as a ground attack plane.


They were in the wooden mockups.


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## P-39 Expert (Oct 11, 2020)

Shortround6 said:


> What is more than a bit strange about this saga of the P-39 holding the two stage engine is that the original XP-39 had a lot trouble with the intercooler (proper airflow for cooling).
> 
> Allison was planning on using an intercooler with the two stage engine, Perhaps Bell was too for the P-76 and P-63, but the subcontractor never delivered a suitable intercooler matrix forcing Bell to use large amount of water injection for the two stage engine. Did simplify the air scoop problem though.
> 
> Without a good intercooler high altitude performance is going to crap or short lived until the ADD fluid runs out.


They did plan on using an intercooler but eventually gave up on it. Should have discarded it earlier and moved the carburetor forward to the normal position on the engine stage supercharger for the additional critical altitude. Intercooler/water injection only needed for WEP. At military power the extra 400hp at 25000' would have been plenty.


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## Shortround6 (Oct 11, 2020)

P-39 Expert said:


> They were in the wooden mockups.


got pictures?

They made a mock up of the Spitifre withe six 20mm cannon too, that didn't get far. 

No photo of the actual P-39E shows any wing guns or even cowl guns.


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## P-39 Expert (Oct 11, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> ASSUMING that the Aux Stage Supercharger actually fit into the engine compartment, there are still a bunch of problems that need to be addressed. *Apparently it did fit.*
> 
> ...


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## P-39 Expert (Oct 11, 2020)

Shortround6 said:


> got pictures?
> 
> They made a mock up of the Spitifre withe six 20mm cannon too, that didn't get far.
> 
> No photo of the actual P-39E shows any wing guns or even cowl guns.


Photos in "Cobra" by Birch Matthews.

Performance test in Mike Williams' site for XP-39E said it had two .50s in each wing. Maybe just ballast instead?


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## P-39 Expert (Oct 11, 2020)

ThomasP said:


> Hey Ivan1GFP,
> 
> Fuel problem solved:
> View attachment 597820
> ...


AAF wanted it to fly nonstop from San Francisco to Hawaii. Thank goodness they gave up on that.

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## Ivan1GFP (Oct 11, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *Only at military power, then only for the max 15 minutes. Tolerated just like on regular P-39s.*



The problem here is that with the ASB and operating at higher altitudes, it ISN'T like on regular P-39s.
The power delivered to the propeller isn't the determining factor for cooling requirements. The extra power required by the ASB also requires extra cooling. The higher altitude and lower air density decreases the effectiveness of radiators as well.



P-39 Expert said:


> *Remember the aux. stage took the space that the coolant tank had occupied, so the small increase in weight in the rear would have been offset by the heavier 4 blade propeller. Balance maintained.*



I would be very interested in seeing how much this "small increase" in weight actually affects that balance.
As was mentioned earlier, the P-39 had a tendency to be very near its aft CoG limit even without any changes.
To correct the handling problems, there needs to be more than just maintaining balance and I am not convinced that a propeller change would do it.



P-39 Expert said:


> *Remove the .30s in the wing and put in fuel tanks.*



There are a couple problems with this idea.
First of all, the outboard sections of the wings where the guns are located are a rather small and flat volume.
Second, without the wing guns, the firepower becomes somewhat inadequate by US if not Soviet standards.

- Ivan.

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## P-39 Expert (Oct 11, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...



Please expand above.


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## fubar57 (Oct 11, 2020)

Going into a fatal spin when nose ammo was expended wasn't a real CG problem?

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## FLYBOYJ (Oct 11, 2020)

ARMY AIR FORCES
MATERIEL COMMAND
Wright Field, Dayton, Ohio
_28 July 1944_
MEMORANDUM REPORT ON
P-39Q Airplane, AAF No. 44-3455


Subject: Report of Spin Tests
Section: Flight
Serial No: ENG-47-1779-A

*Conclusions*
*1. The P-39 should not be spun intentionally under any circumstances.
2. The P-39 should not be snap rolled as the roll usually ends in a spin.
3. The best spin recovery is to simultaneously apply opposite rudder and neutralize the stick.
4. Power should be cut immediately if a power on spin is entered.
5. Care must be excercised during the recovery to prevent an accelerated stall and re-enty into the spin.
6. The wing tip spin chute does not aid recovery of the P-39Q from a flat spin.*

P-39 Performance Tests

*Any aircraft that naturally sits at the most aft end of it's CG envelope will inherently have potential spin issues despite being "within balance" or not! *

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## FLYBOYJ (Oct 11, 2020)

*"As the CG moves aft, a less stable condition occurs, which decreases the ability of the aircraft to right itself after maneuvering or turbulence."*

Weight and balance 101 for those who don't know or understand (or refuse to understand) aircraft weight and balance!

_Balance, Stability, and Center of Gravity – Effects of Adverse Balance_

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## FLYBOYJ (Oct 11, 2020)

Greg's most excellent Weight and Balance calculator.

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## fubar57 (Oct 11, 2020)

For those of us who don't run Excel

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## Shortround6 (Oct 11, 2020)

"The problem here is that with the ASB and operating at higher altitudes, it ISN'T like on regular P-39s.
The power delivered to the propeller isn't the determining factor for cooling requirements. The extra power required by the ASB also requires extra cooling. The higher altitude and lower air density decreases the effectiveness of radiators as well.

*Don't know for sure until you try it."*

Actually you have pretty good idea. That is one reason you have engineers. And ground tests. They KNEW how much power was needed to run a supercharger at a given rpm and airflow. They often used electric motors for such testing and could measure the current flow. Aircraft engines were often "turned over" by electric motors to measure friction from various components. They knew how much extra friction/drag stronger valve springs would cause. You think they were just going to bolt a more powerful engine into an airframe with existing radiators and oil coolers and fly it to see what would happen? Any taxi tests or flight testing was to confirm calculations and ground tests. Maybe they would hope things were more favorable but just hoping the existing cooling systems would handle around a 12% increase in cooling load seems like pretty poor planning. Most test reports of the P-39 mention over the limit cooling temperatures as it was. Over the limit does not mean overheating at that particular point. 
Now consider that any standard text book was going to tell you that the air at 22,000ft was about 75-76% of the mass (density) of the air at 14,000ft and you can see the cooling problem before you even leave the ground (or indeed, when the plane is still on paper). and no, the cooler air temperature at 22,000ft is not going to make up the difference (s bit of it but certainly not all). 

This book (or something like it) 
Fraas. AIRCRAFT POWER PLANTS. 1st ed, 1943. | eBay

can provide a lot of knowledge about aircraft engines in general and what was known at the time (and not classified as secret) Like many things on Ebay, prices are all over the place. 

Not my copy


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## Ivan1GFP (Oct 11, 2020)

Hello P-39 Expert,

It seems like most of these points have already been addressed by other forum members but here goes anyway.



P-39 Expert said:


> *Don't know for sure until you try it.*



Even with existing engines, the P-39 had a serious tendency to overheat on the ground. It also tended to exceed temperature limits in high power operation such as sustained climbs. Putting in a more powerful engine and running at higher altitude makes the problem worse. There is a reason why modern operators of P-39s tend to have spray bars installed to cool the radiators.



P-39 Expert said:


> *Stop trying to invent CG problems. P-39 didn't have any real CG problems. Not like a P-51 with a full fuselage tank. *



The P-51 85 Gallon Fuselage tank certainly created a CoG problem for the aircraft that did not exist before.
To state that, "*P-39 didn't have any real CG problems." *means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation.



P-39 Expert said:


> *All that was needed was 30 extra gallons, 15 in each wing. The two outside tanks on the P-39 held over 8 gallons each. You couldn't fit the equivalent two more of those in each outer wing? *



Let's say it is possible to add another 30 Gallons in fuel cells to the outer wing of the P-39 in place of the wing guns.
That would make a total of 150 Gallons.
Please note that the P-51 already had 184 Gallons of internal fuel BEFORE it was determined to be necessary to add a 85 Gallon fuselage tank that caused some CoG problems without drop tanks.
Note also that the P-51 could carry two drop tanks on the wings.
The P-39 could carry at most one drop tank on the centerline.
What makes you think this is sufficient fuel?



P-39 Expert said:


> *The plane had a 37mm cannon. It could not possibly be under armed.*



The 37 mm cannon certainly is a big hammer, but it has a ridiculously low firing rate, low ammunition capacity and a low duration of fire and of course has a pretty loopy trajectory because of its low muzzle velocity.
This is not an ideal weapon to track maneuvering targets. 12 seconds of fire isn't much at all.
There are many better ideas for motor cannon and neither of the guns that were normally installed in the P-39 qualify as such.
The remaining two synchronized .50 cals even as you pointed out really do not deliver a great weight of fire.

- Ivan.

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## FLYBOYJ (Oct 11, 2020)

Ivan1GFP said:


> To state that, "*P-39 didn't have any real CG problems." *means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation.



Amen...

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## XBe02Drvr (Oct 12, 2020)

Ivan1GFP said:


> The P-51 85 Gallon Fuselage tank certainly created a CoG problem for the aircraft that did not exist before.
> To state that, "*P-39 didn't have any real CG problems." *means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation





FLYBOYJ said:


> Amen...


(Underlines mine.)
Have any of you folks read Eric Hoffer's _The True Believer_? It was required reading in the '60s when I went to school, and laid out the blueprint for ideology over factuality as a motivating force, fulfilling a human need formerly served by religion, except expressed at an even more fanatical level, and without any of the benevolent inluences. Primarily concerned with the mass movements of its era: Fascism, Naziism, and Communism, but discerns behavior patterns still with us today.

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## GrauGeist (Oct 12, 2020)

If the 37mm cannon was all that great, they would have kept the M4 (T9) in the P-38, but they determined that the Hispano M2 and four .50 MGs were the better combination.

The P-39 may have been better served with the same M2, as it had a higher RoF and weighed less.


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## XBe02Drvr (Oct 12, 2020)

GrauGeist said:


> and weighed less.


Uh oh!


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## GrauGeist (Oct 12, 2020)

XBe02Drvr said:


> Uh oh!


I know, right?


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## XBe02Drvr (Oct 12, 2020)

If I had a P39 I'd name her "Rocky" and the nose art would depict a fat booty squirrel wearing a flying helmet with goggles!

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## Peter Gunn (Oct 12, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> *SNIP*
> 
> ...



Interesting point which got me reminiscing about my misspent youth. Had a '72 SS454 Chevelle which one of my dad's buddies (who was an engineer at GM) helped me 'retune' the engine to get a _few_ more ponies out of it.

Most cars from the 60's - 70's just drew carb air from under the hood, it wasn't until the mid to late 70's that (GM at least) ran the carb intake to the high pressure area behind the headlights for better performance.

Long story short, the SS had Cowl Induction at the base of the windshield with a rear facing vacuum operated door that popped open under heavy throttle and closed at idle. I asked my engineer friend about changing that to get better airflow.

"Kid, we put that there for a reason and not just to look cool".

Two things:

1). I know, car =/= airplane

2). I was stupid for selling it.

This is really apropos of nothing and I just wanted to write about my old Chevelle that I NEVER should have sold.

BUT! Ivan brings up a point I had never considered regarding the location of the carb intake on the P-39 vs P-40.

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## windhund116 (Oct 12, 2020)

Interesting computer sim of what looks like a P400 versus M6A5c Zero.

P400 versus M6A5c


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## XBe02Drvr (Oct 12, 2020)

Peter Gunn said:


> This is really apropos of nothing and I just wanted to write about my old Chevelle that I NEVER should have sold.
> 
> BUT! Ivan brings up a point I had never considered regarding the location of the carb intake on the P-39 vs P-40.


MODS: We need a rating icon for KOOWUL!! to fit in somewhere between LIKE and WINNER, especially for mildly off-topic sorties like this one.
ROCKERS: You're welcome too, as long as you play nice.
YOUNG 'UNS: Scratching your heads? Ask your elders. (or any Brit on this forum)

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## XBe02Drvr (Oct 12, 2020)

Peter Gunn said:


> Had a '72 SS454 Chevelle which one of my dad's buddies (who was an engineer at GM) helped me 'retune' the engine to get a _few_ more ponies out of it.


Me ahn my '63 SAAB 850 jes gonna haf ta teach yuh ahn yo mussel cahr a li'l respect aht on th' ice race course, come Febr'ary! Dunnit b'fo, duit agin!

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## SaparotRob (Oct 12, 2020)

XBe02Drvr said:


> Me ahn my '63 SAAB 850 jes gonna haf ta teach yuh ahn yo mussel cahr a li'l respect aht on th' ice race course, come Febr'ary! Dunnit b'fo, duit agin!


Ice is for mint juleps.

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## XBe02Drvr (Oct 12, 2020)

SaparotRob said:


> Ice is for mint juleps.


In February?? Funny you should mention them. There was a specialty tire retreader back in the day who used to do ice racing tires with walnut shell fragments embedded in the tread, a super soft compound, green sidewalls, and trademarked "Mint Juleps". Affordable, and tough to beat on the ice!


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## GregP (Oct 12, 2020)

Hey Peter Gunn

Maybe we could fix the P-39 with some Chevrolet "SS" letters along the lower nose in front of the door? And might as well install a Hurst "pistol-Grip" shifter handle on the control stick, too, along with a push-button radio.

I had a Burgundy 1970 Chevelle SS 454 LS-7 with rock crusher 4-speed and have been weeping about it for 50 years. I've heard people say they had an LS-7, but they always miss when I ask them about the axle ratio. It only came with ONE axle ratio in 1970, and that was a 4.11 . My ex-wife wrapped it around a Police car when she ran a stop sign. Nobody was killed, but the car was a total loss.

At least my 2019 Ford Mustang GT PP1 6-Speed with more horsepower than the Chevelle (not as much torque, though) helps a bit.








It's actually quicker than the old Chevelle and very definitely handles better, but I loved that old Chevelle and the cowl induction. The Mustang is unrelated to the P-39, but likely has a better drag coefficient at sea level!

Reminds me of my favorite kitplane. Take a garden-variety Vans RV-4 kitplane as below:






Remove the 4-cylinder 160 hp and add a six-cylinder 285 hp Lycoming and chop off one wing bay from each side to get a fire-breathing Harmon Rocket:






Outclimbs a stock P-51 handily, at least in the lower altitudes. Just shy of 4,000 fpm (3,950)!

Cheers!

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## XBe02Drvr (Oct 12, 2020)

GregP said:


> Hey Peter Gunn
> 
> Maybe we could fix the P-39 with some Chevrolet "SS" letters along the lower nose in front of the door? And might as well install a Hurst "pistol-Grip" shifter handle on the control stick, too, along with a push-button radio.
> 
> ...


Betcha it ain't tail heavy, neither!

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## XBe02Drvr (Oct 12, 2020)

Damn duplicate post! How do you COMPLETELY delete one of these??

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## P-39 Expert (Oct 12, 2020)

windhund116 said:


> Interesting computer sim of what looks like a P400 versus M6A5c Zero.
> 
> P400 versus M6A5c


That was a P-63.

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## P-39 Expert (Oct 12, 2020)

GrauGeist said:


> If the 37mm cannon was all that great, they would have kept the M4 (T9) in the P-38, but they determined that the Hispano M2 and four .50 MGs were the better combination.
> 
> The P-39 may have been better served with the same M4, as it had a higher RoF and weighed less.


You may be right. 37mm was still very effective though.


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## GrauGeist (Oct 12, 2020)

windhund116 said:


> Interesting computer sim of what looks like a P400 versus M6A5c Zero.
> 
> P400 versus M6A5c


I assume they meant *A6M5c* - and why on earth would they be trying to dogfight with a "Special Attack" variant of the Zero?

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## P-39 Expert (Oct 12, 2020)

FLYBOYJ said:


> ARMY AIR FORCES
> MATERIEL COMMAND
> Wright Field, Dayton, Ohio
> _28 July 1944_
> ...


That was the P-39Q with the underwing .50calMG pods, made the plane a little more unstable.

As you know, spins were prohibited in the pilot's manual on all AAF and USN fighters.


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## P-39 Expert (Oct 12, 2020)

fubar57 said:


> Going into a fatal spin when nose ammo was expended wasn't a real CG problem?


Actually you are referring to the "Tumble" where the P-39 supposedly could tumble end over end when the nose ammo was expended.

You guys make it sound like immediately after the nose ammo was expended the plane crashed. I know most of you are just pulling my chain, but honestly? Even with all the nose ammo expended the P-39 would execute any normal fighter maneuver easily with no trouble. Rolls, turns, climbs, dives, loops, approach and landing, whatever. Only when purposely attempting to stall the plane at the top of a loop could the tumble be induced, and then not on a consistent basis. Tumbling a P-39 was easy to avoid. Chuck Yeager couldn't make it tumble and stated that it wouldn't tumble. 

How many P-39s were lost to this supposed tumble? Anyone know? 

How many P-38s were lost diving from altitude? Or lost an engine on takeoff? Either engine, since both turned the wrong way. How many P-40s crashed on takeoff or landing, especially in a crosswind? How many P-47s crashed on takeoff with the ubiquitous drop tanks from their long takeoff run? Or had to use WEP just to take off? How many P-51s were lost in a tight turn with a full fuselage tank? I know that was alleviated by only partially filling the fuselage tank, but why have a fuel tank if it can't be filled to capacity? How many Wildcats crashed on takeoff or landing at land bases with that narrow, soft landing gear? How many Corsairs crashed on carrier landings due to a severe wing drop during a stall? Corsair couldn't even get carrier qualified until late in the war.

No AAF or USN fighter was without it's faults.


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## GrauGeist (Oct 12, 2020)

From Bill Overstreet's biography:


> Bill was in combat training in June 28th, 1943 when he had his first crash, at the controls of an Bell P-39 Airacobra, which went into a dreaded flat spin, a condition uniquely devastating for the model and which claimed many a pilot’s life. Bill and his squadron-mates were practicing aerobatic maneuvers when his plane strated tumbling and he couldn’t control it. Bill went to release the Airacobra’s doors but the air pressure prevented them from opening. He finally managed to get a knee against one door with his shoulder against the other, trying to overcome the pressure, and the moment he got out, he pulled the ripcord on his parachute. The moment the chute snapped open Bill found himself standing amidst the wreckage of his plane right by the propeller. He was so close to the ground when he escaped his doomed plane that none of his flight-mates even saw his chute deploy, Bill belives he was perhaps the first pilot to survive the crash of a tumbling P-39, and he made a point on tracking down the man who packed his chute to personally thank him for a job well done.


Overstreet was best known for his piloting skills and flying his P-51C (that had custom white-wall tires) with the 357th FS in the ETO.

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## DerAdlerIstGelandet (Oct 12, 2020)

“ Only when purposely attempting to stall the plane at the top of a loop could the tumble be induced”

So all those pilots who entered a stall and discovered the problem were trying to stall the P-39?

I get loving an aircraft, but damn...

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## XBe02Drvr (Oct 12, 2020)

P-39 Expert said:


> Actually you are referring to the "Tumble" where the P-39 supposedly could tumble end over end when the nose ammo was expended.


As has been established here upthread, the "tumble" is essentially a Lomcevak, which the acrobatic world has accumulated plenty of experience with since Airacobra days. Given a CG in the "approved for acrobatics" range, which is usually midrange and slightly forward of midrange of the "normal" CG range, a Lomcevak normally devolves into a typical upright, nose low, garden variety, incipient spin. Now take that same aircraft, load it to its "normal" aft CG limit, and your Lomcevak will occur with a lot more "snap" to it and can easily terminate in a high rate, upright or inverted* flat spin. The P39, with its symmetrical airfoil, can be expected to stall negative or positive with equal ease during the wild fluctuations of the tumble, and lacks the polar moment of forward mounted engine mass to "steer" it in the right direction and unblank the horizontal tail. The ultimate version of "going ballistic"!

*"upright" or "inverted" in this context doesn't refer to the aircraft's attitude relative to earth, but to whether the wing is stalled positive or negative.

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## DerAdlerIstGelandet (Oct 12, 2020)

Besides, Bell was not able to recreate the spin, tumble, whatever you want to call it, because they were flying it with full simulated ammo load for weight. Once they removed that weight and the aircrafts CG shifted aft they were able to recreate it.

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## GregP (Oct 12, 2020)

Hey P-39 Expert, the "tumble" was NOT at the top of a loop when purposely stalled. It was when past rearward CG and inadvertently-stalled with power-on.

Below is a P-63 crash at Biggin Hill. The pilot is flying a perfectly good P-63, but is flying it at low cruise power. He then tries to do a loop which, in any WWII fighter, has a basic speed range that should be used. The pilot here is at lower-than-recommended speed, MUCH lower-than-recommended power, and simply runs out of airspeed and power when he gets vertical. The rest is poor recovery technique - though he DID avoid a spin, at least initially - and then he stalls it a second time during the pull-out with insufficient altitude to recover.



This was a very preventable accident. Don't fly aerobatics if you are afraid to use the engine as required for the maneuver. The P-63 has plenty of power for aerobatics, but trying a loop at a low-cruise hp setting is just not going to work very well. There is a reason the POH has the entry speeds that are published in it.


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## Ivan1GFP (Oct 12, 2020)

Attached is a description of how to initiate a "safe" tumble in the Airacobra.
Imagine what happens if you do not take the precautions this fellow did BEFORE initiating a tumble.
I believe the same pilot was pretty accomplished with aerobatic flying in the Airacobra and had a few observations.
First of all, before flying aerobatics, fly straight and level and give it a sudden pull on the stick.
Observe the reaction.
If the aircraft immediately pitches down and oscillates slightly and returns to level flight it is safe to fly any maneuver.
If the aircraft pauses before pitching down slowly and does not return immediately to level flight, it is NOT safe to fly aerobatics.

- Ivan.

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## XBe02Drvr (Oct 12, 2020)

Ivan1GFP said:


> First of all, before flying aerobatics, fly straight and level and give it a sudden pull on the stick.
> Observe the reaction.
> If the aircraft immediately pitches down and oscillates slightly and returns to level flight it is safe to fly any maneuver.
> If the aircraft pauses before pitching down slowly and does not return immediately to level flight, it is NOT safe to fly aerobatics.


Best lifesaver I've seen all day!


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## FLYBOYJ (Oct 12, 2020)

P-39 Expert said:


> That was the P-39Q with the underwing .50calMG pods, made the plane a little more unstable.
> 
> As you know, spins were prohibited in the pilot's manual on all AAF and USN fighters.



They were - the point here is you either don't understand or continue to ignore the fact that because the P-39 operated on the most aft portion of it's CG envelope, it had handling misgivings despite being in "balance" (as you say).

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## fubar57 (Oct 12, 2020)

From Crowood Aviation, "Bell P-39 Airacobra" -Dorr & Scutts: "In Russia: Russian pilots often had opportunities to engage the Messerschmidt Bf 109 at low altitude, where the American built fighter performed best. The '_cobrastochka' _('dear little Cobra') clearly performed better in Russian hands than American. Lt. Col. Alexander I. Pokryshkin became the Allie's second-ranking ace of the war with fifty-nine aerial victories, forty-eight of them accomplished with his Airacobra. Eight other Soviet P-39 pilots are reported to have claimed twenty or more aerial victories. Pokryshkin assessed the Bell fighter much like many others: "_It was a shapely aircraft. One thing I particularly liked about the Airacobra was the armament. That was really something to shoot the enemy down with - a hard-hitting 37mm cannon, two fast-firing heavy machine guns, and four normal caliber machine guns. I wasn't put off when other pilots warned me that the Cobra was *dangerously prone to spinning because of a C of G located well aft*" (my bold from now on) ....._American ambassador W. Averell Harriman was quoted by Soviet foreign minister Vladimir Molotov on the significance of the P-39: _"There is one type of aircraft, specifically the Airacobra, which is used very well by the Soviet Air Force. Harriman says the Russians use this aircraft even better than the Americans. Therefore it would be a benefit for Vandenberg (Maj. General Hoyt S. Vandenburg, Twelve Air Force commander and future US chief of staff) to become acquainted with the experience of Soviet pilots...Vandenberg would like to be informed about this and visit Soviet squadrons composed of Airacobra pilots." _Molotov blessed the proposed meeting as 'useful' Bell Aircraft expressed a similar request. Gen. Vandenberg and company representatives visited the 6th ZAB (Zapasnaya Aviabrigada, or Reserve Air Brigade) in Ivanovo and two other units. The Soviet pilots had some requests - for example, they wanted* improvement in the ballistics and rate of fire of the 37mm cannon*. The Russians asserted that the late-model P-39Qs *were much less stable *than earlier Airacobras, and that the armoured headrest introduced on this model impaired rearward visibility. Bell representatives said they would take these complaints into account, although it is not clear what they might have done about them. The visit of the American delegation to the 6th ZAB was marred by the crash of a P-39Q-5 when the pilot became disoriented after *recovering from a spin and had to bail out. Sure enough, the spin had been induced by too far aft center of gravity. *If anything, the Russians became more obsessed with the downside of Airacobra's flying characteristics than the Americans. A number of evaluation programmes were undertaken including these: spinning and aerobatic tests of P-39Q-10-BE (43-2467), which showed that the Q model *spun more powerfully and irregulaly than earlier P-39 variants*....spinning and aerobatic tests of a P-39Q-15-BE (44-29115) with *altered centre of gravity *and reinforced tail unit and rear fuselage. The tests apparently raised no problem which justified this much effort and expense; however, there are indications that some Russians continued to have problems with the *C. G. situation*"

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## FLYBOYJ (Oct 12, 2020)

P-39 Expert said:


> You guys make it sound like immediately after the nose ammo was expended the plane crashed.


Not at all! Just pointing out the potential for an inexperienced or negligent pilot!



P-39 Expert said:


> How many P-38s were lost diving from altitude? Or lost an engine on takeoff? Either engine, since both turned the wrong way.


Many from dives, agree! Now your comment "Either engine, since both turned the wrong way" makes totally no sense! Do you know what a critical engine is? Do you know why there were many engine out facilities on the P-38? It definitely wasn't from "Either engine, since both turned the wrong way."



P-39 Expert said:


> No AAF or USN fighter was without it's faults.



Agree - to include the P-39


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## P-39 Expert (Oct 12, 2020)

FLYBOYJ said:


> They were - the point here is you either don't understand or continue to ignore the fact that because the P-39 operated on the most aft portion of it's CG envelope, it had handling misgivings despite being in "balance" (as you say).


I completely understand the CG calculations. 

I just believe that your CG concerns for the P-39 are a little overboard. 

How many P-39s were lost to spinning/tumbling?


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## FLYBOYJ (Oct 12, 2020)

P-39 Expert said:


> I just believe that your CG concerns for the P-39 are a little overboard.


Based on the data presented, show me where I'm "a little overboard." 

The P-39 got a reputation for tumbling a spinning, was all that a myth?

If you really understood "Weight and Balance" calculations, you would not have talked about moving equipment with out "doing the math." Have you ever weighed a real airplane? Have you ever flown a tail heavy airplane? There are some of us on here who have to include warbirds so if some of us are emphasizing something in our posts it's for a reason!


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## Ivan1GFP (Oct 12, 2020)

Hello fubar57,

That particular book is a great reference and is also where I got my tumble description from.
The authors are actually Dorr, not Dover and Scutts. Robert Dorr actually lives in our neighborhood and donates some of his books to the local public library. I have also met him at the local IPMS annual events a couple times.

I came across a report on Soviet Spin Tests of the P-39Q and was wondering why it was done when the P-39 type had been in service for so long. Now it makes sense if the P-39Q had particularly bad spin characteristics.

- Ivan.


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## fubar57 (Oct 12, 2020)

Thanks Ivan, corrected the name


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## P-39 Expert (Oct 12, 2020)

FLYBOYJ said:


> Based on the data presented, show me where I'm "a little overboard."
> 
> The P-39 got a reputation for tumbling a spinning, was all that a myth?


Depends on the actual facts. I don't know how many P-39s were lost to spinning or tumbling. Do you? I'm just asking.

P-40s got a reputation for being extremely hard to take off and land, especially in a crosswind. The P-40 had to be taken off and landed. The P-39 didn't have to be put in a situation where it would spin.


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## fubar57 (Oct 12, 2020)

?

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## FLYBOYJ (Oct 12, 2020)

P-39 Expert said:


> Depends on the actual facts. I don't know how many P-39s were lost to spinning or tumbling. Do you? I'm just asking.



I don't but there were enough lost for it to be given a reputation!




P-39 Expert said:


> P-40s got a reputation for being extremely hard to take off and land, especially in a crosswind. The P-40 had to be taken off and landed. *The P-39 didn't have to be put in a situation where it would spin*.


We're not talking about P-40s and you are correct. My earlier post was edited;

Have you ever weighed a real airplane? Have you ever flown a tail heavy airplane? There are some of us on here who have to include warbirds so if some of us are emphasizing something in our posts it's for a reason!


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## Ivan1GFP (Oct 12, 2020)

P-39 Expert said:


> I completely understand the CG calculations.
> 
> I just believe that your CG concerns for the P-39 are a little overboard.
> 
> How many P-39s were lost to spinning/tumbling?



Hello P-39 Expert,

Losses from spinning in combat, we probably don't know.
Losses from inadvertent spins in stateside training: a few.
Notes from experienced P-39 pilots to be wary of the flat spin, many.

My own belief is that some of the "tumbles" really were just very odd gyrations that happened during accelerated stalls in a P-39 with its CoG too far aft. When controls are released, the nose does not drop immediately as one might expect from a stable aircraft and the aircraft makes an unpredictable rotation or two before the nose ends up pointed into the airstream. Consider it a very unpredictable departure.

- Ivan.

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## P-39 Expert (Oct 12, 2020)

fubar57 said:


> ?


??


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## GrauGeist (Oct 12, 2020)

P-39 Expert said:


> How many P-39s were lost to spinning/tumbling?


A quick glance at Joe Baugher's site shows that six P-39s out of the production batch 41-6722/41-7115 (P-39D-BE) crashed due to spin.
There's many more out of the batch that indicate wrecking with no specifics - those could be crossed with the USAAF MACR reports for details.

There's more, but I don't have all day to look the rest up.


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## GregP (Oct 12, 2020)

With reference to post #527 above and the P-39 doing a "snap and spin" at anything below 250 mph:

1) You take off and land well below 250 mph.
2) You climb at 158 - 162 knots, well below 250 mph.
3) Approach speed is 130 mph.
4) The airplane cruises around 250 mph in high-speed cruise.

In general, go look at a pilot's handbook. Almost ALL speeds given are below 250 mph except the very high speed stuff. I doubt they'd have bought something that was a coffin in most of its operating envelope. It would "snap" only if you stall it.

So, I'm not too sure what is being said. Stall speed is about 105 mph flaps up and about 90 mph flaps down, and the stall is relatively benign unless you are aft of the aft CG limit.

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## P-39 Expert (Oct 12, 2020)

FLYBOYJ said:


> Not at all! Just pointing out the potential for an inexperienced or negligent pilot!
> 
> 
> Many from dives, agree! Now your comment "Either engine, since both turned the wrong way" makes totally no sense! Do you know what a critical engine is? Do you know why there were many engine out facilities on the P-38? It definitely wasn't from "Either engine, since both turned the wrong way."
> ...


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## P-39 Expert (Oct 12, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> It seems like most of these points have already been addressed by other forum members but here goes anyway.
> 
> ...



Please expand above.


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## fubar57 (Oct 12, 2020)

The Bell P-39 Airacobra & P-63 Kingcobra

Another reason was that the Red Air Force thoroughly evaluated the Airacobra before putting it into service, finding out the hard way about its vicious spin characteristics, with several test pilots killed. The faults were documented, however, with rules for flying the aircraft written up for operational pilots -- they were warned to never perform aerobatics if they had expended their ammunition -- and training implemented to make sure P-39 pilots knew how to avoid spins and, when possible, head them off before the point of no return. Procedures had to be devised for maintenance in extreme cold conditions. Bell engineers went to the USSR to assist the Soviets in qualifying the P-39, obtaining feedback for refinements to the design
Sources include:



US AIRCRAFT IN THE SOVIET UNION & RUSSIA by Yefim Gordon, Sergey Komissarov, and Dmitriy Komissarov, Midland Publishing, 2008.


"Bell P-39 / P-63 Variant Briefing" by Robert F. Dorr, WINGS OF FAME, Volume 10, 1998.

EDIT: added sources for above


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## DerAdlerIstGelandet (Oct 12, 2020)

“One normally returned to base instead of doing acrobatics”.



Sorry, I have been trying hard to give you the benefit of the doubt, but with that comment you have lost me.

No one is saying the P-39 was un-flyable, and no one is talking extremes here but you. It is clear you don’t actually understand what you are talking about. You have great “book” knowledge, but you don’t know how to put the pieces together.

You don’t have to be flying acrobatics to be in a deadly situation with a tail heavy rear CG aircraft. Any aircraft may have issues, especially when landing, or recovering from a stall. Any aircraft type can get into a stall, at any speed, and at any mode of flight just by exceeding the angle of attack. If your CG is out of balance or even very close to it, the risk is higher.

The aircraft I fly is not permitted to perform spins or acrobatics, and is a slow little single engine monoplane. Guess what? If I get out of CG, or really close to my limit, I am going to possibly experience problems with control and stability. That includes your beloved P-39.

So please stop, just stop...

Stop with the heresay, and listen to the people trying to help you.

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## Ivan1GFP (Oct 12, 2020)

Hello GregP,

Consider the context of those comments by the pilot.
The P-39 certainly has a CoG either close or behind its aft limits to be able to be tumbled.
It is NOT stable and its ability to weathervane is somewhat lacking.
Its tendency to enter a flat spin is much higher than if the CoG is in a reasonable range.
The recovery from the tumble is a vertical dive which needs some control input to avoid becoming a lawn dart.
It may be quite reasonable to carry a bit extra speed to be able to pull out safely under those conditions without entering an accelerated stall.

- Ivan.


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## Ivan1GFP (Oct 12, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *Would overheat if kept on the ground too long. Not normally a problem since the P-39 had excellent visibility forward while taxiing, while a tail dragger was blind to the front and had to s-turn while taxiing. P-39 just drove to the end of the runway while the pilot performed the pre-flight checks and then took off.*



You MIGHT be correct if your squadron operated a single aircraft with nothing else competing for the same runways.
That is not how fighters are used operationally. They are typically flown in groups. Having an aircraft idle a bit longer than expected and then suffering an engine failure on take-off is not an acceptable outcome. Pilots who flew the P-39 comment on its tendency to overheat. What makes you so much more knowledgeable than the men who flew the actual aircraft that you can declare this not to be a problem when it has been extensively documented to be a problem with the type?



P-39 Expert said:


> *Sufficient because 150gal was the internal tankage of the contemporary P-38F/G and P-40E/F/K. Actually the P-38 didn't see combat on a large scale until late 1942. The Mustang I didn't see combat until April 1943 with the Brits. It already weighed 8600lbs clean. With two 75gal drop tanks it would have weighed 9600lbs and likely couldn't leave the ground with its 1150hp engine.*



The P-38 actually carried twice that amount of internal fuel, but since it had two engines, that is reasonably comparable.
The difference though is that it could also carry two drop tanks of either 150 or 300 Gallons each.
There is no argument that the P-40 carried a pretty comparable fuel load to your hypothetical P-39.
As for the P-51, what you are forgetting is that even with an engine comparable to the P-39D, it was hitting speeds that were about the same as a P-39Q with a much later engine. The Mustang Mk.II still with the single stage Allison was also able to achieve over 400 MPH at 10,000 -12,000 feet which is well beyond what any P-39 could do.

Although you can argue that the fuel loads are comparable, the P-39 has to sacrifice a substantial portion of its armament to get this increased fuel load which was already standard in the other fighters.



P-39 Expert said:


> *Google 37mm M4 cannon and you will see how rapid it's rate of fire was. Trajectory was flat out to 400yards, about the outer limit of accurate air to air gunnery. P-47s wing mounted guns were set to converge at 300-350yds. After that they were diverging instead of converging. *



37 mm T9 / M4 cannon. Rate of Fire: 140-150 rounds per minute
Muzzle Velocity: 610 Meters / second -- 2000 feet per second.

The problem isn't that you can't get all the guns on the P-39 to converge on a point at a distance.
That part is easy.
The problem is that as soon as you start pulling any G while firing, the trajectories don't line up any more.
A uniform battery or at least guns that have similar ballistics avoid that situation. The Hispano 20 mm cannon on some Airacobra is very similar in velocity to the .50 cals but the problem is the lack of duration of fire.

You also might want to keep in mind that bullets don't just disappear past their point of convergence.



P-39 Expert said:


> *60-80% of planes shot down never saw their assailant, so they weren't maneuvering. 12 seconds is exactly what Spitfires had with 120rds. P-38 had 15 seconds. Three whole seconds more.
> .....
> Fine, then use the 20mm cannon with a larger ammunition tray. Save 80lbs over the 37mm.*



The question here is what else do these other fighters have remaining when their cannon ammunition runs out?
These other cannon also have a much higher rate of fire that the 37 mm does not.
Switching to the 20 mm Hispano Mk.I / HS-404 option on the Airacobra only makes things worse.
The duration of fire drops to 6 seconds instead of 12.....



P-39 Expert said:


> *They were centerfire weapons and a .50calMG was certainly capable of shooting down another fighter. The 37mm and twin .50s offered more weight of fire than four .50cal MGs on the P-51A/B/C. You have posed these same statements and gotten the same answers from me before in this thread. *



Your opinion and mine differ. The US Army who was paying for the weapon systems didn't seem to agree with your opinion.
The Soviets seemed to be in pretty good agreement with you but they were not the ones buying the aeroplanes.

ANYTHING can shoot down an aeroplane. That is the principle of the "Golden BB".
I just would not want to depend on it on a large scale.

- Ivan.


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## FLYBOYJ (Oct 12, 2020)

P-39 Expert said:


> *The props both turned outward so if one engine was lost the torque of the good engine wanted to bank the plane toward the heavier side of the dead engine.*


 And that doesn't make a difference! Apparently you never heard of a "critical engine." 

Critical engine - Wikipedia

Depending who you talk to the P-38 didn't have a critical engine or both were critical. In either case the P-38 had great engine out characteristics once you were trained on how to fly a twin!

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## glennasher (Oct 12, 2020)

Ivan1GFP, I think you're typing to a brick wall.

He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional. 

I have learned a lot from this place, but I certainly don't claim to be an "Expert" at anydangedthing. I've often thought that self-declared "experts" are anything but that. I kinda think that he's just trolling you all. I'm moving on to other things.

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## GregP (Oct 12, 2020)

Hi Ivan!

I fully realize the possibilities for the P-39 and agree there was an issue there, but saying it would snap out of control if the controls were moved below 250 mph is ... a bit of an exaggeration.

Below is an example of a twin-engine aircraft again running out of aispeed while climbing, stalling, being unable to recover. This is the classic "out of airspeed, altitude, amd ideas" situation. The Mosquito has the highest engine out Vmc of any twin piston aircraft I know of, at 160 mph or more, depending on load. It's a "Wooden Wonder" when flown with skill and precision, but a bit of a handful when operated without said skill, as below. 




Wish we' stop seeing these basic mistakes!

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## P-39 Expert (Oct 12, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...



Expand above.


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## GregP (Oct 12, 2020)

Avoiding Stalls and Spins in WWII Warbirds

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## FLYBOYJ (Oct 12, 2020)

glennasher said:


> Ivan1GFP, I think you're typing to a brick wall.
> 
> He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.
> 
> I have learned a lot from this place, but *I certainly don't claim to be an "Expert" at anydangedthing. I've often thought that self-declared "experts" are anything but that.* I kinda think that he's just trolling you all. I'm moving on to other things.



I've been in this business for over 40 years and I'm still learning, especially when I come on here!

And the same thing for "master mechanics"


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## FLYBOYJ (Oct 12, 2020)

I think this video might have been posted on here. I've always enjoyed watching it. Some of our pilots, please comment when you see the attitude of the aircraft after some of the spin/ stall sequences. The last portion of the clip drives the point home!

I also think the commentator "sugar coats" this. I'd bet dollars to donuts all of these scenes were flown by seasoned Bell test pilots, to include the last portion!

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## DerAdlerIstGelandet (Oct 12, 2020)

FLYBOYJ said:


> I've been in this business for over 40 years and I'm still learning, especially when I come on here!
> 
> And the same thing for "master mechanics"



I’ve been in the aviation industry (military and civilian) for 20 years now. Mechanic, Aircrew Member, Safety, Engineering (note: I am not an engineer), and a private pilot.

The most important thing I have learned over the last 20 years is that I know exactly enough to get myself in trouble. 

Seriously, in aviation you never stop learning. Every day I learn something new. You also never know everything, or you are never an absolute expert at everything. That does not mean you can’t be proficient and an expert, just that there is always room for continuous growth and improvement.

The day you stop learning in aviation is the day you need to hang it up. You are dangerous, and you’re going to get someone hurt or worse.

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## FLYBOYJ (Oct 12, 2020)

DerAdlerIstGelandet said:


> The day you stop learning in aviation is the day you need to hang it up. You are dangerous, and your going to get someone hurt or worse.


Amen!

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## SaparotRob (Oct 12, 2020)

FLYBOYJ said:


> I think this video might have been posted on here. I've always enjoyed watching it. Some of our pilots, please comment when you see the attitude of the aircraft after some of the spin/ stall sequences. The last portion of the clip drives the point home!
> 
> I also think the commentator "sugar coats" this. I'd bet dollars to donuts all of these scenes were flown by seasoned Bell test pilots, to include the last portion!



That was neat!


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## XBe02Drvr (Oct 12, 2020)

P-39 Expert said:
The props both turned outward so if one engine was lost the torque of the good engine wanted to bank the plane toward the heavier side of the dead engine.

*Good god man, that's normal behavior for any twin with wing mounted engines! But it's not the torque that does it; it's the asymmetric thrust. You need to study up on this before shooting your mouth off while pointing at your foot.
"*Critical engine" comes into play only in the case of twins whose engines both turn in the same direction, and then it's primarily P factor, not torque that's the culprit. I'm not going to lecture you on this; go look it up yourself.
While you're at it you might discover the meanings of things like VMCa and VMCg, VYse, Vxse, Accelerate-Stop, Balanced Field Length, and the takeoff speeds; V1, Vr, and V2.
Don't sweat it; we all get our "night in the barrel" from time to time, when every approach ends in a waveoff or a bolter and the guys in the ready room are critiquing our every clumsy move. It isn't personal, and they've all been through it too. A little ball-busting toughens the hide.

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## Ivan1GFP (Oct 13, 2020)

GregP said:


> Hi Ivan!
> 
> I fully realize the possibilities for the P-39 and agree there was an issue there, but saying it would snap out of control if the controls were moved below 250 mph is ... a bit of an exaggeration.
> 
> ...




Hello GregP,

The situation with the Mosquito in the accident is entirely different. It was a mechanical failure that caused the accident.
The maneuver was intended to run out of airspeed in a vertical climb.
What was NOT intended was to have an engine failure with no airspeed and while both engines were running at very high power settings. At zero airspeed, the remaining engine caused an uncontrollable yaw which the pilot was able to recover from but he could not regain enough flying speed in the altitude remaining.

- Ivan.


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## Milosh (Oct 13, 2020)

There is a video out there of a Mossie flying out of the Downsview deHavilland plant doing single engine maneuvers.


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## Ivan1GFP (Oct 13, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *So now the P-39 can't operate in a group?*



This is your statement, not mine. I just pointed out that this is a common operational situation in which the requirement to avoid ground idling may not always be met.



P-39 Expert said:


> *Again, the P-39 was operational from the beginning of the war. Earliest Mustang I combat was April 1943. With comparable engines (-35 vs -39, -81 vs -85) the P-39 was about 10-15mph slower but outclimbed the P-51. *



First of all, the subject was lack of fuel capacity in the P-39. As for level speed versus climb, it is pretty obvious what the Army Air Forces preferred and it wasn't climb rate.



P-39 Expert said:


> *No, they just keep moving farther away from each other.*



Yes they do and if guns are harmonized to 300 yards, in theory, they should remain no wider than how they started at about twice that distance. Don't forget your Geometry!
Reality and dispersion makes things a bit worse of course.......



P-39 Expert said:


> *The P-39 still had two .50s with a duration of 25 seconds.
> .....
> The 37mm put out more pounds of projectile per second than the 20mm.
> .....
> I said use a bigger ammunition tray for the 20mm. 120rds instead of 60.*



Those two remaining SYNCHRONIZED .50 cals have a fairly low firing rate. Combined, they are perhaps the equivalent of one regular .50 cal. The free firing rate of these cowl guns was particularly low.
.......
Pounds of projectile is great, but firing rate is too low and ballistics are poor.
There is probably a reason why everyone else settled on 20 mm cannon.
.......
If this was so easy, then one has to ask why it wasn't done.
That particular gun fed from a drum. If doubling the ammunition capacity were that easy, one has to wonder why it wasn't done.
Even with double the capacity, that is only 12 seconds of fire.



P-39 Expert said:


> *They only bought 9500 of them, about the same as the P-38.*
> [/QUOTE
> 
> They gave over half of them to the Soviets. Of the remainder, some were used to equip the French and Italians and quite a few were used as training aircraft stateside. This does not sound like an aircraft that was seen as suitable for operational use by US forces.
> ...

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## wuzak (Oct 13, 2020)

P-39 Expert said:


> Again, the P-39 was operational from the beginning of the war. *Earliest Mustang I combat was April 1943*. With comparable engines (-35 vs -39, -81 vs -85) the P-39 was about 10-15mph slower but outclimbed the P-51.





P-39 Expert said:


> Again, the P-39 was operational from the beginning of the war. *Earliest Mustang I combat was April 1943*. With comparable engines (-35 vs -39, -81 vs -85) the P-39 was about 10-15mph slower but outclimbed the P-51.



That may come as a surprise to the RAF pilots using the Mustang I in 1942.



> The first Mustang combat mission was undertaken by Flying Officer G. N. Dawson of No. 26 Squadron on *May 10, 1942*, strafing hangars in France and shooting up a train.





> The first Mustang I operational sortie was on *July 27, 1942*. Mustang Is participated in the disastrous Dieppe landings by British commandos on *August 19, 1942*, where it saw the first air-to-air action. During this operation, pilots of No 414 Squadron of the RCAF were attacked by Fw 190s. An American RCAF volunteer, F/O Hollis H. Hills, shot down one of the enemy, which was first blood for the Mustang.





> In *October of 1942*, On a mission to the Dortmund-Elms Canal and other objectives in Holland, *the Mustang I became the first single- engined fighter based in the UK to penetrate the German border*. By this time, the Mustang I equipped Nos 2, 4, 16, 26, 63, 169,239, 241, 268, and 613 Squadrons of the RAF, plus Nos 400, 414 and 430 Squadrons of the RCAF, and No 309 (Polish) Squadron of the RAF.



Service of Mustang I/IA With RAF

Seems you were almost a whole year out!

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## fubar57 (Oct 13, 2020)

Doesn't seem to matter though does it

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## MiTasol (Oct 13, 2020)

Shortround6 said:


> This book (or something like it)
> Fraas. AIRCRAFT POWER PLANTS. 1st ed, 1943. | eBay



You can download a copy from Aircraft Power Plants : Arthur Fraas, : Free Download, Borrow, and Streaming : Internet Archive. If you want a paper copy then look for it on bookfinder.com

Another, more basic book is the Allison primer that is on this forum - I cant remember the title.

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## P-39 Expert (Oct 13, 2020)

FLYBOYJ said:


> And that doesn't make a difference! Apparently you never heard of a "critical engine."
> 
> Critical engine - Wikipedia
> 
> Depending who you talk to the P-38 didn't have a critical engine or both were critical. In either case the P-38 had great engine out characteristics once you were trained on how to fly a twin!


I understand the critical engine. That refers to a conventional twin engined plane with both propellers turning the same direction. If both props are turning right as viewed from behind then the right engine would be the critical engine. If the left engine is lost then the right engine torque (and the drag of the dead left engine) tends to pull the plane into a left bank. If the right engine is lost the left engine torque works against the inclination of the plane to bank right offering more stability.

On the P-38 both engines turned outward so the loss of either one made the plane want to bank/turn violently toward the dead engine. Both engines were critical.


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## P-39 Expert (Oct 13, 2020)

FLYBOYJ said:


> I think this video might have been posted on here. I've always enjoyed watching it. Some of our pilots, please comment when you see the attitude of the aircraft after some of the spin/ stall sequences. The last portion of the clip drives the point home!
> 
> I also think the commentator "sugar coats" this. I'd bet dollars to donuts all of these scenes were flown by seasoned Bell test pilots, to include the last portion!



"Normal spin characteristics with prompt recovery if proper technique is used." I had seen this film before, thanks for posting.


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## fubar57 (Oct 13, 2020)

Everyone here provides documents about the poor handling of the precious P-39 and all you seem to come back with is..."Because I said so". Back it up with documents, "Expert"

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## P-39 Expert (Oct 13, 2020)

fubar57 said:


> Everyone here provides documents about the poor handling of the precious P-39 and all you seem to come back with is..."Because I said so". Back it up with documents, "Expert"


Did you actually watch the P-39 spin film in post #555? "Normal spin characteristics with prompt recovery if proper technique is used?" Makes my point for me.


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## fubar57 (Oct 13, 2020)

I saw a P-39 crash at the end of a spin. Why wasn’t the proper technique used?


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## P-39 Expert (Oct 13, 2020)

fubar57 said:


> I saw a P-39 crash at the end of a spin. Why wasn’t the proper technique used?


As the film said, in that case proper technique was not used. The whole point of the movie was that P-39 spin characteristics were normal and recovery prompt if proper technique was used.


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## P-39 Expert (Oct 13, 2020)

wuzak said:


> That may come as a surprise to the RAF pilots using the Mustang I in 1942.
> 
> 
> 
> ...


You are correct on the dates on the Mustang I. I stand by my other statements.


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## fubar57 (Oct 13, 2020)

I have no volume on this laptop. Makes listening to music videos a little sketchy at times. Had I made that P-39 video, I would have put the crash in the beginning and then shown proper technique to avoid it

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## MiTasol (Oct 13, 2020)

P-39 Expert said:


> As the film said, in that case proper technique was not used. The whole point of the movie was that P-39 spin characteristics were normal and recovery prompt if proper technique was used.



So long as you had 7000 to 8000 feet of airspace below you according to that pilot report above in post 527.

Now let me think.

Mmmmm. 

How many times do you have 7000-8000 feet below you when you are exhausted after coming down from a combat induced adrenaline high while you are on approach for landing with your aircraft at or approaching its worst CG configuration?

My guess would be never.

You also ask why would a pilot be doing aerobatics at the end of a flight with no ammo on board.

Have you ever heard of a _victory roll_? Pilots did that when still on an adrenaline high after shooting down an enemy plane. Often that would be with zero ammo left.


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## P-39 Expert (Oct 13, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...



Please expand above.


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## PAT303 (Oct 13, 2020)

We have 29 pages of wash rinse repeat, do any of you think the discussion will be any different if we went another 29 pages?, I think this member said it best.

He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.[/QUOTE]

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## P-39 Expert (Oct 13, 2020)

PAT303 said:


> We have 29 pages of wash rinse repeat, do any of you think the discussion will be any different if we went another 29 pages?, I think this member said it best.
> 
> He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.


[/QUOTE]
Sorry that I keep refuting incorrect statements from long ago that have been taken as fact for 75 years. I have been presenting facts, not heresay. 

I'm enjoying the discussion, hope that I have not offended anyone.


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## fubar57 (Oct 13, 2020)

The Russians liked the hitting power of the 37mm but weren’t really fond of the gun itself
“The Soviet pilots had some requests - for example, they wanted* improvement in the ballistics and rate of fire of the 37mm cannon*. The Russians asserted that the late-model P-39Qs *were much less stable *than earlier Airacobras, and that the armoured headrest introduced on this model impaired rearward visibility”


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## DerAdlerIstGelandet (Oct 13, 2020)

PAT303 said:


> We have 29 pages of wash rinse repeat, do any of you think the discussion will be any different if we went another 29 pages?, I think this member said it best.
> 
> He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.



No, but we might remove the expert from his name... 

What did someone say about “self proclaimed” experts?


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## DerAdlerIstGelandet (Oct 13, 2020)

P-39 Expert said:


> Sorry that I keep refuting incorrect statements from long ago that have been taken as fact for 75 years. I have been presenting facts, not heresay.
> 
> I'm enjoying the discussion, hope that I have not offended anyone.



The only thing you are refuting is your “expert” status.


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## DerAdlerIstGelandet (Oct 13, 2020)

Now having said that, I believe this thread has run its course. No amount of facts will change any opinions or lack of understanding present here.

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## MiTasol (Oct 13, 2020)

P-39 Expert said:


> "Normal spin characteristics with prompt recovery if proper technique is used." I had seen this film before, thanks for posting.



yep and that video clearly shows that prompt recovery takes many thousands of feet of precious altitude. If you do not have the altitude you hit the silk, if there is time, or die.

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## MiTasol (Oct 13, 2020)

DerAdlerIstGelandet said:


> The only thing refuting is your “expert” status.



expert -
X = unknown large number
spurt = drip under pressure


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## DerAdlerIstGelandet (Oct 13, 2020)

Drip under pressure...


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## Peter Gunn (Oct 13, 2020)

Well it has been an entertaining thread, I'm still laughing over this whopper:

*The Mustang I didn't see combat until April 1943 with the Brits.  It already weighed 8600lbs clean. With two 75gal drop tanks it would have weighed 9600lbs and likely couldn't leave the ground with its 1150hp engine.* 

What I don't understand is why race cars today blow so many tires at a measly 200 mph +/- when, being able to leave a P-39 in the dust means the Mustang was running on the roads at 400 mph, man Goodyear technology must have been really something in 1942!

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## Peter Gunn (Oct 13, 2020)

GregP said:


> Hey Peter Gunn
> 
> Maybe we could fix the P-39 with some Chevrolet "SS" letters along the lower nose in front of the door? And might as well install a Hurst "pistol-Grip" shifter handle on the control stick, too, along with a push-button radio.
> 
> ...


Hey Greg,

Agreed, I had a 1995 Seville STS back in the nineties that was about as fast in the stoplight wars and absolutely better on the highway. Heck, my XT-6 is probably faster with a 6 cylinder, but nothing can beat the "Cool" factor of those old beasts, and the sound. I'm going to see if I can hunt up some snaps of it, don't think I have any but might be cool to see.

Nice 'stang by the way, except who's the old dude in the drivers seat? 

Trust me, I don't look any younger than that either.

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## Ivan1GFP (Oct 13, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *P-39 had no trouble operating in squadron or group strength. *



....except that it created situations in which a little extra idling on the ground would cause the P-39 to overheat and abort.
The original discussion was about the inadequacy of the cooling system in the P-39 even for the engines that were already installed and the tendency to exceed temperature limits in sustained high power operation at existing altitudes thus making it unsuitable for installation of a ASB and operation at higher altitudes.
The tendency to run hot and overheat has been documented by numerous test reports and pilot accounts.
Your refusal to acknowledge these issues is quite extraordinary.



P-39 Expert said:


> *The AAF didn't buy many Allison powered Mustangs. Less than 1000 P-51s and only a little over 600 Mustang I.*



The production of the last Allison powered P-51, the P-51A stopped because production began of the Merlin powered P-51B with superior altitude performance.



P-39 Expert said:


> *Perhaps the equivalent of 1.5 regular .50cal.
> .......
> Too low for what? You make it sound like the 37mm was hand loaded after every round. Ballistics very good (flat) out to 400yds.
> .......
> 37mm was not more widely used because it had to be a centrally mounted weapon on a single engine plane. Could not be mounted out on the wing like all the other AAF/USN planes required.*



Even 1.5 regular .50 cal MG is pretty inadequate unless you happen to be designing fighters for the Soviets.
.......
A gun with a 2000 fps muzzle velocity has a rather looping trajectory at any range. It doesn't fly flat out to a specific distance.
Check back to your high school physics which should have explained all this.
The problem is when you have a battery of guns with significantly differing ballistics, you can get them to all line up within a certain distance when flying straight and level such as in a bomber intercept but that doesn't work so well when pulling G in a deflection shot.
.......
If the 37 mm M4 were such a fantastic weapon, then there were many aircraft such as twin engine attack aircraft, night fighters, the P-38 that could have used it. Please tell us how many actually did.



P-39 Expert said:


> *20mm was used in the P-39 only briefly because of early shortages of the 37mm, and because the Brits specified it on the P-400. 20mm would have been just fine on the P-39 given more ammunition capacity. Either gun could have been used.*



If it were so easy a solution, then some of the operators of P-39 with 20 mm cannon in New Guinea or Guadalcanal should have done something to address the issue. These folks operating the aircraft probably figured out pretty early that 6 seconds of firing time is really about two good squirts before the ammunition is gone. I suspect increasing the ammunition supply might not have been so easy.
From what I can tell, both the 37 mm and 20 mm guns used magazines that sat above the gun and there may not have been the room above the gun to put in a larger ammunition supply. Remember that this space is also shared with the .50 cal cowl MG.

- Ivan.


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## FLYBOYJ (Oct 13, 2020)

P-39 Expert said:


> "Normal spin characteristics with prompt recovery if proper technique is used." I had seen this film before, thanks for posting.


And if you observe some of those recoveries show the aircraft with the tail low because of the aft CG, not a desirable characteristic. A well trained pilot will deal with this accordingly.


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## FLYBOYJ (Oct 13, 2020)

P-39 Expert said:


> I understand the critical engine. That refers to a conventional twin engined plane with both propellers turning the same direction. If both props are turning right as viewed from behind then the right engine would be the critical engine. If the left engine is lost then the right engine torque (and the drag of the dead left engine) tends to pull the plane into a left bank. If the right engine is lost the left engine torque works against the inclination of the plane to bank right offering more stability.
> 
> On the P-38 both engines turned outward so the loss of either one made the plane want to bank/turn violently toward the dead engine. *Both engines were critical*.



Or both engines weren't. To avoid the adverse yaw you powered back the good engine. This was SOP on the aircraft (and some other twins) and it worked fine if the pilot was well trained.


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## P-39 Expert (Oct 13, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...



Please expand above.


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## DarrenW (Oct 13, 2020)

P-39 Expert said:


> ...As you know, spins were prohibited in the pilot's manual on all AAF and USN fighters.



Yes, this was true for the P-51D and F4U-1, but the P-47D could intentionally spin up to one-half turn and the F6F-3/5 up to two full turns.


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## DarrenW (Oct 13, 2020)

Snip:
_If the 37 mm M4 were such a fantastic weapon, then there were many aircraft such as twin engine attack aircraft, night fighters, the P-38 that could have used it. Please tell us how many actually did.

*P-39, P-59, P-63.* _

Looks like Bell was the only company endeared to the weapon.

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## Mad Dog (Oct 13, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> However long it would have taken to design a new wing, this was a basic design flaw in the P-39 that was a serious limitation. The symmetrical airfoil had a pretty low coefficient of lift relative to more modern airfoils.
> The wing retained good lateral control because the tips did not stall with the rest of the wing, but the rest of the wing tended to stall all at once. (from NACA Report)
> ...



There was a redesign of the wing, it was called the P-63 Kingcobra. The problem was that when the P-63 arrived in October 1943, the USAAC already had the P-38 working in the Pacific and the P-47 in the ETO, Med and Pacific, and there was no real requirement for the P-63 that those other fighters didn't already meet.


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## BiffF15 (Oct 13, 2020)

P39 Expert,

Here are a couple of opinions from my perspective.

Overheating: If during the taxi out a member of your flight has a mechanical fault and returns to the chocks for a quick fix. The rest of the flight has two choices, wait or go. Fighter tactics are built around mutual support. Two aircraft are much more effective / deadly than one. Three are more effective than two in some cases, and can be a serious detriment if split. Four are way more effective than three. Yes, we practice 3 ship ops but it has it’s detriments. Again, four is way more effective than three. So while you are waiting the opportunity for overheating becomes are serious reality, which might take more assets out of the mission. No or not enough assets could cause mission cancel or failure. Also, if there are complaints of overheating, then the P39s peers aren’t experiencing the same problems or the guys would not be mentioning it.

CG: What type of car do you drive and how old is it? The reason I ask is most modern cars understeer when at the limits. Oversteer is when the tail slides around, under steer is when the nose plows or slides. The latter is what is standard today, and the reason is it’s easier to handle as control degrades. Great for masses, doesn’t require above average skills at the limit. Did you watch the spin video? There were a few that I would describe as violent and I did spin training in the T-37. Also realize that the AAF was expanding exponentially at times. So your instructors are all young aviators. Young aviators have less experience to draw on and pass along to neophytes. Next look at all the other single engine fighters / trainers the USAAF had. All of them had engines in the front. Next think about where are the mass is in a single engine piston fighter. Not surprisingly it’s centered on the engine. Now your spin training, from your young instructors, as you came up the pipeline, has been in nothing but nose engined aircraft, and they all behaved in a similar fashion. The P39, can under controlled circumstances, be recovered from a spin. And the CG is within limits. There is a reason there are limits, and exceeding them is NOT a safe way to operate. Yes, the video showed several different spins, and they were recovered from (well except one). I wonder if the AAF made spin videos about the other fighters.

Someone posted comments by a pilot regarding doing intentional spins. The comment talked about pulling on the stick and letting go, and how the plane behaved would determine whether a spin would be accomplished. If I remember correctly, the pilot made comment about if the plane returned quickly to it’s pre-pull on the stick status it was okay, and if it didn’t it wasn’t. What the pilot was doing was checking the dynamic stability of the plane. Dynamically stable aircraft will return to “normal” fairly quickly, dynamically unstable will not. Guess what, the F16 is dynamically unstable, which is what makes it very maneuverable. However, it requires a computer (it has 3) to keep it flyable. The closer to unstable a plane is, the more maneuverable it can be, however the more easily it can be departed (put out of control). Approaching dynamically unstable in 1940s, with neophyte pilots with low experience, without years of history and procedures to fall back on, is / was a recipe for problems.

Regarding the expended ammo and acrobatics. You mentioned if I remember correctly, that a guy would know not to do loops after expending his ammo. That works in peace time. In combat, you are shooting and being shot at. Run out of ammo but not adversaries, and the option of going home or no acrobatics will not always be there.

Looking at the video, and reading quite a bit what’s been posted on here, I can see how you would think it’s no big deal to recover from a spin. However, from the perspective of the late 30s, to mid 40s, the USAAC / USAAF had exponentially grown, had young pilots, low experience instructors, and not much history of procedures, and the benefit of owning a plane for decades to fall back on. Also the P39 sits outside the standard due to it’s mid engine layout as compared to all the trainers or other SE fighters. The guys on this forum have been doing an admirable job of walking you through the CG limits and ramifications, as well as it’s combat record with the Soviets (IE how it compared in quality to their indigenous planes. Add as well their willingness to overboost the engine (works if you are fighting over LAND, and it’s your land (DEFENSIVE), which gives much more opportunity to WALK home vice become a casualty / POW. It was a decent plane, just didn’t fit in with it’s peers.

Cheers,
Biff

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## FLYBOYJ (Oct 13, 2020)

BiffF15 said:


> P39E,
> 
> Here are a couple of opinions from my perspective.
> 
> ...



Biff - always appreciate your perspectives, this forum is blessed to have you (and a few others) around!!!

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## glennasher (Oct 13, 2020)

P-39 Expert said:


> Please expand above.




There's no need to expand further, you either get it, or you don't. By now, if you don't get it, you ain't gonna get it. Quit trolling.


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## DerAdlerIstGelandet (Oct 13, 2020)

Let’s keep it civil gents.

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## P-39 Expert (Oct 13, 2020)

BiffF15 said:


> P39E,
> 
> Here are a couple of opinions from my perspective.
> 
> ...


Biff, was your post addressed to me? Just asking. Thanks.


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## BiffF15 (Oct 13, 2020)

P-39 Expert said:


> Biff, was your post addressed to me? Just asking. Thanks.



Yes, I abbreviated your screen name. My bad. Fixed.


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## P-39 Expert (Oct 13, 2020)

BiffF15 said:


> Yes, I abbreviated your screen name. My bad.


Thank you, just making sure.


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## XBe02Drvr (Oct 13, 2020)

P-39 Expert said:


> I understand the critical engine.


No you don't.



P-39 Expert said:


> If both props are turning right as viewed from behind then the right engine would be the critical engine. If the left engine is lost then the right engine torque (and the drag of the dead left engine) tends to pull the plane into a left bank.


WRONG! You've been corrected on this at least twice, and yet you persist in this erroneous explanation. Critical engine is the engine most dangerous to lose, in this case, left engine. I earned my multi engine rating and multi instructor rating in planes of this sort, then instructed in them. The differences between critical and non-critical engines are due to P factor, and torque has next to nothing to do with it. The real killer here is asymmetric thrust and the yaw and roll it induces, and that happens with EITHER engine out, it's just a little bit worse with the critical engine out.
Don't come to me with your shiny new Whizbang 260 looking for a multi engine rating! From what I've seen of your willingness to absorb new information if it conflicts with your preconceived notions, I wouldn't get in an airplane with you and put both our lives on the line for all the tea in China. Engine-out training is risky enough with a student who's got his/her head screwed on straight. You never know what creative new stunt they'll pull, out of confusion, misunderstanding, or nervousness. In your case it could easily be a suicide mission.

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## pinsog (Oct 13, 2020)

I thought the ‘critical’ engine on the P38 was the one with the generator on it because they only put one generator one one engine for most of the P38’s life and if you lost that engine you would lose electrical power soon after and that would cause issues that I can’t remember resulting in loss of the aircraft.

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## FLYBOYJ (Oct 13, 2020)

pinsog said:


> I thought the ‘critical’ engine on the P38 was the one with the generator on it because they only put one generator one one engine for most of the P38’s life and if you lost that engine you would lose electrical power soon after and that would cause issues that I can’t remember resulting in loss of the aircraft.


That is a classification based on equipment piled on the engine. If we’re talking performance and depending if “the glass is half full or half empty“ The P 38 either has two critical engines or no critical engine. This is been debated for years.

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## XBe02Drvr (Oct 13, 2020)

pinsog said:


> I thought the ‘critical’ engine on the P38 was the one with the generator on it because they only put one generator one one engine for most of the P38’s life and if you lost that engine you would lose electrical power soon after and that would cause issues that I can’t remember resulting in loss of the aircraft.


Different definition of "critical" than the classic twin engine one. Since the P38 didn't have a classic critical engine (or two of them!), then this definition could suffice.
IIRC, that single generator issue only applied to the earliest models, including the non turbo versions built for the Brits.
The Doyne Conversion Apache I got my multi in had a single generator on the left engine and a single hydraulic pump on the right, and since both gear and flaps were electrically controlled and hydraulically actuated, you couldn't afford to lose either engine. I spent lots of time trying to keep the dang thing straight on one engine while wailing away on the the manual hydraulic pump. Executing a single engine go around was an athletic workout, as aileron and rudder forces were *HEAVY *and the hydraulic wobble pump was very stiff to operate and required you to bend down almost to the floor while you struggled to gain 100 feet/minute until you got the plane cleaned up. Only VFR in flat country, as the climb gradient was pretty marginal. If I had to do that night IFR at a "hole in the hills" airport in mountain country, it would be doomed to failure. Just belly it in, wheels up. A year later, the old girl got a second generator (actually, converted to alternators), and an electrically driven aux hydraulic pump. Hallelujah!

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## GregP (Oct 13, 2020)

I always thought the critical engine was the one with the worse performance in a twin with same-turning engines. It is invariably the one that rotates outward at the top of the prop arc. Since the P-38 had BOTH engines turning outward at the top of the prop arc, then either one should perform substantially the same within normal engine variation ... ergo, there doesn't seem to BE a critical engine.

But, as you say, there seem to be room for debate. Actually, there always seems to be some debate, whether there is room for it or not, doesn't there? So, there we have the answer: We have: 1) no critical engine, 2) two critical engines, or 3) one critical engine (only one generator), depending on who is writing the text.

Another victory for clarity ...

Cheers.

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## Ivan1GFP (Oct 13, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *Flat trajectory out to 400yds from "Cobra" by Birch Matthews.*



I have that book as well. It has a lot of nice photographs and references but the author is a "fan boy" for the Airacobra.
His opinions which are asserted as fact often do not stand up to scrutiny so I would be very wary of quoting him.
Regardless of who made that statement of a "Flat trajectory out to 400 yards", you should have the sense to know it can't possibly be true. NOTHING flies flat (mostly true). It is just a matter of HOW curved the trajectory is.



P-39 Expert said:


> _*P-39, P-59, P-63.* _



If the 37 mm were such a great weapon, why was Bell the only company that chose to use it?
Everyone else seemed to go with multiple .50 cal or 20 mm instead even when the aircraft clearly could carry the 37 mm if it needed to.



P-39 Expert said:


> *Should have been easy to reduce the weight also. I have no idea why it wasn't implemented.*



Perhaps because increasing the ammunition capacity wasn't that easy.
As for reducing weight, the operators of the aircraft were of the opinion that more armour and not less was needed.



Mad Dog said:


> There was a redesign of the wing, it was called the P-63 Kingcobra. The problem was that when the P-63 arrived in October 1943, the USAAC already had the P-38 working in the Pacific and the P-47 in the ETO, Med and Pacific, and there was no real requirement for the P-63 that those other fighters didn't already meet.



Hello Mad Dog,

From what I have read about the King Cobra, it seemed to have very good maneuverability as compared to the types already in service. The problem though was that it was also significantly slower than types already in service and those in power seemed to prefer speed over other qualities.

- Ivan.

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## GregP (Oct 13, 2020)

Here's a guy mostly at or below 250 mph who isn't having any trouble.

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## glennasher (Oct 13, 2020)

GregP said:


> Here's a guy mostly at or below 250 mph who isn't having any trouble.





Of course he's not having trouble, they don't let 21 year old kids fly 75-80 year old warbirds worth the big bucks, that means the guy is very experienced and knows his way around one. There's no doubt the young kids flying the 39s and 400s back in the war had a lot less experience, and were possibly more rattled if things went sideways..........


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## Mad Dog (Oct 13, 2020)

glennasher said:


> ......There's no doubt the young kids flying the 39s and 400s back in the war had a lot less experience, and were possibly more rattled if things went sideways..........


 There was a book by Edward Parks called _Nanette_ about his experience of flying the P-39 in New Guinea. It's a very good read. In it, he recounts an event where the electric propeller pitch control failed on a P-39 on a training flight, and the rookie pilot was so flustered he did nothing but carried on flying straight and level until the plane stalled and crashed.


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## SaparotRob (Oct 13, 2020)

Mad Dog said:


> There was a book by Edward Parks called _Nanette_ about his experience of flying the P-39 in New Guinea. It's a very good read. In it, he recounts an event where the electric propeller pitch control failed on a P-39 on a training flight, and the rookie pilot was so flustered he did nothing but carried on flying straight and level until the plane stalled and crashed.


What would have an experienced pilot done?


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## fubar57 (Oct 13, 2020)

SaparotRob said:


> What would have an experienced pilot done?


Flown a P-38

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## GrauGeist (Oct 13, 2020)

SaparotRob said:


> What would have an experienced pilot done?


Not having flown a P-39, I'm not sure of the proceedure to remedy that problem, but I can safely say that if my plane were experiencing issues, I'd call it out and either turn back or, if I was past the PONR, look for a suitable place to put it down (within friendly territory, if possible).
As a last resort, steady her out and hit the silk.

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## Shortround6 (Oct 13, 2020)

On the 37mm,
from a ballistics perspective (and going back to high school physics) we can have a practical range where the guns seems to shoot flat, It is pointed up slightly and so does not vary from the line of sight by very much out to the preset distance. EVERY projectile falls at the same speed, the old high school 32 ft per second per second. the projectile falls 8 feet in the first second of flight, (starts at zero fps in the fall and ends at 32 fps ) it falls 48 feet in the 2nd second of flight. (starts at 32fps and ends at 64fps). The 37mm, 20mm, .50 cal and .30 cal will all fall at the same speed. 
However what really matters to our pilots is the time of flight to the target. This governs both how far the bullet falls and how far the target moves between the bullet leaving the barrel and reaching the target area. With the 20mm and .50 cal both having about 40% higher velocity they will cover around 40% more distance in the same period of time. This is where the flatter shooting comes from. It also makes deflection shooting very difficult with plane that has different guns, forget looping trajectories. if the .50 cal bullets are hitting the 37mm shells are behind the aircraft. If the 37 does hit it means the .50s are flying in front of the nose.

This is a bit of simplification as the 37mm should keep it's velocity better than the others but since the difference is so great the crossover point (where the 20mm and .50 cal bullets do travel slower than the 37mm) may be well beyond any practical range, the .50 and 20mm were well matched out to over 600yds, The closer the firing plane gets to the 6 o'clock position the less difference in velocity makes.

edit, flunk high school math, Projectile falls 16 ft in the first second not 8ft, the 48 feet in the 2nd second of flight would be correct.

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## BiffF15 (Oct 13, 2020)

SaparotRob said:


> What would have an experienced pilot done?



1. Maintain Aircraft Control
2. Analyze the Situation 
3. Take Appropriate Action
4. Land as soon as conditions permit 

1 means fly the plane. If you are about to stall get the nose down and add power (if that’s an option). 2. Using aircraft systems knowledge assess. 3 means coming up with a plan. 4 means get it to a safe conclusion.

Freezing up indicates task saturation / sensory overload.

Cheers,
Biff

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## Ivan1GFP (Oct 13, 2020)

GregP said:


> Here's a guy mostly at or below 250 mph who isn't having any trouble.




Hello GregP,

That Guy probably isn't flying a P-39 with a CoG at or beyond its aft limit either.
The fellow trying to recover from a tumble has an aircraft that doesn't necessarily want to fly nose first.
He also may have some remaining rotational momentum from the tumbling he has just done and wants to give the aeroplane a chance to point itself nose down without any significant yaw or pitch and gain some speed so he can safely pull some G to get out of the vertical dive.

Those late model and war weary P-39 that served state-side as trainers probably never carried full armament and ammunition and were most likely ballasted in a manner so that they simply could not get CoG out of range by expending stores. This would be the same situation as modern airshow aircraft.



SaparotRob said:


> What would have an experienced pilot done?



Hello SaparotRob,

My guess is that an experienced pilot probably would have put the propeller into manual control and tried to adjust the RPM to something reasonable for the power setting.

- Ivan.

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## Mad Dog (Oct 14, 2020)

SaparotRob said:


> What would have an experienced pilot done?


When the P-39 prop pitch control went, the blades went into fine pitch which meant they produced less forward thrust whilst being easier for the engine to spin. If you did nothing, the aircraft speed gradually drops whilst the engine quickly over-revs. Whilst the engine screams, the aircraft loses speed to the point where there is not enough lift generated by the wings, at which point you will stall and usually drop into a spin. Without engine thrust to help you pull out of the spin, you might not recover control before you hit the ground. The textbook answer is to feather the prop (if you still can), switch off the engine and adopt a shallow-angled glide whilst looking ahead for a clear spot to land. If you can't feather the prop then it becomes a big airbrake, meaning you have to dive at a steeper angle to maintain flying speed, which reduces the amount of time you have to either find a landing spot or bail out. Even if you can feather the prop and stretch your glide, if there's no spot to land then you have to take to your parachute. The worst thing you can do is to do nothing, which is what the rookie did in the book.


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## wuzak (Oct 14, 2020)

Mad Dog said:


> The textbook answer is to feather the prop (if you still can), switch off the engine and adopt a shallow-angled glide whilst looking ahead for a clear spot to land.



How many single engine fighters in WW2 had feathering props?

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## SaparotRob (Oct 14, 2020)

Those were great responses guys. Very understandable. 
I especially liked Ivan1GFP’s answer. “..an airplane that doesn’t necessarily want to fly nose first” put it all together for me. I believe I understand what the plane wants to do and why it’s so difficult correct it. Put that whole center of gravity thing into perspective.
The explanations of what the pilot has to respond to made it real to me.


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## windhund116 (Oct 14, 2020)

wuzak said:


> How many single engine fighters in WW2 had feathering props?


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## GregP (Oct 14, 2020)

You can make a VERY safe bet that the P-39 in the clip is not at aft CG! Just seemed like too good a clip not to post is all, considering how dangerous it is purported to be under 250 mph.

Of course, it also doesn't have all the armor or armament since it's a civilian bird, now back in the U.S.A. Just to give you an idea what that means, the Planes of Fame operates a P-51A with Allison power. The wartime specs for it say the empty weight is around 6,433 lbs (2.918 kg). But, ours doesn't have armament, armor, or any wiring not needed for aircraft operation. It also has a modern radio, which weighs about nothing compared with a WWII unit.

The end result of it is that the empty weight is WAY less than stock. That P-39 you see in the clip isn't anywhere NEAR combat weight, and is quite spritely in acceleration.

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## XBe02Drvr (Oct 14, 2020)

Mad Dog said:


> When the P-39 prop pitch control went, the blades went into fine pitch which meant they produced less forward thrust whilst being easier for the engine to spin. If you did nothing, the aircraft speed gradually drops whilst the engine quickly over-revs. Whilst the engine screams, the aircraft loses speed


Mad Dog, what's your information source for these statements? The Curtiss Electric prop we had at mech school was not at all like this. If the governor or the slip rings failed (rare), yes, it would go to full increase, but since it came off a single engine plane (Curtiss SC21? I think), it wasn't featherable. Full increase would be roughly equivalent to a "TO & climb optimized" fixed pitch prop. A modest throttle reduction would get RPM back in the normal range and cruise would be slower than normal, but stalling out of the sky sounds pretty extreme to me.
A much more common failure would be for the electric pitch motor to fail, freezing the pitch at whatever value it's at. Unlike a hydraulic prop, which allows aerodynamic loads on the blades to drive it to the stops when hydraulic pressure is lost to the dome, blade loading on an electric can't drive the motor due to the mechanical advantage of the reduction gear. About like jacking one wheel on a car and trying to turn the engine over by rotating the raised wheel by hand. This changes your constant speed prop into a fixed pitch one, and returns RPM control to the throttle.
If you could feather the prop, the P39 looks like it would be a good glider, with its sleek profile, EXCEPT for that dang symmetrical airfoil. Now with a nice NACA high lift airfoil, I bet it would sport a pretty decent L/D, albeit at an alarmingly high speed and sink rate.

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## MiTasol (Oct 14, 2020)

BiffF15 said:


> 1. Maintain Aircraft Control
> 2. Analyze the Situation
> 3. Take Appropriate Action
> 4. Land as soon as conditions permit
> ...



The three priorities in order in three words - Aviate, Navigate and Communicate.

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## MiTasol (Oct 14, 2020)

XBe02Drvr said:


> Mad Dog, what's your information source for these statements? The Curtiss Electric prop we had at mech school was not at all like this. If the governor or the slip rings failed (rare), yes, it would go to full increase, but since it came off a single engine plane (Curtiss SC21? I think), it wasn't featherable. Full increase would be roughly equivalent to a "TO & climb optimized" fixed pitch prop. A modest throttle reduction would get RPM back in the normal range and cruise would be slower than normal, but stalling out of the sky sounds pretty extreme to me.
> A much more common failure would be for the electric pitch motor to fail, freezing the pitch at whatever value it's at. Unlike a hydraulic prop, which allows aerodynamic loads on the blades to drive it to the stops when hydraulic pressure is lost to the dome, blade loading on an electric can't drive the motor due to the mechanical advantage of the reduction gear. About like jacking one wheel on a car and trying to turn the engine over by rotating the raised wheel by hand. This changes your constant speed prop into a fixed pitch one, and returns RPM control to the throttle.
> If you could feather the prop, the P39 looks like it would be a good glider, with its sleek profile, EXCEPT for that dang symmetrical airfoil. Now with a nice NACA high lift airfoil, I bet it would sport a pretty decent L/D, albeit at an alarmingly high speed and sink rate.



A welded relay was also a failure mode and depending on which relay that would drive the prop to one end or the other of its pitch range. Anecdotally this tended to fail in the full fine pitch which, as you say, is the TO and climb pitch.

The hydromatic and counterweight props go to opposite ends of the range though when there is an oil pressure failure - counterweight goes to cruise pitch and hydromatic to fine pitch if the rusty memory is correct.


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## Peter Gunn (Oct 14, 2020)

BiffF15 said:


> 1. Maintain Aircraft Control
> 2. Analyze the Situation
> 3. Take Appropriate Action
> 4. Land as soon as conditions permit
> ...


I always get the strangest feeling that you've studied some of these issues before, I can't put my finger why though.

I also just noticed there are three "f"s in your screen name.

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## fubar57 (Oct 14, 2020)

Peter Gunn said:


> I also just noticed there are three "f"s in your screen name.


Jaysus H. “Tap Dancing” Christ. Now that you’ve mentioned it.........

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## pinsog (Oct 14, 2020)

I’ve never read “Nanette” and I may be mistaken, but was Nenette the P39 book that was all fiction? Someone wrote an all fiction P39 novel but I can’t remember the name.


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## DerAdlerIstGelandet (Oct 14, 2020)

MiTasol said:


> The three priorities in order in three words - Aviate, Navigate and Communicate.



I can still hear my instructor...

_Fly the plane, fly the plane, fly the plane!_

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## P-39 Expert (Oct 14, 2020)

pinsog said:


> I’ve never read “Nanette” and I may be mistaken, but was Nenette the P39 book that was all fiction? Someone wrote an all fiction P39 novel but I can’t remember the name.


Nanette was fiction, based on fact. Author was Edwards Park who was actually there as a pilot. His companion book "Angels Twenty" was a factual account of the same period January 1943 through the rest of his tour at Port Moresby, NG.

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## Juha3 (Oct 14, 2020)

P-39 Expert said:


> I believe the Russians pulled the .30s from the very first P-400s that the Brits gave them. And the IFF radio in the tail cone. Saved about 330lbs. Made them competitive with German planes...



I began to read this thread late and it seems that I cannot catch up because this is so active. But I have become so irritate to your posts that I answer to this message now.
1st: Russians did not pulled out the .30s from all their P-400s or P-39Ds - Ns. They pulled them out from some and kept them in some, that can easily be checked from photos. E.g. the first famous Soviet Airacobra ace Ivan Bochkov's P-400 had wing guns but e.g. Pavel Klimov's P-39D is photographed without wing guns. There also photos of P-39Ns with wing guns serving with active units.
2nd: Why would .30s be ineffective against unarmoured Japanese planes? Hit into pilot or into a metal fuel tank could be fatal, was it by .30 or .50. Most of men hit by .30 into back of the head were killed, weren't they?

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## P-39 Expert (Oct 14, 2020)

glennasher said:


> There's no need to expand further, you either get it, or you don't. By now, if you don't get it, you ain't gonna get it. Quit trolling.


When I said "Please expand above" I was instructing the sender to expand that condensed box so he could see my replies to his statements directed to me. Not trolling.


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## P-39 Expert (Oct 14, 2020)

Juha3 said:


> I began to read this thread late and it seems that I cannot catch up because this is so active. But I have become so irritate to your posts that I answer to this message now.
> 1st: Russians did not pulled out the .30s from all their P-400s or P-39Ds - Ns. They pulled them out from some and kept them in some, that can easily be checked from photos. E.g. the first famous Soviet Airacobra ace Ivan Bochkov's P-400 had wing guns but e.g. Pavel Klimov's P-39D is photographed without wing guns. There also photos of P-39Ns with wing guns serving with active units.
> 2nd: Why would .30s be ineffective against unarmoured Japanese planes? Hit into pilot or into a metal fuel tank could be fatal, was it by .30 or .50. Most of men hit by .30 into back of the head were killed, weren't they?


Sorry to irritate you. The primary reasons the .30s were deleted by the Russians were to 1. Save weight to improve climb rate/ceiling and 2. The .30s were not effective against armored German planes as compared to the 37mm cannon and the .50cal MGs.

I believe the .30s were deleted for these reasons on the vast majority of Russian P-39s. Of course with almost 5000 P-39s delivered to the Russians some would retain the .30s.

Regarding the effect on the Japanese planes, yes the .30s would be more effective than against armored German planes, but the need for better climb/ceiling was even more urgent since their G4M bombers operated at 18000'-22000'. Sure, more guns are better, but weight is also a primary concern and the P-39 still retained the 37mm cannon and two .50cal MGs.


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## fubar57 (Oct 14, 2020)

You believe....That's your rebuttal?


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## P-39 Expert (Oct 14, 2020)

XBe02Drvr said:


> No you don't.
> 
> 
> WRONG! You've been corrected on this at least twice, and yet you persist in this erroneous explanation. Critical engine is the engine most dangerous to lose, in this case, left engine. I earned my multi engine rating and multi instructor rating in planes of this sort, then instructed in them. The differences between critical and non-critical engines are due to P factor, and torque has next to nothing to do with it. The real killer here is asymmetric thrust and the yaw and roll it induces, and that happens with EITHER engine out, it's just a little bit worse with the critical engine out.
> Don't come to me with your shiny new Whizbang 260 looking for a multi engine rating! From what I've seen of your willingness to absorb new information if it conflicts with your preconceived notions, I wouldn't get in an airplane with you and put both our lives on the line for all the tea in China. Engine-out training is risky enough with a student who's got his/her head screwed on straight. You never know what creative new stunt they'll pull, out of confusion, misunderstanding, or nervousness. In your case it could easily be a suicide mission.


Apparently you don't understand "critical engine" either, see posts #603 and #605. And you don't need to be so snarky.


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## fubar57 (Oct 14, 2020)

A twin engine pilot that doesn't understand "critical engine"?

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## GrauGeist (Oct 14, 2020)

P-39 Expert said:


> The .30s were not effective against armored German planes


So that's why the RAF lost the battle of Britain.

Oh, wait...

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## P-39 Expert (Oct 14, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


Please expand above.


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## P-39 Expert (Oct 14, 2020)

GrauGeist said:


> So that's why the RAF lost the battle of Britain.
> 
> Oh, wait...


And that's why the RAF developed the 20mm cannon as fast as they could.


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## buffnut453 (Oct 14, 2020)

Given the inability of some people to accept that others might actually know better than they do, it's time to break out the obligatory General Sir Anthony Cecil Hogmanay Melchett quote:

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## GrauGeist (Oct 14, 2020)

P-39 Expert said:


> And that's why the RAF developed the 20mm cannon as fast as they could.


It's a shame the Yanks had to struggle against those flying tanks with their piddly .50MGs


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## DerAdlerIstGelandet (Oct 14, 2020)

P-39 Expert said:


> Apparently you don't understand "critical engine" either, see posts #603 and #605. And you don't need to be so snarky.



He is a dual engine commercial pilot. I think he understands critical engine very well.

People might be less snarky with you if you would stop pretending that you are a know it all, and listen to what people are telling. Your inaccuracies have been pointed out by many people here, and you clearly continue to blow them off. At first it was humorous, but now its a lil insulting really.

As I said you can regurgitate book knowledge all day long, but you clearly are incapable of putting it together.

The first step is to admit you are wrong. It’s ok, we all are from time to time. Besides it might humble you a lil.

My intent here is to not insult you, but damn man... Admit when you are wrong, listen to people with experience and knowledge in the matter and learn something.

I get the feeling you would argue with 

 BiffF15
about Eagle tactics just to be “right”.

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## buffnut453 (Oct 14, 2020)

DerAdlerIstGelandet said:


> He is a dual engine commercial pilot. I think he understands critical engine very well.
> 
> People might be less snarky with you if you would stop pretending that you are a know it all, and listen to what people are telling. Your inaccuracies have been pointed out by many people here, and you clearly continue to blow them off. At first it was humorous, but now it’s lil insulting really.
> 
> ...



Not holding my breath on that one. He knew better than "Buzz" Wagner, so the odds of any of us mere mortals being credited as knowledgeable (perhaps, perish the thought, even more knowledgeable than him) are slim to non-existent.

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## fubar57 (Oct 14, 2020)

DerAdlerIstGelandet said:


> I get the feeling you would argue with
> 
> BiffF15
> about Eagle tactics just to be “right”.


There's 3 F's there

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## windhund116 (Oct 14, 2020)

buffnut453 said:


> Not holding my breath on that one. He knew better than "Buzz" Wagner, so the odds of any of us mere mortals being credited as knowledgeable (perhaps, perish the thought, even more knowledgeable than him) are slim to non-existent.



Think that the term is _eristic_. Good trait for debating.

Eristic definition.

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## Peter Gunn (Oct 14, 2020)

DerAdlerIstGelandet said:


> *SNIP*
> 
> I get the feeling you would argue with
> 
> ...



_I_ would but I don't want to make 

 BiffF15
look bad...

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## pinsog (Oct 14, 2020)

I’ve never flown an F15 but I did stay in a Holiday Inn Express last night.

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## fubar57 (Oct 14, 2020)

Didn't they remove the wing guns on the F-15 as well?

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## buffnut453 (Oct 14, 2020)

fubar57 said:


> Didn't they remove the wing guns on the F-15 as well?



Yes, but they kept the armour plate around the gearbox.

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## Peter Gunn (Oct 14, 2020)

fubar57 said:


> Didn't they remove the wing guns on the F-15 as well?


From what I heard tell it turned the F-15 from mediocre into a real scorcher, except it apparently would tumble backwards through its own contrails.

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## SaparotRob (Oct 14, 2020)

windhund116 said:


> Think that the term is _eristic_. Good trait for debating.
> 
> Eristic definition.


Great. Now I’m learning English here too!

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## P-39 Expert (Oct 14, 2020)

DerAdlerIstGelandet said:


> He is a dual engine commercial pilot. I think he understands critical engine very well.
> 
> People might be less snarky with you if you would stop pretending that you are a know it all, and listen to what people are telling. Your inaccuracies have been pointed out by many people here, and you clearly continue to blow them off. At first it was humorous, but now it’s lil insulting really.
> 
> ...


Every single time I have been proven wrong in this thread I have replied "You are correct" to acknowledge. I was wrong about the propeller size on the P-40E and was wrong about the oil tank protruding slightly (a few inches) into the engine compartment on the P-39. But I have been absolutely right on everything else discussed here and backed my statements up with facts and sources. 

I really hope I am not irritating your members here. I shouldn't have made my handle "P-39 Expert", I thought it would be funny like FUBAR. But there is very little humor in this group. 

The point I am attempting to make is a whole lot of the information on the P-39 that we have heard for 75 years is absolutely false. And every time I make a statement on here and back it up with facts someone gets mad and comes back with a snarky reply telling me I don't know what I'm talking about. I'm the one being insulted here. That's okay, people don't like being contradicted. But this is a forum so discussion should be permitted, even with people who don't necessarily agree with you. Everything I say here is backed up by wwiiaircraftperformance.org or another verifiable source. Most of the information on the P-39 in wwiiaircraft is new since 2012 and contradicts most of what has been published prior to that. 

I sure don't mean to insult anyone here and have made every effort to avoid snarky comments. Sorry if I have offended anyone.

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## buffnut453 (Oct 14, 2020)

Peter Gunn said:


> From what I heard tell it turned the F-15 from mediocre into a real scorcher, except it apparently would tumble backwards through its own contrails.



That's because it has an aft CofG, silly!

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## XBe02Drvr (Oct 14, 2020)

Definitions of eristic:
1
*adj: given to disputation for its own sake and often employing specious arguments*

'nuff said!


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## XBe02Drvr (Oct 14, 2020)

P-39 Expert said:


> Everything I say here is backed up by wwiiaircraftperformance.org or another verifiable source. Most of the information on the P-39 in wwiiaircraft is new since 2012 and contradicts most of what has been published prior to that.



The physics of twin engine performance with an engine out hasn't changed since Moby Dick was a minnow. Your sources are either misinformed or you don't understand them; probably the latter. None of my former multi engine students have managed to kill themselves in an airplane yet, so it could be I know what I'm talking about.
Cheers,
Wes


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## DerAdlerIstGelandet (Oct 14, 2020)

P-39 Expert said:


> Every single time I have been proven wrong in this thread I have replied "You are correct" to acknowledge. I was wrong about the propeller size on the P-40E and was wrong about the oil tank protruding slightly (a few inches) into the engine compartment on the P-39. But I have been absolutely right on everything else discussed here and backed my statements up with facts and sources.
> 
> I really hope I am not irritating your members here. I shouldn't have made my handle "P-39 Expert", I thought it would be funny like FUBAR. But there is very little humor in this group.
> 
> ...



You have not been absolutely right. Especially when it comes to WB, CG, how moving weight in an aircraft is affected, critical engines, etc. You regurgitate knowledge and data without understanding it. That is what people are correcting you on. People who actually work and do these things. You have a guy in here who has actually worked on one, and you argue with him. You have a twin engine commercial pilot telling you that your understanding of critical engines is wrong. Do you know how ridiculous that sounds when you do that? It sounds like a War Thunder video gamer telling a pilot how his aircraft works. That is why people get snarky with you. You invite it. Go back and look at your exchange with 
X
 XBe02Drvr
. He is a commercially licensed twin engined pilot. He used to fly 1900D’s a notoriously tail heavy aft CG twin engine turboprop aircraft. He has reached out to you on multiple occasions to correct you, and you blow him off. Of course he got snarky!

It’s obvious you have read a ton of books, and have a lot of knowledge from those books, now let people help you put it all together.


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## GrauGeist (Oct 14, 2020)

DerAdlerIstGelandet said:


> I get the feeling you would argue with
> 
> BiffF15
> 
> ...


What we need, is a MiG pilot (one em) to get into a debate with Biff (two effs) - I would pay money to see that!

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## XBe02Drvr (Oct 14, 2020)

DerAdlerIstGelandet said:


> I can still hear my instructor...
> 
> _Fly the plane, fly the plane, fly the plane!_


"Don't let it fly you! Five degrees bank into the working engine. HOLD YOUR HEADING! DON'T let it creep around toward the dead engine! Right leg getting a little tired? Trim it out! Zero or positive rate? Gear up. HOLD HEADING! Got VYse yet? Alright, now EASE those flaps up. HOLD HEADING, HOLD VYse! Positive rate? Yes? Now identify: 'dead foot, dead engine'. Say it out loud, 'left engine'. Confirm: ease LEFT throttle back; any change? No? LEFT throttle, IDLE; LEFT prop, FEATHER; LEFT mixture, IDLE CUTOFF. Now HOLD HEADING AND VYse, and execute engine shutdown checklist." As the treetops whiz by the wingtips.
A light piston twin is a pretty marginal flying machine on one engine. If you can't be in a clean VYse climb before you reach the departure end, you'd be better off to put it back down after a takeoff engine failure and get on the brakes. Better to go off the end rightside up at 1/3 to 1/2 flying speed than into the treetops beyond the overrun inverted at full flying speed. This decision needs to be made and rehearsed based on local conditions before you push the throttles up for takeoff. "THIS is the time I will lose an engine at Vr, and this is what I'm going to do." Shortens your "deer in the headlights" freeze time when it actually happens.

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## Peter Gunn (Oct 14, 2020)

GrauGeist said:


> What we need, is a MiG pilot (one em) to get into a debate with Biff (two effs) - I would pay money to see that!



Debate hell, I'd pay good money to see them go at it in simulators.

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## Peter Gunn (Oct 14, 2020)

P-39 Expert said:


> *SNIP*
> 
> But there is very little humor in this group.
> 
> *SNIP*


Bruh... have you read this thread?

P.S. I for one think you're pretty well read and have a good book knowledge of your subject, also kudos for keeping it civil, not easy when several are pointing out flaws with your arguments. I have found this thread both informative and entertaining and I urge you to take to heart what the other denizens here are saying to you. You can learn a lot from them and I do believe you have much to share with this group, just dial up the humble meter a bit and you'll be fine.

Cheers.

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## DerAdlerIstGelandet (Oct 14, 2020)

Peter Gunn said:


> Bruh... have you read this thread?
> 
> P.S. I for one think you're pretty well read and have a good book knowledge of your subject, also kudos for keeping it civil, not easy when several are pointing out flaws with your arguments. I have found this thread both informative and entertaining and I urge you to take to heart what the other denizens here are saying to you. You can learn a lot from them and I do believe you have much to share with this group, just dial up the humble meter a bit and you'll be fine.
> 
> Cheers.



Well said. No one thinks P39 Expert is an idiot with no value to the forum. He is very well read, it is just a matter of putting it all together. He adds a lot to this forum and the discussion. This thread is very informative.

but...

When one person corrects you, you can have a debate, when multiple people with working knowledge of the subject begin to correct you maybe its time to think maybe you could learn a thing or two.

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## XBe02Drvr (Oct 14, 2020)

DerAdlerIstGelandet said:


> It’s obvious you have read a ton of books, and have a lot of knowledge from those books, now let people help you put it all together.


He needs a little actual hands-on stick time. Betcha he's never flown in anything but an airliner. Any volunteers? I would if I could still pass a physical. Except it's nigh impossible to find a rental plane or small airport flight school or instructor any more. Insurance costs and the university affiliated "pilot factories" have put them out of business.

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## DerAdlerIstGelandet (Oct 14, 2020)

XBe02Drvr said:


> He needs a little actual hands-on stick time. Betcha he's never flown in anything but an airliner. Any volunteers? I would if I could still pass a physical. Except it's nigh impossible to find a rental plane or small airport flight school or instructor any more. Insurance costs and the university affiliated "pilot factories" have put them out of business.



Someday I will have my CFI, and then can let Karma come back and bite me in my ass for always trying to kill my instructor.

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## XBe02Drvr (Oct 14, 2020)

DerAdlerIstGelandet said:


> and then can let Karma come back and bite me in my ass for always trying to kill my instructor.


DITTO! I was even worse than "Ex-spurt" here when I first started flying. Couldn't pack anything new in on top of all the "mis-info" and Caidinisms my head was stuffed with. I KNEW IT ALL and was in need of some humble meter adjustments by my instructors. These were accomplished with glee upon my fragile E3 ego by the various Chief Petty Officers and Lieutenant JGs who instructed at the flying club. I was eating a lot of crow with humble pie for dessert. It's a wonder they put up with me. I wouldn't have. I've taught pilots who were "naturals", and many more that weren't. I definitely wasn't.


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## GrauGeist (Oct 14, 2020)

I certainly wouldn't qualify, as I was just rated VFR.
The upside to that, is I was taught by WWII combat pilots and it was interesting to note that the former Army pilots had a much different approach to things than the one, who was a former VMF-212 Corsair driver.
Army: good job, nice handling!
Marine: WTF was that? Are you trying to kill my machine? Do NOT kill my machine!

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## P-39 Expert (Oct 14, 2020)

DerAdlerIstGelandet said:


> You have not been absolutely right. Especially when it comes to WB, CG, how moving weight in an aircraft is affected, critical engines, etc. You regurgitate knowledge and data without understanding it. That is what people are correcting you on. People who actually work and do these things. You have a guy in here who has actually worked on one, and you argue with him. You have a twin engine commercial pilot telling you that your understanding of critical engines is wrong. Do you know how ridiculous that sounds when you do that? It sounds like a War Thunder video gamer telling a pilot how his aircraft works. That is why people get snarky with you. You invite it. Go back and look at your exchange with
> X
> XBe02Drvr
> . He is a commercially licensed twin engined pilot. He used to fly 1900D’s a notoriously tail heavy aft CG twin engine turboprop aircraft. He has reached out to you on multiple occasions to correct you, and you blow him off. Of course he got snarky!
> ...


Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery. Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters. 

I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.

I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.


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## Juha3 (Oct 14, 2020)

P-39 Expert said:


> Sorry to irritate you. The primary reasons the .30s were deleted by the Russians were to 1. Save weight to improve climb rate/ceiling and 2. The .30s were not effective against armored German planes as compared to the 37mm cannon and the .50cal MGs.
> 
> I believe the .30s were deleted for these reasons on the vast majority of Russian P-39s. Of course with almost 5000 P-39s delivered to the Russians some would retain the .30s.
> 
> Regarding the effect on the Japanese planes, yes the .30s would be more effective than against armored German planes, but the need for better climb/ceiling was even more urgent since their G4M bombers operated at 18000'-22000'. Sure, more guns are better, but weight is also a primary concern and the P-39 still retained the 37mm cannon and two .50cal MGs.



Have you any proof that the .30s were deleted on the vast majority of Russian P-39s? I can only say that from the photos I have seen of Soviet P-400s/P-39Ds - Ns serving with combat units from which one can see at least one wing leading edge I would say about a half had wing guns and another half had not. The problem is that from most of photos one cannot see the critical part of a leading edge because of that the photo is taken from an angle that does not show a leading edge, it shows only the cockpit area or the nose, or there are men front of the wing.

E.g. many if not most/all of the P-39s of 103 GIAP/2 GIAK PVO in autumn 1943 had their .30s in place. The fighters of the PVO were used as interceptors because the PVO was the air defence arm of the Soviet armed forces and still at least some of its units seem to have thought that the .30s were more useful against German planes than the weight of them and their ammunition was detrimental to their climbing ability. And after all we are talking on P-400s/P-39s of the USAAF in PNG in 1942 facing unprotected Japanese planes and the usefulness of .30s in that situation when after all the 37 mm cannon was suffering badly from unreliability.

Ps: but after all you had kept this very interesting thread alive 34 pages. Thumps up for that!

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## XBe02Drvr (Oct 14, 2020)

Ivan1GFP said:


> My guess is that an experienced pilot probably would have put the propeller into manual control and tried to adjust the RPM to something reasonable for the power setting.


Most constant speed prop failures result from failure of the pitch change mechanism itself, leaving no control of prop pitch at all. There are some modes in which a governor can fail and pitch can be controlled manually, but these are pretty rare.

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## XBe02Drvr (Oct 14, 2020)

]



P-39 Expert said:


> I understand WB and CG as well as the next person on here. It's not brain surgery.


If you do truly understand W&B, you certainly have a problem communicating it to professionals here who work with it regularly and have for a long time.


P-39 Expert said:


> I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it.


Nobody's saying pilots and mechanics are the sole authorities, just that their training and experience gives them the context to better distill raw data derived from books and publications into credible information. They've walked the walk which gives them an edge at talking the talk. Researchers who aren't aviation professionals, but have done rigorous broad based research, carefully vetting sources and examining and comparing their credibility, are also respected here, and we have some onboard that you've tried to correct. Not trying to be a snark, just trying to point out some truths we hold to be self-evident.

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## XBe02Drvr (Oct 14, 2020)

DerAdlerIstGelandet said:


> He is a commercially licensed twin engined pilot. He used to fly 1900D’s


Actually ATP licensed. Never got to fly a "D", as they were just coming out when our company was driven out of business. Pilots who've flown both said they liked the "C" better. Better performance and lighter on the controls.


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## XBe02Drvr (Oct 14, 2020)

GrauGeist said:


> it was interesting to note that the former Army pilots had a much different approach to things than the one, who was a former VMF-212 Corsair driver.
> Army: good job, nice handling!
> Marine: WTF was that? Are you trying to kill my machine? Do NOT kill my machine!


When your life has been defined by landing bentwings on a boat, you might be a little less tolerant of sloppy performance on landing. Gyreens had to carrier qual, too.


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## Ivan1GFP (Oct 14, 2020)

Hello P-38 Expert,



P-39 Expert said:


> *When I say "flat trajectory" it is in comparison to the trajectory of the accompanying .50cal MGs. so that they can be used together. Trajectory drop is only 22" greater than the .50s at 400yds. Relatively flat. His source is Operational Suitability Tests at Eglin Field. By the way he quotes muzzle velocity as 2600-3000fps, a little better than the 2000fps you use. *



Do you have any information on the type of ammunition used in those Operational Suitability tests at Eglin Field?
The actual ammunition typically used in the 37 mm M4 cannon used a projectile weighing just a bit over 600 grams and with that ammunition, it was getting a muzzle velocity typically stated as 2000 fps.
Can you find a source that states otherwise?

Guns with quite differing velocities can be zeroed at the same range if the lower velocity guns are given a bit more elevation.
There is no problem if the target and gun platform are not moving. The problem comes when the gun platform is pulling G as it would be for a deflection shot. In that case, the slower projectile will drop significantly more and depending on the amount of G, will probably not hit to the same point of impact.
Shortround6 gave a pretty thorough explanation. You need to read it and understand it.



P-39 Expert said:


> *So why was 240lbs of armor plate/glass needed on a P-39 when only 111lbs were needed on a contemporary P-40E?*



Glad you finally asked that question.
The basic design of the P-39 put a lot of vulnerable pieces such as the oil tank, coolant tanks, and engine in the back into the most likely path for incoming fire.
Many of these accessories in the P-40 have very limited angles of vulnerability. From the front, the engine is in the way. From the back, the armoured cockpit area is in the way.
Getting a tracking shot against these vulnerable areas on fighter with an engine in front is also a bit more difficult considering the direction of flight of attacking aircraft and target.

By the way, as a general comment, I agree with some of the others here that you are probably quite well read on this subject.
My own opinion is that it is highly unlikely this is the first time that you have seen these arguments that contradict your ideas.
My belief is that you tend to discount any ideas that disagree with yours without evaluating them for validity.

- Ivan.

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## vikingBerserker (Oct 14, 2020)

Juha3 said:


> Have you any proof that the .30s were deleted on the vast majority of Russian P-39s? I can only say that from the photos I have seen of Soviet P-400s/P-39Ds - Ns serving with combat units from which one can see at least one wing leading edge I would say about a half had wing guns and another half had not.



According to "Soviet Air Power in World War 2" by Yefim Gordon 
Page 446: The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s so it could match the Bf 109F-4/G-2/G-4 as well as the Soviet Lagg 5 and Yak-9s
Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.
..and of course the P-63s didn't have them either.

Not sure of that covers the vast majority however.


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## fubar57 (Oct 14, 2020)

Went through these books, 151 page of photos....








​.....18 of which showed wings. 15 had wing guns, from the -D to -M. The three that never had wing guns were Ms

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## GregP (Oct 14, 2020)

This might be interesting ...

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## P-39 Expert (Oct 14, 2020)

Ivan1GFP said:


> Hello P-38 Expert,
> 
> 
> 
> ...



Please expand above.


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## fubar57 (Oct 14, 2020)

vikingBerserker said:


> Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.



There's a photo of one of those aircraft in this book




​


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## FLYBOYJ (Oct 14, 2020)

P-39 Expert said:


> Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery.


Based on your comments, you really don't. You seem to ignore the ramifications of an aft CG (even though you're within manufacturer's limits) and some of your terminology in trying to explain yourself further revealed your understanding of , or lack of the subject.


P-39 Expert said:


> Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.


 Hmmmm. NO. Wes explained it well to you.


P-39 Expert said:


> I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.


 I'll give you the benefit of the doubt, but read on...


P-39 Expert said:


> *I'm not a pilot nor a mechanic.* But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.


And understand that some of us have "been there/ done that" and it's not to toot our horn but understand that at the same time you have tied to dispel some myths and folklore about the P-39, we have seen in our experiences situations that either confirm or disqualify what was said 75 years ago and having someone with either no flight or wrench twisting experience trying to tell us about something we've done for years, well I think you should get the message. Some of us been around these machines and then some, perhaps listen more and ask questions, but I'll say in the same breath I (we) are always learning and you have enlightened me on many aspects of the P-39!

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## windhund116 (Oct 14, 2020)

XBe02Drvr said:


> He needs a little actual hands-on stick time. Betcha he's never flown in anything but an airliner. Any volunteers? I would if I could still pass a physical. Except it's nigh impossible to find a rental plane or small airport flight school or instructor any more. Insurance costs and the university affiliated "pilot factories" have put them out of business.



Are computer game/flight simulators pretty good at giving the user some 3D awareness? What are the best ones for PC and PlayStation?

Thanks!


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## vikingBerserker (Oct 14, 2020)

vikingBerserker said:


> According to "Soviet Air Power in World War 2" by Yefim Gordon
> Page 446: The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s so it could match the Bf 109F-4/G-2/G-4 as well as the Soviet Lagg 5 and Yak-9s
> Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.
> ..and of course the P-63s didn't have them either.
> ...



Same book on Page 434 listing the Imported aircraft in inventory as of May 1st, 1945 shows 84% of the 2,272 P-39s still in service had no wing guns.

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## FLYBOYJ (Oct 14, 2020)

windhund116 said:


> Are computer game/flight simulators pretty good at giving the user some 3D awareness? What are the best ones for PC and PlayStation?
> 
> Thanks!



This has been beat to death on this forum. PC sims can provide some basic perspectives and some good "numbers" (I use one to help me when I was earning my instrument rating, but understand in the end, they are toys. 

So to answer your question; "Are computer game/flight simulators pretty good at giving the user some 3D awareness?"

_*"Include the toxic cockpit fumes, the extreme heat or cold, sitting on a lumpy seat while restrained with belts that almost cut through your soaking wet flight suit and have a 300 pound woman sit on you every time you pull Gs - oh while breathing smelly oxygen through a face mask that smells like a prophylactic." *_

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## DerAdlerIstGelandet (Oct 14, 2020)

P-39 Expert said:


> Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery. Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.
> 
> I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.
> 
> I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.



I never said that only pilots and mechanics can know things. I never said they are the final authority. Did I? Of course not. They don’t know everything either, as we have all stated. You know much smoke I have had blown up my ass by fellow mechanics and pilots? Shit, try being around military mechanics and pilots, especially AH-64 pilots. You will hear nothing but over embellished “No Shit There I Was Stories”. 

But when not one, not two, not three, but four or five or more point out you are not understanding something correctly, even if your data might be ok, chances are they are on to something, right?

Anyone can read books and data, but that does not mean they get it completely. That does not mean they understand it completely.I can read a book on medicine, come in here and post the data all I want. But if a doctor comes in and says, that it is not how it works, who is probably right?

And there is nothing wrong with not knowing everything. There is nothing wrong with not understanding anything. No one thinks you are stupid either. Blowing off actual experts in the field of specific subjects, though, sure as hell comes off as snarky to me.

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## Ivan1GFP (Oct 14, 2020)

Hello P-39 Expert



P-39 Expert said:


> *Matthews also lists a Dr. W. F. Atwater, U.S.Army Ordnance Museum, Aberdeen Proving Ground, Md. *



Does this mean that you are sticking with your claim that the typical muzzle velocity of the 37 mm M4 cannon as installed in the P-39 was achieving 2600 - 3000 fps?



P-39 Expert said:


> *The 37mm gun didn't have to be used in conjunction with the .50s. It had a separate firing button on the stick and could be used independently.*



This sounds like you are accepting that the 37 mm cannon and .50 cal MG did not work well together.
Be careful. This is not in agreement with what you appear to be stating above.



P-39 Expert said:


> *The P-40 also has a big fat fuel tank right behind the pilot.*



The Airacobra also has a fairly large area in the wings occupied by fuel tanks that are no better protected.



P-39 Expert said:


> *Absolutely. The ideas you are repeating have been around since the war ended. What I am trying to show you is information that has surfaced more recently from wwiiaircraftperformance.org, recently ('90s) released information from the Russians, and other more current sources. Keep believing the older information if it makes you comfortable, but the P-39 was quite a different airplane than we all have been led to believe.*



I have also read through a fair number of those reports from ww2aircraftperformance.
What they tend to indicate is that for specific examples, often the performance may be a touch higher than one might have expected. I am not discounting that information. I am just noting that the numbers from those test reports do not seem to be supported by actual combat reports. The other question to ask is whether the results of the test report are representative of the type or just of a particularly good example.
There are also test reports from the same time period that do seem to be much more in line with performance in the field.

Also, many of your CLAIMS of performance increases are based on ESTIMATES of the results of stripping off of "unnecessary" weight in equipment that the operators determined was necessary.

You also might want to note that many of the issues that have been brought up have been about handling problems, CoG issues, overheating problems and other issues which have not received mention in reports at ww2aircraftperformance. So far, your response to CoG issues seems to be to declare them to be incorrect. Interesting!

- Ivan.


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## DerAdlerIstGelandet (Oct 14, 2020)

XBe02Drvr said:


> Actually ATP licensed. Never got to fly a "D", as they were just coming out when our company was driven out of business. Pilots who've flown both said they liked the "C" better. Better performance and lighter on the controls.



I’ve never flown a C. Only bled the hydraulic brake system on one before. I’ve done a test flight on a D (As a mechanic), done dozens of ground run and taxi tests, and completed two complete phases on two D’s.

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## BiffF15 (Oct 14, 2020)

XBe02Drvr said:


> "Don't let it fly you! Five degrees bank into the working engine. HOLD YOUR HEADING! DON'T let it creep around toward the dead engine! Right leg getting a little tired? Trim it out! Zero or positive rate? Gear up. HOLD HEADING! Got VYse yet? Alright, now EASE those flaps up. HOLD HEADING, HOLD VYse! Positive rate? Yes? Now identify: 'dead foot, dead engine'. Say it out loud, 'left engine'. Confirm: ease LEFT throttle back; any change? No? LEFT throttle, IDLE; LEFT prop, FEATHER; LEFT mixture, IDLE CUTOFF. Now HOLD HEADING AND VYse, and execute engine shutdown checklist." As the treetops whiz by the wingtips.
> A light piston twin is a pretty marginal flying machine on one engine. If you can't be in a clean VYse climb before you reach the departure end, you'd be better off to put it back down after a takeoff engine failure and get on the brakes. Better to go off the end rightside up at 1/3 to 1/2 flying speed than into the treetops beyond the overrun inverted at full flying speed. This decision needs to be made and rehearsed based on local conditions before you push the throttles up for takeoff. "THIS is the time I will lose an engine at Vr, and this is what I'm going to do." Shortens your "deer in the headlights" freeze time when it actually happens.



Wes,

I went through 800ALLATPS for my ATP back in 96. I did two flights in a Seminole with an "IP", then did the check with a retired USAF guy as the designated FAA Examiner. I was completely shocked at the performance of the Seminole engine out. It was slightly better than "the good engine gets you to the crash site". But not much.

I figured out during the second sortie with the "IP" that he was just there building time, and was very light on the IP ability. Basically self taught with a safety observer along. So we are flying towards the end of the second flight when he casually says to me, lets make this one a full stop. I know full well that I'm doing my check ride after this flight unless I want to buy a "third" sortie. Ugh. They want you to buy a third sortie, and the kid doesn't care about anything but logging the shortest flight possible as he gets some sort of kick back on every 1/10th under a preset amount. So after he makes his comment I say nope, lets do two more patterns and I will make the call then. He looks at me a bit flustered, and then mutters okay. I was pissed to say the least, and briefed all the guys in my wing on how things worked so they would be prepared.

I show up for the check ride and the examiner is on the phone. He motions for me to take a seat and starts the oral while he is on the phone. First question is what are the engine oil limits. I look at him like an RCA dog, and he laughs and says it's a color. I respond "in the green". He laughs again and continues the oral, all the while having a great convo with someone else. Then we step, he follows me through the walk around, then before we crawl in I hand him the weather and NOTAMS while briefing him. He looks at me like I have three heads, and replies "I've been doing this for ten years and you are the first guy who ever checked the WX & NOTAMS". I'm thinking to myself WTFO (what were the other guys thinking as the WX / NOTAMS are the basics), but hey he seems happy so maybe that will carry over to the rest of the sortie. I taxi out and get permission from tower to take off. So I do what every fighter guy does, which is switch to departure before starting the takeoff roll. He didn't notice and there was some frequency change hair pulling going on shortly after take off. Fighter guys do this as we take off via interval take offs, and the first guy will be 4-5 miles airborne before #4 gets his gear up (and you want everyone on the same freq - if you abort you have to switch back to tower to notify them). We go flying about the Pensacola local area, shoot an approach then I notice him reach down between the seats to shut off the fuel to one of the engines. Sure enough it sputters and dies, and I go through the relight / restart procedure and get it running. Except now it's running rough as hell. So for the next 30 minutes I finish the profile and he farts with the engine the entire time. I figure if he is busy with that he isn't paying total attention to me so all the better. 

We finally land and he tells me i pass. He then fills out my new license and when he is done I ask him for an honest debrief. He looks at me again like I'm a three headed snake, then laughs and says you fly great, but suck on the radios. I laughed and agreed.

Cheers,
Biff

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## XBe02Drvr (Oct 14, 2020)

windhund116 said:


> Are computer game/flight simulators pretty good at giving the user some 3D awareness? What are the best ones for PC and PlayStation?
> 
> Thanks!


Flight sim games CAN be useful at gaining practice with aircraft procedures, provided the source data for the procedures is verifiably accurate, and the program is patched to show the actual cockpit configuration in question. I've practiced on my FSX computer with airline pilot friends who were waiting for their training date at the schoolhouse for an upgrade or an equipment transition, but only under certain conditions. They've got to have the actual current AFM, checklists, procedures, and flight maneuver profiles for the version they'll be flying, and I have to be able to find and download patches for the aircraft version and cockpit configuration they'll be flying. For procedures practice, they always need another cockpit crew member, something I'm happy to do.
Situational awareness? The computer sim helps that in some ways due to enhanced system and procedural awareness, which is useful in an airline scenario, but in terms of overall flying ability, it's no substitute for the real thing, be it a full function simulator or an actual airplane.

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## DerAdlerIstGelandet (Oct 14, 2020)

FLYBOYJ said:


> This has been beat to death on this forum. PC sims can provide some basic perspectives and some good "numbers" (I use one to help me when I was earning my instrument rating, but understand in the end, they are toys.
> 
> So to answer your question; Are computer game/flight simulators pretty good at giving the user some 3D awareness?
> 
> _*"Include the toxic cockpit fumes, the extreme heat or cold, sitting on a lumpy seat while restrained with belts that almost cut through your soaking wet flight suit and have a 300 pound woman sit on you every time you pull Gs - oh while breathing smelly oxygen through a face mask that smells like a prophylactic." *_



The good quality ones can be good for learning procedural stuff, like for instrument flying like you pointed out, but thats about it.

I asked my instructor if I should invest in one for my private license. He forbid it.  Told me to fly my couch every evening.

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## XBe02Drvr (Oct 14, 2020)

FLYBOYJ said:


> _*"Include the toxic cockpit fumes, the extreme heat or cold, sitting on a lumpy seat while restrained with belts that almost cut through your soaking wet flight suit and have a 300 pound woman sit on you every time you pull Gs - oh while breathing smelly oxygen through a face mask that smells like a prophylactic."*_


Ahh...sheer ecstacy!

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## GrauGeist (Oct 14, 2020)

FLYBOYJ said:


> "Include the toxic cockpit fumes, the extreme heat or cold, sitting on a lumpy seat while restrained with belts that almost cut through your soaking wet flight suit and have a 300 pound woman sit on you every time you pull Gs - oh while breathing smelly oxygen through a face mask that smells like a prophylactic."


And some types were noisey as hell, too.

This day and age, we have nice David Clark or Flightcomm headsets, but back then, the speakers were bakelite with hard rubber or leather on the rim and crushed your ears - while doing squat for cancelling out the engine noise.

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## XBe02Drvr (Oct 14, 2020)

BiffF15 said:


> We finally land and he tells me i pass. He then fills out my new license and when he is done I ask him for an honest debrief. He looks at me again like I'm a three headed snake, then laughs and says you fly great, but suck on the radios. I laughed and agreed.


On my first CFI attempt, at Miami (Opa Locka) GADO, the FAA Inspector gave me a thorough oral, then put me through my paces in the air, then as we were getting out of the plane, was summoned into the office, just after he'd said "Nice flight". Five minutes later he came out of the office and handed me a DISAPPROVAL OF APPLICATION notice and said: "You fly well, but your teaching needs work. See you again some day".
"Can you at least brief me on where my teaching was inadequate?" (I had worked long and hard on the teaching part with my instructor, who was very good at it, and got a glowing recommendation)
"No, you need to figure that out for yourself. Go reread your _Flight Instructor Handbook _and_ Principles of Instruction, _you'll get it eventually. See you then. Safe flight home!" This after he'd complimented me on the lesson plans and lecture in the oral.
When I got back to the flying club, my instructor said he figured that would happen. He said the FAR 141 FAA approved flight school downtown had sent three poorly prepared CFI candidates in a row to the Miami GADO, and they'd all failed, resulting in "corrective action" being taken against the school (read the riot act), and the Feds couldn't afford to have one of their approved schools shown up by an FAR 91 club operation. "You'll do better next time."

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## Shortround6 (Oct 14, 2020)

I would note that the americans used a rather confusing set of 37mm guns and ammo in the P-39 through P-63 series.

The P-39s used the M4 cannon that fired the 37mm X 145mm cartridge.






this had about 2000fps velocity.

Many of the P-63s got the M10 cannon which used the same ammo, fired just a bit faster and used an actual belt instead of magazine and held more ammo. Used the same ammo as the M4 cannon.

_however _there was also an M9 cannon which was flown in one (?) P-63D-1 which used the same ammo (or at least cartridge case) as the 37mm AT gun and the 37mm AA gun.
37mm x 223mm ammo




this is the 2600-3000fps ammo. This automatic cannon was used on some very late war PT boats much like the earlier M4 cannon.

Now what adds to the confusion is that M4 cannon it it's early days was known as the T9 cannon.
The T9 and the M9 had nothing to do with each other except the 37mm diameter of the shells and barrels.

Some old authors claim the M9 was used in the P-39 and P-38 (?) but it never happened. It does thoroughly muddy up the waters concerning the velocity of the shells fired by the P-39 though.

Source for most of this is "Flying Guns World War II" by Anthony Williams and Dr Emmanuel Gustin.

Page 195 of Birch Mathews book has a sidebar that says, in part,
" The following data pertains to the M9 cannon, but these characteristics are representative of all Kingcobra 37mm weapons" and goes on to give barrel lengths, weights and velocities that are correct for the M9 cannon. Just before the above quote it is stated that only one P-63D used the M9 cannon.
BTW the weight for the M9 cannon was 405lbs without magazine.

You can't have it both ways, you either have the high velocity heavy cannon or you have the low velocity but lighter weight M4/M10 cannon.
You don't have a light 37mm gun with high velocity.

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## XBe02Drvr (Oct 14, 2020)

Shortround6 said:


> You don't have a light 37mm gun with high velocity.


I don't have my featherweight .30-06 any more, either. The fun went out of it when shoulder pain became permanent.

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## Mad Dog (Oct 14, 2020)

wuzak said:


> How many single engine fighters in WW2 had feathering props?


IIRC, the RR Merlin II was the first version of the Merlin with the ability to take a Rotol or de Ha.villand variable pitch prop with feathering capability, though the feathering props were put on RAF bombers before they were put on Spitfires and Hurricanes with the Merlin III. The VDM prop on the Bf109E-3 was also capable of fully-feathering. With regard to the Allison in the P-39 (and P-38, P-40 and P-51A), I know at least the Aeroproducts prop on the P-39Q (V01710-89) had full feathering, and I think the Curtis Electric on the P-38J (V-1710-89/91) has full-feathering, though I'm not sure if that was the same Aeroproducts and Curtis props as fitted to the earlier P-39s. But I suspect even the XP-39 had feathering capability seeing as Curtis had props with full feathering as early at least as 1937 (see here)


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## Shortround6 (Oct 14, 2020)

XBe02Drvr said:


> I don't have my featherweight .30-06 any more, either. The fun went out of it when shoulder pain became permanent.



Your not supposed to shoot it (much) just carry it

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## GrauGeist (Oct 14, 2020)

XBe02Drvr said:


> I don't have my featherweight .30-06 any more, either. The fun went out of it when shoulder pain became permanent.


Since my wreck several years ago, I haven't been able to shoot my .300 Savage, but I still have it, she's a beauty to behold.


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## pinsog (Oct 14, 2020)

Mine are great to shoot but suck to carry, 375 Remington ultra mag 9 pounds 8 ounces 26 inch barrel, 458 Lott 10 pounds 2 ounces, 300 win mag 12 pounds 8 ounces 28 inch barrel, 22-250 ackley improved 17 pounds 4 ounces

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## Ivan1GFP (Oct 14, 2020)

pinsog said:


> Mine are great to shoot but suck to carry, 375 Remington ultra mag 9 pounds 8 ounces 26 inch barrel, 458 Lott 10 pounds 2 ounces, 300 win mag 12 pounds 8 ounces 28 inch barrel, 22-250 ackley improved 17 pounds 4 ounces



Hello pinsog,

All those critters weigh just a bit less than a M1927 Thompson Carbine with a 50 round drum. (A bit over 18 pounds.)
That had to be the heaviest pistol I have ever fired. Yes, it CAN be fired with one hand.

- Ivan.

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## pinsog (Oct 14, 2020)

Ivan1GFP said:


> Hello pinsog,
> 
> All those critters weigh just a bit less than a M1927 Thompson Carbine with a 50 round drum. (A bit over 18 pounds.)
> That had to be the heaviest pistol I have ever fired. Yes, it CAN be fired with one hand.
> ...


Shot a full auto Thompson sub machine gun one time at a range. Very nice weapon. My 22-250 is a long range benchrest varmint gun, the 300 win mag is a longer range benchrest varmint gun. The 375 ultra mag is my deer rifle


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## Mad Dog (Oct 15, 2020)

XBe02Drvr said:


> Mad Dog, what's your information source for these statements? The Curtiss Electric prop we had at mech school was not at all like this.....


 I do recall that the Curtis Electric prop in the P-39K/L had a manual speed/angle control, but the Aeroproducts one did not. No idea about the earlier P-39s that might have been used in training (P-400s, P-39C/D, etc.). If anyone has a flight manual for the early P-39s it should show the propeller controls by the mixture controls to the left side of the instrument panel.
One interesting bit of tech with the Curtis Electric prop (sorry, do not know if this applied to the Aeroproducts prop) was that it had a little heating element to keep the hydraulic fluid and lubricating grease from freezing at altitude. I guess that would be another source of failure if the heating element burned out.

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## Ivan1GFP (Oct 15, 2020)

pinsog said:


> Shot a full auto Thompson sub machine gun one time at a range. Very nice weapon. My 22-250 is a long range benchrest varmint gun, the 300 win mag is a longer range benchrest varmint gun. The 375 ultra mag is my deer rifle



That .375 Ultra Mag sounds like a bit of overkill for deer? I only have perhaps two rifles that are suitable for deer in this area though I don't hunt and have never hunted (unless you count insects). Just about everything else is a heavy scoped gun or collectible (to me) or service rifle type. My preference is mostly .308 semi autos these days.
My Wife recently got into bicycling and commented that the plastic valve stem cap on one of my Daughter's bikes had disintegrated.
I told her that those caps were probably almost two decades old so it wasn't surprising. They were salvaged along with metal caps from valve stems that I sometimes found when processing wheel weights for cast bullets. I literally went through hundreds of pounds of wheel weights back then for black powder guns, .45-70 and pistols. Lead doesn't actually go far when you are only getting about 14-15 bullets per pound.

- Ivan.


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## GrauGeist (Oct 15, 2020)

Ivan1GFP said:


> Hello pinsog,
> 
> All those critters weigh just a bit less than a M1927 Thompson Carbine with a 50 round drum. (A bit over 18 pounds.)
> That had to be the heaviest pistol I have ever fired. Yes, it CAN be fired with one hand.
> ...


My Stepdad always tasked me with loading the drum for his Thompson.
Yeah, there was a winding key on it, but one slip while sticking a .45 round in and there goes your thumbnail.
I much preferred the stick mags...


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## Stig1207 (Oct 15, 2020)

Interesting site Oleg Kaminsky in Russian, but Google translate works reasonably.

This particular article Messerschmitts do not want to burn and fall has a lot of Airacobra victory claims in a couple of weeks in June 1944. I was expecting a high level of overclaiming, but still....


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## Juha3 (Oct 15, 2020)

vikingBerserker said:


> According to "Soviet Air Power in World War 2" by Yefim Gordon
> Page 446: The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s so it could match the Bf 109F-4/G-2/G-4 as well as the Soviet Lagg 5 and Yak-9s



Yes but he continues: "Still, most aircraft were delivered unmodified". The North Fleet Air Arm removed the wing guns along with some armor from their Airacobra Mk Is after lightening tests in late 1942.



vikingBerserker said:


> Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.
> ..and of course the P-63s didn't have them either.
> 
> Not sure of that covers the vast majority however.



Yes, but there was no need to remove the .30s from Qs because they never had them. Qs were in essence Ns with .5 gunpods instead of .3 wing guns.


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## Juha3 (Oct 15, 2020)

vikingBerserker said:


> Same book on Page 434 listing the Imported aircraft in inventory as of May 1st, 1945 shows 84% of the 2,272 P-39s still in service had no wing guns.



In the list (L-L aircraft in VVS KA 1 May 1945) I have 84% of P-39s are Qs without any mention have they their gunpods still installed or not. And strangely no Ns, besides Qs only Ks, L,s Ms, Ds, D-1s and D-5s. VVS KA had Ns at that time, probably included in Qs, i.e. late production P-39s, because Ks, Ls and Ms (mid-production) are one group and Ds, D-1s and D-5s (early production) another.


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## XBe02Drvr (Oct 15, 2020)

Mad Dog said:


> I know at least the Aeroproducts prop on the P-39Q (V01710-89) had full feathering, and I think the Curtis Electric on the P-38J (V-1710-89/91) has full-feathering, though I'm not sure if that was the same Aeroproducts and Curtis props as fitted to the earlier P-39s. But I suspect even the XP-39 had feathering capability seeing as Curtis had props with full feathering as early at least as 1937


What sense does it make to put a full feathering propeller on a single engine airplane? It has very little utility other than to stretch the glide for a dead stick landing, and is one more thing that can go catastrophically wrong. A failed liquid cooled engine will most likely seize up anyway, solving the wind milling problem. Now if they are only manufacturing a single version for singles and twins both, it would make sense to install "aftermarket" high pitch stops on the props for singles, as the last thing in the world you want is for a runaway pitch motor to drive it into feather when you're pulling WEP or other high power setting. Something's going to come unglued, probably spectacularly. Far more disastrous on a single than on a multi.
If you're going to feather a prop, you have to have some way of unfeathering it. An electric prop whose pitch motor has locked itself at the feather end of its travel is going to have to be dismounted and disassembled to be recovered, which may be awkward to impossible, depending on where the plane came to rest after its debacle, and if it's even salvageable.
FIE on electric props!! Bad idea! That's not bigotry, that's fact!

PS: Now I get it. The fluid coupling in the P39's drive train would allow the prop to windmill even if the engine is seized. My apologies for the rant above. Electric props are still a bad idea!

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## wuzak (Oct 15, 2020)

XBe02Drvr said:


> PS: Now I get it. The fluid coupling in the P39's drive train would allow the prop to windmill even if the engine is seized. My apologies for the rant above. Electric props are still a bad idea!



What fluid coupling?

The P-63 had a fluid coupling - in the auxiliary supercharger drive system.


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## vikingBerserker (Oct 15, 2020)

Juha3 said:


> Yes but he continues: "Still, most aircraft were delivered unmodified". The North Fleet Air Arm removed the wing guns along with some armor from their Airacobra Mk Is after lightening tests in late 1942.



Delivered unmodified after which the North Fleet Air Arm removed them is how I read it based on the statement the North Fleet Air Arm removed them in that same section




Juha3 said:


> Yes, but there was no need to remove the .30s from Qs because they never had them. Qs were in essence Ns with .5 gunpods instead of .3 wing guns.



Your question was "Have you any proof that the .30s were deleted on the vast majority of Russian P-39s?" Were you asking about the P-39's in Russian service or if Russia removed them theirselves? If in total then at least as of this date the answer would be yes. If you're asking fi the Russians removed them I could only find in the book where the North Fleet removed them.




Juha3 said:


> In the list (L-L aircraft in VVS KA 1 May 1945) I have 84% of P-39s are Qs without any mention have they their gunpods still installed or not. And strangely no Ns, besides Qs only Ks, L,s Ms, Ds, D-1s and D-5s. VVS KA had Ns at that time, probably included in Qs, i.e. late production P-39s, because Ks, Ls and Ms (mid-production) are one group and Ds, D-1s and D-5s (early production) another.



I did think it was odd that N's were not listed, however off in the far right column listed over 2,000 having been lost. When that is added to what was listed on being on hand in that same chart it comes close to the total accepted by Russia (I dont have the book in front of me, but it was one of the first pages in this chapter). Still, it would be odd that none were in service unless converted and I did not see any mention of it. In regards to the 0.50 pods, the question was about the removal of the 0.30 guns in the wings and I assume the pods could be removed and used as needed, like bombs in a bomb rack.


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## XBe02Drvr (Oct 15, 2020)

wuzak said:


> What fluid coupling?
> 
> The P-63 had a fluid coupling - in the auxiliary supercharger drive system.


My bad! Short circuit in the memory banks. Wrong airplane, wrong location. Not at peak efficiency at 0500.

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## Peter Gunn (Oct 15, 2020)

P-39 Expert said:


> Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery. Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.
> 
> I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.
> 
> I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.



Hey man, I see where you're coming from but allow me to share.

I was born and raised on the family airfield, my dad and his brothers came back from WWII and turned the family farm in lower Michigan into a bona fide grass strip. We had two runways, four hangars, two of them quite large, repair shop with a mechanic and a pilots lounge. By the time I was 12 I probably spent more time in a Cessna than on my bicycle. (Although I haven't flown since 1978, but that's another story)

As a young lad I couldn't read enough about aerial combat from WWI - Korea, my book knowledge of ACM was essentially "attack from the sun, when bounced, turn into the attack, if in trouble dive away".

I haven't gone near a GA aircraft in decades, but what you can learn and discuss here makes me feel like I never left the GA world.

So when I found this place you can imagine how happy I was to find like minded (and VERY knowledgeable) fellows that are not only cordial, but go out of their way many times to help answer questions and share their years of experience and knowledge.

Why do I blather on like this? Because after YEARS of nothing but book learning, imagine again how exciting it was to learn that here I could actually talk to an F-15 pilot, I give 

 BiffF15
(with two "ffs" + 1) a little razzing every now and then but it's all in good fun and he knows it. But when he discusses ACM I listen and when in doubt ask questions, some of them may be dumb but I don't let ego get in the way of learning.

Or 

 drgondog
my love of the P-51 is borderline fanatical, to get to ask questions and receive correct answers on a subject near and dear is simply outstanding, especially the minutiae he can come up with.

I have only illustrated two out of MANY here that you can learn from, I'd list them all but I don't want to leave anyone out and I think you already know who they are anyway.

I like you, you have proven you have knowledge and integrity, as I said before, it isn't easy to stay civil when your arguments are being refuted from all comers, but for the most part I believe you have kept the snark to a minimum and that speaks very highly of you. I doubt I could say the same for me in the same situation, just read my sig line...

In the end, I just wanted you to know that I think highly of what you know, just dial it back a bit and LISTEN to what these guys are saying, I'd NEVER question Wes ( 
X
 XBe02Drvr
) on what a critical engine may or may not be. He has age, wisdom and experience... well mostly age, which I respect.

I still think you are a valuable addition to the community here and can make valid contributions to our discussions, just my opinion but remember, my contribution here is just snark and dumb questions so take that for what it's worth.

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## Ivan1GFP (Oct 15, 2020)

GrauGeist said:


> My Stepdad always tasked me with loading the drum for his Thompson.
> Yeah, there was a winding key on it, but one slip while sticking a .45 round in and there goes your thumbnail.
> I much preferred the stick mags...



Hello GrauGeist,

That should not have been so dangerous from what I remember.
The procedure was to put the drum on a flat surface and unlatch and remove the cover plate to load the 50 rounds.
We never loaded less than 50. After that, the cover plate was latched back in place.
You don't touch the winding key while loading rounds in the magazine. It is on the cover plate which is not installed.
Without any spring tension, the rounds are just dropped into the appropriate compartments each of which holds about 5 rounds between the spokes of the drive mechanism.
We never wound up the spring in the Drum until we were ready to shoot it because it is not possible to unwind the drum and storing it with a spring under tension wasn't a good idea.
I don't remember how much to wind the drum but it was stamped on the 50 round drum.
Never wind an empty drum.....

The biggest problem we had was that the Thompson we were using was a semi-auto which fired from a closed bolt.
Getting the empty Drum out was a B*TCH. 
On a regular full auto Thompson, it was easy:
Pull back the bolt as if you are about to fire and it will lock back. 
Then activate the magazine catch with one hand and slide out the Drum with the other....
On a semi, the sear doesn't lock the bolt back.
The Drum also does NOT activate the bolt stop like regular stick magazines do.
You can't reach the bolt stop with the Drum in place.
You need to hold the bolt back with one hand to keep it out of the track of the Drum,
Activate the magazine catch so the Drum can slide out of the gun,
Use your THIRD hand to slide the Drum out of the gun.

Stick Magazines were so much easier but had other problems.
The Receiver of a semi Thompson is not quite as deep as a full auto Thompson.
As a result, the Stick Magazines do not go in as far.
What some people do is re-grind the hole in the magazine that the Magazine Catch goes into so that it still latches.
I always thought this was a stupid idea because it meant that new Stick Magazines would not work until modified.
On this gun, we modified the Magazine Catch so that an unmodified Stick Magazine would fit.
Of course that meant that the Stick Magazines that came with the gun would not work any more.
Brand new Stick Magazines were not hard to find at the time and were not expensive either.

There was one other interesting problem with the Thompson Carbine.
It would NOT run on commercial .45 ACP ammunition.

Military .45 Auto ammunition out of a 5 inch M1911 type is spec'ed at 830 fps or 850 fps with a 230 grain bullet.
The commercial 230 grain ammunition typically gets only about 805 fps and sometimes as low as 780-790 fps average on a chronograph.
That wasn't enough to reliably cycle the bolt of the Thompson with its much heavier springs. Military ammunition worked pretty reliably though.
The longer barrel on the semi auto Thompson also gave considerably higher velocity with the same ammunition. Typically, military ammunition was getting pretty close to 100 fps higher than what it was doing in a 5 inch M1911.

- Ivan.

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## pinsog (Oct 15, 2020)

Ivan1GFP said:


> That .375 Ultra Mag sounds like a bit of overkill for deer? I only have perhaps two rifles that are suitable for deer in this area though I don't hunt and have never hunted (unless you count insects). Just about everything else is a heavy scoped gun or collectible (to me) or service rifle type. My preference is mostly .308 semi autos these days.
> My Wife recently got into bicycling and commented that the plastic valve stem cap on one of my Daughter's bikes had disintegrated.
> I told her that those caps were probably almost two decades old so it wasn't surprising. They were salvaged along with metal caps from valve stems that I sometimes found when processing wheel weights for cast bullets. I literally went through hundreds of pounds of wheel weights back then for black powder guns, .45-70 and pistols. Lead doesn't actually go far when you are only getting about 14-15 bullets per pound.
> 
> - Ivan.


I had my 375 ultra mag built for a trip to Africa back in 2005. Sako action, McMillan stock, Schneider match grade barrel. It’s a tack driver. My son started shooting it at 13 years old, took it away from me and killed his next 14 deer with it. He was 14 and my brother was teasing him about something and my son looked at him and said “well at least I don’t hunt with a woman’s gun”. My brother was hunting with a 3006. I about wet my pants laughing. I had a 375 built for my son when he was 14, turned out a bit heavy so he carried mine until he got bigger. We are shooting 260 grain Nosler Accubonds at 2900 feet per second. We don’t have to track wounded deer that’s for certain...

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## Juha3 (Oct 15, 2020)

vikingBerserker said:


> Delivered unmodified after which the North Fleet Air Arm removed them is how I read it based on the statement the North Fleet Air Arm removed them in that same section
> 
> 
> 
> ...



I'm not a native English speaker, but the quote is: "The North Fleet Air Arm followed these recommendations and reduced the P-400's weight by 247 kg. Still, most aircraft were delivered unmodified." I read that that the North Fleet Air Arm removed wing guns but most other commands did not. IMHO all P-400s and P-39Ds - Ns arrived to the USSR with wing guns as did most of Qs, on them the wing armament was the two .5 gunpods instead of the four .3s inside wings on the earlier models. So I understand the sentence means that most of the planes were delivered to the units without any weight reductions.

I meant to ask does P-39 Expert has any proof for his belief that the .30s were deleted on the vast majority of Russian P-39s. And I did not count Qs because nobody could remove .30s from them because they had none. And yes, gunpods were removable.

Many P-39s were lost by Russians before the first Ns arrived and after that many older models were lost as were many Qs, even we (the Finns) got two in fairly good condition (they could have easily repaired to flying condition because we also recovered several wrecks), one is at our AF museum and the other was shown some time at our AA Museum.

Ps. I checked from my photos and noted that the P-39 shown at the AA Museum was the same _White 26_ that was shown at the AF Museum.

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## P-39 Expert (Oct 15, 2020)

Peter Gunn said:


> Hey man, I see where you're coming from but allow me to share.
> 
> I was born and raised on the family airfield, my dad and his brothers came back from WWII and turned the family farm in lower Michigan into a bona fide grass strip. We had two runways, four hangars, two of them quite large, repair shop with a mechanic and a pilots lounge. By the time I was 12 I probably spent more time in a Cessna than on my bicycle. (Although I haven't flown since 1978, but that's another story)
> 
> ...


Thanks.


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## P-39 Expert (Oct 15, 2020)

Juha3 said:


> I'm not a native English speaker, but the quote is: "The North Fleet Air Arm followed these recommendations and reduced the P-400's weight by 247 kg. Still, most aircraft were delivered unmodified." I read that that the North Fleet Air Arm removed wing guns but most other commands did not. IMHO all P-400s and P-39Ds - Ns arrived to the USSR with wing guns as did most of Qs, on them the wing armament was the two .5 gunpods instead of the four .3s inside wings on the earlier models. So I understand the sentence means that most of the planes were delivered to the units without any weight reductions.
> 
> *Did the quote say what recommendations were used to reduce the weight by 247kg? That would be about 543lbs, right?*
> 
> ...



Please expand above.


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## P-39 Expert (Oct 15, 2020)

Ivan1GFP said:


> Hello P-39 Expert
> 
> 
> 
> ...


Please expand above.


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## fubar57 (Oct 15, 2020)

Found this picture....





​....in this book...





PUBLISHED BY ALASKA-SIBERIA RESEARCH CENTER - 2007​Its a P-63C-5-BE. Its the caption of the photo though, "Bell P-63 Kingcobra in flight over the Northwest Route with the inscription written in chalk on its fuselage reading "Bell Booby Trap" so named because the Bell planes, held up for mechanical repairs and delayed for extended periods of time in the outdoor cold, tended to be involved in a greater number of crashes than other aircraft. May 1945

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## XBe02Drvr (Oct 15, 2020)

Shortround6 said:


> Your not supposed to shoot it (much) just carry it


I mostly just shoot my old style muzzle loaders now. More fun. Ever hear of "primitive biathlon"? Pre-1860 style muzzle loaders, traditional style snowshoes, and mountain trapper or period military costume if you're shooting in the "Classic" class. Davy Crockett/Daniel Boone or Native American style is OK too.


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## glennasher (Oct 15, 2020)

XBe02Drvr said:


> I mostly just shoot my old style muzzle loaders now. More fun. Ever hear of "primitive biathlon"? Pre-1860 style muzzle loaders, traditional style snowshoes, and mountain trapper or period military costume if you're shooting in the "Classic" class. Davy Crockett/Daniel Boone or Native American style is OK too.


I drifted from "deer rifles" to varmint rifles, and now I'm kind of obsessed with rimfires of various natures, mostly well-crafted bolt-actions like CZ452s and 455s. Before I went nuts on rifles in general, I was a pretty good pistol shot, mostly USPSA/IPSC, with highly modified 1911 pistols, among others. I pretty much kept my rifles to .30/06 and under, though. I still keep a .270 around, along with some smallish varmint rifles, in case something needs killin'. Firearms are fun.


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## Ivan1GFP (Oct 15, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *Not at all. Worked just fine together out to 400yds. Past that they may need to be used separately.*



You really don't understand deflection shooting or physics, do you?



P-39 Expert said:


> *Except by the main wing spar.*



Are you trying to convince us that the rear wing spar offers significant protection from weapons fire?



P-39 Expert said:


> *Estimates after removing unnecessary weight are only on the early D/F/K/L models with the -35 or -63 engines. N model didn't need any weight reduction at all, although it certainly would have benefitted from it. Q model certainly didn't need the .50cal wing gun pods. Just unnecessary drag that reduced speed by 14mph.*



Has anyone ever told you that trying to push a solution that the client clearly does not want is NOT a recipe for success?



P-39 Expert said:


> *Right. Most P-39s caught fire from overheating on the ground. If they did manage to take off firing one shell from the nose cannon caused an immediate tumble from CG problems.*



I hadn't heard this before, but you must be right. The P-39 really must have been a piece of junk.

- Ivan.

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## Ivan1GFP (Oct 15, 2020)

XBe02Drvr said:


> I mostly just shoot my old style muzzle loaders now. More fun. Ever hear of "primitive biathlon"? Pre-1860 style muzzle loaders, traditional style snowshoes, and mountain trapper or period military costume if you're shooting in the "Classic" class. Davy Crockett/Daniel Boone or Native American style is OK too.



Hello XBe02Drvr, 

My own black powder shooting has never really been about Muzzle Loaders though I do own a couple.
The majority of my BP shooting has been with Sharps Rifles (reproductions) and I have run enough ammunition through a couple to put some pretty significant wear on the breech seals. Most of the other BP shooters were going through 3-10 rounds in an afternoon after work. I was going through 50-100 most of the time and sometimes a lot more.
These are the kinds of rifles that get pretty expensive to shoot if you don't cast your own bullets.

At one point I got pretty serious about seeing how accurate the M14/M21 platform could be made to be by using the appropriate Benchrest techniques on ammunition. Most folks shooting service rifle aren't really that interested in testing to see how accurate the system can be made. They are interested in competition in which a gun shooting 1 MOA is fantastic and 1.5 MOA is really quite sufficient to shoot a clean score.
I actually had a pretty good amount of success. The Benchrest shooters thought I was crazy to even try. A very good friend of mine tried to give me some ideas on how to improve my ammunition until I showed him how violent the cycling of the gun was and what it did to ammunition. After that, he shook his head and wondered how I was able to get any kind of accuracy much less the level of accuracy the targets were showing.

- Ivan.

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## vikingBerserker (Oct 15, 2020)

Juha3 said:


> I'm not a native English speaker, but the quote is: "The North Fleet Air Arm followed these recommendations and reduced the P-400's weight by 247 kg. Still, most aircraft were delivered unmodified." I read that that the North Fleet Air Arm removed wing guns but most other commands did not. IMHO all P-400s and P-39Ds - Ns arrived to the USSR with wing guns as did most of Qs, on them the wing armament was the two .5 gunpods instead of the four .3s inside wings on the earlier models. So I understand the sentence means that most of the planes were delivered to the units without any weight reductions.
> 
> I meant to ask does P-39 Expert has any proof for his belief that the .30s were deleted on the vast majority of Russian P-39s. And I did not count Qs because nobody could remove .30s from them because they had none. And yes, gunpods were removable.
> .



Your English is perfectly fine, I believe Yefim's book was originally published is Russian so there might be a few things lost in translation. Based on your calcification then I have to agree with you, the only wholesale removal of the 0.30's from the wings I could find were those of the North Fleet Arm as mentioned.


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## pinsog (Oct 15, 2020)

glennasher said:


> I drifted from "deer rifles" to varmint rifles, and now I'm kind of obsessed with rimfires of various natures, mostly well-crafted bolt-actions like CZ452s and 455s. Before I went nuts on rifles in general, I was a pretty good pistol shot, mostly USPSA/IPSC, with highly modified 1911 pistols, among others. I pretty much kept my rifles to .30/06 and under, though. I still keep a .270 around, along with some smallish varmint rifles, in case something needs killin'. Firearms are fun.


My 458 Lott and my sons 375 ultra mag are both on CZ550 Safari Magnum actions. Love the actions, the 458 holds 5+1. It actually holds 6 in the magazine but can’t strip the top round off so I only load 5


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## XBe02Drvr (Oct 15, 2020)

Ivan1GFP said:


> I only have perhaps two rifles that are suitable for deer in this area


My 1951 JC Higgins .270 (actually an FN postwar Mauser 98 action with a chrome lined barrel) tack driver and my early 60s Marlin 336 .30-30 brush gun are all sighted in and ready, so it's back to playing with my two .50 cal Hawkens, my .45 Kentucky flint, and my Remington .44 1861 New Model Army, among my other toys. I just might take one of my Hawkens hunting this year and leave my smokeless burners at home. You don't get many long range shots around here.

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## Ivan1GFP (Oct 15, 2020)

XBe02Drvr said:


> My 1951 JC Higgins .270 (actually an FN postwar Mauser 98 action with a chrome lined barrel) tack driver and my early 60s Marlin 336 .30-30 brush gun are all sighted in and ready, so it's back to playing with my two .50 cal Hawkens, my .45 Kentucky flint, and my Remington .44 1861 New Model Army, among my other toys. I just might take one of my Hawkens hunting this year and leave my smokeless burners at home. You don't get many long range shots around here.



Hello XBe02Drvr,

I suppose just about any old military bolt action might work as a hunting rifle. If that is the case, then I have a bunch.
The two actual "Hunting Rifles" I was thinking of are a first year production Remington 700 in 7 mm Magnum and a Ruger Number 1 in .25-06.
I have never gotten any great accuracy out of that Ruger, but that 7 mm does quite well out to 200 meters which is as far as I have shot it. Obviously I didn't buy it new because the gun is older than I am. The gun has a bunch of scratches and a replacement synthetic stock but I was still surprised at how little money the previous owner wanted for it.

What kind of bullets do you use for the .44 Remington revolver?
I have a couple Ruger Old Army revolvers that are probably the same caliber.
What I found is that it isn't worth bothering to stock up on lead balls for the .44 revolvers because cast bullets for a .45 ACP work just fine and are much easier to come by. I usually use 200 grain SWC that I cast out of wheel weights. Commercial castings work fine as well.

BTW, One of the things I believe I have figured out from running so much ammunition through the Sharps guns is that Black Powder is erosive.
I believe it has to do with the amount and type of solid residue from combustion. I believe Pyrodex is much less erosive if there is an antique you wish to preserve.

Don't you find it odd that a modern Knight Disc rifle qualifies for Black Powder Season but a period Sharps 1858 rifle does not?

- Ivan.


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## GrauGeist (Oct 15, 2020)

When black powder is burnt, it leaves behind a layer of soot that contains potassium and sodium oxides. The moisture in the air turns that mixture into a hydroxide and will quickly attack iron/steel.


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## Ivan1GFP (Oct 16, 2020)

GrauGeist said:


> When black powder is burnt, it leaves behind a layer of soot that contains potassium and sodium oxides. The moisture in the air turns that mixture into a hydroxide and will quickly attack iron/steel.



Hello GrauGeist,

The residues are actually not oxides but chlorides: Salts.
It is the same thing with Pyrodex and with corrosive primers in old military ammunition.

That is NOT what I am describing here.
Have you ever looked at the forcing cone and the top strap of a Magnum revolver that has been shot a lot with full power loads?
The metal has been burned away. The effect is much worse with Chrome Moly guns than with Stainless guns. I have a revolver that I believe I have put almost 9,000 full power rounds through. The effect is very distinct. No corrosive primers were ever used in that gun.
The breech seal on a BP Sharps on the originals is a chrome plated flat plate that uses some of the force of the powder that gets into the recess behind the plate to force it into a tight seal against the rear of the chamber. On the reproduction guns, this plate is typically made of Stainless Steel.
The seal is generally not bad but not completely gas-tight either. What was happening was that the Stainless plate was getting a ring etched into it just inside where it sealed against the chamber.

You also have to remember that the BP Sharps isn't like a typical BP Muzzleloader. You can fire a lot of shots pretty quickly.
I was using a test tube rack and measuring my charges about 20-30 at a time between relays.
With a pile of bullets at hand, it is pretty easy to keep up a firing rate fast enough that the gun gets pretty hot.
i was going through so much powder in those days that I was buying it in 5 pound bags and refilling the same 1 pound cans over and over again.

- Ivan.


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## Juha3 (Oct 16, 2020)

P-39 Expert said:


> Please expand above.



Hello P-39 Expert
As vikingBerserker wrote in his message #671 "_The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s_" The test plane was Airacobra Mk I BX382 and exact quote for the armour is "_part of the armour plating_" so no exact info on what pieces of armour were removed.


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## Stig1207 (Oct 16, 2020)

XP-39 II

Just to summarize what the researhcer writes in his article: in Romania June 1-22 5 VA claim 240 (+4 ground) Axis aircraft destroyed, of which 122 were Me 109's and 17 VA another 11 (+9 ground) incl. 6 Me 109's (+ 3 ground). P-39's of 5 VA accounted for 61 Me 109's (by my count).

The opponents were Jg 52 whose losses were 6 Me109s lost and 8 damaged; 1 lost to AA, 2 lost + 2 damaged in combat with fighters. One pilot killed and 2 wounded.

If this case is anything to go by, then maybe the most spectacular achievement by P-39's in Soviet service may well be the overclaiming by the pilots that flew the plane.

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## XBe02Drvr (Oct 16, 2020)

Ivan1GFP said:


> I suppose just about any old military bolt action might work as a hunting rifle. If that is the case, then I have a bunch.


I have a Model 95 Mauser 7x57 made for Chile in 1898 that I bought in 1966 for $19, still in the factory cosmolene and brown paper, which I've hunted with. Century Arms in St Albans bought and imported an entire warehouse full of them, as well as Model 98s ($34.99) and FN 7x57 assault rifles ($54.99), all in mint condition. As a college student working a summer job for $66 every two weeks, I couldn't afford the "high priced spread".
My JC Higgins .270 isn't an "old military bolt action rifle". It's a new manufacture Fabrique Nationale sporting rifle with chrome lined barrel and a classy checkered and engraved stock. The Germans put FN to work during the war building 98s, which towards the end were getting rather sloppy with slave labor and poorer quality steel. Once they were liberated, the FN people were kind of embarrassed to be associated with their wartime products, so set out to "make a better mousetrap". They had the patterns and tooling for the 98, and once again had access to high strength ordnance steel, so they started cranking out high class sporting rifles. Trouble was, in the war-torn global economy, nobody had the affluence to buy these jewels except the US, and we were kind of partial to Winchester and Remington, and Savage and Stevens, etc. Enter Sears Roebuck, who gave FN entry to the US market under an American brand name, alongside some serious junk that also carried the JC Higgins name. I bought mine in a local sporting goods store with a Leupold scope on it for $325. It was tagged $350, but the owner wanted to move "that Sears junk" along so he offered it for $25 off with his condolences. He hadn't done his homework. I had.



Ivan1GFP said:


> What kind of bullets do you use for the .44 Remington revolver?


I have a .445 round ball mold and a .445 "slug" mold that casts a dead ringer for an ACP bullet. About 230 grains, I think. I don't shoot the slugs much because they restrict the powder volume in the chambers. I haven't cast any slugs in ten years, and still have almost a hundred on hand.

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## XBe02Drvr (Oct 16, 2020)

Ivan1GFP said:


> Don't you find it odd that a modern Knight Disc rifle qualifies for Black Powder Season but a period Sharps 1858 rifle does not?


In Vermont, we call it muzzle loader season and they have to be muzzle loaders. There's a bunch of us (nowhere near a majority) who think all "modern style" muzzle loaders should be banned and traditionals only allowed. If you want to get seriously laughed at, just show up at a primitive biathlon with a modern "muzzle loader", a pocket full of speed loads, wearing camo gear, and running on Sherpas.


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## Juha3 (Oct 16, 2020)

Stig1207 said:


> XP-39 II
> 
> Just to summarize what the researhcer writes in his article: in Romania June 1-22 5 VA claim 240 (+4 ground) Axis aircraft destroyed, of which 122 were Me 109's and 17 VA another 11 (+9 ground) incl. 6 Me 109's (+ 3 ground). P-39's of 5 VA accounted for 61 Me 109's (by my count).
> 
> ...



It is not so simple, the LW also had recon 109s and also Rumanians had 109s. Hungarian 109s probably were not participating this campaign. But it is true that Soviets overclaimed badly on the southern part of the Eastern Front in 1944. JG 52 lost 15 109s to enemy actions in June 1944 and 10 to other causes. But what made the situation more complicated was that the USAAF conducted active bombing campaign against Rumania and Hungary in June 1944 so many of LW Rumanian and Hungarian losses were by the USAAF.

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## Mad Dog (Oct 16, 2020)

Stig1207 said:


> ......If this case is anything to go by, then maybe the most spectacular achievement by P-39's in Soviet service may well be the overclaiming by the pilots that flew the plane.


 Yeah, and Luftwaffe reporting was so reliable - NOT! If you went by Luftwaffe loss reports alone they won the Battle of Britain, Siege of Malta and every Russian campaign. The Germans were far more interested in reporting their successes (many over-claimed and some downright imaginary) than they were admitting their failures, and that was in all theatres.


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## Ivan1GFP (Oct 16, 2020)

XBe02Drvr said:


> ..... and FN 7x57 assault rifles ($54.99), all in mint condition.
> .....
> My JC Higgins .270 isn't an "old military bolt action rifle". It's a new manufacture Fabrique Nationale sporting rifle with chrome lined barrel and a classy checkered and engraved stock. The Germans put FN to work during the war building 98s, which towards the end were getting rather sloppy with slave labor and poorer quality steel. Once they were liberated, the FN people were kind of embarrassed to be associated with their wartime products, so set out to "make a better mousetrap". They had the patterns and tooling for the 98, and once again had access to high strength ordnance steel, so they started cranking out high class sporting rifles. Trouble was, in the war-torn global economy, nobody had the affluence to buy these jewels except the US, and we were kind of partial to Winchester and Remington, and Savage and Stevens, etc. Enter Sears Roebuck, who gave FN entry to the US market under an American brand name, alongside some serious junk that also carried the JC Higgins name. I bought mine in a local sporting goods store with a Leupold scope on it for $325. It was tagged $350, but the owner wanted to move "that Sears junk" along so he offered it for $25 off with his condolences. He hadn't done his homework. I had.



Hello XBe02Drvr,

The FN "Assault Rifle" sounds like the FN-49. In 7x57. it was probably a Venezuelan contract gun. Excellent guns but with the annoying habit of breaking firing pins. I have had a couple in different calibers.

Regarding the FN commercial Model 98: I said what I meant to say but the timing was all wrong. I didn't mean to imply a lack of quality in the FN Model 98s. Even their military guns were excellent quality though the finish may not have been as nice. I have one of those.
I am actually pretty familiar with the commercial model 98 Mausers made by various manufacturers. They don't turn up as often today as they did perhaps 30 years ago, but I never could find anything lacking in them for fit and finish

My comment about military bolt actions was just the realization that just about any military bolt gun would make a pretty fair hunting rifle except perhaps for a lack of optics. The weight and caliber would not be unreasonable though it might be a bit harsh to carry a really nice Springfield rifle into the field. I am not a fan of "Sporterized" Rifles and have never bought one.



XBe02Drvr said:


> In Vermont, we call it muzzle loader season and they have to be muzzle loaders. There's a bunch of us (nowhere near a majority) who think all "modern style" muzzle loaders should be banned and traditionals only allowed. If you want to get seriously laughed at, just show up at a primitive biathlon with a modern "muzzle loader", a pocket full of speed loads, wearing camo gear, and running on Sherpas.



For a few years, my weekly range sessions was during the weekly gathering for the local Muzzle Loaders group. These gentlemen were pretty tolerant of other firearms present during their meetings. Most of the time, I was probably shooting a scoped M14 type in those days which is only a few generations out of date. There were a lot of very odd things that showed up. One was a match lock that was probably closer to a cannon than a musket.

- Ivan.


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## P-39 Expert (Oct 16, 2020)

Juha3 said:


> Hello P-39 Expert
> As vikingBerserker wrote in his message #671 "_The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s_" The test plane was Airacobra Mk I BX382 and exact quote for the armour is "_part of the armour plating_" so no exact info on what pieces of armour were removed.


Thanks.


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## XBe02Drvr (Oct 16, 2020)

Ivan1GFP said:


> There were a lot of very odd things that showed up. One was a match lock that was probably closer to a cannon than a musket.


A high school classmate of mine whom I hadn't seen since graduation showed up at this year's Smugglers Notch Primitive Biathlon toting a Spanish pattern matchlock conquistador gun with which he shot a better score than I did with my .45 Kentucky. At least his ignition was reliable. Misfire = missed shot.

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## GrauGeist (Oct 17, 2020)

Thought I'd toss this out there in case anyone is interested.
The forum's own "gun thread":
The Guns We Own


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## Stig1207 (Oct 17, 2020)

Juha3 said:


> It is not so simple, the LW also had recon 109s and also Rumanians had 109s. Hungarian 109s probably were not participating this campaign. But it is true that Soviets overclaimed badly on the southern part of the Eastern Front in 1944. JG 52 lost 15 109s to enemy actions in June 1944 and 10 to other causes. But what made the situation more complicated was that the USAAF conducted active bombing campaign against Rumania and Hungary in June 1944 so many of LW Rumanian and Hungarian losses were by the USAAF.



I only summarized the numbers from the article, which is itself much more detailed and takes into account the points you mention.



Mad Dog said:


> Yeah, and Luftwaffe reporting was so reliable - NOT! If you went by Luftwaffe loss reports alone they won the Battle of Britain, Siege of Malta and every Russian campaign. The Germans were far more interested in reporting their successes (many over-claimed and some downright imaginary) than they were admitting their failures, and that was in all theatres.



Kaminsky also mentions loss disputes that inevitably will occur; however, as he points out, only one Jg52 pilot is reported killed. Tbo, I myself thought that he surely must have missed some German/ Axis losses , and maybe he has, but on the whole his research seems pretty solid

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## PAT303 (Oct 17, 2020)

So have we turned a sows ear into a silk purse after 37 pages or are you all getting bored repeating the same argument over and over and would rather talk about rifles?. I shot shot my 1908 Swedish Mauser today at 100m with cast bullets over 16grns of 2400 and put 5 of them into a genuine 1'' group sitting post.

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## P-39 Expert (Oct 17, 2020)

PAT303 said:


> So have we turned a sows ear into a silk purse after 37 pages or are you all getting bored repeating the same argument over and over and would rather talk about rifles?. I shot shot my 1908 Swedish Mauser today at 100m with cast bullets over 16grns of 2400 and put 5 of them into a genuine 1'' group sitting post.


Let's have more of the same old argument and move the guns to it's own thread.


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## XBe02Drvr (Oct 17, 2020)

P-39 Expert said:


> Let's have more of the same old argument and move the guns to it's own thread.


I agree with P39 Expert (surprise!), and apologize for my hijacker tendencies. Mods, can you shift the gun chatter over to the appropriate thread, so this dead horse can absorb a few more kicks undistracted?

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## SaparotRob (Oct 17, 2020)

Then we can fix the Buffalo.

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## DerAdlerIstGelandet (Oct 17, 2020)

PAT303 said:


> So have we turned a sows ear into a silk purse after 37 pages or are you all getting bored repeating the same argument over and over and would rather talk about rifles?. I shot shot my 1908 Swedish Mauser today at 100m with cast bullets over 16grns of 2400 and put 5 of them into a genuine 1'' group sitting post.



I think people are tired of repeating the same things over and over to no avail.

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## XBe02Drvr (Oct 17, 2020)

SaparotRob said:


> Then we can fix the Buffalo.


Why bother, didn't the Finns already do it for us?

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## Juha3 (Oct 17, 2020)

Stig1207 said:


> I only summarized the numbers from the article, which is itself much more detailed and takes into account the points you mention.
> 
> 
> 
> Kaminsky also mentions loss disputes that inevitably will occur; however, as he points out, only one Jg52 pilot is reported killed. Tbo, I myself thought that he surely must have missed some German/ Axis losses , and maybe he has, but on the whole his research seems pretty solid



Hello Stig
I appreciate your effort and my intention was not criticize you, only to note that JG 52 was not the only formation in the area with 109s at that time and while it suffered greater losses than mentioned during one week longer period at least some of those were caused by the USAAF and that anyway JG 52 did not suffer catastrophic losses in June 44.

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## Reluctant Poster (Oct 17, 2020)

P-39 Expert said:


> I'm not Ivan but thought I would reply anyway.
> 
> The whole "British added weight to kill the P-39/400" is my theory and mine alone as far as I know.



Bell didn’t need any help. They died of self inflicted wounds. Bell simply wasn’t particularly good at designing fighter aircraft. The Airacuda was a fundamentally flawed design, badly executed. The same could be said of the XP-77. With the P-59 Bell achieved the virtually impossible by designing a jet fighter that was slower then contemporary piston engine fighters. The XP-83 was Bells last hurrah and proved inferior to the competition. After WWII the only fixed wing aircraft Bell built were purely experimental. A common theme with Bell’s aircraft was stability issues. In addition they tended to be overweight.

Bells success with helicopters after the war had nothing to do with the Bell aircraft design team. Arthur Young approached Bell with his design for a helicopter, which morphed into the very successful Model 47.

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## davparlr (Oct 17, 2020)

Reluctant Poster said:


> Bell didn’t need any help. They died of self inflicted wounds. Bell simply wasn’t particularly good at designing fighter aircraft. The Airacuda was a fundamentally flawed design, badly executed. The same could be said of the XP-77. With the P-59 Bell achieved the virtually impossible by designing a jet fighter that was slower then contemporary piston engine fighters. The XP-83 was Bells last hurrah and proved inferior to the competition. After WWII the only fixed wing aircraft Bell built were purely experimental. A common theme with Bell’s aircraft was stability issues. In addition they tended to be overweight.
> 
> Bells success with helicopters after the war had nothing to do with the Bell aircraft design team. Arthur Young approached Bell with his design for a helicopter, which morphed into the very successful Model 47.


The problem with the P-59 in my mind is the huge wing. The P-59 wing area is 386 sqft, the Me 262 is 238 sqft, the P-80 is 237 sqft. This could have been driven by incorrect customer requirements or, poor engineering of builder.


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## SaparotRob (Oct 17, 2020)

There was a thread recently that dealt with the P-59. Either from posts or links, it was mentioned that Bell was given the job of building an airframe without the actual weight, dimensions or thrust of the engines. So that’s what they came up with.

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## P-39 Expert (Oct 17, 2020)

Reluctant Poster said:


> Bell didn’t need any help. They died of self inflicted wounds. Bell simply wasn’t particularly good at designing fighter aircraft. The Airacuda was a fundamentally flawed design, badly executed. The same could be said of the XP-77. With the P-59 Bell achieved the virtually impossible by designing a jet fighter that was slower then contemporary piston engine fighters. The XP-83 was Bells last hurrah and proved inferior to the competition. After WWII the only fixed wing aircraft Bell built were purely experimental. A common theme with Bell’s aircraft was stability issues. In addition they tended to be overweight.
> 
> Bells success with helicopters after the war had nothing to do with the Bell aircraft design team. Arthur Young approached Bell with his design for a helicopter, which morphed into the very successful Model 47.


The P-39 was the least overweight of the other Allison powered single engine planes. Still overweight.

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## FLYBOYJ (Oct 17, 2020)

Overweight.... Hmmm...

What constitutes "overweight"?


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## Shortround6 (Oct 17, 2020)

FLYBOYJ said:


> Overweight.... Hmmm...
> 
> What constitutes "overweight"?




four .30 cal guns with 300rpg and 70-100lbs of armor

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## GrauGeist (Oct 17, 2020)

The original P-59 (not the P-59A jet) wasn't all that bad looking.
Definately has a bit of Airacuda styling to it.

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## SaparotRob (Oct 17, 2020)

That’s pretty neat!


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## Mad Dog (Oct 18, 2020)

Reluctant Poster said:


> .....Bell simply wasn’t particularly good at designing fighter aircraft....


 According to whom? After all, despite carrying the much heavier 37mm cannon and the weight of the long driveshaft, the P-39 was lighter than the P-40 models with the same engine versions. This was reflected in the P-39s higher speed, higher rate of climb and superior ceiling to equivalent P-40 models. Indeed, it's fair to suggest the Allied war effort would have been better off it Curtiss had been told to build P-39s instead of P-40s.


Reluctant Poster said:


> .....The Airacuda was a fundamentally flawed design, badly executed.....


 The Airacuda suffered due to a *bad concept,* but was still faster and heavier-armed than equivalent attack aircraft such as the A-18 Curtiss Shrike


Reluctant Poster said:


> .....The same could be said of the XP-77.....


 The XP-77 was as unlikely as many other similar lightweight fighter designs made in France, but it still managed to reach 330mph on a 500hp engine, which was quite an engineering achievement.


Reluctant Poster said:


> .........With the P-59 Bell achieved the virtually impossible by designing a jet fighter that was slower then contemporary piston engine fighters.....


 The XP-59 was vastly constrained by both the restrictions of the requirement and the restrictions on information about the new jet engines given to Bell by the USAAC. They weren't given any design information on the engines other than rough external dimensions! At the same time, they were told they had to make the aircraft big enough to carry two engines, lots of fuel and be very safe for pilots unused to the new jets. The result was designed more as a trainer than a fighter. BTW, the only other operational fighter to get the same J-31 engine was the Ryan Fireball, which was actually slower than the XP-59. Bell's development of a better fighter design, the XP-59B, was transferred to Lockheed and was developed into the P-80 Shooting Star, which _was_ far superior to contemporary prop fighters.


Reluctant Poster said:


> .........The XP-83 was Bells last hurrah and proved inferior to the competition. After WWII the only fixed wing aircraft Bell built were purely experimental.....


 And how many successful fighter designs did Bell's much bigger competitor Curtiss make after the P-40? Yup, zero.

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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> . Bell's development of a better fighter design, the XP-59B, was transferred to Lockheed and was developed into the P-80 Shooting Star



Oh boy....

Can you show us your source for that one?!?!?


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## Mad Dog (Oct 18, 2020)

FLYBOYJ said:


> Oh boy....
> 
> Can you show us your source for that one?!?!?


Can't recall where I first heard that many (many!) years ago, but here's one. And Joe Baugher also mentions it here.


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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> Can't recall where I first heard that many (many!) years ago, but here's one.



Well that is completely and utterly false!!!

The only thing Lockheed gained from Bell as the dimensions of of the H-1 engine. After that, Kelly Johnson and his team had the XP-80 produced in 143 days and the rest of the design had nothing to do with anything Bell was doing on the P-59.

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## GrauGeist (Oct 18, 2020)

Bell had the XP-83 as a follow-on to the P-59A.
McDonnell had the FD.
Lockheed started on the P-80 in *1939* as the L-133 project and it went through several revisions, HOWEVER, the Bell XP-59B that was dumped on Lockheed was entirely seperate from the P-80 project and one should not confuse the two.

This is the XP-59B:

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## FLYBOYJ (Oct 18, 2020)

The only thing Lockheed picked up (or was dumped with) with regards to the P-59B was the requirement to build a jet aircraft. Parts of the P-80 actually came from the P-38 (the nose section and wingtips IIRC). Bottom line, Bell couldn't deliver the goods, the rest is history.


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## GrauGeist (Oct 18, 2020)

Lockheed was urged to ramp up their jet project in 1943, so they fell back on the L-133 to develop the P-80.
The fact that the XP-59B project was given to Lockheed to sort out didn't have any influence on the P-80. You could say *technically* that the P-80 was a clean-sheet design.
With the P-59A being a dead end and the XP-83 not proving to be any better, I'm pretty sure that Lockheed told the Army that the 58B wasn't worth the effort to pursue.


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## FLYBOYJ (Oct 18, 2020)

GrauGeist said:


> Lockheed was urged to ramp up their jet project in 1943, so they fell back on the L-133 to develop the P-80.
> The fact that the XP-59B project was given to Lockheed to sort out didn't have any influence on the P-80. You could say *technically* that the P-80 was a clean-sheet design.
> With the P-59A being a dead end and the XP-83 not proving to be any better, I'm pretty sure that Lockheed told the Army that the 58B wasn't worth the effort to pursue.



I don't think we'll ever know if Johnson even looked at what Bell started. The company designation for the XP-80 was the L-140 and Johnson went to Wright Patterson in June 1943 to sell the Lockheed concept to the AAF. Johnson promised to deliver a prototype in 150 days, again the rest is history.

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## Mad Dog (Oct 18, 2020)

GrauGeist said:


> ....Lockheed started on the P-80 in *1939* as the L-133 project.....


 Sorry, but the L-133 was nothing at all to do with the P-80. The L-133 was a twin-engined, blended-body, canard design exercise that went no further than paper, and nothing like the much smaller P-80. The L-133 was actually even bigger and heavier than the P-59! This is an artist's impression of the L-133-2-01 design, and it's clear the XP-59B was a lot closer to the eventual P-80 than the L-133:


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## Mad Dog (Oct 18, 2020)

FLYBOYJ said:


> Well that is completely and utterly false!!!
> 
> The only thing Lockheed gained from Bell as the dimensions of of the H-1 engine. After that, Kelly Johnson and his team had the XP-80 produced in 143 days and the rest of the design had nothing to do with anything Bell was doing on the P-59.


Oh no, someone else is repeating that "completely and utterly false" story! How dare they! Quick, Flyboy, go sort 'em out!

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## GrauGeist (Oct 18, 2020)

Sorry but the L-133 project was started in *1939* - sound familiar?

AND AS I SAID EARLIER, Lockheed fell back on the L-133 project experience to develop the XP-80, which, again, as I said, was a "CLEAN SHEET DESIGN".

Not sure how I could make that point any clearer...

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## XBe02Drvr (Oct 18, 2020)

Hoo boy, Brits and Yanks again!
Clash of the narratives! Step right up and get your tickets here!

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## Stig1207 (Oct 18, 2020)

Juha3 said:


> Hello Stig
> I appreciate your effort and my intention was not criticize you, only to note that JG 52 was not the only formation in the area with 109s at that time and while it suffered greater losses than mentioned during one week longer period at least some of those were caused by the USAAF and that anyway JG 52 did not suffer catastrophic losses in June 44.



Your comment on there being other units and Axis allies that need to be taken into account was well founded and prudent; I would have done the same. Fortunately Kaminsky seems to have applied due diligence.


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## fubar57 (Oct 18, 2020)

Briefly from the book "P-80/F-80 Shooting Star" by David R. McLaren. The Lockheed Aircraft Corporation indicated that they were interested in the "jet propelled aircraft program" but was officially discouraged by the War Department wanting Lockheed to continue on with the P-38 and other projects. Verbatim from the book..."Finally, in 1943, their Chief Research Engineer, Clarence "Kelly" Johnson was approached by Army Air Force officials while he was observing some P-38 armament trials at Elgin Field, Fl. and was informed that the Air Force was now interested in seeing a proposal from Lockheed for a new jet propelled fighter. The idea for which had never been far from Johnson's mind to begin with, and on the way back to California, Johnson roughed out his thoughts on foolscap. Johnson then presented his sketches to Lockheed's Vice President and Chief Engineer, Hall L. Hibbard, and other Lockheed representatives, and with their blessings, he flew back to Wright Field, Ohio later in the month to present a rough draft of what Lockheed had in mind, their Model L-140, to the Air Force.

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## DerAdlerIstGelandet (Oct 18, 2020)

Mad Dog said:


> Oh no, someone else is repeating that "completely and utterly false" story! How dare they! Quick, Flyboy, go sort 'em out!



You can make your argument without being a snarky prick...

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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> Oh no, someone else is repeating that "completely and utterly false" story! How dare they! Quick, Flyboy, go sort 'em out!



Yep, saw that on several other sites, I'll raise the ante, *utter BS! So run with that!* Wright Pat asked Lockheed to come up with another turbine design. As Lockheed was already working on the L-133, the course changed after Kelly Johnson met with AAF officials and promised an airframe in 180 days. As stated, the XP-80 was ready in 143 days.

If you look at the L-133, it's wings are similar to the XP-80 (and P-38). There is a slight resemblance to the XP-59B concept drawing but that's where it stopped. The XP-80's design began around the dimensions of the H-1 engines and other production components were adopted where and when possible. 

As stated, the XP-80's nose was based on the P-38 nose section. With the P-38 already in production, there was tooling available for fabrication. Although the nose sections were similar, IIRC they were not interchangeable.

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## P-39 Expert (Oct 18, 2020)

FLYBOYJ said:


> Overweight.... Hmmm...
> 
> What constitutes "overweight"?


Well, a Spitfire V weighed 6600lbs and had a 1200hp engine. A 109G weighed 7000lbs and had a 1475hp engine. An early P-39D/F/K/L weighed 7650lbs and had a 1150hp engine. See the power/weight ratios? EarlyP-39 was overweight.

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## FLYBOYJ (Oct 18, 2020)

P-39 Expert said:


> Well, a Spitfire V weighed 6600lbs and had a 1200hp engine. A 109G weighed 7000lbs and had a 1475hp engine. An early P-39D/F/K/L weighed 7650lbs and had a 1150hp engine. See the power/weight ratios? EarlyP-39 was overweight.



Again, based on what? Yes, we have power to weight ratios and we can compare them to the contemporizes of the day so where's the "line" to consider these aircraft were "overweight"?

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## buffnut453 (Oct 18, 2020)

Must admit I'm a bit confused by the whole "power to weight" comparison given that propulsive power for a given engine hp will vary depending on the gearing and propeller, while the weight component really only becomes a factor as a proportion of available lift generated by the flying surfaces.

Or am I missing something?


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## GregP (Oct 18, 2020)

When the AAF said that the L-133 was a bit too much for them and asked Lockheed to build something more conventional without canards, Kelly Johnson designed a new single-engine fuselage and took the complete L-133 wing set and grafted them onto the new fuselage. He had already expended the effort to design the L-133 wings, they were still "current," as far as airfoil went, and wasn't about to do it again.

In hindsight, they may have been better off with the L-133 airplane. It would have been at least interesting to see how it would have performed. I seriously doubt the L-133 would have been a turkey like the XP-55 Ascender was. Alas, it never got built. The only real innovation we saw from the L-133 design was the production of the first axial-flow turbojet designed in the United States, the L-100 / J-37. Below is a pic of one we have at the Planes of Fame Museum.







It was actually built only as a mockup and never ran, but it definitely DID get the U.S.A. into axial-flow turbojet engine design. The test engine could not be made to start running on its own, and only actually turned over on the power of the starter. Nobody has gone back with some engineering talent to see what the issue was because engine development passed the L-1000 rather rapidly.

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## SaparotRob (Oct 18, 2020)

GregP said:


> When the AAF said that the L-133 was a bit too much for them and asked Lockheed to build something more conventional without canards, Kelly Johnson designed a new single-engine fuselage and took the complete L-133 wing set and grafted them onto the new fuselage. He had already expended the effort to design the L-133 wings, they were still "current," as far as airfoil went, and wasn't about to do it again.
> 
> In hindsight, they may have been better off with the L-133 airplane. It would have been at least interesting to see how it would have performed. I seriously doubt the L-133 would have been a turkey like the XP-55 Ascender was. Alas, it never got built. The only real innovation we saw from the L-133 design was the production of the first axial-flow turbojet designed in the United States, the L-100 / J-37. Below is a pic of one we have at the Planes of Fame Museum.
> 
> ...


When was development started on L-1000 engine?


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## FLYBOYJ (Oct 18, 2020)

SaparotRob said:


> When was development started on L-1000 engine?


Tails Through Time: The L-1000: Lockheed's Own Jet Engine

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## SaparotRob (Oct 18, 2020)

FLYBOYJ said:


> Tails Through Time: The L-1000: Lockheed's Own Jet Engine


Another “what might have been”.


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## pinsog (Oct 18, 2020)

buffnut453 said:


> Must admit I'm a bit confused by the whole "power to weight" comparison given that propulsive power for a given engine hp will vary depending on the gearing and propeller, while the weight component really only becomes a factor as a proportion of available lift generated by the flying surfaces.
> 
> Or am I missing something?


I would say power to weight is entirely based on what the other guys are building. The Wildcat would have had a fine power to weight ratio if the Zero had weighed 9,000 pounds, but as it was the Wildcat and P39 and P40 were all a bit porky

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## Shortround6 (Oct 18, 2020)

You also have the variable of power to weight at what altitude

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## P-39 Expert (Oct 18, 2020)

FLYBOYJ said:


> Again, based on what? Yes, we have power to weight ratios and we can compare them to the contemporizes of the day so where's the "line" to consider these aircraft were "overweight"?





pinsog said:


> I would say power to weight is entirely based on what the other guys are building. The Wildcat would have had a fine power to weight ratio if the Zero had weighed 9,000 pounds, but as it was the Wildcat and P39 and P40 were all a bit porky


Exactly. Power to weight will affect climb more than any other measurement. Early P-39D/F/K/L P/W ratio was 18% higher than Spitfire V and 29% higher than 109G. Was quite overweight. Less weight improved climb, which was what the early P-39D/F/K/L needed most. Later N model with more powerful engine climbed very well.


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## Mad Dog (Oct 18, 2020)

GregP said:


> When the AAF said that the L-133 was a bit too much for them and asked Lockheed to build something more conventional without canards, Kelly Johnson designed a new single-engine fuselage and took the complete L-133 wing set and grafted them onto the new fuselage.....


 Sorry, but please go look at the P-80 then look at the L-133 - not only is the P-80 wing much, much smaller (38ft 9in vs 46ft 8in), it is completely different shape. The P-80's wing is narrow and straight with slight double taper, whereas the L133's wing is a conformal double triangle with engines buried in the roots. I suspect the idea that anything was carried over from the L-133 came out of the Lockheed marketing department. The idea that Lockheed miraculously converted the L-133 into a new design that was nothing like the L-133, but a lot like the XP-59B proposal they claim they ignored, all in 143 days, is a massive pile of male bovine manure.


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## Mad Dog (Oct 18, 2020)

DerAdlerIstGelandet said:


> You can make your argument without being a snarky prick...


Apologies to snarky pricks everywhere for besmirching their good names.

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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> Sorry, but please go look at the P-80 then look at the L-133 - not only is the P-80 wing much, much smaller (38ft 9in vs 46ft 8in), it is completely different shape. The P-80's wing is narrow and straight with slight double taper, whereas the L133's wing is a conformal double triangle with engines buried in the roots. I suspect the idea that anything was carried over from the L-133 came out of the Lockheed marketing department.



Are you basing this on your highly calibrated eyeballs or are you really good at guessing loft dimensions based on professional experience.


Mad Dog said:


> The idea that Lockheed miraculously converted the L-133 into a new design that was nothing like the L-133, but a lot like the XP-59B proposal they claim they ignored, all in 143 days, is a massive pile of male bovine manure.


 Well go get your shovel - I worked with people in the mid 1980s who were on the XP-80 program and it was designed from the ground up. The only thing Lockheed got from Bell was a great opportunity based on their failure to further their basic design. Had Lockheed actually used a Bell design or any engineering data there would have been a paper trail documenting this and the AAF would have had to approve it, so since you're talking about "male bovine manure," "SHOW US THE BEEF"!!!

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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> Apologies to snarky pricks everywhere for besmirching their good names.


And one more SNARKY remark and your journey into cyber space will be long and vast!


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## DerAdlerIstGelandet (Oct 18, 2020)

Mad Dog said:


> Apologies to snarky pricks everywhere for besmirching their good names.



Believe me, you are not damaging anyones reputation but your own.

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## FLYBOYJ (Oct 18, 2020)

P-39 Expert said:


> Exactly. Power to weight will affect climb more than any other measurement. Early P-39D/F/K/L P/W ratio was 18% higher than Spitfire V and 29% higher than 109G. Was quite overweight. Less weight improved climb, which was what the early P-39D/F/K/L needed most. Later N model with more powerful engine climbed very well.



And agree - to say something is "overweight" based on power to weight is only comparable to similar aircraft of the day. My point.


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## XBe02Drvr (Oct 18, 2020)

P-39 Expert said:


> Well, a Spitfire V weighed 6600lbs and had a 1200hp engine. A 109G weighed 7000lbs and had a 1475hp engine. An early P-39D/F/K/L weighed 7650lbs and had a 1150hp engine. See the power/weight ratios? EarlyP-39 was overweight.





buffnut453 said:


> Must admit I'm a bit confused by the whole "power to weight" comparison given that propulsive power for a given engine hp will vary depending on the gearing and propeller, while the weight component really only becomes a factor as a proportion of available lift generated by the flying surfaces.





pinsog said:


> I would say power to weight is entirely based on what the other guys are building. The Wildcat would have had a fine power to weight ratio if the Zero had weighed 9,000 pounds, but as it was the Wildcat and P39 and P40 were all a bit porky


What are you willing to do without? A6M and BF109 were essentially minimalist machines, both more susceptible to battle damage than the US machines mentioned, which can't be accused of flimsyness. "Hell for stout" was our motto, and we had this tendency to "gadgetize" anything with wings.
Zero achieved its performance with lightness and slickness and "zero" protection, on a rather weak engine, while the Messerschmitt did it with small size and a cutting edge powerplant. Spitfire was an aerodynamic tour de force with an exceptionally fine engine, but a little more fragile than US was comfortable with. Built to US structural standards by anyone other than Reg Mitchell, our X-spurt friend would be calling it porky.
You can't have your cake and eat it too. Larry Bell was not a Horikoshi, or a Mitchell or a Messerschmitt, witness missed opportunities such as the carburetor air intake, or adjusting wing positioning to ameliorate the CG issue.
Several suggestions have been made to lighten the early P39, most of which are impractical for CG, structural, or operational reasons, would not at the time have been recognized as necessary or desirable, and come with overly optimistic claims of performance enhancements. What I see is still a sow's ear.

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## Mad Dog (Oct 18, 2020)

FLYBOYJ said:


> Are you basing this on your highly calibrated eyeballs or are you really good at guessing loft dimensions based on professional experience.....


 No, just a plain understanding of written English. The L-133 was a *conformal design* - the *wing thickness altered* to allow it to engulf the axial engines in the *wingroots*. That means the wing was *a lot thicker at the root*, then thinned out toward the midsection, and was finally a conventional wing much further out. The P-80s is a simple, straight wing from the wingroot right to the tip.


FLYBOYJ said:


> ......Well go get your shovel.....


 You use a shovel to type? I'm impressed! Instead, I'll just put up some 3-views of the L-133 and the P-80, you can compare them to the 3-view of the XP-59B, and then you can shovel off a reply telling us how the much bigger L-133 is somehow closer to the P-80 than the XP-59B:













FLYBOYJ said:


> .....I worked with people in the mid 1980s who were on the XP-80 program and it was designed from the ground up.....


 And I'm sure, after several decades of repeating the company line, those Lockheed employees actually believed it.


FLYBOYJ said:


> .....The only thing Lockheed got from Bell was a great opportunity based on their failure to further their basic design....


 Actually, the authorities took the design away from Bell because Bell's design staff were already overloaded with other projects, just as the authorities had not given it to Lockheed to start with because Lockheed were too busy sorting out the flaws with the P-38. Now, personally, I think that was a *good thing* because the P-38 was really needed for the PTO, and the resulting P-80 was very good design. Had Germany held out longer then the P-80 would have been a far better fighter for the USAAF in the ETO than the Bell P-83 could have been, though the P-83's superior range might have made it the better choice for the PTO if the Manhattan Project had not succeeded. The idea that Bell were massively incompetent, and Lockheed were somehow simply devine, simply doesn't gell with the history of the P-38's development alone.


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## pinsog (Oct 18, 2020)

I don’t think 2 airplanes looking alike means they were designed by the same people. All ww2 single engine fighters had the engine in the front (except the P39)etc. There are only so many ways to do an airplane that will fly. All current pickup trucks look basically alike.

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## tomo pauk (Oct 18, 2020)

P-39 Expert said:


> Well, a Spitfire V weighed 6600lbs and had a 1200hp engine. A 109G weighed 7000lbs and had a 1475hp engine. An early P-39D/F/K/L weighed 7650lbs and had a 1150hp engine. See the power/weight ratios? EarlyP-39 was overweight.



P-39Ds were having less than 1150 HP at 12000 ft (sometimes under 1100 HP at that altitude). Later the situation slightly improved, engines were indeed making 1150 HP at 12000 ft.
Spitfire V was enjoying ~1350 HP at 12000 ft. 
Bf 109F4 (fully rated engine) and early G (de-rated, 2600 rpm operation) = 1350 PS or 1300 PS at 12000 ft, respectively.

At 20000 ft:
P-39 D-K: 850-870 HP
Spitfire V: ~1050 HP
The 109s from above: ~1150 PS or ~1240 PS

Non-turbo V-1710 was a decent engine, but it was not as good engine as Merlin or DB 601/605 were.


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## pinsog (Oct 18, 2020)

XBe02Drvr said:


> What are you willing to do without? A6M and BF109 were essentially minimalist machines, both more susceptible to battle damage than the US machines mentioned, which can't be accused of flimsyness. "Hell for stout" was our motto, and we had this tendency to "gadgetize" anything with wings.
> Zero achieved its performance with lightness and slickness and "zero" protection, on a rather weak engine, while the Messerschmitt did it with small size and a cutting edge powerplant. Spitfire was an aerodynamic tour de force with an exceptionally fine engine, but a little more fragile than US was comfortable with. Built to US structural standards by anyone other than Reg Mitchell, our X-spurt friend would be calling it porky.
> You can't have your cake and eat it too. Larry Bell was not a Horikoshi, or a Mitchell or a Messerschmitt, witness missed opportunities such as the carburetor air intake, or adjusting wing positioning to ameliorate the CG issue.
> Several suggestions have been made to lighten the early P39, most of which are impractical for CG, structural, or operational reasons, would not at the time have been recognized as necessary or desirable, and come with overly optimistic claims of performance enhancements. What I see is still a sow's ear.


I completely understand your point, but I guess there is a middle ground somewhere which is where aircraft manufacturers play. Of course we all want armor and self sealing fuel tanks along with good weapons, but who here if given the choice between flying a Zero and F2F-3 Buffalo against each other 1 on 1 would choose the F2F-3? When your limited to engines less than 1200 hp your simply limited on what you can carry or at least how well you can carry it.

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## PAT303 (Oct 18, 2020)

All I way say is Lockheed, aka Kelly Johnson taking design advise from anyone, especially from the likes of Bell flies in the face of everything I have read about the man.

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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> No, just a plain understanding of written English. The L-133 was a *conformal design* - the *wing thickness altered* to allow it to engulf the axial engines in the *wingroots*. That means the wing was *a lot thicker at the root*, then thinned out toward the midsection, and was finally a conventional wing much further out. The P-80s is a simple, straight wing from the wingroot right to the tip.
> You use a shovel to type? I'm impressed! Instead, I'll just put up some 3-views of the L-133 and the P-80, you can compare them to the 3-view of the XP-59B, and then you can shovel off a reply telling us how the much bigger L-133 is somehow closer to the P-80 than the XP-59B:



*You're making assumptions based on non-scale 3 view drawings that were done by a graphic artist! That's laughable!*



Mad Dog said:


> And I'm sure, after several decades of repeating the company line, those Lockheed employees actually believed it.




No, again I'll tell you those employees I knew *WORKED *on the project - *they were in the Skunk Works AS I WAS FOR 3 YEARS!*

Lockheed XP-80 "Lulu Belle"




Mad Dog said:


> Actually, the authorities took the design away from Bell because Bell's design staff were already overloaded with other projects, just as the authorities had not given it to Lockheed to start with because Lockheed were too busy sorting out the flaws with the P-38. Now, personally, I think that was a *good thing* because the P-38 was really needed for the PTO, and the resulting P-80 was very good design. Had Germany held out longer then the P-80 would have been a far better fighter for the USAAF in the ETO than the Bell P-83 could have been, though the P-83's superior range might have made it the better choice for the PTO if the Manhattan Project had not succeeded. The idea that Bell were massively incompetent, and Lockheed were somehow simply devine, simply doesn't gell with the history of the P-38's development alone.



*Well show us proof that the government "took the design" away from Bell and gave it to Lockheed!!!! *And what "projects" was Bell working on that made them sooooo busy? And for sorting out P-38 "flaws," yea, Lockheed was so busy that they managed to build something like 35 P-38s a day, build B-17s down the street (literally) at the Vega plant and open up the P-80 production line right along side the P-38 line!

Oh - and they were building Constellations and starting the P2 Neptune program at the same facility!!!


Sorry if you have a hard time believing history


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## FLYBOYJ (Oct 18, 2020)

Mad Dog said:


> You use a shovel to type?



*You're too stupid to play here - bye-bye!*


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## XBe02Drvr (Oct 18, 2020)

FLYBOYJ said:


> *You're too stupid to play here - bye-bye!*


Tsk, tsk, did you actually banish him? Too bad, he was fun to watch! Worth a chuckle now and again, even if he did insult your former employer.

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## FLYBOYJ (Oct 18, 2020)

XBe02Drvr said:


> Tsk, tsk, did you actually banish him? To bad, he was fun to watch! Worth a chuckle now and again.



I know he was entertaining but he was warned twice. I was intrigued about his ability to determine dimensions and loft data from internet 3 view drawings!


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## XBe02Drvr (Oct 18, 2020)

FLYBOYJ said:


> I know he was entertaining but he was warned twice. I was intrigued about his ability to determine dimensions and loft data from internet 3 view drawings!


People like that not only entertain us they keep us on our toes and keep our diplomacy skills physically fit.

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## FLYBOYJ (Oct 18, 2020)

XBe02Drvr said:


> People like that not only entertain us they keep us on our toes and keep our diplomacy skills well exercised.



Yep! Along with patience from your mods and admins!

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## GregP (Oct 18, 2020)

I have a book, actually two, on lofting, and though I COULD get through it, I'm not needing to loft just now. But, I can tell you that math for good lofting, while not too complicated, is also not simple, and you're NOT going to get it from a drawing. I do 3-views myself, and I use a bezier tool for lofting. They might have back in the day, too, IF they had been available ... but they weren't. So, they had to do actual lofting.

Here's one of my efforts:





and I can tell you, the lofting was NOT done with classic lofting data. I used a bezier tool. It ain't a bad drawing, but it's also not 100% scale. The rivets are close, but not exact in number. the lines could be off by 1/4 inch or so, the NAA logo is my own reproduction, not an official company logo. I could go on, but this is good enough for a museum drawing or an illustration in a book.

I would not use it for scale documentation ... although I DID compete in RC aerobatics (not scale) for some years a couple of decade back (RC Pattern), I can tell you that the scale judges I used to see working at contests would not know what was not to scale in my drawing above. Some people in here might.

There is ONE rather glaring error in the drawing above ... the side view. Anybody want to make a stab at it?

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## fubar57 (Oct 18, 2020)

Off to Google "lofting". Knowing Google, I'll probably get, "relaxing in the attic"......................................................

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## BiffF15 (Oct 18, 2020)

GregP said:


> I have a book, actually two, on lofting, and though I COULD get through it, I'm not needing to loft just now. But, I can tell you that math for good lofting, while not too complicated, is also not simple, and you're NOT going to get it from a drawing. I do 3-views myself, and I use a bezier tool for lofting. They might have back in the day, too, IF they had been available ... but they weren't. So, they had to do actual lofting.
> 
> Here's one of my efforts:
> View attachment 598767
> ...



Side view is missing guns?

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## GregP (Oct 18, 2020)

Hi Biff, Yup, that was QUICK. I didn't notice it myself until I posted this! At least I can go back and fix it easily.

My point was that FlyboyJ is correct; you ain't gonna' get accurate interior spaces, lofting data, or even 100% correct lines from a small, non-factory 3-view drawing that wasn't used in the actual production process.

So, while I think my P-51 is pretty decent, you wouldn't want to drill CNC holes using my drawing for a reproduction full-scale aircraft. I HAVE made new skins for a WWII warbird. But I didn't use a drawing. I copied an old, original skin by laying it flat over a new piece of Aluminum, drilling and using clecos through both skins to copy the rivet hole placement.

Cheers!

Hey Fubar 57, lofting is the process of forming the curves between skins, such as where the wing joins the fuselage. Basically they join with many straight lines and the curve is formed by following the outside of the lines. Sort of like below, where many straight lines are used to come up with a good-looking, streamlined curve between two surfaces. The curve shown is not lofted correctly, but is illustrative of what I mean. I didn't calculate the lofting lines ... I just threw some lines in and followed the curve as an illustration. If you do, maybe, 25 of these, correctly ... each one different, you come up with the wing fairings between the wing and fuselage. A good example might be the fairings between the wing and fuselage of a P-36.

Or lofting might be "relaxing in the attic ... with a good, cold beer!"






Lofting was BC ... before computers and, actually, before computers with decent software on them. See the wing fairings on the P-36 below. All done with actual lofting.






Nothing magic about it, but also not as simple as you might think to get the exact curves right.

Cheers again!

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## rochie (Oct 19, 2020)

3 view looks good Greg.

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## PAT303 (Oct 19, 2020)

XBe02Drvr said:


> Tsk, tsk, did you actually banish him? Too bad, he was fun to watch



I must admit members like that are funny, that one we had a few weeks ago that was convinced the USA won the air war single handily was a scream, there are rules we all have to follow but the fanatical ones are hilarious to listen too.

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## Peter Gunn (Oct 19, 2020)

As an aside, why do people find it so hard to believe that some designs gel so quickly? Why is it hard to believe that an engineering/aeronautical genius like Kelly Johnson and crew can't come up with the XP-80 in 140+/- days or that Edgar Schmued and company came up with the Mustang in 120+/- days. The argument is always that they had either "help" or they got design leads and plans from someone else because it's "impossible" to do it on their own. I've seen it in more places than here.

I find that highly dismissive and insulting to the men who designed and built some of the greatest aircraft ever to take wing. I really don't know why it's so hard to fathom that a talented group of engineers led by brilliant chief designers, working full time must take some inordinate amount of months to come up with a superlative design.

Hell, the formative design for the U.S.S. South Dakota class battleships was sketched on a cocktail napkin by the chief designer one evening, I'd have to dig out my Garsky and Dulin's to get the particulars and it really was just a silhouette but it's pretty damn close to the end result.

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## XBe02Drvr (Oct 19, 2020)

Peter Gunn said:


> As an aside, why do people find it so hard to believe that some designs gel so quickly?





Peter Gunn said:


> I find that highly dismissive and insulting to the men who designed and built some of the greatest aircraft ever to take wing.


I think that in most cases these genius types have a lot of ideas up their sleeve they've been working on in the back of their minds for awhile. When somebody squeezes the trigger, they're spring loaded to the "Go!" position and just have to put their ideas on paper without a lot of head scratching and imagineering. Like Kelly Johnson and his "pre-engineered" P80 wing. And Edgar Schmued and his laminar flow wing and Meredith effect radiator. It helps if they have a team who can intuitively think on the same page and streamline the detail work. Assembling said team is part of the genius factor.

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## windhund116 (Oct 19, 2020)

XBe02Drvr said:


> I think that in most cases these genius types have a lot of ideas up their sleeve they've been working on in the back of their minds for awhile. When somebody squeezes the trigger, they're spring loaded to the "Go!" position and just have to put their ideas on paper without a lot of head scratching and imagineering. Like Kelly Johnson and his "pre-engineered" P80 wing. And Edgar Schmued and his laminar flow wing and Meredith effect radiator. It helps if they have a team who can intuitively think on the same page and streamline the detail work. Assembling said team is part of the genius factor.



"Necessity is the mother of invention." And "Form follows function."


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## XBe02Drvr (Oct 19, 2020)

windhund116 said:


> "Necessity is the mother of invention." And "Form follows function."


And genius is 10% inspiration and 90% perspiration.

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## P-39 Expert (Oct 19, 2020)

FLYBOYJ said:


> And agree - to say something is "overweight" based on power to weight is only comparable to similar aircraft of the day. My point.


And my point is the early P-39 was overweight. As compared to other contemporary fighters. In relation to it's engine power. 

They could not increase engine power quickly.

They could reduce weight quickly. And every pound saved increased climb rate by 1.2fpm.

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## pinsog (Oct 19, 2020)

P-39 Expert said:


> And my point is the early P-39 was overweight. As compared to other contemporary fighters. In relation to it's engine power.
> 
> They could not increase engine power quickly.
> 
> They could reduce weight quickly. And every pound saved increased climb rate by 1.2fpm.



I would go the other way, I would add 250 pounds of turbo charger and larger inter cooler (I know I know it wouldn’t fit). It’s climb would still be poor (although much better at altitude) but you fly it like an early P47, slow climb but fast level speed, slowly climb to altitude then use your level speed a zoom ability to do diving passes at G4M Betty bombers while using your superior speed to avoid Zeroes altogether.


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## P-39 Expert (Oct 19, 2020)

pinsog said:


> I would go the other way, I would add 250 pounds of turbo charger and larger inter cooler (I know I know it wouldn’t fit). It’s climb would still be poor (although much better at altitude) but you fly it like an early P47, slow climb but fast level speed, slowly climb to altitude then use your level speed a zoom ability to do diving passes at G4M Betty bombers while using your superior speed to avoid Zeroes altogether.


Turbo wouldn't work, but the mechanical two stage -93 would have worked just fine.

Easier and quicker to just reduce the weight and increase the climb.


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## GregP (Oct 19, 2020)

1 pound increased the rate of climb by 1.2 fpm? Maybe not.

From “Aerodynamic for Naval Aviators,” rate of climb is: RC = 33,000 * (Pa - Pr)/(W), where: RC = rate of climb in feet per minute, Pa = power available (hp), Pr = power required for level flight, W = weight in lbs. I took a P-38Q aircraft. Rate of climb at 7,400 feet was 3,805 fpm. Power available was 1,200 hp. Weight I am taking at 7,550 lbs, which is about 20 lbs under normal takeoff weight. If you run that out in Excel, Pr for level flight is 329.46 hp.

If I change the weight by 1 pound, it weighs 7,549 pounds with everything else the same ... and rate of climb is 3,805.504 fpm, which is an improvement if 0.504 fpm, or about 1/2 fpm not 1.2 fpm. In reality, the weight might be slightly less, but it won't get to 1.2 fpm for a 1 pound difference.

I wasn't trying to bust your chops here, but since I am an engineer, I just got curious about the 1.2 fpm.

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## FLYBOYJ (Oct 19, 2020)

GregP said:


> 1 pound increased the rate of climb by 1.2 fpm? Maybe not.
> 
> From “Aerodynamic for Naval Aviators,” rate of climb is: RC = 33,000 * (Pa - Pr)/(W), where: RC = rate of climb in feet per minute, Pa = power available (hp), Pr = power required for level flight, W = weight in lbs. I took a P-38Q aircraft. Rate of climb at 7,400 feet was 3,805 fpm. Power available was 1,200 hp. Weight I am taking at 7,550 lbs, which is about 20 lbs under normal takeoff weight. If you run that out in Excel, Pr for level flight is 329.46 hp.
> 
> ...



You beat me to the punch Greg, I couldn't remember where I seen that formula ( “Aerodynamic for Naval Aviators” once sat on my coffee table). I tried to explain earlier (when all this weight and balance discussion started) that weight reduction in the matter explained by the OP is not linear!

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## XBe02Drvr (Oct 19, 2020)

FLYBOYJ said:


> weight reduction in the matter explained by the OP is not linear!


There you guys go again; speaking in tongues and handling serpents at worship!

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## windhund116 (Oct 19, 2020)

How many variants of the basic P39 design was made throughout WW2? Were there any active combat units using it, by mid 1945? 

Just curious. I don't remember seeing any US units using them on front lines by the end of the war.

Thanks!


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## P-39 Expert (Oct 19, 2020)

GregP said:


> 1 pound increased the rate of climb by 1.2 fpm? Maybe not.
> 
> From “Aerodynamic for Naval Aviators,” rate of climb is: RC = 33,000 * (Pa - Pr)/(W), where: RC = rate of climb in feet per minute, Pa = power available (hp), Pr = power required for level flight, W = weight in lbs. I took a P-38Q aircraft. Rate of climb at 7,400 feet was 3,805 fpm. Power available was 1,200 hp. Weight I am taking at 7,550 lbs, which is about 20 lbs under normal takeoff weight. If you run that out in Excel, Pr for level flight is 329.46 hp.
> 
> ...


My method is a little simpler, and specific to the early P-39. From wwiiaircraftperformance.org:

P-39C vs. P-39D I know C didn't have self sealing tanks and armor plate/glass, but we're comparing climb rate and weight only. Same engine and propeller. Same airplane.

P-39C weighed 6689lbs. Climbed at 3720fpm.
P-39D weighed 7525lbs. Climbed at 2720fpm.
Difference 836lbs. 1000fpm. 

1000fpm divided by 836lbs = 1.2fpm at 10000' Same airplane, same engine, propeller, rpm (3000) and HP (1150). Only difference is weight. 

For every pound lost climb is increased by 1.2fpm. Example: 300lbs lost, climb is increased by 360fpm.


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## fubar57 (Oct 19, 2020)

Simpler isn't always righter

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## XBe02Drvr (Oct 19, 2020)

P-39 Expert said:


> P-39C vs. P-39D I know C didn't have self sealing tanks and armor plate/glass, but we're comparing climb rate and weight only. Same engine and propeller. Same airplane.


Nothing in fluid dynamics is ever that simple. Two powerplants of the same model series and rated at the same horsepower and using the same model number propeller can give significantly different thrust values, depending on many variables such as atmospheric conditions, fuel compounds, prop reduction and supercharger gear ratios, propeller rig, etc, etc. And thrust is the significant value here. And do you KNOW the airframes are rigged and detailed identically? How do you KNOW that all of these conditions are IDENTICAL on two different aircraft on two different days, and possibly, locations? You don't. So what you have are approximate, not absolute numbers.
"Your mileage may be different."


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## GregP (Oct 19, 2020)

That method is not sound, P-39 Expert. The C and D are different airframes, and no two engine, airframe, and prop combinations perform exactly the same. The atmosphere is also not the same between tests.

You could add 300 pounds to the lighter one and re-do the test, but you can't remove 300 lbs from the heavier one and do the same. I don't know of any test where they actually did that to check the rate of climb difference with weight change between variants. Usually is was only to one variant in a test, and climb charts at different weights for the same airframe are not numerous for WWII fighters.

Also, you have to make yourself be logical, even using the correct aerodynamics formulas. For instance, you could calculate that the rate of climb would be 2,052 fpm at a weight of 14,000 pounds! But, the landing gear would not handle 14,000 pounds and, if it could, the P-39 could not take off from any WWII runway at that weight. It would sink into the earth on a dry day or the tires would go flat!

The theoretical climb figure can only be achieved AFTER the airframe is airborne, up to height, and is at the best climb airspeed. The P-39 might well DO that at 14,000 pounds, but it could never GET THERE to run the test. The formula is best used within normal weight variation for the airframe.

Max takeoff weight for the P-39Q was 8,400 lbs and the rate of climb at that weight at 7,400 feet would be around 3,420 fpm. Empty weight was 6,516 lbs. If we allow at LEAST for 250 lbs of fuel and a 200 pound pilot, we get 6,966 lbs and, at that weight, it would achieve 4,124 fpm. But, without any ammunition for a fight, what would the point be?

The main reason why we see flight tests at "typical loadouts" is because the fighters in question were being used in combat at or near the test weights and loadouts. No other "weird" test weights were contemplated because they weren't wartime realistic loads.

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## Shortround6 (Oct 19, 2020)

Occasionally you will find tests of aircraft with and without drop tanks or a bomb (or bombs) but then we have two variables, the
_Pr = power required for level flight _already mentioned above.

The power needed maintain level flight changes due the change in drag of slightly greater incidence of the wing to generate the lift plus the drag of the bomb or drop tank (and the interference drag). 

and then the weight.

In the case of the P-39C and D is the P-39C fully outfitted? Is there any changes between the two aircraft that would affect drag? 
do four protruding gun barrels in the wings cause more or less drag than two guns in the cowl? Do the ejection ports for the fired cartridges cause any drag? 
Anything in the canopy area or engine exhausts? 

Do both airplanes fly the same speed at the same altitude at the same power? If not you have a difference in drag which is going to show up in the climb rate even if the weights are the same.

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## GregP (Oct 19, 2020)

Hey windhund 116, the Soviet Union used them throughout the war ... VERY effectively, and they stayed in service until at least 1949. The last aerial victory of WWII was by A Soviet P-39 against an Fw 189 on 9 May 45. The last Luftwaffe victory was by an Me 262 against a Soviet P-39 on 8 Aug 45.

The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict. Strange, considering the U.S.A. didn't like them or come up with successful tactics for employing them. That was left to the Soviet Union. The P-39 was always a formidable ground attack airplane, but the Soviet Union mostly used them in an air-to-air role, in support of ground forces ... though they DID fly all types of missions in Soviet service.

I am not sure exactly when it as retired from U.S. service, but it was after WWII as some were still operational in 1946.

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## XBe02Drvr (Oct 19, 2020)

GregP said:


> against a Soviet P-39 on 8 Aug 45.


Huh? August 1945??

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## GregP (Oct 19, 2020)

Ya' got me there, XBe02Drvr ... 8 May 45. Must have been poor toilet training as a kid ... or a typo on my part, one or the other.

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## XBe02Drvr (Oct 19, 2020)

GregP said:


> Ya' got me there, XBe02Drvr ... 8 May 45. Must have been poor toilet training as a kid ... or a typo on my part, one or the other.


If you don't eat the right brainfood at the right time you're liable to experience brainfarts!


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## Milosh (Oct 19, 2020)

Could helium tank be installed in the P-39 to make it lighter?

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## DerAdlerIstGelandet (Oct 19, 2020)

So are we just making up our own formulas now? With simpler methods?

Why the hell does Boeing and Lockheed pay so much for these engineers? I’m going to recommend to my boss that we replace all the engineers with guys from web forums. Not only will we save a lot of money, we’ll improve the F-22’s performance. At least on paper...

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## GregP (Oct 19, 2020)

Wait, I HAD my Harry Potter chocolate frogs brainfood! I SHOULD be a genius ... but, of all the things I have lost, I miss my mind the most!

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## Stig1207 (Oct 20, 2020)

GregP said:


> Hey windhund 116, the Soviet Union used them throughout the war ... VERY effectively, and they stayed in service until at least 1949. The last aerial victory of WWII was by A Soviet P-39 against an Fw 189 on 9 May 45. The last Luftwaffe victory was by an Me 262 against a Soviet P-39 on 8 Aug 45.
> 
> The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict. Strange, considering the U.S.A. didn't like them or come up with successful tactics for employing them. That was left to the Soviet Union. The P-39 was always a formidable ground attack airplane, but the Soviet Union mostly used them in an air-to-air role, in support of ground forces ... though they DID fly all types of missions in Soviet service.
> 
> I am not sure exactly when it as retired from U.S. service, but it was after WWII as some were still operational in 1946.



Greg, please see post #700 Messerschmitts do not want to burn and fall and #726 Summary.

The phenomena called overclaiming can really skew the actual results dramatically.


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## windhund116 (Oct 20, 2020)

GregP said:


> Hey windhund 116, the Soviet Union used them throughout the war ... VERY effectively, and they stayed in service until at least 1949. The last aerial victory of WWII was by A Soviet P-39 against an Fw 189 on 9 May 45. The last Luftwaffe victory was by an Me 262 against a Soviet P-39 on 8 Aug 45.
> 
> The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict. Strange, considering the U.S.A. didn't like them or come up with successful tactics for employing them. That was left to the Soviet Union. The P-39 was always a formidable ground attack airplane, but the Soviet Union mostly used them in an air-to-air role, in support of ground forces ... though they DID fly all types of missions in Soviet service.
> 
> I am not sure exactly when it as retired from U.S. service, but it was after WWII as some were still operational in 1946.



Must have been a fairly formidable ground assault airplane, if the Soviets thought so. Since they did have the famous IL-2 Sturmovik, from fairly early in the Great Patriotic War.


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## P-39 Expert (Oct 20, 2020)

windhund116 said:


> Must have been a fairly formidable ground assault airplane, if the Soviets thought so. Since they did have the famous IL-2 Sturmovik, from fairly early in the Great Patriotic War.


Their main role was battlefield air superiority. Escorting bombers and intercepting German bombers.


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## Peter Gunn (Oct 20, 2020)

Milosh said:


> Could helium tank be installed in the P-39 to make it lighter?



See page 16 post #306 of this thread...

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## Peter Gunn (Oct 20, 2020)

XBe02Drvr said:


> There you guys go again; speaking in tongues and handling serpents at worship!



*HEY!* Careful now, you're treading into dangerous territory, Troll George and I own the copyrights to snark in this here forum. I'm the one that's easily confused when you big brain types start spouting all your book learnin' nonsense. (check how many times I've had to take drgondog to task...)

It's hard to countenance this faux pas on your part but I can be magnanimous in this instance, George on the other hand, well, he's the one you have to watch out for.


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## P-39 Expert (Oct 20, 2020)

FLYBOYJ said:


> Ouch, my ears! LOL!
> 
> Hi MiTasol -
> 
> ...


Would like to see your calculations, thanks.


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## Milosh (Oct 20, 2020)

Peter Gunn said:


> See page 16 post #306 of this thread...



But that would make the a/c very unstable > tail heavy. I was thinking in the outer wings.


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## FLYBOYJ (Oct 20, 2020)

P-39 Expert said:


> Would like to see your calculations, thanks.



I tossed my numbers when this discussion seemed over.

Look at Greg's calculator, he's got it down pretty good and you're able to play with some of things we discussed.

The error on the page I mentioned, I'll post later


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## GregP (Oct 20, 2020)

Hey Stig1207!

Overclaiming? Surely you jest. 

Never happened, especially on the Russian Front where Stalin never executed anyone for lack of performance!

"OK, you two guys get one rifle and 5 rounds. When the first man is killed, the second man takes his rifle and continues fighting! In the Soviet Army, it's hard not to be a hero!"

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## XBe02Drvr (Oct 20, 2020)

Peter Gunn said:


> *HEY!* Careful now, you're treading into dangerous territory, Troll George and I own the copyrights to snark in this here forum.


And I contest those copyrights as invalid! Call your attorney; see you in court. Or would you prefer pistols at twenty paces or sabers toe to toe? In that case, call your second; see you on the meeting ground. 


Peter Gunn said:


> It's hard to countenance this faux pas on your part but I can be magnanimous in this instance, George on the other hand, well, he's the one you have to watch out for.


Well, St George awarded me a "Funny" for this post, so I see no threat there...unless there's an implied "Farm" after it, in which case, "Them's fightin' wuhds, Suh!"


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## Peter Gunn (Oct 20, 2020)

XBe02Drvr said:


> And I contest those copyrights as invalid! Call your attorney; see you in court. Or would you prefer pistols at twenty paces or sabers toe to toe? In that case, call your second; see you on the meeting ground.
> 
> *SNIP*

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## XBe02Drvr (Oct 20, 2020)

Peter Gunn said:


> View attachment 598944


My challenge, your call, Sir: pistols or sabers? I have a matched pair of John Wilkes Booth style .41 cal Derringers. Will that suffice? Our seconds will attend to the loading, if that suits.

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## fubar57 (Oct 20, 2020)

​

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## Peter Gunn (Oct 20, 2020)

XBe02Drvr said:


> My challenge, your call, Sir: pistols or sabers? I have a matched pair of John Wilkes Booth style .41 cal Derringers. Will that suffice? Our seconds will attend to the loading, if that suits.


_Being a Southern Gentleman, I choose pistols suh..._

*Yours:*






*Mine:*





*Unless you prefer long guns, but I warn you suh, I'm a master tactician when it comes to those...*

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## FLYBOYJ (Oct 20, 2020)

P-39 Expert said:


> Would like to see your calculations, thanks.



Follow up to my previous post:

XP-39 II






Basic weight and balance - weight x arm = moment

Moments on chart;

Wheels up - 1016062

Wheels down - 1011053

My math;

7570 x 134.22 = 1016045.4 wheels up

7570 x 133.56 = 1011049.2 wheels down

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## jmcalli2 (Oct 21, 2020)

P-39 Expert said:


> P-39 weight was always confusing. Actually the early P-39D and the much later P-39Q-1 empty weights were about the same. AHT lists the D at 5523lbs and the Q-1 at 5680lbs but the Q-1 had the additional IFF radio that weighed about 120lbs. Empty weights of all the production P-39 models (D/F/K/L/M/N/Q) were about the same.
> 
> Loaded weights varied because of the differences in .30cal ammunition and armor plate, both of which were included in the "load" total and not the empty weight. .30cal ammunition boxes held 1000 rounds per gun but normal load was 300 rounds per gun, a difference of about 200lbs. That's why you sometimes see 7650lbs and 7850lbs quoted al loaded weight. The armor plate varied from about 265lbs on the P-400 to about 195lbs on the later N and Q models.
> 
> The British went a little crazy with armor on the P-400 by armoring the oxygen bottles etc. Compare that 265lbs to the contemporary P-40E with 111lbs of armor plate and glass. Deleting the 100lb nose armor that didn't protect anything and a few small pieces outside of the rear armored glass would get the armor plate/glass to a more reasonable 130lbs while still providing excellent protection.



It is interesting to compare models' weights as tested. Most test reports tell you that they have ammo on board, etc. On some reports you need to click on the “See entire report HERE” to get the weights.
The 'as tested' weights grew from 6592 in the YP-39 to 7871 in the P-39Q. That's a significant change at just under 20%, while bhp went up from 1090 to 1420, ~30%.


Model...........weight as tested in pounds.........bhp................max speed.................time to 15,000'

YP-39..............................6592.......................1090..................368 mph....................4.6 min

P-39C.............................6689........................1150..................379 mph...................~4.3 min

P-39D.............................7525........................1150.................Not given....................Not given 

P-39D.............................~7800......................1170.................368 mph....................5.7 min

P-39D.............................7450........................1172.................370 mph....................Not given

P-39M.............................7430........................1420.................385.5 mph.................4.38 min

P-39N.............................7274........................1420.................398.5 mph.................4.15 min

P-39N.............................7301........................1390................. Not given..................3.82 min

P-39Q.............................7871........................1405.................385 mph....................4.5 min

P-400 British tests..........7845........................Not given...........355 mph...................~5.3 min


Source: P-39 Performance Tests

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## Stig1207 (Oct 21, 2020)

GregP said:


> Hey Stig1207!
> 
> Overclaiming? Surely you jest.
> 
> ...



It is the elephant in the room.

Btw, what is your source for this?


GregP said:


> *The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict.*


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## Peter Gunn (Oct 21, 2020)

FLYBOYJ said:


> Follow up to my previous post:
> 
> XP-39 II
> 
> ...



Looks like you could save 61.5lbs by leaving the engine and gear box oil out, I mean who needs that right?

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## XBe02Drvr (Oct 21, 2020)

Peter Gunn said:


> _Being a Southern Gentleman, I choose pistols suh..._
> 
> *Yours:*
> View attachment 598955
> ...


You chose the weapons, I choose the attire. Agreed?
Yours:






Mine:





DEAL?

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## P-39 Expert (Oct 21, 2020)

GregP said:


> Hey Stig1207!
> 
> Overclaiming? Surely you jest.
> 
> ...


Supposedly Stalin also said "It takes a very brave man to be a coward in the Soviet army." Referencing the "Political" officers in the rear who shot anyone retreating.


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## P-39 Expert (Oct 21, 2020)

jmcalli2 said:


> It is interesting to compare models' weights as tested. Most test reports tell you that they have ammo on board, etc. On some reports you need to click on the “See entire report HERE” to get the weights.
> The 'as tested' weights grew from 6592 in the YP-39 to 7871 in the P-39Q. That's a significant change at just under 20%, while bhp went up from 1090 to 1420, ~30%.
> 
> 
> ...


Agree. The YP had a derated engine because the -35 had not passed the 150 hour test and didn't have self sealing tanks and armor plate/glass.
The C model had the standard -35 engine but did not have self sealing tanks and armor plate/glass. Some sources say it had the rear armor glass behind the pilot's head.
The D model had the -35 engine, self sealing tanks and 240lbs of armor plate/glass and was the first model to be considered combat ready.
My climb comparison was between the C and D since they had the same engine, propeller, horsepower etc, only difference was weight and internal equipment.


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## Ivan1GFP (Oct 21, 2020)

P-39 Expert said:


> Agree. The YP had a derated engine because the -35 had not passed the 150 hour test and didn't have self sealing tanks and armor plate/glass.
> The C model had the standard -35 engine but did not have self sealing tanks and armor plate/glass. Some sources say it had the rear armor glass behind the pilot's head.
> The D model had the -35 engine, self sealing tanks and 240lbs of armor plate/glass and was the first model to be considered combat ready.
> My climb comparison was between the C and D since they had the same engine, propeller, horsepower etc, only difference was weight and internal equipment.



Hello P-39 Expert,

At the risk of resuming the last world war, have you considered the possibility that the P-39C was much better balanced and may have flown "better" than the P-39D?

You may not like where this might lead but here goes anyway:
From the discussions thus far, the general consensus and analysis is that even with late model P-39N and P-39Q in normal loaded condition, the CoG was fairly close to its aft limits.
My own belief is that earlier models were substantially worse in their balance because of different locations of equipment and the CoG at basic weight was 1-3 inches FURTHER AFT than the late models.

Note that in the typical testing that was conducted, the CoG was typically much further forward (24-25% MAC) than it the weight and balance charts would indicate for normal loaded weight. I am not sure how this was done, but it MIGHT have improved performance.

I had also wondered why the designers at Bell had been so stupid as put together the Airacobra in such a way that its CoG was always at or near its aft CoG limit.
Thinking about it a bit more, I don't believe they actually screwed up in that aspect.
Look over the armament of the P-39C. Note that although it carried no armour and probably not the Gearbox Armour that you dislike so much that we all believe was necessary to maintain proper balance, it had an extra pair of .30 cal MG in the nose along with 300 rounds of ammunition per gun. It carried about 30 pounds less ammunition for the 37 mm but the net effect is a lot more weight up front where it was needed for balance.
This might have substantially improved its flying qualities as compared to the later P-39D.

- Ivan.


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## GregP (Oct 21, 2020)

Source are detailed-but-unsubstantiated claims over the internet about Soviet aerial victories.

All the "lists" I have seen of Soviet victories have been rather detailed, but low on primary sources. Yet ALL show the P-39 as being used by very many pilots with more than 30 victories in P-39s. If you add them all up, you get more victories than the P-51 has in air-to-air combat ... at the cost of very vague sources for the data. Almost all of the lists I got back in the day were internet addresses ending in " .RU".

There is absolutely nothing wrong with Russian data, and they would have been worth saving if the sources were known and actually available to the public. Telling me the source is in a semi-publically-available archive in Moscow at some address doesn't help me get to the source, but that's what I got back in the 1980s / 1990s.

I have several books on Soviet WWII aircraft, all of which are currently in storage. Again, the sources are there, but unavailable to westerners, AFAIK. Even though I was interested, I wasn't about to buy a ticket to Moscow and show up at an archive on the vague chance I'd be admitted.


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## fubar57 (Oct 21, 2020)

Have you seen this site Greg? Soviet top Aces of WWII rating

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## P-39 Expert (Oct 21, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> At the risk of resuming the last world war, have you considered the possibility that the P-39C was much better balanced and may have flown "better" than the P-39D?
> 
> ...


Please expand above.


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## Peter Gunn (Oct 21, 2020)

XBe02Drvr said:


> You choose the weapons, I choose the attire. Agreed?
> Yours:
> View attachment 599041
> 
> ...



*Agreed:*

*Yours:*






*Mine:*








Rats... are they talking about the P-39 again?

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## Stig1207 (Oct 21, 2020)

GregP said:


> Source are detailed-but-unsubstantiated claims over the internet about Soviet aerial victories.
> 
> All the "lists" I have seen of Soviet victories have been rather detailed, but low on primary sources. Yet ALL show the P-39 as being used by very many pilots with more than 30 victories in P-39s. If you add them all up, you get more victories than the P-51 has in air-to-air combat ... at the cost of very vague sources for the data. Almost all of the lists I got back in the day were internet addresses ending in " .RU".
> 
> ...



So the Soviets got such an impreesive performance by removing some excess weight from the P-39? More victories than the P-51!
I would then rather suggest a more plausible reason: the Soviet pilots were simply superior to the American pilots. Perhaps we should add to the good old 'Overpaid, oversexed, overthere'.... overrated?


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## Ivan1GFP (Oct 21, 2020)

Hello P-39 Expert



P-39 Expert said:


> *Is that what made it climb 1000fpm better than the D? I think it was because it was 800+lbs lighter.*



There were obviously some other differences besides the difference in weight. Unless of course you are not following the explanations that have already been presented. What do YOU think the differences were?



P-39 Expert said:


> *Need to prove that.
> .....
> Need to prove that too.*



I don't have to prove a thing if you actually read the reports you are selectively quoting from.



P-39 Expert said:


> *Bell was a real moron. Designed a single engine fighter around a 37mm cannon and a tricycle landing gear. *



Bell actually didn't do that. Bell designed a single engine INTERCEPTOR around a 37 mm cannon. When that failed, he attempted to make it fill the role of a fighter but it didn't have the stretch for the extra equipment and armour.



P-39 Expert said:


> *The .30s in the nose weighed about 100lbs with ammunition. Less the additional 30lbs for the additional 15 37mm rounds and the net decrease is about 70lbs. The nose armor plate was between 70lbs and 100lbs depending on the model. About the same weight. *



I don't think you understand. This isn't the P-39D.
Is the nose armour plate or any other armour plate installed in the P-39C?

- Ivan.


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## P-39 Expert (Oct 21, 2020)

Ivan1GFP said:


> Hello P-39 Expert
> 
> 
> 
> ...


Please expand above.


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## GregP (Oct 21, 2020)

Thanks for that Fubar 57. Yes, I have seen it. Again, no mention of sources except thanks to Alexey Koliush, Alexander Abramov, Igor Utkin, Andrey Mikhailov, Alexander Melnikov, Allan Magnus, Hakkan Gustavson at the bottom of the data. 

Not sure if the Soviet victories match with the Magnus family website, which I have liked for years, as I have not compared them. But that would at least make me feel better about the data. Again, no way to break out the P-39 victories unless the P-39 was the only aircraft they flew. So, it's interesting, but hardly authoritative. 

You can say the same about a lot of data on Soviet activities. Perhaps getting identified as a data source in the former Soviet Union might have been fatal? I can't say and would speculate that the data are difficult to find since so little data with primary sources has been forthcoming from the former Soviet Union after it's collapse. I doubt anyone in Russia is all that interested in releasing the data to the western public.


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## P-39 Expert (Oct 21, 2020)

FLYBOYJ said:


> I tossed my numbers when this discussion seemed over.
> 
> Look at Greg's calculator, he's got it down pretty good and you're able to play with some of things we discussed.
> 
> The error on the page I mentioned, I'll post later


I tried to calculate how far aft the CG moved if the nose armor (71lbs) was removed. I came up with:

Weight 7570lbs CG Arm 134.22 Moment 1016045 From the P-39Q weight chart
Less 71lb Arm 21 Moment 1485 
New Wt. 7499lbs New CGArm 135.29 New Moment 1014560

New CG arm calculated by dividing new moment 1014560 by new weight 7499lbs.

New CG is 1.07 inches aft of old CG (134.22-135.29=1.07).

MAC is 80.64", CG limits 23% to 31% of MAC, or 5.6". 1.07" should be within the CG limits. Sorry I can't make the columns line up.


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## GregP (Oct 21, 2020)

The main difference between the P-39C and P-39D was the addition of self-sealing fuel tanks to the P-39D, but you cannot take data from one airplane and transfer it to another one in another test. You've already been told that. If you want to see the difference, you have to add weight to the same airframe and attempt to test at the same or very nearly the same atmospheric conditions, before too long a time has gone by and things have started wearing out ... like a propeller that is operated on rough strips will lose some thrust over time with use and, if the dust is coral, the engines will wear out 10 times faster or more due to the dust alone.

We already told you most of this, P-39 Expert, and we already told you they didn't typically vary weight in WWII tests because they were interested in the performance of production aircraft with typical war loads, not confirmation of aerodynamic formulas that they KNEW were correct. You either have to go out and buy a P-39 and do the tests yourself or you have to be satisfied with the real data available or in aerodynamic formulas that everyone knows are correct. Making up your own comparisons with data unrelated to real aerodynamic performance won't make them correct.

Maybe I'll stop responding to trolling. I can't believe it's gone 43 pages! ... but it has. Some good stuff in here, but enough would seem to be enough.

I apologize for putting it that way since I am not a moderator in here ... just my impatience showing through. So, cheers and good luck to you, P-39 Expert.

Whatever you do, don't so this to you P-39 / P-63.






It killed Mike Carroll when he did it! He struck the stabilizer when he bailed out and never opened his chute.

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## XBe02Drvr (Oct 21, 2020)

Peter Gunn said:


> *Agreed:*
> 
> *Yours:*
> 
> ...


You defile the honor of the southron gentleman you claim to be! You made your weapons choice in post 837, and are honor bound to stick with it, else I have no obligation to defend my honor against a disgraced, dis-honored item of southron trash! This disreputable affair is dismissed! My Airacobra squadron is on it's way to strafe your hillbilly shack.

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## P-39 Expert (Oct 21, 2020)

GregP said:


> The main difference between the P-39C and P-39D was the addition of self-sealing fuel tanks to the P-39D, but you cannot take data from one airplane and transfer it to another one in another test. You've already been told that. If you want to see the difference, you have to add weight to the same airframe and attempt to test at the same or very nearly the same atmospheric conditions, before too long a time has gone by and things have started wearing out ... like a propeller that is operated on rough strips will lose some thrust over time with use and, if the durst is coral, the engines will wear out 10 times faster or more due to the dust alone.
> 
> *I'm simply determining how weight affects climb on one airplane. Same engine, propeller and horsepower at the same altitude. In the same airframe. Both planes were virtually brand new right off the production line. Only difference was internal equipment resulted in different weights. *
> 
> ...



Please expand above.


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## fubar57 (Oct 21, 2020)

XBe02Drvr said:


> You defile the honor of the southron gentleman you claim to be! You made your weapons choice in post 837, and are honor bound to stick with it, else I have no obligation to defend my honor against a disgraced, dis-honored item of southron trash! This disreputable affair is dismissed! My Airacobra squadron is on it's way to strafe your hillbilly shack.


Gentlemen....gentlemen. Lets's make this fair.....kinda. Choose one but be warned. One has fired off all it's nose ammo and is now dangerously unstable




​In hindsight I should have made one Russian

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## GregP (Oct 21, 2020)

P-39 Expert, I can only answer with a suitable story:

Wants pawn term, dare worsted ladle gull hoe lift wetter murder inner ladle cordage, honor itch offer lodge dock florist. Disk ladle gull orphan worry ladle cluck wetter putty ladle rat hut, an fur disk raisin pimple colder Ladle Rat Rotten Hut.

Wan moaning, Rat Rotten Hut's murder colder inset, "Ladle Rat Rotten Hut, heresy ladle basking winsome burden barter an shirker cockles. Tick disk ladle basking tutor cordage offer groin-murder hoe lifts honor udder site offer florist. Shaker lake! Dun stopper laundry wrote! An yonder nor sorghum-stenches, dun stopper torque wet strainers!"

"Hoe-cake, murder," resplendent Ladle Rat Rotten Hut, an tickle ladle basking an stuttered oft. Honor wrote tutor cordage offer groin-murder, Ladle Rat Rotten Hut mitten anomalous woof. "Wail, wail, wail!" set disk wicket woof, "Evanescent Ladle Rat Rotten Hut! Wares are putty ladle gull goring wizard ladle basking?"

"Armor goring tumor groin-murder's," reprisal ladle gull. "Grammar's seeking bet. Armor ticking arson burden barter an shirker cockles."

"O hoe! Heifer blessing woke," setter wicket woof, butter taught tomb shelf, "Oil tickle shirt court tutor cordage offer groin-murder. Oil ketchup wetter letter, an den - O bore!"

Soda wicket woof tucker shirt court, an whinney retched a cordage offer groin-murder, picked inner widow, an sore debtor pore oil worming worse lion inner bet. Inner flesh, disk abdominal woof lipped honor bet an at a rope. Den knee poled honor groin-murder's nut cup an gnat-gun, any curdled dope inner bet.

Inner ladle wile, Ladle Rat Rotten Hut a raft attar cordage, an ranker dough belle. "Comb ink, sweat hard," setter wicket woof, disgracing is verse. Ladle Rat Rotten Hut entity bet rum an stud buyer groin-murder's bet.

"O Grammar!" crater ladle gull, "Wood bag icer gut! A nervous sausage bag ice!"

"Battered lucky chew whiff, doling," whiskered disk ratchet woof, wetter wicket small.

"O Grammar, water bag noise! A nervous sore suture anomolous prognosis!"

"Battered small your whiff," insert a woof, ants mouse worse waddling.

"O Grammar, water bag mousy gut! A nervous sore suture bag mouse!"

Daze worry on-forger-nut gulls lest warts. Oil offer sodden, thoroughing offer carvers an sprinkling otter bet, disk curl and bloat-thursday woof ceased pore Ladle Rat Rotten Hut an garbled erupt.

Mural: Yonder nor sorghum stenches shut ladle gulls stopper torque wet strainers.


The truth is somewhere in Little Red Riding Hood, spoken with an accent.

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## FLYBOYJ (Oct 21, 2020)

P-39 Expert said:


> I tried to calculate how far aft the CG moved if the nose armor (71lbs) was removed. I came up with:
> 
> Weight 7570lbs CG Arm 134.22 Moment 1016045 From the P-39Q weight chart
> Less 71lb Arm 21 Moment 1485
> ...



You'll be within limits but you better not fire off any ammo or consume much fuel. Use the excel spread sheet Greg put together, he nailed it from what I can see.

Armor removed






No Nose Ammo, Full tanks






No nose ammo, half tanks

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## XBe02Drvr (Oct 21, 2020)

Ivan1GFP said:


> Note that in the typical testing that was conducted, the CoG was typically much further forward (24-25% MAC) than it the weight and balance charts would indicate for normal loaded weight. I am not sure how this was done, but it MIGHT have improved performance.


Oops! I think you're barking up the wrong tree here. For parameters such as top speed, best climb, and to a lesser extent, ceiling, best measured performance occurs with the least airframe drag, which is with CG at the aft limit. This is usually not the most desirable from a handling standpoint, but this is where the horizontal stabilizer is required to generate the least amount of negative lift with its attendant drag.

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## Ivan1GFP (Oct 21, 2020)

Hello P-39 Expert,



P-39 Expert said:


> *That was my point in comparing the C with the D. There were no differences except internal. Same outside, engine, propeller, horsepower. Only difference was weight.*



The point I was trying to raise was that WHERE that weight difference was might make a significant difference in performance.
I believe GregP's explanation is correct but I am still thinking there was something else that wasn't so obvious that might explain the difference in performance.



P-39 Expert said:


> *Please stop with the handling issues. You keep trying to make this plane unflyable when it was obviously easy and pleasant to fly.*



Under some load conditions, it WAS easy and pleasant to fly. Under some load conditions it was NOT. For a P-39 Expert, you really don't seem to have been reading too many pilot reports. Don't just read the ones you like. Read the others as well and figure out why those pilots came up with something different when they are flying "the same" airplane.



P-39 Expert said:


> *You're splitting hairs. Interceptor vs fighter.*



Not hardly. The requirements were just a bit different. Without the Turbo, the P-39 was no longer an interceptor.



P-39 Expert said:


> *No nose armor in the C. You were talking about the difference in weight in the nose, I was explaining that it was about the same after deducting the .30s and adding the nose armor.
> Some reports say that the C did have the armor glass behind the pilot, some don't.*



Actually I was discussing the possible differences in flight performance because of a difference in weight distribution.

- Ivan.


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## Ivan1GFP (Oct 21, 2020)

XBe02Drvr said:


> Oops! I think you're barking up the wrong tree here. For parameters such as top speed, best climb, and to a lesser extent, ceiling, best measured performance occurs with the least airframe drag, which is with CG at the aft limit. This is usually not the most desirable from a handling standpoint, but this is where the horizontal stabilizer is required to generate the least amount of negative lift with its attendant drag.



Hello XBe02Drvr,

I agree you are correct on this. I was thinking more along the lines that without an autopilot, it would be more difficult to hold a marginally stable aircraft at a constant attitude for an optimal climb.

I have attached NACA L-602.
Please read Stability and Control results starting at page 4 and see if you come up with the same conclusions I did.
Seems to me that these people were not convinced that 31% MAC was the correct Aft limit.



P-39 Expert said:


> I tried to calculate how far aft the CG moved if the nose armor (71lbs) was removed. I came up with:
> 
> Weight 7570lbs CG Arm 134.22 Moment 1016045 From the P-39Q weight chart
> Less 71lb Arm 21 Moment 1485
> ...



Hello P-39 Expert,

With the Gear Box Armour in place, the P-39Q at Basic Weight + 200 pound Pilot has a CoG at 30.1623% MAC which is still within the limits of 23-31% MAC.

WITHOUT the Gear Box Armour of 70.74 Pounds at Station 21, The P-39Q at Basic Weight + 200 Pound Pilot has a CoG at 31.6876% MAC which is outside the allowable limits.

- Ivan.

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## XBe02Drvr (Oct 22, 2020)

Ivan1GFP said:


> I have attached NACA L-602.
> Please read Stability and Control results starting at page 4 and see if you come up with the same conclusions I did.


What format is that attachment in? My Android phone says CAN NOT OPEN FILE. No explanation.
However, judging by the W&B worksheets posted by Joe upthread, it appears your conclusions are supported FOR A P39Q. BUT, as pointed out by some of the wiser heads aboard this vessel, extrapolating from one model to another on the assumption that all things remain equal puts one on shaky ground. Devil is in the details, and I haven't seen any credible W&B data yet for the D.
In my experience with aircraft at or near the aft CG limit, at high speed, steady state conditions such as a climb or max speed run, the squirrelliness manifests itself primarily in maneuvering rather than "hunting" in trimmed out steady state flight. I have been slightly out of limits aft on a few occasions, mostly as a result of using standard weights for passengers and baggage. (We used to double the bag count for soldiers going in and out of Ft. Drum, and that probably wasn't adequate still.) You suspect you're slightly out when the nose starts to "hunt" up and down in level flight and you're constantly adjusting pitch trim. On a hot day at 6000 feet between ART and SYR with a full boat and an aft CG, every little thermal bump makes your bird waddle and wag its tail and soon you're driving a barfwagen.


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## XBe02Drvr (Oct 22, 2020)

XBe02Drvr said:


> Devil is in the details, and I haven't seen any credible W&B data yet for the D.


I take that back. I got to digging through the stuff jmcalli2 linked for us back in post 839 (thanks jm!), and found a NACA test report on a P39D s/n 28378, done in early 1943, (no NACA Report # given) which had some scary details mentioned in matter-of-fact language.
1. CG @ 30.2% MAC (0.8% MAC fwd of AFT limit!) is referred to as "Normal". This leaves 0.8% for fuel burn and ammo expenditure. (20MM on test a/c, w/4 .30s in wing LE, 2 .50s in nose)
2. Stall is described as abrupt without buffet warning, accompanied by wing drop, roll oscillations, and a tendency of the stick to thrash laterally if not firmly held. This seems to happen in all speed ranges and configurations. Specifically stated that this makes for an unsatisfactory gun platform for deflection shooting in a turning fight.
3. If ailerons are not exactly centered at the stall, the stall tends to roll sharply away from direction of aileron deflection.
4. Stick force gradient @ "Normal" CG of 30.2% is described as 1.8 lbs/G! A 14.4 lb. pull (which you can EASILY accomplish between fingertips and thumb of your right hand, especially when adrenelated) will put you at *8Gs! Scary!*
This is well below USAAF minimum acceptable value.
5. Ailerons effectiveness is described as unsatisfactory. 
6. Have I scared anybody yet? This is all outlined in straightforward unemotional test pilot language which the uninitiated could easily read without the context to bring out the meaning. The exclamation points, bold print, and caps are mine.
7. I haven't even got into the graphs yet as they aren't easily readable on my Android phone.

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## P-39 Expert (Oct 22, 2020)

Ivan1GFP said:


> Hello XBe02Drvr,
> 
> I agree you are correct on this. I was thinking more along the lines that without an autopilot, it would be more difficult to hold a marginally stable aircraft at a constant attitude for an optimal climb.
> 
> ...


Can you give a specific location in the report?


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## Peter Gunn (Oct 22, 2020)

XBe02Drvr said:


> You defile the honor of the southron gentleman you claim to be! You made your weapons choice in post 837, and are honor bound to stick with it, else I have no obligation to defend my honor against a disgraced, dis-honored item of southron trash! This disreputable affair is dismissed! My Airacobra squadron is on it's way to strafe your hillbilly shack.



SO! Just as I suspected, you would find a tiny loophole to escape an affair of honor! So be it! But fair warning sir fair warning... I will NOT be so generous in any future "disagreements", you are a cad sir, A CAD! But I will magnanimously forego satisfaction at this time.

Send your vaunted Airacobras SUH, there is a flight of Fairey Battles that will be more than a match for your tail heavy - ground loving - spin happy - engine behinders.

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## Peter Gunn (Oct 22, 2020)

fubar57 said:


> Gentlemen....gentlemen. Lets's make this fair.....kinda. Choose one but be warned. One has fired off all it's nose ammo and is now dangerously unstable
> 
> View attachment 599079
> ​In hindsight I should have made one Russian



In the spirit of reconciliation I invite Wes ( 
X
 XBe02Drvr
) to join hands and sing with me now "Don't give me a Pee Thirty Nine... The one with the engine behind..."

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## XBe02Drvr (Oct 22, 2020)

Peter Gunn said:


> you are a cad sir, A CAD!


The ultimate insult, to accuse an organic all-natural guy of being a Computer Aided Design! I'm adding my Kingcobra squadron, all flown by former Soviet aces to the strike force. Say your prayers, laddie!

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## Peter Gunn (Oct 22, 2020)

XBe02Drvr said:


> The ultimate insult, to accuse an organic all-natural guy of being a Computer Aided Design! I'm adding my Kingcobra squadron, all flown by former Soviet aces to the strike force. Say your prayers, laddie!


*KING*cobras you say? You've heard the expression "twice nothing..."

Bring it big boy, we're ready...

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## XBe02Drvr (Oct 22, 2020)

Peter Gunn said:


> *KING*cobras you say? You've heard the expression "twice nothing..."
> 
> Bring it big boy, we're ready...
> 
> View attachment 599146


Funny looking Battles! Might as well be a Sever-sky!


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## Peter Gunn (Oct 22, 2020)

XBe02Drvr said:


> Funny looking Battles!


We upted the ante for your *KING*cobras...

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## Peter Gunn (Oct 22, 2020)

Ivan1GFP said:


> *SNIP*
> 
> With the Gear Box Armour in place, the P-39Q at Basic Weight + 200 pound Pilot has a CoG at 30.1623% MAC which is still within the limits of 23-31% MAC.
> 
> ...



OK, I'm obviously not an expert on this, but to my untrained eye, for a plane that tips the scales at roughly 3.5 - 4.0 TONS, the removal of a mere 70.74 pounds puts the CoG outside of the allowable limits by 1.5253%. To me that means this thing is CLOSE to being out of whack even on a good day with everything in place. Going back several dozen pages, I believe the case was made that the Gear Box Armour was probably added to keep the CoG issue from cropping up.

It seems to me that that theory holds quite a bit of water.

*EDIT*

Also regarding something I saw in post #852 "Interceptor vs. fighter"
In 1939 there _*was*_ a difference. Actually, there probably still is.

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## Ivan1GFP (Oct 22, 2020)

XBe02Drvr said:


> I take that back. I got to digging through the stuff jmcalli2 linked for us back in post 839 (thanks jm!), and found a NACA test report on a P39D s/n 28378, done in early 1943, (no NACA Report # given) which had some scary details mentioned in matter-of-fact language.



Hello XBe02Drvr,

The NACA Memorandum Report L-602 which I attached is in PDF format. It IS a fairly lousy quality scan but readable.
The aircraft tested is the same one 41-28378 (P-39D-1) as the report you are reading and the conclusions are the same so it is probably the same report. It is also why I asked you to start reading at Page 4 for the Stability and Controls section. It kind of struck me as a bit scary as well.

If you have the same report, please observe the CoG range for testing.
The most forward CoG was 25% MAC
at Take-Off Weight 7800 pounds. Actual Flying Weight for testing estimated at 7620 pounds

The most rearward CoG was 30.8% MAC
at Take-Off Weight 7600 pounds. Actual Flying Weight for testing estimated at 7420 pounds

Note that the weights at the test for Aft CoG were still much higher than the numbers we were getting for the Basic Weight + Pilot for the P-39Q. For the P-39Q, that Basic Weight + Pilot is as low as the aircraft can get and the P-39D-1 wasn't even close to its lowest possible weight.
That is why I believe the P-39D and others of the era had a CoG that was several inches further Aft than the later versions.
As for how much, it isn't possible to determine with the data presented in this report because what the loads were to get to 7600 or 7420 pounds were not specified.



P-39 Expert said:


> Can you give a specific location in the report?



Hello P-39 Expert,

I already stated Page 4 in the message YOU QUOTED! Did you even read the message before you quoted it???



Peter Gunn said:


> OK, I'm obviously not an expert on this, but to my untrained eye, for a plane that tips the scales at roughly 3.5 - 4.0 TONS, the removal of a mere 70.74 pounds puts the CoG outside of the allowable limits by 1.5253%. To me that means this thing is CLOSE to being out of whack even on a good day with everything in place. Going back several dozen pages, I believe the case was made that the Gear Box Armour was probably added to keep the CoG issue from cropping up.
> 
> It seems to me that that theory holds quite a bit of water.



Hello Peter Gunn,

That is the thing about the P-39. When the CoG is at the forward end of the allowable range, it handles very well. Burning fuel doesn't really affect it to a great degree because the fuel tanks are very near where the CoG should be. The problem is that when the CoG migrates aft handling gets much less predictable.
The L-602 report also brought up another point: The allowable aft CoG limit was stated to be 31% MAC, but in testing at even 30.8% MAC, they were getting some pretty nasty handling and their Take-Off weight to get to this situation was 7600 pounds which is only 50 pounds below the "Normal" Loaded Weight for the aircraft.
The problem as I stated earlier is that the report doesn't say how they got to 7600 pounds.

The problem as you may be noticing is that SOMEONE, presumably the manufacturer made the determination that 31% MAC was safe. The NACA Test Pilots didn't seem to agree in their report. Handling also normally doesn't go instantly from great to lousy at a specific number. There are generally plenty of degrees in between.



Peter Gunn said:


> Also regarding something I saw in post #852 "Interceptor vs. fighter"
> In 1939 there _*was*_ a difference. Actually, there probably still is.



I believe the best illustration of the difference is the Lockheed F-104 Starfighter.
Interceptor, Yes. Fighter..... Not Really, regardless of how it was employed.

- Ivan.

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## BiffF15 (Oct 22, 2020)

XBe02Drvr said:


> 4. Stick force gradient @ "Normal" CG of 30.2% is described as 1.8 lbs/G! A 14.4 lb. pull (which you can EASILY accomplish between fingertips and thumb of your right hand, especially when adrenelated) will put you at *8Gs! Scary!*
> This is well below USAAF minimum acceptable value..



As a point of reference the F-15 uses about 45lbs of pull at 9 Gs.

Cheers,
Biff

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## P-39 Expert (Oct 22, 2020)

XBe02Drvr said:


> I take that back. I got to digging through the stuff jmcalli2 linked for us back in post 839 (thanks jm!), and found a NACA test report on a P39D s/n 28378, done in early 1943, (no NACA Report # given) which had some scary details mentioned in matter-of-fact language.
> 1. CG @ 30.2% MAC (0.8% MAC fwd of AFT limit!) is referred to as "Normal". This leaves 0.8% for fuel burn and ammo expenditure. (20MM on test a/c, w/4 .30s in wing LE, 2 .50s in nose)
> 2. Stall is described as abrupt without buffet warning, accompanied by wing drop, roll oscillations, and a tendency of the stick to thrash laterally if not firmly held. This seems to happen in all speed ranges and configurations. Specifically stated that this makes for an unsatisfactory gun platform for deflection shooting in a turning fight.
> 3. If ailerons are not exactly centered at the stall, the stall tends to roll sharply away from direction of aileron deflection.
> ...


You're doing your best to scare everyone over basically nothing.

The stick only oscillated laterally in one condition, when high accelerations were reached from recovery from rolls.

"In any condition, at any time after the stall occurred, recovery could be effected promptly by applying down elevator." This was stated more than once.

The report was generally complimentary and all requirements were met.


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## P-39 Expert (Oct 22, 2020)

GregP said:


> P-39 Expert, I can only answer with a suitable story:
> 
> Wants pawn term, dare worsted ladle gull hoe lift wetter murder inner ladle cordage, honor itch offer lodge dock florist. Disk ladle gull orphan worry ladle cluck wetter putty ladle rat hut, an fur disk raisin pimple colder Ladle Rat Rotten Hut.
> 
> ...


Translation?


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## SaparotRob (Oct 22, 2020)

P-39 Expert said:


> Translation?


I think GregP said what we were all thinking.

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## DerAdlerIstGelandet (Oct 22, 2020)

Stop trying to scare me 
X
 XBe02Drvr
!!!!

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## DerAdlerIstGelandet (Oct 22, 2020)

Can someone tell me what we are supposed to be afraid of?


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## Peter Gunn (Oct 22, 2020)

DerAdlerIstGelandet said:


> Can someone tell me what we are supposed to be afraid of?



Flying this...

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## DerAdlerIstGelandet (Oct 22, 2020)

Peter Gunn said:


> Flying this...
> 
> View attachment 599159



What is there to be scared of?

1. All of us supposed scared people have an understanding of weight and balance and CG, and how not to get into that type of situation.

2. None of scared people will ever actually fly that overrated thing, so...

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## Peter Gunn (Oct 22, 2020)

DerAdlerIstGelandet said:


> What is there to be scared of?
> 
> 1. All of us supposed scared people have an understanding of weight and balance and CG, and how not to get into that type of situation.
> 
> 2. None of scared people will ever actually fly that overrated thing, so...



*Resp:*

*1). A few belts of this and I'll wager different:*






*2). See number 1*

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## DerAdlerIstGelandet (Oct 22, 2020)

Peter Gunn said:


> *Resp:*
> 
> *1). A few belts of this and I'll wager different:*
> 
> ...



Not a fan of Ouzo. Now you throw in a good Birnen Schnapps or a quality Scotch or Irish Whiskey and you might be on to something.


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## DerAdlerIstGelandet (Oct 22, 2020)

Are you saying P-39 Exper...

...ehr, I’ll just call him P-39, drinks too much Ouzo?


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## fubar57 (Oct 22, 2020)

Schnapps....yikes. I got my ear pierced after drinking this

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## Peter Gunn (Oct 22, 2020)

Actually I'm not a fan of Ouzo either, except that I will say the two most alcohol induced "dumbass" moments came at the hands of said Ouzo.

One involving a Corvette and another involving a mailbox (and a very nice police officer)...

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## DerAdlerIstGelandet (Oct 22, 2020)

fubar57 said:


> Schnapps....yikes. I got my ear pierced after drinking this
> 
> View attachment 599177​



I will have to take a picture of my good stuff later. You should be able to taste the fruit in a good quality schnapps. Every year when I go home to Germany, I bring some back.

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## jmcalli2 (Oct 22, 2020)

Stig1207 said:


> So the Soviets got such an impreesive performance by removing some excess weight from the P-39? More victories than the P-51!
> I would then rather suggest a more plausible reason: the Soviet pilots were simply superior to the American pilots. Perhaps we should add to the good old 'Overpaid, oversexed, overthere'.... overrated?


My understanding was that the Russians also pushed the Allison way past the USAAC's limits. The price was more frequent overhauls. It would be interesting to know how many V-1710s the USA sent to Russia. outside of those mounted in aircraft.


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## windhund116 (Oct 22, 2020)

BiffF15 said:


> As a point of reference the F-15 uses about 45lbs of pull at 9 Gs.
> 
> Cheers,
> Biff



F15 is not fly-by-wire?


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## DerAdlerIstGelandet (Oct 22, 2020)

windhund116 said:


> F15 is not fly-by-wire?



Correct me if I am wrong 

 BiffF15
, but the latest generation of F-15’s are fly-by-wire.


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## GregP (Oct 22, 2020)

Have we bought any of the latest F-15s or are they just offered for sale? The F15EX is being touted right now as a good choice and is FBW. I think we ordered 8 of them, but am not exactly sure.

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## DerAdlerIstGelandet (Oct 22, 2020)

GregP said:


> Have we bought any of the latest F-15s or are they just offered for sale? The F15EX is being touted right now as a good choice and is FBW. I think we ordered 8 of them, but am not exactly sure.



The USAF has placed an order for brand new F-15EX’s.

Boeing lands the first order of the F-15EX

My office is just upstairs from the F-15 line. Sometimes I go down there to use the bulk mail room. I know a few guys on the line. Needless to say they are all pretty stoked about it. In the same building they will be manufacturing the T-7.

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## BiffF15 (Oct 22, 2020)

windhund116 said:


> F15 is not fly-by-wire?



The F-15QA (Qatar), the late model F-15SA (Saudi) and F-15EX are all FBW. The rest are not. However, it’s a great flying plane.

Cheers,
Biff

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## windhund116 (Oct 22, 2020)

BiffF15 said:


> The F-15QA (Qatar), the late model F-15SA (Saudi) and F-15EX are all FBW. The rest are not. However, it’s a great flying plane.
> 
> Cheers,
> Biff



Air superiority fighter supreme!


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## nuuumannn (Oct 23, 2020)

fubar57 said:


> Schnapps....yikes. I got my ear pierced after drinking this



At least it'll grow over, most people end up with regretful tattoos!


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## Stig1207 (Oct 23, 2020)

jmcalli2 said:


> My understanding was that the Russians also pushed the Allison way past the USAAC's limits. The price was more frequent overhauls. It would be interesting to know how many V-1710s the USA sent to Russia. outside of those mounted in aircraft.



I have read that P-40's were standing around awaiting overhaul/ new engines , but whether that was just one unit or whether it was general I'm not sure. It's one thing, though, to excced the redline limits in a critical situation and get out of dodge; but if it's to bridge a performance gap with the enemy on a regular basis, then it's a less effective combat aircraft, imo.

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## XBe02Drvr (Oct 23, 2020)

P-39 Expert said:


> The stick only oscillated laterally in one condition, when high accelerations were reached from recovery from rolls.


In other words, when you're trying to recover from the unwarned high G stall/snaproll out of your turn when you were trying to pull enough lead on your victim to get a shot, and there you are recovering from an upset right in front of his wingman's guns. GAME OVER. That matter of fact test pilot language is full of pitfalls for those who don't understand the context.


P-39 Expert said:


> "In any condition, at any time after the stall occurred, recovery could be effected promptly by applying down elevator." This was stated more than once.


Once again you missed the context. That statement was made in reference to simple, coordinated, one G stalls in various configurations and maneuvers. It then went on to glaze the reader's eyes over with a lengthy discussion of sideslip angles and control surface deflections ("test pilot talk"), the gist of which was that any stall at higher G with even the slightest sideslip will result in a sharp roll without warning AGAINST aileron deflection. After you've read that sort of test pilot verbiage and then gone out and banged your helmet HARD against the side of the canopy while your world turned sharply upside down in the hands of Zeus a few times, you develop a sense of context. If you're as hard headed as I am, it takes a few tries and an aching neck before enlightenment dawns. Once preconceived notions give way to understanding, it's kind of fun. You're no longer sitting in the airplane and driving it; you're wearing it like a tightly strapped backpack, and it becomes an extension of your body and your will.



P-39 Expert said:


> The report was generally complimentary and all requirements were met.


Cherry picking again. In several places it stated in low key unobtrusive language that the test aircraft fell short of USAAF published standards in one way or another, most notably stick free static stability (displacement oscillation damping) and stick force gradient/G. That last one is a biggie. A 14.4 lb pull (thumb and fingertips of your right hand) can put 8Gs on you and your aircraft at "normal" (30.2% MAC) CG. The plane can take it; you can't. This is well below USAAF minimum standard, and WAY below desirable values.
That super light stick force gradient combined with the no-warning abrupt stall under G load sets up a scenario which may not be apparent to nonflyers, the accelerated secondary stall. If the pilot pulls hard enough in a high G maneuver to stall the plane and the ailerons and rudder aren't perfectly coordinated, the resulting sudden snap AGAINST the ailerons is apt to set the adrenaline pumping and the right arm tensing. As the plane sorts itself out and is once again flying and the windshield is full of trees getting bigger FAST, the resulting pull on the stick is apt to be greater than the 7-8 pounds required for a smooth manageable pullout, and a secondary stall results at 4 or 5 Gs with another departure from controlled flight, recovery, and panicked secondary stall, until altitude runs out. Desirable stick force gradients are a lesson written in blood.
BTW, they somehow managed to ballast the test airplane to a 24% MAC CG, where it managed a much more reasonable stick force gradient.
Not trying to scare anybody, just verifying some of the less than complimentary opinions that have circulated about the plane. No silk purses here.

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## DerAdlerIstGelandet (Oct 23, 2020)

Ahhhhh you’re scaring me!!

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## Ivan1GFP (Oct 23, 2020)

Hello XBe02Drvr,

One of the other things worth noting is that with the CoG at 30.2% MAC, the stick only needs to move 1 inch to go from CL 0.2 to CLmax of 1.4.
In combination with very light stick forces, this is not a good thing.
This is why I have commented that control harmony was poor. Aileron forces were noted as fairly high.
It gets a bit better at 2.7 inches with CoG at the forward end of the range.

- Ivan.


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## DerAdlerIstGelandet (Oct 23, 2020)

Ivan1GFP said:


> Hello XBe02Drvr,
> 
> One of the other things worth noting is that with the CoG at 30.2% MAC, the stick only needs to move 1 inch to go from CL 0.2 to CLmax of 1.4.
> In combination with very light stick forces, this is not a good thing.
> ...



Aaaaarrrrggghhhh, stop scarying me!!!


----------



## Ivan1GFP (Oct 23, 2020)

DerAdlerIstGelandet said:


> Aaaaarrrrggghhhh, stop scarying me!!!



Halloween IS coming up!

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## P-39 Expert (Oct 23, 2020)

XBe02Drvr said:


> In other words, when you're trying to recover from the unwarned high G stall/snaproll out of your turn when you were trying to pull enough lead on your victim to get a shot, and there you are recovering from an upset right in front of his wingman's guns. GAME OVER. That matter of fact test pilot language is full of pitfalls for those who don't understand the context.
> 
> Once again you missed the context. That statement was made in reference to simple, coordinated, one G stalls in various configurations and maneuvers. It then went on to glaze the reader's eyes over with a lengthy discussion of sideslip angles and control surface deflections ("test pilot talk"), the gist of which was that any stall at higher G with even the slightest sideslip will result in a sharp roll without warning AGAINST aileron deflection. After you've read that sort of test pilot verbiage and then gone out and banged your helmet HARD against the side of the canopy while your world turned sharply upside down in the hands of Zeus a few times, you develop a sense of context. If you're as hard headed as I am, it takes a few tries and an aching neck before enlightenment dawns. Once preconceived notions give way to understanding, it's kind of fun. You're no longer sitting in the airplane and driving it; you're wearing it like a tightly strapped backpack, and it becomes an extension of your body and your will.
> 
> ...


"In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.

Chuck Yeager's favorite plane. Until he got a Merlin P-51.


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## fubar57 (Oct 23, 2020)

Chuck Yeager never flew it in combat

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## P-39 Expert (Oct 23, 2020)

jmcalli2 said:


> My understanding was that the Russians also pushed the Allison way past the USAAC's limits. The price was more frequent overhauls. It would be interesting to know how many V-1710s the USA sent to Russia. outside of those mounted in aircraft.


I have read that they used combat power 3000rpm from takeoff until they returned from their mission. Engine life was something like 50 hours. Of course with only 87 gallons of gas and no drop tank their missions were only on the order of about a half hour.

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## Ivan1GFP (Oct 23, 2020)

P-39 Expert said:


> "In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.



Hello P-39 Expert,

That recovery might be just a LITTLE slower if your aeroplane just snap rolled and is inverted.



P-39 Expert said:


> Chuck Yeager's favorite plane. Until he got a Merlin P-51.



His comment about the P-39 was that he was willing to fight anyone AT LOW ALTITUDE.
Apparently he didn't think it had any useful high altitude capability either.

.......

Have you thought about what it meant for the P-39D-1 to have a CoG at 30.2% MAC when loaded to 7600 pounds?
This is not light for a P-39D. There isn't a lot to leave off to get down to that weight which is only about 50 pounds below its normal loaded weight.

- Ivan.


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## GregP (Oct 23, 2020)

*Make Me Operations*

Don't give me a P-38 with props that counter-rotate
They'll loop, roll and spin but they'll soon auger in
Don't give me a P-38!

CHORUS:
Just make me Operations
Way out on some lonely atoll
For I am too young to die
I just want to go home.*

Don't give me a P-39 with an engine that's mounted behind
She'll tumble and spin, she'll auger you in
Don't give me a P-39.

Don't give me an old Thunderbolt. It gave many pilots a jolt
It looks like a jug and it flies like a tug
Don't give me an old Thunderbolt!

Don't give me a Peter Four Oh, a hell of an airplane, I know
A ground loopin' bastard. You're sure to get plastered
Don't give me a Peter Four Oh.

Don't give me a P-51, it was all right for fighting the hun
But with coolant tank dry. you'll run out of sky
Don't give me a P-51.

Don't give me a P-61, for night flying is no fun
They say it's a lark. but I'm scared of the dark
Don't give me a P-61.

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## glennasher (Oct 23, 2020)

fubar57 said:


> Chuck Yeager never flew it in combat




And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile. 
And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.

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## P-39 Expert (Oct 23, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> That recovery might be just a LITTLE slower if your aeroplane just snap rolled and is inverted.
> 
> ...


P-39D was a dog at 7650lbs. Could be made competitive by losing the nose armor and the .30s. Move the radio up from the tail cone for balance. For the umpteenth time.


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## P-39 Expert (Oct 23, 2020)

glennasher said:


> And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
> There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile.
> And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.


The Russians beat the Luftwaffe with the P-39, after they lightened it a little.


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## DerAdlerIstGelandet (Oct 23, 2020)

glennasher said:


> And he wasn't an average, everyday pilot, either, he was pretty gifted at the job. An average schmuck like me would have been in serious trouble with a 39.
> There's a reason we gave them to the Russians, we didn't really want them. That's been abundantly clear. I'm pretty sure the only reason we used them at all, was because that's all we had available for awhile.
> And after the "new and improved" P-63 came out, we (the US) used it for target practice, which says enough, right there. We used it for TARGET PRACTICE. I don't much give a rip what the Russians did with it, we used it for TARGET PRACTICE. Enough said.



For god sakes, stop scaring me!!!

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## fubar57 (Oct 23, 2020)

And for the umpteenth time, if it was that easy, why didn't Bell do it?

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## glennasher (Oct 23, 2020)

P-39 Expert said:


> The Russians beat the Luftwaffe with the P-39, after they lightened it a little.


Of course they did, all those Yaks and Lavochkins, Migs and others had nothing whatsoever to do with that, right?

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## DerAdlerIstGelandet (Oct 23, 2020)

fubar57 said:


> And for the umpteenth time, if it was that easy, why didn't Bell do it?



They were not experts.



And they were scared.

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## GrauGeist (Oct 23, 2020)

glennasher said:


> Of course they did, all those Yaks and Lavochkins, Migs and others had nothing whatsoever to do with that, right?


Or the P-40, depending on who you talk to...


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## XBe02Drvr (Oct 23, 2020)

Ivan1GFP said:


> One of the other things worth noting is that with the CoG ta 30.2% MAC, the stick only needs to move 1 inch to go from CL 0.2 to CLmax of 1.4.


Only test pilots notice or care how much travel of the controls it takes to make various maneuvers, unless they threaten to hit their stops, or are so extreme as to be awkward in the cockpit. (6'5" instructor in a J3 Cub trying to keep hands and feet clear while student enters and recovers from spins.) What matters to everyday pilots is control pressures, not control displacements.


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## XBe02Drvr (Oct 23, 2020)

P-39 Expert said:


> "In ANY condition, at ANY time after the stall occurred, recovery could be effected promptly by applying down elevator". Stated in the report more than once. I read the entire report.
> 
> Chuck Yeager's favorite plane. Until he got a Merlin P-51.


And like the prudent pilot he was, he saw to it his "favorite plane" was ballasted so that it's behavior was safe and responsive. Less renowned and less experienced pilots who had to fly it "loaded for bear" weren't so privileged.


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## FLYBOYJ (Oct 23, 2020)

P-39 Expert said:


> The Russians beat the Luftwaffe with the P-39, after they lightened it a little.



The Russians beat the Luftwaffe with superior numbers, the P-39 was just part of the equation.

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## GrauGeist (Oct 23, 2020)

Yeager never flew the P-39 in combat, though.
He was assigned to the 363rd FS, 357th FG and he may have flown a P-39 stateside, but the 357th FG was the first 8th AF outfit supplied with the Mustang in February 1944.


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## Ivan1GFP (Oct 24, 2020)

P-39 Expert said:


> P-39D was a dog at 7650lbs. Could be made competitive by losing the nose armor and the .30s. Move the radio up from the tail cone for balance. For the umpteenth time.



Hello P-39 Expert,

For the umpteenth time:
If this is really your response after all the information and explanations and evidence presented to you, either you are incapable of understanding weight and balance of aircraft or cannot comprehend how this information fits together.
You can wish whatever you want, but there were many intelligent and skilled people on the scene when YOU were not and I would trust their conclusions over yours. You clearly do not qualify as a P-39 "Expert".

- Ivan.

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## XBe02Drvr (Oct 24, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> For the umpteenth time:
> If this is really your response after all the information and explanations and evidence presented to you, either you are incapable of understanding weight and balance of aircraft or cannot comprehend how this information fits together.
> ...


Send him to UPT. Hopefully that would knock some sense into him before he washes out. I would even go back on active duty if I could be his instructor in Primary. Oh, the fun we would have!

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## PAT303 (Oct 24, 2020)

Ivan1GFP said:


> If this is really your response after all the information and explanations and evidence presented to you, either you are incapable of understanding weight and balance of aircraft or cannot comprehend how this information fits together.



Didn't someone say this about 15 pages back, post 576, that handsome fella, from Australia I think

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## Stig1207 (Oct 24, 2020)

P-39 Expert said:


> The Russians beat the Luftwaffe with the P-39, after they lightened it a little.



The 8th wasn't mighty, it was a myth. They never met a Luftwaffe aircraft over Germany; LW wrecks were strewn all over the steppes.

Did you by any chance follow the link I provided somewhere about post #700? It could give you a bit of an insight into what sought of overclaiming that was going on and how that is going to effect the P-39s combat record. The Soviets did better with the P-39 than the Americans, but not 20-fold better. 

The Lutwaffe certainly didn't seem to notice that they were beaten by the P-39 on the EF.


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## Reluctant Poster (Oct 24, 2020)

Mad Dog said:


> According to whom? After all, despite carrying the much heavier 37mm cannon and the weight of the long driveshaft, the P-39 was lighter than the P-40 models with the same engine versions. This was reflected in the P-39s higher speed, higher rate of climb and superior ceiling to equivalent P-40 models. Indeed, it's fair to suggest the Allied war effort would have been better off it Curtiss had been told to build P-39s instead of P-40s.
> The Airacuda suffered due to a *bad concept,* but was still faster and heavier-armed than equivalent attack aircraft such as the A-18 Curtiss Shrike
> The XP-77 was as unlikely as many other similar lightweight fighter designs made in France, but it still managed to reach 330mph on a 500hp engine, which was quite an engineering achievement.
> The XP-59 was vastly constrained by both the restrictions of the requirement and the restrictions on information about the new jet engines given to Bell by the USAAC. They weren't given any design information on the engines other than rough external dimensions! At the same time, they were told they had to make the aircraft big enough to carry two engines, lots of fuel and be very safe for pilots unused to the new jets. The result was designed more as a trainer than a fighter. BTW, the only other operational fighter to get the same J-31 engine was the Ryan Fireball, which was actually slower than the XP-59. Bell's development of a better fighter design, the XP-59B, was transferred to Lockheed and was developed into the P-80 Shooting Star, which _was_ far superior to contemporary prop fighters.
> And how many successful fighter designs did Bell's much bigger competitor Curtiss make after the P-40? Yup, zero.



The Airacuda wasn't an attack aircraft it was supposed to be a bomber destroyer, comparisons to the A-18 are moot.

Did the XP-77 actually achieve 330 mph? The testing program was very short lived. One look at the The XP-77 with the pilot sitting so far aft makes you wonder how effective it could have been. Deflection shooting would be out of the question 

The P-59A was not designed as a trainer. It was supposed to be a fighter. Due to it poor performance orders were cut back and it was relegated to the training role.
The J-31 you disparage is basically the Welland used in the Meteor MkI (Both based on the Whittle WB.2/23) which despite being heavier than the P-39A was much faster. As to the Me 262 there is no comparison.
From ch11-2
_Although having about the same total thrust as the Me 262, along with a thrust-to-weight ratio over 30 percent greater than that of the German aircraft, the P-59A was slower by about 130 miles per hour. Analysis shows that the 65-percent-greater wing area and consequent greater drag area of the P-59A was responsible for much but not all of the difference in performance of the two aircraft. Perhaps the thick airfoil sections of the P-59A or some other sources of added drag contributed to its poor performance, or perhaps the engines did not perform as anticipated. An obvious question concerns the choice of so large a wing area for the aircraft. In comparison with the 60-poundper-square-foot wing loading of the Me 262, the corresponding value for the Airacomet was 28 pounds per square foot. The use of sophisticated leading-edge and trailing-edge high-lift devices on the Me 262 gave acceptable takeoff, landing, and maneuver characteristics with a small wing area and high wing loading on this aircraft. Only small, simple, inboard trailing-edge flaps were used on the P-59A, and the resultant low maximum lift coefficient no doubt played a large part in dictating the choice of a low wing loading and associated large wing area.
In any event, the poor performance of the P-59A precluded its adoption as a production fighter for the U.S. Armed Forces. The P-59 is included here only because of its historic interest as the first jet aircraft developed in the United States. _

As I stated in another post Curtiss, in my opinion, was a basket case long before the end of WWII. Saying Bell was better than Curtiss is, as my uncle used to say, like beating a one legged man in an ass kicking contest. I believe he meant donkeys.


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## Ivan1GFP (Oct 24, 2020)

PAT303 said:


> Didn't someone say this about 15 pages back, post 576, that handsome fella, from Australia I think



Hello PAT303,

You were probably correct, but I try to give folks the benefit of the doubt.
I just don't expect to find religious fanatics when it comes to WW2 aircraft and there is a pretty good chance that is what is happening here.

The discussion wasn't a total waste. Think of all the entertainment we have gotten in the last 15 pages.

- Ivan.

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## Reluctant Poster (Oct 24, 2020)

I think this point has been made before. The P-39 had a very high accident rate in the training programs in the US.

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## fubar57 (Oct 24, 2020)

But of course, almost all the P-39's weren't lost from uncontrollable tumbling. We know that for a fact

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## Reluctant Poster (Oct 24, 2020)

Reluctant Poster said:


> I think this point has been made before. The P-39 had a very high accident rate in the training programs in the US.
> View attachment 599408


I should also note that you were more likely to die in a P-39 accident that in any other fighter except for the P-38. Doing the math the fatality rate per 100,000 flying hours was 46.7 for the P-39, with the “runner up” P-38 at 33.4. The P 40 was 17.1, the P-47 was 16.8 and the P-51 was 16.7.

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## Peter Gunn (Oct 24, 2020)

DerAdlerIstGelandet said:


> For god sakes, stop scaring me!!!


*BOOOOOOOO!!!*






*BOOOOO I SAYS!!!*

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## FLYBOYJ (Oct 24, 2020)

P-39 Expert said:


> P-39D was a dog at 7650lbs. Could be made competitive by losing the nose armor and the .30s. Move the radio up from the tail cone for balance. For the umpteenth time.


And for the umpteenth time, we showed you what will happen if you remove nose armor and any weight forward of the CG. Unless you calculate exactly where you think you can put this radio, you're delusional!


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## DerAdlerIstGelandet (Oct 24, 2020)

Peter Gunn said:


> *BOOOOOOOO!!!*
> 
> View attachment 599417
> 
> ...

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## glennasher (Oct 24, 2020)

Am I reading that chart right? Almost 10% of the total P-39 production was lost in accidents? That percentage says quite a bit, right there...........


Ivan1GFP said:


> Hello PAT303,
> 
> You were probably correct, but I try to give folks the benefit of the doubt.
> I just don't expect to find religious fanatics when it comes to WW2 aircraft and there is a pretty good chance that is what is happening here.
> ...



That percentage of "wastage" in training alone should have cancelled the whole program, except maybe in the eyes of those who can't absorb information contrary to their dogmatic beliefs, maybe.


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## GrauGeist (Oct 24, 2020)

From post #541 in this thread:


GrauGeist said:


> A quick glance at Joe Baugher's site shows that six P-39s out of the production batch 41-6722/41-7115 (P-39D-BE) crashed due to spin.
> There's many more out of the batch that indicate wrecking with no specifics - those could be crossed with the USAAF MACR reports for details.


While I was glancing through that batch of S/Ns looking for spin incidents, I did see a considerable amount of accidents (many fatal) due to training incidents.
And that was just in the 41-6722 through 41-7115 production.


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## fubar57 (Oct 24, 2020)



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## XBe02Drvr (Oct 24, 2020)

Is this horse dead yet? Can we avast kicking now?


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## GregP (Oct 24, 2020)

You can't just look at airplane accidents ... I think you have to add in sorties or hours so you can compare apples to apples.

Table 214 lists the accident rates (per hundred thousand flying hours). The highest accident rate was the A-36 at 274, followed by the P-39 at 245. The P-38 was at 139, the P-40 at 188. The P-47 was at 127 and the P-51 was at 105.

So, aside from the A-36, the P-39 had the highest accident rate. We can excuse the A-36 because it was a light bomber and dive bombing is inherently more dangerous than not dive bombing, especially in training. But the P-39 was THE most dangerous fighter (in U.S. service anyway) that was not a dive bomber, too, to fly.

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## GrauGeist (Oct 24, 2020)

XBe02Drvr said:


> Is this horse dead yet? Can we avast kicking now?


Like this, perhaps?




_(image source: Fubar57's gallery of nessecary and practical illustrations)_

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## GregP (Oct 24, 2020)

So, where exactly is Fubar 57's gallery? Looks like a great source!

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## jmcalli2 (Oct 24, 2020)

Reluctant Poster said:


> The Airacuda wasn't an attack aircraft it was supposed to be a bomber destroyer, comparisons to the A-18 are moot.
> 
> Did the XP-77 actually achieve 330 mph? The testing program was very short lived. One look at the The XP-77 with the pilot sitting so far aft makes you wonder how effective it could have been. Deflection shooting would be out of the question
> 
> ...



Just a thought on the P-59A; could the huge wing be a 'safety' feature, anticipating engine failures, designed to allow the plane to glide back to base?
P-39 wing loading was much higher than 28 lbs/sqft.


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## GregP (Oct 24, 2020)

At 11,040 lbs, the P-51B's wing loading ws 28.6 lbs.sq in. and 11,040 was takeoff weight for the aircraft. Oh, and they did a lot of gliding because they ran out of fuel semi-often, according to the pilots who flew them. At the Planes of Fame, we've had 3 or 4 guys who flew OUR tail number come and give a talk. Many P-59 pilots ran out of fuel and glided to the nearest airport and called for jet fuel from the nearest bar, which usually had a telephone. Jet fuel wasn't very widely available , even in 1949.

According to the book "Flame Powered" as well as former Bell employees, the huge wings were because they didn't give Larry Bell much information except a big block of wood and told him the engines would not be any bigger than the block of wood. So, Bell designed an engine bay around it, and even had to add engine mounts later when the exact location of them was passed along. They put the big wing on because they didn't have any information and erred on the "more area" side.

Also, they didn't tell Bell how much air the engines used, so the intakes are WAY oversize, and create a lot of drag when air goes in, circulates around in the intake, and leaks back out the front because there isn't enough air used to take it all. I can tell you from personal experience that the build quality is pretty good. But, Bell Aircraft simply didn't have much information about the engines and built what is basically a test bed for the engines.

The follow-on Bell XP-83 flew in Feb 1945 and did 522 mph (840 km/h) at 15,660 ft (4,773 m).

The top speed of the Me 262 A-1 was 560 mph, so the XP83 wasn't far off when Bell had more information. The Me 262 had a service ceiling of 37,000 feet and XP-83's service ceiling was 45,000 feet. The XP-83's rate of climb was 5,650 fpm versus 3,900 fpm for the Me 262. The XP-83's range was 1,730 miles versus 650 miles for the Me 262.

So, again, when Bell had more information, they didn't exactly do badly. The XP-83 beat the Me 262 in all specs except top speed, and the top speeds were very close.

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## windhund116 (Oct 24, 2020)

What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?

Thanks!


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## wuzak (Oct 24, 2020)

GregP said:


> The follow-on Bell XP-83 flew in Feb 1945 and did 522 mph (840 km/h) at 15,660 ft (4,773 m).
> 
> The top speed of the Me 262 A-1 was 560 mph, so the XP83 wasn't far off when Bell had more information. The Me 262 had a service ceiling of 37,000 feet and XP-83's service ceiling was 45,000 feet. The XP-83's rate of climb was 5,650 fpm versus 3,900 fpm for the Me 262. The XP-83's range was 1,730 miles versus 650 miles for the Me 262.
> 
> So, again, when Bell had more information, they didn't exactly do badly. The XP-83 beat the Me 262 in all specs except top speed, and the top speeds were very close.



Having twice the thrust of the Me 262 helped (2 x 4,000lbf vs 2 x 1,980lbf).

The XP-83 was about 30mph faster than the Meteor F.III, which was in service by late 1944, first flying in April 1943. Again the thrust of the F.III's engines were well down on the XP-83's (2 x 2,400lbf).

When the XP-83 was making its first flight the Meteor F.IV was entering production. The F.IV had more powerful engines (3,500lbf) and was about 50mph faster (best speed was at sea level and 60mph faster than XP-83's best speed).

And the XP-83 didn't match the P-80A, which was in production at the time, and also had about half the thrust of the XP-83.

So Bell wasn't doing _that _well.


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## GregP (Oct 24, 2020)

Actually, I didn't mean the XP-83 was a real winner. I meant that, for the time, after they got the information needed for a successful design, their design was right there in the ballpark.

Wasn't the best of the lot, but also wasn't bad. I don't think it should have been bought over what WAS bought, but it wasn't a P-59, either.


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## P-39 Expert (Oct 25, 2020)

FLYBOYJ said:


> And for the umpteenth time, we showed you what will happen if you remove nose armor and any weight forward of the CG. Unless you calculate exactly where you think you can put this radio, you're delusional!


I have always said that removing the nose armor would require moving the radio (approx. 50lbs) from the tail cone (arm approx. 278) up to just aft of the aft cabin armor plate (arm approx. 154). This would move the CG from arm 134.32 to arm 134.56, a difference of .24 of one inch, still within CG limits. By the way, your excel weight and balance chart is great.

Even though Bell (the manufacturer) said that the nose armor plate was not necessary for balance.


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## FLYBOYJ (Oct 25, 2020)

P-39 Expert said:


> I have always said that removing the nose armor would require moving the radio (approx. 50lbs) from the tail cone (arm approx. 278) up to just aft of the aft cabin armor plate (arm approx. 154). This would move the CG from arm 134.32 to arm 134.56, a difference of .24 of one inch, still within CG limits. By the way, your excel weight and balance chart is great.



Now you're getting it, and thanks, but that chart was Greg's invention. 


P-39 Expert said:


> Even though Bell (the manufacturer) said that the nose armor plate was not necessary for balance.


And I guess we showed, based on Bell's own data, they were wrong.


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## P-39 Expert (Oct 25, 2020)

Reluctant Poster said:


> I think this point has been made before. The P-39 had a very high accident rate in the training programs in the US.
> View attachment 599408


Again, training flights would probably result in more accidents than operational flights by experienced pilots who have completed training.


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## P-39 Expert (Oct 25, 2020)

FLYBOYJ said:


> Now you're getting it, and thanks, but that chart was Greg's invention.
> 
> And I guess we showed, based on Bell's own data, they were wrong.


The manufacturer was wrong and we guys on a message board are right?


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## fubar57 (Oct 25, 2020)

P-39 Expert said:


> Again, training flights would probably result in more accidents than operational flights by experienced pilots who have completed training.


...and these were quite possibly due to the tumbling that an inexperienced pilot could not get out of


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## ThomasP (Oct 25, 2020)

Don't know how much this applies, but the P-40 was also used for advanced flight training (don't know if that is the correct term), which is part of the reason there were so many lost stateside. If the number of P-40 crashes per flight hour is significantly lower than for the P-39, that may imply the P-39 was not as safe to fly (at least during the learning period).


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## FLYBOYJ (Oct 25, 2020)

P-39 Expert said:


> The manufacturer was wrong and we guys on a message board are right?



It hasn't been the first time!!!

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## P-39 Expert (Oct 25, 2020)

windhund116 said:


> What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?
> 
> Thanks!


Early P-39D/F/K/L with the -35 or -63 engines (8.8 supercharger gears) couldn't get much above 18000' with a drop tank. As with any contemporary fighter most aerobatic maneuvers were prohibited, the drop tank had to be jettisoned before combat. Without the drop tank about 22500' could be gained at normal power (2600rpm) and about 27500' at combat power (3000rpm). But the drop tanks were almost always used. The Russians hardly ever used drop tanks and lightened their planes by removing the .30cal MGs, some armor and the IFF radio so their performance was much better.

A bomb could be accurately delivered with little practice by dive bombing, really more glide bombing. Normally high altitude wasn't needed on a bombing mission as the only way to accurately deliver the bomb was by diving.

Later N/Q models would cruise at 25000' with a drop tank and the N would cruise at 30000' in clean condition per the pilot's manual.

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## GregP (Oct 25, 2020)

But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.

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## Stig1207 (Oct 26, 2020)

GregP said:


> But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.



The most important thing about high altitude is getting up there first; over New Guinea the P-39's usually gained altitude advantage over the Zero's due to the early warning provided by the Coast Watchers.

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## P-39 Expert (Oct 26, 2020)

GregP said:


> But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.


I don't know about that. With the early P-39D/K/L in 1942 you are still looking at 360mph at 22500', very competitive in the Pacific. 40mph faster than a Zero. Would climb that high easily without a drop tank. 

A P-39N speed graph is attached. There are more graphs of the Q that show even faster speeds.

In 1943 there aren't going to be any FW190As at 30000'. No F4Fs. Not many Zeros or Oscars. I agree that there were not many P-39Ns cruising at 30000' but the capability was there.

I cringe whenever I hear 30000' mentioned. I just don't see it. Highest need for a fighter to go is maybe 27000' in Europe with the B-17s and B-24s at 25000'. Getting to 30000' was such a chore at wide open throttle crawling up at less than 1000fpm. Hard enough in test situations, much less actual combat. Certainly not by any Japanese bombers.


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## jmcalli2 (Oct 26, 2020)

GregP said:


> At 11,040 lbs, the P-51B's wing loading ws 28.6 lbs.sq in. and 11,040 was takeoff weight for the aircraft. Oh, and they did a lot of gliding because they ran out of fuel semi-often, according to the pilots who flew them. At the Planes of Fame, we've had 3 or 4 guys who flew OUR tail number come and give a talk. Many P-59 pilots ran out of fuel and glided to the nearest airport and called for jet fuel from the nearest bar, which usually had a telephone. Jet fuel wasn't very widely available , even in 1949.
> 
> According to the book "Flame Powered" as well as former Bell employees, the huge wings were because they didn't give Larry Bell much information except a big block of wood and told him the engines would not be any bigger than the block of wood. So, Bell designed an engine bay around it, and even had to add engine mounts later when the exact location of them was passed along. They put the big wing on because they didn't have any information and erred on the "more area" side.
> 
> ...



Great info! Thanks.

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## jmcalli2 (Oct 26, 2020)

windhund116 said:


> What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?
> 
> Thanks!



http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf

Hope that helps.

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## Ivan1GFP (Oct 26, 2020)

Hello P-39 Expert,



P-39 Expert said:


> The manufacturer was wrong and we guys on a message board are right?



Bell made a lot of unsubstantiated claims to sell his aircraft.

It is quite astonishing to see this statement from YOU. You want us to believe your performance and handling claims when the trained test pilots, and combat pilots who actually flew the aircraft report something quite different.



P-39 Expert said:


> I don't know about that. With the early P-39D/K/L in 1942 you are still looking at 360mph at 22500', very competitive in the Pacific. 40mph faster than a Zero. Would climb that high easily without a drop tank.



Here you go again with the "40 mph faster than a Zero". The facts simply don't agree with you.
When a captured and beat to crap and rebuilt aircraft can hit 335 MPH in testing without emergency power, what do you think one that HASN'T been wrecked and rebuilt can do when its pilot chooses to use emergency power?
Your numbers don't add up.
These early P-39s also were equipped with engines that had a critical altitude at around 12,000 feet. They made their maximum speeds around 13,000 feet.

They also weren't carrying drop tanks for decoration. They were not going to have the range to do anything useful without drop tanks.



P-39 Expert said:


> In 1943 there aren't going to be any FW190As at 30000'. No F4Fs. Not many Zeros or Oscars. I agree that there were not many P-39Ns cruising at 30000' but the capability was there.



You have a very interesting view of history. Do you really believe those other types were not there in 1943? Some of those other types were already being replaced by aircraft with better altitude capability by 1943.

Another couple questions for you are: Would your hypothetical P-39N cruising at 30,000 feet be carrying a drop tank?
Would it be a P-39N with 120 gallons of internal fuel or only 87 gallons?
If it is NOT carrying a drop tank, then where would it be going at 30,000 feet where internal fuel would be sufficient for the mission?

Also, as GregP pointed out, just because an aircraft can get to 30,000 feet doesn't mean it can fight there. The A6M2 had a service ceiling somewhere between 35,000 feet and 38,000 feet depending on the information source but it most certainly wasn't a high altitude aircraft either.

- Ivan.

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## P-39 Expert (Oct 26, 2020)

jmcalli2 said:


> http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf
> 
> Hope that helps.


There are more P-39D tests and some graphs on the P-39K which has the same 8.8 supercharger gears also.


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## Ivan1GFP (Oct 26, 2020)

jmcalli2 said:


> http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf
> 
> Hope that helps.



Hello jmcalli2,

Actually that helps a lot.

Note that the P-39D In this particular test was only able to achieve 358 MPH @ 13,000 feet.
The aircraft was not carrying a belly tank or any of the mounting hardware in that particular test configuration.
It was making about 20 HP more than nominal and at the typical critical altitude for the early model P-39.

The only way this is 40 MPH faster than the A6M2 is if the A6M2 is puttering along at cruise power +50 mm Boost 2350 RPM (275 Knots).

- Ivan.

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## P-39 Expert (Oct 26, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...



Please expand above.


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## wuzak (Oct 26, 2020)

P-39 Expert said:


> In 1943 there aren't going to be any FW190As at 30000'. No F4Fs. Not many Zeros or Oscars. I agree that there were not many P-39Ns cruising at 30000' but the capability was there.





P-39 Expert said:


> Initial combat dates: P-38 November 1942, Corsair Feb 1943, P-47 May 1943, Hellcat August 1943, Merlin P-51 December 1943. P-38 barely made combat in 1942 a full year after the war started. P-39, P-40 and F4F were all that was available in 1942.



Interesting that you omit aircraft that were around in 1941/42 that could fly and fight at 30,000ft and above. Such as the Bf 109 and Spitfire.


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## buffnut453 (Oct 26, 2020)

wuzak said:


> Interesting that you omit aircraft that were around in 1941/42 that could fly and fight at 30,000ft and above. Such as the Bf 109 and Spitfire.



Cherry-picking data to suit an argument? Surely not!


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## glennasher (Oct 26, 2020)

It's tiresome to beat a dead horse, or to feed a troll. I vote on quitting both endeavors.

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## GregP (Oct 26, 2020)

The speed test you showed in post 958 is at 13,000 feet. At wide open throttle, the P-39 went 358 mph on 1170 hp. Figure cruise at maybe 75% of that, or 877 hp. Your chart shows 321.5 mph at 850 hp. According to wwiaircraftperformance, the P-39D climbed at 1,880 fpm at 15,000 feet at wide open throttle.

Figure an A6M3 since we are in 1943.

According to wwiaircraftperformance, they operated their Zero at* 36” MAP and 2,400 rpm!* The Sakae 21 engine made 1,130 hp at 2,750 rpm for takeoff. So, they only ran it at about 900 hp or less out of the possible 1,130 to get their performance numbers. Think a Japanese Naval pilot would do that in combat? I doubt it. At that reduced power, reduced even further by altitude, the A6M3 climbed at 2,180 fpm at 15,000 feet. Compare that to the P-39D above (1,880 fpm). They only tested the Zero at 36” MAP @ 2,400 rpm, where it went 310 mph at 9,300 feet. I don’t know why they only tested at 36” MAP (which is only about 3” of boost). The A6M3 is often quoted at 4,500 fpm climb, but that’s at full power and 2,700 rated rpm (not 2,750 for takeoff only), and not restricted to 36” MAP.

They deliberately ran the zero at low power as far as I can see. WAY low power.

To me, it as advantage Zero, big time. I think the P-39 was pretty competitive below 10,000 feet.

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## Ivan1GFP (Oct 26, 2020)

Hello P-39 "Expert",



P-39 Expert said:


> *Like what?
> .....
> And plenty of test pilots and combat pilots report that it handled just fine. P-39 was a perfectly good handling airplane that served the country well when there wasn't anything else except the P-40 and F4F.*



If you have to ask what unsubstantiated claims Bell made, then you need to do a lot more reading.
.....
Perfectly good handling as long as it was loaded correctly.... If not, then not so much.



P-39 Expert said:


> *I have no idea, but there were sure a lot of captured Zeros tested. And after the war Zero pilots who were interviewed substantiated the results of those tests. The Zero was many things, but fast wasn't one of them.*



There are actually very few reports with a fully functional A6M of any version tested.
I never claimed the A6M2 was all that fast. I am saying your repetitive claim that the early P-39 had a 40 MPH speed advantage is total garbage.



P-39 Expert said:


> *More like around 14000' with ram, and they were able to hold that speed up to around 16000'. You talk like they stopped running when they reached their critical altitude.*



Then performance reports must be lying and the people testing the P-39D must have been really stupid to be testing at only 13,000 feet. I think not. Putting a supercharger intake into a low pressure area isn't going to make it work particularly well.



P-39 Expert said:


> *And those tanks were dropped for combat, weren't they.*



....and that would be a really bad time to find that your enemy has a significant altitude advantage over you because you couldn't climb worth anything with the drop tank.



P-39 Expert said:


> *Initial combat dates: P-38 November 1942, Corsair Feb 1943, P-47 May 1943, Hellcat August 1943, Merlin P-51 December 1943. P-38 barely made combat in 1942 a full year after the war started. P-39, P-40 and F4F were all that was available in 1942.*



I was replying to your comment about numerous axis fighters that were not available in 1943 when they were available in 1942 and being replaced with newer versions by 1943.



P-39 Expert said:


> *Returning from a mission where it had to drop the tank it would have 120gal less a 20 minute landing reserve (10gal) less 15 minute combat reserve (18gal at 25000') leaving 92gal left* *using 48gal/hr at 30000' resulting in 1.92hr at 305mphTAS or 585mi after reserves. A radar alerted interception mission with no drop tank and 120gal internal would be reduced by the takeoff allowance of 16gal, 15min combat allowance at 30000' of 14gal and a landing reserve of 10gal resulting in 80gal useable at 48gph or 1.7hours patrol time. Plenty of time to intercept a bombing raid.*



You are conveniently forgetting a few things here. 
First, you can't magically gain altitude without expending fuel. How did you get to 30,000 feet?
Second, it would be amazingly convenient to retain ALL (remember that "All") internal fuel when heading home.
Third, Are you forgetting that the Reserve tank is used for Take-Off?



P-39 Expert said:


> *Why couldn't it fight there? All it had to do was be above the enemy and dive on him.*



You are assuming that 30,000 feet puts you above the enemy. What if your opponent is there too?

- Ivan.

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## Ivan1GFP (Oct 26, 2020)

Hello GregP,

Which Zero report are you reading from?

It sounds like it is from the A6M2 captured by the AVG, beaten to crap when it was transported to the USA and then rebuilt by Curtiss to fly in 1943. After its ocean voyage, it never was in good shape again and the reason the RPM was so low was that IIRC Curtiss never figured out what the propeller pitch range was supposed to be.

- Ivan.


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## DerAdlerIstGelandet (Oct 26, 2020)

glennasher said:


> It's tiresome to beat a dead horse, or to feed a troll. I vote on quitting both endeavors.



I finally broke out the Pear Schnapps. Makes it easier.

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## fubar57 (Oct 26, 2020)

I need to start drinking again

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## GrauGeist (Oct 26, 2020)

I never quit...

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## GregP (Oct 26, 2020)

A6M3 report.

The closest U.S. engine to the Sakae 21 (1,687 cubic inches) is the Pratt & Whitney R-1830-S1C-G (1,830 cubic inches). It produces 1,200 hp at 2,700 rpm and 48" MAP. It likely makes the 1,200 hp instead of 1,130 hp of the Sakae due to more displacement ... but there is no way the Sakae 21 will make rated power at only 2,400 rpm and only 36" MAP. It just won't move enough air/fuel to do that.

I have several reference that state the Sakae 21 made its power at 2,700 rpm ... not 2,400 rpm, but none that specify the manifold pressure. My estimate would be around 48" MAP.


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## Ivan1GFP (Oct 27, 2020)

Hello GregP,

EB-201, right? That was the A6M3 Model 32 "Hap" rebuilt from a collection of wrecks at Eagle Farm.

The reality of the Sakae 21 performance may surprise you a bit.
It wasn't quite as much of an improvement over the Sakae 12 as you might be thinking.
The Sakae 21 wasn't that much more powerful than the Sakae 12. It just had a greater critical altitude because of its two speed supercharger instead of the single speed supercharger on the earlier engine.

I believe their Take-Off is equivalent to War Emergency and that is how TAIC evaluated it even though Japanese never listed in their manuals as anything but Take-Off and never listed it as something that could be used at altitude though evidence is that some pilots obviously did this.
Rated is probably equivalent to what we consider "Military Power".
Normal Power is most likely equivalent to "Maximum Continuous"
Boost pressures are mm Hg over ambient at Sea Level (760 mm Hg).

Sakae 12:
Take-Off
+250 mm Hg @ 2550 RPM - 940 HP

Rated Power - Sea Level
+150 mm Hg @ 2500 RPM - 830 HP

Critical Altitude 4200 Meters - Single Stage, Single Speed.
Rated Power - 4200 Meters
+150 mm Hg @ 2500 RPM - 950 HP

Normal Power
+50 mm Hg @ 2350 RPM -??? HP.

.......

Sakae 21
Take-Off
+300 mm Hg @ 2750 RPM - 1130 HP

Rated Power - Sea Level (Low Blower)
+200 mm Hg @ 2700 RPM - 1010 HP

Rated Power - Sea Level (High Blower) - Yes, this is listed in the manual.
+200 mm Hg @ 2700 RPM - 810 HP

Critical Altitude - Low Blower -2850 Meters
Rated Power Critical Altitude Low Blower
+200 mm Hg @ 2700 RPM - 1100 HP

Critical Altitude - High Blower - 6000 Meters
Rated Power Critical Altitude High Blower
+200 mm Hg @ 2700 RPM - 980 HP

Normal Power
+75 mm Hg @ 2500 RPM - ??? HP

.......

Now here is a rather screwy thing and probably a reason the folks at Eagle Farm and others got a bit confused:
The manifold pressure gauge apparently was the same on aircraft equipped with the Sakae 12 and Sakae 21.
Please see attached image which is a crop from NASM A6M5 panel image.
Note that it reads from -450 mm to +250 mm which is just fine for a Sakae 12 engine.
Who-da thunk they would use the SAME gauge for aircraft with a Sakae 21 that can get to +300 mm at Take-Off???

To save some calculation time: (GregP, I already know you know this, but others may not.)
+50 mm == 31.89 inches Hg
+75 mm == 32.87 inches Hg
+150 mm == 35.83 inches Hg
+ 200 mm == 37.80 inches Hg
+250 mm == 39.76 inches Hg
+300 mm == 41.73 inches Hg

- Ivan.

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## rochie (Oct 27, 2020)

GrauGeist said:


> I never quit...


Me either but after reading this,

*"P-38 barely made combat in 1942 a full year after the war started"*

Im gonna drink a bit more


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## DerAdlerIstGelandet (Oct 27, 2020)

rochie said:


> Me either but after reading this,
> 
> *"P-38 barely made combat in 1942 a full year after the war started"*
> 
> Im gonna drink a bit more



What, the war started in 1942??? 

Now I’m really getting scared.


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## fubar57 (Oct 27, 2020)

I like this one...


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## Peter Gunn (Oct 27, 2020)

Regarding the Zeke/Zero testing referenced above, were the test pilots also probably aware that this was a finite resource that they did not want to push too hard lest they lose it? I always speculated that these EA were not pushed to the edge so as to preserve them for continued testing and not cause irreparable damage ergo cancel further testing.

As GregP points out, that particular test is at a lower RPM and MAP than the SAKAI seems capable of.

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## SaparotRob (Oct 27, 2020)

As long as we’re on the subject, in World War 2, was the A6M more popularly known as the Zeke or the Zero?


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## Peter Gunn (Oct 27, 2020)

SaparotRob said:


> As long as we’re on the subject, in World War 2, was the A6M more popularly known as the Zeke or the Zero?


I'm probably wrong but as far as I remember "Zero" was what most Navy/Marine pilots called them, "Zeke" seemed more of an AAF designation. Forum experts feel free to correct me.

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## SaparotRob (Oct 27, 2020)

Thanks!

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## buffnut453 (Oct 27, 2020)

Every Japanese fighter was a Zero (at least until sometime in 1942)...saying that with tongue slightly in cheek, but only slightly. 

Note that the A6M had 2 reporting names: Zeke and Hamp,

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## fubar57 (Oct 27, 2020)

You could include the "Rufe" A6M float-plane as well.

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## Ivan1GFP (Oct 27, 2020)

Peter Gunn said:


> Regarding the Zeke/Zero testing referenced above, were the test pilots also probably aware that this was a finite resource that they did not want to push too hard lest they lose it? I always speculated that these EA were not pushed to the edge so as to preserve them for continued testing and not cause irreparable damage ergo cancel further testing.
> 
> As GregP points out, that particular test is at a lower RPM and MAP than the SAKAI seems capable of.



Hello Peter Gunn,

I don't think this was really the problem. This A6M3 was rebuilt from wrecks. There were plenty of engines. There were plenty of wrecks that they were working from.
They simply had no experience with the Mark II fighter and the Japanese were not kind enough to supply a manual, so they had to make best guesses. They might have also been using some equipment from A6M2 aircraft without knowing any better.

Hello SaparotRob,

The A6M2 was the Navy Type Zero Carrier Fighter Model Two One.
The 'Zero' was for the year of adoption (1940 or 2600 in the Japanese calendar).
The Allied code name was "Zeke".
The A6M3 short wing version was the Navy Type Zero Carrier Fighter Model Three Two.
The Allied code name was "Hap" because they originally thought it was a completely new fighter.
Eventually it was renamed "Hamp" and then "Zeke-32".

There were many "Type Zero" aircraft in Japanese Service.

The Army used a pretty similar system.
The Ki 43 Hayabusa was the Army Type 1 Single Engine Fighter.
The Allied code name was "Oscar" or "Ben" earlier in the war.

- Ivan.

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## SaparotRob (Oct 27, 2020)

I knew about the reporting names but I was wondering what name the A6M (any variant) was most popularly known by. BTW, the A6M3 reporting name was changed to Hamp because General “Hap” Arnold said so. At least that’s the “Caidin” version.

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## SaparotRob (Oct 27, 2020)

fubar57 said:


> You could include the "Rufe" A6M float-plane as well.


That was a classy airplane.


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## fubar57 (Oct 27, 2020)

I'm not quoting Caidin but from what I've read, Arnold was mightily P.O.'d and hauled the guy in charge, Captain Frank T. McCoy in for a severe keester kickin' and the name was quickly changed

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## SaparotRob (Oct 27, 2020)

fubar57 said:


> I'm not quoting Caidin but from what I've read, Arnold was mightily P.O.'d and hauled the guy in charge, Captain Frank T. McCoy in for a severe keester kickin' and the name was quickly changed


You must have been posting this just before my comment about General Arnold.


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## GregP (Oct 27, 2020)

The official designation of the early A6M was "Navy Type 0 Carrier Fighter." If was a "Type 0" because the Japanese calendar rolled over to 0 (actually 2600) in 1940. The designation was A6M. The "A" in "A6M" meant carrier-based fighter. It was the 6th carrier-based fighter built for the IJN, and the M meant the manufacturer, Mitsubishi. Hence, A6M was literally "carrier-based fighter, 6the type, by Mitsubishi."

It was called a Zero because that was the Japanese term for it and we used it, too. If was given the Allied Code name "Zeke." We gave make name to fighters. Japanese pilots called it the Reisen (rei sen = Zero sen). 

Later, two variants received their own code name. The floatplane was called Rufe, and the A6M3 was originally thought to be a new type and was called "Hap," but that was an embarrassment to General Henry "Hap" Arnold, so it was changed to "Hamp." After it became known the A6M3 was just another Zero, the name stayed because it was already in use.

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## jmcalli2 (Oct 27, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> Actually that helps a lot.
> 
> ...



Seems to me you're cherry picking your test results.
The fastest P-39 was the N, clocked at 398.5.
The fastest A6M couldn't hit 360, even the versions with increased HP.
And the A6M had a very hard time maneuvering above 300; those big ailerons were very hard to move.

The problem the P-39 had in the PTO was in large part due to the USAAC being at the bottom of the learning curve in tactics and maintenance while the Japanese were experienced in both.
The Japanese had their logistics worked out, the USAAC did not.
The P-39s were often sent up to intercept Japanese bombers flying at 20,000 ft. It would take 6-8 minutes for a P-39 to reach them, by which time the bombers would be gone. Meanwhile, the climbing P-39s would be bounced by A6Ms.
Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.

As for the A6M having a service ceiling of 35-38,000 ft, that didn't mean that it fought at that height.
Service ceiling means the rate of climb is 100 feet/minute.
A6M performance fell off at 20-22,000 ft, like the P-39's did at 18,000 ft. That 2-4,000 ft made a difference.

Also recommended is this December 1942 comparison report between the A6M-2 and various US aircraft including the P-39D: http://www.wwiiaircraftperformance.org/japan/intelsum85-dec42.pdf

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## jmcalli2 (Oct 27, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> Actually that helps a lot.
> 
> ...


An interesting thing is the variation in performance from one aircraft to another. it could be due to many things; better/worse tune on the engines, length of time for the speed run, etc.
Remember the purpose of the test was to measure the difference in performance with and without the drop tank and shackles. It could be that the test was to run at altitude X for Y seconds at WO throttle. The aircraft may not have reached maximum speed. We'll never know.


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## GrauGeist (Oct 27, 2020)

SaparotRob said:


> As long as we’re on the subject, in World War 2, was the A6M more popularly known as the Zeke or the Zero?


Their own pilots were known to call it a zero as well: reisen or rei-sen.

There were at least three other Type 0 aircraft in service, two being recon and one was the L2D (Douglas license) transport.

All were Type 0 because the Japanese used the last one or two digits of the Imperial year to denote "type" when the aircraft enters service.
Imperial year 2600 (1940) = Type 0

The A6M meant:
A = Fighter, Carrier based
6 = 6th type in the A class
M = Mitsubishi

The number following A6M meant revisions to the aircraft production (A6M2, A6M5, etc.)
And the Model number that followed denoted modifications to that particular production type.

As an aside, the aforementioned L2D Type 0 transport was manufactured by Nakajima, but it's designation is as follows:
L = transport
2 = second type in the transport class
D = Douglas

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## P-39 Expert (Oct 27, 2020)

wuzak said:


> Interesting that you omit aircraft that were around in 1941/42 that could fly and fight at 30,000ft and above. Such as the Bf 109 and Spitfire.


Was listing the planes that couldn't cruise at 30000' in 1942.


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## DerAdlerIstGelandet (Oct 27, 2020)

Well since the war was only going on for a year in 1942, they had not developed aircraft that could cruise at 30K.


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## SaparotRob (Oct 27, 2020)

Right, Zero it is.


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## Ivan1GFP (Oct 27, 2020)

jmcalli2 said:


> Seems to me you're cherry picking your test results.
> The fastest P-39 was the N, clocked at 398.5.
> The fastest A6M couldn't hit 360, even the versions with increased HP.
> And the A6M had a very hard time maneuvering above 300; those big ailerons were very hard to move.
> ...



Hello jmcalli2,

I referenced the report you listed because P-39 Expert was constantly claiming "40 MPH faster" when we were comparing the early P-39 and A6M2.
The P-39N was that fast in one test. Most references don't ist it as quite that fast.
As I commented recently, I am not claiming any version of the A6M was really particularly fast.

Regarding IIS 85, I am quite familiar. I have already quoted from it quite a few times.

- Ivan.

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## GregP (Oct 27, 2020)

The A6M didn't have especially big ailerons. They were long but rather narrow. The gearing left something to be desired.

In general ailerons should have from 1/8 to 1/4 chord and the length can run from about 1/4 span to half span minus fuselage half-width.

The ailerons on the Zero are about 8.7% of the wing area and about 7.8% on the P-39. There is not much difference there, but the internal gearing of control surfaces in another story. Both the Bf 1098 and the A6M could have had the aileron gearing addressed during the war, but neither was.

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## windhund116 (Oct 27, 2020)

SaparotRob said:


> I knew about the reporting names but I was wondering what name the A6M (any variant) was most popularly known by. BTW, the A6M3 reporting name was changed to Hamp because General “Hap” Arnold said so. At least that’s the “Caidin” version.



Yes. Also according to _Japanese Aircraft Code Names_, by Robert Mikesh. Schiffer Military Press. 1993. Pages 15 & 63.
-----

"The Ki 43 Hayabusa was the Army Type 1 Single Engine Fighter.
The Allied code name was "Oscar" or "Ben" earlier in the war."

AFAIK, "Ben" was another early name for the IJ Navy Zero. "Oscar" were reported by early encounters in CBI Theater as a separate fighter "Jim." Until later intelligence ID'ed both "Oscars" and "Jims" as the same Nakajima Army Type 1 fighter.

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## ThomasP (Oct 27, 2020)

Hey guys,

re:"(rei sen = Zero sen)"

With the understanding that I do not speak or read Japanese, I thought that the meaning of the words "rei sen" was literally "model new" or maybe "type new", with "rei" = type or model and "sen" = new. In spoken English it would be "new model" or "new type". Maybe the word "sen" can also mean 0 in Japanese usage? Does anyone know for sure?


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## P-39 Expert (Oct 27, 2020)

jmcalli2 said:


> Seems to me you're cherry picking your test results.
> The fastest P-39 was the N, clocked at 398.5. *A graph in wwiiaircraftperformance shows a P-39Q-30 without wing guns at 410mph at 10000' and 400mph at 16000'.*
> The fastest A6M couldn't hit 360, even the versions with increased HP.
> And the A6M had a very hard time maneuvering above 300; those big ailerons were very hard to move.
> ...


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## fubar57 (Oct 27, 2020)

How fast did the P-39 climb with 300lbs of less weight?


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## XBe02Drvr (Oct 27, 2020)

ThomasP said:


> Does anyone know for sure?



According to Google Translate, "Zero fighter" translates to "Reisen" in contemporary Japanese. Oddly enough, it doesn't come up the same translating in the opposite direction. Contemporary Japanese has many usage variations from "classic" prewar Japanese.
My mother, born in Shizuoka in 1924 and brought to US in 1933, had a reunion with some of her Japanese elementary school classmates before she died. What remained of her prewar Japanese was the subject of some amusement for her former classmates.

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## Ivan1GFP (Oct 27, 2020)

ThomasP said:


> Hey guys,
> 
> re:"(rei sen = Zero sen)"
> 
> With the understanding that I do not speak or read Japanese, I thought that the meaning of the words "rei sen" was literally "model new" or maybe "type new", with "rei" = type or model and "sen" = new. In spoken English it would be "new model" or "new type". Maybe the word "sen" can also mean 0 in Japanese usage? Does anyone know for sure?



Hello ThomasP,

The full name should be:
Rei Shiki Kanjo Sentohki
or 
Zero Type Carrier Fighter

but just like everyone else, the Japanese had a tendency to abbreviate, so we get Rei Sen.
Now keep in mind I don't speak or read Japanese either.
I am sure there are some Japanese speakers who can do better.

- Ivan.

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## GregP (Oct 27, 2020)

Sorry Fubar57, my stopwatch broke and I don't know.

I'll guess its better than the top speed of a Vespa, though ... the old 2-stroke Vespa, not the modern one fitted with emissions crap. Maybe the Vespa would win if you put an expansion chamber on it ... but where O where would you put an expansion chamber on a Vespa? That's the question. Maybe if you shaped it like a question mark?

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## XBe02Drvr (Oct 27, 2020)

jmcalli2 said:


> A6M performance fell off at 20-22,000 ft, like the P-39's did at 18,000 ft. That 2-


P39 Expert replied:
With a little less weight (300lbs or so) P-39 would climb with a Zero.

Maybe on paper, or under flight test conditions. Doesn't mean it would respond comparably in combat. Even with a "weight watchers" P39, Zero has a significant weight advantage as well as a slight thrust advantage and a better L/D wing in the high teens altitudes, leading to better acceleration from cruise to combat, and better instantaneous "pop up" performance in response to a bounce. Steady state numbers derived from flight tests don't account for the dynamics of air combat.
Plus, the Zero pilots had already had plenty of experience fighting heavier western type aircraft in China, Philippines, Malaya, DEI, and Ceylon before they met P39s in NG.

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## ThomasP (Oct 27, 2020)

Hey guys,

Thanks for the reply. The Japanese characters 零戦 do seem to mean 'zero fighter' via Google translate.

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## P-39 Expert (Oct 27, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> 
> 
> ...


Double post.


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## DerAdlerIstGelandet (Oct 27, 2020)

GregP said:


> Sorry Fubar57, my stopwatch broke and I don't know.
> 
> I'll guess its better than the top speed of a Vespa, though ... the old 2-stroke Vespa, not the modern one fitted with emissions crap. Maybe the Vespa would win of you put an expansion chamber on it ... but where O where would you put an expansion chamber on a Vespa? That's the question. Maybe if you shaped it like a question mark?



That depends. Is that Vespa from 1942? When the war had only been going for a year?

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## P-39 Expert (Oct 27, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> I referenced the report you listed because P-39 Expert was constantly claiming "40 MPH faster" when we were comparing the early P-39 and A6M2.
> The P-39N was that fast in one test. Most references don't ist it as quite that fast.
> ...


Attached please find a performance graph for the P-39K which had the same 8.8 supercharger gears as the P-39D. Also attached is a P-39D performance test. The numbers are virtually the same. 

As you can see from the graph the top speed of the K model was 370mph up to 16000'. The A6M2 is commonly listed at 330mph at 15000' with speed falling off at higher altitudes at the same rate as the K. That's a 40mph difference at all altitudes.

The climb numbers on the chart and the report show that power was reduced from combat power (3000rpm) to normal power (max. continuous) when the 5 minute limit was reached. This limit was increased to 15 minutes in mid 1942, just after these tests. The red dots represent rate of climb at combat power 3000rpm. This closely approximates the A6M2 climb rate.


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## XBe02Drvr (Oct 27, 2020)

P-39 Expert said:


> This closely approximates the A5M2 climb rate.


Well of course, that was an open cockpit fixed gear monoplane of a little over 700 HP. Worthy opponent for the P39!

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## GregP (Oct 27, 2020)

Vespa probably made from melted MC.200s ... or maybe melted CR.42s.

Oh, and ...

At 15,000 feet, the P-39D shows about 1,800 fpm on one curve above and about 1,550 fpm on the other, but I can’t tell what the difference is between the curves … can’t read the legend writing. The A6M5 Model 52 climbs at between 1,950 and 2,600 fpm at 15,000 feet in one report from wwIIaircraftperformance, so it outclimbs the P-39D handily at 15,000 feet, which is about the upper limit of where you’d want to fight the P-39D. The speed of the A6M5 Model 52 was anywhere from 300 mph to around 335 mph at 15,000 feet from the same report.

So, the P-39D, at full power might be able to slightly close or maybe slightly get away from the Zero but, when he DID close, the Zero would outperform him in climb and turn easily.

That is not a good place to be if you’re flying a P-39D and the enemy knows you are there. At least, I would not want to be flying the P-39D in those circumstances if I had a choice. Might be OK if you are doing the ambushing.


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## P-39 Expert (Oct 27, 2020)

XBe02Drvr said:


> Well of course, that was an open cockpit fixed gear monoplane of a little over 700 HP. Worthy opponent for the P39!


Thanks, I mistyped. Original corrected.


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## P-39 Expert (Oct 27, 2020)

GregP said:


> Vespa probably made from melted MC.200s ... or maybe melted CR.42s.
> 
> Oh, and ...
> 
> ...


Pardon me, I'm comparing the 1942 P-39s and A6M2. The A6M5 was later and should be compared to the P-39N of late 1942 early 1943.


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## GrauGeist (Oct 27, 2020)

The A6M5 variant went into service mid-1943, supplementing the A6M3 that was produced between '42 and '43.


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## P-39 Expert (Oct 27, 2020)

fubar57 said:


> How fast did the P-39 climb with 300lbs of less weight?


300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.


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## fubar57 (Oct 27, 2020)

"Would mean?" You're just guessing?


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## DerAdlerIstGelandet (Oct 27, 2020)

P-39 Expert said:


> 300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.



It his own factual method.


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## P-39 Expert (Oct 27, 2020)

fubar57 said:


> "Would mean?" You're just guessing?


Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.

The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.


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## Ivan1GFP (Oct 27, 2020)

Hello jmcalli2,

I was a bit busy earlier today when I was responding to your post, so I figured I go into a bit more detail now that I have a bit more time.



jmcalli2 said:


> The problem the P-39 had in the PTO was in large part due to the USAAC being at the bottom of the learning curve in tactics and maintenance while the Japanese were experienced in both.
> The Japanese had their logistics worked out, the USAAC did not.



The Japanese really didn't have any particular advantage in experience in terms of maintenance. Their types were just as new.
As for Japanese logistics, in some places it was pretty good. In places such as New Guinea, it was much worse than what the Allies were experiencing. The Japanese Army had it particularly bad. Anything past basic repairs needed to be shipped out because facilities did not exist in theater.



jmcalli2 said:


> The P-39s were often sent up to intercept Japanese bombers flying at 20,000 ft. It would take 6-8 minutes for a P-39 to reach them, by which time the bombers would be gone. Meanwhile, the climbing P-39s would be bounced by A6Ms.



The biggest problem which P-39 Expert pointed out was that the early P-39 with a drop tank could not really get up past 17-18,000 feet. It also had very reduced performance past 20,000 feet even without a drop tank as noted from the IIS 85 Report you mentioned and I have quoted the section in a prior post.



jmcalli2 said:


> Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.



The P-39 had a speed advantage at just about every altitude. Sometimes it wasn't very large but speed isn't the only thing.
At low to medium speeds, the A6M in most models had a very significant Acceleration advantage. That is why the acceleration tests in IIS 85 were started at such odd speeds (generally only about 30-40 MPH below the maximum level speed of the A6M2).
When an aircraft is near its maximum speed, acceleration isn't going to be good.

As I see it, there are quite a few reasons why the Japanese pilots may not have done so well. Lack of communications and coordination is a major factor.



jmcalli2 said:


> As for the A6M having a service ceiling of 35-38,000 ft, that didn't mean that it fought at that height.
> Service ceiling means the rate of climb is 100 feet/minute.



I actually pointed out the same thing in a prior post when I commented that although the A6M2 had a service ceiling of 35,000 to 38,000 feet depending on the data source, that doesn't mean it was a high altitude fighter.



jmcalli2 said:


> A6M performance fell off at 20-22,000 ft, like the P-39's did at 18,000 ft. That 2-4,000 ft made a difference.



This depends on which version of the A6M you are comparing. The A6M2 had a critical altitude of 4200 Meters which is not substantially higher than the early P-39 and performance past 20,000 feet was not so good. The A6M3 had a critical altitude in high blower of 6000 Meters (19,685 feet), so 20-22,000 feet was where it should have been performing best. Below that altitude, it was not as effective as the A6M2.

- Ivan.


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## fubar57 (Oct 27, 2020)

P-39 Expert said:


> Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.
> 
> The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.


So your numbers mean nothing then, just fluff.


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## wuzak (Oct 27, 2020)

P-39 Expert said:


> Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.
> 
> The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.



Might need some more data points.


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## wuzak (Oct 27, 2020)

At 30,000ft the P-39N had approximately 650hp at wide open throttle and 3,000rpm. That is War Emergency Power!


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## windhund116 (Oct 27, 2020)

Kanji 零戦 means Zero Fighter. "Reisen" is a contraction of *Rei*_shi Kikanjo *Sen*touki. _ 

Reishi Kikanjo Sentouki

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## windhund116 (Oct 27, 2020)

ThomasP said:


> Hey guys,
> 
> Thanks for the reply. The Japanese characters 零戦 do seem to mean 'zero fighter' via Google translate.



Yeah, contraction of Kanji (Chinese) characters.


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## ThomasP (Oct 27, 2020)

Hey windhund116,

Thanks for the link.

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## Ivan1GFP (Oct 27, 2020)

Hello P-39 Expert....

Why do I get the feeling I have been here before?



P-39 Expert said:


> Attached please find a performance graph for the P-39K which had the same 8.8 supercharger gears as the P-39D. Also attached is a P-39D performance test. The numbers are virtually the same.



The test report you gave on the P-39D is actually quite interesting. You should actually read it for content instead of just picking the maximum speed figures out of it.
Please note the following:
These people were tweaking manual mixture controls to get the P-39D up to 368 MPH. This is not something that is done in combat. With Auto Rich, it was doing 365 MPH which is still pretty good though.
From other test reports (358 MPH), it is pretty obvious that maximum speed varied a bit as one might expect for production aircraft.




P-39 Expert said:


> As you can see from the graph the top speed of the K model was 370mph up to 16000'. The A6M2 is commonly listed at 330mph at 15000' with speed falling off at higher altitudes at the same rate as the K. That's a 40mph difference at all altitudes.



If you are still going with the "commonly listed" number for the A6M2, you obviously are forgetting the IIS 85 test report you claim to have read or don't understand it.
If a crashed and repaired A6M2 can achieve 335 MPH in tests (corrected down to 332 MPH for dissemination) while NOT running War Emergency Power, then 330 MPH for a fighter in good condition in Japanese service is unlikely.

Here is a pretty good discussion along with anecdotes from combat encounters that supports a substantially higher number.
I just went through the article again and am more inclined to believe Mr. Dunn's conclusion is correct.
*A6M2 Performance*

Please note that the manifold pressure conversions are not quite correct. I contacted him years ago about this issue and he acknowledged the issue but never corrected the article.



P-39 Expert said:


> The climb numbers on the chart and the report show that power was reduced from combat power (3000rpm) to normal power (max. continuous) when the 5 minute limit was reached. This limit was increased to 15 minutes in mid 1942, just after these tests. The red dots represent rate of climb at combat power 3000rpm. This closely approximates the A6M2 climb rate.



The IIS 85 report was based on testing after mid 1942 and shows P-39D climb rate as distinctly slower past about 12,500 feet or so.

- Ivan.

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## Ivan1GFP (Oct 27, 2020)

P-39 Expert said:


> Pardon me, I'm comparing the 1942 P-39s and A6M2. The A6M5 was later and should be compared to the P-39N of late 1942 early 1943.



If you don't like comparing climb rates at 15,000 feet between P-39D and A6M5, then you will probably like a comparison between P-39D and A6M2 even less.
15,000 feet is well below the critical altitude for the A6M5 but it is very close to the 4200 Meter critical altitude for the A6M2 and the A6M2 is quite a bit lighter.


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## Stig1207 (Oct 28, 2020)

jmcalli2 said:


> Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.



Surprised me too, not least the way the combat records are interpreted; 44 P-39's were lost in engagements with Zero's, of which 15 also were lost. All 15 Zeros were shot down by P-39's, and 15 P-39's were shot down by Zeros. Some P-39's were lost to AAA, running out of fuel, mechanical defects, etc; but in many cases no one actually saw what happened and there were some MIA with no probable cause given. 

Perhaps it would be more right to say that it cost 44 P-39s too shoot down 15 Zeros.

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## P-39 Expert (Oct 28, 2020)

windhund116 said:


> Kanji 零戦 means Zero Fighter. "Reisen" is a contraction of *Rei*_shi Kikanjo *Sen*touki. _
> 
> Reishi Kikanjo Sentouki


Shows the top speed of an A6M2 as 330mph at 15500'.


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## P-39 Expert (Oct 28, 2020)

fubar57 said:


> So your numbers mean nothing then, just fluff.


How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.


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## P-39 Expert (Oct 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert....
> 
> Why do I get the feeling I have been here before?
> 
> ...


Please expand above.


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## XBe02Drvr (Oct 28, 2020)

P39 Expert said:
*Just the pilot slightly varying the mixture control to get the best power based on feel and sound. Why wouldn't that be done in combat?*

Spoken like a true ground pounder, devoid of flight experience or knowledge thereof!! Getting accurate, safe (you don't want to burn up YOUR ONLY engine over the sea or the Owen Stanley mountains) lean mixture settings requires stabilized steady state flight and engine temperatures settled down from any climb or maneuvering demands, and time to tweak and analyze it. Fine for flight testing or long distance cruising; ain't happ'nin in combat, where you're already suffering from a situational awareness overload.
Best power comes just on the near side of the onset of detonation, and detonation under the demands of combat maneuvering will result in engine damage or destruction. Auto rich is your safety margin if you're going to be hammering on your engine. The risk is not worth the few (3??) extra MPH. Today's planes have both Cylinder Head Temperature and Exhaust Gas Temperature gauges, making it easier and safer to tweak mixture at altitude. Back then, they weren't equipped with the critical component, the EGT.

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## XBe02Drvr (Oct 28, 2020)

P-39 Expert said:


> How do you account for the additional 1000fpm climb?


Quite likely partly due to differences in test conditions buried in the small print. Achieving identical test conditions (or correction factors to compensate if not achieved) is more involved than it may seem to the uninitiated.
Who actually conducted each test? Where and when? Corrected to standard atmosphere values? A P39C prepped at the Bell plant and tested in wintertime in Niagara will certainly put up better performance differential numbers vs a P39D in combat trim randomly selected from the flight line at Langley in summertime than the actual difference in the aircrafts warrants. Larry Bell was not above "detailing" a plane about to be tested to maximize performance. How do you KNOW such shenanigans didn't happen?


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## glennasher (Oct 28, 2020)

DerAdlerIstGelandet said:


> That depends. Is that Vespa from 1942? When the war had only been going for a year?


It was a postwar Vespa, made from the scrap metal of the P-39s crashed by the Italians after the USAAF gave them some.

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## P-39 Expert (Oct 28, 2020)

XBe02Drvr said:


> Quite likely partly due to differences in test conditions buried in the small print. Achieving identical test conditions (or correction factors to compensate if not achieved) is more involved than it may seem to the uninitiated.
> Who actually conducted each test? Where and when? Corrected to standard atmosphere values? A P39C prepped at the Bell plant and tested in wintertime in Niagara will certainly put up better performance differential numbers vs a P39D in combat trim randomly selected from the flight line at Langley in summertime than the actual difference in the aircrafts warrants. Larry Bell was not above "detailing" a plane about to be tested to maximize performance. How do you KNOW such shenanigans didn't happen?


Both were official performance tests conducted at Wright Field by the AAF on brand new airplanes. Larry Bell was back in Buffalo. No "shenanigans" would account for a 1000fpm difference in climb rate. One was 836lbs lighter than the other.


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## wuzak (Oct 28, 2020)

P-39 Expert said:


> How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.



"Airplane equipped with Allison V-1710-35 engine and 3-bladed constant speed propeller, blade design No. *614CC1.5-21*, blades are not equipped with cuffs."

"Oil and Prestone temperatures do not meet Air Corps requirements in climb"

http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf


The test on the P-39D did not evaluate cooling, and so whether it met the required standards was unknown.

"Airplane equipped with Allison V-1710-35 engine and 3-bladed constant speed propeller, blade design No. *614-1C1.5-21*."

"Individual port backfire screens not installed in engine."

http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6722_PHQ-M-19-1325-A.pdf


But, by all means remove self sealing tanks, armour plating, armoured screen, ditch the radios and IFF, lose the .30" mgs. Then you will have an aircraft with 40 extra gallons of fuel and that extra 1,000fpm climb. It should be able to take the Luftwaffe on over Berlin!

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## wuzak (Oct 28, 2020)

Also, for the P-39C:

"The [cooling] flaps are spring loaded and are therefore not positive in action; with the controls in the wide open position the flaps are pushed up towards the flush position by the force of the air stream."

That was referring to the level speed runs, not sure if it applied to climb conditions too - maybe the springs were good enough for climb speeds.

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## P-39 Expert (Oct 28, 2020)

wuzak said:


> "Airplane equipped with Allison V-1710-35 engine and 3-bladed constant speed propeller, blade design No. *614CC1.5-21*, blades are not equipped with cuffs."
> 
> "Oil and Prestone temperatures do not meet Air Corps requirements in climb"
> 
> ...


Same propeller. Cooling was a problem with most AAF fighters. Backfire screens were eliminated in mid 1942 on Allison engines without turbochargers, and in September on turbocharged P-38s. If the backfire screens were installed in the P-39C then performance would have improved with their removal. Even better climb.

I've never advocated removing the self sealing tanks. Only remove the nose armor, no other planes had the reduction gear armored. Never advocated removing the voice radio. C and D models didn't have the IFF radio anyway. And yes, definitely lose the .30cal MGs on the early D/F/K/L. The 37mm cannon and two .50cal MGs were plenty of armament. 

The P-39N available from late 1942 had the extra 1000fpm climb even with the items I've advocated for removal. It did successfully take on the Luftwaffe. But removal of the .30s and substituting additional fuel tanks would have greatly improved endurance.


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## Peter Gunn (Oct 28, 2020)

P-39 Expert said:


> 300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.


While an interesting and compelling argument, I think I read somewhere that it's not _quite_ that easy.

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## Milosh (Oct 28, 2020)

P-39 Expert said:


> Same propeller.


A different 'dash' number means there was a difference in the part.
614-*CC1.5*-21
614-*1C1.5*-21


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## DerAdlerIstGelandet (Oct 28, 2020)

P-39 Expert said:


> How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.



Where are you including atmospheric conditions in your calculations? What are the test conditions?

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## buffnut453 (Oct 28, 2020)

Oh good grief...this really is the Groundhog Day thread. 

After 52 pages, we're still hitting the reset button and going back to the same discussions we were having right at the start. 

I think it's time to take a jump to the left...

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## DerAdlerIstGelandet (Oct 28, 2020)



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## XBe02Drvr (Oct 28, 2020)

P-39 Expert said:


> The P-39N available from late 1942 had the extra 1000fpm climb even with the items I've advocated for removal. It did successfully take on the Luftwaffe.


On the eastern front at lower altitudes, in modified form, and without regard for published engine limits!


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## rochie (Oct 28, 2020)

buffnut453 said:


> Oh good grief...this really is the Groundhog Day thread.
> 
> After 52 pages, we're still hitting the reset button and going back to the same discussions we were having right at the start.
> 
> I think it's time to take a jump to the left...



i used to work in the hotel where that was filmed !

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## P-39 Expert (Oct 28, 2020)

Peter Gunn said:


> While an interesting and compelling argument, I think I read somewhere that it's not _quite_ that easy.


Please prove me wrong.


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## DerAdlerIstGelandet (Oct 28, 2020)

P-39 Expert said:


> Please prove me wrong.



Whats the point? Not like you care. You’re the “expert” remember.

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## P-39 Expert (Oct 28, 2020)

Obviously somebody cares or this thread would not be 1000 posts long.

Question is, does weight influence climb? Obviously it does. Then we should be able to quantify how much weight influences climb, all other factors being equal.


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## DerAdlerIstGelandet (Oct 28, 2020)

P-39 Expert said:


> Obviously somebody cares or this thread would not be 1000 posts long.
> 
> Question is, does weight influence climb? Obviously it does. Then we should be able to quantify how much weight influences climb, all other factors being equal.



I think its starting to wear thin on everyone...

Do you really think that only weight influences climb, and that all factors are equal? That when removing weight at one location, and adding weight at another won’t have differing effects. How is your new CG going to effect performance. Oh wait who cares about CG right?

The point that all us “non experts” are trying to tell you is that simply dividing weight and horsepower (excuse me rate of climb) will not give you a rate of climb. But hey what does everyone know right? Working knowledge means shit all.

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## pbehn (Oct 28, 2020)

The Spitfire doubled in weight in its life, it also doubled its initial rate of climb. This is conclusive proof that increasing weight increases rate of climb, any discussion of thrust, residual thrust and lift are the babblings of the deranged.

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## GrauGeist (Oct 28, 2020)

The P-51D had almost a 400 pound increase in empty weight over the P-51B and while it's RoC was almost identical, it's max. speed improved considerably.

So weight isn't always going to be the smoking gun...

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## fubar57 (Oct 28, 2020)

LMAO.....just noticed. Appropriate methinks

​

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## windhund116 (Oct 28, 2020)

GrauGeist said:


> The P-51D had almost a 400 pound increase in empty weight over the P-51B and while it's RoC was almost identical, it's max. speed improved considerably.
> 
> So weight isn't always going to be the smoking gun...



Engine could play a factor. HP per weight? No?

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## pbehn (Oct 28, 2020)

Above planet earth there are two extremes to the atmosphere, one has air at sea level and the other has almost no air on the edge of space. An air breathing engined aeroplane is happy at sea level. Some like helicopters and the Fairey Rotodyne don't need fixed wings to take off vertically, the propellers/ rotors can do it all on their own. The higher you go the more problems you have developing power and lift. Eventually there is a point where the maximum speed and the minimum speed become the same. It cant make more power and it cant make more lift and it cant make less power or it wont have enough lift, it can only fly in a straight line because any input increases drag and causes a stall. You could put almost anything inside a 2000BHP fighter and it would make little difference to sea level performance but Spitfires tasked with intercepting recon planes above 40,000ft even took the radio of one plane out and flew in pairs. How much effect weight has depends on "stuff" lots of "stuff" and usually involves terms and calculations that give me a headache.

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## Peter Gunn (Oct 28, 2020)

P-39 Expert said:


> Please prove me wrong.


Uh...

Have you actually been _reading_ this thread?

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## DerAdlerIstGelandet (Oct 28, 2020)

Peter Gunn said:


> Uh...
> 
> Have you actually been _reading_ this thread?

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## buffnut453 (Oct 28, 2020)

Peter Gunn said:


> Uh...
> 
> Have you actually been _reading_ this thread?



Reading? Maybe. 

Comprehending? Maybe not.

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## P-39 Expert (Oct 28, 2020)

DerAdlerIstGelandet said:


> I think its starting to wear thin on everyone...
> 
> Do you really think that only weight influences climb, and that all factors are equal? That when removing weight at one location, and adding weight at another won’t have differing effects. How is your new CG going to effect performance. Oh wait who cares about CG right? *CG remains within limits if radio is moved up above the engine, proven with excel CG table.*
> 
> The point that all us “non experts” are trying to tell you is that simply dividing weight and horsepower will not give you a rate of climb. But hey what does everyone know right? Working knowledge means shit all. *Wasn't dividing weight by horsepower, horsepower has nothing to do with this situation. Horsepower of the two planes was identical. Was dividing the increase in climb rate by the increase in weight to find the climb rate increase per pound.*


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## DerAdlerIstGelandet (Oct 28, 2020)

Even if you are within limits the shift in CG may still have an effect on performance. Everyone single person here has explained that to you already.

Dividing increase in climb rate by increase in weight has also been pointed out as a fallacy, but no need to repeat that, you don’t care. Rate of climb is effected by so much more than just weight. So why would dividing weight and rate of climb be accurate?

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## Ivan1GFP (Oct 28, 2020)

Hello P-39 Expert,

This is looking a lot like the movie Groundhog Day.
Hopefully you might learn something like Bill Murray did.



P-39 Expert said:


> *Just the pilot slightly varying the mixture control to get the best power based on feel and sound. Why wouldn't that be done in combat?*



You obviously don't know how the carburetors work in these aircraft.
The Auto Rich setting gives a slight margin for detonation under maximum throttle settings and the automatic mixture controls also compensate for altitude (air density) changes with varying flight conditions.
To achieve the extra 25 HP and 3 extra MPH, the pilot had to switch to manual mixture control and lean out the mixture.
This might work just fine if you are flying along straight and level with nothing else is going on, but in COMBAT, this is just plain STUPID. Without the automatic mixture control working, the pilot would need to compensate for any altitude changes immediately. Losing a few thousand feet of altitude and finding that your engine is now detonating or burning valves is a pretty lousy way to find you need to walk or swim home.



P-39 Expert said:


> *Highest speed listed in that report is 321mph at 18000'.*



You are correct. IIS 85 is not the correct reference.
You are also not reading the report correctly. It actually says 326 MPH.
It is interesting though that the actual information that was eventually distributed more widely was 332 MPH.

This is a better reference.
*Memorandum 23 Oct 1942*

Note that maximum speed in this report is 335 MPH @ 16,000 feet and the test aircraft is still achieving 331 MPH at 20,000 feet.

Do you remember my comment that if you didn't like a comparison of climb rate with the A6M5 at 15,000 feet, you would like the comparison with the A6M2 even less?
Note that the climb rate is 2480 feet/minute at 15,000 feet. How does that compare with the P-39D????

The most interesting information listed in this memorandum report is the note at the bottom which states that the manifold pressure was limited to 35 inches Hg. This is only +129 mm boost which isn't even Military Power.
Military Power would be +150 mm or 35.83 inches Hg
Emergency Power would be +250 mm or 39.76 inches Hg
I had missed this note in my earlier readings.......

This is why I am tending to believe now that Mr. Dunn's argument is probably correct considering that a rebuilt wreck can achieve 335 MPH without even using MILITARY power and with a carburetor that wasn't working correctly.



P-39 Expert said:


> *See Windhund's post #1020, 330mph at 15500'.*



First of all, the source of information that is listed in that table is a book from 1981.
Second, your conversion isn't entirely correct. Speed should be 331.5 MPH (288 Knots).
Third, you should read the footnote to that entry. The information that is listed there suggests that the author is a bit confused:

"The speed was increased after thickening the outer wing panel"? How does THAT improve speed?
Sounds like he was confusing level speed with maximum diving speed..... There is much more detail to this discussion about the authors errors that is beyond the scope of this discussion.
Note also that earlier speed was specified as 275 Knots. This was NEVER the maximum speed as we understand the term here.
275 Knots (316 MPH) was the maximum speed under "Normal Power" settings of +50 mm boost at 2350 RPM.



P-39 Expert said:


> *That was the D-1 model that weighed 7850lbs. Could have easily weighed 7250lbs after removing redundant or unnecessary equipment. Read the chart in my post #1006 and compare those climb numbers to IIS 85 test. That P-39 weighed 7650lbs.*



If you have information that can confirm that the P-39D-1 in the test was loaded to 7850 pounds please post it.
Considering that the pilot in the test was willing to try 70 inches Hg at Take-Off to prove he could beat the Zero off the line suggests that they were not above a few tricks.

In any case, 7250 pounds was not the loaded weight of operational P-39D-1 in service and your hypotheses are not proven and irrelevant.

- Ivan.


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## GrauGeist (Oct 28, 2020)

windhund116 said:


> Engine could play a factor. HP per weight? No?


Perhaps, but the P-51B had the Packard-Merlin V-1650-3 @ 1,620hp. and the P-51D had the Packard-Merlin V-1650-7 @ 1,695hp.
So there was an increase of hp. but again, there was also an increase in weight between the two variants.

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## pbehn (Oct 28, 2020)

P-39 Expert said:


> 300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.


 You have made a mistake with your units, the pounds are minus pounds or you could add "per pound *reduction*" this is how you start to argue increasing weight increases climb. Dont worry though, I have seen engineers do it on pipeline bundles discussing "negative boyancy".


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## Peter Gunn (Oct 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> This is looking a lot like the movie Groundhog Day.
> Hopefully you might learn something like Bill Murray did.
> ...


What's interesting to me is how the A6M2 holds its speed at all altitudes (almost), the deviation from 12k to 20k doesn't fluctuate more than 15mph.

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## Peter Gunn (Oct 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert....
> 
> *SNIP*
> 
> ...


Finally had time to read this, I see that stateside testing wasn't getting the same results that combat pilots were facing in the SWPA re Zero performance. I see mention of the P-39 being 40MPH faster than the test Zero's but over Guadalcanal and New Guinea Airacobras were decidedly NOT outrunning Japanese fighters at any altitude. One pilot even mentioned a Zero staying with him in a power dive up to 450MPH.

I must confess I don't know where this "40MPH faster than a Zero at any altitude" mantra is coming from in reality. Testing was one thing but it is glaringly apparent that in combat those test results pretty much went out the window.


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## P-39 Expert (Oct 28, 2020)

pbehn said:


> The Spitfire doubled in weight in its life, it also doubled its initial rate of climb. This is conclusive proof that increasing weight increases rate of climb, any discussion of thrust, residual thrust and lift are the babblings of the deranged.


Doesn't prove anything. Spitfire also doubled its horsepower in its life.


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## P-39 Expert (Oct 28, 2020)

Peter Gunn said:


> What's interesting to me is how the A6M2 holds its speed at all altitudes (almost), the deviation from 12k to 20k doesn't fluctuate more than 15mph.


From 12000' to 22500' the P-39K only lost 4mph.


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## XBe02Drvr (Oct 28, 2020)

*P39 Expert said:
Was dividing the increase in climb rate by the increase in weight to find the climb rate increase per pound.*

Do you understand the meaning of the terms "linear" and "non-linear"? Have you noticed that almost all lines on performance charts are curved, not straight? Aerodynamics is full of non-linear relationships because the compressibility of air (or any other gas) is exponential, not linear.
Consequently, putting two points on a graph anchored by data points of ROC/weight for two aircraft and connecting them with a straight line and expecting all the points between to be correct is a fallacious assumption. Only a person with zero understanding of practical aeronautics would fall for it.
Add to that, your assertion that the C and D were identical except for weight ignores the fact that they had similar but not identical propellers, so while rated horsepower may have been identical, it doesn't automatically mean effective thrust is the same at all altitudes, speeds, and power settings.

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## P-39 Expert (Oct 28, 2020)

Peter Gunn said:


> Finally had time to read this, I see that stateside testing wasn't getting the same results that combat pilots were facing in the SWPA re Zero performance. I see mention of the P-39 being 40MPH faster than the test Zero's but over Guadalcanal and New Guinea Airacobras were decidedly NOT outrunning Japanese fighters at any altitude. One pilot even mentioned a Zero staying with him in a power dive up to 450MPH.
> 
> I must confess I don't know where this "40MPH faster than a Zero at any altitude" mantra is coming from in reality. Testing was one thing but it is glaringly apparent that in combat those test results pretty much went out the window.


Testing was factual and comparable. Pilot reports were hearsay and opinion.

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## P-39 Expert (Oct 28, 2020)

XBe02Drvr said:


> *P39 Expert said:
> Was dividing the increase in climb rate by the increase in weight to find the climb rate increase per pound.*
> 
> Do you understand the meaning of the terms "linear" and "non-linear"? Have you noticed that almost all lines on performance charts are curved, not straight? Aerodynamics is full of non-linear relationships because the compressibility of air (or any other gas) is exponential, not linear.
> ...



Do you understand that all rate of climb lines ARE linear above the critical altitude (except the Me109G)? Above critical altitude every single Lightning, Warhawk, Cobra, Thunderbolt, Mustang, Wildcat, Hellcat, Corsair, Fw190A, Zero, Oscar Spitfire, Hurricane and Typhoon has a rate of climb that declines in a straight line as altitude is gained above their critical altitude? Every single one.

And please stop worrying about what I understand and don't understand. You're not talking above my head.


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## fubar57 (Oct 28, 2020)

Never believe the people who were there.

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## FLYBOYJ (Oct 28, 2020)

P-39 Expert said:


> *Was dividing the increase in climb rate by the increase in weight to find the climb rate increase per pound*



I mentioned this on October 5, 6 and 19th. *THIS WILL DEPEND WHERE YOU ARE REMOVING THE WEIGHT FROM. *

*NONLINEAR*

non·lin·e·ar
/nänˈlinēər/

_adjective_


1.
not denoting, involving, or arranged in a straight line.


2.
not linear, sequential, or straightforward; random.

From Chris...

*"Do you really think that only weight influences climb, and that all factors are equal? That when removing weight at one location, and adding weight at another won’t have differing effects. How is your new CG going to effect performance. Oh wait who cares about CG right?"*

*Does anyone want a ground horse meat burger? *

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## Ivan1GFP (Oct 28, 2020)

P-39 Expert said:


> Testing was factual and comparable. Pilot reports were hearsay and opinion.



Testing may have been factual, but hardly comparable. From what I have been able to find, there never actually was a test of a A6M of ANY version that was in good running order.
Many of the reports also don't list critical details. When those details are considered, all that is certain is that the performance of the actual aircraft in Japanese service was better than the test results.

- Ivan.

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## XBe02Drvr (Oct 28, 2020)

Ivan1GFP said:


> Without the automatic mixture control working, the pilot would need to compensate for any altitude changes immediately.


Not just altitude changes! If you've manually fine tuned your mixture for best power, any change in stress on the engine (WEP, high power zoom climb, etc) can push you over the line into detonation unless you're compensating your mixture second by second. That's a distraction you don't need in a dogfight. They put that aneroid altitude compensator in your carburetor for a reason. Use it!

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## Ivan1GFP (Oct 28, 2020)

Peter Gunn said:


> Finally had time to read this, I see that stateside testing wasn't getting the same results that combat pilots were facing in the SWPA re Zero performance. I see mention of the P-39 being 40MPH faster than the test Zero's but over Guadalcanal and New Guinea Airacobras were decidedly NOT outrunning Japanese fighters at any altitude. One pilot even mentioned a Zero staying with him in a power dive up to 450MPH.
> 
> I must confess I don't know where this "40MPH faster than a Zero at any altitude" mantra is coming from in reality. Testing was one thing but it is glaringly apparent that in combat those test results pretty much went out the window.



Hello Peter Gunn,

I believe that "40 MPH faster" is pure garbage. I suspect it is from a book written by a P-39 Fanboy but haven't had the time to go hunting for the book to go look for the quote. Even Koga's A6M2 in less than perfect shape and not running full power was able to do better than this.

Keep in mind though that 450 MPH indicated is actually beyond the limitations (340 Knots) listed in the manual for the A6M2.
The Aleutian A6M2 was actually pushed past its official dive speed limits as well because the US pilots didn't know any better and apparently didn't suffer for it. Maybe the Japanese were a little conservative?

This is my OPINION, but is fairly well supported by anecdotes: The A6M series was actually quite strong structurally. Horikoshi was a very good engineer and didn't build anything stronger or heavier than it absolutely needed to be. The problem with that idea was that it had no redundancy and didn't tolerate battle damage.
(Strong ENOUGH, but I still think it was flimsy.)
The Sakae engine also seemed to tolerate maximum or emergency settings pretty well without failures. I am guessing that this might be because it wasn't highly boosted and also it was one of the better designed powerplants.
Note that even later in the war, when more was known about the Sakae, TAIC made an odd note about "Flash performance" in the Hayabusa that used the same engine and comment that the Japanese pilots apparently didn't take the official limitations very seriously and were apparently getting away with it.
Note also Saburo Sakai's encounter with multiple Hellcats in which he overboosted his engine without any real consequence.

- Ivan.

P.S. Another indication that the Sakae might have been able to tolerate a bit more than the typical engine is the maximum RPM limits.
The Sakae 12 allowed a maximum of 2550 RPM at its Take-Off rating and 2500 RPM at its Military rating.
The manual stated that it would tolerate up to 3100 RPM.
The Sakae 21 allowed a maximum of 2750 RPM at its Take-Off rating and 2700 RPM at its Military rating.
The manual stated that it would tolerate up to 3250 RPM.

I believe these numbers are a bit higher than typical for a big radial engine.

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## P-39 Expert (Oct 28, 2020)

Ivan1GFP said:


> Hello P-39 Expert,
> 
> This is looking a lot like the movie Groundhog Day.
> Hopefully you might learn something like Bill Murray did.
> ...


Expand above.


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## DerAdlerIstGelandet (Oct 28, 2020)

A simple adjustment of a mixture control is probably not so simple in combat, as others have kindly pointed out already...


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## P-39 Expert (Oct 28, 2020)

DerAdlerIstGelandet said:


> View attachment 599915
> 
> 
> A simple adjustment of a mixture control is probably not so simple in combat, as others have kindly pointed out already...


Probably. Maybe. Maybe not.


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## pbehn (Oct 28, 2020)

P-39 Expert said:


> From 12000' to 22500' the P-39K only lost 4mph.


And in the same altitude range a Spitfire Mk XIV gains around 50 MPH.

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## XBe02Drvr (Oct 28, 2020)

*P39 Expert said:*

*As in the test all the pilot had to do was adjust the mixture control slightly. It was a lever on the throttle quadrant. Again we're talking about 3mph.*
Clearly you've got no comprehension of what manual mixture leaning entails in maneuvering flight. It requires very fine adjustment of the mixture control while feeling for the first increment of increased vibration to indicate rough running, in the absence of an EGT gauge. Since none of these vintage planes had perfect intake manifold mixture distribution, you'll always have leaner running and richer running cylinders, even in your beloved V1710. Rough running while leaning at altitude means your leaner cylinders are starting to detonate, which is not conducive to health and long life.
Considering how attention demanding this process is, is it worth the risk while you're maneuvering violently and trying to keep track of what several Zeroes and several P39s are doing and trying to stay out of everyone's gunsights and avoid midair collisions, while in a massive adrenaline rush and frequent G loads? If you think you're that cool a customer, more power to you. I think not. Somebody needs to take you out for a session of bank and yank. Take your motion sickness pills, you're going to need them.

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## P-39 Expert (Oct 28, 2020)

pbehn said:


> And in the same altitude range a Spitfire Mk XIV gains around 50 MPH.


Seriously? You're comparing a 1944 two stage airplane to a 1942 single stage airplane.


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## DerAdlerIstGelandet (Oct 28, 2020)

P-39 Expert said:


> Probably. Maybe. Maybe not.



Please elaborate. Do you have any first hand knowledge?

While I have never flown a warbird in combat, I do regularly adjust mixture when I fly. I have to make very fine adjustments, listening to my engine, and seeing how it responds. Not terribly hard to do while straight and level in a lil slow private plane, not getting shot at and flying combat maneuvers. I, however, can imagine it being pretty difficult to adjust mixture, while flying combat maneuvers, keeping an eye on your enemy, and also trying to shoot your opponent down, while possibly yanking and banking to avoid getting shot down yourself.

In my combat flying experience (656 hours of combat time, as a crew member not pilot), I do know that a lot is going on, and that was in an aircraft with 4 crew members working together, not a cramped high performance single pilot aircraft.

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## DerAdlerIstGelandet (Oct 28, 2020)

P-39 Expert said:


> Seriously? You're comparing a 1944 two stage airplane to a 1942 single stage airplane.



Why not? You think you are the only one who can move the goal posts?

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## pbehn (Oct 28, 2020)

P-39 Expert said:


> Seriously? You're comparing a 1944 two stage airplane to a 1942 single stage airplane.


I was just pointing out that it was actually normal for aeroplanes to get faster not slower between that altitude range. The Spitfire Mk V gained about 27 MPH between 10,000 and 25,000 with its single stage supercharger, basically what I am saying is it isn't simple, as you are obviously aware since you mentioned the two stage engine of the Mk XIV straight away.


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## GregP (Oct 28, 2020)

Watching this thread is better than watching The Big Bang Theory, unless Penny is in the scene. If she is, I'd go with Penny and her assets as better.

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## glennasher (Oct 28, 2020)

It's like talking (typing) to a brick wall, or trying to teach a pig to sing.


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## GregP (Oct 28, 2020)

https://media1.tenor.com/images/269b15d6b4095bb339b9f47f67758317/tenor.gif?itemid=17846431

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## DerAdlerIstGelandet (Oct 28, 2020)

While this is frustrating, lets all try and keep it civil.

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## FLYBOYJ (Oct 28, 2020)

P-39 Expert said:


> Testing was factual and comparable. Pilot reports were hearsay and opinion.



So if a "Test Pilot" submitted a "pilot report" would it be "factual and comparable" or "hearsay and opinion"?

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## Ivan1GFP (Oct 28, 2020)

Hello P-39 "Expert",

I guess you really do have a comprehension problem.



P-39 Expert said:


> *As in the test all the pilot had to do was adjust the mixture control slightly. It was a lever on the throttle quadrant. Again we're talking about 3mph.*



Have you actually figured out how adjusting the mixture control for best power actually works? There isn't a "Best Power" label.
Trying to do this in maneuvering flight while also trying to avoid catching bullets is just not an intelligent thing to do.
You will never have a chance for conditions to stabilize enough.



P-39 Expert said:


> *Glad you finally found your 335mph reference. Most other references say 330mph. You're fighting over 5mph like it won or lost the war.
> .....
> P-39K did 370mph at 16000' and was still achieving 364mph at 20000'.*



You obviously didn't read the rest of the memorandum or don't understand what achieving 335 MPH on partial power really means.
.....
ONE P-39K achieved 370 MPH, just like a P-39D achieved only 358 MPH. The big difference in the tests I am quoting for the P-39s as versus the A6M2 is that the P-39 were aircraft deemed to be in good condition and the tests were representative of their type by the service that normally operated them.
The A6M2 was a crashed aircraft repaired but never had all its systems working properly and tested by its captors who didn't really know how to run it properly.



P-39 Expert said:


> *Look at the P-39K graph in post #1006. I think you'll find the climb rates very comparable.*



Glad it is comparable to a A6M2 running at partial power with a poorly working carburetor.



P-39 Expert said:


> *Probably?
> .....
> Correct or not, you're talking 5mph.*



Probably because the only service that had the opportunity to test the A6M2 to determine the actual maximum speed apparently never cared to do so. They only listed the speed at "Normal Power". This is pretty typical for Japanese aircraft.
.....
Actually we are talking about more like 15 MPH. The claim is 345 MPH as maximum speed for the A6M2.
The USN apparently agreed with this assessment and issued a memorandum to that effect later in the war.
I have not yet found the document though it is mentioned in Mr. Dunn's article.



P-39 Expert said:


> *7850lbs was the listed weight of the P-39D-1.*



I did not ask what the listed weight of he P-39D-1 was. I asked if you had any proof that the test aircraft was loaded to that weight. You are making an assumption here. Please observe that in many other test reports specifying a specific model of aircraft, the weight, CoG, loads and other specific details are mentioned and most of the time they do NOT agree with the standard details of the aircraft being tested.



P-39 Expert said:


> *More tricks? The pilot overboosted the engine at takeoff indicating he either was new in the P-39 or was a lousy pilot.*



I believe he was a good pilot trying to use a few tricks to make his aeroplane look better than it should have.



P-39 Expert said:


> *I have always stated that this weight was easily achievable at forward bases and this was hypothetical. You have not proven anything either.*



First of all, I am not trying to "prove" anything other than the fact that you can't do math.
Even when I claim that the A6M2 was probably faster than 335 MPH, I qualify what I claim as a GUESS.
Perhaps the Aleutian A6M2 rebuilt after a crash and with a poorly rebuilt carb and running at part throttle was the fastest Zero ever built. I don't think so, but maybe SOME people do. People also tend to write books very often without primary sources by just quoting from others who have written books. Just because a statistics is often repeated doesn't mean it is correct.

You might observe that Richard Dunn, who certainly knows more about the A6M2 than I do, does not state his conclusion as an absolute but just as "very likely". Saburo Sakai states that 345 MPH was the maximum speed of the A6M2 based on his personal experience but you will note that Dunn did not take that as conclusive evidence either though it certainly was a strong data point.

You are also making claims for performance when:
1. The client DIDN'T WANT the changes you propose.
2. The operators didn't agree that those changes were a good idea. They wanted more armour, not less.
3. You are using techniques to estimate performance that do not follow good aerodynamic principles.

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## GregP (Oct 28, 2020)

Mea Culpa, DerAdler. I was trying to make a funny and perhaps got carried away. Will correct it. Cheers to all.

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## DerAdlerIstGelandet (Oct 28, 2020)

GregP said:


> Mea Culpa, DerAdler. I was trying to make a funny and perhaps got carried away. Will correct it. Cheers to all.



Was not directed at you, but at all of us. As frustration settles in, we all run the risk of going overboard.

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## wuzak (Oct 28, 2020)

GrauGeist said:


> Perhaps, but the P-51B had the Packard-Merlin V-1650-3 @ 1,620hp. and the P-51D had the Packard-Merlin V-1650-7 @ 1,695hp.
> So there was an increase of hp. but again, there was also an increase in weight between the two variants.



The V-1650-3 and V-1650-7 had different rated altitudes. The -7 was adopted as it gave better performance in the lower to mid altitudes, while maintaining good performance at the higher altitudes.


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## jmcalli2 (Oct 28, 2020)

Stig1207 said:


> Surprised me too, not least the way the combat records are interpreted; 44 P-39's were lost in engagements with Zero's, of which 15 also were lost. All 15 Zeros were shot down by P-39's, and 15 P-39's were shot down by Zeros. Some P-39's were lost to AAA, running out of fuel, mechanical defects, etc; but in many cases no one actually saw what happened and there were some MIA with no probable cause given.
> 
> Perhaps it would be more right to say that it cost 44 P-39s too shoot down 15 Zeros.



I believe that is how most kill ratios for US aircraft are traditionally calculated; all combat losses vs combat kills of the enemy. As I remember the book, there were some records of Zeros disappearing on their homeward flights, well after combat. Don't know how many.
My overall take was this; USAAC had to figure out how to maintain a new type of engine (V-1710 - almost all previous aircraft had radials) in a jungle under attack. They also had to fight a more experienced foe with little advanced warning of the attacks. Add to that conservative engine use doctrine developed from a time when funding was scarce (priority given to reducing maintenance over performance) and you see they had an uphill battle. Yet, they managed to hold the Japanese at bay for the first two 'lean' years of the war.
As for the P-39, there was not a USAAC fighter that would have faired any better at that time.
Also interesting, and something I don't see many talking about, is that of the USAAC single seat fighters, the P-38, P-39, P-40, P-47, and P-51, the P-39 was by far the smallest of the lot, for whatever that's worth.

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## FLYBOYJ (Oct 28, 2020)

jmcalli2 said:


> Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.



I've heard similar, somewhere I think it was calculated a 1 to 1.45 kill/ loss ratio, Zero to P-39



Stig1207 said:


> Surprised me too, not least the way the combat records are interpreted; 44 P-39's were lost in engagements with Zero's, of which 15 also were lost. All 15 Zeros were shot down by P-39's, and 15 P-39's were shot down by Zeros. Some P-39's were lost to AAA, running out of fuel, mechanical defects, etc; but in many cases no one actually saw what happened and there were some MIA with no probable cause given.
> 
> *Perhaps it would be more right to say that it cost 44 P-39s too shoot down 15 Zeros*.



If you want to include all causes



jmcalli2 said:


> I believe that is how most kill ratios for US aircraft are traditionally calculated; all combat losses vs combat kills of the enemy. As I remember the book, there were some records of Zeros disappearing on their homeward flights, well after combat. Don't know how many.
> My overall take was this; USAAC had to figure out how to maintain a new type of engine (V-1710 - almost all previous aircraft had radials) in a jungle under attack. They also had to fight a more experienced foe with little advanced warning of the attacks. Add to that conservative engine use doctrine developed from a time when funding was scarce (priority given to reducing maintenance over performance) and you see they had an uphill battle. Yet, they managed to hold the Japanese at bay for the first two 'lean' years of the war.
> *As for the P-39, there was not a USAAC fighter that would have faired any better at that time.*



Some points made, the P-39, despite it's reputation in the SWP did hold it's own but at the same time look at some of the P-39 units that transitioned into the P-38 in the later part of 1942 and the leap in combat victories. Those same early P-38 units operated under dismal conditions as well and had the P-38 been available earlier it would have made a huge difference. Research the 39th and 80th fighter squadrons and some of the aces that emerged from those units and how things turned around into 1943, all occurring when they got the P-38.

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## FLYBOYJ (Oct 28, 2020)

P-38, *P-39* and P-40 ops in New Guinea. Note comments at 4:35 and 19:35

The First Fighters in New Guinea 1942-1944

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## Ivan1GFP (Oct 29, 2020)

jmcalli2 said:


> My overall take was this; USAAC had to figure out how to maintain a new type of engine (V-1710 - almost all previous aircraft had radials) in a jungle under attack. They also had to fight a more experienced foe with little advanced warning of the attacks. Add to that conservative engine use doctrine developed from a time when funding was scarce (priority given to reducing maintenance over performance) and you see they had an uphill battle. Yet, they managed to hold the Japanese at bay for the first two 'lean' years of the war.
> As for the P-39, there was not a USAAC fighter that would have faired any better at that time.
> Also interesting, and something I don't see many talking about, is that of the USAAC single seat fighters, the P-38, P-39, P-40, P-47, and P-51, the P-39 was by far the smallest of the lot, for whatever that's worth.



Hello jmcalli2,

The most effective Japanese Naval Fighter Unit that was fighting from Lae was the Tainain Air Group.
The unit was formed in October 1941, so it was hardly a veteran unit.
Although they had some experienced pilots from the war in China, that war was hardly comparable to a modern war.

Here are a couple questions for you regarding inexperience with the V-1710:
How much more experience would the AVG have had with their P-40s in China?
Did it make a difference that all the USAAC personnel in New Guinea were at least US Army instead of a mix of USN, Marines, US Army and civilians? Would these other people have had better experience working on V-1710 engines?
Would their supply chain have been any better than a base in New Guinea that was within shipping distance of Australia?
How well did P-40s do in New Guinea?
Did the Australians have the same problems with Allison equipped aircraft?
They could not possibly have had any more knowledge than the service that gave them the aircraft or could they?

- Ivan.


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## GrauGeist (Oct 29, 2020)

The RAAF was operating out Milne Bay, as well - so it wasn't just the USAAF that was contesting Japanese air power.


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## XBe02Drvr (Oct 29, 2020)

FLYBOYJ said:


> P-38, *P-39* and P-40 ops in New Guinea. Note comments at 4:35 and 19:35
> 
> The First Fighters in New Guinea 1942-1944



Did you note how the P39s taking off had to rotate to an exaggerated nose high attitude to break ground, and climbed out in the same exaggerated attitude? Betcha a high speed high positive lift airfoil would have performed better than the symmetrical one they had. The only true benefit of a symmetrical airfoil is a better L/D in inverted flight or negative G maneuvering, performance arenas that are not tactically or doctrinally relevant to the P39. Did it even have a pressure carb and inverted fuel and oil header tanks? If not, then why the symmetrical airfoil? AFAIK it was a positive G airplane, and could have benefited from a positive lift wing. I believe most planes of the era that were inverted capable had header tanks of limited (seconds rather than minutes) endurance, though I've read of Zeroes flying inverted for extended periods when exuberant young pilots were (in the vernacular) "showin their ass".
The T34 I used to fly (a 1954 product) had a high lift Bonanza wing and DID have a syllabus reason to engage in inverted flight, which required an exaggerated nose high attitude and a lot of forward stick pressure to maintain altitude and stay out of a split S. Its header tanks were good for 90 seconds inverted, but Grandpa NATOPS said not over 60. Kinda cool looking "down" at the soft blue and "up" at the hard blue with waves and boats and whitecaps on it. Letting it pitch down into a split S when your personal discomfort limit was reached (well before 60 seconds) was a real blast! Makes you appreciate a tight 5 point harness and stirrups on your rudder pedals.

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## Ivan1GFP (Oct 29, 2020)

Hello XBe02Drvr,

I have been commenting on why the symmetrical airfoil was a bad idea for quite some time.
Considering that the outer wing sections about even with the inboard side of the main gear wells were detachable, it would not have been too difficult to integrate a new outer wing section to the rest of the aeroplane and also add some sweep similar to IL 2/M3 or P-39E to push the center of lift back a bit and correct the CoG issues.

The outer wing sections already had a NACA 23000 series airfoil at the tip to try to prevent a stall from affecting aileron control, but apparently it wasn't enough to prevent the aircraft from flipping if the stall were slightly asymmetrical. This was shown by a tuft test in the L-602 report.

- Ivan.


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## XBe02Drvr (Oct 29, 2020)

Ivan1GFP said:


> Considering that the outer wing sections about even with the inboard side of the main gear wells were detachable, it would not have been too difficult to integrate a new outer wing section to the rest of the aeroplane and also add some sweep similar to IL 2/M3 or P-39E to push the center of lift back a bit and correct the CoG issues.


The only drawback to this approach is likely higher torsional loads on the center section to wing panel attach points, which the center section points may not be stressed to handle. IIRC, that problem arose with the Sturmovik, and turned out to be more than a simple bolt-on field mod.


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## Stig1207 (Oct 29, 2020)

FLYBOYJ said:


> If you want to include all causes



It is all losses in *engagements between P-39's and Zeros *; 44 P-39's lost vs 15 Zero's. Both sides suffered other losses in combat and operational non-combat losses so the overall totals are higher for both sides.


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## Peter Gunn (Oct 29, 2020)

P-39 Expert said:


> Testing was factual and comparable. Pilot reports were hearsay and opinion.


I. AM. SPEECHLESS.

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## FLYBOYJ (Oct 29, 2020)

Stig1207 said:


> It is all losses in *engagements between P-39's and Zeros *; 44 P-39's lost vs 15 Zero's. Both sides suffered other losses in combat and operational non-combat losses so the overall totals are higher for both sides.


You said 15 P-39s were shot down by zeros, 44 lost total, this against 15 zeros lost to P-39s, this is a 1 to 1 ratio in the air. If you include the total 44 lost P-39s this comes out to 2.9 to 1

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## Peter Gunn (Oct 29, 2020)

FLYBOYJ said:


> You said 15 P-39s were shot down by zeros, 44 lost total, this against 15 zeros lost to P-39s, this is a 1 to 1 ratio in the air. If you include the total 44 lost P-39s this comes out to 2.9 to 1


Also wouldn't it be more fair/factual if we're going with 44 TOTAL Airacobras lost with how many TOTAL Zeros were lost, if that number were possible to find? I mean, apples to apples right?

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## Ivan1GFP (Oct 29, 2020)

XBe02Drvr said:


> The only drawback to this approach is likely higher torsional loads on the center section to wing panel attach points, which the center section points may not be stressed to handle. IIRC, that problem arose with the Sturmovik, and turned out to be more than a simple bolt-on field mod.



Hello XBe02Drvr,

The Sturmovik was just one illustration of the idea. There are a bunch of others that were done.
The Me 262 had a much more drastic change to its wing planform to hang a pair of rather heavy engines further back to maintain CoG.
The FW 200 Condor in later versions had swept outer wing sections presumably for the same type of CoG issue.

The P-39 had a three spar wing. The objective as I see it would be to move the Center of Lift about 3.5% or 4% MAC (about 3.22 inches) aft. The problem though is that a bit over 1000 pounds of structure would also be moving so the calculations are obviously not quite that simple. The benefit is that the fuel tanks would also be moving which means that a disposable load is now further back from the CoG and would balance out the disposable loads in the nose.

If there are some torsional loads to be considered, I believe they could be compensated for by reducing the maximum G load from the standard 8/12 G down to something like 7.5/11.25 G as for other aircraft that gained some weight from their initial designs. Even the last versions of the Airacobra had not gained substantial weight from the initial service versions.

I believe the best idea would have been a much more thorough redesign instead of a patch job when the P-39 lost its interceptor mission.

- Ivan.

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## FLYBOYJ (Oct 29, 2020)

Peter Gunn said:


> Also wouldn't it be more fair/factual if we're going with 44 TOTAL Airacobras lost with how many TOTAL Zeros were lost, if that number were possible to find? I mean, apples to apples right?


Yes - my point. If we're just talking air-to-air, it was a draw. According to the posted numbers 15 Zeros and 15 P-39s were lost air-to-air but we don't know if additional Zeros were lost to other causes.

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## pbehn (Oct 29, 2020)

Peter Gunn said:


> I. AM. SPEECHLESS.


So am I, someone doesn't know what hearsay means, a pilots report is not hearsay, someone saying "I heard a pilot say" is hearsay. Pilots reports on the P-39 including reports on those who died in non operational missions in UK, played a part in them all being shipped to Russia. An individual pilots report may or maynot be in error, when many pilots report the same thing only a fool would discount it. 
hearsay
[ˈhɪəseɪ]

NOUN


information received from other people which cannot be substantiated; rumour.


the report of another person's words by a witness, which is usually disallowed as evidence in a court of law.


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## GrauGeist (Oct 29, 2020)

Peter Gunn said:


> Also wouldn't it be more fair/factual if we're going with 44 TOTAL Airacobras lost with how many TOTAL Zeros were lost, if that number were possible to find? I mean, apples to apples right?


Exactly - cull the P-39 operational losses out of the total number and it becomes a wash.
ONLY include the P-39's operational losses in the total number if the A6M group's operational losses can be added.

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## P-39 Expert (Oct 29, 2020)

FLYBOYJ said:


> P-38, *P-39* and P-40 ops in New Guinea. Note comments at 4:35 and 19:35
> 
> The First Fighters in New Guinea 1942-1944



In the 19:35 comments "they were too heavy and lacked a supercharger". Everyone knew they were too heavy, why didn't they reduce the weight? And the lack of a supercharger is another myth that has been perpetuated for 75 years.


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## Reluctant Poster (Oct 29, 2020)

GrauGeist said:


> Perhaps, but the P-51B had the Packard-Merlin V-1650-3 @ 1,620hp. and the P-51D had the Packard-Merlin V-1650-7 @ 1,695hp.
> So there was an increase of hp. but again, there was also an increase in weight between the two variants.


Late model P-51 B and Cs switched to the -7. The difference between the two versions was the supercharger drive ratio. The -7 used lower ratios and therefore developed more HP at lower altitudes at the expense of high altitude performance.


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## GrauGeist (Oct 29, 2020)

And the original point of the P-51B/P-51D comparison, was that the P-51D (empty) was *heavier* than the P-51B (empty), yet had better performance - contrary to someone's insistence that a lighter P-39 would have had better performance.

So again: weight alone is not the magic solution to a type's performance.


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## P-39 Expert (Oct 29, 2020)

Ivan1GFP said:


> Hello P-39 "Expert",
> 
> I guess you really do have a comprehension problem.
> 
> ...


Please expand above.


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## P-39 Expert (Oct 29, 2020)

FLYBOYJ said:


> I've heard similar, somewhere I think it was calculated a 1 to 1.45 kill/ loss ratio, Zero to P-39
> 
> 
> 
> ...


And nobody ever notes the attrition of the best Japanese pilots by the P-39, P-40 and F4F. The P-39 and P-40 were still the most numerous AAF fighters in NG until Sept '43. The newer AAF pilots were much better trained than the earlier pilots, and the Japanese replacements were much worse in their training. The P-38, Corsair and Hellcat pilots were facing declining competition.


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## DerAdlerIstGelandet (Oct 29, 2020)

Anybody else getting a headache in here?

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## GregP (Oct 29, 2020)

As far as I know, there are two ways to calculate kill-to-loss ratio:

1) Own losses in air-to-air combat alone against air-to-air victories, and
2) All combat losses against all victories.

The real issue is that the USAAF and the USN / USMC do NOT save the data the same way.

The Navy breaks out losses as losses on action sorties and losses to non-action missions. Losses on action sorties are losses to: 1) Enemy aircraft, 2) losses to AAA, and 3) Operational losses on combat mission unrelated to combat (ran out of fuel, engine malfunction, mid-air collision, post a prop). Losses on non-action sorties are losses: 1) Losses on Ship (carrier sank) or Ground, and 2) Losses on Other Flights (such as repositioning flights, maintenance flights, etc.).

The USAAC/F, on the other hand, just tracks all Combat losses, but they break victories up into: 1) Air-to-air, and 2) Ground.

By way of example, take the F6F Hellcat: Air-to-air: 270 air-to-air losses; 5,163 kills = 19.1 : 1 in air-to-air combat. But, if you look at ALL combat losses, you get: 1,163 losses against 5,163 kills = 4.44 : 1 overall.

If you look at the P-51 Mustang, we see: 2,520 combat losses, 4,950 air-to-air victories = 1.96 : 1 in air-to-air combat. But, the P-51 also had 4,131 ground kills. If you add air and ground kills, you get 9,081 kills. So, we have 2,520 combat losses against 9,081 kill = 3.60 : 1 kill-to-loss combat total.

We can’t break out air-to-air losses for the P-51 and we can’t break out air versus ground kills for the F6F. So, the only real comparison is total ratio: F6F = 4.44 : 1 and P-51 =3.60 : 1. The only thing we CAN say is that the F6F kills can’t have too many on the ground versus the P-51’s total because the ocean won’t support stationary airplanes. Therefore, there are many fewer ground kills in the case of the F6F. But, we can’t say how many.

By the way, the data for the P-51 is ETO-only from Ray Wagner’s American Combat Planes. The data for the F6F is from Naval Combat Statistics of World War II.

I show the P-39 as 107 combat losses against 32 kills for a kill-to-loss ratio of 0.3 : 1. But, that is for the ETO only. I don't have the P-39's Pacific numbers and am not sure where to find them.

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## BiffF15 (Oct 29, 2020)

P-39 Expert said:


> In the 19:35 comments "they were too heavy and lacked a supercharger". Everyone knew they were too heavy, why didn't they reduce the weight? And the lack of a supercharger is another myth that has been perpetuated for 75 years.



P-39 Expert,

I heard / noticed that as well. Not sure if the guy narrating the film is a pilot or not. Did you notice how he said the P-38 had a supercharger? I know of the supercharger myth surrounding these engines, but when he mentioned that the 38 had a supercharger, and the 39 did not, I assumed he meant turbo, or turbosupercharger for period speak.

*“Testing was factual and comparable. Pilot reports were hearsay and opinion.” P-39 *Expert

This comment is astounding. If testing was so factual and comparable, why did it get repeated so often? Why were there so many comments about engines running rough, large sections of rebuilt aircraft, and no manual?

If pilot reports were hearsay, why did the guys who were running the war want them? So the first guy who reported a Me-262, or long nosed FW-190, or a Me-109 with a bigger spinner were all speaking hearsay? I fought a non-export version of another countries primary fighter. I was talked to before the fight by several different people, and after the fight I did a AAR (After Action Report) and received several phone calls plus more debriefings by Intel. I was only a 4 ship flight lead, not an IP / Test Pilot. I wonder why they (Intel) wanted my opinion / experience so badly.

You also mentioned Chuck Yeagers fondness of the P-39. Did he fly it only in training, where the CG was most likely as far forward as could be made for the safety of new / novice fighter pilots? Have you ever reached out to him to ask his opinion on whether it would have made him an ace like the P-51 did? Be careful, he doesn’t tolerate what he deems silly questions very well.

You never replied to my earlier, rather long post (594) so I don’t hold much hope here either but will say it regardless. There are aviation mechanics, pilots, engineers who are mechanics and pilots, all whose experience with aircraft, military and otherwise, is quite large. They have stated and made known their collective background, experience yet you don’t believe or give them due credit. 

I have to ask, what is your aviation / mechanical experience? Have you sat down with and discussed P-39s with the guys who flew it, or other fighters in WW2? Have you worked on / restored / raced any as members here have? Have you taken flight lessons? Or are you like the majority of us gleaning through piles of old information, often with contradictory “facts”, trying to sort out what really happened and why? There is a blend of both on here, and you aren’t giving ANY credit to the other group or anyone who doesn’t agree with your assumptions. Be careful, that’s not the way to gain credibility.

Cheers,
Biff

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## DerAdlerIstGelandet (Oct 29, 2020)

And by the way, pilot reports are not even close to the definition of hearsay.

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## Stig1207 (Oct 29, 2020)

FLYBOYJ said:


> You said 15 P-39s were shot down by zeros, 44 lost total, this against 15 zeros lost to P-39s, this is a 1 to 1 ratio in the air. If you include the total 44 lost P-39s this comes out to 2.9 to 1


That is what Claringbold writes, but not clearly; it can be misconstrued that these are the total combat losses for both sides during the campaign/ time period. That is not the case, for both sides lost P-39's and Zero's to enemy action on missions where they didn't meet in combat. 



Peter Gunn said:


> Also wouldn't it be more fair/factual if we're going with 44 TOTAL Airacobras lost with how many TOTAL Zeros were lost, if that number were possible to find? I mean, apples to apples right?



That is the total losses in the combats in which P-39's met Zero's in combat. So 44 P-39's lost to all causes against 15 Zero's lost to all causes (all causes in this case being P-39's).

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## GregP (Oct 29, 2020)

And a "pilot report" is not the same thing as a "hangar story" to impress the locals many years after active duty. Active-duty pilot reports are solicited to give other active-duty pilots an edge in combat. If they are "inflated" or false in any way, everyone will know when they try the suggested tactic(s) in the pilot report, so nobody gives false active-duty pilot reports, even the show-off guys.

On the other hand, very specific numbers recalled 50 years later are suspect since our memories are generally rose-colored. I'd not trust an old WWII pilot who thought the best climb speed for some fighter was some exact number, but I DO trust him when he says that he never reached his airplane's top speed on a combat mission unless he was in a dive, because who wants to run their engine at absolute full power when you are 500 miles from home over hostile territory with a currently-good-running engine? That's why I believe the old guys when they say combat speeds were in the 250 - 350 mph range unless the fight was a descending chase. When combat joined, they went to military power and mostly only used WEP if their life was in danger, not just to get an offensive kill. There were exceptions, but not very many after the crew chief reamed the pilot for breaking the throttle gate wire without a good reason. That sometimes meant an engine change for the crew, and they would not be happy about it.

Luckily, today's jets don't have quite the issue the WWII planes did. They routinely go into afterburner (and usually track hot temperature cycles) on takeoff, whereas NOBODY used (or uses) WEP for takeoff in a piston fighter. There might not be enough rudder or aileron to stay on the runway if they did. Of course, we also don't have 150 performance number fuel today, either, so nobody runs the old engines at what used to be WEP.

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## FLYBOYJ (Oct 29, 2020)

P-39 Expert said:


> And nobody ever notes the attrition of the best Japanese pilots by the P-39, P-40 and F4F. The P-39 and P-40 were still the most numerous AAF fighters in NG until Sept '43. The newer AAF pilots were much better trained than the earlier pilots, and the Japanese replacements were much worse in their training. *The P-38, Corsair and Hellcat pilots were facing declining competition*.


Not in late 1942/ early 1943 and it depends where we are talking. Many seasoned JN pilots were lost at Midway and that attrition never fully recovered. JAAF pilots were a different story. The P-39, P-40 and F4F over the Solomons barely scraped over a 1 to 1 kill/ claim ratio. Once the P-38 came on scene scores jumped. This is well documented in the 39th and 80th FS histories as well as other units that gave up their P-39s for P-38s. With that said, the P-39 did serve a purpose, it did hold the line but we weren't going to win the war with a 1:1 kill ratio.

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## Reluctant Poster (Oct 29, 2020)

GregP said:


> As far as I know, there are two ways to calculate kill-to-loss ratio:
> 
> 1) Own losses in air-to-air combat alone against air-to-air victories, and
> 2) All combat losses against all victories.
> ...


These are not kills they are claims. There is usually a large difference.


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## tomo pauk (Oct 29, 2020)

GrauGeist said:


> And the original point of the P-51B/P-51D comparison, was that the P-51D (empty) was *heavier* than the P-51B (empty), yet had better performance - contrary to someone's insistence that a lighter P-39 would have had better performance.
> 
> So again: weight alone is not the magic solution to a type's performance.



Without the racks, the P-51B was probably faster, not slower. With racks on, the positions switched. P-51D used more streamlined racks, 4 mph cost vs. 12 mph on the B.

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## XBe02Drvr (Oct 29, 2020)

tomo pauk said:


> Without the racks, the P-51B was probably faster, not slower. With racks on, the positions switched. P-51D used more streamlined racks, 4 mph cost vs. 12 mph on the B.


So many variables! Nothing's simple anymore!

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## XBe02Drvr (Oct 29, 2020)

FLYBOYJ said:


> The P-39, P-40 and F4F over the Solomons barely scraped over a 1 to 1 kill/ claim ratio.


Which we could afford and the Japanese could not. That our less experienced pilots in lower performing planes could manage that ratio against the experten of IJNAF is an amazing achievement itself.
Probably partly due to our "overweight" and overbuilt aircraft. They didn't call Grumman "the Iron Works" for nothing.

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## GrauGeist (Oct 29, 2020)

tomo pauk said:


> Without the racks, the P-51B was probably faster, not slower. With racks on, the positions switched. P-51D used more streamlined racks, 4 mph cost vs. 12 mph on the B.


A quick overview from Joe Baugher:


> Specification of P-51B-1-NA:
> One 1620 hp Packard Merlin V-1650-3 twelve cylinder Vee liquid-cooled engine. Maximum speed was 388 mph at 5000 feet, 406 mph at 10,000 feet, 427 mph at 20,000 feet, 430 mph at 25,000 feet, 440 mph at 30,000 feet.
> Range on internal fuel was 550 miles at 343 mph at 25,000 feet, 810 miles at 253 mph at 10,000 feet. With maximum external fuel, maximum range was 2200 miles at 244 mph.
> An altitude of 5000 feet could be attained in 1.8 minutes, 10,000 feet in 3.6 minutes, 20,000 feet in 7 minutes.
> ...





> Specification of P-51C-10-NT:
> One 1695 hp Packard Merlin V-1650-7 twelve cylinder Vee liquid-cooled engine. Maximum speed was 395 mph at 5000 feet, 417 mph at 10,000 feet, 426 mph at 20,000 feet, 439 mph at 25,000 feet, 435 mph at 30,000 feet.
> Range on internal fuel was 955 miles at 397 mph at 25,000 feet, 1300 miles at 260 mph at 10,000 feet. With maximum external fuel, maximum range was 2440 miles at 249 mph.
> An altitude of 5000 feet could be attained in 1.6 minutes, 10,000 feet in 3.1 minutes, 20,000 feet in 6.9 minutes.
> ...





> Specification of the P-51D-25-NA:
> One 1695 hp Packard Merlin V-1650-7 twelve-cylinder Vee liquid-cooled engine.
> Maximum speed: 395 mph at 5000 feet, 416 mph at 10,000 feet, 424 mph at 20,000 feet, 437 mph at 25,000 feet.
> Range was 950 miles at 395 mph at 25,000 feet (clean), 2300 miles with maximum fuel (including drop tanks) of 489 US gallons under most economical cruise conditions. Initial climb rate was 3475 feet per minute. An altitude of 5000 feet could be reached in 1l7 minutes, 10,000 feet in 3.3 minutes, 20,000 feet in 7.3 minutes.
> ...

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## XBe02Drvr (Oct 29, 2020)

P-39 Expert said:


> And the lack of a supercharger is another myth that has been perpetuated for 75 years.


C'mon, man, the guy was a maintenance officer. He wasn't that ignorant. All the engine types in question had integral gear driven superchargers built in. Part of the engine, in wrench twister jargon. None of these guys had probably ever seen an external extra stage supercharger like European engines had, so to them an outboard turbocharger was just "a supercharger". "Turbo" was understood. The fact that in our ex post facto concise semantics we misconstrue their words is our (the modern world's) fault, not theirs.

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## Peter Gunn (Oct 29, 2020)

P-39 Expert said:


> And nobody ever notes the attrition of the best Japanese pilots by the P-39, P-40 and F4F. The P-39 and P-40 were still the most numerous AAF fighters in NG until Sept '43. The newer AAF pilots were much better trained than the earlier pilots, and the Japanese replacements were much worse in their training. The P-38, Corsair and Hellcat pilots were facing declining competition.


I doubt very much any Allied pilot fighting the Japanese during the calendar years 1942 and 1943 would be very inclined to agree with you. A case could even be made for the first several months of 1944, but then again, it would only be pilots reports, not actual test data.

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## DerAdlerIstGelandet (Oct 29, 2020)

Peter Gunn said:


> I doubt very much any Allied pilot fighting the Japanese during the calendar years 1942 and 1943 would be very inclined to agree with you. A case could even be made for the first several months of 1944, but then again, it would only be pilots reports, not actual test data.

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## GregP (Oct 29, 2020)

Hi Reluctant Poster.

Show me a list of vetted kills. The only ones I know of are the USAAF Report 85 and Naval Aviation Combat Statistics - World War II, and people fight over those.

So, we are left with claims only. I have zero confidence in someone who says they have the kill information unless they state: 1) exactly what IS a "kill" (widely differing opinions), 2) where did they get their kill numbers exactly and how? (who did the vetting? Is it "official" and recognized by anyone).

When I think about it, all I see to really use is acknowledged losses versus claims because claims is all we really have. I have a great file of German claims ... 68,000+ claims. I don't have and have not seen a list of vetted German victories. As far as I know, Hartmann is sill at 352 victories.


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## P-39 Expert (Oct 29, 2020)

BiffF15 said:


> P-39 Expert,
> 
> I heard / noticed that as well. Not sure if the guy narrating the film is a pilot or not. Did you notice how he said the P-38 had a supercharger? I know of the supercharger myth surrounding these engines, but when he mentioned that the 38 had a supercharger, and the 39 did not, I assumed he meant turbo, or turbosupercharger for period speak.
> 
> ...


Biff,

Please accept my apology, I should never have said that pilot reports were heresay and opinion. But any report from an individual will contain some opinion.

I am neither a pilot, mechanic or engineer. I just like to read about history. I will be 70 in February and my Dad served in WWII, so that is my favorite period. 

You are correct, I'm just gleaning through piles of old contradictory information trying to sort out what happened and why. I became more interested when M. Williams started publishing the actual performance reports in wwiiaircraftperformance.org. This information cleared up a lot of confusion for me, since most prior published information was very contradictory, meaning some of it was wrong.

I'm just expressing my opinions based on that newer information, and getting almost 100% pushback from everyone who would rather believe what they have heard for 75 years rather than newer factual information and recently released information from the fall of the Soviet Union.

I'm not worried about credibility, I know I don't have any. But I do have a lot of facts that nobody else wants to believe.

I always enjoy your posts and please feel free to contact me anytime.

Thanks.

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## XBe02Drvr (Oct 29, 2020)

Are there any existing loss records of Japanese forces in New Guinea?


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## P-39 Expert (Oct 29, 2020)

GregP said:


> And a "pilot report" is not the same thing as a "hangar story" to impress the locals many years after active duty. Active-duty pilot reports are solicited to give other active-duty pilots an edge in combat. If they are "inflated" or false in any way, everyone will know when they try the suggested tactic(s) in the pilot report, so nobody gives false active-duty pilot reports, even the show-off guys.
> 
> On the other hand, very specific numbers recalled 50 years later are suspect since our memories are generally rose-colored. I'd not trust an old WWII pilot who thought the best climb speed for some fighter was some exact number, but I DO trust him when he says that he never reached his airplane's top speed on a combat mission unless he was in a dive, because who wants to run their engine at absolute full power when you are 500 miles from home over hostile territory with a currently-good-running engine? That's why I believe the old guys when they say combat speeds were in the 250 - 350 mph range unless the fight was a descending chase. When combat joined, they went to military power and mostly only used WEP if their life was in danger, not just to get an offensive kill. There were exceptions, but not very many after the crew chief reamed the pilot for breaking the throttle gate wire without a good reason. That sometimes meant an engine change for the crew, and they would not be happy about it.
> 
> Luckily, today's jets don't have quite the issue the WWII planes did. They routinely go into afterburner (and usually track hot temperature cycles) on takeoff, whereas NOBODY used (or uses) WEP for takeoff in a piston fighter. There might not be enough rudder or aileron to stay on the runway if they did. Of course, we also don't have 150 performance number fuel today, either, so nobody runs the old engines at what used to be WEP.


Agree with you about WEP. Your crew chief was not to happy to see that wire broken and would want to know why you abused HIS airplane. And it was for EMERGENCY only as using it risked engine damage or failure.

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## DerAdlerIstGelandet (Oct 29, 2020)

P-39 Expert,

No one thinks you are dumb. No one thinks you don’t have facts. We don’t think you are putting it together right.

When you make comments such as saying mixture adjustment is simple, and that simply removing weight will make something better, and then completely blow off people with actual experience explaining how things in the real world work, you kind of lose them.

You are a valued member here, but maybe try listening a lil more...

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## P-39 Expert (Oct 29, 2020)

FLYBOYJ said:


> Not in late 1942/ early 1943 and it depends where we are talking. Many seasoned JN pilots were lost at Midway and that attrition never fully recovered. JAAF pilots were a different story. The P-39, P-40 and F4F over the Solomons barely scraped over a 1 to 1 kill/ claim ratio. Once the P-38 came on scene scores jumped. This is well documented in the 39th and 80th FS histories as well as other units that gave up their P-39s for P-38s. With that said, the P-39 did serve a purpose, it did hold the line but we weren't going to win the war with a 1:1 kill ratio.


The early planes were attriting Japanese pilots, whether it be from combat losses, accidents, weather or mechanical problems. Not just victory claims. The Japanese lost those planes and pilots because of combat, if not actually from combat. And those losses were the best of the best, since their pilot training fell off as the war progresses and they didn't rotate their pilots back home to teach the trainees. The P-38, Corsair and Hellcat pilots had it easier because of the work done before they arrived.

I'm just saying that early work would have been a lot more productive if the P-39 was made lighter.

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## P-39 Expert (Oct 29, 2020)

DerAdlerIstGelandet said:


> P-39 Expert,
> 
> No one thinks you are dumb. No one thinks you don’t have facts. We don’t think you are putting it together right.
> 
> ...


I have never blown off anyone on here, never told them they didn't know what they were talking about, and certainly never even mentioned the word stupid. I have always been as courteous as I possibly can to everybody on here that disagrees with me, which is everybody. 

But how anyone can say that removing weight will not make an airplane perform better is someone I'm going to disagree with every time.

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## XBe02Drvr (Oct 29, 2020)

P-39 Expert said:


> I'm just saying that early work would have been a lot more productive if the P-39 was made lighter.


Nobody's quibbling with the idea that a lighter P39 would have performed better. The devil is in the details, and the real world impracticality of most of the solutions you suggest are what is generating the pushback. The personnel at Port Moresby and Milne Bay were stuck with playing the hand they were dealt, and from the perspective of 3/4 century later, I think we can say they played that hand as successfully as was possible under the circumstances.

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## Dash119 (Oct 29, 2020)

P-39 Expert said:


> I have never blown off anyone on here, never told them they didn't know what they were talking about, and certainly never even mentioned the word stupid. I have always been as courteous as I possibly can to everybody on here that disagrees with me, which is everybody.
> 
> But how anyone can say that removing weight will not make an airplane perform better is someone I'm going to disagree with every time.


Like you, I am not an engineer, A&P or a pilot. I don't disagree with everything you say. I have not posted in this thread up until this point, as I didn't think I had anything to add.

Having said that, you are dealing with many knowledgable individuals here and yet you continue to use very simplistic language which continues to get you in trouble. So...

I think an Allison V-1710 weighs about 1400 lbs. dry. If I remove that weight from the P-39 I can state categorically that the airplane will not perform better...

So maybe going forward; "But how anyone can say that removing weight, *while maintaining proper weight and balance,* will not make an airplane perform better is someone I'm going to disagree with every time."

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## FLYBOYJ (Oct 29, 2020)

P-39 Expert said:


> The early planes were attriting Japanese pilots, whether it be from combat losses, accidents, weather or mechanical problems. Not just victory claims. The Japanese lost those planes and pilots because of combat, if not actually from combat. *And those losses were the best of the best, since their pilot training fell off as the war progresses and they didn't rotate their pilots back home to teach the trainees. The P-38, Corsair and Hellcat pilots had it easier because of the work done before they arrived.*
> 
> I'm just saying that early work would have been a lot more productive if the P-39 was made lighter.



You're making a generalization that spans about 8 months, in some cases I can agree, but in other areas no. Again, the JAAF did not lose it's best pilots during the first 6 months and there plenty of them still around when better aircraft showed up.


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## XBe02Drvr (Oct 29, 2020)

Dash119 said:


> I think an Allison V-1710 weighs about 1400 lbs. dry. If I remove that weight from the P-39 I can state categorically that the airplane will not perform better...
> 
> So maybe going forward; "But how anyone can say that removing weight, *while maintaining proper weight and balance,* will not make an airplane perform better is someone I'm going to disagree with every time.


How you going to define "performance"; miles/hour, ft/min, degrees/sec, OR total losses during a period of combat ops (including operational) vs VERIFIED enemy combat losses?
Quite likely that which you sacrifice in pursuit of weight reduction will negatively effect your victory/loss ratio. (IFF, protection, firepower, etc) It's not just an airplane, it's a weapons system.

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## FLYBOYJ (Oct 29, 2020)

Dash119 said:


> So maybe going forward; "But how anyone can say that removing weight, *while maintaining proper weight and balance,* will not make an airplane perform better is someone I'm going to disagree with every time.



And this statement is about 98/99% correct. Depending WHERE in the weight and balance envelope the aircraft falls will also be a determining factor. Tail heavy aircraft (within the envelope) will generally fly faster but be less stable, nose heavy aircraft (within the envelope) may be a little more stable, require more elevator back pressure to maintain level flight (to be trimmed out) but may not gain maximum lift efficiency (slower flight at a given power setting). Removing weight will of course make the aircraft lighter (and will more than likely make the aircraft perform better) but you also have to consider WHERE you are removing that weight from, thus *this IS NOT a linear calculation* and I think GregP even gave the correct equation to figure this out about 100 posts ago!

PS - I actually witnessed this when I crewed a Jet at Reno. In once case the weight removed didn't make a difference until we got the C/G aft and then we saw results.

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## DerAdlerIstGelandet (Oct 29, 2020)

P-39 Expert said:


> I have never blown off anyone on here, never told them they didn't know what they were talking about, and certainly never even mentioned the word stupid. I have always been as courteous as I possibly can to everybody on here that disagrees with me, which is everybody.
> 
> But how anyone can say that removing weight will not make an airplane perform better is someone I'm going to disagree with every time.


 
I think you are not listening. People are telling you that you can’t just remove the weight and it will magically get better. Removing weight also affects things such as CG. Depending on where that CG now lies will effect how it performs as well. Thats a real simple view of it. There is much more to it than that. Engineers sit down, perform calculations, and together with test pilots figure it out. You cannot simply modify an aircraft and think it will make it better. Trust me I have done countless modifications, and currently work in retrofit and modification engineering. This stuff has to be carefully evaluated.



XBe02Drvr said:


> Nobody's quibbling with the idea that a lighter P39 would have performed better. The devil is in the details, and the real world impracticality of most of the solutions you suggest are what is generating the pushback. The personnel at Port Moresby and Milne Bay were stuck with playing the hand they were dealt, and from the perspective of 3/4 century later, I think we can say they played that hand as successfully as was possible under the circumstances.



Thank you. Said much better than I have.



FLYBOYJ said:


> And this statement is about 98/99% correct. Depending WHERE in the weight and balance envelope the aircraft falls will also be a determining factor. Tail heavy aircraft (within the envelope) will generally fly faster but be less stable, nose heavy aircraft (within the envelope) may be a little more stable, require more elevator back pressure to maintain level flight (to be trimmed out) but may not gain maximum lift efficiency (slower flight at a given power setting). Removing weight will of course make the aircraft lighter (and will more than likely make the aircraft perform better) but you also have to consider WHERE you are removing that weight from, thus *this IS NOT a linear calculation* and I think GregP even gave the correct equation to figure this out about 100 posts ago!
> 
> PS - I actually witnessed this when I crewed a Jet at Reno. In once case the weight removed didn't make a difference until we got the C/G aft and then we saw results.



And this as well.

Again no one is saying reducing weight will not improve performance. But has to be done correctly.

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## davparlr (Oct 29, 2020)

It is my understanding that American aircraft were designed to higher stress standards than the British so that for a similar size aircraft the American craft would be heavier. I also understand that part of the lightening of the P-51H was designing to the lighter standards which worked quite well. However to do so was a major impact and the P-51H is a significantly different aircraft than the P-51D. I do wonder if the P-39 was originally designed to the lighter British standards, how would it have performed.

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## SaparotRob (Oct 29, 2020)

davparlr said:


> It is my understanding that American aircraft were designed to higher stress standards than the British so that for a similar size aircraft the American craft would be heavier. I also understand that part of the lightening of the P-51H was designing to the lighter standards which worked quite well. However to do so was a major impact and the P-51H is a significantly different aircraft than the P-51D. I do wonder if the P-39 was originally designed to the lighter British standards, how would it have performed.


Something new!


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## GregP (Oct 30, 2020)

Hi P-39 Expert, let me try once here.

I am a volunteer at the Planes of Fame Museum in Chino, CA. We have a P-39 (static) and Fighter Rebuilders is located onsite, owned by Steve Hinton and son. They have built up a P-39 on at least one if not more occasions and I have looked pretty closely at the static P-39. None of what I am saying here is from Fighter Rebuilders or the Museum, it is my observations only. I mention the above only so you know that WWII fighters are very much present there all the time, not just on occasion. They operate WWII fighters VERY regularly, even several times per week ... that is ... pre-COVID anyway.

There isn't a lot you can remove from a P-39 that is not structural or in the wrong place, CG-wise, for removal. If you remove the nose guns, I assume you remove the ammunition, too. You have to do something to keep in CG. If you remove the nose guns, except the cannon, the ammunition, and the nose armor plate, the airplane WILL be lighter, but you can't fly it since the CG is out of limit aft. There is NOTHING heavy in the tail cone except maybe the radio, and nobody was going to let their radio be deleted. They might need it to communicate where they ditched in the ocean, if for nothing else. It wasn't going to "go away" without the pilots rebelling.

So, I fully support your contention that lightening the P-39 would have been a good thing. I'm just having a hard time trying to decide WHAT to delete that would make a difference while remaining flyable and maintaining combat effectiveness. See the image below.

The cutaway below is an early P-39 and had 30-cal guns, but later variants had 50-cal guns. I'll assume 50-cals.










The only thing I see that is removable behind the center of gravity, which is about 1/3 of the way back from the wing leading edge, is the radio receiver (#12 above), and it ain't going anywhere. The pilot's back armor is #28 above, and is about right on the CG (18.2 pounds). Most pilots would not remove it even though the engine is a pretty good armor by itself. You might remove the #74 wing guns (145 pounds) and #79 ammunition (186 pounds), but what else can you suggest that would effect a significant weight change aft of the CG? I may be blind, but I don't see it. There is no significant structure to get rid of.

If you DO remove the wing guns, you are lighter by 331 pounds but you also have only a cannon that jams easily and has few rounds anyway and two 50-cal nose guns. This ain't no German MG 151/20, it's an Oldsmobile jamming fool and, if it DOES jam, you are down to two 50-cal MG ... just mildly better than what a P-26 Peashooter had. I'd rather leave the armament, operate the engine beyond recommended limits for better performance, and play fighter below 12,000 - 15,000 feet.

You might only remove ONE gun (the outer one) and ammunition in each wing, and you'd save 165 pounds or so. But, is that going to make your airplane a noticeably-better fighter in a dogfight against your likely opponent? I think not. It might climb marginally better, but not enough to catch a Zero by LONG shot. The Zero had more than a little better climb rate at P-39 combat altitudes.

Kick me if you can see it differently, but all the structure behind the wing trailing edge seems necessary for flight and structural integrity to me.

I'd not remove the #17 oil tank armor for any reason whatsoever.

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## Ivan1GFP (Oct 30, 2020)

P-39 Expert said:


> *There is no "best power" label but the mixture control can be adjusted between the settings.*



You have said absolutely NOTHING with that statement. The process is the important part and what I and everyone else is telling you is that it is not something that can be done when maneuvering as in combat. With the constantly changing conditions of engine load, altitude, speed, how can the pilot decide whether the mixture needs to be leaner or richer? By the time he has observed and decided, the conditions have most likely changed.



P-39 Expert said:


> *Please stop telling me what I have read and what I haven't read. Keep the personal attacks to yourself.*



This is not an attack but a simple statement of fact. You either did not read the note at the bottom of the report that I directed you to or you did not understand what you were reading.



P-39 Expert said:


> *That's the only Zero available to test. It was restored to the best available condition.*



Hmmm..... You are contradicting your next statement below......
Just because it was the only aircraft available to test and that it was restored as well as the captors knew how doesn't mean that it was representative of the ones the enemy was currently using. Many if not most cases of captured aircraft tests are that way.
Another good example that came up in discussion recently was the La 5FN tested at Rechlin. Good for a handling evaluation, but worthless for a performance evaluation.



P-39 Expert said:


> *Other A6M2s were tested and the vast majority topped out at 330mph. *



Great Assertion! Now please back up your claim and provide your source for other A6M2 in good running order that were tested.
Test reports would be a good start.



P-39 Expert said:


> *Like overboosting the engine on takeoff? Risking engine damage or failure? What did takeoff run matter in these tests? More likely a novice pilot in an unfamiliar airplane.*



The fellow was probably trying beat the A6M2 in a time to height race by any means that he could.
I suspect this pilot was quite experienced. Over revving the engine and running boost up past 70 inches Hg at low altitude was something that had been done with some P-40s with similar model engines in combat conditions.
It got to be bad enough that Allison wrote a memo about it.



P-39 Expert said:


> *I saw a documentary on TV once and the veteran surviving Japanese pilot said the top speed of the Zero was 308mph.*



First question I should ask you since you actually saw the documentary is WHAT did the Japanese pilot actually say?
Was he speaking Japanese or English? If Japanese, did he have a translator?

Keep in mind that the Air Speed Indicator on the A6M series reads in Knots.
Saburo Sakai's statement about 345 MPH wasn't actually that but the equivalent in Knots.
Richard Dunn did the conversion and I have been using the number in MPH because outside of Naval Aviation, MPH was the more common unit used in aviation until the 1960's.

If he was saying 308 Knots, it sounds about right for a late model A6M5 at altitude.
If he really meant 308 MPH, it sounds pretty reasonable for a A6M5's maximum speed at Sea Level.



P-39 Expert said:


> *Who is the client? The AAF? Or the combat pilots? Who wouldn't want a faster climbing airplane? At the expense of four .30caMGs?
> .....
> According to which operators? The Russians certainly didn't agree.*
> .....
> *My only premise is that weight affects climb, all other things being equal. In other words if a plane is made lighter it will climb better, and the improvement in climb can be quantified by the amount of weight removed. Can you argue with that?*



The client is the organization that is paying the bills.
.....
The operators, Boyd Wagner et al. stated that they wanted more armour.

The Russians were great believers in all central armament and very lightly armed fighters. The US were not.
To say that the Russians liked something and used an aircraft effectively so the US Army should do the same is not a good argument because the two nations did not operate their aircraft in the same way.
The Russians were quite satisfied with wearing out aircraft and engines quickly because the lifespan of their aircraft was measured in weeks.
.....
As you have been told MANY times, the real problem is keeping "all things equal". You have been told your "formula" doesn't work, WHY it doesn't work, been given a better formula (which still makes a few assumptions that nothing else is changing), and yet you stick with a formula that doesn't follow aerodynamic principles.

Here is an example of how your argument of weight reduction falls apart. Let's take the P-39F. It is pretty much the same as a P-39D but always had 37 mm cannon. Weight is no different. Flies about like any other early P-39 with a V-1710-35.

Now let's start reducing weight for ONE objective: to make it climb!
First remove the Cannon. There goes 240 pounds.
Next goes the ammunition for 60 pounds more.
Get rid of the Cowl MG for about 160 pounds.
No need for 120 pounds of .50 cal ammunition if the nose guns are not there.
Remove the 96 pound Gear Box armour.

Aircraft is now 676 pounds lighter and should seriously climb!
What do you think will REALLY happen?

- Ivan.


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## Stig1207 (Oct 30, 2020)

GregP said:


> Show me a list of vetted kills. The only ones I know of are the USAAF Report 85 and Naval Aviation Combat Statistics - World War II, and people fight over those.



Even then they are not vetted against enemy losses, just in case someone should misunderstand.

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## buffnut453 (Oct 30, 2020)

GregP said:


> So, I fully support your contention that lightening the P-39 would have been a good thing. I'm just having a hard time trying to decide WHAT to delete that would make a difference while remaining flyable and maintaining combat effectiveness.



And that's the nub of my comments pages ago that the USAAF operational users didn't remove weight from their P-39s, at least not the nose armour or the wing guns, which were the main items P39Expert was proposing to remove. 

If the operational users couldn't identify such "obvious" changes, perhaps the operational benefits didn't outweigh (pun intentional) the risks? 

Clearly, Wagner wanted the wing guns and, as you observe, MORE armour, not less. However, those points simply get ignored in this thread. 

It seems we're expected to trust test reports but ignore operational users (including Wagner himself). I can tell you from experience that such an approach is a recipe for disaster but, since it doesn't fit the narrative that P39Expert is pushing, it gets ignored.

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## XBe02Drvr (Oct 30, 2020)

davparlr said:


> I do wonder if the P-39 was originally designed to the lighter British standards, how would it have performed.


Suppose we take the P39 away from Larry Bell and give it to Reg Mitchell for a quick makeover, a la P51H? Rational weight distribution, a positive G airfoil, British stress standards, and a Merlin engine: the stuff of dreams!

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## XBe02Drvr (Oct 30, 2020)

Ivan1GFP said:


> Keep in mind that the Air Speed Indicator on the A6M series reads in Knots.
> Saburo Sakai's statement about 345 MPH wasn't actually that but the equivalent in Knots.


1 knot = 1.15 MPH. Sakai's 345 MPH comes out to 300 knots. "Surviving Veteran" (probably Harada) gives 308, which, if it is actually knots, (makes sense from the gauge) comes out to 354 MPH, more in keeping with what US combat pilots estimated. Makes a dent in that "40 MPH advantage".

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## Peter Gunn (Oct 30, 2020)

*P-39 Expert* - I don't mean to pick on you but the statement:

"*More likely a novice pilot in an unfamiliar airplane.* "

Does not make sense to me. When flight testing ANY aircraft, they generally don't use novice pilots that don't know their airplane. Those are the kinds of statements you really should shy away from.

In fact, to me, it sounds like a rather highly proficient pilot that knows his airplane and is trying his best to come out on top, possibly even was told to try it by his superiors. Remember, they had to try to figure out the best way to get the better of the enemy plane.


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## Ivan1GFP (Oct 30, 2020)

XBe02Drvr said:


> 1 knot = 1.15 MPH. Sakai's 345 MPH comes out to 300 knots. "Surviving Veteran" (probably Harada) gives 308, which, if it is actually knots, (makes sense from the gauge) comes out to 354 MPH, more in keeping with what US combat pilots estimated. Makes a dent in that "40 MPH advantage".



Hello XBe02Drvr,

Despite the accusations from P-39 Expert, I don't believe the A6M2 was a particularly fast aircraft.
I believe 345 MPH is credible. I don't believe 354 MPH is credible for the A6M2.

For that matter, I don't even believe EVERY A6M2 was capable of that speed.
If you go back to the Japanese Wikipedia page, you will see that Nakajima continued to build the A6M2 long after Mitsubishi had switched to the A6M3.
The Nakajima aircraft had some "improvements". They were often equipped with the longer barreled Type 99-II long barrel 20 mm cannon and 100 round ammunition drums. Some of them even had a sheet of armour plate behind the pilot and a fire extinguishing system IIRC. These were mostly "Baku-Sen" or Bomber Fighters and carried bomb racks as well.
With that combination of changes, I don't believe they were quite as fast as earlier A6M2.

I believe that the reason that US combat pilots were estimated speed a bit higher than the A6M2 might have been capable of is that as shown in the testing of the Aleutian A6M2, it had a very good zoom climb and if it gained a little speed in a dive, it would retain it much longer than one might expect.

Pinning down the actual maximum speed for Japanese aircraft tends to be pretty difficult in general. They never seemed to care enough to test for maximum speeds in a manner comparable to Allied aircraft.

My OPINION based on a lot of reading and trying to fit things together in a way that makes sense is this:
The A6M3 series was only about 5 MPH faster than the A6M2 and probably even less than that.
The problem was that the engine wasn't really that much more powerful as shown by a Military rating that was only 30 HP higher. The advantage was that it was 5000 feet higher.
This was combined with an airframe that probably had a bit more drag even though it looked more sleek. The cowl was a bit bigger and there were often exposed cannon barrels in the wings and bigger bulges for the drums for the cannon.
I believe the TAIC numbers for the A6M5 at 351 MPH to 358 MPH are most probably correct and perhaps a touch generous on the high end.
The cowl is slightly different on the A6M5 but I don't believe that really makes any difference. I believe the biggest difference was a switch to ejector stacks for the engine.
This more or less fits with the "Japanese Veteran" if he was reading the gauge in Knots.

- Ivan.

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## XBe02Drvr (Oct 30, 2020)

Ivan1GFP said:


> I believe that the reason that US combat pilots were estimated speed a bit higher than the A6M2 might have been capable of is that as shown in the testing of the Aleutian A6M2, it had a very good zoom climb and if it gained a little speed in a dive, it would retain it much longer than one might expect.


Good point! Guess it's time to pull out Reardon and re-read him. Thanks, Ivan!


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## P-39 Expert (Oct 30, 2020)

GregP said:


> Hi P-39 Expert, let me try once here.
> 
> I am a volunteer at the Planes of Fame Museum in Chino, CA. We have a P-39 (static) and Fighter Rebuilders is located onsite, owned by Steve Hinton and son. They have built up a P-39 on at least one if not more occasions and I have looked pretty closely at the static P-39. None of what I am saying here is from Fighter Rebuilders or the Museum, it is my observations only. I mention the above only so you know that WWII fighters are very much present there all the time, not just on occasion. They operate WWII fighters VERY regularly, even several times per week ... that is ... pre-COVID anyway.
> 
> ...


Sorry for the confusion. Never advocated removing any guns in the nose. Don't understand where you got that. 

Remove the wing .30calMGs, their ammunition, mounts heaters and chargers like the Russians did. They were ineffective anyway, especially with a 37mm cannon and two .50s.

Remove the nose armor plate and any armor on the oxygen bottles. No other planes armored the nose reduction gear or the oxygen bottles. Move the radio (#12) up over the engine right behind the turnover bulkhead to restore balance. Lots of P-39 photos show a radio in this position. That's all I have ever advocated removing. Save about 300lbs, increase climb about 360fpm.


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## glennasher (Oct 30, 2020)

"
Now let's start reducing weight for ONE objective: to make it climb!
First remove the Cannon. There goes 240 pounds.
Next goes the ammunition for 60 pounds more.
Get rid of the Cowl MG for about 160 pounds.
No need for 120 pounds of .50 cal ammunition if the nose guns are not there.
Remove the 96 pound Gear Box armour.

Aircraft is now 676 pounds lighter and should seriously climb!
What do you think will REALLY happen?

- Ivan. "

Well, since it doesn't have any guns (except in the wings), it pretty much forfeits it's whole reason for existing, which was as an interceptor, right?


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## buffnut453 (Oct 30, 2020)

P-39 Expert said:


> Remove the wing .30calMGs, their ammunition, mounts heaters and chargers like the Russians did. They were ineffective anyway, especially with a 37mm cannon and two .50s..



The wing .30 cals were ineffective? According to who? 

YET AGAIN...Buzz Wagner didn't want them removed. Clearly HE thought they weren't ineffective. But let's not get the operational pilot's combat experience get in the way, right?


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## P-39 Expert (Oct 30, 2020)

Ivan1GFP said:


> You have said absolutely NOTHING with that statement. The process is the important part and what I and everyone else is telling you is that it is not something that can be done when maneuvering as in combat. With the constantly changing conditions of engine load, altitude, speed, how can the pilot decide whether the mixture needs to be leaner or richer? By the time he has observed and decided, the conditions have most likely changed.
> 
> *Don't need to adjust the mixture in combat. Simply push the throttle forward, move the propeller control to 3000rpm, and adjust the mixture control one time. All set for combat. Much easier than on a P-38.*
> 
> ...


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## P-39 Expert (Oct 30, 2020)

Peter Gunn said:


> *P-39 Expert* - I don't mean to pick on you but the statement:
> 
> "*More likely a novice pilot in an unfamiliar airplane.* "
> 
> ...


A highly proficient pilot would not overboost his engine causing detonation in any situation. He was risking engine damage or failure. And he would know that the D-1 did not have an automatic boost control meaning he could not firewall the throttle on takeoff, but must use the manifold pressure gauge to not exceed the maximum takeoff boost.


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## GregP (Oct 30, 2020)

It won't increase the climb by that amount. Covered that already.

I mentioned the nose guns just to address all the guns. The nose guns need to stay there for CG. If you have a later P-39 and the wing guns are 50s, I'd rather have them than another 75 - 150 fpm of climb. No way I'd move a tube radio above a running engine. The tubes make enough heat on their own and moving a spark ignition closer a radio than it HAS to be is not smart!

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## Ivan1GFP (Oct 30, 2020)

P-39 Expert said:


> *Don't need to adjust the mixture in combat. Simply push the throttle forward, move the propeller control to 3000rpm, and adjust the mixture control one time. All set for combat. Much easier than on a P-38.*



You just described setting the mixture control to Auto Rich which is what we have been trying to tell you was the correct approach all this time.
In case you forgot, you were advocating using manual mixture controls to tune for best power in combat.....



P-39 Expert said:


> *It was the only plane we had at the time. Why wouldn't it be representative of other planes of the same model?
> .....
> I'm not going to list all the test reports that I have seen that show the top speed of the A6M2 to be 330mph or less. Most all of them show 330mph or less.*



Because it was not in the same condition as ones in service or operated the same way.
.....
Listing just ONE test report for PROOF would be good. Without the proof, this is just Hearsay and not deemed to be not even as reliable as a "Hangar Story".



P-39 Expert said:


> *He spoke English. I remember thinking that was a lot lower than I had seen quoted.
> Clearly he said 308mph.*



Did he give the conditions?
Context is important.



P-39 Expert said:


> *He asked for that piece or armor plate behind the oil tank, which was added to the P-39.*



For Boyd Wagner to ask for a piece of armour to be installed in the P-39 when it ALREADY came as STANDARD would have been interesting. You do know that the Oil Tank armour came as standard on every production Airacobra after the P-39C, right?



P-39 Expert said:


> *The Russians had engines that would accomodate a nose cannon firing through the propeller. The US did not. If you believe wing armament to be superior to nose armament, then why didn't later jets have guns out on the wings?*



The Russian philosophy was simply different, and no, many of their engines did not allow a gun firing through the propeller.
Radial engines have a bunch of things in the middle which get in the way of a gun.
Jets are a whole different story. You can start a different discussion if you want to go there.



P-39 Expert said:


> *There is absolutely nothing aerodynamic about reducing the weight of a particular model airplane to improve climb and ceiling. The aerodynamics were the same. Only difference was the weight. When 836lbs extra internal weight was added to the P-39D the climb rate went down by 1000fpm. There is no argument to that statement. *



You have yet to prove the aerodynamics are EXACTLY the same. Many knowledgeable people have been trying to convince you of that.



P-39 Expert said:


> A highly proficient pilot would not overboost his engine causing detonation in any situation. He was risking engine damage or failure. And he would know that the D-1 did not have an automatic boost control meaning he could not firewall the throttle on takeoff, but must use the manifold pressure gauge to not exceed the maximum takeoff boost.



Many highly proficient pilots did indeed over boost their engines staying below the limits for detonation. This was documented with the P-40 models using the V-1710-39 which was similar to the -35 engine in the P-39D-1 and when using V-1710-73 engines similar to the P-39's -63 engines.
Have you ever seen the Allison memo on the subject?

- Ivan.


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## XBe02Drvr (Oct 30, 2020)

P-39 Expert said:


> Move the radio (#12) up over the engine right behind the turnover bulkhead to restore balance.


Do you know why the radio is way back in the tailcone? It's to get it as far as possible away from the vibration, heat, and ignition interference from the engine. You're proposing to put it "right in the lion's den". Same reason they didn't put it in the only other logical place, up in the nose by the guns. I've never been up close and personal with an Oldsmobile 37MM cannon, but I have with 20MM and .50 cal, and I can tell you it's an earth shaking experience. Have you ever disassembled an old fashioned vacuum tube radio? Even "ruggedized" for airborne use their tolerance for vibration and heat is pretty limited. One of the failures of the Zero was the inability of its voice radio to cope with the (supposedly shielded) electronic noise from the engine.



P-39 Expert said:


> A highly proficient pilot would not overboost his engine causing detonation in any situation. He was risking engine damage or failure.


Did it ever occur to you that that boost limit could be an arbitrary number with considerable safety margin built in, set by conservative engineers wary of the exuberance of testosterone driven young pilots? And that the pilot selected for the test might be proficient enough and knowledgeable enough to realize he could shave those margins a bit without too much risk, considering he may have been under pressure not to let the Zero show him up too badly? Your faith in the incorruptibility of pilots is touching.

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## P-39 Expert (Oct 30, 2020)

buffnut453 said:


> The wing .30 cals were ineffective? According to who?
> 
> YET AGAIN...Buzz Wagner didn't want them removed. Clearly HE thought they weren't ineffective. But let's not get the operational pilot's combat experience get in the way, right?


Wagner actually said that the pilots preferred the .50s to the less effective .30s. And he said that the .30s were less reliable than the .50s. He may not have advocated their removal, but he clearly said they were less effective and less reliable. Remember he said all this about two weeks after their first combat.


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## P-39 Expert (Oct 30, 2020)

GregP said:


> It won't increase the climb by that amount. Covered that already.
> 
> I mentioned the nose guns just to address all the guns. The nose guns need to stay there for CG. If you have a later P-39 and the wing guns are 50s, I'd rather have them than another 75 - 150 fpm of climb. No way I'd move a tube radio above a running engine. The tubes make enough heat on their own and moving a spark ignition closer a radio than it HAS to be is not smart!


Lots of photos of radios in that exact spot. Just because you don't agree with the climb numbers doesn't mean they are wrong.

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## buffnut453 (Oct 30, 2020)

P-39 Expert said:


> Wagner actually said that the pilots preferred the .50s to the less effective .30s. And he said that the .30s were less reliable than the .50s. He may not have advocated their removal, but he clearly said they were less effective and less reliable. Remember he said all this about two weeks after their first combat.



And "less effective" is not the same as "ineffective". You're inserting your own interpretation and passing it off as fact. 

YET AGAIN you keep banging on about Wagner's report being after 2 weeks of combat. However, the P-39s remained in combat for MONTHS. Did they remove the "useless" 30 cals at any time? NO. Other than "I don't know", you don't have an answer for why that might be. 

I'd really appreciate it if you'd stop hitting the reset button and acknowledge that the operational crews maybe...just maybe...had a clue about what they were doing and kept the 30 cals because, despite being "less effective" they were still deemed mission critical for the sorties flown over PNG and Guadalcanal.

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## P-39 Expert (Oct 30, 2020)

Ivan1GFP said:


> You just described setting the mixture control to Auto Rich which is what we have been trying to tell you was the correct approach all this time.
> In case you forgot, you were advocating using manual mixture controls to tune for best power in combat.....
> 
> *The mixture control could be varied between the pre determined settings. How else did the pilot get a "best power" setting?*
> ...


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## P-39 Expert (Oct 30, 2020)

buffnut453 said:


> And "less effective" is not the same as "ineffective". You're inserting your own interpretation and passing it off as fact.
> 
> YET AGAIN you keep banging on about Wagner's report being after 2 weeks of combat. However, the P-39s remained in combat for MONTHS. Did they remove the "useless" 30 cals at any time? NO. Other than "I don't know", you don't have an answer for why that might be.
> 
> I'd really appreciate it if you'd stop hitting the reset button and acknowledge that the operational crews maybe...just maybe...had a clue about what they were doing and kept the 30 cals because, despite being "less effective" they were still deemed mission critical for the sorties flown over PNG and Guadalcanal.


I was using Wagner's exact words, not my interpretation. The .30s were clearly less effective and less reliable. I guess the Russians were crazy to get rid of them and increase the performance of their planes.


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## P-39 Expert (Oct 30, 2020)

XBe02Drvr said:


> Do you know why the radio is way back in the tailcone? It's to get it as far as possible away from the vibration, heat, and ignition interference from the engine. You're proposing to put it "right in the lion's den". Same reason they didn't put it in the only other logical place, up in the nose by the guns. I've never been up close and personal with an Oldsmobile 37MM cannon, but I have with 20MM and .50 cal, and I can tell you it's an earth shaking experience. Have you ever disassembled an old fashioned vacuum tube radio? Even "ruggedized" for airborne use their tolerance for vibration and heat is pretty limited. One of the failures of the Zero was the inability of its voice radio to cope with the (supposedly shielded) electronic noise from the engine.
> *Look in any P-39 pilots manual and radios are clearly shown exactly where I advocate locating them. *
> 
> Did it ever occur to you that that boost limit could be an arbitrary number with considerable safety margin built in, set by conservative engineers wary of the exuberance of testosterone driven young pilots? And that the pilot selected for the test might be proficient enough and knowledgeable enough to realize he could shave those margins a bit without too much risk, considering he may have been under pressure not to let the Zero show him up too badly? Your faith in the incorruptibility of pilots is touching. *The pilot in the test caused his engine to detonate by using excessive manifold pressure way beyond any safety margin.*


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## buffnut453 (Oct 30, 2020)

P-39 Expert said:


> I was using Wagner's exact words, not my interpretation. The .30s were clearly less effective and less reliable. I guess the Russians were crazy to get rid of them and increase the performance of their planes.



You have repeatedly said in prior posts that the 30 cals were "ineffective". That's YOUR word, not Wagner's.

Why is it so hard for you to accept that Russia wasn't PNG or Guadalcanal, and that the U.S. pilots flying in the Pacific clearly wanted the 30 cals?


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## P-39 Expert (Oct 30, 2020)

buffnut453 said:


> You have repeatedly said in prior posts that the 30 cals were "ineffective". That's YOUR word, not Wagner's.
> 
> Why is it so hard for you to accept that Russia wasn't PNG or Guadalcanal, and that the U.S. pilots flying in the Pacific clearly wanted the 30 cals?


show me a quote where any AAf pilot wanted the .30s.


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## Ivan1GFP (Oct 30, 2020)

P-39 Expert said:


> *The mixture control could be varied between the pre determined settings. How else did the pilot get a "best power" setting?*



So HOW did the pilot determine which way to adjust the mixture?



P-39 Expert said:


> *Do your own research, it's all in wwiiaircraftperformance.*



Actually there are aren't any test reports of a A6M2 in good operational condition that were operated correctly on *wwiiaircraftperformance.*
I am no expert, but I am certain that I have done considerably more research on Japanese aircraft than you have.



P-39 Expert said:


> *Same airframe. Wouldn't two P-39Ds have the same aerodynamics? Only difference between the C and D were internal.*



Same airframe, different propeller part number. Different arrangement of equipment and balance may cause some very different aerodynamic consequences. This has been explained to you.



P-39 Expert said:


> *The pilot in the test caused his engine to detonate, was he highly proficient?*



This pilot probably was fairly certain he could over boost that particular engine. Problem is that he guessed wrong about the actual limit before detonation. Even highly proficient pilots make mistakes and guess wrong. Being proficient and being perfect are different things.

- Ivan.


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## buffnut453 (Oct 30, 2020)

P-39 Expert said:


> show me a quote where any AAf pilot wanted the .30s.



Two can play at that game. Show me a quote where any AAF pilot said they wanted the 30 cals taken out? Better yet, show me any instance where any AAF P-39 had the 30 cals removed for performance reasons. 

C'mon...I want to see the evidence to contradict my points. Are you at least willing to accept that the USAAF P-39s flew with the 30 cals and that, given the simplicity of removing them, that does at least indicate that the pilots thought it was better to have the 30 cals than not to have them?


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## pbehn (Oct 30, 2020)

buffnut453 said:


> Two can play at that game. Show me a quote where any AAF pilot said they wanted the 30 cals taken out? Better yet, show me any instance where any AAF P-39 had the 30 cals removed for performance reasons.
> 
> C'mon...I want to see the evidence to contradict my points. Are you at least willing to accept that the USAAF P-39s flew with the 30 cals and that, given the simplicity of removing them, that does at least indicate that the pilots thought it was better to have the 30 cals than not to have them?


What was an ineffective gun against a Japanese aircraft? In aviation history planes were continually loaded with more stuff, fuel guns ammunition armour radios mirrors radars, the cases of "stuff" being taken out are rare and for special reason, generally pilots wanted guns and armour.


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## wuzak (Oct 30, 2020)

P-39 Expert said:


> Lots of photos of radios in that exact spot.



In aircraft that kept the nose armour?


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## P-39 Expert (Oct 30, 2020)

Ivan1GFP said:


> So HOW did the pilot determine which way to adjust the mixture?
> 
> *Either way by feel and sound. We're talking about 3mph. *
> 
> ...


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## GregP (Oct 30, 2020)

By feel? Here's from an Allison user's manual:







Of course, the Allison was behind the pilot, so he may have had some difficulty with this procedure. Alternately, if you have climbed, you are likely lean. If you have descended you are likely rich. Both assume you haven't touched the mixture before changing altitude. Generally speaking, you either lean or rich to get peak exhaust gas temperature and then adjust from there. In WWII, they always ran rich of peak temperature, maybe 100° rich of peak. Today, we generally run lean of peak.

But is isn't a quick thing. Usually, setting the mixture correctly in a Cessna takes maybe 1-1.5 minutes. 1 minute of straight and level inattention in a combat zone may mean you are dead. The rule of thumb is never fly straight and level in a combat zone for more than 30 seconds.

That's why the "Auto Rich" setting was so handy in combat. You could set it there and forget it until combat was over or you had rejoined and were on the way home. "auto lean" ws a great way to cruise home, but not a good for combat when power changes were required.

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## ThomasP (Oct 30, 2020)

I do not know if this helps with the radio(s) being moved, but although I have run across pictures with multiple electronics boxes on the panel above the engine, in most (all?) of the pictures of P-39Q & N when only a single box is present, the box appears to be the IFF set.

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## FLYBOYJ (Oct 30, 2020)

P-39 Expert said:


> So HOW did the pilot determine which way to adjust the mixture?
> 
> *Either way by feel and sound*


So this will be done when?


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## P-39 Expert (Oct 30, 2020)

FLYBOYJ said:


> So this will be done when?


The performance test said the P-39D developed 368mph at a mixture setting of "Best Power" and 365mph at a mixture setting of "Auto Rich". We are talking about 3mph with a slightly different mixture setting, right? When do you think it was done? At this point I would really like to know. For 3mph.


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## P-39 Expert (Oct 30, 2020)

pbehn said:


> What was an ineffective gun against a Japanese aircraft? In aviation history planes were continually loaded with more stuff, fuel guns ammunition armour radios mirrors radars, the cases of "stuff" being taken out are rare and for special reason, generally pilots wanted guns and armour.


Yes they did, but they also wanted to be able to climb above their adversaries. If deleting the .30s meant being able to get above your opponent then I think the vast majority of pilots would prefer being above their opponent. What good are .30s when your opponent has the advantage? And you still have plenty of firepower without them.


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## FLYBOYJ (Oct 30, 2020)

P-39 Expert said:


> When do you think it was done?



Well if you're manually adjusting for the best air/ fuel mixture AKA *stoichiometric mixture*, you're either doing it on the ground or you can try in the air in level flight at either cruise or high rpm settings.


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## glennasher (Oct 30, 2020)

It's not about "3 mph". It's about getting the best out of the engine without blowing it up.

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## Ivan1GFP (Oct 30, 2020)

P-39 Expert said:


> *Either way by feel and sound. We're talking about 3mph. *



First of all, you are looking at the wrong detail. The important thing is NOT the 3 MPH difference in maximum speed because in a maneuvering fight with changing altitudes you will never see the difference in maximum speed.
The objective here is the extra 25 HP that gives that extra 3 MPH maximum speed.
The fuel mixture requirements of the engine will be constantly changing as the power (torque) demands and altitude are changing. In combat, the pilot has many other things demanding constant attention. Assessing the instantaneous fuel needs of the engine is not a smart distraction in that situation.



P-39 Expert said:


> *wwiiaircraftperformance. Not a single one? All were wrong? What about the one that showed the 335mph top speed?*
> 
> *Okay, show me all the reports that said the A6N2 was faster then 330mph.*



If you are asking an honest question, I will give you an explanation because you obviously think there is more there than there actually is.
Only the first five entries for the Zero are for the A6M2.
There are five entries, but only two aircraft were tested.
One was a A6M2 that fell into the hands of the AVG in China. It was tested against a P-40K and a P-43.
Its Propeller was never in spec and it could not make more than about 2075 RPM, thus its performance is hardly indicative of a properly functioning A6M2.

The second aircraft tested was the crashed and rebuilt Aleutian A6M2 and I won't rehash what was wrong with that testing which I have covered before. Its testing and summaries for different audiences covers about 4 of the 5 reports.

As I have stated before, the only service that had good operational A6M2 and knew how to operate them properly (the only service that had the opportunity) never chose to test for maximum speed in a manner comparable to the Allies.



P-39 Expert said:


> *It certainly hasn't been explained to me adequately.
> 
> Same airplane. Same everything except internal weight. Both planes were in balance. None of these factors would account for a 1000fpm difference in climb rate except the 836lbs of weight. Weight affects climb. *



We have been here before. We got here several times over the last couple days.



P-39 Expert said:


> N*ow you know what that pilot was thinking? I don't think so. He overboosted the engine past the point of detonation. In a test. Not a contest. The whole point of the test was to see how both planes performed when operated properly. If he had known how to properly operate the plane he wouldn't have risked engine damage or failure.*



The testing of the Aleutian A6M2 was meant to show the superiority of American fighters as much as possible.
I have already explained the evidence (I believe to the satisfaction of others here). Maybe it should not have been a contest, but the participating pilots were most likely informed of the intended results. I have seen government "tests" in other areas that were conducted that way.

- Ivan.

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## DerAdlerIstGelandet (Oct 30, 2020)

P-39 Expert said:


> The performance test said the P-39D developed 368mph at a mixture setting of "Best Power" and 365mph at a mixture setting of "Auto Rich". We are talking about 3mph with a slightly different mixture setting, right? When do you think it was done? At this point I would really like to know. For 3mph.



Lets start with do you know why you adjust mixture?

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## XBe02Drvr (Oct 30, 2020)

Does anybody remember the 1970s movie: _Sometimes a Great Notion_? This thread reminds me of the Henry Fonda character: "DONCHA GIVE A GODDAM INCH...EVER!"

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## GregP (Oct 30, 2020)

Hey guys, there is something screwy about the two tests in wwiaircraftperformance for the P-39C and P-39D.

If we go to the P-39D at 7,525 pounds test and use the rate of climb formula from Aerodynamics for Naval Aviators, we get the power required for level flight at 5,000 feet to be 529.76 hp, no problem. But, if we go to 20,000 feet and solve for it, we get 413.56 hp! No way! Something is fishy here, and I think it is because they got the engine power from a tech order instead of using a torque meter reading in the airplane. Could be wrong here, but I don't think they were getting the full power at lower altitudes.

If I look at the P-39C at 6,689 pounds, the power required for level flight at 5,000 feet is 395.97 hp and at 20,000 feet is 401.36 hp - which sounds much closer to normal. I'd expect more power to be required at 20,000 feet, not less!

I think the P-39D test had a sour engine or something that they never documented or seem to have noticed. Perhaps it never got to full rated MAP.

Maybe Bill Marshall should look at the tests, especially the P-39D climb tests. Something just looks wrong to me and I can't put a solid finger on it.

Just saying ... cheers! Sorry to drop a bomb at THIS point!

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## jmcalli2 (Oct 31, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> The most effective Japanese Naval Fighter Unit that was fighting from Lae was the Tainain Air Group.
> The unit was formed in October 1941, so it was hardly a veteran unit.
> ...


Hi, Ivan;
ANY combat experience was more than the P-39 pilots had. And that goes for logistics too.
My impression, and I could be wrong, was that New Guinea was not at the top of the "supply first" list.
AVG had their problems with logistics and maintenance too, but they and the Australians had better early warning of incoming attacks than New Guinea did.
Again, that's my impression. Could be wrong.

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## Ivan1GFP (Oct 31, 2020)

Hello GregP,

There seems to be a bit of weirdness in the engine output versus altitude for the P-39N as well.
I didn't find anything quite as radical as you did but it does strike me as a bit curious.
Note that the T.O. specifies engine critical altitude for WEP as 10,900 feet.
Maximum speed however is achieved at 9,700 feet and is noted as being 1.5 MPH SLOWER at 10,900 feet.
One would normally expect some ram effect.

I was thinking that perhaps the propeller tips might be going supersonic but that is pretty unlikely.
I can't tell the propeller diameter from the blade part number given but the largest diameter propeller installed in the N was 11 feet 7 inches which would give a tip speed of 639.5 feet / second.

- Ivan.


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## jmcalli2 (Oct 31, 2020)

FLYBOYJ said:


> I've heard similar, somewhere I think it was calculated a 1 to 1.45 kill/ loss ratio, Zero to P-39
> 
> 
> 
> ...


Definitely agree on the improvement when the P-38s got there, but one caveat to that: were the pilots now veterans? They certainly benefited from having a 5,000 ft + altitude advantage instead of a 5,00 ft disadvantage. That's the turbos. 
In reading "Twelve to One V Fighter Command Aces of the Pacific" by Tony Holmes, I noticed that the aces all said to keep above the enemy, keep your speed up and get close before firing. I didn't get the impression from the P-39 guys that they'd figured that out.
There's no argument that the P-38 was a better fighter than the P-39.


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## Ivan1GFP (Oct 31, 2020)

jmcalli2 said:


> Hi, Ivan;
> ANY combat experience was more than the P-39 pilots had. And that goes for logistics too.
> My impression, and I could be wrong, was that New Guinea was not at the top of the "supply first" list.
> AVG had their problems with logistics and maintenance too, but they and the Australians had better early warning of incoming attacks than New Guinea did.
> Again, that's my impression. Could be wrong.



Hello jmcalli2,

I figure that if it was experience working with the Allison engine, the air service from the country manufacturing the engine would have the most experience especially since they had operated it in the P-40 for over a year.
In any case one would expect Army mechanics to have more experience with a piece of Army equipment than the assortment of mechanics that were rounded up from various places for the AVG.
I believe AVG logistics and support was wherever they could get it and usually they did not. If they did, it was coming through the port of Rangoon, Burma or from India. Technically they were not a part of any major air service. They were just a bunch of mercenaries fighting for China.

Saburo Sakai's books make pretty good reading if you are curious as to the issues faced by the other side and that was from the unit with the greatest success. Other naval units were doing rather poorly in general. The Japanese pilots were not going to places like Australia every so often. They only way they were leaving was if they were injured too badly to fight or if they died.

- Ivan.

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## Stig1207 (Oct 31, 2020)

jmcalli2 said:


> Hi, Ivan;
> ANY combat experience was more than the P-39 pilots had. And that goes for logistics too.
> My impression, and I could be wrong, was that New Guinea was not at the top of the "supply first" list.
> AVG had their problems with logistics and maintenance too, but they and the Australians had better early warning of incoming attacks than New Guinea did.
> Again, that's my impression. Could be wrong.



The P-39 units had better early warning (Coast Watchers) of incoming attacks than their opponents, who had no early warning at all.


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## XBe02Drvr (Oct 31, 2020)

Stig1207 said:


> The P-39 units had better early warning (Coast Watchers) of incoming attacks than their opponents, who had no early warning at all.


If you habitually abuse the natives, they're more likely to eat your coast watchers than help them.
"Oomm gahwa, yellow long pig tonight!"

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## GregP (Oct 31, 2020)

Hi Ivan1GFP,

If I have it right, the prop diameter is 124.5 inches or 10.375 feet. Suppose we are at 13,800 feet and the forward speed is 368 mph.

The Allison V-1710-35 had a prop reduction gear ratio of 1.8 : 1. All that being the case, the radius is 5.1875 feet, prop rpm is 1,666.667 rpm, so rotational speed is 174.5329 radians per second, and tangential speed is 905.39 feet / sec or 617.34 mph. Forward speed is 368 mph or 539.71 ft/sec. Helical tip speed would be the square root of tangential speed squared (905.39^2) plus forward speed squared (539.71^2), or 1054.05 ft/sec, which is 718.7 mph. At 13,800 feet, the standard speed of sound is 722.953 mph.

So, I calculate the helical tip speed at 718.7 mph and the Speed of Sound is 722.953 mph. Mach Number is 0.99412.

An efficient prop will have a propeller efficiency of 0.85 to 0.90 at best, and we definitely have an issue with prop tip speed since we don't really want the prop tip going any faster than M.84 to M.88 or so before the prop efficiency starts to drop off. I'd say the airplane is going slower than it should because the prop tip speed is too fast. In fact, the tip speed will be over M.88 at any airspeed above 154 mph! To lower the tip speed to M.88, we'd need to reduce the rpm to 2,525 at 368 mph forward speed at 13,800 feet on a standard day.

Most later Allisons had a propeller reduction gear ration of 2 : 1, instead of 1.8 : 1. If we had been running an Allison with a 2 : 1 ratio, the Mach number would be M.92 at the conditions above and we'd still have to reduce rpm to 2,803 to get M.88.

These things figure rather prominently at Reno and in world airspeed record attempts. This stuff is well known now, but wasn't exactly precisely known before WWII. Maybe the XP-39 would have gone faster than it did if the prop tip Mach number wasn't above what is now accepted as best efficiency velocity.

If I missed anything, let me know.

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## FLYBOYJ (Oct 31, 2020)

jmcalli2 said:


> Definitely agree on the improvement when the P-38s got there, but one caveat to that: *were the pilots now veterans?* They certainly benefited from having a 5,000 ft + altitude advantage instead of a 5,00 ft disadvantage. That's the turbos.
> In reading "Twelve to One V Fighter Command Aces of the Pacific" by Tony Holmes, I noticed that the aces all said to keep above the enemy, keep your speed up and get close before firing. I didn't get the impression from the P-39 guys that they'd figured that out.
> There's no argument that the P-38 was a better fighter than the P-39.



Some were, some weren't. There were leaders there like Tom Lynch who tutored new arrivals, Ken Sparks, Tom McGuire and of course Dick Bong who first flew with the 39th FS. On one of his first missions he shot down 2 aircraft, late Dec., 1942.


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## P-39 Expert (Oct 31, 2020)

Ivan1GFP said:


> First of all, you are looking at the wrong detail. The important thing is NOT the 3 MPH difference in maximum speed because in a maneuvering fight with changing altitudes you will never see the difference in maximum speed.
> The objective here is the extra 25 HP that gives that extra 3 MPH maximum speed.
> The fuel mixture requirements of the engine will be constantly changing as the power (torque) demands and altitude are changing. In combat, the pilot has many other things demanding constant attention. Assessing the instantaneous fuel needs of the engine is not a smart distraction in that situation. *I never said the pilot would be adjusting the mixture control after initially going to full power. *
> 
> ...


Expand above.


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## Ivan1GFP (Oct 31, 2020)

GregP said:


> Hi Ivan1GFP,
> 
> If I have it right, the prop diameter is 124.5 inches or 10.375 feet. Suppose we are at 13,800 feet and the forward speed is 368 mph.
> 
> ...



Hello GregP,

Some of MY calculations in the spreadsheet last night were simply wrong. I left out a little number called Pi.....
Some of the details you have for the P-39 are not for the correct version.

The P-39N has a propeller diameter of either 11 feet 4 inch or 11 feet 7 inch
Propeller reduction is 2.23:1 as stated in the test report.
Altitude is around 10,000 feet.
Forward speed is 398.5 MPH @ 9,700 feet.

What I am getting WITH Pi... (embarrassing mistake) is 1003.65 fps and Mach 1 at 10,000 feet from a table is 1077.43 fps.
Mach = 0.93. Much closer.....

- Ivan.


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## Ivan1GFP (Oct 31, 2020)

P-39 Expert said:


> *never said the pilot would be adjusting the mixture control after initially going to full power. *



So your idea is that the pilot goes to full throttle, sets maximum RPM, and then spends a couple minutes twiddling with the mixture to get something that SOUNDS like full power.......
THEN doesn't change altitude, engine loads or any other conditions IN COMBAT which would completely invalidate those results?
You have an interesting view of what happens in combat flying.



P-39 Expert said:


> *So how do we determine the top speed of the A6M2? British trials of the Mk. II Hap with the more powerful -21 engine operating at 2600rpm showed only 328mph. *



You determine the maximum speed of the A6M2 any way you want. I have presented the information to you. You choose not to read it. I can't do any more. You can go back and re-read what has already been presented. Some of the posts were not directed to you.

The British trials of Mk.II HAP are a garbage test as well. Those folks got even less right when they ran the test.
The Mk.II "Hap" is an entirely different aeroplane with a different engine, different engine, different wing span, wing area, etc.
Test has no real relationship to performance of A6M2.

If someone wants to discuss what was wrong with the testing of the A6M3 Model 32 "Hap", we can go there but it isn't relevant to A6M2.



P-39 Expert said:


> *And we'll stay here until you acknowledge that the C and D were the same plane except the D had more weight from different internal components. Nothing about those two planes could account for a 1000fpm (37%) different climb rate except the 836lbs of weight. Reduce the weight and increase the climb. Simple math.*



First of all, if you are really serious, you should observe that the propeller blades are NOT the same part number between the two aircraft. Also note that the testers did not believe the engines were quite the same. Note that the source for the engine output information was from DIFFERENT DOCUMENTS.
Please read the recent posts from GregP and try to understand their significance.
As I see it, the engine output or SOMETHING does not seem to be quite right in the P-39D testing.
Since there wasn't an actual torque meter installed to show actual power output (which will never be EXACTLY the same between any two engines or even the SAME engine at different times or conditions) so we don't know what power output each aircraft was actually making.

As everyone has been trying to tell you, there are way too many variables to assume everything is the same between two aircraft.
This is just comments about engine power. The way the aircraft were loaded and the consequences of differences in CoG and balance have already been explained.

If you are going to base an argument on comparing a couple test reports, you should probably read the entire reports and UNDERSTAND them instead of just picking out a couple numbers.



P-39 Expert said:


> *Your opinion. More likely just a means of evaluating the performance of the A6M2 vs US planes.*



Can you explain why the acceleration tests were started at different speeds when flying against each US fighter?
What are the significance of those speeds? I have already given an explanation.

- Ivan.


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## Ivan1GFP (Oct 31, 2020)

Hello GregP,

Since we are already on this track, and I already know you are pretty good with spreadsheets,
you might get some amusement with calculating the same values for the Lockheed P-3 Orion.
I had do this for a Flight Simulator discussion with some friends a few months ago and the result was quite revealing.

- Ivan.


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## P-39 Expert (Oct 31, 2020)

Ivan1GFP said:


> So your idea is that the pilot goes to full throttle, sets maximum RPM, and then spends a couple minutes twiddling with the mixture to get something that SOUNDS like full power....... *More like a second or two. One time. Let's move on from this, we're talking about 3mph.*
> THEN doesn't change altitude, engine loads or any other conditions IN COMBAT which would completely invalidate those results?
> You have an interesting view of what happens in combat flying.
> 
> ...


Please expand above.


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## Peter Gunn (Oct 31, 2020)

*Hello P-39 Expert,*

*"Let's move on from this, we're talking about 3mph."*
No we are NOT, re read what Ivan said, we're talking about the extra 25 _horsepower_ it takes to get that 3 miles per hour.

*"Now the British don't know how to run a test?"*
Convenient comeback but that's NOT what he's alluding to.

*"Let's move on from this, the A6M2 was slower than the P-39."*
Boyd Wagner clearly didn't think so.

*"By the way, the C model didn't have the nose armor, how did it keep from falling out of the sky?"*
Pixie Dust.

*"Splitting hairs again. I'd like to move on from this and concentrate on weight and climb."*
Not possible unless you start to understand what Ivan et. al. have been saying.


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## P-39 Expert (Oct 31, 2020)

Peter Gunn said:


> *Hello P-39 Expert,*
> 
> *"Let's move on from this, we're talking about 3mph."*
> No we are NOT, re read what Ivan said, we're talking about the extra 25 _horsepower_ it takes to get that 3 miles per hour.
> ...


Could it possibly be that you and Ivan need to start understanding what I am saying? Both of you have a very condescending attitude, getting old.


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## XBe02Drvr (Oct 31, 2020)

P39 Expert said:
*More like a second or two. One time. Let's move on from this, we're talking about 3mph.*
3 MPH is insignificant in combat. The 25 HP it represents at top speed IS, because of its effect on maneuvering performance: acceleration in a dive, energy retention in a zoom, airspeed retention in a high G turn. The problem is: 1) tweaking to get that extra 25 HP as you go into combat is likely to get you shot down, as it's a major distraction, and 2) you've just shaved your detonation margin to the hairy edge, and combat maneuvering IS GOING to push you over. Your throttle setting is not the only factor affecting stress on your engine. Full throttle at enforced lower airspeed (sustained high G turns, high angle climbs, etc) will quickly raise engine temps into the detonation range. That's what AUTO RICH is there for.
*Now the British don't know how to run a test?*
As previously pointed out, nobody on the allied side had a correctly set up and correctly operated, fully performing Zero until much later when it was no longer relevant.


P-39 Expert said:


> Could it possibly be that you and Ivan need to start understanding what I am saying? Both of you have a very condescending attitude, getting old.


We all thoroughly understand what you're saying. How could we help it? Sounds like a broken record, skipping at the same drum riff, repeating over and over, and immune to rest of the symphony. The recording is Walt Disney's _Fantasia._

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## XBe02Drvr (Oct 31, 2020)

This thread sounds like a reflection of the current national hysteria level. I'm taking a vacation until after Tuesday is over with.
See you on the other side.
Wes

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## P-39 Expert (Oct 31, 2020)

XBe02Drvr said:


> P39 Expert said:
> *More like a second or two. One time. Let's move on from this, we're talking about 3mph.*
> 3 MPH is insignificant in combat. The 25 HP it represents at top speed IS, because of its effect on maneuvering performance: acceleration in a dive, energy retention in a zoom, airspeed retention in a high G turn. The problem is: 1) tweaking to get that extra 25 HP as you go into combat is likely to get you shot down, as it's a major distraction, and 2) you've just shaved your detonation margin to the hairy edge, and combat maneuvering IS GOING to push you over. Your throttle setting is not the only factor affecting stress on your engine. Full throttle at enforced lower airspeed (sustained high G turns, high angle climbs, etc) will quickly raise engine temps into the detonation range. That's what AUTO RICH is there for.
> *Now the British don't know how to run a test?*
> ...


And I thoroughly understand what you are saying. Thoroughly. That doesn't mean that I agree.

If Ivan is correct, then lets just put that propeller from the C back onto the D, adjust the CG (if needed) and recover that lost 1000fpm of climb. 

Why can't you just admit that the extra weight is the reason the C climbed better than the D, instead of acting like 836lbs of weight had no effect?


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## buffnut453 (Oct 31, 2020)

P-39 Expert said:


> Why can't you just admit that the extra weight is the reason the C climbed better than the D, instead of acting like 836lbs of weight had no effect?



For the simple reason that nothing, and I mean NOTHING, in an aircraft's performance is a straightforward binary association. Certainly lower weight will contribute to improved climb performance but lots of other factors come into play, as others on the thread have repeatedly tried to point out. Unfortunately, that doesn't seem to align with your viewpoint so you discount or ignore their comments.

Speaking of ignoring comments, have you found any USAAF pilots who said they wanted the 30 cals removed from the wings of their P-39s yet?


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## Juha3 (Oct 31, 2020)

Stig1207 said:


> That is what Claringbold writes, but not clearly; it can be misconstrued that these are the total combat losses for both sides during the campaign/ time period. That is not the case, for both sides lost P-39's and Zero's to enemy action on missions where they didn't meet in combat.
> 
> 
> 
> That is the total losses in the combats in which P-39's met Zero's in combat. So 44 P-39's lost to all causes against 15 Zero's lost to all causes (all causes in this case being P-39's).



I had difficulties to understand what Claringbould means. Some of my thoughts.
_But on page 76 he writes that of the 44 Aircobras lost in combat in 1942 in New Guinea only 15 were shot down by Zeros. Who shot down the rest, ground fire got some but the first JAAF fighters unit, the 1st Chutai of the 11th Sentai, became active in New Guinea on 26 December 1942 and it did not claim Airacobras during the last few days of 1942. Japanese air gunners seems to have got a few but what about the rest. Did the combat losses include those destroyed on ground by bombing and strafing? But Claringbould notices earlier that the results of Japanese strafing attacks against Port Moresby airfields were minimal. Some Airacobras were destroyed by bombing, that is true but still the figures seem not to add up. And it seems that the 15 Zero losses does not include losses on ground because already the first Airacobra strafing attack on Lae on 30 April 1942 destroyed three Zeros according to Claringbould and according to Tagaya burned one and wrecked another Zero. Lae and other Japanese airfields in the area were also bombed rather regularly.
I could have read the book one more time and count the P-39/P-400 losses, but did not bother. Instead I went through the P-39/P-400 losses in New Guinea in 1942 on the *Pacific Wrecks *site. When it in few cases does not give a clear reason, I checked what Claringbould says. All Airacobra losses are not mentioned on the site. Results were: 
*P-39s/P-400s reason of loss:*_
*Zeros 20
Possibly Zeros 5
Forced landing because of Zero, plane not recovered, *_so lost _*1
Ground fire 3
Friendly fire 1 possible
Engine 4
Probably engine 1
Weather 4*

*Claringboult says that operational losses were 14 Airacobras and 13 Zero-sens*

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## DerAdlerIstGelandet (Oct 31, 2020)

P-39 Expert said:


> Could it possibly be that you and Ivan need to start understanding what I am saying? Both of you have a very condescending attitude, getting old.



Whats getting old is your lack of comprehension.

Answer the question. Do you know why you adjust mixture? 

Here is a hint, it has nothing to do with 3 mph. So quit harping on it.


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## P-39 Expert (Oct 31, 2020)

buffnut453 said:


> For the simple reason that nothing, and I mean NOTHING, in an aircraft's performance is a straightforward binary association. Certainly lower weight will contribute to improved climb performance but lots of other factors come into play, as others on the thread have repeatedly tried to point out. Unfortunately, that doesn't seem to align with your viewpoint so you discount or ignore their comments.
> 
> Speaking of ignoring comments, have you found any USAAF pilots who said they wanted the 30 cals removed from the wings of their P-39s yet?


Not discounting or ignoring their comments. I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that. A slightly different propeller or a slightly altered CG or slightly varying HP are just small discrepancies that would be present in any test of the exact same airplane. Especially when there is no proof whatsoever that the CG was not proper in either airplane, or that the HP varied at all. In regards to the propeller, what was the exact difference in the two propellers? Any at all? They were of the same diameter.

There is a straightforward binary association between two airplanes of the same type and model, when the only difference is a substantial amount of weight. And again, please explain to me the difference between the two propellers.

None of that other crap mattered to the climb rate except the nearly half ton of weight. Somebody just say okay I agree with you and I will go away.


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## DerAdlerIstGelandet (Oct 31, 2020)

P-39 Expert said:


> Somebody just say okay I agree with you and I will go away.


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## rochie (Oct 31, 2020)

no, Karl dont do it ........

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## buffnut453 (Oct 31, 2020)

P-39 Expert said:


> Not discounting or ignoring their comments. I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that. A slightly different propeller or a slightly altered CG or slightly varying HP are just small discrepancies that would be present in any test of the exact same airplane. Especially when there is no proof whatsoever that the CG was not proper in either airplane, or that the HP varied at all. In regards to the propeller, what was the exact difference in the two propellers? Any at all? They were of the same diameter.
> 
> There is a straightforward binary association between two airplanes of the same type and model, when the only difference is a substantial amount of weight. And again, please explain to me the difference between the two propellers.
> 
> None of that other crap mattered to the climb rate except the nearly half ton of weight. Somebody just say okay I agree with you and I will go away.



You said "I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that." Please read (and I mean READ) my post that you quoted. Did I not say "Certainly lower weight will contribute to improved climb performance"? Isn't that acknowledging that weight will affect climb rate? Many others have also made such an acknowledgement.

The problem is you keep ignoring any other factor that may complicate your simplistic perspectives. You also have a penchant for inserting adjectives that reflect your own biases rather than an objective assessment of the situation. One example that I've identified is your habit of calling 30 cal machine guns "useless". I'm still waiting for you to recognize that the OPERATIONAL PILOTS didn't think they were useless.

Now you're introducing a new adjective, assuming that the differences in the propeller were "slight". We don't know that for sure, and so we can't quantify how much impact the different propeller had on the performance deltas between the 2 airframes. 

GregP and others are trying to dig into the details of the test reports that you keep citing, but rather than engage in conversation about what cumulative effects might be at play, you keep reverting back to a single topic and issue. 

Meanwhile, I'm still waiting for any kind of acknowledgement from you that the operational pilots continued to fly with 30 cals in the wings precisely because they WEREN'T useless.

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## P-39 Expert (Oct 31, 2020)

buffnut453 said:


> You said "I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that." Please read (and I mean READ) my post that you quoted. Did I not say "Certainly lower weight will contribute to improved climb performance"? Isn't that acknowledging that weight will affect climb rate? Many others have also made such an acknowledgement.
> 
> The problem is you keep ignoring any other factor that may complicate your simplistic perspectives. You also have a penchant for inserting adjectives that reflect your own biases rather than an objective assessment of the situation. One example that I've identified is your habit of calling 30 cal machine guns "useless". I'm still waiting for you to recognize that the OPERATIONAL PILOTS didn't think they were useless.
> 
> ...


Sorry my use of adjectives offends you. Russians considered the .30s useless on P-39s. US must have considered them useless since no P-38, P-40, P-47, P-51, F4F, F6F, F4U, B-17, B-24, B-25, B-26, A-26, SB2C, TBF had them. The AAF P-39 pilots may have been required to keep them, again I don't know. Wagner did say that they weren't as effective or dependable as .50s. Had the P-39 pilots known how much better their planes would climb without them then they may have removed them. We're only talking about the period between May and November 1942.


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## buffnut453 (Oct 31, 2020)

P-39 Expert said:


> Sorry my use of adjectives offends you. Russians considered the .30s useless on P-39s. US must have considered them useless since no P-38, P-40, P-47, P-51, F4F, F6F, F4U, B-17, B-24, B-25, B-26, A-26, SB2C, TBF had them. The AAF P-39 pilots may have been required to keep them, again I don't know. Wagner did say that they weren't as effective or dependable as .50s. Had the P-39 pilots known how much better their planes would climb without them then they may have removed them. We're only talking about the period between May and November 1942.



Interesting that you still won't concede that someone on this thread has agreed with you. Is it really so hard for you to admit you're wrong? Your use of adjectives doesn't offend me. It's the bias they impose in your argument, and your inability to recognize that someone else might actually have a relevant point to make in this discussion. Even when I've pointed out to you that I acknowledged affect of weight on aircraft performance, you still don't show the good grace to recognize it. 

Your point about USAAF aircraft not using 30 cals is entirely irrelevant (ignoring for a moment that you're wrong - the P-40 DID fly with 30 cals in the wings!). None of those aircraft flew with 20mm cannon (with the possible exception of the A-26). Are we therefore to suppose that the 20mm cannon was useless? We're not talking about any of those airframes. We're talking about the P-39 which DID have 30 cals. They were specified by the customer and they were flown by operational pilots in that configuration. 

So...you insist that removing guns to improve climb performance is blindingly obvious, and yet the pilots who flew the P-39s operationally couldn't figure it out? 

As to the "period between May and November 1942", that's a lifetime in combat. Again, the Aussies swapped 50 cals for 303s in their Buffalos after just 2 weeks of combat experience and yet the USAAF couldn't figure it out after 6 months? Or are you suggesting that the USAAF was so rule-bound that operational squadron commanders on a far-flung forward base couldn't make decisions about how to get the most out of their aircraft? 

You may not know why the 30 cals were not removed from USAAF P-39s but can't you at least consider, for a moment, that one LOGICAL conclusion is that the P-39 pilots still wanted the 30 cals in the wings? You've criticized everyone else for not acknowledging your facts or opinions. How about you acknowledging the possibility that the P-39 drivers kept the 30 cals because they weren't useless?


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## Ivan1GFP (Oct 31, 2020)

P-39 Expert said:


> *More like a second or two. One time. Let's move on from this, we're talking about 3mph.*



If you really wanted to "move on" from these subjects, then you would not keep making assertions that are pure garbage.
To make these assertions is to throw out a challenge and see if you can get away with it. YOU CAN'T!

As you have been told repeatedly, it isn't about 3 MPH because you will never see that 3 MPH while maneuvering in combat.
It is about the difference in engine power and observations to determine engine power take more than a couple seconds.

Here is an example that may hit a little closer to home:
For a moment, let's talk about cars and tuning for engine power.
Even in a modern computer controlled car, sometimes you can tune things like Fuel Pressure and Initial Timing for the Ignition.
Adjusting Fuel Pressure is actually pretty much the same idea as adjusting mixture in a carburetor engine.
How do you tell what the result of that tuning is? By Sound? I can tell you that method doesn't work.
When I was doing this, we used a Chassis Dynamometer or an Accelerometer to test for differences.
Some changes might give an extra 5-10 HP which is a higher percentage in a 250 HP engine than 25 HP is in the 1150 HP engine in the Airacobra, but you can't tell by sound.
(I have actually been told about a man who could, but I don't know how true that story was and the man is dead now.)

In the Airacobra, you would observe by noticing performance changes and to do that takes longer than a couple seconds.



P-39 Expert said:


> *Now the British don't know how to run a test?*



The Japanese were not kind enough to supply the British with an intact A6M3 and a manual to go with it either.



P-39 Expert said:


> *More powerful engine, smaller wing etc, all things that should make the MkII faster, but still only 328mph. Let's move on from this, the A6M2 was slower than the P-39. *



First of all, you are making some rather general assumptions here. Even for the A6M3, the speeds listed in the manual for the larger wing Model 22 are faster than those for the smaller wing Model 32.

I have never stated that the A6M2 was faster than the early P-39. I only stated that the early P-39 wasn't 40 MPH faster as you keep claiming.



P-39 Expert said:


> *No amount of slightly different propeller blades of the same diameter, slight differences of CG (if there were any) or slight differences of HP (if there were any) will account for 1000fpm of climb. They were the same airplane, same contract, same engine, same airframe, same plane, simply different internal equipment. If you take any airplane and reduce the weight the climb rate will improve. The only thing that will account for 1000fpm of climb is almost half a ton of weight.
> 
> By the way, the C model didn't have the nose armor, how did it keep from falling out of the sky?*



First of all, YOU can't quantify the differences between the test aircraft in propeller or engine performance nor can you determine what the airframe differences were. All you can really state with reasonable certainty is that they were built to the same basic design.
These two tests were not on the same aeroplane!
The lighter aeroplane did climb faster but there were probably other factors that made a difference in performance as well.
If you follow performance cars, you would know that even cars that are "the same" that came off the same production line might differ pretty significantly in performance. I have seen plenty of dyno testing that has shown this.

The P-39C had an extra pair of MG and ammunition in the nose and less weight in the back. There may be more differences, but those are the obvious ones. We have been through this already.....



P-39 Expert said:


> *Splitting hairs again. I'd like to move on from this and concentrate on weight and climb.*



If you really think those acceleration tests were splitting hairs, then you really don't understand them.
Why is it that the Aleutian A6M2 compared so poorly in THESE tests when combat reports always described it as having very fast acceleration?
If you really wanted to move on from a subject, then stop bringing it up.

- Ivan.


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## GregP (Oct 31, 2020)

Hi Ivan1GFP,

Reference post #1193 and the P-3 Orion, just for fun.

I find the prop to be 13.5 feet in diameter or 162 inches. From what I see on the internet, the max T-56 engine speed is 13,800 rpm and the max propeller rpm is 1020. That puts rotation at 106.81 radians per second and the tangential speed at 720.9955 feet per second or 491.6 mph.

Assume it is operating at 105,000 pounds at 20,000 feet and the speed would be 244 KTAS or 280.8 mph forward speed. So, the helical tip velocity would be the square root of 491.6^2 plus 280.8^2, which is 566.15 mph.

The speed of sound at 20,000 feet is 705.757 mph on a standard day, so the propeller tip speed is M.802, which is in the vicinity of VERY GOOD design for turboprop propeller efficiency.

Assuming my numbers for the P-3 are correct, that is.


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## Ivan1GFP (Oct 31, 2020)

XBe02Drvr said:


> As previously pointed out, nobody on the allied side had a correctly set up and correctly operated, fully performing Zero until much later when it was no longer relevant.



Hello XBe02Drvr,

It is even worse than that. I don't believe the Allies EVER had a perfectly running A6M in ANY version and tested it properly.
If they did, I haven't found the report yet or ever heard it mentioned..... Though just because I don't know about it doesn't mean it doesn't actually exist.

- Ivan.

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## GregP (Oct 31, 2020)

They had a good-running Zero for the 1944 Fighter Conference. The Planes of Fame is still flying it, and it STILL runs good.

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## Ivan1GFP (Oct 31, 2020)

GregP said:


> They had a good-running Zero for the 1944 Fighter Conference. The Planes of Fame is still flying it, and it STILL runs good.



Hello GregP,

Do you happen to know which performance test used that particular aircraft?

- Ivan.


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## GregP (Oct 31, 2020)

Hi Ivan,

I am sitting here with the 1944 Fighter Conference Report in front of me, and I see the evaluation of the handling qualities, but the actual performance charts only are shown for the Allied airplanes that we were flying.

However, the Planes of Fame Zero is an AM5 Model 52. The specs say max speed at 19,685 feet was 348 mph. Climb to 19,685 feet was 7 minutes and 1 second, so the initial climb rate was likely around 3,600 fpm, tapering off as you climb. Cruise speed was 230 mph. The A6M5 added exhaust ejector exhaust, and the speed bumped up by some 11 - 13 mph over the A6M3, so that puts that A6M3 at about 335 - 337 mph at the same height.

Happy Haloween.

Oh, and, I do not believe they ran a complete performance test on the A6M5 Model 52 Zero used at the 1944 Fighter Conference. After the conference, it wound up as a squadron commander's hack on the west coast, and eventually went inoperative. After some years, Ed Maloney bought it, and it sat inoperative for some 25+ years until about 1977. It was restored with the assistance of Mitsubishi and Nakajima (Fuji Heavy Industries, today), flew again in 1978 and still flies. The Planes of Fame / Fighter Rebuilders did a 100% disassembly overhaul down to bare aluminum a few years back. EVERYTHING was redone except the engine and propeller since they were running great and still are.

Here is the Zero about to make the first post-restoration test flight in 2016:






All the paint colors are 100% authentic, even the interior and oxygen bottles, etc. The guys did a superb job! I helped a very little in initial disassembly and prep for control surface fabric only, which doesn't amount to much at all. But, I DID get to help a little  . The regular crew knows that A6M5 VERY well indeed. Corey O'Brian did most of the restoration with help from the other Fighter Rebuilders people. If I win a big lottery, he can restore whatever fighter I get for myself then!

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## Ivan1GFP (Oct 31, 2020)

GregP said:


> Hi Ivan1GFP,
> 
> Reference post #1193 and the P-3 Orion, just for fun.
> 
> ...



Hello GregP,

Try THESE numbers instead:

The P-3 Orion has a maximum speed of 473 MPH at 15,000 feet.
Propeller Diameter is 13.5 feet.
Propeller RPM at N1=100% is 1105 RPM.

Interesting thing to note is that the C-130 uses basically the same engine and propeller and reaches maximum speed at 20,000 feet....

- Ivan.


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## Ivan1GFP (Oct 31, 2020)

GregP said:


> Hi Ivan,
> 
> I am sitting here with the 1944 Fighter Conference Report in front of me, and I see the evaluation of the handling qualities, but the actual performance charts only are shown for the Allied airplanes that we were flying.
> 
> ...



Hello GregP,

My Wife is also setting up for Halloween while I am sitting here typing away....

19,685 feet would be the exact critical altitude of the engine (6000 Meters).
What do you suppose the actual critical altitude of the aircraft would be?
Your initial climb rate sounds about right.

- Ivan.

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## Peter Gunn (Oct 31, 2020)

P-39 Expert said:


> Sorry my use of adjectives offends you. Russians considered the .30s useless on P-39s. US must have considered them useless *since no P-38, P-40, P-47, P-51, F4F, F6F, F4U, B-17, B-24, B-25, B-26, A-26, SB2C, TBF had them.* The AAF P-39 pilots may have been required to keep them, again I don't know. Wagner did say that they weren't as effective or dependable as .50s. Had the P-39 pilots known how much better their planes would climb without them then they may have removed them. We're only talking about the period between May and November 1942.


Not to put too fine a point on it but the P-40, P-51, B-17, B-25, B-26 and TBF *ALL* sported .30 caliber guns on early marques and some well into the development cycle.

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## fubar57 (Oct 31, 2020)

The SB2C-1 replaced its single .50 Mg with twin .30s in the observers position

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## glennasher (Oct 31, 2020)

IIRC, the SBD went from ONE .30 to a twin .30 mount during it's time of service, too. Apparently, the .30s were sufficient for the task at hand.


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## GregP (Oct 31, 2020)

Hi Ivan1GFP,

When I plug in 1105 rpm, 13.5 feet diameter, 473 mph, at 15k feet, I get M.98977! Standard conditions. Definitely above M.88. 

I'd say that is in the area of degrading propeller efficiency, but it IS going 473 mph. And it's probably quite LOUD, too, at that speed and rpm.

The Russians still fly the Bear bomber, and it supposedly has supersonic flow over 1/3 or more of the prop at maximum speed of 575 mph or so. It could be that all the research into supersonic propellers isn't all that accurate since the Bear is the fastest propeller-driven aircraft of all times. But ... and here's the rub, it works for the rest of us in our flight regimes.


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## buffnut453 (Oct 31, 2020)

glennasher said:


> IIRC, the SBD went from ONE .30 to a twin .30 mount during it's time of service, too. Apparently, the .30s were sufficient for the task at hand.



No they weren't. They were useless. P-39 Expert said so....so it must be true.

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## glennasher (Oct 31, 2020)

buffnut453 said:


> No they weren't. They were useless. P-39 Expert said so....so it must be true.




Well, I'm not any kind of ex-spurt, so I'll defer to your vast knowledge, and his, I guess, maybe........................................


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## jmcalli2 (Oct 31, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> The most effective Japanese Naval Fighter Unit that was fighting from Lae was the Tainain Air Group.
> The unit was formed in October 1941, so it was hardly a veteran unit.
> ...


There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.


Ivan1GFP said:


> Hello jmcalli2,
> 
> I figure that if it was experience working with the Allison engine, the air service from the country manufacturing the engine would have the most experience especially since they had operated it in the P-40 for over a year.
> In any case one would expect Army mechanics to have more experience with a piece of Army equipment than the assortment of mechanics that were rounded up from various places for the AVG.
> ...


Good points.

I looked up a little on the AVG. It seems their Maine fighter opposition was the Nick, and later the Oscar. They started out with P-40Bs and eventually got some P-40Es. The Chinese they flew with also had a mixture, including P-43s & P-66s. Their original hit & run while keeping your speed high was formulated against the Nicks.

I also found something interesting; I was looking for P-40 encounter reports 9never found any) on WWII Aircraft performance when I found these at the bottom of the P-40 page:
http://www.wwiiaircraftperformance.org/P-40/Performance_Data_Pursuit_Airplanes.pdf
http://www.wwiiaircraftperformance.org/P-40/PHQ-M-19-1307-A.pdf
And finally this on high power use of the Allison:
http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf

The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
I'd love to see performance figures on them with 1700+hp!

Anyway I found them interesting.


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## GregP (Oct 31, 2020)

Hey Ivan, 

I went back to a post of mine on the last page and posted a pic of the Planes of Fame Zero about to taxi out for the first post-restoration test flight in 2016. Just FYI. It's a beautiful airplane!

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## wuzak (Oct 31, 2020)

jmcalli2 said:


> The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
> I'd love to see performance figures on them with 1700+hp!



1700hp at sea level only.


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## wuzak (Oct 31, 2020)

P-39 Expert said:


> Not discounting or ignoring their comments. I just believe that 836lbs of weight will affect climb rate and nobody on here will acknowledge that. A slightly different propeller or a slightly altered CG or slightly varying HP are just small discrepancies that would be present in any test of the exact same airplane. Especially when there is no proof whatsoever that the CG was not proper in either airplane, or that the HP varied at all. In regards to the propeller, what was the exact difference in the two propellers? Any at all? They were of the same diameter.
> 
> There is a straightforward binary association between two airplanes of the same type and model, when the only difference is a substantial amount of weight. And again, please explain to me the difference between the two propellers.



We don't know what the difference between the propellers were, but a design changed could change the performance on climb or all out level speed. The change to paddle blade props improved the climb performance of the P-47, for example.

Joe Baugher notes that the propeller was different on the P-39D and that there were other differences:



> A different 10 foot 5-inch Curtiss Electric propeller was fitted and the fuselage length was increased to 30 feet 2 inches. In addition, a very small dorsal fin was added just ahead of the rudder.



Bell P-39D Airacobra

Not sure how much the fuselage length was changed.




Ivan1GFP said:


> First of all, YOU can't quantify the differences between the test aircraft in propeller or engine performance nor can you determine what the airframe differences were. All you can really state with reasonable certainty is that they were built to the same basic design.
> These two tests were not on the same aeroplane!
> The lighter aeroplane did climb faster but there were probably other factors that made a difference in performance as well.



The engines were also not the same, even though they were the same model.

Engines were allowed to vary by a small percentage from the rated power, so the power from on engine on the production line to the next could vary by 5 or 6%. Maybe even more.

And there may be evidence in this in the tests of the P-39C and P-39D.
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf
http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6722_PHQ-M-19-1325-A.pdf

As noted by others, the engine powers were derived from different documents. This may indicate minor detail changes to the engine, or that it was re-certified.

The critical altitude for the P-39C in its test was at 13,050ft, at which its speed was 379mph at 3,000rpm and 1,150hp (obtained from chart in TO No. 025AD-1).

The critical altitude for the P-39D as 13,800ft, at which it made 368mph at 3,000rpm and 1,150hp (obtained from chart in Specification No. 123E).

Critical altitude for Normal rated power (1,000hp @ 2,600rpm) for the P-39C was 12,600ft at 362mph, for the P-39D it was 13,100ft @ 347.5mph.

Critical altitude in climb for the P-39D was 12,400ft. The report for the P-39C doesn't identify the critical altitude for climb in military power, but it appears to be 10,000ft (last altitude listed with max power).

Cruising speed at 2,280rp and 750hp was 327mph @ 11,600ft for the P-39C and 311mph @ 13,000ft for the P-39D.

Clearly the aircraft were not identical other than the weight.

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## wuzak (Oct 31, 2020)

Also, would the guns in the wings cause more drag, reducing climb and speed?

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## DerAdlerIstGelandet (Oct 31, 2020)

glennasher said:


> Well, I'm not any kind of ex-spurt, so I'll defer to your vast knowledge, and his, I guess, maybe........................................



Actually we all started out as a spurt, so that would make us ex-spurts.

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## pbehn (Oct 31, 2020)

A soldier in WW1 could cross no mans land faster without his rifle ammunition and helmet. A C-47 can carry more paratroops if they leave all their equipment weapons and clothes back in their base. Taking military equipment off military machines is just an argument for Reno racers being superior in performance to planes they were developed from. Taking guns off a fighting machine is a very hard "sell".

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## Ivan1GFP (Oct 31, 2020)

GregP said:


> Hi Ivan1GFP,
> 
> When I plug in 1105 rpm, 13.5 feet diameter, 473 mph, at 15k feet, I get M.98977! Standard conditions. Definitely above M.88.
> 
> ...



Hello GregP,

Another thing worth examining is the Advance Ratio and most likely propeller pitch that would represent for these two aircraft at maximum speed and the likely propeller efficiency that would suggest. 
The other thing to remember is the actual shaft horsepower that these Turboprops are putting to the propeller. It isn't something even the best Turbo-Compound engine could ever do though I suspect some of the Unlimited class racers you hang around with can come close to what the P-3 Orion is doing.
The last thing to consider is that the exhaust thrust from these engines is relatively high and it becomes a very large portion of the thrust at high speeds.
No, they really aren't playing by quite the same rules.

- Ivan.


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## Ivan1GFP (Oct 31, 2020)

jmcalli2 said:


> There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.
> 
> Good points.
> 
> I looked up a little on the AVG. It seems their Maine fighter opposition was the Nick, and later the Oscar. They started out with P-40Bs and eventually got some P-40Es. The Chinese they flew with also had a mixture, including P-43s & P-66s. Their original hit & run while keeping your speed high was formulated against the Nicks.



Hello jmcalli2,

Those were not Nick which is a twin engine fighter. They were Ki 27 Nate which is a little tiny fighter with fixed landing gear.
The other thing worth mentioning is that from the Curtiss aircraft Construction Numbers, the batch of "P-40s" which were technically just "Hawk 81s" fell into the range for the P-40C and not P-40B.
Curtiss basically used the contract to get rid of old parts that would not satisfy current military contracts because the contract fr the Chinese did not specify a lot of features that the military contracts did. So much for Mil-Spec.
That is why older fuel selectors without provision for drop tanks and fuselage fuel tanks with external sealing material were found on these planes. The folks in China saw these pieces and thought they were flying earlier models, but they were not.



jmcalli2 said:


> And finally this on high power use of the Allison:
> http://www.wwiiaircraftperformance.org/P-40/V-1710_Service_Use_of_High_Power_Outputs.pdf
> 
> The last I thought at first was talking about the P-38, but then it gave the model numbers as -81, -83, and -85. These were P-40, P-39, and P-51 models.
> I'd love to see performance figures on them with 1700+hp!



That document you found is the Allison Memo that I have mentioned a few times. I didn't find it on that site though.
The engines models they cover are not actually the ones you are thinking though.
They were the F3R (V-1710-39 and V-1710-35) and F4R (V-1710-73 and V-1710-63). Basically the 1150 HP and 1325 HP engines for the P-40 and P-39.
This is probably why the P-39D-1 pilot flying against the Aleutian A6M2 probably figured he could run a LOT more boost than the manual allowed.

- Ivan.

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## GregP (Nov 1, 2020)

If you look at the Zero pic I posted, you can see the ejector exhaust stacks. They add significant thrust at high power settings.

Some of the Reno guys are making 3800 or so hp, and the R-4360 guys can probably make maybe 500 more ... at least for awhile. None of the race engines would last to Berlin and back at high powers, but its possible they could be operated at ... say ... 2300 hp for some time. I don't know myself and would have to ask the racers. I don't know how much heat (in BTUs) a stock radiator in a P-51, for instance, can dissipate. I don't know any who can put out torque like an Allison T-56 turboprop, though.

But, their answers might be a guess, because they build for the engines to last maybe 60 - 70 laps of 6.5 miles each at high power, with some lower-power breathing in between the high power laps (a Reno race campaign). That definitely won't get you to Berlin from the U.K. much less back again.

Pretty much everyone in here knows that, of course. For you new guys, we have moderators who crew or have crewed on Reno races planes and work as A&Ps.

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## GrauGeist (Nov 1, 2020)

P-39 Expert said:


> ...Russians considered the .30s useless on P-39s. US must have considered them useless since no P-38, P-40, P-47, P-51, F4F, F6F, F4U, B-17, B-24, B-25, B-26, A-26, SB2C, TBF had them. The AAF P-39 pilots may have been required to keep them, again I don't know. Wagner did say that they weren't as effective or dependable as .50s. Had the P-39 pilots known how much better their planes would climb without them then they may have removed them. We're only talking about the period between May and November 1942.


The list of types that had .50 MGs is a bit off. Keep in mind that most types in production before 1940/41 had .30 MGs.
The SBD was one of the first American aircraft that was designed to have two .50 MGs instead of the traditional .30/.50 cowl combination - however, it retained the .30 MG defensive armament.

The P-40B had .30 MGs.
The F4F-1/2 had .30 MGs.
The B-17 was originally armed with .30 MGs and even the B-17E still had one .30 MG left (skylight position).
The early B-25 models were armed with .30 MGs and the .30 MG remained in the nose position for several variants.
The B-26 was designed to have flexible .30 MGs in the nose and tail.
The P-38 prototype had two .30 MGs, two .50 MGs and a 23mm cannon...

P-47, F6F, TBF, A-26, F4U and so on, were after the USAAC moved toward the .50 MG as a standard.

For what it's worth, early war Soviet types (I-16, I-153, MiG-1/3, IL-2, Pe-2, AR-2, Su-2, etc.) were armed with 7.62mm MGs. - 7.62mm is...you guessed it: .30 caliber.

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## Stig1207 (Nov 1, 2020)

Juha3 said:


> I had difficulties to understand what Claringbould means. Some of my thoughts.
> _But on page 76 he writes that of the 44 Aircobras lost in combat in 1942 in New Guinea only 15 were shot down by Zeros. Who shot down the rest, ground fire got some but the first JAAF fighters unit, the 1st Chutai of the 11th Sentai, became active in New Guinea on 26 December 1942 and it did not claim Airacobras during the last few days of 1942. Japanese air gunners seems to have got a few but what about the rest. Did the combat losses include those destroyed on ground by bombing and strafing? But Claringbould notices earlier that the results of Japanese strafing attacks against Port Moresby airfields were minimal. Some Airacobras were destroyed by bombing, that is true but still the figures seem not to add up. And it seems that the 15 Zero losses does not include losses on ground because already the first Airacobra strafing attack on Lae on 30 April 1942 destroyed three Zeros according to Claringbould and according to Tagaya burned one and wrecked another Zero. Lae and other Japanese airfields in the area were also bombed rather regularly.
> I could have read the book one more time and count the P-39/P-400 losses, but did not bother. Instead I went through the P-39/P-400 losses in New Guinea in 1942 on the *Pacific Wrecks *site. When it in few cases does not give a clear reason, I checked what Claringbould says. All Airacobra losses are not mentioned on the site. Results were:
> *P-39s/P-400s reason of loss:*_
> ...



There are definitely more combat losses than 44 P-39's and 15 Zeros in Claringbould's book; but it does seem to me that the 44 vs 15 comparison he makes is losses that occurred on missions where they met each other in combat; I am not sure if losses here means failed to return or whether it includes DBR, except that the 15 Zeros all FTR along with the pilots. About half the P-39 pilots survived and returned and could relate what had happened; but for those that remained MIA, the cause of loss was not always observed by their squadron mates. In the majority of cases some cause is given as a likely cause of loss but in some cases no assumption of the cause of the loss is given.
I would think that on the Japanese side, for those Zero's that FTR the cause was probably not always observed either but it may be that the Japanese recorded the loss as being to P-39's because that was what they were in combat with.

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## GregP (Nov 1, 2020)

Not to beat a dead horse, but attached is a spreadsheet I just made to calculate propeller tip Mach Number at Standard Conditions.

We know all conditions are NOT standard, but this is only for forum conjecture, so I didn't add compensation for non-standard conditions. Instructions are included on the first tab. If you want to account for non-standard conditions, then enter the density altitude as your altitude.

The spreadsheet is protected, but without a password, so you can unprotect it if you want to do so.

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## pbehn (Nov 1, 2020)

GregP said:


> But, their answers might be a guess, because they build for the engines to last maybe 60 - 70 laps of 6.5 miles each at high power, with some lower-power breathing in between the high power laps (a Reno race campaign). That definitely won't get you to Berlin from the U.K. much less back again.
> 
> .


During the war it was bombers who most frequently had engines running for long periods at high power ratings. An unladen Lancaster could limp home on two engines, of course you don't hear so much about those who didn't.

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## P-39 Expert (Nov 1, 2020)

wuzak said:


> We don't know what the difference between the propellers were, but a design changed could change the performance on climb or all out level speed. The change to paddle blade props improved the climb performance of the P-47, for example.
> 
> Joe Baugher notes that the propeller was different on the P-39D and that there were other differences:
> 
> ...


Clearly the additional 836lbs had nothing to do with the P-39D being 11mph slower or climbing 1000fpm slower.

How about this, what if the P-39D weight was reduced to that of the P-39C? Would it not have the same performance as the P-39C?


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## windhund116 (Nov 2, 2020)

jmcalli2 said:


> There were also a few missions with P-40s in the New Guinea combat book. I didn't get the impression they did any better or worse than the P-39s, but then again they were not the feature of the book either.



Interesting. Couple books and articles I've read said the units (like 8th FG) with P400 fared not-so-well against the IJNAF fighters, early in those New Guinea air battles. Later, these early units were replaced with P40s.


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## Ivan1GFP (Nov 2, 2020)

GregP said:


> Hi Ivan,
> 
> I am sitting here with the 1944 Fighter Conference Report in front of me, and I see the evaluation of the handling qualities, but the actual performance charts only are shown for the Allied airplanes that we were flying.
> 
> ...



Hello GregP,

I did a little more checking yesterday. Here is a little more history that might interest you:
I am sure you already know most of it but I restate it for others here who may not know.

The A6M5 that is currently flying with Planes of Fame was originally captured on Saipan in 1944.
Its original markings which it carries today were "61-120". 61 was the unit identification: 261 Kokutai.
There were quite a few A6M captured there along with a lot of spares.
About a dozen A6M (A6M5 mostly and a couple A6M2) and a bunch of engines were packed aboard a CVE and shipped back to the US.
61-120 was one of the aircraft that was in the best condition. It was assigned the number TAIC 5 which replaced the 61-120 marking and WAS flown in performance testing.
The differences with this aircraft were that it was equipped with a Sakae 31 engine which is normally the version equipped with Water Methanol injection however this aircraft was not so equipped.
The test report can be found here:
*TED PTR 1111
*
The interesting results are that the maximum speed achieved seems quite low: 335 MPH @ 18,000 feet which is well under the critical altitude.
There are no discrepancies or faults noted in the aircraft however on page 2 in note 2, there is a statement that tests are of a "qualitative" rather than a "quantitative" nature.

- Ivan.

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## GregP (Nov 2, 2020)

They didn't need quantitative test because all the active PTO combat pilots knew what they could do.

When we did the full airframe overhaul, about a 30-cal bullet in the canopy frame was found, just inside about a 30-cal hole. The bullet was removed and the hole was repaired.

I doubt the flight test got to "best power" and :max speed" as they didn't seem all that sure what that might be at the time. They put about 190 hours on the airframe during the 1944 Fighter Conference. In that time, Zero 61-120 was the only fighter aircraft being flown that didn't break down even once ... it was dead reliable.

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## Ivan1GFP (Nov 2, 2020)

GregP said:


> They didn't need quantitative test because all the active PTO combat pilots knew what they could do.
> 
> When we did the full airframe overhaul, about a 30-cal bullet in the canopy frame was found, just inside about a 30-cal hole. The bullet was removed and the hole was repaired.
> 
> I doubt the flight test got to "best power" and :max speed" as they didn't seem all that sure what that might be at the time. They out about 190 hours on the airframe during the 1944 Fighter Conference. In that time, Zero 61-120 was the only fighter aircraft being flown that didn't break down even once ... it was dead reliable.



Hello GregP,

From what I remember, the Sakae 31 aircraft have a slight difference that is externally visible at the aft end of the cowl.
The gap between the cooling flaps and the fuselage appears to be slightly longer than for the Sakae 21.
Perhaps this was to allow room for the Water Methanol tank?
This might also explain the 348 MPH speed you were quoting as compared to the more common 351 MPH speed listing, or perhaps it was the later additional wing guns or larger cutouts for the 13.2 mm MG in the cowl?

In any case, in this particular TAIC Report No. 17 there is no listing for details on engine power or throttle settings or any real performance detail regarding speed other than 335 MPH. Best climb speed seems a bit low to me at 105 Knots indicated which suggests engine power was a bit low (Note that best climbing speed in testing for A6M5 No. EB-2 was 135 MPH which seems a bit more reasonable) and another odd characteristic was the note on vibrations in dives at airspeeds over 250 Knots IAS which should not be happening. This wasn't even noted for the A6M2 and the A6M5 had much higher diving speeds according to the manual. In any case, I do not believe these results are indicative of what a A6M5 in perfect condition could actually do.

In the other comparable TAIC Report No. 38, from what I can tell from the graph, maximum speed achieved was about 326 MPH but there WERE many discrepancies noted and they DID attempt to run the engine at full Emergency Power when they figured out what was wrong with it. The majority of the tests were not run at full manifold pressure but the performance tests were and there is a note that there were some problems with the airframe that limited performance results.

I am pretty sure that by the time these aircraft were being tested, a couple manuals had been captured. Whether they were widely distribute and to the people doing the testing is uncertain though. The thing to note in TAIC Report No. 38 is that from what I can tell, they were running a maximum of 42 inches Hg for manifold pressure in their testing which translates to +306.8 mm Hg which isn't too far from the official limit in the manual of +300 mm Hg. The difference may be due to my reading of the graph, but it does not seem that they were running the engine too low.

- Ivan.

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## wuzak (Nov 2, 2020)

P-39 Expert said:


> Clearly the additional 836lbs had nothing to do with the P-39D being 11mph slower or climbing 1000fpm slower.



The extra weight would make a difference, as would a variation in engine performance. 

I would have expected the heavier aircraft to have its peak numbers at lower altitudes than the lighter aircraft. Not sure if that is a fair assumption.




P-39 Expert said:


> How about this, what if the P-39D weight was reduced to that of the P-39C? Would it not have the same performance as the P-39C?



That I cannot say, and nor can you. 

There were detail differences in the two aircraft - the D was longer and had a fillet in the tail fin. The D had a different propeller and had the extra guns in the wings, which would have had some aerodynamic effect (I guess you would say to remove these).

And we don't know the actual power the engines produced on the tests. The power numbers come from (two different) standard charts.


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## GregP (Nov 2, 2020)

A few pages back, I observed that the climb numbers for the P-39C make sense while the climb numbers for the P-39D do not. The predicted rate of climb follows the P-39C decently but not perfectly, and the climb numbers for the P-39D do NOT look logical.

Don't know why since I wasn't there, but they got the power numbers from a two charts instead of from rpm and manifold pressure. They MIGHT have used MAP and rpm but, if so, they didn't note the readings for the report, so it's hard to see what might be wrong when you don't know any particulars. 

It is almost like they made the P-39D chart all at 2,600 rpm but recorded it differently. I can't say, really.


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## BiffF15 (Nov 2, 2020)

Gents,

I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I’m curious if they got the same results out of our equipment without manuals or instruction.

Cheers,
Biff

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## fubar57 (Nov 2, 2020)

I’ve got several captured aircraft books, Biff (3 F’s) and will look through them when I get home

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## GregP (Nov 2, 2020)

Hi Biff.

I don't read German, so I'm sort of left out in the dark there. The reports are usually scanned pictures instead of pdf's so you can't copy and paste into a translator. But, I'll se what I can find on the P-39 in German and maybe Russian. The numbers are usually selfevident.

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## DerAdlerIstGelandet (Nov 2, 2020)

GregP said:


> Hi Biff.
> 
> I don't read German, so I'm sort of left out in the dark there. The reports are usually scanned pictures instead of pdf's so you can't copy and paste into a translator. But, I'll se what I can find on the P-39 in German and maybe Russian. The numbers are usually selfevident.



I speak German, so I can translate if necessary. It is just a matter of if I have time or not.

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## Ivan1GFP (Nov 2, 2020)

BiffF15 said:


> Gents,
> 
> I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I’m curious if they got the same results out of our equipment without manuals or instruction.
> 
> ...



Hello BiffF15,

The Germans tested a captured Soviet Lavochkin La 5FN at Rechlin. This is obviously not an American aeroplane but it is interesting to note that the performance that they got was much lower than that typically attributed to the same aircraft by the Soviets.
This report has been translated into English and is not that hard to find. I have attached a copy.
As a simple comparison, the maximum speed of the La 5FN in Soviet service tended to vary a bit in Soviet Service but a fair estimate is something in the 390-403 MPH range.

Maximum speed of tested aircraft was 560 KPH. 403 MPH would be around 648 KPH.
Other performance figures are correspondingly low.
The Germans seemed to have good information on how to operate the engine of this aircraft.
The fuel quality (C3) available to Germans was at least as good quality as that typically available to the Soviets.
Perhaps this was a worn out aircraft?

In the report "8" is the category for single engine fighter, so "8-109" is the Me 109 and "9-190" is the FW 190.

Incidentally, the book by Hans Werner Lerche that came up in discussion a while back is full of his evaluations of captured aircraft.

- Ivan.

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## BiffF15 (Nov 3, 2020)

Ivan1GFP said:


> Hello BiffF15,
> 
> The Germans tested a captured Soviet Lavochkin La 5FN at Rechlin. This is obviously not an American aeroplane but it is interesting to note that the performance that they got was much lower than that typically attributed to the same aircraft by the Soviets.
> This report has been translated into English and is not that hard to find. I have attached a copy.
> ...



Ivan,

That’s an excellent report. I find it interesting that the German view of Russian aircraft at that time was so poor. Especially in the handling department. This is considering particularly the landing phase as compared to the Me-109 with it’s known vices. Also, given the short legs of the Me-109 and the FW-190 that they thought the La-5 was short legged. 

Also, as per the Zero in US hands, the top speed tested was not the same as claimed by the country of manufacture. I’m curious to see if this is a trend among other nations (not just the US).

Cheers,
Biff


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## Peter Gunn (Nov 3, 2020)

BiffF15 said:


> Gents,
> 
> I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I’m curious if they got the same results out of our equipment without manuals or instruction.
> 
> ...


Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.

FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:

*Type | Max Speed | Climb | Ceiling | Range*

*American*

*B-17F* *|* 325MPH @ 25,000ft *|* 20,000 - 25min 42sec *|* 37,500ft *|* 4,420 miles

*B-17G* *|* 302MPH @ 25,000ft *|* 20,000ft - 37min 0sec *|* 35,000ft *|* 1,800 miles

*B-24D* *|* 303mph @ 25,000ft *|* 20,000ft - 22min 0sec *|* 32,000ft *|* 1,800 miles

*B-24J* *|* 300mph @ 30,000ft *|* 20,000ft - 25min 0sec *|* 35,000ft *|* 1,700 miles

*B-26B* *|* 317mph @ 14,500ft *|* 15,000ft - 12min 0sec *|* 23,000ft *|* 1,150 miles

*P-39D* *|* 335mph @ 5000ft *|* 5,000ft - 1min 54sec *|* 29,000ft *|* 600 miles

*P-47D-2* *|* 420mph @ 30,000ft *|* 20,000ft - 11min 0sec *|* 42,000ft *|* 835 miles

*P-47D-10* *|* 433mph @ 30,000 *|* 25,000 - 15min 0sec *|* 42,000ft *|* 835 miles

*P-51B* *|* 446mph @ 30,000ft *|* 10,000ft - 1min 48sec *|* 42,000ft *|* 2250 miles

*British*

*Lancaster Mk 1* *|* 281mph @ 11,000ft *|* 20,000ft - 41min 36sec *|* 24,500 *|* 1,730 miles

*Wellington Mk IV* *|* 247mph @ 14,500ft *|* 10,000ft - 18min 0sec *|* 17,700ft *|* 2,250 miles

*Tempest Mk V* *|* 426mph @ 18,500 *|* 15,000 - 5min 0sec *|* 36,500ft *|* 1,530 miles

*Typhoon Mk IB* *|* 405mph @ 18,000ft *|* 15,000 - 6min 12sec *|* 34,000ft *|* 1,000 miles

*Spitfire Mk IIA* *|* 357mph @ 17,000ft *|* 20,000ft - 7min 0sec *|* 37,230ft *|* 406 miles

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## Ivan1GFP (Nov 3, 2020)

BiffF15 said:


> Ivan,
> 
> That’s an excellent report. I find it interesting that the German view of Russian aircraft at that time was so poor. Especially in the handling department. This is considering particularly the landing phase as compared to the Me-109 with it’s known vices. Also, given the short legs of the Me-109 and the FW-190 that they thought the La-5 was short legged.
> 
> ...



Hello BiffF15,

The FW 190 was a particularly nice handling aircraft. The British acknowledged in their testing of a captured example.
In another, there was the possibility of the aircraft not having the ailerons set up properly which caused a few issues.
In comparison, even some of the other users of the Lavochkin fighters were not so impressed with their handling.
They just had the engine power and performance that prior Soviet fighters lacked.

If flown by the manual, the 1180 mm Hg @ 2500 RPM setting was only good for about 5 minutes and only useable in Low Blower.
This would give 1850 HP and in theory was a Take-Off setting and not useful much past 1650 Meters critical altitude for low blower.
The equivalent of military power was 1700 HP with 1000 mm Hg @ 2400 RPM in Low Blower.

From what I have been able to find, climb rate at "military power" was somewhere under 3500 fpm which is good but not that special, but at its take-off setting, climb rate is about 4000 fpm which was very competitive for the time.

I have a lot more detail in the Soviet manuals for the aircraft if you wish to calculate the actual fuel consumption of the aircraft for range purposes. One odd thing to note is that the fuel in the Rechlin report seems to weigh more than the typical 6 pounds per US Gallon that one might expect.

I believe that in this particular test at Rechlin, the Germans may have captured the La 5FN AFTER it had been beaten to heck by the prior Soviet users. Soviets didn't tend to stick by the manuals with the Airacobra and probably didn't with anything else either. It generally didn't matter when the lifespan of an aircraft measured in weeks.

Regarding the Zero and Japanese claims for speed. From what I can tell, there actually are no official claims for what we would consider "Maximum Speed".
In their manual for the A6M2, they only list a maximum speed for "Normal Power" +50 mm @ 2350 RPM which is what we might consider max continuous or something close and that was for 275 Knots or 316 MPH.
The 345 MPH claim was by an experienced pilot, Saburo Sakai. For a long time, I was certain this number was inaccurate but not because Sakai was dishonest, but after reviewing the reports recently and other sources in the context of these discussions, I am now more certain he was correct.

- Ivan.

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## vikingBerserker (Nov 3, 2020)

Just as an FYI, the App Google Translate will use your phone camera and translate live time so you don't need to cut and paste, just point and read.


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## windhund116 (Nov 3, 2020)

Peter Gunn said:


> Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
> Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.
> 
> FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:
> ...





Robert Mikesh has a nice book (found this link), on captured B-17s by the Japanese in WW2. 

Captured B-17s

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## swampyankee (Nov 3, 2020)

Peter Gunn said:


> Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
> Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.
> 
> FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:
> ...



I'm looking at the Time-to-height value for the P-51B. The average rate of climb is about 5,500 fpm, which strikes me as _very_ high. Is there a typo in there?

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## Peter Gunn (Nov 3, 2020)

swampyankee said:


> I'm looking at the Time-to-height value for the P-51B. The average rate of climb is about 5,500 fpm, which strikes me as _very_ high. Is there a typo in there?


Agreed, I was a bit suspicious of that myself, that's the way it is in the book so it may very well have gotten a bit mixed up when the publisher set the type.

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## Juha3 (Nov 3, 2020)

Ivan1GFP said:


> Hello BiffF15,
> 
> The FW 190 was a particularly nice handling aircraft. The British acknowledged in their testing of a captured example...



I would not call 190 a particularly nice handling a/c because its nasty/violent stall behaviour and it stalled practically without warning. That with clean a/c, at landing configuration there was plenty of warning and the stall itself was much milder. A Geschwaderkommodore of JG 51 killed one of his Gruppenkommandeure when soon after take-off and still a steep, climbing turn he lost control of his 190 which whipped over onto its opposite wing and smashed into Kommandeur's 190. Hauptmann Busch (40 victories) was flying as wingman to Geschwaderkommodore Oberstleutnant Nordmann (78 victories), who survived with injures but it was also the end of his combat career even if he recovered from his injuries he was unable to get over the accident. Otherwise 190 had fairly nice handling with exceptionally high rate of roll and very good harmony of control.



Ivan1GFP said:


> In comparison, even some of the other users of the Lavochkin fighters were not so impressed with their handling.



I agree. When one of his top aces, Klubov (33 + 3 shared victories) crashed on 1 Nov 1944 during his first La-7 flight was killed Pokryshkin decided to forget La-7 and his fighter division kept its P-39s to the end of the war.



Ivan1GFP said:


> I believe that in this particular test at Rechlin, the Germans may have captured the La 5FN AFTER it had been beaten to heck by the prior Soviet users. Soviets didn't tend to stick by the manuals with the Airacobra and probably didn't with anything else either. It generally didn't matter when the lifespan of an aircraft measured in weeks.



IIRC The La-5FN tested at Rechlin was old and worn-out a/c. On La-5FN max speed, the new production a/c usually were capable to 625 to 635 km/h and the 648 km/h was the speed of a prototype. Soviet prototypes in early 40s tended to be faster than the production a/c.



Ivan1GFP said:


> Regarding the Zero and Japanese claims for speed. From what I can tell, there actually are no official claims for what we would consider "Maximum Speed".
> In their manual for the A6M2, they only list a maximum speed for "Normal Power" +50 mm @ 2350 RPM which is what we might consider max continuous or something close and that was for 275 Knots or 316 MPH.
> The 345 MPH claim was by an experienced pilot, Saburo Sakai. For a long time, I was certain this number was inaccurate but not because Sakai was dishonest, but after reviewing the reports recently and other sources in the context of these discussions, I am now more certain he was correct.
> 
> - Ivan.



I agree with that, too.

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## P-39 Expert (Nov 3, 2020)

wuzak said:


> The extra weight would make a difference, as would a variation in engine performance.
> 
> I would have expected the heavier aircraft to have its peak numbers at lower altitudes than the lighter aircraft. Not sure if that is a fair assumption.
> 
> ...


Just to be clear, the loss of 1000fpm of climb was due to a few inches of extra length, the fin fillet, the different propeller (of the same diameter and manufacturer) and the aerodynamic effect of the wing .30s (not the weight)? And the same model engine maybe producing different power? Any other differences in the two planes? 

I'm still going with the 836lbs less weight.


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## Peter Gunn (Nov 3, 2020)

P-39 Expert said:


> Just to be clear, the loss of 1000fpm of climb was due to a few inches of extra length, the fin fillet, the different propeller (of the same diameter and manufacturer) and the aerodynamic effect of the wing .30s (not the weight)? And the same model engine maybe producing different power? Any other differences in the two planes?



All possible issues yes, as has been pointed out by various posters many times already. Setting aside of course, any CoG issues.



P-39 Expert said:


> I'm still going with the 836lbs less weight.



Certainly a logical and _possible_ reason, but again, others more versed in actual aviation experience have pointed out the whys and why nots.


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## P-39 Expert (Nov 3, 2020)

Peter Gunn said:


> All possible issues yes, as has been pointed out by various posters many times already. Setting aside of course, any CoG issues.
> 
> 
> 
> Certainly a logical and _possible_ reason, but again, others more versed in actual aviation experience have pointed out the whys and why nots.


Oh, I forgot about the CG issues. Should have added that to the list. Were there actually any CG issues in either plane? None were mentioned in either test. And the C model didn't have any nose armor. Should have made it unflyable, right?


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## buffnut453 (Nov 3, 2020)

Hmmm...methinks I smell troll.

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## gordonm1 (Nov 3, 2020)

i'm not sure if it fits here but were the P39 and P40 all steel and the P51 aluminum? Curious about the aluminum P40 what if....


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## GregP (Nov 3, 2020)

P-39 and P-40 are aluminum airplanes. At least the ones operated by the Planes of Fame are. There is some steel, but the structure is aluminum. Landing gear oleos are steel along with a few other items. The engine crankshaft, camshaft, and other parts are steel, but the engine case is aluminum. Mixed material is normal due to strength and heat requirements.

If you tried out aluminum valves in the engine, they wouldn't last longer than a couple of minutes, if that long. In an Allison V-1710, the valve are Stellite (cobalt-chromium alloy) with powdered sodium fill for heat dissipation.

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## windhund116 (Nov 3, 2020)

GregP said:


> P-39 and P-40 are aluminum airplanes. At least the ones operated by the Planes of Fame are. There is some steel, but the structure is aluminum. Landing gear oleos are steel along with a few other items. Th engine crankshaft, camshaft, and other parts are steel, but the engine case is aluminum. Mixed material is normal due to strength and heat requirements.
> 
> If you tried out aluminum valves in the engine, they wouldn't last longer than a couple of minutes, if that long. In an Allison V-1710, the valve are Stellite (cobalt-chromium alloy) with powdered sodium fill for heat dissipation.



I'd imagine a cast-iron block engine would yield an airplane which is capable of taxiing. Only. 

Were the valve seat also made of Stellite? Very strong material.


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## pbehn (Nov 3, 2020)

gordonm1 said:


> i'm not sure if it fits here but were the P39 and P40 all steel and the P51 aluminum? Curious about the aluminum P40 what if....


 A lot of duralumin or variants of it Duralumin - Wikipedia


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## jmcalli2 (Nov 3, 2020)

wuzak said:


> 1700hp at sea level only.


Still, that's 300 more than the highest takeoff HP in a P-39 that I know of, in the Q model.
It could be why the Russians did so well with the P-39.


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## jmcalli2 (Nov 3, 2020)

Ivan1GFP said:


> Hello jmcalli2,
> 
> Those were not Nick which is a twin engine fighter. They were Ki 27 Nate which is a little tiny fighter with fixed landing gear.
> The other thing worth mentioning is that from the Curtiss aircraft Construction Numbers, the batch of "P-40s" which were technically just "Hawk 81s" fell into the range for the P-40C and not P-40B.
> ...


Thanks for the correction on the Nates. I blame spell check. LOL

Good points.


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## jmcalli2 (Nov 3, 2020)

windhund116 said:


> Interesting. Couple books and articles I've read said the units (like 8th FG) with P400 fared not-so-well against the IJNAF fighters, early in those New Guinea air battles. Later, these early units were replaced with P40s.


I think it was along the lines of, 'escort mission covering B-25s (or B-26s or B-24s) along with P-40s.' I'll have to look for it to be sure I'm recalling it correctly.

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## jmcalli2 (Nov 3, 2020)

jmcalli2 said:


> I think it was along the lines of, 'escort mission covering B-25s (or B-26s or B-24s) along with P-40s.' I'll have to look for it to be sure I'm recalling it correc
> 
> 
> 
> ...


OK, I was confusing the P-38 book with the P-39 book; the P-38s were on escort missions with P-40s.
The P-39s fought with RAAF Kittyhawks in New Guinea, mostly on intercept missions. The P-39s did escort RAAF B-26s, USAAF B-25s, A-20s, and A-24s.
Here are a few screen shots:

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## BiffF15 (Nov 3, 2020)

Peter Gunn said:


> Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
> Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.
> 
> FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:
> ...



Peter,

Thank you! The numbers look fairly close (I don’t have them memorized). Did the Germans use Allied fuel to get these results? Did Allied fighters and bombers use the same grade fuel? I would guess it was all the same...

Cheers,
Biff


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## BiffF15 (Nov 3, 2020)

Ivan1GFP said:


> Hello BiffF15,
> 
> The FW 190 was a particularly nice handling aircraft. The British acknowledged in their testing of a captured example.
> In another, there was the possibility of the aircraft not having the ailerons set up properly which caused a few issues.
> ...



Ivan,

I can easily see the Russian pilots over boosting their planes, for the simple reason as you said they didn’t tend to last long. Also, as for the P39 it was someone else who was building it and its engines, so no skin in the game and it was truly an asset to be used up and thrown away. And it appeared to have less vices than their indigenous production. 

As for the Zero and it’s top speed I agree. I always thought of it being a 350‘ish type of plane mostly because of what the combat reports said (Allied pilot reports). It’s fairly easy to compare your planes performance to another even in a fight. It’s quite obvious who is faster, and by how much, or who turns / climbs better and by what sort of margin.

Cheers,
Biff

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## Mike Williams (Nov 3, 2020)

BiffF15 said:


> Did the Germans use Allied fuel to get these results? Did Allied fighters and bombers use the same grade fuel? I would guess it was all the same...
> 
> Cheers,
> Biff



Allied bombers generally used 100/130 grade fuel while USAAF 8th AF Mustangs used 100/150 GRADE FUEL starting in early June 1944. 9th AF used 100/130 grade after moving to the continent. RAF Mustangs, some Spitfires, Mossies and Tempests starting using 100/150 Grade in ADGB (Air Defense of Great Britain) during the summer of 44, with 2nd TAF fighters switching over in early 45 on the continent.

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## Mike Williams (Nov 3, 2020)

jmcalli2 said:


> OK, I was confusing the P-38 book with the P-39 book; the P-38s were on escort missions with P-40s.
> The P-39s fought with RAAF Kittyhawks in New Guinea, mostly on intercept missions. The P-39s did escort RAAF B-26s, USAAF B-25s, A-20s, and A-24s.
> Here are a few screen shots:



What's the book? Some operational history and pilot's accounts of the P-39 would be most welcome here instead of the endless drama over trivial matters and ongoing personal smears.

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## tomo pauk (Nov 3, 2020)

Mike Williams said:


> What's the book? Some operational history and pilot's accounts of the P-39 would be most welcome here instead of *the endless drama over trivial matters and ongoing personal smears*.



(my bold)
I have nothing against keeping the bolded stuff in a single thread, vs. having to wade through that multiple threads...


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## windhund116 (Nov 3, 2020)

BiffF15 said:


> Ivan,
> 
> I can easily see the Russian pilots over boosting their planes, for the simple reason as you said they didn’t tend to last long. Also, as for the P39 it was someone else who was building it and its engines, so no skin in the game and it was truly an asset to be used up and thrown away. And it appeared to have less vices than their indigenous production.
> 
> ...



At least before 1945, most Russian pilots fought over Russian soil. So, if they fried an engine --- bailing out & survival was not as harrowing, as a German pilot bailing out over the same territory.

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## BiffF15 (Nov 3, 2020)

Mike Williams said:


> Allied bombers generally used 100/130 grade fuel while USAAF 8th AF Mustangs used 100/150 GRADE FUEL starting in early June 1944. 9th AF used 100/130 grade after moving to the continent. RAF Mustangs, some Spitfires, Mossies and Tempests starting using 100/150 Grade in ADGB (Air Defense of Great Britain) during the summer of 44, with 2nd TAF fighters switching over in early 45 on the continent.



Mike,

I would not have guessed that, however it stands to reason due to shear quantities. What happened when a fighter guy diverted / landed short at a bomber base, did they have a supply of the 100/150 or did he get 100/130 and use lower power settings on the way home?

Cheers,
Biff


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## pbehn (Nov 3, 2020)

BiffF15 said:


> Mike,
> 
> I would not have guessed that, however it stands to reason due to shear quantities. What happened when a fighter guy diverted / landed short at a bomber base, did they have a supply of the 100/150 or did he get 100/130 and use lower power settings on the way home?
> 
> ...


On missions from the UK, when really short of fuel returning planes landed at the three emergency bases set up for the purpose RAF Manston Woodbridge or Carnaby. I presume they had all sorts of fuel, they had everything else.

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## Mike Williams (Nov 3, 2020)

BiffF15 said:


> Mike,
> 
> I would not have guessed that, however it stands to reason due to shear quantities. What happened when a fighter guy diverted / landed short at a bomber base, did they have a supply of the 100/150 or did he get 100/130 and use lower power settings on the way home?
> 
> ...



Hi Biff,
One example that comes to mind is Operation of Spitfire IX LF with 25 lbs/sq.in. Boost. _"Aircraft may land at an airfield where only 130 grade (normal 100 octane) fuel is available. The pilot should always bear in mind that it is not harmful to use this fuel provided he does not REPEAT not exceed 18 lbs. boost."_ 8th AF mustangs could use 2nd TAF's 150 grade on the continent beginning in early 1945, otherwise I presume they would use 9th AF stocks of 100/130 fuel and limit boost for the ride home.

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## Mike Williams (Nov 3, 2020)

Does any one know what kind of fuel Russian P-39s used?


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## GrauGeist (Nov 3, 2020)

Mike Williams said:


> Does any one know what kind of fuel Russian P-39s used?


Not sure what was used in the Soviet P-39 specifically, but they did have aviation fuel that ranged from 70 to 85 octane, with fuel supplied to them by the Allies that was 95 and 100 octane.

The lower octane fuel was used in older aircraft types.

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## Juha3 (Nov 3, 2020)

Mike Williams said:


> Does any one know what kind of fuel Russian P-39s used?



front line units usually used 91-95 oct Soviet fuels or 100 oct LL fuel (outside mid-1942 - early 43, when Soviet fuel supply was in crisis), I have seen Soviet speed graphs for P-39Q showing the speeds with 95 and 100 oct fuel. Soviet 95 oct was usually used by M-82F and FN engines, so La-5F, -FN, La-7 and Tu-2. Spitfires and P-39s used usually 100 oct LL fuel. IIRC one big offensive was delayed a couple of days so that they could store enough LL fuel for a P-39 fighter division for the operation.

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## Mike Williams (Nov 3, 2020)

Juha3 said:


> front line units usually used 91-95 oct Soviet fuels or 100 oct LL fuel (outside mid-1942 - early 43, when Soviet fuel supply was in crisis), I have seen Soviet speed graphs for P-39Q showing the speeds with 95 and 100 oct fuel. Soviet 95 oct was usually used by M-82F and FN engines, so La-5F, -FN, La-7 and Tu-2. Spitfires and P-39s used usually 100 oct LL fuel. IIRC one big offensive was delayed a couple of days so that they could store enough LL fuel for a P-39 fighter division for the operation.


Thank you for the informative post Juha!  If you ever get a chance and can put your hands on those P39Q charts showing speeds with 95 and 100 octane, it would be very much appreciated if you can share them here.

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## Juha3 (Nov 3, 2020)

As asked




Ps. and my previous message was mostly based on messages made by the pseudo name Altea here in 2009.

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## Ivan1GFP (Nov 3, 2020)

Juha3 said:


> IIRC The La-5FN tested at Rechlin was old and worn-out a/c. On La-5FN max speed, the new production a/c usually were capable to 625 to 635 km/h and the 648 km/h was the speed of a prototype. Soviet prototypes in early 40s tended to be faster than the production a/c.



Hello Juha3,

My original statement regarding maximum speeds for the La 5FN was that anything from about 390 MPH to 403 MPH seems pretty reasonable and that they seemed to vary.
What do you believe the altitude was that the aircraft achieved its maximum speed?

- Ivan.


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## Ivan1GFP (Nov 3, 2020)

GregP said:


> P-39 and P-40 are aluminum airplanes. At least the ones operated by the Planes of Fame are. There is some steel, but the structure is aluminum. Landing gear oleos are steel along with a few other items. The engine crankshaft, camshaft, and other parts are steel, but the engine case is aluminum. Mixed material is normal due to strength and heat requirements.
> 
> If you tried out aluminum valves in the engine, they wouldn't last longer than a couple of minutes, if that long. In an Allison V-1710, the valve are Stellite (cobalt-chromium alloy) with powdered sodium fill for heat dissipation.



Hello GregP,

Don't forget there are often Magnesium wheels, Copper alloys in the heater / radiator cores.

The Sodium in the valve stems is actually liquid..... Nasty stuff if it should get out.

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## GregP (Nov 3, 2020)

I'm sure it was liquid back in WWII. Not so sure about today, but cannot speak for the state of it before it is exposed to air when a valve gets destroyed. Generally, I leave broken valves alone, and not just because they are not repairable.


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## ThomasP (Nov 3, 2020)

Hey Mike Williams,

In the early-2000s (around 2008?) I ran across a serious paper written on the history of the Russian/Soviet Union/Russian/Ukranian/etc oil industry from the 1800s on to the early 2000's. The author is an accredited historian and his name is Alexander Matveichuk. The paper covers most of the things related to the Russian/Soviet oil industry - ie history and exploitation of oil fields, quality of the crude oil, transport, refining/production, and changing technology. It had a fairly extensive section on the subject of aviation fuel quality and availability in the WWII period. I have not been able to find the original paper/history in a complete form on the internet, however there appear to be pieces of it available on various websites. Some of the websites require memberships.

An abbreviated account of the section on WWII aviation fuel quality, production, and acquisition can be found here:

"Oil of Russia : www.oilru.com : No. 2, 2011 / A HIGH-OCTANE WEAPON FOR VICTORY"

If anyone finds the complete paper on the internet I would very much appreciate it if you would let me know.

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## ThomasP (Nov 3, 2020)

Hey guys,

re sodium filled valves

Metallic sodium is solid at room temperatures, but melts at around 208°F. The value in using it in valves is that it has a very high heat transfer coefficient in liquid form (about 2x liquid water), a boiling point of about 1620°F, and a vaporization temp of about 1645°F. The critical temperature of sodium is also much higher than water (4172F vs 705F) so while sodium is under pressure inside the valve stem it retains a better heat transfer rate to much higher temperatures.

Also the low boiling temperature of water (212°F) and expansion ration of 1600 would result in such high pressures inside the valves that I do not know if valves of the usual stem/wall thickness and weight would survive, meaning a heavier valve body.

These properties of liquid sodium are the reason it is used in sodium cooled nuclear reactors.

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## Mike Williams (Nov 3, 2020)

Juha3 said:


> As asked
> View attachment 600662
> 
> 
> Ps. and my previous message was mostly based on messages made by the pseudo name Altea here in 2009.



Thanks Juha, I'll study on that chart a bit and try to figure out how the P-39 compares with US tests. The first question that comes to mind is - was the engine operated at lesser RPM, boost or both with the differing fuels. Looks like they were using Military power and I wonder what manifold pressure was used. Also wondering if it had external wing guns.

Hmmm, From: Pilot's Flight Operating Instructions for Army Model P-39Q-1 Airplane

War emergency 3000 RPM, 57" MP, critical alt with ram 9,000'
Military power: 3000 RPM, 44.5" MP, critical alt with ram, 15,500'
Max continuous: 2600 RPM, 39.2" MP, critical alt with ram. 14,000'

From MEMORANDUM REPORT ON Pursuit Single Engine P-39Q-5, AAF No. 42-19615

329 mph at SL with 57" Hg.
374 mph at 10,000' with 57" Hg.


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## Mike Williams (Nov 3, 2020)

ThomasP said:


> Hey Mike Williams,
> 
> In the early-2000s (around 2008?) I ran across a serious paper written on the history of the Russian/Soviet Union/Russian/Ukranian/etc oil industry from the 1800s on to the early 2000's. The author is an accredited historian and his name is Alexander Matveichuk. The paper covers most of the things related to the Russian/Soviet oil industry - ie history and exploitation of oil fields, quality of the crude oil, transport, refining/production, and changing technology. It had a fairly extensive section on the subject of aviation fuel quality and availability in the WWII period. I have not been able to find the original paper/history in a complete form on the internet, however there appear to be pieces of it available on various websites. Some of the websites require memberships.
> 
> ...



Thanks Tom!


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## Ivan1GFP (Nov 4, 2020)

GregP said:


> I'm sure it was liquid back in WWII. Not so sure about today, but cannot speak for the state of it before it is exposed to air when a valve gets destroyed. Generally, I leave broken valves alone, and not just because they are not repairable.



Hello GregP,

I have seen a LOT of destroyed valves. A few of them have even come from cars that we owned.
One of the cars we bought was sold to us after the timing belt broke while the car was running on the highway.
Mr. Piston meet Mr. Valve..... The Pistons were not significantly damaged but the Valves were bent pretty badly.
My Dad mounted quite a few of them into the machine used for grinding valves and spun them to show me that a few that looked just fine were slightly bent.
Plenty of minor to seriously burned valves and various associated pieces were to be found because mechanics have a tendency to keep the more interesting looking destroyed pieces as souvenirs. I don't believe I ever saw one that looked like it once contained Sodium though. 

I am still pretty sure that even today the Sodium inside the valves are liquid. Sodium is a liquid at room temperature and the main purpose for it to be inside the valve is to conduct heat away from the head to reduce the likelihood of burned valves.

Some of the early shipboard nuclear reactors even used Sodium as a primary coolant for the reactor core.

Update:
Sodium: Liquid v Solid.... Maybe I wasn't as good in Chemistry as I thought.... <sigh>

-- Ivan.

-


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## Stig1207 (Nov 4, 2020)

So to strip 1500 pounds from the P-39, what should be removed?
USAF Historical Study No. 101
Report pgno. 90 (PDF pgno. 101)


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## ThomasP (Nov 4, 2020)

Hey IvanGFP,

re "Sodium is a liquid at room temperature"

Metallic sodium is solid at room temperatures. Melting point is about 208°F.

See "Sodium - Wikipedia" right hand column under "Physical Properties"

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## XBe02Drvr (Nov 4, 2020)

ThomasP said:


> Metallic sodium is solid at room temperatures. Melting point is about 208°F.


That's what they taught us in mech school.

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## windhund116 (Nov 4, 2020)

XBe02Drvr said:


> That's what they taught us in mech school.



IIRC, pure liquid sodium metal looks like Mercury (Hg).


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## Peter Gunn (Nov 4, 2020)

BiffF15 said:


> Peter,
> 
> Thank you! The numbers look fairly close (I don’t have them memorized). Did the Germans use Allied fuel to get these results? Did Allied fighters and bombers use the same grade fuel? I would guess it was all the same...
> 
> ...


Hey BiffF,

In the book the author only states that at times he had to wait for the correct high octane fuel before a flight, specifically with the P-47 and the P-51. I'd have to double check but I do believe he was using German fuel as he never makes any mention of using captured Allied Avgas. He was extremely impressed with the Mustang as were his comrades, his written opine was that the only (barely - his word) equal planes to the P-51B he tested were the FW-190D-9 and the Bf-109G-10.

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## Juha3 (Nov 4, 2020)

Ivan1GFP said:


> Hello Juha3,
> 
> My original statement regarding maximum speeds for the La 5FN was that anything from about 390 MPH to 403 MPH seems pretty reasonable and that they seemed to vary.
> What do you believe the altitude was that the aircraft achieved its maximum speed?
> ...



It varied between 5700 m (N 39211525 625 km/h) and 6200 m (N 39210466, 633 km/h) and one figure 634 km/h at 6250 m without info on the serial number and Gordon & Khazanov gives 620 km/h at 6150 m. I don't know are the figures compression corrected.


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## Juha3 (Nov 4, 2020)

Mike Williams said:


> Thanks Juha, I'll study on that chart a bit and try to figure out how the P-39 compares with US tests. The first question that comes to mind is - was the engine operated at lesser RPM, boost or both with the differing fuels. Looks like they were using Military power and I wonder what manifold pressure was used. Also wondering if it had external wing guns.
> 
> Hmmm, From: Pilot's Flight Operating Instructions for Army Model P-39Q-1 Airplane
> 
> ...



Yes, the max speeds at around 5000 m indicates the use of Military power, I don't have any specifics because I don't have the book, only many scans from its graphs and tables. But from Gordon's _Soviet Air Power in World War 2:_ P-39Q-10-BE Serial 42-20561 MTOW 3570 kg, max speed 467 km/h at SL, 598 km/h at 5300 m, time to 5000 m 6.4 min, 360 deg turning time, 20-21 sec, 1x37 mm + 4x12.7 mm.
P-39Q-25-BE Serial 43-2467 MTOW 3547 kg, max speed 462 km/h at SL, 586 km/h at 5400 m, time to 5000 m 6.2 min, 360 deg turning time, 19-20 sec, 1x37 mm + 2x12.7 mm.

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## Ivan1GFP (Nov 4, 2020)

Juha3 said:


> It varied between 5700 m (N 39211525 625 km/h) and 6200 m (N 39210466, 633 km/h) and one figure 634 km/h at 6250 m without info on the serial number and Gordon & Khazanov gives 620 km/h at 6150 m. I don't know are the figures compression corrected.



Hello Juha3,

The M-82FN engine installed in these aircraft had a critical altitude in high blower of only 4650 Meters.
Do you find it a bit odd that the aircraft would reach its maximum speed that much higher?
The altitude difference seems a bit much for ram effect.

- Ivan.


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## fubar57 (Nov 4, 2020)

Something similar to Post #1291, 561pgs..."USAAF in the South Pacific 1941-1942"

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## pbehn (Nov 4, 2020)

The valve stem in a sodium cooled valve was hollow with the sodium not filling the void, the sodium moved up and down the valve stem as the engine ran giving much more rapid heat transfer from the hottest to the coolest part.

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## windhund116 (Nov 4, 2020)

pbehn said:


> The valve stem in a sodium cooled valve was hollow with the sodium not filling the void, the sodium moved up and down the valve stem as the engine ran giving much more rapid heat transfer from the hottest to the coolest part.



Yeah. That is what I was taught by a mechanic. Convection action.


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## Juha3 (Nov 4, 2020)

Ivan1GFP said:


> Hello Juha3,
> 
> The M-82FN engine installed in these aircraft had a critical altitude in high blower of only 4650 Meters.
> Do you find it a bit odd that the aircraft would reach its maximum speed that much higher?
> ...



I don't know, I'm a historian by training without any formal technical training, being only interesting in also the technical side of warfare. One Soviet graph attached.


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## P-39 Expert (Nov 4, 2020)

Stig1207 said:


> So to strip 1500 pounds from the P-39, what should be removed?
> USAF Historical Study No. 101
> Report pgno. 90 (PDF pgno. 101)


Gosh, this report stated that lightened P-39Ks could fight up to 27000'. Only reduced by 600lbs. Wonder who came up with that idea?


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## Ivan1GFP (Nov 4, 2020)

P-39 Expert said:


> Gosh, this report stated that lightened P-39Ks could fight up to 27000'. Only reduced by 600lbs. Wonder who came up with that idea?



You need to read that entry again. The statement was that after reducing the weight, the P-39K had its SERVICE CEILING increased to 27,000 feet. It doesn't mean the aircraft could fight there. It just means the aircraft could finally GET THERE. I wonder how low the service ceiling was before weight was removed.

I can't quite read the number but it looks like either 630 or 650 pounds.

- Ivan.


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## GregP (Nov 4, 2020)

The weight would likely be the 30-cal wing guns and installation kits, plus a little extra. I did notice that the weight saved by changing the 37 mm cannon for a 50-cal was negligible and not worth the engineering effort. Removing the wing guns would not have affected the CG much, either.

The P-39C had a service ceiling of 33,300 feet, already comfortably above 27,000 feet.
The P-39D had a service ceiling of 31,100 feet, already comfortably above 27,000 feet.
The P-39N had a service ceiling of 35,900 feet, already comfortably above 27,000 feet.

The report cited was about P-39Ks, and I can't find a test report on a P-39K just now. I'm assuming it was as good as a P-39D and not better than a P-39N. *I am surmising that the P-39K could, in fact, get to 27,000 feet, but not in time to stop the Japanese raiders with the warning time they had available*.

Taking out the wing guns would have made it climb better, but not by all that much. But losing 650 pounds WOULD have made the climb slightly better at the expense of losing firepower. Sounds like what they wanted at the time, but I'm having trouble getting my brain around how a slightly better climb would allow them to get up to the bombers without knowing the warning time they had for the raids. We'd have to know their warning time to see how much climb difference would have resulted in a good outcome. But, it seems that whatever climb improvement they got, it made a difference.

It still would not have made the P-39 dogfight with a Zero at 27,000 feet (or anywhere else, for that matter), but it could give them a firing pass at the bombers.

This is an interesting report, but it doesn't have enough meat in it to make an intelligent analysis of what they removed to save 650 pounds or how much change in climb it made. The P-39K had a 1,325 hp Allison instead of a 1,200 hp unit, and removing the wing guns, installation kits, and ammunition was the likely source of most of the weight.

If you look at the P-39N (same engine hp), the rate of climb at 25,000 feet was 1940 fpm. From the data I have ...

The Allison should have been making about 1,050 hp at 15,000 feet, where it had a climb rate of 3,340 fpm at 7,274 pounds. If we remove 650 pounds, we get 6,624 pounds, where the climb rate SHOULD be about 3,668 fpm, an improvement of 327 fpm or 9.8%. The time to climb to 15,000 feet was 4.15 minutes. Shaving off 9.8% makes it close to 3.75 minutes. If we assume about a 9.8 % gain to 25,000 feet, we go from 8.04 minutes stock to 7.25 minutes when 650 pounds lighter. This is, admittedly, a 1st-order approximation and is likely a bit optimistic.

So, logically, a change of somewhere around 45 seconds to 27,000 feet made the difference. That assumes the P-39s were unopposed and could hit the bombers when they got there. Sounds a bit unlikely, but this report would indicate that it was the case.

All I can say is that if a change in climb of 45 seconds made the difference, then maybe removing the wing guns was a good answer. I just have never seen much indication they DID that on a large-scale basis in the USAAC/F in WWII.

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## GrauGeist (Nov 4, 2020)

Service Ceiling - means as high as it can fly with operational stability, not effectively engage and fight.
The same goes for the often mistaken Maximum Range, which means flying from Point "A" to Point "B", not Combat Radius, which is a much different range.

For example, the Fw190A-8 had a service ceiling of nearly 34,000 feet, but it was at a disadvantage in combat at those higher altitudes.


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## Ivan1GFP (Nov 4, 2020)

Hello GregP,

The P-39K and P-39D-2 used the V-1710-63 engine which performed pretty much the same as the V-1170-35 engine in P-39D above the 12,000 feet critical altitude. The superchargers were the same but the -63 could run more boost down low and that is where it gained its extra power.

From the combat reports that I have read, it appears that the P-39 in various models never seemed to perform quite as well in the field as specifications and test reports would indicate. Maybe this is yet another case.
Another possibility is that the P-39K was carrying a drop tank.

- Ivan.


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## Ivan1GFP (Nov 4, 2020)

Juha3 said:


> I don't know, I'm a historian by training without any formal technical training, being only interesting in also the technical side of warfare. One Soviet graph attached.
> View attachment 600747



Hello Juha3,

My credentials are fewer than yours.....
What document did that page come from? There are a few odd aspects of the M-82FN that I am interested in and perhaps I have the document you are referencing. I don't like to read through a bunch of Russian manuals unless I know I will find something.

From what we KNOW:
The critical altitude of the M-82FN was 4650 Meters.

From what various sources state:
The maximum speed has been given as low as 625 KPH and as high as 648 KPH.
The critical altitude for the La 5FN has been given to be as low as 5000 Meters and as high as 6250 Meters.

How do we reconcile all these?

Here is what I BELIEVE. (Emphasis on Believe but it seems to fit all the data points.)
With an engine making its best power at 4650 Meters, I believe a very good example of the La 5FN could reach 648 KPH at 5000 meters. This would be more typical of expectations for ram effect.
By 6000 Meters, its speed may have dropped to 635 KPH which is also pretty reasonable.
If you believe that speeds were 10 KPH slower at each altitude, I won't argue. Production quality did vary quite a bit.

- Ivan.


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## GregP (Nov 4, 2020)

Hi Ivan.

I show the P-39D with the V-1710-35. 1,150 hp at 12,000 feet and 3,000 rpm
I show the P-39K with the V-1710-63. 1,100 hp at 13,800 feet and 3,000 rpm. I am assuming it dropped about 50 hp from there at 15,000 feet. The P-39K with the -63 also had a WEP rating of 1,580 hp at 2,500 feet and 60" MAP, but that would not have still been in use at 27,000 feet since it was a 5 minute rating. I based my estimate on Military power, not WEP.

I fully realize that the P-39 was not considered a great airplane, but the performance of the P-39N at 15,000 feet from wwiiaircaftperformance shows 3,340 fpm climb. That's about P-51D territory. At 26,000 feet, a test on a P-51D shows 2,780 fpm climb. The P-39N shows 1,940 at 25,000 feet. Clearly, the P-51D is better up high.

But at 17,400 feet, the P-51D shows 2,965 fpm while the P-39N at 15,000 feet shows 3,340 fpm. Different story. Down near 15,000 feet, the P-39 is right in there with the P-51D. At least, the test airplane was. The dog of the group seems to be the P-39D which, for some unexplained reason, shows poor climb perfomance that was "recovered" in later models. That tells me there is something wrong with the P-39D test. I just don't quite know what it is and the interest level is dropping fast since the P-39 was never considered a great fighter by the U.S.A. ... only the Soviet Union loved it, and they did great with it.

Maybe we needed to look at their operations!


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## Ivan1GFP (Nov 4, 2020)

Hello GregP,

The big difference in the later models of the P-39 was that their superchargers were different.
They couldn't run the run the 70 inches Hg boost levels that the early (-35, -39, -63, -73) engines could without damage, but they also had higher critical altitudes.
For these early engines, WEP didn't matter past 12,000 feet because there wasn't enough capacity in the supercharger left to provide the extra boost. They could only provide boost for the Military rating up at 12,000 feet and boost dropped after that.

The engines in the P-39 were all single stage, single speed engines, so critical altitude was never very high in any version.

With the P-51D, you have a TWO Stage supercharger and at 17,400 feet, it still is WAY BELOW its critical altitude in high blower which I believe was around 21,000 to 22,000 feet but also way above its critical altitude in low blower which was only 8,500 feet.

- Ivan.


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## P-39 Expert (Nov 4, 2020)

GregP said:


> The weight would likely be the 30-cal wing guns and installation kits, plus a little extra. I did notice that the weight saved by changing the 37 mm cannon for a 50-cal was negligible and not worth the engineering effort. Removing the wing guns would not have affected the CG much, either.
> 
> The P-39C had a service ceiling of 33,300 feet, already comfortably above 27,000 feet. *Right, the South Pacific doc probably meant 27000' combat ceiling (climb 1000fpm) *
> The P-39D had a service ceiling of 31,100 feet, already comfortably above 27,000 feet.
> ...



Please expand above.

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## Peter Gunn (Nov 4, 2020)

GregP said:


> *SNIP*
> 
> The Allison should have been making about 1,050 hp at 15,000 feet, where it had a climb rate of 3,340 fpm at 7,274 pounds. If we remove 650 pounds, we get 6,624 pounds, where the climb rate SHOULD be about 3,668 fpm, an improvement of 327 fpm or 9.8%. The time to climb to 15,000 feet was 4.15 minutes. Shaving off 9.8% makes it close to 3.75 minutes. If we assume about a 9.8 % gain to 25,000 feet, we go from 8.04 minutes stock to 7.25 minutes when 650 pounds lighter. This is, admittedly, a 1st-order approximation and is likely a bit optimistic.
> 
> *SNIP


Waaaaaiitt...

I thought I read somewhere that for every pound of weight removed you got an extra 1.2fpm climb performance (as a guess).
Or 650lbs means 780fpm added (as a guess).

Now you come along with these "calculations" with all your fancy formulas and aviation knowledge and only show an increase of .50fpm, or .50307 to be more specific for removing 650lbs. What kind of shenanigans are these?

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## P-39 Expert (Nov 4, 2020)

GregP said:


> Hi Ivan.
> 
> I show the P-39D with the V-1710-35. 1,150 hp at 12,000 feet and 3,000 rpm
> I show the P-39K with the V-1710-63. 1,100 hp at 13,800 feet and 3,000 rpm. I am assuming it dropped about 50 hp from there at 15,000 feet. The P-39K with the -63 also had a WEP rating of 1,580 hp at 2,500 feet and 60" MAP, but that would not have still been in use at 27,000 feet since it was a 5 minute rating. I based my estimate on Military power, not WEP.
> ...



Please expand above.


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## GregP (Nov 4, 2020)

So, this P-39K shows a true airspeed of 353 mph at 25,000 feet, and the rate of climb is about 760 fpm or so. But, if you look at the P-39N test, at the same altitude, the rate of climb is 1,940 fpm and the speed is 370 mph.

Interesting, to say the least but, thinking of the attachment above and the statement that the P-39s could not reach 27,000 feet, the actual tests show ANY of the P-39s could have gotten to 27,000 feet, but the particular model of the airplane has a LOT to do with what the climb rate and top speeds are when you get there. I am left with the dictinct impression that my earlier premise was correct, the P-39 could get to 27,000 feet, but not within the time allowed for by the early warning system in the above report. In that case, perhaps removing the wing guns would actually make the mission possible. It would NOT make the P-39 a better mount against the Zero, maneuverability-wise, but could make it possible to actually intercept bombers at 27,000 feet and interrupt their mission.

Most Japanese bombing missions were NOT at 27,000 feet, if you go look at the after action reports that I have seen. Things don't always stay the same, and the Japanese apparently didn't always come in at low altitudes. At least the P-39 had a good cockpit heater!

Thank you Mike Williams for saving these performance test data charts and reports!  Nice to have test data when you look at specific questions.


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## P-39 Expert (Nov 4, 2020)

GregP said:


> So, this P-39K shows a true airspeed of 353 mph at 25,000 feet, and the rate of climb is about 760 fpm or so. But, if you look at the P-39N test, at the same altitude, the rate of climb is 1,940 fpm and the speed is 370 mph.
> 
> *Keep in mind that in the test the K was climbing at normal power 2600rpm and the N was climbing at combat power 3000rpm. The K was still under the 5 minute limit until mid 1942. After mid year 1942 the K would be able to climb at combat power 3000rpm for 15 minutes. K still wouldn't climb like the N since the N had a more powerful engine, but it would climb better than the test (3000rpm vs 2600rpm). The curved lines between 12500' and 15000' on the climb test attached shows the 5 minute mark when the rpm was reduced from 3000 to 2600. The blue dots estimate the climb rate at 3000rpm. That would show a climb rate of 1000fpm at 27000' with NO weight reduction. (The red dots are for the A6M2).*
> 
> ...


Please expand above.


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## GregP (Nov 4, 2020)

Found all these charts myself, but thanks for posting. It tells me the P-39 was exactly waht we all thought, basically a low-to medium altitude fighter. Once you get above mid-teens, it starts running out of power. Since single-stage engines do that, where did 66 pages of posts come from?

Cheers everyone.


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## Ivan1GFP (Nov 4, 2020)

GregP said:


> Found all these charts mysalef, but thanks for posting. It tells me the P-39 was exactly waht we all thought, basically a low-to medium altitude fighter. Once you get above mid-teens, it stats running out of power. Since single-stage engines do that, where did 66 pages of posts come from?
> 
> Cheers everyone.



Hello GregP,

Well, there are plenty of single stage but multiple SPEED or variable SPEED superchargers that do a lot better than that.
Most of the German fighters used single stage superchargers.
The single stage but two SPEED V-1650-1 installed in the P-40F and P-40L was a lot more capable at altitude than the single stage single SPEED Allison.

66 Pages of posts???

The Title for this thread should actually be the same as the Dr Seuss book:
"The Places You'll Go".
We seem to cover a lot of ground in this thread and you never know where we will end up next!

- Ivan.

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## Dash119 (Nov 4, 2020)

Ivan1GFP said:


> Hello GregP,
> 
> Well, there are plenty of single stage but multiple SPEED or variable SPEED superchargers that do a lot better than that.
> Most of the German fighters used single stage superchargers.
> ...


Any reference to Dr. Seuss gets a Bacon rating...

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## Peter Gunn (Nov 4, 2020)

66 Pages of still trying to turn a sow's ear into a silk purse.

Lots of coulda' shoulda' woulda' mumbo jumbo about trying to turn a mediocre low altitude fighter into a world beater.

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## GregP (Nov 4, 2020)

Perhaps it was more of trying to make the interim fill-in fighter perform a bit better since they were flying it anyway. "A bit better" by shedding sonme dubious weight ain't gonna' get you 1,000 fpm climb rate, even at critical altitude and below. But, it LOOKS like shedding some DID allow the airplane to make an interception where it couldn't before shedding the weight, assuming you read between the lines as they were intended to be read.

If the report REALLY says the P-39 could not GET to 27,000 feet, then I have to question the truth of it. Clearly, all variants could. So, I'm making the assumption that shedding the weight allowed it to make an intercept within a given time frame that it couldn't make before shedding the weight. While that seems logical, it wasn't much used by P-39 units in the Pacific as a tactic for perrformance enhancement.

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## windhund116 (Nov 4, 2020)

Peter Gunn said:


> 66 Pages of still trying to turn a sow's ear into a silk purse.
> 
> Lots of coulda' shoulda' woulda' mumbo jumbo about trying to turn a mediocre low altitude fighter into a world beater.



Isn't all of this more of a mental exercise than a reflection of history?

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## fubar57 (Nov 4, 2020)

Could go in the "What If" section

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## P-39 Expert (Nov 4, 2020)

Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.

The early P-39s (D/F/K/L) would have been competitive with anything in 1942 had they not been 800+lbs overweight, as the AAF finally figured out. Except the two stage Spitfires.

If the P-39 had received the two stage V-1710-93 in early 1943, it would have been competitive with pretty much everything. Not nearly as heavy as the P-63 and much earlier.

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## XBe02Drvr (Nov 5, 2020)

Hey guys, I'm back from my vacation from this thread, and notice it's grown a few pages. Just curious; when you all were discussing the weight differences between the P39C and D, did anybody bring up the added structural weight and moment of the elongated aft fuselage and enlarged tailfeathers of the D? The added moment would certainly require added weight forward (gearbox armor?) to keep the CG out of lomcevak land.

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## P-39 Expert (Nov 5, 2020)

XBe02Drvr said:


> Hey guys, I'm back from my vacation from this thread, and notice it's grown a few pages. Just curious; when you all were discussing the weight differences between the P39C and D, did anybody bring up the added structural weight and moment of the elongated aft fuselage and enlarged tailfeathers of the D? The added moment would certainly require added weight forward (gearbox armor?) to keep the CG out of lomcevak land.


So, just exactly how much longer was the D model than the C model?


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## P-39 Expert (Nov 5, 2020)

Peter Gunn said:


> 66 Pages of still trying to turn a sow's ear into a silk purse.
> 
> Lots of coulda' shoulda' woulda' mumbo jumbo about trying to turn a mediocre low altitude fighter into a world beater.


Actually 66 pages of me telling you that the 1942 P-39s (D/F/K/L) were way too heavy (836lbs) and could have climbed much better (1000fpm) if redundant/unneeded items were deleted, and showing you the official performance tests. 

And you all telling me that the 1000fpm difference in climb between the two planes was from a slightly different propeller of the same diameter, an inch or two more length, a fin fillet, phantom CG issues that weren't there in the test planes, and other irrelevant mumbo jumbo.

And a few pages of your personal firearms.

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## Stig1207 (Nov 5, 2020)

Gen. Harmon was unhappy with the performance of the P-400 over Guadalcanal; 67th Sqd had been roughly handled in it's first engagement, and in consequent engagements, the inability to get up to the altitude of the incoming bombers. The main reason being that the P-400, originally intended for the British, were equipped with a high pressure oxygen system; 'no supply of high pressure oxygen bottles were available om Guadalcanal' so they were forced to operate at low altitude (p. 85 of the report). There were other issues as well, even if the oxygen supply problem was solved, Harmon (and Vandegrift) did not consider the plane suitable as an interceptor and out-classed by the Zero. 

In the attachment I have highlighted the suggestion given Harmon that the P-39's enroute to New Caledonia could be stripped of some *1500* pounds (20% of it's operational weight, in the field ?!?) and pointed to Australia where ...'considerable success with P-39's against Zeros is being achieved'.

By Australia I guess was meant New Guinea, which I believe was the only scene of combat between P-39's and Zero's at this time. The P-39 units there were credited with 95 victories against Zero's (15 actual losses), so the percieved success was not all that 'considerable'.


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## Stig1207 (Nov 5, 2020)

GregP said:


> only the Soviet Union loved it, and they did great with it.



This is, imo, the main reason this thread is still going; the Soviets did better but maybe not great. I have earlier posted a link to actions over Roumania in 1944, where Soviet flown P-39's overclaimed massively. Here is a quote from another, this time from the Kuban in 1943:



> So, the total losses of the Messerschmitts amounted to exactly 103 ******* aircraft, including 42 destroyed and 61 damaged. Of these, only 27 "Messers" were destroyed in air battles and 23 more received various damage. In other words, Soviet fighter pilots, who during the battles in the Kuban were credited with more than 700 (!!!) "shot down" Me-109s (calculations are made on the basis of data from the book by M. Yu. Bykov), in reality, can celebrate victory over them only, exactly, in fifty cases. And, if the Germans exaggerated their successes, on average, 2.5 times, then ours increased this indicator, on average, up to 14 times, although there were exaggerations and much more.



Luftwaffe fighters in the sky of the Kuban

These not just P-39's, but they were involved and among the claimants are some of the big names, Rechkalov and Pokryshkin .

Also, the P-39's in New Guinea did great too against Zero's, if you go by the credited victories, per my post above.

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## Ivan1GFP (Nov 5, 2020)

fubar57 said:


> Could go in the "What If" section



Hello Fubar57,

I believe a much better place for this thread would have been the Religion section.
These discussions are looking a lot like religious arguments.
Creationism versus Evolution anyone?

- Ivan.

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## Juha3 (Nov 5, 2020)

Ivan1GFP said:


> Hello Juha3,
> 
> My credentials are fewer than yours.....
> What document did that page come from? There are a few odd aspects of the M-82FN that I am interested in and perhaps I have the document you are referencing. I don't like to read through a bunch of Russian manuals unless I know I will find something.
> ...



Hello Ivan
The docu, unfortunately I cannot recall where I got it, my memory is not as good as it was say 30 years ago and as a pensioner my procedures have became more sloppy. 

On La-5FNs, I must disagree, Russian authors clearly state that those speeds are max. speeds, and because the altitudes varied the question is not speeds at certain altitude. Some tables show max speed for both stages and also max speed at 5,000 m, for some reason Soviet authorities thought that 5,000 m is an important altitude, usually the climb times shown in Soviet WWII docus are to 5,000 m. And in the attached table you see that the speeds at 5,000 m is lower than the max speeds for 2nd stage. There is also the La-5FN proto with its 648 km/h max. speed, it achieved 622 km/h at 5,000 m.

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## Ivan1GFP (Nov 5, 2020)

Juha3 said:


> Hello Ivan
> The docu, unfortunately I cannot recall where I got it, my memory is not as good as it was say 30 years ago and as a pensioner my procedures have became more sloppy.
> 
> On La-5FNs, I must disagree, Russian authors clearly state that those speeds are max. speeds, and because the altitudes varied the question is not speeds at certain altitude. Some tables show max speed for both stages and also max speed at 5,000 m, for some reason Soviet authorities thought that 5,000 m is an important altitude, usually the climb times shown in Soviet WWII docus are to 5,000 m. And in the attached table you see that the speeds at 5,000 m is lower than the max speeds for 2nd stage. There is also the La-5FN proto with its 648 km/h max. speed, it achieved 622 km/h at 5,000 m.
> View attachment 600837



Hello Juha3,

There is only one stage in the supercharger, so we are really talking about first speed or second SPEED.
First speed hit its critical altitude at 1650 Meters.
Blower shift to Second speed happens at 4000 Meters.
Second speed hits its critical altitude at 4650 Meters.

Now, this is for "Military Power" or 1000 mm Hg @ 2400 RPM.
Although the supercharger cannot provide any additional boost past 4650 Meters, do you happen to know if some of these tests ran up to 2500 RPM (Take-Off RPM) at altitude?
Is it possible the superchargers were different in the prototypes?

It just seems quite unusual for an aeroplane to make its best speed at 5700 Meters to 6250 Meters when its maximum engine power was achieved at 4650 Meters.
Anyone more knowledgeable care to comment?

- Ivan.

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## Ivan1GFP (Nov 5, 2020)

Regarding the Tail Feathers on the P-39D versus P-39C:

P-39D actually did not come from the factory with the Fin Fillet.
The first model of the P-39 to come from the factory with the Fin Fillet was the P-39D-1 though many if not most P-39D were retrofitted with Fin Fillets later in their career.

- Ivan.

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## pbehn (Nov 5, 2020)

P-39 Expert said:


> Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.
> 
> The early P-39s (D/F/K/L) would have been competitive with anything in 1942 had they not been 800+lbs overweight, as the AAF finally figured out. Except the two stage Spitfires.
> 
> If the P-39 had received the two stage V-1710-93 in early 1943, it would have been competitive with pretty much everything. Not nearly as heavy as the P-63 and much earlier.


This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.

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## Peter Gunn (Nov 5, 2020)

P-39 Expert said:


> Actually 66 pages of me telling you that the 1942 P-39s (D/F/K/L) were way too heavy (836lbs) and could have climbed much better (1000fpm) if redundant/unneeded items were deleted, and showing you the official performance tests.
> 
> And you all telling me that the 1000fpm difference in climb between the two planes was from a slightly different propeller of the same diameter, an inch or two more length, a fin fillet, phantom CG issues that weren't there in the test planes, and other irrelevant mumbo jumbo.
> 
> And a few pages of your personal firearms.


ACTUALLY...

It's been a fair amount of those 66 pages of _*qualified*_ guys from the aviation industry saying that what you have been proposing (over and over and over ad infinitum ad nauseam) isn't that simple of an equation. That you would quibble about "3mph" when the real issue is the 25 horsepower it takes to get that 3mph and what that means in combat, even though THAT was explained to you (more than once).

Even then I could probably take your arguments seriously except then you come off with:


P-39 Expert said:


> Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.



Are you seriously contending that the P-39 was a match for the FW-190 or Bf-109 in the skies over Western Europe? Man Eaker, Spaatz and Arnold must have been either dullards or totally in cahoots with Republic, Lockheed and North American to make sure Bell got screwed over.

Sorry, but the proof is in the pudding, how many missions did the P-39 fly for the 8th AF? Or the 9th?

I believe the RAF flew one (1) mission and said "Nyet" and shipped them to the Soviets, ah but that's right, the Brits were in on the conspiracy to add weight to it and make it a dog.

Tell me again of it's stunning record in the SWP as it handily brought down Zero's by the fistful.

All said and done, don't take this as a dislike for you, hell, you posts have kept me in stitches for while now but obviously there's no way to enlighten you, so the best I got is a shoulder shrug and a "whatever dude".

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## Shortround6 (Nov 5, 2020)

XBe02Drvr said:


> Just curious; when you all were discussing the weight differences between the P39C and D


Tail feathers were pretty much the same but the C had two .30 cal guns and ammo in the nose (a bit further forward of the .50 cal guns) so several feet in front of the CG .but these were shifted to the wings and one more added on each side, Weight went up but the wing guns and ammo are pretty much on the CG, probably didn't do much for roll response though.


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## windhund116 (Nov 5, 2020)

Not sure about exact numbers, but I was under the impression that the kill ratio for the P39 variants, in the SWPA was around 1:1 against Imperial Japanese Navy and Army air foes. In the same time frame the F4F Wildcat was around 5:1.

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## GregP (Nov 5, 2020)

Hi Stig.

I'd really love to see a list of vetted German losses. I have an absolutely great list of German claims, both east and west, but have yet to see a vetted list of losses. Unless there is some reasonable check on it's accuracy, how would we know that this list with MANY fewer losses than Soviet claims wasn't "oversated," as the Soviet victories are allegedly so-overstated? Wouldn't the Germans have a vested interest in admitting fewer claims? Since we know the Germans built some 29,000 or more Bf 109s during WWII, and maybe 34,000 total including post-war, these had to be lost SOMEWHERE.

Not dismissing your link or your contention, just thinking about where the notion that many fewer Bf 109s were lost than claimed came from. The German operated as few as 19 He 100s and claimed they were in widespread squadron service ... to intinidate the world with propaganda. Why would we belive their loss figures are absolutely accurate? The Luftwaffe lied to Hitler about the level of their success for several years before he found out. Included in there are some loss figures that are well understated.

The Soviets claimed they destroyed more F-86s in Korea than we sent over. We KNOW how many were built, how many were sent, how many came back, how many we sold to other countries, and how many were still in service when we retired them, and the the Soviet Union and Chinese didn't shoot down as many Sabres as they later claimed. So, Soviet data is somewhat suspect, too. Is it likely that the overclaiming is limited to only victories, or is it more likely that losses were understated as well?

In the U.S.A., we only count losses in direct contact with enemy aircraft while in ongoing combat as combat losses. If some airplane got damaged, and then had an engine failure on the way home, we count that as an "operational loss," not a combat loss, even though the engine most likely would not have failed without the damage from combat. So, our loss figures, while pretty accurate in total, aren't exactly "squeaky clean" when it comes to combat losses in air-to-air combat, either.

Just saying we may never know what the real numbers were except to say that the data are a bit suspect.


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## Juha3 (Nov 5, 2020)

Ivan1GFP said:


> Hello Juha3,
> 
> There is only one stage in the supercharger, so we are really talking about first speed or second SPEED.
> First speed hit its critical altitude at 1650 Meters.
> ...



Hello Ivan
Of course, 2 hours sleep and too much on 60-series Merlins lol!
Igor Kopilow in his article on La-5s in feeniks 3/2014 says that during 1944 there were improvements in the supercharger air intake.

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## P-39 Expert (Nov 5, 2020)

Stig1207 said:


> Gen. Harmon was unhappy with the performance of the P-400 over Guadalcanal; 67th Sqd had been roughly handled in it's first engagement, and in consequent engagements, the inability to get up to the altitude of the incoming bombers. The main reason being that the P-400, originally intended for the British, were equipped with a high pressure oxygen system; 'no supply of high pressure oxygen bottles were available om Guadalcanal' so they were forced to operate at low altitude (p. 85 of the report). There were other issues as well, even if the oxygen supply problem was solved, Harmon (and Vandegrift) did not consider the plane suitable as an interceptor and out-classed by the Zero.
> 
> In the attachment I have highlighted the suggestion given Harmon that the P-39's enroute to New Caledonia could be stripped of some *1500* pounds (20% of it's operational weight, in the field ?!?) and pointed to Australia where ...'considerable success with P-39's against Zeros is being achieved'.
> 
> By Australia I guess was meant New Guinea, which I believe was the only scene of combat between P-39's and Zero's at this time. The P-39 units there were credited with 95 victories against Zero's (15 actual losses), so the percieved success was not all that 'considerable'.


Weight was actually only reduced by 600+lbs which allowed the P-39K to fight at 27000'. Best Japanese bombers G4M came in at 18000'-22000'.


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## P-39 Expert (Nov 5, 2020)

pbehn said:


> This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.


Please go to wwiiaircraftperformance.org and look at the P-39N climb numbers. Then look at the P-51A, Typhoon, P-47(1943), Hellcat, Corsair, Spitfire V, FW190 and Zero climb numbers. P-39N substantially outclimbed all those planes in 1943.

I never said to remove any cannons, only the wing .30cal MGs. Only armor I recommend removing is the nose armor.


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## P-39 Expert (Nov 5, 2020)

Peter Gunn said:


> ACTUALLY...
> 
> It's been a fair amount of those 66 pages of _*qualified*_ guys from the aviation industry saying that what you have been proposing (over and over and over ad infinitum ad nauseam) isn't that simple of an equation. That you would quibble about "3mph" when the real issue is the 25 horsepower it takes to get that 3mph and what that means in combat, even though THAT was explained to you (more than once). *3mph. *
> 
> ...


Please expand above.


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## pbehn (Nov 5, 2020)

P-39 Expert said:


> I never said to remove any cannons, only the wing .30cal MGs. Only armor I recommend removing is the nose armor.


And I didn't say remove all guns just the cannons, the Spitfire didn't need nose armour it had an engine there, it needed armour behind the pilot and that was specified standard equipment.


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## P-39 Expert (Nov 5, 2020)

pbehn said:


> And I didn't say remove all guns just the cannons, the Spitfire didn't need nose armour it had an engine there, it needed armour behind the pilot and that was specified standard equipment.


Your point being?


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## pbehn (Nov 5, 2020)

P-39 Expert said:


> Your point being?


The P-39 needed nose armour as a military machine, the Spitfire would certainly have been better in every way without cannon, speed climb and roll would have all been improved, but they were mainly concerned with those few seconds when the pilot presses the fire button, the reason it is called a fighter and not a Reno racer.

Quote"I believe the RAF flew one (1) mission and said "Nyet" and shipped them to the Soviets, ah but that's right, the Brits were in on the conspiracy to add weight to it and make it a dog. *They certainly added a lot of weight that certainly wasn't needed, and that certainly affected its performance."*
This (your bold), as I said, has been the issue from the start, you contend that the weight was not needed, but the RAF disagreed and the pilots who were relieved to switch to Spitfires that had that equipment on them did also.


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## jmcalli2 (Nov 5, 2020)

Mike Williams said:


> What's the book? Some operational history and pilot's accounts of the P-39 would be most welcome here instead of the endless drama over trivial matters and ongoing personal smears.



P-39: "P-39/P-400 vs A6M2/3 ZERO-SEN New Guinea 1942" by Michael John Claringbould

P-38: " 'Twelve to One' V Fighter Command Aces of the pacific" by Tony Holmes

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## Stig1207 (Nov 5, 2020)

P-39 Expert said:


> Weight was actually only reduced by 600+lbs which allowed the P-39K to fight at 27000'. Best Japanese bombers G4M came in at 18000'-22000'.



Yes, but it was suggested, (I can't make out exactly what the abbreviation given in the text is, due to the poor quality) that 1500 pounds could be stripped.


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## GregP (Nov 5, 2020)

P-39 Expert,

There is not a 1,000 fpm climb difference between a P-39C and D, despite the test. For more than the 3rd time, there is something wrong with the P-39D test climb data. And the difference, whatever it is, is due to several factors, not just weight.

If you remove just nose armor, you move the CG aft. We already covered that. You could take off that way, sure. But, if you expended your ammunition, you might be a fatal danger, maybe not. Depends on what gets removed and the weight and balance of that partcular airplane.

Regardless of a sentence in a report, you can't remove 1,500 pounds from a P-39 and still have a fighter aircraft that flies, regardless of what the memo says. There isn't 1,500 pounds of stuff to be removed. There is only 193 pounds of armor including the windscreen glass. There is only 331 pounds of 30-cal guns and ammo. Where are you going to get the rest of your 1,500 pounds, huh?

You showed us a memo report on removing the wing 30's, but that was NOT a common practice, even in the South Pacific. While it might have worked for some specific missons at specific bases, it was not adopted widely. Let it go guy. The P-39, in these specific cases, didn't score a significant number of victories to get the practice noticed and emulated by anyone else.

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## P-39 Expert (Nov 5, 2020)

pbehn said:


> The P-39 needed nose armour as a military machine, the Spitfire would certainly have been better in every way without cannon, speed climb and roll would have all been improved, but they were mainly concerned with those few seconds when the pilot presses the fire button, the reason it is called a fighter and not a Reno racer.
> 
> Quote"I believe the RAF flew one (1) mission and said "Nyet" and shipped them to the Soviets, ah but that's right, the Brits were in on the conspiracy to add weight to it and make it a dog. *They certainly added a lot of weight that certainly wasn't needed, and that certainly affected its performance."*
> This (your bold), as I said, has been the issue from the start, you contend that the weight was not needed, but the RAF disagreed and the pilots who were relieved to switch to Spitfires that had that equipment on them did also.


P-39 did not need nose armor, Spitfire did not have armor for it's nose reduction gear, no other plane had armor for it's reduction gear. Bell theater tech reps never saw one instance where the nose armor was struck by an an enemy shell.


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## fubar57 (Nov 5, 2020)

Did the Bell tech reps check the P-39s that were shot down to see if the nose armour was struck by enemy shells? Aircraft that survive rarely have damage to vital parts

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## P-39 Expert (Nov 5, 2020)

GregP said:


> P-39 Expert,
> 
> There is not a 1,000 fpm climb difference between a P-39C and D, despite the test. For more than the 3rd time, there is something wrong with the P-39D test climb data. And the difference, whatever it is, is due to several factors, not just weight.
> 
> ...


Expand above.


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## fubar57 (Nov 5, 2020)

Not all VVS squadrons removed the wing guns


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## pbehn (Nov 5, 2020)

P-39 Expert said:


> P-39 did not need nose armor, Spitfire did not have armor for it's nose reduction gear, no other plane had armor for it's reduction gear. Bell theater tech reps never saw one instance where the nose armor was struck by an an enemy shell.





fubar57 said:


> Did the Bell tech reps check the P-39s that were shot down to see if the nose armour was struck by enemy shells? Aircraft that survive rarely have damage to vital parts


Beat me too it Fubar, in fact that was a branch of military statistical research. There is a "sampling error" here in that those who didn't return are not included causing "survivorship bias", it is actually a fairly convincing argument for more armour. Bullet Holes in Bombers: Operations Research and Management Science Applied to Marketing

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## GregP (Nov 5, 2020)

The gearbox armor was 71 pounds out of 172 pounds of armor exculding the windscreen glass. If you add in the wing guns and wing gun ammuntion, that is only 503 pounds, not 1,500 pounds. Is there something you are missing here?

The empty weight of the P-39Q was 5,684 pounds. Then you add windscreen glass, armor, guns and ammunition, oil, fuel, pilot, and parachute. The total useful load was 1,886 pounds, guy, and the pilot was 200 pounds of the 1,886. Remove the pilot and you have 1,686 pounds of armor, guns, ammo, oil, and fuel. We need the oil. We need the fuel. If we don;t have guns and ammo, we might as well not take off. If we ditch ALL the armo, we only save 172 pounds.

Either you are not reading the weight and balance, not reading the posts, or are just being a troll.

Which is it? Help us out here. If you want to remove anything, identify it specifically. Please don't suggest leaving out the oil or fuel or pilot.

If I remove ALL the armor, I can take off just fine. But if I shoot all the ammunition, then I am out of CG aft, not good. Are you understanding this?


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## Mike Williams (Nov 5, 2020)

jmcalli2 said:


> P-39: "P-39/P-400 vs A6M2/3 ZERO-SEN New Guinea 1942" by Michael John Claringbould
> 
> P-38: " 'Twelve to One' V Fighter Command Aces of the pacific" by Tony Holmes



Thanks jmcalli2!

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## Stig1207 (Nov 5, 2020)

GregP said:


> The gearbox armor was 71 pounds out of 172 pounds of armor exculding the windscreen glass. If you add in the wing guns and wing gun ammuntion, that is only 503 pounds, not 1,500 pounds. Is there something you are missing here?
> 
> The empty weight of the P-39Q was 5,684 pounds. Then you add windscreen glass, armor, guns and ammunition, oil, fuel, pilot, and parachute. The total useful load was 1,886 pounds, guy, and the pilot was 200 pounds of the 1,886. Remove the pilot and you have 1,686 pounds of armor, guns, ammo, oil, and fuel. We need the oil. We need the fuel. If we don;t have guns and ammo, we might as well not take off. If we ditch ALL the armo, we only save 172 pounds.
> 
> ...



Post #1346 Greg; it's not P-39Expert advocating removing 1500 pounds, it's from the USAF Historical Study no. 101 and is suggested by some presumably official organisation or command to Gen. Harmon.
As you point out, and why I brought up, is that it doesn't seem at all possible , from what I have read in this thread.

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## GregP (Nov 5, 2020)

My mistake, P-39 Expert.

Slap me. More than one in here likely wants to do just that ...


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## Stig1207 (Nov 5, 2020)

jmcalli2 said:


> P-39: "P-39/P-400 vs A6M2/3 ZERO-SEN New Guinea 1942" by Michael John Claringbould


Somewhere in the depths of this thread FLYBOYJ posted a report by Lt. Col. Boyd Wagner, wherein he reported on the April 30 combat, and from his (and probably his pilots) perspective 4 Zeros were shot down (3 by Boyd, 1 by Greene), one Zero was actually lost. Boyd wrote that 3 P-39's were hit by Zero's and forcelamded due to cooling leaks, but all 3 pilots survived. Four P-39's were lost, Boyd makes no mention of Durand, who didn't return and remains MIA.
I reponded to the post here #261 with links to the fate of the respective planes and pilots on Pacific Wrecks.

To summarize, Pacific Wrecks has 1 forcelanded damaged by AAA (Andres), 1 sustained damage during combat and forcelanded (Brown); 1 short of fuel and likely lost, forcelanded (Bevlock); Durand last seen bailing out, MIA.

Claringbould has on p. 38, Andres as a focus, and writes that Andres (his own words) was chased by a Zero which he outran, but also ran short of fuel and bellied in18 miles SE of Buna.

On p.42-43, describing the combat, Claringbould has Andres forced to land due to damaged coolant system and both Brown and Bevlock forcelanding low on fuel. Andres was one of the few to witness Durands demise, but no mention of him bailing out.

So four differing versions, two from the same book.

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## Stig1207 (Nov 5, 2020)

GregP said:


> My mistake, P-39 Expert.
> 
> Slap me. More than one in here likely wants to do just that ...



Not me, I'm tired of standing in queues.

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## GregP (Nov 5, 2020)

Tough to be precise when your sources disagree with themselves, isn't it?

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## P-39 Expert (Nov 5, 2020)

fubar57 said:


> Did the Bell tech reps check the P-39s that were shot down to see if the nose armour was struck by enemy shells? Aircraft that survive rarely have damage to vital parts


The only planes that they could check would be the ones that returned to base, right? They did not say that no nose armor had ever been struck, just that they had not seen one that had been struck.


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## P-39 Expert (Nov 5, 2020)

fubar57 said:


> Not all VVS squadrons removed the wing guns


No, I'm sure they didn't. I'm also sure that those that kept the wing guns didn't climb as well as those that discarded them.


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## fubar57 (Nov 5, 2020)

Your words, "*They removed the wing guns and IFF radio equipment, not the voice radios. They removed the .30s and beat the Luftwaffe, but the AAF never did remove the .30s.*" You would be more correct to say some removed the wing guns. Your words make it sound like it was across the entire airforce

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## P-39 Expert (Nov 5, 2020)

GregP said:


> The gearbox armor was 71 pounds out of 172 pounds of armor exculding the windscreen glass. If you add in the wing guns and wing gun ammuntion, that is only 503 pounds, not 1,500 pounds. Is there something you are missing here?
> 
> The empty weight of the P-39Q was 5,684 pounds. Then you add windscreen glass, armor, guns and ammunition, oil, fuel, pilot, and parachute. The total useful load was 1,886 pounds, guy, and the pilot was 200 pounds of the 1,886. Remove the pilot and you have 1,686 pounds of armor, guns, ammo, oil, and fuel. We need the oil. We need the fuel. If we don;t have guns and ammo, we might as well not take off. If we ditch ALL the armo, we only save 172 pounds.
> 
> ...


You are talking about the P-39Q, but the AAF South Pacific doc was talking about the P-39K. It said that they removed 600+lbs. The print is blurry, I think it said 650lbs but the middle number is illegible. So what did they remove?

Back in the footnotes it describes the P-39K as having 4 .30s in the wings with 1000rounds per gun. Remove those and you save about 400lbs if you include the mounts, chargers, heaters and ammunition boxes. Keep the voice radio and remove the IFF radio which AHT said weighed 110-130lbs. That radio was in the tail so now you need to remove the nose armor, about 71lbs. Now we're pretty close to 600lbs and still within CG. Now this is just a suggestion, I have no way of knowing exactly what was removed. 

With 1000rounds per gun for the .30s the normal P-39K weighed about 7850lbs. Reduce that by the 650lbs and the K model now weighs about 7200lbs. with the 37mm cannon, two .50cal MGs, self sealing fuel tanks, armor plate/glass protection for the pilot and oil tank and a voice radio. The AAF South Pacific doc said that the K would now fight at 27000', probably meaning it would still climb at 1000fpm. Certainly adequate for intercepting Japanese bombers and fighting the A6M2. 

Should have been done much earlier.


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## P-39 Expert (Nov 5, 2020)

fubar57 said:


> Your words, "*They removed the wing guns and IFF radio equipment, not the voice radios. They removed the .30s and beat the Luftwaffe, but the AAF never did remove the .30s.*" You would be more correct to say some removed the wing guns. Your words make it sound like it was across the entire airforce


One of our friends on this board found a statistic that something like 85% of the Russian P-39s had their wing guns removed. And I'm sure that some of the AAF P-39s had their wing guns removed, but not many. 

Do you nitpick every generalization?  Or just the ones I make?


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## fubar57 (Nov 5, 2020)

Just make correct statements and all is good regardless of who you are

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## pbehn (Nov 5, 2020)

fubar57 said:


> Just make correct statements and all is good regardless of who you are


Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.


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## BiffF15 (Nov 5, 2020)

pbehn said:


> Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.



It‘s very difficult to tell the altitude of another airplane that’s more than a few miles away. The difficulty lies in the true horizon line isn’t visible to the eye. The one you see is at the edge of your visual acuity, not the true line. With that in mind, guys tend to use the one we see and use that as level with us. It’s below and by how much varies with the range away from us the target aircraft is. In the Eagle the HUD displays the true horizon line, and it’s about 2” above the visible line.

Airliners have Traffic Collision Avoidance System (TCAS) and in my airliner displays difference in altitude of other aircraft as plus or minus in thousands of feet (and hundreds if close enough IIRC).

Cheers,
Biff

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## pbehn (Nov 5, 2020)

BiffF15 said:


> It‘s very difficult to tell the altitude of another airplane that’s more than a few miles away. The difficulty lies in the true horizon line isn’t visible to the eye. The one you see is at the edge of your visual acuity, not the true line. With that in mind, guys tend to use the one we see and use that as level with us. It’s below and by how much varies with the range away from us the target aircraft is. In the Eagle the HUD displays the true horizon line, and it’s about 2” above the visible line.
> 
> Airliners have Traffic Collision Avoidance System (TCAS) and in my airliner displays difference in altitude of other aircraft as plus or minus in thousands of feet (and hundreds if close enough IIRC).
> 
> ...


They are human senses, touching a straw bale with your shoulder going through a chicane at 90MPH at Carnaby feels a lot faster than blasting down the back straight at Silverstone at 130 MPH which at times felt oddly like standing still. When I have been high up in a civilian aircraft looking at others I could see, when the ground is 40,000 ft below you have no idea whether they are higher or lower and as far as I know they were probably not at the same height (due to safety protocols) but most of them seemed to be.

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## GregP (Nov 5, 2020)

It has BEEN expanded on, P-39 Expert. Nothing more is needed.


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## Ivan1GFP (Nov 5, 2020)

P-39 Expert said:


> Weight was actually only reduced by 600+lbs which allowed the P-39K to fight at 27000'. Best Japanese bombers G4M came in at 18000'-22000'.



Service ceiling of 27,000 feet does NOT mean the P-39K can fight there. It just means that it can FINALLY reach 27,000 feet.

- Ivan.

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## XBe02Drvr (Nov 6, 2020)

P-39 Expert said:


> the K would now fight at 27000', probably meaning it would still climb at 1000fpm. Certainly adequate for intercepting Japanese bombers and fighting the A6M2.


Whoever wrote that document must have been a number crunching ground pounder, certainly not a combat pilot. While a P39 that had been able to straggle it's way up to 27000' could probably manage an insipid diving firing pass on bombers several thousand feet below, there's no way a P39 with its single stage, single speed Allison, its inefficient airfoil, and its higher wing loading is going to fight effectively against an A6M2, with its higher lift, lower drag, and lighter loaded wing, despite the fact its engine performance will be degraded as much as the Cobra's.
Standard format flight test reports will give you all sorts of interesting numbers, but they can't measure combat performance. Aggressively maneuvering an airplane near its service ceiling is a lot like driving a car fast around a race course on glare ice. The margin of control is pretty slender. It was a lot of fun, back in the day.

PS: How many pages does it take for a thread to qualify for the EPIC category? Think this one will make it someday?

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## wuzak (Nov 6, 2020)

P-39 Expert said:


> Back in the footnotes it describes the P-39K as having 4 .30s in the wings with 1000rounds per gun. Remove those and you save about 400lbs if you include the mounts, chargers, heaters and ammunition boxes. Keep the voice radio and remove the IFF radio which AHT said weighed 110-130lbs. That radio was in the tail so now you need to remove the nose armor, about 71lbs. Now we're pretty close to 600lbs and still within CG. Now this is just a suggestion, I have no way of knowing exactly what was removed.



AHT says 110-130lb for "Other (Radio)". It does not say that was for IFF only, but for radio equipment, which may be more than one type and multiple units, the difference in weight is possibly due to differences in the types being carried.

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## P-39 Expert (Nov 6, 2020)

Ivan1GFP said:


> Service ceiling of 27,000 feet does NOT mean the P-39K can fight there. It just means that it can FINALLY reach 27,000 feet.
> 
> - Ivan.


As has been explained before, a standard P-39D/F/K/L at normal weight before any weight reduction had a service ceiling of over 30000' as defined by still climbing at 100fpm. The term "service ceiling" was obviously being used incorrectly in the AAF South Pacific report. Why would the General be pleased that a P-39K that had been lightened by 650lbs have a "service ceiling" below that of a standard P-39K? The meaning of "service ceiling" in the report obviously referred to an altitude at which the plane could fight.


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## P-39 Expert (Nov 6, 2020)

wuzak said:


> AHT says 110-130lb for "Other (Radio)". It does not say that was for IFF only, but for radio equipment, which may be more than one type and multiple units, the difference in weight is possibly due to differences in the types being carried.


AHT actually says "Misc Equip-Radio" 129lbs in the "Basic Weight" section along with the guns and armor plate. In the "Empty Weight" section "Communication" is listed at 80lbs. Leads me to believe "communication" was the voice radio.


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## Milosh (Nov 6, 2020)

P-39 Expert said:


> As has been explained before, a standard P-39D/F/K/L at normal weight before any weight reduction had a service ceiling of over 30000' as defined by still climbing at 100fpm. The term "service ceiling" was obviously being used incorrectly in the AAF South Pacific report. Why would the General be pleased that a P-39K that had been lightened by 650lbs have a "service ceiling" below that of a standard P-39K? The meaning of "service ceiling" in the report obviously referred to an altitude at which the plane could fight.



... because the atmospherics are different in different parts of the world. That is why you see "adjusted to standard atmosphere" of data sheets.

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## P-39 Expert (Nov 6, 2020)

pbehn said:


> Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.


And a larger reduction in weight would give a larger increase in climb, right?


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## P-39 Expert (Nov 6, 2020)

pbehn said:


> This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.


According to the tests, the P-39N (available from Nov 1942) outclimbed the Griffon Spitfire and was about the same speed. The N would substantially outclimb the P-51A (same engine) and was very close in top speed. The N outclimbed the 1943 Thunderbolt, Corsair and Hellcat substantially at 20000', just like I said. The P-39N was equipped with full armament including the wonderful four .30s for the tests, no weight reduction needed.


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## pbehn (Nov 6, 2020)

P-39 Expert said:


> And a larger reduction in weight would give a larger increase in climb, right?


Yes, strap a pilot to the engine and it will take off vertically, give him a colt revolver to confront the enemy. It is clear you think climb is everything, you even consider the P-39 to be superior to all other planes in service in 1943 because of it, it is no longer a serious discussion. No one in 1943 saw the P-39 as an answer to anything except possibly the need for trainers. I see you have re booted the discussion back to the start with "the British put unnecessary weight on it". Every possible thing that can be discussed has been on this and other threads. Yes taking weight off improves performance, taking guns and armour off a military machine does not improve performance because it becomes less of a military machine, quoting survivor bias is no answer to the issue.

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## Peter Gunn (Nov 6, 2020)

If nothing else, this thread has been good for garnering positive ratings such as BACON - WINNER - AGREE and of course plain old LIKEs.


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## pbehn (Nov 6, 2020)

Peter Gunn said:


> If nothing else, this thread has been good for garnering positive ratings such as BACON - WINNER - AGREE and of course plain old LIKEs.


This topic has been discussed longer than the P-39 was in service.

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## Peter Gunn (Nov 6, 2020)

A few (dozen?) pages back I believe Wes brought up that the difference on one P-39 test where the propeller had a different model number, I believe that some here poo pooed that a bit as not seeming to be relevant.

I was looking into P-40 data this morning (an aircraft I consider superior to the P-39 for several reasons) and found this, it's been a while since I did much Excel work so I just did a couple of screen shots. Hopefully they are the same size. I call attention to the RoC FPM columns on this table and what an influence just a different prop can have on performance.







*And here's one further down with a V-1650-1 Packard - Merlin*

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## SaparotRob (Nov 6, 2020)

Peter Gunn said:


> If nothing else, this thread has been good for garnering positive ratings such as BACON - WINNER - AGREE and of course plain old LIKEs.


Does a thread starter get an award for opening a thread that gets over a thousand posts or something? I know nothing about aeronautical engineering and even I’m recognizing terms and concepts I had no idea about.

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## P-39 Expert (Nov 6, 2020)

Peter Gunn said:


> A few (dozen?) pages back I believe Wes brought up that the difference on one P-39 test where the propeller had a different model number, I believe that some here poo pooed that a bit as not seeming to be relevant.
> 
> I was looking into P-40 data this morning (an aircraft I consider superior to the P-39 for several reasons) and found this, it's been a while since I did much Excel work so I just did a couple of screen shots. Hopefully they are the same size. I call attention to the RoC FPM columns on this table and what an influence just a different prop can have on performance.
> 
> ...


Yes, these are gigantic differences in performance. 4.5mph in speed from the slowest to the fastest, and 80fpm in climb at 15000'. That's going to make up for a *1000fpm *climb rate difference.

Not too concerned about the P-40F tests since neither the P-39C nor D had a Merlin engine. But the standard propeller had within 1mph of the best speed and 40fpm of the best climb. 

Please note that even with the Merlin engine the P-40F was still slower than the P-39D/F/K/L. Climb was about the same at combat power.


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## fubar57 (Nov 6, 2020)

Never go near the whales

​

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## XBe02Drvr (Nov 6, 2020)

Milosh said:


> ... because the atmospherics are different in different parts of the world. That is why you see "adjusted to standard atmosphere" of data sheets.


Ever hear of "density altitude"? The warmer and more humid the air, the more your performance suffers.
Standard atmosphere is 69°F/15°C at MSL, 29.92" Hg, 65% RH. This is what aircraft performance numbers are corrected to. Now fly your Supercobra from a South Pacific island where the ground temp is pushing 90°F, the RH is 90+%, and the lapse rate through the altitudes behaves accordingly, and your single speed, single stage Allison, WAY above its critical altitude, isn't going to give your inefficient symmetrical airfoil Supercobra anywhere near the observed performance your "standardized" test reports would lead you to expect.
I used to see 1,000 FPM climb performance differences between a July afternoon and predawn on a January morning on the same routes at the same altitudes with the same planes. BUF -> BOS, we'd be level at FL 250 before passing ROC in January, and nearly to SYR before we got up there in July. We would also see significant climb rate deterioration on individual aircraft as the engines aged.

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## Peter Gunn (Nov 6, 2020)

P-39 Expert said:


> Yes, these are gigantic differences in performance. 4.5mph in speed from the slowest to the fastest, and 80fpm in climb at 15000'. That's going to make up for a *1000fpm *climb rate difference.
> *And over 300' at 28k - I can cherry pick stats too.*
> 
> Not too concerned about the P-40F tests since neither the P-39C nor D had a Merlin engine. But the standard propeller had within 1mph of the best speed and 40fpm of the best climb.
> ...


As they say, please expand.

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## P-39 Expert (Nov 6, 2020)

Peter Gunn said:


> As they say, please expand.


Okay, how are you going to make up the other 700fpm? Phantom CG problems? A tail fin fillet? The extra inch of fuselage length? 

Think it was maybe the 836lbs of extra weight?


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## P-39 Expert (Nov 6, 2020)

XBe02Drvr said:


> Ever hear of "density altitude"? The warmer and more humid the air, the more your performance suffers.
> Standard atmosphere is 69°F/15°C at MSL, 29.92" Hg, 65% RH. This is what aircraft performance numbers are corrected to. Now fly your Supercobra from a South Pacific island where the ground temp is pushing 90°F, the RH is 90+%, and the lapse rate through the altitudes behaves accordingly, and your single speed, single stage Allison, WAY above its critical altitude, isn't going to give your inefficient symmetrical airfoil Supercobra anywhere near the observed performance your "standardized" test reports would lead you to expect.
> I used to see 1,000 FPM climb performance differences between a July afternoon and predawn on a January morning on the same routes at the same altitudes with the same planes. BUF -> BOS, we'd be level at FL 250 before passing ROC in January, and nearly to SYR before we got up there in July. We would also see significant climb rate deterioration on individual aircraft as the engines aged.


And the A6M2 would be flying through the same atmosphere, right? With it's single stage engine? WAY above it's critical altitude? 

And isn't the air temperature the same all over the world at 25000'?


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## GregP (Nov 6, 2020)

I can't believe I'm still trying, but the P-39D test must have been done at normal power (2600 rpm), not military power (3000 rpm). 

That is one out of several possible explanations, and they DID say they got the power from a tech order unrelated to the test, not a torque meter in the airplane.

It wouldn't be the first flight test to be misrecorded and likely won't be the last.

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## P-39 Expert (Nov 6, 2020)

GregP said:


> I can't believe I'm still trying, but the P-39D test must have been done at normal power (2600 rpm), not military power (3000 rpm).
> 
> That is one out of several possible explanations, and they DID say they got the power from a tech order unrelated to the test, not a torque meter in the airplane.
> 
> It wouldn't be the first flight test to be misrecorded and likely won't be the last.


The P-39C test was at normal power 2600rpm for climb after the 5 minute limit, just like the D model.

Standard performance test at Wright Field where most all the fighters were tested. Please don't blame the test, that's all we really have to compare the planes.

It may have been the 836lbs extra weight in the D model.


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## XBe02Drvr (Nov 6, 2020)

P-39 Expert said:


> And the A6M2 would be flying through the same atmosphere, right?


Righto, old chap, and better able to handle it for the aerodynamic reasons mentioned in my previous post (#1371). Any way you slice it, combat between single stage single speed fighters in the upper twenties is going to be a sort of slow motion minuet, rather than high energy rock n' roll, as neither plane has much stall margin or excess power, and there's not much G available for maneuvering. The P39 will bleed energy faster in any maneuver due to its less efficient wing in that regime.

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## XBe02Drvr (Nov 6, 2020)

P-39 Expert said:


> And isn't the air temperature the same all over the world at 25000'?


If it were, do you think we'd have the jetstream?

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## GrauGeist (Nov 6, 2020)

P-39 Expert said:


> And isn't the air temperature the same all over the world at 25000'?


Simple answer: No.

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## FLYBOYJ (Nov 6, 2020)

P-39 Expert said:


> And the A6M2 would be flying through the same atmosphere, right? With it's single stage engine? WAY above it's critical altitude?
> 
> *And isn't the air temperature the same all over the world at 25000'?*



Today at 24,000'

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## Milosh (Nov 6, 2020)

P-39 Expert said:


> Not too concerned about the P-40F tests since neither the P-39C nor D had a Merlin engine. But the standard propeller had within 1mph of the best speed and 40fpm of the best climb.


It is NOT about the engine being used BUT the difference ROC with different props.


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## Ivan1GFP (Nov 6, 2020)

P-39 Expert said:


> As has been explained before, a standard P-39D/F/K/L at normal weight before any weight reduction had a service ceiling of over 30000' as defined by still climbing at 100fpm. The term "service ceiling" was obviously being used incorrectly in the AAF South Pacific report. Why would the General be pleased that a P-39K that had been lightened by 650lbs have a "service ceiling" below that of a standard P-39K? The meaning of "service ceiling" in the report obviously referred to an altitude at which the plane could fight.



Perhaps there were other conditions in theater or about the aircraft that made the normal expected performance unachievable.
I find it very unlikely that this many professionals would let a mistake like this pass without comment.

My SUSPICION is that the P-39K was carrying a drop tank.

- Ivan.


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## P-39 Expert (Nov 6, 2020)

FLYBOYJ said:


> Today at 24,000'
> 
> View attachment 600936


Total variance less than 20 degrees? About 17 to about 37?


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## P-39 Expert (Nov 6, 2020)

XBe02Drvr said:


> Righto, old chap, and better able to handle it for the aerodynamic reasons mentioned in my previous post (#1371). Any way you slice it, combat between single stage single speed fighters in the upper twenties is going to be a sort of slow motion minuet, rather than high energy rock n' roll, as neither plane has much stall margin or excess power, and there's not much G available for maneuvering. The P39 will bleed energy faster in any maneuver due to its less efficient wing in that regime.


I'm not buying the less efficient wing. I put that in there with the fin fillet, one inch extra length fuselage and phantom CG issues.

Think it might be the 836lbs?

Come on guys, its the weight. We all know it. And the more weight the less climb. The AAF South Pacific report pretty much proved it.


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## FLYBOYJ (Nov 6, 2020)

P-39 Expert said:


> Total variance less than 20 degrees? About 17 to about 37?



Yes - 20 degrees C (36F) and when computing performance calculations, it will make a difference.


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## P-39 Expert (Nov 6, 2020)

Ivan1GFP said:


> Perhaps there were other conditions in theater or about the aircraft that made the normal expected performance unachievable.
> I find it very unlikely that this many professionals would let a mistake like this pass without comment.
> 
> My SUSPICION is that the P-39K was carrying a drop tank.
> ...


The chart says that even with a drop tank the "service ceiling" was over 27000'. Wish the report had been more specific.

I think most would be inclined to believe that the P-39K could handle itself at 27000' with the weight reduction. General was pleased with the results.

Reducing the weight increased the climb rate and ceiling just like I have been telling you.


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## P-39 Expert (Nov 6, 2020)

FLYBOYJ said:


> Yes - 20 degrees C (36F) and when computing performance calculations, it will make a difference.





FLYBOYJ said:


> Yes - 20 degrees C (36F) and when computing performance calculations, it will make a difference.


Okay, how much would that 20 degrees affect the performance of a P-39K or A6M2 at 24000'?


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## Ivan1GFP (Nov 6, 2020)

P-39 Expert said:


> The chart says that even with a drop tank the "service ceiling" was over 27000'. Wish the report had been more specific.
> 
> I think most would be inclined to believe that the P-39K could handle itself at 27000' with the weight reduction. General was pleased with the results.



You are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling.
General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.



P-39 Expert said:


> Reducing the weight increased the climb rate and ceiling just like I have been telling you.



I don't believe anyone is disputing that reducing weight will usually increase climb rate and ceiling. The question is really how much effect they will have. We just don't believe your "calculations" have any basis in reality and that there were other more important factors that differed between the P-39C and P-39D tests.

Just to humour you for a second, what do your calculations tell you the increase in climb rate would be at 25,000 feet and please show your work. What do your calculations show the increase in service ceiling would be?

- Ivan.

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## FLYBOYJ (Nov 6, 2020)

P-39 Expert said:


> Okay, how much would that 20 degrees affect the performance of a P-39K or A6M2 at 24000'?



That would be indicated in performance charts based on the flight testing of both aircraft.


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## P-39 Expert (Nov 6, 2020)

FLYBOYJ said:


> That would be indicated in performance charts based on the flight testing of both aircraft.


I was wanting a number, like 3mph or 50fpm.


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## P-39 Expert (Nov 6, 2020)

Peter Gunn said:


> As they say, please expand.


So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?

The differences in the other props were in the 200fpm range, barely measurable.

We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?


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## pbehn (Nov 6, 2020)

P-39 Expert said:


> So, they throw one really crappy propeller (Rotol) in with the other 4


Rotol props needed a Spitfire behind them to produce a decent climb performance up to 40,000 feet.

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## Ivan1GFP (Nov 6, 2020)

P-39 Expert said:


> We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?



Very often, two different propellers have characteristics that give them advantages under different conditions.
A propeller's efficiency curve is not constant but varies with speed and RPM. Usually this is simplified to just Advance Ratio (J).
The simplest difference is that one propeller may have an advantage in climb while the other is better for maximum speed or cruising speed.

You seem to be hung up on climb rate. The US Army folks were much more interested in maximum speed over just about everything else when it came to fighters.

- Ivan.

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## XBe02Drvr (Nov 6, 2020)

P-39 Expert said:


> I'm not buying the less efficient wing.


Whether you buy it or not doesn't change the fact that a wing of that design with that loading is just not going to perform as efficiently in air that thin with so little excess power available as the more lightly loaded, better airfoil, higher L/D Zero wing will.
The only planes that could match or exceed the Zero in combat performance at those altitudes were those of later generations that had significantly more surplus power available at altitude.

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## Peter Gunn (Nov 6, 2020)

P-39 Expert said:


> So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?
> 
> The differences in the other props were in the 200fpm range, barely measurable.
> 
> We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?


On my office wall behind my desk I have a 3' x 3' picture of an F-86 Sabre. When I have to explain to someone whatever issue is at hand and I get that blank stare, I point to the Sabre, as in the point went over your head like this Sabre.

Perhaps... the Air Corps was oh, I don't know, TESTING different propellers? I mean why else would they use the same plane weighted the same with different props? It does happen.

Also, if Wes talks about wing efficiency I wouldn't really argue with him unless you're a pilot with a sh!t ton of hours or a aerodynamic engineer, just my opinion of course.


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## P-39 Expert (Nov 6, 2020)

Ivan1GFP said:


> You are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
> As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling. *As has been explained to you, the "service ceiling" of a standard P-39K was over 30000' BEFORE any weight reduction. They reduced the weight by 650lbs and increased the combat ceiling to 27000.*
> General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.
> 
> ...





Ivan1GFP said:


> You are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
> As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling.
> General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.
> 
> ...


Expand above


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## fubar57 (Nov 6, 2020)

Armchair experts have way more knowledge than anyone

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## P-39 Expert (Nov 6, 2020)

XBe02Drvr said:


> Whether you buy it or not doesn't change the fact that a wing of that design with that loading is just not going to perform as efficiently in air that thin with so little excess power available as the more lightly loaded, better airfoil, higher L/D Zero wing will.
> The only planes that could match or exceed the Zero in combat performance at those altitudes were those of later generations that had significantly more surplus power available at altitude.


Absolutely nothing wrong with a symmetrical airfoil. The A6M2 will be gasping for air just like the P-39K at 27000'. Sure it has a much lower wing loading, and will be more maneuverable at 27000' just like it is at 10000'. But it won't climb any better and it sure won't dive any better.


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## pbehn (Nov 6, 2020)

fubar57 said:


> Armchair experts have way more knowledge than anyone


Especially in the technical ideas supermarket, if you don't like it for some reason, you don't buy it, and that, is that.


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## Ivan1GFP (Nov 6, 2020)

P-39 Expert said:


> I'm not buying the less efficient wing.



You can buy the less efficient wing or not, but just consider that if it was such a great idea, then why didn't anyone else use such a simple idea as a symmetrical airfoil?
From what I have read in various accounts, the symmetrical airfoil seemed to be a very quickly passing fad in the 1930's that some people thought might give an advantage in speed.
Actually one other major US type DID use a symmetrical airfoil and its results were at least as bad as those in the Airacobra.
The B-26 Marauder used a symmetrical airfoil and a tiny wing to start and was a relative speed demon for the time. It had to lose that in stages as more practical requirements became more important and in its last model ended up with the entire (now muh larger) wing offset several degrees from the fuselage to provide additional lift at more practical speeds.

When interviewed after the war, Peyton Magruder, the designer admitted that the symmetrical wing was probably not a good idea.

Symmetrical airfoils make sense if the plane is intended to do a lot of inverted flying as might be expected of an aerobatic plane.

This is why I have been commenting from the start that one of the fixes to the Airacobra should have been replacing the outer wing sections with something with a more modern airfoil such as the NACA 23000 series that everyone else was using. Bell clearly knew about it because the wing tips of the Airacobra were NACA 23000 series airfoils.
They were meant to prevent the outboard sections at the ailerons from stalling when the rest of the wing stalled. In this manner, the pilot could retain lateral control. The problem is that if there was a bit of yaw, the entire inboard symmetrical section of one side would stall at the same time and flip the plane.

- Ivan.


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## P-39 Expert (Nov 6, 2020)

Peter Gunn said:


> On my office wall behind my desk I have a 3' x 3' picture of an F-86 Sabre. When I have to explain to someone whatever issue is at hand and I get that blank stare, I point to the Sabre, as in the point went over your head like this Sabre.
> 
> Perhaps... the Air Corps was oh, I don't know, TESTING different propellers? I mean why else would they use the same plane weighted the same with different props? It does happen.
> 
> Also, if Wes talks about wing efficiency I wouldn't really argue with him unless you're a pilot with a sh!t ton of hours or a aerodynamic engineer, just my opinion of course.


Yes the AAF tested different propellers on the P-40F. Obviously some were better than others. The P-39 had an Allison engine. The props tested on the Allison P-40E were all remarkably similar in performance, both in speed and climb. One would think that would be the better comparison in this case.

If you all are done patting yourselves on the back, can any of you divide 1000 by 836?


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## FLYBOYJ (Nov 6, 2020)

P-39 Expert said:


> I was wanting a number, like 3mph or 50fpm.



Again, that would be shown on a performance chart that includes temperature and density altitude into the equation. I believe most if not all US WW2 fighters computed at "Standard Altitude" (59F at sea level 29.92"HG).


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## DerAdlerIstGelandet (Nov 6, 2020)

Milosh said:


> ... because the atmospherics are different in different parts of the world. That is why you see "adjusted to standard atmosphere" of data sheets.



Not just different parts of the world. It can very anywhere. Different times of the day. Different seasons. Different anything really.

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## XBe02Drvr (Nov 6, 2020)

Ivan1GFP said:


> Very often, two different propellers have characteristics that give them advantages under different conditions.


Case in point: a prop with the same blade count but a higher propulsive surface area (a "paddle blade", if you will). In the denser air at lower altitudes the added rotational drag of the blades will keep trying to slow RPM, driving the governor to "fine" the propeller pitch to keep RPM constant, reducing the efficiency of converting HP to thrust. This is not so much an issue with a behemoth like the R2800, as the P47 so impressively proved. But where the paddle comes into it's own is at altitude, where the thinner air reduces drag, allowing more efficient pitch angles, but also demanding more propulsive surface area to convert the limited available HP into thrust.
Any non-turbocharged Allison fighter equipped with a more paddle oriented prop would show a deficit in low altitude performance in trade for improved performance at upper levels compared to the stock setup.

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## Dash119 (Nov 6, 2020)

P-39 Expert said:


> Okay, how are you going to make up the other 700fpm? Phantom CG problems? A tail fin fillet? The extra inch of fuselage length?
> 
> Think it was maybe the 836lbs of extra weight?





P-39 Expert said:


> If you all are done patting yourselves on the back, can any of you divide 1000 by 836?



Am I supposed to divide 1000 by 836, or 700 by 836?


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## Milosh (Nov 6, 2020)

P-39 Expert said:


> So, they throw one really crappy propeller (Rotol) in with the other 4 and it's 330fpm less than the standard prop. Wonder why the HP was so low on that one?
> 
> The differences in the other props were in the 200fpm range, barely measurable.
> 
> We're talking about the P-39C and D, and two props by the same manufacturer, same diameter, different blade (if it was really different). Why would the AAF specify a different prop if it hurt climb rate that much?


I suggest you look at the Me109K which was tested with one prop but used a different prop for serial production. Iirc one was best in climb and the other for speed.


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## GregP (Nov 6, 2020)

I'm inclined to desist.

I hope I can still be taught some new tricks since we're about the same age.

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## XBe02Drvr (Nov 6, 2020)

GregP said:


> I'm inclined to desist.
> 
> I hope I can still be taught some new tricks since we're about the same age.


Me too.


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## BiffF15 (Nov 6, 2020)

P-39 Expert said:


> Yes the AAF tested different propellers on the P-40F. Obviously some were better than others. The P-39 had an Allison engine. The props tested on the Allison P-40E were all remarkably similar in performance, both in speed and climb. One would think that would be the better comparison in this case.
> 
> If you all are done patting yourselves on the back, can any of you divide 1000 by 836?



P39 Expert,

I think all of us can do division. The point you are ignoring is there is more to it than that. Something was different between those two tests, and it wasn’t just the weight. Peter Gun published the German test results for the Mustang, and they recorded 1’48” to 10000, or a little better than 5k per/min initial climb rate. Should I use that going forward as the standard climb rate for the P51D? If not, why?

As for wing behavior at altitude, please understand that they are not linear and the results at one altitude will not be the same at another. The F16 can easily out turn an F15 at low altitude, however there is an altitude that they become even, and then it swings in favor of the F15. And at all altitudes the F15 has a thrust to weight deficit compared to the F16. Again, all things are not linear nor can they all be extrapolated based on one data point.

I don’t know what type of car you drive, or if when you get on it you can tell the difference in performance between a hot humid day and a cool day. But in the aviation world, as Wes pointed out earlier, it makes a huge difference. I’ve taken off in an F15C on a cool day, full afterburner, and had 540 KIAS at the end of the runway. I’ve taken off on the same runway, in the same configuration, on a hot day, and had 100 KIAS less. Temp makes a huge difference. 

Several guys have passed on reasons they suspect the test you are hanging your hat on is flawed. It doesn’t fit. The reason there are some times barbs passed out in here is because you are being shown that 1+1+1=3, yet you have a piece of paper that says 1+1=3 and you won’t budge. And those last three words is why this thread is 71 pages deep so far.

Cheers,
Biff

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## Ivan1GFP (Nov 6, 2020)

P-39 Expert said:


> *As has been explained to you, the "service ceiling" of a standard P-39K was over 30000' BEFORE any weight reduction. They reduced the weight by 650lbs and increased the combat ceiling to 27000.*



As has been explained to YOU, Those test results are under standard conditions or corrected to standard conditions.
Today happens to be a reasonably cool Fall day and Temperature is in the low 60's or not too far off standard temperature of 59 degrees Fahrenheit. Most of this Summer was way above that.
How many nice cool 59 degree days do you think you will find in the SWPA? What do you think happens when you run the same aeroplane in 110 degree temperatures? Do you think performance gets better?

If you are calling 27,000 feet the new combat ceiling, you are simply making things up.



P-39 Expert said:


> *This has been explained to you before. The difference in climb rate between the two virtually identical (except weight) planes was 1000fpm at 10000'. The difference in weight of the two planes was 836lbs. Divide 1000' by 836lbs and you get 1.2fpm per pound of weight. That means if you reduce the weight of the P-39D by 300lbs the climb rate improves by 360fpm. If you add 200lbs to the P-39C then you decrease the climb rate by 240fpm. That's at 10000'. *



You have ABSOLUTELY NO EVIDENCE that the two planes were "virtually identical".
On the other hand, you have quite a lot of evidence that SOMETHING, most likely engine power or thrust was significantly different between the two aircraft. As GregP pointed out, the Power Required for the P-39D didn't even match well with what it was doing in its climb at higher altitudes.

Now how does your 1.2 fpm per pound rule translate to higher altitudes and improved service ceiling????



P-39 Expert said:


> *No amount of slightly different propellers (of the same diameter by the same manufacturer), an inch in length, fin fillet, symmetrical airfoil, adjustments to standard atmosphere or ANY OTHER FACTOR is going to make a difference of 1000fpm climb except almost a half ton of weight. The planes were virtually identical except for 836lbs weight.*



Again, you make the assertion that the planes were virtually identical except you have no evidence that was true.
There certainly were external aerodynamic differences such as the .30 cal MG in the Cowl, the .30 Cal MG in the Wings.
I am not convinced that there was any extra length between the C and D models.
Most of the other factors you brought up are from a different discussion and not relevant here.

As for the Propeller, Your statement really tells us that you know nothing about propellers.
Take a look at the propellers on the Curtiss P-40. I believe the majority of them were made by Curtiss Electric and I believe all were 11 feet 0 inches in diameter. The blade designs are quite different and their performance is different.

You have been told that the engine outputs listed in the P-39D test do not match the climb performance and given evidence that you choose to ignore.
Any of these other factors alone would make the planes NOT identical.

- Ivan.

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## Ivan1GFP (Nov 6, 2020)

Juha3 said:


> Hello Ivan
> Of course, 2 hours sleep and too much on 60-series Merlins lol!
> Igor Kopilow in his article on La-5s in feeniks 3/2014 says that during 1944 there were improvements in the supercharger air intake.



Hello Juha3,

There were some pretty obvious improvements between the La 5F and La 5FN.
If these were improvements to the La 5FN, they do not seem to have translated to the later La 7 which shows the same critical altitude for its M-82FN engine.
The La 9 manual lists some slightly different statistics though.....

- Ivan.


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## Juha3 (Nov 6, 2020)

Ivan1GFP said:


> Hello Juha3,
> 
> There were some pretty obvious improvements between the La 5F and La 5FN.
> If these were improvements to the La 5FN, they do not seem to have translated to the later La 7 which shows the same critical altitude for its M-82FN engine.
> ...



Hello Ivan
The sc air intake mods or more specifically mods in the sc air intake duct were inside -5FN production run. And because in La-7 the supercharger air intake was completely different, from the wing roots, so it was completely new design.


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## Dash119 (Nov 6, 2020)




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## Peter Gunn (Nov 6, 2020)

P-39 Expert said:


> Yes the AAF tested different propellers on the P-40F. Obviously some were better than others. The P-39 had an Allison engine. The props tested on the Allison P-40E were all remarkably similar in performance, both in speed and climb. One would think that would be the better comparison in this case.
> 
> If you all are done patting yourselves on the back, can any of you divide 1000 by 836?


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## SaparotRob (Nov 6, 2020)

Peter Gunn said:


> View attachment 600957


Sweet!

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## XBe02Drvr (Nov 6, 2020)

Dash119 said:


>



"And the carousel goes round and round,
and the painted ponies go up and down,"*
all in the same flight path, all with identical rates of climb and descent, regardless of each one's gross weight. Doesn't that prove the point?
*Apologies to Joni Mitchell


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## GregP (Nov 6, 2020)

Nice pic of the Planes of Fame F-86F.

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## DerAdlerIstGelandet (Nov 6, 2020)

I think this thread has run its course everyone. There is no point. There is no getting through to people who have no desire to listen.

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## Dash119 (Nov 6, 2020)

Yes, but is has been entertaining...


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## XBe02Drvr (Nov 6, 2020)

Dash119 said:


> Yes, but is has been entertaining...


...and educational to everyone except the one most in need. Thanks, guys.

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## fubar57 (Nov 6, 2020)

Hey....let's start a new P-39 thread. It'll be swell

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## ThomasP (Nov 6, 2020)

Hey GregP,

FWIW when I do the math it appears the power settings and ROC for P-39D S/N 41-6722 are correct.

However, the values for P-39C S/N 40-2988 cannot be correct - at least not for a sustained climb at the power setting and weight listed. My math says that the AC can do 3270 ft/min at 6680 lbs with 1160 BHP. (Don't know if the 3270 as opposed to 3720 is an indication of anything, could just be a coincidence.)

The only way I can get the sustained 3720 ft/min ROC is if the engine is putting out ~1300 BHP, or If you accelerate to Vmax at SL and go into a zoom climb at max power, then divide the height gained before you have to reduce power by the time it took to reach said height. I suspect the latter is what they did.


Hey P-39 Expert,

This is not an attack on the quality of the P-39. I too think that the P-39 got an unfairly poor reputation in common history.

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## Peter Gunn (Nov 7, 2020)

GregP said:


> Nice pic of the Planes of Fame F-86F.


Thanks, thought it'd be a nice tip of the hat to you while referencing my post #1409. 

She is a beauty.

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## Milosh (Nov 7, 2020)

Not all airplanes are the same. Two consecutive a/c off the assembly line will have different performances. They all must be within a certain performance tolerance, of say +/-5%. P-39 Expert, I will let you do the math.


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## P-39 Expert (Nov 7, 2020)

Ivan1GFP said:


> You are quoting performance under standard conditions. As has been explained to you, there is no evidence these were "standard" conditions and the greatest likelihood is that the conditions were much less than optimal.
> As for being "inclined to believe", you are welcome to believe what you want as you tend to anyway, but that does not change the contents of the document which states that 27,000 feet was a service ceiling.
> General Harmon should have been pleased with this experiment; it actually worked! The other experiments did not work out nearly as well.
> 
> ...


Double post.


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## P-39 Expert (Nov 7, 2020)

Milosh said:


> Not all airplanes are the same. Two consecutive a/c off the assembly line will have different performances. They all must be within a certain performance tolerance, of say +/-5%. P-39 Expert, I will let you do the math.


3720fpm x 5% = 186fpm maximum deviation. That's a long way from 1000fpm.


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## P-39 Expert (Nov 7, 2020)

FLYBOYJ said:


> Again, that would be shown on a performance chart that includes temperature and density altitude into the equation. I believe most if not all US WW2 fighters computed at "Standard Altitude" (59F at sea level 29.92"HG).


Okay. The average high temperature for the hottest month on Guadalcanal is 88 degrees at sea level and average low temperature is 73 degrees.
Average high for the hottest month in Dayton, OH (Wright Field) is 84 degrees, average low is 65 degrees.

How much will speed and climb be degraded at Guadalcanal if the test was done in Dayton?


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## Ivan1GFP (Nov 7, 2020)

P-39 Expert said:


> Okay. The average high temperature for the hottest month on Guadalcanal is 88 degrees at sea level and average low temperature is 73 degrees.
> Average high for the hottest month in Dayton, OH (Wright Field) is 84 degrees, average low is 65 degrees.
> 
> How much will speed and climb be degraded at Guadalcanal if the test was done in Dayton?



Depends on if the test results are corrected for STP which they usually are.

- Ivan.


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## FLYBOYJ (Nov 7, 2020)

P-39 Expert said:


> Okay. The average high temperature for the hottest month on Guadalcanal is 88 degrees at sea level and average low temperature is 73 degrees.
> Average high for the hottest month in Dayton, OH (Wright Field) is 84 degrees, average low is 65 degrees.
> 
> How much will speed and climb be degraded at Guadalcanal if the test was done in Dayton?



You will have to factor in air pressure (as mentioned) and understand DENSITY ALTITUDE

Let's start here;

Density altitude - Wikipedia

In the P-39N flight manual I found this:







Notice the note at the bottom of the chart (my red circle). Unfortunately on the climb data the % for each 10C (50F) above 0C (32F) free air temp (circled in yellow) is missing.


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## FLYBOYJ (Nov 7, 2020)

FLYBOYJ said:


> You will have to factor in air pressure (as mentioned) and understand DENSITY ALTITUDE
> 
> Let's start here;
> 
> ...



From the P-39 L/K 10% for every 20F over 32F

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## FLYBOYJ (Nov 7, 2020)

P-39 Expert said:


> How much will speed and climb be degraded at Guadalcanal if the test was done in Dayton?



So to answer your question - *you can lose 28% climb time combat load, no head wind *according to the way I read the 2nd chart*. *

*Why this is removed from the P-39Q flight manual - I don't know???*


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## Simon Thomas (Nov 7, 2020)

ThomasP said:


> However, the values for P-39C S/N 40-2988 cannot be correct - at least not for a sustained climb at the power setting and weight listed. My math says that the AC can do 3270 ft/min at 6680 lbs with 1160 BHP. (Don't know if the 3270 as opposed to 3720 is an indication of anything, could just be a coincidence.)
> 
> The only way I can get the sustained 3720 ft/min ROC is if the engine is putting out ~1300 BHP, or If you accelerate to Vmax at SL and go into a zoom climb at max power, then divide the height gained before you have to reduce power by the time it took to reach said height. I suspect the latter is what they did.


When I did the calc with an f of 3.77929, e of 1.56299 & prop eff of 0.81 (Perkins & Hage Fig 3-20b), I got an ROC of 3706 ft/min.
e and f calculated per Prof Rogers "Finding e & f from GPS flight test data." Prof Rogers


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## GregP (Nov 7, 2020)

Hi ThomasP,

I used Aerodynamics for Naval Aviators. There is a free pdf download at: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80t-80.pdf .
If you look on page 154, there is a formula for Rate of Climb: RC = 33,000 * [(Pa - Pr) / W], where RC = Rate of Climb (fpm), Pa = power available (hp), Pr = power required for level flight (hp), W = weight (lbs).

Since I had tests and some data, I could plug in a known rate of climb at a known altitude and a known power (hp) and back into the required hp for level flight.

Let's look at the P-39C. At 10,000 feet, the rate of climb is 3,720 fpm. An Allison V-1710-35 makes 1,150 hp at 12,000 feet and the airplane is at a weight of 6,689 lbs. It just so happens we have data for 10,000 feet. Rate of climb is 3,720 fpm. Calculating backwards, the power required for level flight at that altitude is 396 hp. Personally, I'd expect the power required for level flight to go up as the altitude goes up becasue there is less air density, so the wing has to "work harder." By work harder, I mean a slightly higher angle of attack, and that creates more induced drag, requiring more power.

Now, I go to 20,000 feet and I have 1,530 fpm, same weight (for ballpark estimates, anyway). The table says 675 hp from the Allison. The power required for level flight is 365 hp, which is logical to me. Suppose I play P-39 Expert's game and assume the weight dropped by 350 lbs and I'm still at 20,000 feet. Using the same numbers as just above, the expected rate of climb would be 1,614 fpm, a gain of 84 fpm.

Now, let's look at the P-39D. Same engine. At 10,000 feet, the rate of climb shows 2,720 fpm and the rest of the data is the same except 7,525 lbs. I calculate Pr to be 530 hp. First, that is very strange because the two airplanes are so similar. The P-39D should not require 1/3 more power in level flight. Nevertheless, let's go to 20,000 feet. Same 675 hp available, same 7,525 lbs. I calculate Pr to be 378 hp! Somehow, it takes much less power to fly at 20,000 feet in thin air than it does at 10,000 feet in much thicker air?

No way. Something is very strange.

Now, go back to the 10,000 feet for the P-39D and assume about an equal difference between power required for the P-39D as for the P-39C. For the P-39C, the power required changed by about 30 hp between 10,000 feet and 20,000 fet. So, I take the P-39D power required at 20,000 feet ( 378 hp) and add 30 hp (408 hp) and calculate the expected rate of climb at 1,150 hp to be 3,254 fpm. That is significantly different from 2,720 fpm. If I next plug in the achieved rate of climb (2,720 fpm), I see the power avilable was only 1,028 hp and not 1,150.

Coincidentally, the normal power at 10,000 feet for the V-1710-35 at 2,600 rpm is 1,000 hp.

On the whole, it looks to me as if the P-39D test was likely carried out at Normal power and not military power. Again, if I lose the 350 lbs that P-39 Expert is wanting to lose, the expected rate of climb at 1,150 hp would go from 3,254 fpm to 3,413 fpm, a gain of 159 fpm. The differences between the P-39C and P-39D can be propeller, a sour engine, or any of many factors. But, it should NOT climb at only 2,720 fpm at 10,000 feet with 1,150 hp avaialble.

I am using the formula from Aerodynamics for Naval Aviators because most of the formulas were developed and checked for military-type airplanes with military type horsepower piston engines. There's the right way, the wrong way, and the Navy way. But the Navy doesn't make too many aircraft design calculation mistakes.

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## XBe02Drvr (Nov 7, 2020)

GregP said:


> Personally, I'd expect the power required for level flight to go up as the altitude goes up becasue there is less air density, so the wing has to "work harder." By work harder, I mean a slightly higher angle of attack, and that creates more induced drag.


Yes, there's an increased induced (and parasite) drag effect due to increased AoA, but isn't that more than compensated for by reduced total drag from the significantly lower air density? I've read AfNA too.


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## XBe02Drvr (Nov 7, 2020)

P-39 Expert said:


> Okay. The average high temperature for the hottest month on Guadalcanal is 88 degrees at sea level and average low temperature is 73 degrees.
> Average high for the hottest month in Dayton, OH (Wright Field) is 84 degrees, average low is 65 degrees.
> 
> How much will speed and climb be degraded at Guadalcanal if the test was done in Dayton?


Properly done, it doesn't matter whether the test is done in Dayton, Guadalcanal, or Shangri La. The test report doesn't quote raw data, it quotes observed performance mathematically corrected to standard atmosphere. Without standard conditions you have no basis for comparison of aircraft at different times and places.
So your P39D pilot taking off from Henderson Field at 88°F, 29.82"Hg, and 95%RH has no reason to expect his tired, patched, high time mount to match the performance numbers printed on his Wright Field test report. Dream on.

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## GregP (Nov 7, 2020)

Hi XBe02Drvr,

For top speed, you are correct. 

But for power required to maintain level flight at Vx, I'd expect the required power to go up as you go higher. The rate of climb test is not a top speed test and is run mostly at whatever best rate of climb airspeed is. I'd say it's somehwere around 1.4 * stall speed and slightly increases as you climb, and the power required to maintain level flight at Vx increases, too, as you climb.

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## fubar57 (Nov 7, 2020)

Well now.....lets see if someone who has never flown agrees with you guys or not......................................

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## P-39 Expert (Nov 7, 2020)

FLYBOYJ said:


> So to answer your question - *you can lose 28% climb time combat load, no head wind *according to the way I read the 2nd chart*. *
> 
> *Why this is removed from the P-39Q flight manual - I don't know???*


I believe the chart says add 10% to elapsed climbing time for every 20 degrees above 32 degrees. Guadalcanal averages 81 degrees. 81 less 32 = 49 degrees. 49 degrees divided by 20 degrees is 2.4min. Adding 2.4min to 14.5min to 25000' is 16.9min. Normal climb 14.5min averages 1724fpm. Adjusted climb 16.9min averages 1479fpm. Difference is 244fpm. 

Still not quite 1000fpm. It's the weight.


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## FLYBOYJ (Nov 7, 2020)

P-39 Expert said:


> I believe the chart says add 10% to elapsed climbing time for every 20 degrees above 32 degrees. Guadalcanal averages* 81 degrees.* 81 less 32 = 49 degrees. 49 degrees divided by 20 degrees is 2.4min. Adding 2.4min to 14.5min to 25000' is 16.9min. Normal climb 14.5min averages 1724fpm. Adjusted climb 16.9min averages 1479fpm. Difference is 244fpm.
> 
> Still not quite 1000fpm. It's the weight.



You mentioned 88F in your original post.

*You're reading/ using the chart wrong as well as doing the math wrong!!*

_"49 degrees divided by 20 degrees is 2.4min."_

*Wrong!*

*"10% for every 20 degrees"! 49 degrees = 24% NOT 2.4 minutes!*

*YOU ADD ON 24% TO THE CLIMB TIME!*

_ALSO_

It's broken down in segments and the rate of climb changes. Chart edited in blue and yellow boxes.


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## FLYBOYJ (Nov 7, 2020)

P-39 Expert said:


> I believe the chart says add 10% to elapsed climbing time for every 20 degrees above 32 degrees. Guadalcanal averages 81 degrees. 81 less 32 = 49 degrees. 49 degrees divided by 20 degrees is 2.4min. Adding 2.4min to 14.5min to 25000' is 16.9min. Normal climb 14.5min averages 1724fpm. Adjusted climb 16.9min averages 1479fpm. Difference is 244fpm.
> 
> Still not quite 1000fpm. It's the weight.



And on this chart it gives you the time! It's not "the weight," it's *"DENSITY ALTITUDE."  *This is why these charts were made!


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## FLYBOYJ (Nov 7, 2020)

P-39 Expert said:


> I believe the chart says add 10% to elapsed climbing time for every 20 degrees above 32 degrees. Guadalcanal averages 81 degrees. 81 less 32 = 49 degrees. *49 degrees divided by 20 degrees is 2.4min ???*. Adding 2.4min to 14.5min to 25000' is 16.9min. Normal climb 14.5min averages 1724fpm. Adjusted climb 16.9min averages 1479fpm. Difference is 244fpm.
> 
> Still not quite 1000fpm. It's the weight.


*READ WHAT THE CHART SAYS!*



SO - the chart says time to 25,000' at 8400 pounds is 17.1. I'll use your 81F. 81F is 49F warmer than 32F. 10% *FOR EACH 20F above 32F* so *24% Increase* (40F = 20% and then add another 9F = 4%, 24%) *to 17.1 = 21.2 Minutes to 25K! This at 8400 Pounds!*

*17.1 x .24 = 4.104 (24% of 17.1) + 17.1 = 21.20 minutes to 25K at 8400 Pounds!*

*14.5 + 24% = 17.98 minutes to 25K at 7800 Pounds!*

*13.0 + 24% = 16.12 minutes to 25K at 7400 Pounds!*


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## P-39 Expert (Nov 7, 2020)

Ivan1GFP said:


> As has been explained to YOU, Those test results are under standard conditions or corrected to standard conditions.
> Today happens to be a reasonably cool Fall day and Temperature is in the low 60's or not too far off standard temperature of 59 degrees Fahrenheit. Most of this Summer was way above that. *The average daily temperature on Guadalcanal is 81 degrees.*
> How many nice cool 59 degree days do you think you will find in the SWPA? What do you think happens when you run the same aeroplane in 110 degree temperatures? Do you think performance gets better?
> 
> ...


Expand above.


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## GregP (Nov 7, 2020)

P-39 Expert,

Weight is not quite what you seem to believe it is as a parameter.

For example, a Schweizer 2-33 sailplane and a Boeing 747 happen to share about the same glide angle. 

But the Schweizer's best glide speed is 52 mph and the 747 is at about 250 knots, which results in quite an actual descent rate in feet per minute.

This is not straight-line algebra.

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## fubar57 (Nov 7, 2020)

You guys feel free to use this. I use it when I'm trying to deal with muppet truck drivers

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## Snautzer01 (Nov 7, 2020)

I think all would be clear if we had a colour picture of a p-39 in flight.

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## GregP (Nov 7, 2020)

Your wish is my command.






It is in flight, fleeing the water, a task at which it seems moderately successful, much like it's success as an interceptor. All it needs to do is to get over a barrel. Would that be a barrel roll? Or a roll out the barrel?

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## FLYBOYJ (Nov 7, 2020)



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## fubar57 (Nov 7, 2020)

LMAO

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## XBe02Drvr (Nov 7, 2020)

P39 Expert said:
*The average daily temperature on Guadalcanal is 81 degrees.*
Whoa! Average daily temperatures are 24 hour averages. The P39 isn't a night fighter. You were closer to the mark when you quoted average daily high as 88°F, as that's likely much closer to the actual SL temperature by the time the Japanese arrive on their long trek from Rabaul.
I endured four years on Boca Chica Key, a coral island with a climate very similar to Guadalcanal. Our official summer daytime highs (measured at the civilian airport downtown) ranged 87°-90°F, but when you went out to your plane on the ramp, the OAT gauge would read 93°-95°. Now which air mass is my airplane going to perform in, the "official" 89° measured under the palm trees behind the NWS station downtown, or the 94° over the runway at the airbase?

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## pbehn (Nov 7, 2020)

Milosh said:


> Not all airplanes are the same. Two On an aircraft a difference of a/c off the assembly line will have different performances. They all must be within a certain performance tolerance, of say +/-5%. P-39 Expert, I will let you do the math.


When I was 16, myself and many of my friends had Yamaha mopeds. 50cc and all "new" as in less than a year old. The difference from fastest to slowest was 5MPH which is 10%. Yamaha did a race series where they provided the bikes and invited riders competed with riders just being given the keys. Despite all bikes being run on a dyno to be nominally the same output, that is only peak output on one day, come race day the difference between fastest and slowest bike was over a second per lap. On an aircraft a difference of 3MPH or 50 ft/min is no difference at all, a week or two later the difference could be reversed.


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## GregP (Nov 7, 2020)

Reversed? Does that change the meaning?

Let's see: A man a plan a canal panama.

Go ahead and reverse it!

How about: racecar?

Hey! This is fun!


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## pbehn (Nov 7, 2020)

GregP said:


> Reversed? Does that chang the meaning?
> 
> Let's see: A man a plan a canal panama.
> 
> ...


What I meant was in a week or two, one plane gets cleaned, has an overhaul, new paint job, filled all the tanks etc etc etc. 3MPH is less than 1%


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## GregP (Nov 7, 2020)

Yah. Knew that, but tried to inject some dry palindrome humor ... and obviously failed.

But, I might succeed tomorrow, after a new paint job. 

And supposedly "identical" racecars and fun ,too. The Sports Renault class was fun! All the engines were tuned to makle the exact same horsepower on a dyno and had the same brakes and tires and weight. Then you race! What it actually meant in real life was that the drivers tended to trade paint more often becasue they couldn't pull away from their competition. Still, someone usually won the race. But it wasn't usually the same someone every weekend.

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## Peter Gunn (Nov 7, 2020)

Snautzer01 said:


> I think all would be clear if we had a colour picture of a p-39 in flight.


See post #881 waaaaaaay back in the thread...

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## Peter Gunn (Nov 7, 2020)

P-39 Expert said:


> Absolutely nothing wrong with a symmetrical airfoil. The A6M2 will be gasping for air just like the P-39K at 27000'. Sure it has a much lower wing loading, and will be more maneuverable at 27000' just like it is at 10000'. But it won't climb any better and it sure won't dive any better.


Wait, are you actually trying to contradict and then instruct a real pilot with more hours behind the stick than Carter's got pills?

You know, if 
X
 XBe02Drvr
or 

 FLYBOYJ
or 

 GregP
or 

 BiffF15
or 

 DerAdlerIstGelandet
just to name five (5) guys that did or do fly ACTUAL airplanes, work in the industry and have backed up everything they've told you with actual data... I'd listen.

You've been trying to contradict 
I
 Ivan1GFP
and 

 nuuumannn
as well, even though they too have shown you facts and figures to illuminate the error of your ways.

I now believe that you're just a time wasting troll with no desire to learn and even when you're wrong you won't admit it, if others want to continue a discourse (to no useful end) that's fine. Harsh words perhaps but I'll risk a "vacation" for speaking my mind on this, I mean, did you not learn anything when 

 drgondog
took you to task last year on this subject?

But please, go ahead an argue thy book knowledge with fellows that are in the industry, there's no popcorn shortage at my house.

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## pbehn (Nov 7, 2020)

Peter Gunn said:


> Wait, are you actually trying to contradict and then instruct a real pilot with more hours behind the stick than Carter's got pills?
> 
> You know, if
> X
> ...


You miss the point, this is an ideas supermarket thread, "I don't buy it" is some sort of technical argument, I have two pounds, three shillings and four penny three farthings, so I am unsure of what technical information I can take from a discussion.

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## fubar57 (Nov 7, 2020)

pbehn said:


> You miss the point, this is an ideas supermarket thread, "I don't buy it" is some sort of technical argument, I have two pounds, three shillings and four penny three farthings, so I am unsure of what technical information I can take from a discussion.


I'm sure glad I went to Great Britain after the currency change-over

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## special ed (Nov 7, 2020)

If I may submit a scenario with no intent to demean, I put forth a what if in a thread already scattered with what ifs. P-39 Expert is transported by time machine to mid 1942 and is flying alone in his P-39 customized to his specs ( no nose armor, wing guns or radio in the tail). He sees a lone A6M2 flying at his level and he engages. He is turning tightly about to pull lead.... Later that evening, as Saburo Sakai is painting another P-39 silhouette on his fuselage, He remarks to his crew chief, " He was very good. He ALMOST turned inside me. He did not know I have no armor, radio or wing guns).

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## Snautzer01 (Nov 7, 2020)

GregP said:


> Your wish is my command.
> 
> View attachment 601126
> 
> ...





Peter Gunn said:


> See post #881 waaaaaaay back in the thread...


I take it you do know the longest running joke on this forum? It is not post 881.


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## pbehn (Nov 7, 2020)

fubar57 said:


> I'm sure glad I went to Great Britain after the currency change-over


I just remember the old currency but my experience of "farthings" was we had them all over the place and they were worthless. There is something magnificently comic about it all, and I didn't even venture into "guineas".

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## fubar57 (Nov 7, 2020)

I was there in '78 and remember the ½ penny. I thought it was a great coin

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## GregP (Nov 7, 2020)

Hi Snautzer01,

I forgot. That was back before there was mass hand sanitizer, wasn't it?


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## ThomasP (Nov 7, 2020)

Hey Simon Thomas & GregP,

Interesting. I started out with the assumption that the test for the P-39D was accurate and the P-39C test was possibly/probably incorrect. The reason I chose the P-39D as the basis for my calculations is that the values for climb and speed are more in line with test results of other aircraft (ie Spitfire, Hurricane, P-40, etc) with similar weight, engine power, drag, etc. Plus the tests were at a later date for an airframe already in production, hopefully meaning that there was no reason to overhype the test results.

Would you guys do me a favor (seriously) and do your calculations again, but this time treat the values for the P-39D as if they are the correct ones? Then apply the appropriate values to the calculations for the P-39C. I would like to see if your results are then similar to mine.

PS. If it matters I used a Cd of .020 for the P-39C and .022 for the P-39D.
[EDIT: My apologies, I used a Cd of .021 for the P-39C]


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## Simon Thomas (Nov 7, 2020)

GregP said:


> Let's look at the P-39C. At 10,000 feet, the rate of climb is 3,720 fpm. An Allison V-1710-35 makes 1,150 hp at 12,000 feet and the airplane is at a weight of 6,689 lbs. It just so happens we have data for 10,000 feet. Rate of climb is 3,720 fpm. Calculating backwards, the power required for level flight at that altitude is 396 hp. Personally, I'd expect the power required for level flight to go up as the altitude goes up becasue there is less air density, so the wing has to "work harder." By work harder, I mean a slightly higher angle of attack, and that creates more induced drag, requiring more power.


You need to use THP not BHP. During climb, I got a prop eff of 0.81, which drops 1150 BHP to 931.5 THP.

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## Simon Thomas (Nov 7, 2020)

Hi ThomasP. It will take me a day, but I will get to it. I like number crunching like this - although all my calcs come with a 30 second / 30 yard warranty.

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## GregP (Nov 7, 2020)

If I don't misremember, the flat plate area of a P-39D is 4.60 square feet.

However, to get any better numbers, I'd want an L/D plot for the P-39D, and I'm not to sure where (or if) I can find that. It's not as if the P-39D was a popular and well-documented WWII fighter. I know there is an airspeed for L/D max and it varies as the square toot of the weights. so: V2 / V1 = sqrt (W2 / W1), where V = L/D max airspeed and W - wirhgts. So, if weight (W2) goes up, then V2 goes up, too.

Let me think about this.

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## pbehn (Nov 7, 2020)

Simon Thomas said:


> Hi ThomasP. It will take me a day, but I will get to it. I like number crunching like this - although all my calcs come with a 30 second / 30 yard warranty.


In this discussion 50ft/minute is considered important, have you ever tried walking at 50ft/min? Slower than any bride or funeral cortege down a cathedral aisle. Without modern laser or other sensors I don't see how any 1940s aeroplane could be measured to such limits of accuracy.

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## wuzak (Nov 7, 2020)

Milosh said:


> Not all airplanes are the same. Two consecutive a/c off the assembly line will have different performances. They all must be within a certain performance tolerance, of say +/-5%. P-39 Expert, I will let you do the math.



I believe the engines had to be within +/- 5% of the rated power to be considered acceptable.

Not sure how much performance testing the factory acceptance tests went into. Certainly they checked for proper running and operation.


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## wuzak (Nov 7, 2020)

P-39 Expert said:


> They were as identical (except weight) as the manufacturer could make them. Same contract, same engine, same HP, same airframe. Different internal equipment.





P-39 Expert said:


> The two planes were as identical as the manufacturer could make them, except for weight. The difference in climb wasn't from different propellers, atmospheric conditions, symmetrical airfoils, tail fillets, .30cal gun ports etc. It was because one was 836lba heavier than the other.



Clearly the aircraft were not "as identical as the manufacturer could make them, except for weight", considering that the propeller was different and there were small changes to the airframe.

How much do these differences make? We will never know unless we test the differences independent of other factors (such as weight).

As I said above, the engine performance can vary from one to the next, and since they did not have torquemeters installed we will never know if the the P-39C and P-39D engines varied from the published performance ratings (ie we don't know if the engine was producing more or less power than the standard rating).




P-39 Expert said:


> Expand above.



There has been a lot of expanding in this thread, just maybe not knowledge or opinion.

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## Simon Thomas (Nov 7, 2020)

pbehn said:


> In this discussion 50ft/minute is considered important, have you ever tried walking at 50ft/min? Slower than any bride or funeral cortege down a cathedral aisle. Without modern laser or other sensors I don't see how any 1940s aeroplane could be measured to such limits of accuracy.


Naturally it is only as accurate as the inputs. Based on reading numerous Air Corp reports, some of which have calibration info, I have a confidence the results are better than a WAG.
Fortunately the calc method I used for the P-39C test has effectively 3 unknowns, and there is far more test results than that, so there is some degree of error checking possible.


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## wuzak (Nov 7, 2020)

P-39 Expert said:


> According to the tests, the P-39N (available from Nov 1942) outclimbed the Griffon Spitfire and was about the same speed. The N would substantially outclimb the P-51A (same engine) and was very close in top speed. The N outclimbed the 1943 Thunderbolt, Corsair and Hellcat substantially at 20000', just like I said. The P-39N was equipped with full armament including the wonderful four .30s for the tests, no weight reduction needed.



Well, that depends on which engine and propeller the XII was using.

Of the two tests on Spitfire Mk XII Performance Testing the first was using an experimental propller:



> DP.845 was the prototype Spitfire XII. It was fitted with a Griffon IIB engine and normal span wings. The report noted a Rotol "experimental" propeller was fitted, however, it was previously reported that this model propeller was *"rather inferior" in climb* and that maximum level speed did "not show any appreciable difference" to production propellers. AFDU Report No. 61 noted that speeds of a production Spitfire XII (EN.223) with Griffon III and clipped wings "were found to be almost identical" to DP.845. For comparison, Spitfire XII MB.878 with Griffon VI operating at +12 lbs/2750 RPM achieved 394 mph at 18,100 ft. (15th part of Report No. AAEE/692,o). The Spitfire XII Aircraft Data Sheet is in good agreement with these test results.




The same Spitfire XII tested with the Griffon VI (report mid 1943) had a peak climb rate of nearly 5,000fpm.


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## ThomasP (Nov 7, 2020)

Hey GregP,

A Cd of .021 gives a flat plate of 4.5 ft2
A Cd of .022 gives a flat plate of 4.7 ft2

So I think a flat plate of 4.6 ft2 will do just fine.


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## Milosh (Nov 7, 2020)

wuzak said:


> I believe the engines had to be within +/- 5% of the rated power to be considered acceptable.
> 
> Not sure how much performance testing the factory acceptance tests went into. Certainly they checked for proper running and operation.


For the Germans it was performance, like climb and speed.


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## wuzak (Nov 7, 2020)

wuzak said:


> Clearly the aircraft were not "as identical as the manufacturer could make them, except for weight", considering that the propeller was different and there were small changes to the airframe.
> 
> How much do these differences make? We will never know unless we test the differences independent of other factors (such as weight).
> 
> As I said above, the engine performance can vary from one to the next, and since they did not have torquemeters installed we will never know if the the P-39C and P-39D engines varied from the published performance ratings (ie we don't know if the engine was producing more or less power than the standard rating).



The P-39D test also had the CoG at 25.8% MAC. The P-39C test does not mention this.

How much performance difference is there between a forward CoG (as the P-39D appears to be) and a rear CoG?


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## Ivan1GFP (Nov 7, 2020)

P-39 Expert said:


> *I haven't made anything up, just quoting an AAF report. Why would a General quote a figure for climb at 100fpm? *



You are NOT quoting from the report. The report says "Service Ceiling". Anything else is your (wishful) interpretation.
FWIW, the "General" did not quote any figures. The report simply stated that he was pleased with the result.



P-39 Expert said:


> *It translates to 10000'. It will decrease with altitude. Just like all climb rates.*



In other words, you don't really have a clue as to how much things change.



P-39 Expert said:


> *Agree with you and it wouldn't make any difference anyway.*



Length changes MAY make a difference though in this case it is not relevant.



P-39 Expert said:


> *And you are an expert?
> .....
> Very slightly different performance. The propeller with the biggest difference was a British Rotol propeller. What are the odds of that propeller being used on an American plane? The propellers used on the Allison engine (like in the P-39) had very small differences.*



I do not claim to be an expert on the subject of propellers though I have done a substantial amount of reading on the various theories of how they work and measurement of performance. You obviously have not and are making generalizations you cannot substantiate.
I find this to be an interesting reply when confronted with an example to contradict your assertion about similarity based on manufacturer, and diameter of propellers.
.....
You have no basis for assuming that propellers used on Allison engines (like in the P-39) had very small differences.
If we are discussing different models of P-39, there were vast differences as shown by the over 1 foot increase in diameter from the early to late models.
I already gave you an example of the P-40 which used quite different propellers with the Allison engine during its service life.
Even with propellers of the same diameter, there were often obvious differences such as pitch range.
I suggest you calculate the Propeller Power Coefficient to compare a few of the propellers used.



P-39 Expert said:


> *The two planes were as identical as the manufacturer could make them, except for weight. *



What evidence do you have for this assertion that you keep making?

- Ivan.


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## Snautzer01 (Nov 8, 2020)

GregP said:


> Hi Snautzer01,
> 
> I forgot. That was back before there was mass hand sanitizer, wasn't it?


Indeed . That thread was in the time of tranquility. The age before this Age of Repetition.


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## Ivan1GFP (Nov 8, 2020)

pbehn said:


> I just remember the old currency but my experience of "farthings" was we had them all over the place and they were worthless. There is something magnificently comic about it all, and I didn't even venture into "guineas".



Hello pbehn,

This sounds a bit like when I was in Thailand for a few days. I like to collect a few coins from various places I have been and was trying to do the same there. The problem was that I was never getting any 1 Baht coin.

After a couple days, I was running a bit short on cash and had to change more money. I casually made the comment about never seeing a 1 Baht coin to the fellow who was behind the counter. He just said "wait here" and came back a minute or so later with several of them. They were about the size of a typical thumb tack and looked brand new. He told me to just take them and when I asked what he wanted for them, he said "Nothing".
Those tiny little coins are probably still floating around in one of the places I keep souvenirs from trips.

- Ivan.

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## GrauGeist (Nov 8, 2020)

But could the P-39 nuke Japan?

Wait...is this the wrong thread?

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## buffnut453 (Nov 8, 2020)

GrauGeist said:


> But could the P-39 nuke Japan?
> 
> Wait...is this the wrong thread?



Yes it could...but you'd have to strip off excess weight, fit bulged bomb-bay doors, and add a Merlin 86 engine.

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## Dash119 (Nov 8, 2020)

buffnut453 said:


> Yes it could...but you'd have to strip off excess weight, fit bulged bomb-bay doors, and add a Merlin 86 engine.


Don't forget, once you do all that you need to move the radio forward or the CG will be out of whack...

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## XBe02Drvr (Nov 8, 2020)

GregP said:


> for power required to maintain level flight at Vx, I'd expect the required power to go up as you go higher. The rate of climb test is not a top speed test and is run mostly at whatever best rate of climb airspeed is. I'd say it's somehwere around 1.4 * stall speed and slightly increases as you climb, and the power required to maintain level flight at Vx increases, too, as you climb.


Are you sure you mean Vx, best angle of climb speed? My creaky old memory is that Vy, best rate, is the low point on the power required curve, which would put Vx on the backside of the curve and would actually require more power to maintain level flight. If you're holding waiting for a landing clearance, your best endurance speed is at or about Vy, as long as icing is not a factor. If it is, you have to hold at a higher speed to keep from icing your under surfaces. Tail stalls are generally fatal. (AmEagle ATR at Roselawn, IN, Colgan Q400 at BUF).

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## XBe02Drvr (Nov 8, 2020)

ThomasP said:


> If it matters I used a Cd of .020 for the P-39C and .022 for the P-39D.
> [EDIT: My apologies, I used a Cd of .021 for the P-39C]


I used a Cox .020 for my P39C, but had to step up to a Wen Mac .024 for my P39D because of the 836 grains of extra weight. The D snapped its "down" control line and went into a series of tight loops until it hit the ground.

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## glennasher (Nov 8, 2020)

You folks are probably forgetting to factor in the pilot's breakfast choices before those flights, too. Did he have grits and bacon, or grits and sausage, or SOS? Did he have oatmeal and maybe a grapefruit?
If he was on Cactus Airstrip, did he have breakfast at all? Surely all the weight added by the well-fed pilot will alter the climbing rate of a P-39D more than a P-39C, right?

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## XBe02Drvr (Nov 8, 2020)

glennasher said:


> Surely all the weight added by the well-fed pilot will alter the climbing rate of a P-39D more than a P-39C, right?


You forgot the buoyancy effect differences of the methane gas created by various dietary choices!

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## glennasher (Nov 8, 2020)

XBe02Drvr said:


> You forgot the buoyancy effect differences of the methane gas created by various dietary choices!


My apologies, sir. There's only so much stuff I can process at one time, and that slipped by. Mea culpa, mea maxima culpa!

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## Milosh (Nov 8, 2020)



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## rochie (Nov 8, 2020)

you guys are getting way too bogged down by details !

all you got to do is paint black crosses on a P-39 and bingo !
the greatest fighter ever built, even better than those P-39's with red stars on them, Easy peasy lemon squeezy

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## SaparotRob (Nov 8, 2020)

Even I should have remembered that aerodynamic fix.

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## P-39 Expert (Nov 8, 2020)

XBe02Drvr said:


> P39 Expert said:
> *The average daily temperature on Guadalcanal is 81 degrees.*
> Whoa! Average daily temperatures are 24 hour averages. The P39 isn't a night fighter. You were closer to the mark when you quoted average daily high as 88°F, as that's likely much closer to the actual SL temperature by the time the Japanese arrive on their long trek from Rabaul.
> I endured four years on Boca Chica Key, a coral island with a climate very similar to Guadalcanal. Our official summer daytime highs (measured at the civilian airport downtown) ranged 87°-90°F, but when you went out to your plane on the ramp, the OAT gauge would read 93°-95°. Now which air mass is my airplane going to perform in, the "official" 89° measured under the palm trees behind the NWS station downtown, or the 94° over the runway at the airbase?


And the high temperature is 88 degrees. Use whatever temperature you want. The weather is not going to make up 1000fpm climb.


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## P-39 Expert (Nov 8, 2020)

special ed said:


> If I may submit a scenario with no intent to demean, I put forth a what if in a thread already scattered with what ifs. P-39 Expert is transported by time machine to mid 1942 and is flying alone in his P-39 customized to his specs ( no nose armor, wing guns or radio in the tail). He sees a lone A6M2 flying at his level and he engages. He is turning tightly about to pull lead.... Later that evening, as Saburo Sakai is painting another P-39 silhouette on his fuselage, He remarks to his crew chief, " He was very good. He ALMOST turned inside me. He did not know I have no armor, radio or wing guns).


Actually the P-39 pilot would not attempt to turn with the A6M2, that had been drummed into him since he arrived in theater. In his lighter P-39 he would have the choice of outclimbing the A6M2 or diving away as he had previously done.


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## P-39 Expert (Nov 8, 2020)

wuzak said:


> Clearly the aircraft were not "as identical as the manufacturer could make them, except for weight", considering that the propeller was different and there were small changes to the airframe.
> 
> How much do these differences make? We will never know unless we test the differences independent of other factors (such as weight).
> 
> ...


None of these differences matter. No minor propeller change, minute changes to the airframe (moving the .30s from the nose to the wings), a fin fillet, an extra inch of length, a symmetrical airfoil or the weather will make up 1000fpm climb. Only 836lbs of weight will do that.


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## glennasher (Nov 8, 2020)

glennasher said:


> I think you're typing to a brick wall.
> 
> He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.
> 
> I have learned a lot from this place, but I certainly don't claim to be an "Expert" at anydangedthing. I've often thought that self-declared "experts" are anything but that. I kinda think that he's just trolling you all. I'm moving on to other things.




I pegged it back on page 28 of this thread. This thread has run it's course. It oughta be stomped into a mudhole and left for dead.

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## P-39 Expert (Nov 8, 2020)

Ivan1GFP said:


> You are NOT quoting from the report. The report says "Service Ceiling". Anything else is your (wishful) interpretation.
> FWIW, the "General" did not quote any figures. The report simply stated that he was pleased with the result.
> 
> *You know this is wrong. Why would the commanding general be pleased with a lower ceiling AFTER the weight reduction?*
> ...


Expand above.


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## Peter Gunn (Nov 8, 2020)

P-39 Expert said:


> Expand above.


Ahh...

So my post #1,469 on Page 74 was correct then.

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## XBe02Drvr (Nov 8, 2020)

Peter Gunn said:


> Ahh...
> 
> So my post #1,469 on Page 74 was correct then.


Ayup!

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## SaparotRob (Nov 8, 2020)

I like this thread. Things come up that I learn from. The explanation of tumbling by putting weights on either end of a paper airplane made it clear to me. No math. I don’t remember who posted it and I’m not going to start scrolling back.

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## Ivan1GFP (Nov 8, 2020)

P-39 Expert said:


> *You know this is wrong. Why would the commanding general be pleased with a lower ceiling AFTER the weight reduction?*
> .....
> *One of us is definitely clueless.*



Read what the report actually says, not what you WANT it to say.
.....
I think folks have already concluded a few things and you are most definitely clueless.



P-39 Expert said:


> *Look at the Allison P-40 tests in post #1489. Discard the "impregnated wood" propeller (#2) and the maximum difference in climb was 40fpm at any of the altitudes tested. And the best performing propeller was the standard production propeller. 40fpm is a long, long way from 1000fpm.*



Good try on switching the subject. You commented that the same manufacturer and same diameter of propellers meant that the propellers had to be nearly the same. I gave you a simple example where that was not the case.
A specific test of different propellers proves nothing.



P-39 Expert said:


> *I suggest you stop this charade and admit that the C climbed better than the D because it was 836lbs lighter.*



I suggest you stop being so dogmatic and get a clue. There are plenty of knowledgeable people here who have vastly more experience in the industry than you do. Take a moment and try to understand what they are patiently trying to explain to you.
Your calculation of taking the climb rate and dividing by the weight difference is something most of us figured out by around the 5th Grade was too simplistic an explanation to be useful for anything except perhaps sounding smart to a 4th Grader.
If Aeronautical Engineering were so simple as you seem to imply, people wouldn't have to go to school to learn the subject.



P-39 Expert said:


> *The official Wright Field performance tests. It wasn't a slightly different (if any) propeller, phantom CG problems, an inch in length (if any), a symmetrical airfoil, a fin fillet, slight aerodynamic differences due to the positioning of the .30s or the weather. And the tests weren't flawed as some here maintain. They were official Wright Field tests. You guys are all working really hard to refute the fact that the C climbed better than the virtually identical D because it was 836lbs lighter. *



That bit of redirection won't fool anyone. I asked you how you know the P-39C and P-39D were "virtually identical" except for weight and this is not an answer. It IS starting to sound a lot like a discussion on religion though.
No one is telling you that the weight difference didn't mean something. We just don't believe it explains the entire difference in climb rate and that there were other important factors involved which you keep denying without evidence.

This thread so far has been very useful. It has established that any impression of credibility that you may have had was unjustified.

- Ivan.

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## XBe02Drvr (Nov 8, 2020)

SaparotRob said:


> I like this thread. Things come up that I learn from. The explanation of tumbling by putting weights on either end of a paper airplane made it clear to me. No math. I don’t remember who posted it and I’m not going to start scrolling back.


Obviously! You've got 76 pages worth of company in that opinion. On what other forum would a troll be allowed to lead such a long, entertaining, and merry chase? I haven't run out of popcorn yet.

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## SaparotRob (Nov 8, 2020)

SaparotRob said:


> I like this thread. Things come up that I learn from. The explanation of tumbling by putting weights on either end of a paper airplane made it clear to me. No math. I don’t remember who posted it and I’m not going to start scrolling back.


Shortround6. Page 19. Post #365. I forgot that one has to do research to stay here.


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## GregP (Nov 8, 2020)

Hi XBe02Drvr.

Vy it is, not Vx. Must be the absolute annoyance of having to come up with ANOTHER explanation that gets ignored. Or I simply wasn't playing attention very well. Take your pick ...

I am just tired of "1,000 fpm and 836 lbs" without ANY acknowledgement of the fact that the tests as shown are not very well documented for *analysis*. But they are well documented like wartime production tests would be ... a typical combat airplane at typical combat loadings and typical combat power settings. There is not enough information to go back and dissect the reports since the weight and balance charts are not shown, nor are all the little "nice to have" details given, like finish quality, hours on the airframe, condition of the propeller, MAP readings along with the rpm settings, etc.

I did notice the rate of climb in both reports does not seem to be the indicated ROC at the current altitude, but rather the altitude divided by the time to height, or average rate of climb, which seems strange. We also have the climb airspeeds, which run from 153 mph at S.L. to 200 mph at 20,000 feet for the P-39C, and from 157 mph at S.L. to 203 mph at 20,000 feet for the P-39D. So we have Vy for selected altitudes.

We know the P-39C was basically the same as the YP-39 except for the V-1710-35 engine. I see the fuel consumption was noted as “excessive” and instructions for correcting that were forthcoming from the Power Plant Laboratory (!). If the carburetor needed adjustment to the point where it was noted in the test report, I wonder how much different the actual power delivered was from the Tech Order power table that was used for the report. This airplane seems like sort of a "test mule" type since only 20 were built. I am not surprised it was a lot lighter since it lacked armor and self-sealing fuel tanks. It was VERY similar to the YP-39. We do not know the %MAC for this test but it was tested at 6,689 lbs takeoff weight. The P-39C had the 37 mm cannon (but only 15 rounds!), two 50-cal on top of the nose, and two 30-cal on the bottom of the nose, and no wing guns. I cannot find a definite good set of specs for the P-39C, but the empty weight of the airplane was very much lighter than the P-39D.

There were 60 P-39D-BE's and 336 P-39D-1's. It had the 37 mm cannon, two 50-cals in the upper nose, four 30-cals in the wings, and no 30-cals in the bottom of the nose. They went to a V-1710-63 engine with 1,325 hp for the P-39D-2. The test airplane had the V-1710-35 engine, so it was either a P-39D-BE or P-39D-1. With wheels up, it was at 25.8% MAC, so it definitely has some ammunition in the nose. The P-39D had 30 cannon rounds, not 15 like the P-39C.

So we know the P-39D had armor that the P-39C lacked, 15 more cannon rounds, 2 more 30-cal MG and ammunition for them, with all of the 30-cals mounted in the wings, and self-sealing fuel tanks. That may well and likely does account for the extra 836 pounds. But 836 pounds won't supbract 1,000 fpm from climb. In fact, if we add the 836 pounds to the P-39C, the rate of climb should drop to 3,443 fpm, right about where the P-39D SHOULD have been if it had been developing full power.

I was using the formula from Aerodynamics for Naval Aviators agian: RC = 33,000 * [(Pa - Pr)/W].

That's why I think the P-39D test was run at normal rated power, not military power.

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## SaparotRob (Nov 8, 2020)

Okay, let’s get this settled. One of you guys must know someone with a P-39. I’m looking at you, “Not Greg”. Let’s all kick in a couple hundred grand each and modify it to -D and -C and get out the stopwatches.

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## SaparotRob (Nov 8, 2020)

Maybe a little more if government officials need bribing. The Walmart near me is out of General Motors 37mm cannon and rounds.

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## XBe02Drvr (Nov 8, 2020)

SaparotRob said:


> Shortround6. Page 19. Post #365. I forgot that one has to do research to stay here.


To respond (belatedly) to Shortround's question in that prehistoric post: in conventionally configured planes, handling differences throughout the approved CG range are relatively minor. The limits are determined by where they start to become problematic.
There are caveats. Exceeding the forward moment limit, either by exceeding forward CG limit or by exceeding max gross with the CG at or near its forward limit can cause loss of elevator authority in the flare, or in transition to slow flight. This can come as a surprise, as there is no warning like the buffet preceeding a conventional stall, and can be deadly at low altitude. This is rare, as most planes are difficult to load to this condition in normal use. My first "stretch body" plane was a Cherokee 6, which my instructor insisted I experience in this condition. 100 pounds in forward baggage, two big guys in the front seats, and nothing aft. It lifted off at nearly 10 knots higher speed than normal with me maintaining heavy back pressure to make it climb. Trimming out the back pressure took trim nearly to the limits of its travel. At 6500 feet we attempted some power off and power on stalls. It wouldn't stall, just pitched down with no buffet and no stall warning light. My instructor said to note the speed where that happened and think about the landing. We made a no flaps high speed landing at a nearby former military base with a long runway, switched our "ballast" to aft baggage, and were rewarded with a sweet flying airplane once again. We both violated FARs in conducting this exercise, but my young impressionable brain was imprinted with a lesson that many "pilot error" accident victims never learned. I asked my instructor if there was an aft CG exercise as well, and he said: "Too risky, we won't go there, but aft CG is a known and constant issue with this airplane, and won't sneak up on you unsuspecting as forward will. Calculate always."
Aft CG limits are set with the idea of maintaining a reasonable stick force gradient, to keep pitch control from becoming too sensitive. This generally works well for planes of conventional layout, as pitch response is sensitive to polar moment of large forward masses as well as displacement of CG forward of CL. Unorthodox layouts such as pushers (Ascender), pylon mounts (Lake amphibian) and mid engines (P39) tend to behave a little outside the accumulated body of aeronautical experience and expectations.
Wait, why am I telling YOU guys all this stuff you already know? Dang! Caught preaching to the choir...again!

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## GregP (Nov 8, 2020)

Fighter Rebuilders built up a P-39 or two before and Steve Hinton tested them. The thing is, they don't try to see if it meets factory specs after a warbird restoration. They run the engine in to seat the rings and put some "slow time" on it and fly it just enough to verify everything works. Then, they hand over a good-running, reliable warbird to the owner.

Steve Hinton flew the restored Fw 190 for Paul Allen and spoke to us volunteers about it very briefly, but noted the test card was not a performance verification, but rather gradually creeping up on ensuring a reliable airplane is delivered. He said none of the planes they build are tested to maximum performance unless so specified by the owners, and none of them DO that. Aircraft are restored, made airworthy, broken in, delivered, and then are flown by the owners when they so desire. Occasioanlly, they herd them around the Unlimited race course in Reno, as we can see in YouTube.

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## XBe02Drvr (Nov 8, 2020)

GregP said:


> But they are well documented like wartime production tests would be ... a typical combat airplane at typical combat loadings and typical combat power settings. There is not enough information to go back and dissect the reports since the weight and balance charts are not shown, nor are all the little "nice to have" details given, like finish quality, hours on the airframe, condition of the propeller, MAP readings along with the rpm settings, etc.


Bet they had no idea they were creating a historical document that "historians" 78 years hence would be scratching their heads over.

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## GregP (Nov 8, 2020)

I'm done head-scratching about the P-39 unless something interesting comes up.

It was an overall mediocre fighter at best, given the requirements in Europe, but was pretty good down low if the mission was short. It could hit hard, but the big gun was very prone to jamming and had few rounds to boot. Still, several 37 mm hits on small boats were heavy damage.

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## XBe02Drvr (Nov 8, 2020)

GregP said:


> I see the fuel consumption was noted as “excessive” and instructions for correcting that were forthcoming from the Power Plant Laboratory (!). If the carburetor needed adjustment to the point where it was noted in the test report, I wonder how much different the actual power delivered was from the Tech Order power table that was used for the report.


That might be consistent with a "max performance takeoff/unrestricted climb" profile where the aircraft cleans up, accelerates in ground effect to a predetermined zoom climb speed, than pops up into a climb, slowly bleeding back to Vy. This will give an exaggerated "time to climb" performance value, if someone is trying to prove a point, but is not practical in a combat situation, especially if you're trying to get multiple fighters into the air in close proximity as quickly as possible.

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## pbehn (Nov 8, 2020)

XBe02Drvr said:


> That might be consistent with a "max performance takeoff/unrestricted climb" profile where the aircraft cleans up, accelerates in ground effect to a predetermined zoom climb speed, than pops up into a climb, slowly bleeding back to Vy. This will give an exaggerated "time to climb" performance value, if someone is trying to prove a point, but is not practical in a combat situation, especially if you're trying to get multiple fighters into the air in close proximity as quickly as possible.


No one would do such a thing just to post a better result would they? Surely not. British tests are sometimes criticised because of the state of the planes tested, that was the state of the planes pilots were flying. What is the point in testing something hotted up just for the test, another issue that has dogged the P-39 since the P-400 tag was made.


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## XBe02Drvr (Nov 8, 2020)

pbehn said:


> What is the point in testing something hotted up just for the test


Possibly to justify expenditure on a plane seen as having potential, but in danger of being labeled "a dog"? IAC, hoist on its own petard when the combat ready D1 came along.
IIRC, the unconventional P39 faced opposition from some circles in the Army, an organization not known for its futuristic attitudes.

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## GrauGeist (Nov 8, 2020)

P-39 Expert said:


> Actually the P-39 pilot would not attempt to turn with the A6M2, that had been drummed into him since he arrived in theater. In his lighter P-39 he would have the choice of outclimbing the A6M2 or diving away as he had previously done.


The P-39D is lighter?

With the A6M2 at 3,700 pounds empty (6,160 pounds gross) and the P-39D at 5,450 pounds empty (7,500 pounds gross) I am thinking you have that backwards?

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## special ed (Nov 8, 2020)

Indeed. He is a combat pilot, there to fly combat. Why would he dive away or climb away when he thought his modifications gave him a superior P-39


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## Ivan1GFP (Nov 8, 2020)

GregP said:


> .....
> I was using the formula from Aerodynamics for Naval Aviators agian: RC = 33,000 * [(Pa - Pr)/W].
> 
> That's why I think the P-39D test was run at normal rated power, not military power.



Hello GregP, et al.

That formula you are using makes pretty good sense as long as speed doesn't change.... but there is one factor that has been nagging at me. Shouldn't the propeller efficiency be taken into account as well? Shouldn't it be Thrust available - Thrust required?

Some folks have already commented that they were estimating propeller efficiency at 81% which I am thinking might be a bit high considering that the Advance Ratio at 153 MPH TAS is only about J=0.78.

- Ivan.


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## Ivan1GFP (Nov 8, 2020)

GregP said:


> There were 60 P-39D-BE's and 336 P-39D-1's. It had the 37 mm cannon, two 50-cals in the upper nose, four 30-cals in the wings, and no 30-cals in the *bottom of the nose*. They went to a V-1710-63 engine with 1,325 hp for the P-39D-2. The test airplane had the V-1710-35 engine, so it was either a P-39D-BE or P-39D-1. With wheels up, it was at 25.8% MAC, so it definitely has some ammunition in the nose. The P-39D had 30 cannon rounds, not 15 like the P-39C.



Hello GregP,

The extra .30 cal nose guns on the P-39C were actually between the two .50 cal MG.
See attached photographs.



GregP said:


> I was using the formula from Aerodynamics for Naval Aviators agian: RC = 33,000 * [(Pa - Pr)/W].



I have been looking through my copy of Aerodynamics for Naval Aviators and can't seem to find that formula though there is a lot of coverage about Jets in my copy.

Edit: Found it. The "Power" that is specified IS Horsepower but not nearly as simple as first thought and is based on thrust and angle of climb..... So it does take into account the factors, I was asking about and the calculations are a bit more complicated.

- Ivan.

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## DerAdlerIstGelandet (Nov 8, 2020)

GrauGeist said:


> But could the P-39 nuke Japan?
> 
> Wait...is this the wrong thread?



That depends on whether it uses 2% or 20% of its fuel between engine start and takeoff.

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## GregP (Nov 8, 2020)

Hi Ivan1GFP,

Since we know a data point ... say ... 3,720 fpm climb at 1,150 hp at 10,000 feet, weight = 6,689 lbs, we can back into the other factor. You could start with the P-39D numbers, too, and then assume something close to the difference bwteen Pr at 10,000 feet and Pr at 20,000 feet for the P-39C, but the P-39D data are very suspect to me. I'd trust the P-39C data more at this point. But, perhaps I'm wrong.

So, Pa = 1,150 hp, RC = 3,720 fpm, W = 6,689, solve for Pr (power required for level flight at 10,000 and 20,000 feet conditions) ... in the configuration you flew the test, with whatever prop, etc.

As long as you are reasonably close to the staring point (vary ...say ...±25%), you should not be too far off. Now, speed isn't taken into account in the rate of climb formula, and they assume that if you increase or decrease the power, you're still going to climb it at close to the same configuration. The formula probably falls apart if you elect to do something like double the climb airspeed. But, if your test conditions are similar, the formula should get you very close.

Cheers!


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## Simon Thomas (Nov 8, 2020)

Hi ThomasP. I re-ran the calc for P-39D A.C. No. 41-6722, however I only noticed once I finished that the level test were with the oil cooler and prestone shutters flush and the climb data was with the Prestone and oil cooler shutter wide open. The f I got with level flight was 4.3 ft^2 and e of 1.65. My calc gave answers within 1% of the test data. My climb data was wonky until I saw the shutters were different. I'll look at the other P-39D tests tomorrow.


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## Ivan1GFP (Nov 8, 2020)

Hello GregP,

The problem is that actually speed IS taken into account in that formula if you go up a page and see that the first examples determine the climb angle work via thrust. This is what was throwing me off because I knew it had to be there but it wasn't reflected in your calculation. The examples were all for Thrust versus Drag as for Jets.
The formula with just power was at the very tail end after a bunch of preceding formulas about thrust, so I didn't see it at first.
At the very end, the Thrust is translated to Power but THAT power if we are discussing Piston Engines isn't really the HP from the engine itself but the Engine HP * Propeller Efficiency at whatever J the TAS translates to and the Drag also changes because that would be determined by the IAS (which probably hasn't changed much).... Though the induced drag has probably increased a bit?

The bottom line is that at some point, the Engine Power has to be reduced by the propeller efficiency for the numbers to work out and it is highly unlikely that the propeller efficiency will be the same at 10,000 feet as at 20,000 feet because at least the speed is different.

- Ivan.


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## GrauGeist (Nov 8, 2020)

DerAdlerIstGelandet said:


> That depends on whether it uses 2% or 20% of its fuel between engine start and takeoff.


They can have a fuel truck waiting there to top it off after it's run-up

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## ThomasP (Nov 8, 2020)

Hey Simon Thomas,

If it is any help, NACA War Time report No.8843 FLIGHT INVESTIGATION OF THE VARIATION OF DRAG COEFFICIENT WITH MACH NUMBER FOR THE BELL P-39N-1 AIRPLANE gives a minimum CD of .022 with CL of .06 (so flat plate area of just under 4.7 ft2) between M0.2 and M0.6. The AC was standard except for instrumentation. with normal armament fitted (I think, the photo of the test airframe clearly shows the 37mm barrel, but I cannot make out if the MG ports are taped over or not and it does not say in the text) with ballast for ammunition. Weight as flown was ~7630 lbs with CG at .285 MAC.


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## XBe02Drvr (Nov 9, 2020)

GrauGeist said:


> They can have a fuel truck waiting there to top it off after it's run-up


Hot fueling avgas with a gravity nozzle? Not me, friend!

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## Stig1207 (Nov 9, 2020)

XBe02Drvr said:


> Bet they had no idea they were creating a historical document that "historians" 78 years hence would be scratching their heads over.



That USAF Historical Study #101 would indicate that they might have been doing a fair bit of head scratching 78 years ago as well!


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## XBe02Drvr (Nov 9, 2020)

P-39 Expert said:


> None of these differences matter. *No minor propeller change,* minute changes to the airframe (moving the .30s from the nose to the wings), a fin fillet, an extra inch of length, a symmetrical airfoil or the weather will make up 1000fpm climb. Only 836lbs of weight will do that.


Now let's take a little walk back to Peter Gunn's post #1381 on page 70 for an apples-to-apples comparison of three different blade sets on the same model hub, same engine, same airplane (in this case, a P40F, same s/n for all tests), and same test conditions for all trials. The parameter being tested is rate of climb at 18,000 feet. The hub is a C-532D, which, in a version with a cannon channel, is also used on some P39s.
Blade #89306-19S climbs at 1460 ft/min.
Blade #89301-03 climbs at 1970 ft/min.
Blade #89303-24W climbs at 2010 ft/min.
I'm no math whiz, but that looks like a 550 ft/min difference to me between best and worst. The fact that the engine is a Merlin, not an Allison is irrelevant, as this is merely a test of different prop blades, with all other factors kept equal. Admittedly the Allison will have a little less horsepower available at this altitude, but not enough to erase that large a difference between prop blades. This, plus the weight difference, plus added drag from additional antennas that weren't on the C and other small incremental drag increases (wing guns for example) can easily add up to the performance deficit of the P39D. The best thing you could do for the P39D, IMHO, would be to get the carburetor air intake out of that dead zone behind the canopy so it could get some ram effect.
836 lbs alone ain't gonna do it.

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## GrauGeist (Nov 9, 2020)

XBe02Drvr said:


> Hot fueling avgas with a gravity nozzle? Not me, friend!


Amen, mister - but that was a reference stolen from the "Lancaster as a potential nuclear bomber" thread, which seems to parallel this thread quite closely.

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## DerAdlerIstGelandet (Nov 9, 2020)

GrauGeist said:


> Amen, mister - but that was a reference stolen from the "Lancaster as a potential nuclear bomber" thread, which seems to parallel this thread quite closely.



Its a parallel universe.

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## Peter Gunn (Nov 9, 2020)

XBe02Drvr said:


> Hot fueling avgas with a gravity nozzle? Not me, friend!


Don't worry, we'll wrap you in asbestos and you'll be fine...

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## Peter Gunn (Nov 9, 2020)

Ivan1GFP said:


> Hello GregP,
> 
> The extra .30 cal nose guns on the P-39C were actually between the two .50 cal MG.
> See attached photographs.
> ...


Hello Ivan,

Any info as to why they didn't go with the two .30's in the nose like the photo you posted? Looks like a rather lethal setup ala P-38 to me. Also, could they have ditched the .30's for 4 .50's? Or even 5 by replacing the 37mm hub cannon?

Thanks


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## P-39 Expert (Nov 9, 2020)

GrauGeist said:


> The P-39D is lighter?
> 
> With the A6M2 at 3,700 pounds empty (6,160 pounds gross) and the P-39D at 5,450 pounds empty (7,500 pounds gross) I am thinking you have that backwards?


By "lighter P-39" I meant lighter than the heavier P-39.  No P-39 will ever be as light or lighter than an A6M2.


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## P-39 Expert (Nov 9, 2020)

special ed said:


> Indeed. He is a combat pilot, there to fly combat. Why would he dive away or climb away when he thought his modifications gave him a superior P-39


Those were his two choices, since he knows not to dogfight an A6M2. Simply climb away then use the altitude advantage to dictate combat. Or dive away depending on the situation since the A6M2 could not follow that either.


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## special ed (Nov 9, 2020)

Is he a combat pilot or not? Is he up there to run away? What is the purpose of the mods to the P-39 if not to give it a better advantage? If it is still inferior after the mods, stay home or get another type of fighter.


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## P-39 Expert (Nov 9, 2020)

special ed said:


> Is he a combat pilot or not? Is he up there to run away? What is the purpose of the mods to the P-39 if not to give it a better advantage? If it is still inferior after the mods, stay home or get another type of fighter.


One would think that having a speed, climb and dive advantage might be better than just outturning your opponent.


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## special ed (Nov 9, 2020)

If you run away, what good is your climb and dive advantage, except to save your life? You must get guns on in order to eliminate the enemy, or he will be back.


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## FLYBOYJ (Nov 9, 2020)

special ed said:


> If you run away, what good is your climb and dive advantage, except to save your life? You must get guns on in order to eliminate the enemy, or he will be back.


If you don't have a tactical advantage, you run away (disengage), you could be in a P-39, P-51 or F-22. Fighter tactics, 101

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## special ed (Nov 9, 2020)

Unfortunately, there are times when you "run what you brung" and do the best you can with what you have. A P-39 example from May 1942 N. Guinea is on the front cover of P-39 aces, who low on fuel chose to engage. He did have an initial altitude advantage which he used for first contact but the remaining part of the battle was at the same altitude and he did pick up holes in his P-39D but still made it home. Of course, he could have used his height advantage to dive away and go to base, but that was not why he was in New Guniea.

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## SaparotRob (Nov 9, 2020)

special ed said:


> Unfortunately, there are times when you "run what you brung" and do the best you can with what you have. A P-39 example from May 1942 N. Guinea is on the front cover of P-39 aces, who low on fuel chose to engage. He did have an initial altitude advantage which he used for first contact but the remaining part of the battle was at the same altitude and he did pick up holes in his P-39D but still made it home. Of course, he could have used his height advantage to dive away and go to base, but that was not why he was in New Guniea.


I haven’t heard “run what you brung” in decades. A friend of mine raced his clapped out ‘63(?) Dodge Dart with a push button transmission against a new ‘87 Monte Carlo and won. He got “blowed away” by a guy in a pickup.


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## P-39 Expert (Nov 9, 2020)

XBe02Drvr said:


> Now let's take a little walk back to Peter Gunn's post #1381 on page 70 for an apples-to-apples comparison of three different blade sets on the same model hub, same engine, same airplane (in this case, a P40F, same s/n for all tests), and same test conditions for all trials. The parameter being tested is rate of climb at 18,000 feet. The hub is a C-532D, which, in a version with a cannon channel, is also used on some P39s.
> Blade #89306-19S climbs at 1460 ft/min.
> Blade #89301-03 climbs at 1970 ft/min. *This is the standard production propeller, why are you comparing it with the lower climbing propeller? Same standard production propeller as in the P-40E Allison test in the same post. And why wouldn't you use the Allison comparison since the P-39 also used the same Allison engine? Unless you can prove that the lower climbing propeller was used on the P-39D this is an invalid comparison. *
> Blade #89303-24W climbs at 2010 ft/min.
> ...


Please expand above.


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## fubar57 (Nov 9, 2020)

I don't buy it

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## Ivan1GFP (Nov 9, 2020)

Peter Gunn said:


> Hello Ivan,
> 
> Any info as to why they didn't go with the two .30's in the nose like the photo you posted? Looks like a rather lethal setup ala P-38 to me. Also, could they have ditched the .30's for 4 .50's? Or even 5 by replacing the 37mm hub cannon?
> 
> Thanks



Hello Peter Gunn,

The P-39C also had the option of two additional .30 cal MG in the wings that could be installed if needed.
I believe the Nose Gun setup on the C was the best that was installed in any Airacobra which is why I was recommending going back to it. Those .30 cals had 300 rounds per gun. I don't think they could have replaced them with .50 cals for lack of room.

It sounds like General Harmon's crew did try replacing the 37 mm with an additional .50 cal and the higher rate of fire wasn't enough of a compensation for the hitting power of the cannon.

If I had to work on the Airacobra with factory resources and starting with a P-39D, I would have:
1. Put back the .30 cal Nose Guns. That and the ammunition supply should be a pretty close replacement for the Gear Box armour for balance but probably not quite.
2. Replace the 37 mm motor cannon with a 20 mm Hispano but with a 250 round belt feed instead of the 60 round drum.
3. Try to move the Oil Tank from the tail up to the nose. There might be room where the belt for the 37 mm cannon used to be.
The oil lines might be a bit longer, but the oil coolers are under the cockpit and about equal distance from the nose or tail anyway. The shape of the oil tank does not have to remain the same and without the oil tank so far back, the armour plate that protected it may not be needed or could be moved further forward to protect the coolant tank.
The original oil tank had a heating element inside and changing the shape might mean deleting that feature. Hopefully the Soviets won't get too upset.

Edit: And standardize on 270 rounds per .50 cal gun in the nose instead of 200 rounds. There was room for the extra ammunition and some US test aircraft flew with up to 250 rounds per gun.

The basic idea is to move the CoG forward so the normal loaded condition isn't sitting at 28.5% but without any permanent ballast.

- Ivan.

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## GregP (Nov 9, 2020)

Hi Ivan,

I found an online reference that said the P-39C guns were over and under the nose (and the P-39D guns had 2 more 30s that werre all four wing-mounted) and used it. Very nice pic you found that disproves that one. Appreciate it.

Just curious ... where did you find those pictures? They are very good.

*Edit*: Nevermind, found the pics. Not labeled as a P-39C, but HAS to be a YP-39 or a P-39C because none of the other P-39s had four nose MG.

Cheers.

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## Ivan1GFP (Nov 9, 2020)

Hello GregP,

I just tried out the same formula that you were working with from Naval Aviators but with just one change.
I threw in a propeller efficiency factor.
The conclusion is.... It doesn't seem to make a difference other than change the Power Required.
I haven't tried it for different altitudes though.

Assuming that the P-39C and P-39D REALLY were identical except for weight, the only explanation for the difference in performance would be that the P-39D was running 133.79 HP less --- 1016 HP instead of 1150 HP at 10,000 feet.

- Ivan.


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## GregP (Nov 9, 2020)

I used the actual data points at 10,000 and 20,00 feet to get Pr at those two altitudes. Then I changed the weight. Since I was always using data obtained at the altitude of the data point and I only changed the weight after gettinf Pr, the results for rate of climb should be pretty accurate.

My conclusion was the same as yours ... the power used in the P-39D test at 10,000 feet was not quite military power. However, it is tough to state it categorically since we can't talk with the people involved and the recorded test doesn't have all the data we want to look at. I'm thinking that whoever looked up the power in the tech order just went to the Military power line, but teh actual test was at normal rated power and 2,600 rpm.

Since I can't ask anyone, I'm left with the fact that the climb data for the P-39D shows and airplane that needs 1/3 more power in level flight at 10,000 feet than the P-39C did, and that doesn't sit nearly as well as the alternate conclusion, at least to me.

Cheers.

*Edit*: I wanted to do a reasonability check on it, so I went to the P-39M test. They don't have a data point at 10,000 feet, but they DO have one at 9,900 feet. Close enough. Short version of what I found: Something is off kilter ...

At 9,900 feet, the P-39M did 3,320 fpm with power at 1,250 / 3000 rpm, and the aircraft at 7,430 pounds. Low and behold, the power required for level flight is 502 hp, which is not all that far off from the P-39D number.

And, they have a data point at 20,000 feet. Since we are "ballparking" it, let's use the same weight. Pa = 880 hp, weight = 7,430 lbs, RC = 2,000 fpm, and Pr = 430 hp.

So, the P-39M matches more closely with the P-39D numbers than the P-39C does.

So far, the only conclusion I can come to is that the P-39C is not quite nearly as identical to the P-39D as we might suppose from the available reading. The report says the aircraft was at 28.6% MAC at takeoff, wheels up, propeller is the same as the P-39D, and the armament is the same as the P-39D (doesn't say which cannon was installed).

This might get interesting, from an analysis standpoint! That assumes the interest is there to keep going. I will, to a popint, but not just now since some "honeydos" are creeping into the picture.

Again, Cheers


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## Ivan1GFP (Nov 9, 2020)

Hello GregP,

The big difference between what I am doing and what you are doing is that I am throwing in an assumed propeller efficiency.
The idea that there needs to be a propeller efficiency is explained at the end of Page 154 and beginning of Page 156 (After the rather lousy picture of the F11F Tigers from the Blue Angels).
With the propeller efficiencies, the Power Required I am getting isn't the same as what you are getting.
The only problem is that I have to make a lot of assumptions to go any further and the data isn't that good to begin with and once a few assumptions are thrown in, all we can be sure of is that it is an aeroplane and not a pterodactyl.

- Ivan.


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## GregP (Nov 9, 2020)

I was thinking ... pterodactyl myself with low-drag skin and automotive style doors. But, hey, I could be mistaken.

I THOUGHT I was mistaken once, but I was wrong ...

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## P-39 Expert (Nov 9, 2020)

Ivan1GFP said:


> Hello Peter Gunn,
> 
> The P-39C also had the option of two additional .30 cal MG in the wings that could be installed if needed.
> I believe the Nose Gun setup on the C was the best that was installed in any Airacobra which is why I was recommending going back to it. Those .30 cals had 300 rounds per gun. I don't think they could have replaced them with .50 cals for lack of room.
> ...


This isn't addressed to me, hope I'm not intruding but made some comments above.


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## ThomasP (Nov 9, 2020)

Hey GregP,

The relative end result discrepancies you are running into are more or less the same ones I ran into. When I run the numbers for:

the P-39C tests in the US
the P-39C/Airacobra I trials in the UK
the P-39D-1/Airacobra IA trials in the UK
the P-39D/D-1/M-3/N-1/Q-5 test tests in the US
and the P-39N-1 drag test done by NACA

the only signifiant outlier I get is the original P-39C ROC test. Hence I am forced to conclude that the original P-39C climb test value of 3750 ft/min sustained ROC is either:

incorrect and should be ~3270 ft/min, or
the power used was somewhere 1300 BHP+ for the first ~10,000 ft, or
the power used was 1150 BHP and a zoom climb was used (from Vmax of ~290 mph at SL) to get the additional ROC claimed.

Interesting stuff.

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## GregP (Nov 9, 2020)

Hi ThomasP.

I pretty much came to the same conclusion. There is something hokey about the P-39C test, but I don't know what.

If I assume you are correct and the P-39C ROC should be 3270 fpm, then the Pr rises to 478 hp, which about in line with the P-39D and M. Then, if I vary the hp to get 3720 fpm, the hp turns out to be 1241 hp, not 1150. Here's the thing, we do NOT have the MAP readings for climb. When I was working at an Allison shop for a few years, we had retired General Davey Allison come by the shop for a visit. He told us they used to fight the P-40s in the AVG at 70" MAP. They had early Allisons, similar to the P-39C engine, but it had a prop shaft on the front in the P-40 and was probably a C-series engine ... likely a V-1710-33 in it. He did not know the horsepower, but it was definitely above what the stock MAP reading gave.

The early C-series nose cases were not too strong, but the -35 in the P-39C/D didn't HAVE the early nose case; they were early E-series engines and connected to a driveshaft, so they didn't need a nose case. They were strong enough for a LOT more popwer than stock.

If the P-39C pilot for the flight test we are looking at ran higher than normal MAP, he could well have been climbing at more than 1,150 hp, and may well have seen 3,720 fpm at the elevated hp and MAP. The thing is, we don't have any way to find out. But it is definitely different from the P-39D and M and other tests on the P-39.

As you said, interesting. Isn't precise analysis fun? 

We know what we don't know, but we aren't sure what we know ... there's a joke in there somewhere. Either they ran the P-39D test at lower-than-reported hp or they ran the P-39C test at higher-than-reported hp ... or somebody misreported something ... or they held their tongue wrong during flight ... or ... a pretty girl walked past when they were recording the numbers.

At this point, I am leaning toward the P-39C test being run at higher-than-reported MAP and hp, combined maybe with a propeller that was better for climbing. But, the weight difference alone won't give you 1,000 fpm difference in climb. Some other factor was at work here. It may be forever a mystery unless we can find other P-39C tests. They only made 20 of them. How many tests were conducted? I surely don't know.

Poor toilet training as a kid on the part of the report writer might be in there somewhere, too.

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## ThomasP (Nov 9, 2020)

Hey GregP,

Thanks for taking the time to look at the numbers again. I was pretty sure I had it ~right, but aerodynamics is not my specialty, and there is always a chance of missing something important in either the math or the data used. And yes, I do find the analysis fun, as do I find the discussion of such things with you and others on this forum enjoyable.

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## SaparotRob (Nov 9, 2020)

Never thought that technobabble would interest me. But I’ve been following this thread and now it’s become a mystery! Far out!


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## wuzak (Nov 9, 2020)

GregP said:


> Hi ThomasP.
> 
> I pretty much came to the same conclusion. There is something hokey about the P-39C test, but I don't know what.
> 
> ...



Don't forget the engine rating acceptance tolerance of +/- 5%.

That equates to +/- 57.5hp from the rated 1150hp. Or a total of 115hp difference.

Could that be a contributing factor to the performance difference?


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## ThomasP (Nov 9, 2020)

Hey wuzak,

Yes, that much HP could definitely make a difference.

The problem in this case is that the climb rates for all of the types we have info on (except the C) generate values that are close to the power curve stated in the tests, ie the calculated values vary only a small +/- from the stated BHP. For the variance in engine power to explain the test C's 3720 ft/min ROC, all (I think) of the other tests would have to have been run with underpowered engines, and have engines that are close to the same in underperformance. The maximum speeds on some of the other tests may indicate slight variances in engine power, but without detailed drag indexes for the differences between the models I (we?) can not really factor that in meaningfully.

GregP got 1241 BHP needed (I assume upto about 12,000-13,000 ft), and I got 1275-1300 BHP+ needed upto about 10,000 ft, if the P-39C is going to have a 3720 ft/min ROC. Plus I had to use a Cd of .020-.021 (depending on the BHP used) for the C, as opposed to .022 for the others (I am not sure what value of Cd GregP used, but I would bet it is closer to .020 for the 3720 ft/min ROC).

PS. As mentioned up-thread, significant variance in propeller efficiency could have a significant effect also. But again, to match the test results for the other models, all of them would have to be using props of about the same efficiency, and all of the props would have to be significantly less efficient than the one used on the C model.


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## fubar57 (Nov 10, 2020)

Found this on the site, listed as a contemporary of the P-39. Only one was made...Piaggio P.119 - Wikipedia

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## GrauGeist (Nov 10, 2020)

Always thought the P.119 was interesting in the fact that they used a radial instead of a "V", which would have been a pain in the a** in regards to cooling issues.

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## Ivan1GFP (Nov 10, 2020)

P-39 Expert said:


> This isn't addressed to me, hope I'm not intruding but made some comments above.



I wasn't sure I really wanted to reply to your post because I don't think our back and forth posts ever really accomplish anything.
I will warn you in advance: My basic premise is that the NACA L-602 Report was generally correct and that when the CoG reached about 30.2% MAC, handling became dangerous even though this was still ahead of the "aft CoG Limit".

The primary goal for most of these changes is to ensure that the CoG of the Airacobra never goes beyond the range of 23% MAC as a forward limit and 28.5% MAC which appears to be a Safe aft limit. If you do not agree that this is a reasonable goal, then you will probably not agree with the changes.



P-39 Expert said:


> *Problem was space, with the .30s there was not enough room for the full 30 rounds of 37mm cannon ammo. Not much punch from the .30s and even less with prop synchronization.*



I don't believe you are correct that the .30 cal MG were the reason for only 15 rounds of 37 mm ammunition in the P-39C.
Please see the attached diagram. The magazine for the 37 mm was simply different on the P-39C. The .30 cal MGs do not appear to be in the space that would be taken by the 30 round endless belt magazine for the 37 mm that was installed in P-39D and later models.

As for punch from the .30 cals, note that they are comparable to or even slightly more powerful than the .303 Vickers MG (Japanese Type 97) that were installed in the A6M2 through A6M5. With the low capacity of the 20 mm in the wings, many folks believe that the majority of kills by the A6M early in the war AGAINST Allied aircraft were with those synchronized MG.

As for weight, I believe these guns and their ammunition and associated equipment could substitute for the Gear Box armour.



P-39 Expert said:


> *Excellent idea, I think you could have made do with 120-150 rounds. Spitfire had 120 rounds and P-38 had 150rounds. Save about 80-100lbs weight vs the .37mm. Some early Allison P-51s had 20mms with belt feed, so it was doable.*



The intention is NOT to reduce weight up in the nose because it would need to be made up with additional equipment, or ballast in the form of armour such as the pieces of cheek armour in the British Airacobra. For this reason, I believe 250 rounds would be a very reasonable ammunition load.

Without the 37 mm endless belt magazine or the 20 mm Hispano 60 round drum, there should be enough room above the cannon and between the .50 cal MG to mount an oil tank. There is a fairly small drive mechanism for the belt above the 20 mm Hispano, but it doesn't anywhere near the amount of room that the drum did.



P-39 Expert said:


> *Excellent idea, especially if the .30s are deleted. Only added about 45lbs but increased firing time about 9 seconds. A 20mm w/120rds and 2x.50s w/270rds each is pretty potent.*



I don't believe the 30 cal in the nose should be deleted because they would be a substitute for the ballast up in the nose that the Gear Box armour represented.
The idea was not really to reduce weight but to shift the CoG as far forward as possible

Other potential spaces for the oil tank might be in the wing center section or fuselage just ahead of the radiators and oil coolers.

-Ivan.


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## GrauGeist (Nov 10, 2020)

Adding more weight to the wings will affect roll-rate, so be careful of that adventure.


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## Peter Gunn (Nov 10, 2020)

I dunno, from some of the claims made through this thread apparently the Air Force brass were a bunch of chuckle heads that were out to "get" Larry Bell. I mean this plane obviously out performs the Mustang, Thunderbolt and Lightning combined and the Navy was stupid for not buying the Airbonita. I mean, its performance above 20,000 ft is simply stunning, it out climbs anything in the sky and is faster than anything else in the inventory, Allied or Axis.

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## BiffF15 (Nov 10, 2020)

Peter Gunn said:


> I dunno, from some of the claims made through this thread apparently the Air Force brass were a bunch of chuckle heads that were out to "get" Larry Bell. I mean this plane obviously out performs the Mustang, Thunderbolt and Lightning combined and the Navy was stupid for not buying the Airbonita. I mean, its performance above 20,000 ft is simply stunning, it out climbs anything in the sky and is faster than anything else in the inventory, Allied or Axis.





P39 Expert,

And based on one test that is different from all others. You just aren’t assimilating that there is something wrong with this test. I think Greg has probably guessed correctly that the guy did a zoom climb after accelerating to a speed well above climb speed. Also realize that “test pilots” have variations among group as well.

Cheers,
Biff

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## XBe02Drvr (Nov 10, 2020)

P-39 Expert said:


> In his lighter P-39 he would have the choice of outclimbing the A6M2 or diving away as he had previously done.


Huh?


GrauGeist said:


> The P-39D is lighter?
> 
> With the A6M2 at 3,700 pounds empty (6,160 pounds gross) and the P-39D at 5,450 pounds empty (7,500 pounds gross) I am thinking you have that backwards?


I wouldn't count on "climbing away" from the Zero. That would only reliably work if the P39 started out in a high energy state and the Zero at cruise or other low energy state. Even IF (big IF) the P39 can outclimb the Zero, it'll be only by a small margin (don't trust climb numbers from allied tests of reconstructed Zeroes), and with its SIGNIFICANTLY heavier weight and its higher wing loading, will NOT have enough advantage in the acceleration and climb transition to get out of range unperforated unless it starts out with an energy advantage.


FLYBOYJ said:


> If you don't have a tactical advantage, you run away (disengage), you could be in a P-39, P-51 or F-22. Fighter tactics, 101


BINGO!


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## buffnut453 (Nov 10, 2020)

XBe02Drvr said:


> BINGO!



And that's another reason to disengage from the fight.

Did you see what I did there? 

Ok...I'll get my coat!

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## XBe02Drvr (Nov 10, 2020)

buffnut453 said:


> Did you see what I did there?
> 
> Ok...I'll get my coat!


US senator George Aiken after the Tet offensive in Vietnam: "Just declare victory and get the heck out of there!"

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## XBe02Drvr (Nov 10, 2020)

BiffF15 said:


> Also realize that “test pilots” have variations among group as well.


Really? I thought they had to be perfect clones of Steve Canyon before they'd let them out of Test Pilot School. My faith is shattered!

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## Ivan1GFP (Nov 10, 2020)

GrauGeist said:


> Adding more weight to the wings will affect roll-rate, so be careful of that adventure.



Hello GrauGeist,

With this "idealized" armament, there wouldn't be any wing guns at all.
I was thinking:
20 mm motor cannon - 250 Rounds.
2 x .50 cal synchronized MG - 270 Rounds per Gun
2 x .30 cal synchronized MG - 300 Rounds per Gun

All the guns have pretty similar ballistics. All the guns except the .30 cals have a pretty good duration of fire.
With this much armament and ammunition in the nose, the CoG will still shift aft pretty seriously when the ammunition is expended but hopefully the moving the oil tank from the tail to the nose will address much of that problem as would deleting the oil tank armour at the tail of the aircraft.
There is also the possibility of shifting radios a bit forward when the oil tank and armour are no longer there.

- Ivan.


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## XBe02Drvr (Nov 10, 2020)

Ivan1GFP said:


> Hello GrauGeist,
> 
> With this "idealized" armament, there wouldn't be any wing guns at all.
> I was thinking:
> ...


"Bridge, Port Forward Lookout. Visual surface contact, twenty degrees port bow, four or five miles. Can't quite make out what it is, Sir."
"Conn, come left two zero degrees, course three one zero, all ahead two thirds. Port Forward, I need an ID, get with it, son! All hands, stand by General Quarters!"
"Bridge, Port Forward, I can make out a triangular shape through the mist, perhaps a small sailboat? Way out here?"
"C'mon, son, I need that ID! Forward Mounts, man up and stand by!"
"OMIGOD! It's the biggest pig's ear I've ever seen, floating upright in the water!...Sir."

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## SaparotRob (Nov 10, 2020)

To quote that brilliant American naval hero, Ensign Charles W. Parker;
“Gee, I LOVE that kind of talk”.

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## P-39 Expert (Nov 10, 2020)

Ivan1GFP said:


> I wasn't sure I really wanted to reply to your post because I don't think our back and forth posts ever really accomplish anything.
> I will warn you in advance: My basic premise is that the NACA L-602 Report was generally correct and that when the CoG reached about 30.2% MAC, handling became dangerous even though this was still ahead of the "aft CoG Limit".
> 
> The primary goal for most of these changes is to ensure that the CoG of the Airacobra never goes beyond the range of 23% MAC as a forward limit and 28.5% MAC which appears to be a Safe aft limit. If you do not agree that this is a reasonable goal, then you will probably not agree with the changes.
> ...


Almost forgot, the coolant tank could be moved up right behind the pilot very near the CG like on the P-63 and XP-39E. The oil tank could then be moved up to the space formerly occupied by the coolant tank. That may be the ultimate fix for any CG issues. Just a thought.


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## P-39 Expert (Nov 10, 2020)

Peter Gunn said:


> I dunno, from some of the claims made through this thread apparently the Air Force brass were a bunch of chuckle heads that were out to "get" Larry Bell. I mean this plane obviously out performs the Mustang, Thunderbolt and Lightning combined and the Navy was stupid for not buying the Airbonita. I mean, its performance above 20,000 ft is simply stunning, it out climbs anything in the sky and is faster than anything else in the inventory, Allied or Axis.


My whole purpose of continuing this thread is that the climb of the early P-39D/F/K/L of 1942 could be improved by reducing the weight (.30s and nose armor). A P-39D/F or P-400 without those items would weigh about 7200lbs. At this weight it would outclimb the A6M2 and still have a significant speed advantage. In that case air combat in NG in 1942 could have been much different.

P-39N didn't need those modifications since it had the more powerful -85 engine and had an excellent climb rate.


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## pbehn (Nov 10, 2020)

Peter Gunn said:


> I dunno, from some of the claims made through this thread apparently the Air Force brass were a bunch of chuckle heads that were out to "get" Larry Bell. I mean this plane obviously out performs the Mustang, Thunderbolt and Lightning combined and the Navy was stupid for not buying the Airbonita. I mean, its performance above 20,000 ft is simply stunning, it out climbs anything in the sky and is faster than anything else in the inventory, Allied or Axis.


There were chuckleheads all over. The Spitfire MkII was slower than the Mk I despite having a more powerful engine and a better propeller. It had a better climb performance and ceiling and carried more armour, this improvement was noted by LW pilots which means it was worth it.. The chuckleheads were concerned with getting a better military machine, not winning some arbitrary speed record. As with the P-51D which was marginally down on speed against the P-51B but was an all around better fighting machine.

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## Dash119 (Nov 10, 2020)

pbehn said:


> There were chuckleheads all over. The Spitfire MkII was slower than the Mk I despite having a more powerful engine and a better propeller. It had a better climb performance and ceiling and carried more armour. The chuckleheads were concerned with getting a better military machine, not winning some arbitrary speed record. As with the P-51D which was marginally down on speed against the P-51B but was an all around better fighting machine.


Okay, now I'm really confused... Is it chuckle heads or chuckleheads?


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## pbehn (Nov 10, 2020)

Dash119 said:


> Okay, now I'm really confused... Is it chuckle heads of chuckleheads?


That depends on the colour of your color. Chucklehead doesn't show as a spelling mistake with the forum spell check.

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## Dash119 (Nov 10, 2020)

pbehn said:


> That depends on the colour of your color. Chucklehead doesn't show as a spelling mistake with the forum spell check.


Neither does chuckle head... So the mystery deepens. I guess the next question is how would Larry Bell spell it?

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## pbehn (Nov 10, 2020)

Dash119 said:


> Neither does chuckle head... So the mystery deepens. I guess the next question is how would Larry Bell spell it?


Chuckle and head wouldn't, they are words on their own anyway.

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## buffnut453 (Nov 10, 2020)

pbehn said:


> That depends on the colour of your color. Chucklehead doesn't show as a spelling mistake with the forum spell check.


 
You say tomayto, I say tomahto.

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## pbehn (Nov 10, 2020)

buffnut453 said:


> You say tomayto, I say tomahto.


Chucklehead is understood on both sides of the pond, unless you are in Glasgow or Newcastle of course.

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## P-39 Expert (Nov 10, 2020)

XBe02Drvr said:


> Huh?
> 
> I wouldn't count on "climbing away" from the Zero. That would only reliably work if the P39 started out in a high energy state and the Zero at cruise or other low energy state. Even IF (big IF) the P39 can outclimb the Zero, it'll be only by a small margin (don't trust climb numbers from allied tests of reconstructed Zeroes), and with its SIGNIFICANTLY heavier weight and its higher wing loading, will NOT have enough advantage in the acceleration and climb transition to get out of range unperforated unless it starts out with an energy advantage.
> 
> BINGO!


A standard P-39 would climb with an A6M2 at military power (3000rpm). I was talking about a lighter P-39 without wing guns and nose armor in the 7200lb range which would outclimb an A6M2.


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## P-39 Expert (Nov 10, 2020)

Ivan1GFP said:


> I wasn't sure I really wanted to reply to your post because I don't think our back and forth posts ever really accomplish anything.
> I will warn you in advance: My basic premise is that the NACA L-602 Report was generally correct and that when the CoG reached about 30.2% MAC, handling became dangerous even though this was still ahead of the "aft CoG Limit".
> 
> The primary goal for most of these changes is to ensure that the CoG of the Airacobra never goes beyond the range of 23% MAC as a forward limit and 28.5% MAC which appears to be a Safe aft limit. If you do not agree that this is a reasonable goal, then you will probably not agree with the changes.
> ...


Here's a photo of the arrangement. Don't think the 37mm horsecollar magazine fits in there, but a 20mm belt feed might.

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## XBe02Drvr (Nov 10, 2020)

P-39 Expert said:


> A standard P-39 would climb with an A6M2 at military power (3000rpm). I was talking about a lighter P-39 without wing guns and nose armor in the 7200lb range which would outclimb an A6M2.


Which P39, even the dog D1? Even your hot rod custom P39, which may measure a steady state climb rate higher than Koga's (90%) Zero, isn't going to pop up from level cruise into its best climb fast enough to get out of range without being hit. Lighter weight, lower wing loading, and a better L/D are going to give a 100% Zero quicker initial response. Sure, the P39 may eventually pull away, if it's still intact, but Saburo will get in a good long burst before it does.

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## P-39 Expert (Nov 10, 2020)

XBe02Drvr said:


> Which P39, even the dog D1? Even your hot rod custom P39, which may measure a steady state climb rate higher than Koga's (90%) Zero, isn't going to pop up from level cruise into its best climb fast enough to get out of range without being hit. Lighter weight, lower wing loading, and a better L/D are going to give a 100% Zero quicker initial response. Sure, the P39 may eventually pull away, if it's still intact, but Saburo will get in a good long burst before it does.


Are we already in gun range? Did we not detect each other visually before we are close enough to start shooting?


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## fubar57 (Nov 10, 2020)

Many get shot down without realizing the opponent was there

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## GregP (Nov 10, 2020)

If the P-39 would climb with a Zero, it might not have been such a dud in the Pacific Theater. Early encounters with the zero certainly don't support that.

Actual war performance makes your statement a bit suspect, P-39 Expert. Granted we had novice pilots, but we had abysmal sucess early-on, and it didn't get a lot better until after we had some experience, and that was with other types of airplanes. The P-39's success never DID get good in US hands. It only had success in Soviet hands.

In U.S. service, for the entire war, the P-39 had 32 kills (14 air, 18 ground) against 107 combat losses in the ETO. I don't have numbers for other theaters. The Statistical Digest of WWII gives enemy ariplanes destroyed by fighters for all threaters, but does not show the model of airplane that achieved the victories. So, we know how many were destroyed by all fightrers, but not by the P-39 or any other model alone.

In any case, the P-39 was NOT a favorite combat airplane of anybody on the US military in any theater. It probably represented the highest-performance airplane that a new pilot in training ever flew the first time he flew one, but that didn't mean it remained his favorite when he went operational overseas.

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## P-39 Expert (Nov 10, 2020)

BiffF15 said:


> P39 Expert,
> 
> And based on one test that is different from all others. You just aren’t assimilating that there is something wrong with this test. I think Greg has probably guessed correctly that the guy did a zoom climb after accelerating to a speed well above climb speed. Also realize that “test pilots” have variations among group as well.
> 
> ...


Biff, those teste were conducted at Wright Field by AAF staff whose only job was to test those planes under very strict testing standards and criteria. If some guys on a message board try to invalidate a test done 70 years ago then we have no basis for evaluating the differences in those planes. We must assume that the tests were conducted properly and the information is accurate. Otherwise, what's the point if we're making the rules up as we go along?


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## MIflyer (Nov 10, 2020)



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## pbehn (Nov 10, 2020)

fubar57 said:


> Many get shot down without realizing the opponent was there


Thats why, from the start the Spitfire traded a few MPH for better visibility and many others followed suit with the Malcolm hood or later teardrop canopies.


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## SaparotRob (Nov 10, 2020)

fubar57 said:


> Many get shot down without realizing the opponent was there


I remember reading that in Mr. Sakai’s book. I think it was a P-39 he got.

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## GregP (Nov 10, 2020)

P-39 Expert, I am with you on respecting the tests as run at the time. But, in this case, we have one test that is markedly different from all the OTHER tests.

The basic differences between the P-39C and P-39D were armor, 2 more guns and ammunition (with an existing two relocated to the wings), and self-sealing tanks. The weight difference you keep harping on, "836 pounds," WILL NOT result in an extra 1,000 feet per minute climb difference. Period. A 12% reduction in weight does NOT give you a 37% increase in climb rate.

So, either the P-39C was operated at higher MAP than reported or the other P-39s were operated at lower power. There is no third option. If I'm going to say a test is recorded incorrectly, it makes a LOT more sense to me that ONE test (the P-39C) is misreported than all the rest of them (P-39D, et al) being incorrect. For all I know, the Allison in the P-39C test was "hot-rodded" by being ported and polished to give more power than normal. I DOUBT that, but there is SOMETHING wrong for sure. I hesitate to even question ONE test, but we have this wide discrepancy in climb rate that only shows up in the P-39C test.

Saying that 836 pounds accounts for it just isn't going to cut it because it doesn't account for it. The LEAST history-disturbing conclusion is that the P-39C test was run in some non-standard manner.

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## FLYBOYJ (Nov 10, 2020)

P-39 Expert said:


> Biff, those teste were conducted at Wright Field by AAF staff whose only job was to test those planes* under very strict testing standards and criteria. * If some guys on a message board try to invalidate a test done 70 years ago then we have no basis for evaluating the differences in those planes. We must assume that the tests were conducted properly and the information is accurate. Otherwise, what's the point if we're making the rules up as we go along?



For that time period, absolutely, but it's quite evident, looking in hindsight, there's room to dispel some data based on what we now know about these aircraft and some of the methodology used to collect data.


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## MIflyer (Nov 10, 2020)

GregP said:


> In any case, the P-39 was NOT a favorite combat airplane of anybody on the US military in any theater.



Really good pilots loved the P-39 because it was very responsive, with a gearing between the stick and the control surfaces that meant that it required very small movements to get a lot of results. They did not love it because it was easy to fly but rather because it was hard. 

Chuck Yeager loved it. "Winkle" Brown loved it. A friend of mine who had flown in WWII delivered an airplane to a museum back in the 90's and found they were distraught because they completed restoration of a P-39 but had no one checked out in it. He told them he was, took it up, and had a ball.

But that does not mean that they would want to fly it in combat.


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## XBe02Drvr (Nov 10, 2020)

SaparotRob said:


> I remember reading that in Mr. Sakai’s book. I think it was a P-39 he got.


Yup, with four cannon shells and no machine guns.


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## nuuumannn (Nov 10, 2020)

EIGHTY pages! Dammit, got a bit of catching up to do on the Lancaster nuclear bomber thread...

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## wuzak (Nov 10, 2020)

Is it odd that the listed climb rate in both eth P-39C and P-39D tests are constant up to, basically, the critical altitude?

And that power is constant below that as well, according to the charts?


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## BiffF15 (Nov 10, 2020)

fubar57 said:


> Many get shot down without realizing the opponent was there



From the gun footage I have seen, I think it could be easily argued that more than half had no idea they were being attacked until to late.

Cheers,
Biff


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## pbehn (Nov 10, 2020)

BiffF15 said:


> From the gun footage I have seen, I think it could be easily argued that more than half had no idea they were being attacked until to late.
> 
> Cheers,
> Biff


In the Battle of Britain it was much more than half, it was very difficult to make a kill when a lot of planes were in a fur ball, plus it is estimated up to 10% were hit by friendly fire or enemy fire not actually meant for them.... and then there were more than a few collisions too.

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## BiffF15 (Nov 10, 2020)

P-39 Expert said:


> Biff, those teste were conducted at Wright Field by AAF staff whose only job was to test those planes under very strict testing standards and criteria. If some guys on a message board try to invalidate a test done 70 years ago then we have no basis for evaluating the differences in those planes. We must assume that the tests were conducted properly and the information is accurate. *Otherwise, what's the point if we're making the rules up as we go along?*



P39 Expert,

Realize that you are making up the rules as you go along with the P39C to D difference of 836lbs accounting for a 1000 fpm increase in climb.

*"The basic differences between the P-39C and P-39D were armor, 2 more guns and ammunition (with an existing two relocated to the wings), and self-sealing tanks. The weight difference you keep harping on, "836 pounds," WILL NOT result in an extra 1,000 feet per minute climb difference. Period. A 12% reduction in weight does NOT give you a 37% increase in climb rate." GregP*

I quoted and bolded Gregs' comment above to *re-iterate* what you are choosing to ignore. You are also giving no credit to those guys who were there and doing the fighting and or decision making. The US decided it didn't cut the mustard. Russia loved them. They also over boosted them (could walk home if it failed), and kept the war low which played into the P-39s strengths. Compared to it's contemporary Russian counterpart it was probably a step up, or the motor could take a thrashing that others couldn't (don't know but am making an assumption based on the testing that occurred regarding the actual limits of the V-1710).

Also my earlier post regarding the handling / spin characteristics of the P39 as compared to it's US contemporaries went unanswered. If the USAAC went to the lengths of making a spin video, including showing a crash, then there had to be something in its handling as compared to its counterparts. I've done spins, come down through the contrails in a tail slide, negative G stalls, a negative G guns track (very uncomfortable), near mid airs, and all sorts of fun (scary) stuff but after watching that video I would want a serious demo or 3 from an IP before attempting one. 

The guys on here are trying to help, let them.

Cheers,
Biff

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## Ivan1GFP (Nov 10, 2020)

P-39 Expert said:


> Here's a photo of the arrangement. Don't think the 37mm horsecollar magazine fits in there, but a 20mm belt feed might.



I don't really think keeping the 37 mm with its penalties was such a good idea but if it had to be done.....
How about running the endless belt magazine UNDER the cannon instead of over it?
I also wonder if shifting the .30 cals a few inches forward would cause problems.


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## GregP (Nov 10, 2020)

Hi Miflyer.

Yes, it was a "favorite" of low-altitude hot dogs and was quite a good aircraft below 10,000 feet MSL. I'm sure that the P-39 would have been a good mount for almost any low-altitude mission that wasn't out of range. But, if the fight was above maybe 12,000 feet, then they would have chosen some other aircaft ... IF there was a choice. If your unit was flying P-39s, then you flew a P-39 and figured out how to get the most out of it.

Some P-39 info:
1) Australia: 31st Pursuit Group, Michigan. 39, 40, 41 Squadrons. 1941. Then they went to Australia. Not great success.
2) New Guinea: 8th Fighter group. 35 and 36 Squadrons. 1942. 26 of 41 P-39s remained when they reached Port Moresby, most of them lost in accidents before combat was ever joined. Combat in Apr 42. Buzz Wagner evaluated the P-39 versus the Zero. The Zero out-maneuvered, out-climbed, and out-accelerated the P-39, but the P-39 was faster at sea level. He rated the P-39 as 10% better than the P-40 in everything but maneuverability. The flaws he listed included gun reliability, lack of engine armor, leaky propellers, weak undercarriage, poor performance above 18,000 feet (higher than often reported), and – most important – lack of range. The Airacobra could cope above New Guinea and Guadalcanal, but was out of the picture for most “next targets” due to lack of range. The Airacobras about held their own (kills and losses about even), but they were always outnumbered. By the end of 1942 the P-39 squadrons in V Fighter Command had claimed 80 victories but had lost a similar number of aircraft themselves at a cost of 25 pilots killed or missing.
3) Aleutians: 54th FG, Jun - Oct 42. Not much to say ... no enemy there.
4) Guadalcanal: P-400s. 67th FS. 22 Aug 42. Lost 10 of 14 P-400s in 4 days. Oct 42, 339th FS arrived with P‑39s. Unreliable guns. Jamming 37 mm cannons, usually after 2 – 3 shots. Lt. William Fielder scored 5 kills in a P-39 – only America P-39 Ace. Not much other successes.
5) Kwajalein Island: 318th FG, 46 and 77 FS. Phased out in 1944. Last P-39 groups in Pacific.
6) North Africa and Italy: 81st and 350th FG, 68th OG (PR). End of 1942. Lost 107 P-39s, mostly to ground fire. 20 air kills and about the same on the ground. Final kill 6 Apr 44.
7) Training: Most important advanced trainer inside U.S.A. At least we found a use for them.

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## Stig1207 (Nov 11, 2020)

GregP said:


> The Airacobras about held their own (kills and losses about even), but they were always outnumbered. By the end of 1942 the P-39 squadrons in V Fighter Command had claimed 80 victories but had lost a similar number of aircraft themselves at a cost of 25 pilots killed or missing.



According to Claringbould they were credited with shooting down 95 Zero's, so one would think that they would have considered themselves as doing pretty well; that kills were well in access of losses, and much better than 'holding their own'.
Maybe they percieved that they were always outnumbered? There was not actually any real difference in numbers of available P-39's vs Zero's.


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## XBe02Drvr (Nov 11, 2020)

Stig1207 said:


> Maybe they percieved that they were always outnumbered? There was not actually any real difference in numbers of available P-39's vs Zero's.


You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.

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## PAT303 (Nov 11, 2020)

81 pages and you are all still arguing about how easy it is to turn a donkey into a war winning by simply removing a couple of .30 cals and some armor????.


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## XBe02Drvr (Nov 11, 2020)

PAT303 said:


> 81 pages and you are all still arguing about how easy it is to turn a donkey into a war winning by simply removing a couple of .30 cals and some armor????.


Amazing, ain't it?

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## buffnut453 (Nov 11, 2020)

XBe02Drvr said:


> You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.



It's not just a reliability issue. The force that's on the offensive can pick the time and location of their attack, so they can plan for how to mass their force. The defensive side is responsive, which presents challenges when it comes to massing force.

Basically, the defending side has 2 choices: maintain a standing CAP or try to scramble to respond. CAPs consume a lot of airframes (typically an entire squadron to maintain a 3-4 aircraft CAP.) and the continual flight hours eat through serviceable airframes very quickly. If you don't have standing patrols, then the challenge is scrambling large numbers of defensive fighters in a short timeframe.

Bottom line: it's easier to mass force for offensive ops than it is for defensive ops, which means defenders will often be outnumbered.

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## P-39 Expert (Nov 11, 2020)

fubar57 said:


> Many get shot down without realizing the opponent was there


Most never knew their opponent was there. 60%+ by many estimates.


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## MIflyer (Nov 11, 2020)

GregP said:


> Yes, it was a "favorite" of low-altitude hot dogs and was quite a good aircraft below 10,000 feet MSL.



Erich Hartman said, "At low altitude the P-39 performed like the 109."


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## Stig1207 (Nov 11, 2020)

XBe02Drvr said:


> You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.



Sure, but over New Guinea, there was no one side bringing consistantly more aircraft to the fight than the other, mostly it seems to have been pretty even. Nor was one side offensive and the other only defensive; they attacked each other, 'tit for tat' as Claringbould calls it. 
These were small scale operations, and the P-39's for most smart had the altitude advantage to due adequate forewarning by Coastal spotters. The P-39's were caught out on a few occasions where the spotters didn't see the attacking Japanese formations, but that was not the norm.


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## Stig1207 (Nov 11, 2020)

MIflyer said:


> Erich Hartman said, "At low altitude the P-39 performed like the 109."



On the ground?

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## P-39 Expert (Nov 11, 2020)

GregP said:


> P-39 Expert, I am with you on respecting the tests as run at the time. But, in this case, we have one test that is markedly different from all the OTHER tests.
> 
> The basic differences between the P-39C and P-39D were armor, 2 more guns and ammunition (with an existing two relocated to the wings), and self-sealing tanks. The weight difference you keep harping on, "836 pounds," WILL NOT result in an extra 1,000 feet per minute climb difference. Period. A 12% reduction in weight does NOT give you a 37% increase in climb rate. *All those differences were internal. They had no aerodynamic effect whatsoever. The only difference in the two planes was weight. *
> 
> ...


Expand above.


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## MIflyer (Nov 11, 2020)

Stig1207 said:


> On the ground?



I have flown both taildraggers and nosegear airplanes and I can say with great confidence that the P-39 was vastly superior on the ground to the 109. According to reports, the 109 was one of the worst airplanes ever built for handling on the ground. 

And the attitude the P-39 was sitting at on the ground meant it could still shoot targets. Supposedly there was a P-38 pilot who actually used to land, drive around, and shoot up Japanese airbases on the ground in the Pacific, but I never heard of any P-39's doing that.

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## Stig1207 (Nov 11, 2020)

I should have written _parked on the ground_, but anyway I just being funny (trying to).

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## glennasher (Nov 11, 2020)

Stig1207 said:


> I should have written _parked on the ground_, but anyway I just being funny (trying to).




It's quite all right, I understood it immediately, and got a good chuckle out of it. 

It's almost as funny as one member's deliberate obtuseness and refusal to understand facts.

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## BiffF15 (Nov 11, 2020)

P-39 Expert said:


> Expand above.



P39 Expert,

Your ability to repeat something, while faced with information that refutes it, is truly something to see.

Good luck,

Biff

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## MIflyer (Nov 11, 2020)

BiffF15 said:


> Your ability to repeat something, while faced with information that refutes it, is truly something to see.



You don't understand! Something is because it is, it is, it is!

Or so say the 6 year olds.


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## Ivan1GFP (Nov 11, 2020)

MIflyer said:


> I have flown both taildraggers and nosegear airplanes and I can say with great confidence that the P-39 was vastly superior on the ground to the 109. According to reports, the 109 was one of the worst airplanes ever built for handling on the ground.
> 
> And the attitude the P-39 was sitting at on the ground meant it could still shoot targets. Supposedly there was a P-38 pilot who actually used to land, drive around, and shoot up Japanese airbases on the ground in the Pacific, but I never heard of any P-39's doing that.



I used to do that in one of the very old flight simulators! (SubLogic Jet)
Taxi around at high speed, blast a few targets with tracking missiles....
Taxi through the hangar for a reload.
It got to be kind of boring.

- Ivan.

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## XBe02Drvr (Nov 11, 2020)

P39 Expert said:
*Weight influences climb more than any other factor.*

*Negative! *Run the numbers. A 10% change in Thrust Available will have a greater effect on RoC than 10% change in weight. They advocated weight reduction because thrust was already maxed out in practical terms.


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## GregP (Nov 11, 2020)

Hi Stig1207. What book did Claringbould write? I ask becasue:

1) I have the Statistical Digest of World War II. The total victories are shown, but not by model of aircraft.
2) I have Naval Aviation Combat Statistics for WWII. The Navy didn't fly P-39s, so it is of no help.
3) I have many WWII aviation books, including Frank Olynyk's Stars and Bars. It is ovr 650 pages, but the data are there. It is just a bear trying to get through it. I may well make the effort, but finding such a treasure for other nations is impossible to date.
4) I have a file with more than 68,000 German claims, but the claim file doesn't tell you the aircraft being flown. It shows the pilot name, unit, victim, and location and date, but not the airplane being flown. I don't know how to find out what dates the various units were flying what aircraft.

So, I'm curious, but not curious enough to buy a book to settle a P-39 question. It was not a very good airplane during the war and is of interest, but not to the point of spending much money on it, specifically. I might change my mind if I OWNED a P-39, but I don't. It would be quite nice to fly one.

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## pbehn (Nov 11, 2020)

XBe02Drvr said:


> P39 Expert said:
> *Weight influences climb more than any other factor.*
> 
> *Negative! *Run the numbers. A 10% change in Thrust Available will have a greater effect on RoC than 10% change in weight. They advocated weight reduction because thrust was already maxed out in practical terms.


This why it is a groundhog thread, weight influences climb when you cant change anything else, neither a Jumbo Jet nor a Saturn V rocket had any trouble getting to 40,000 ft faster than a P-39 and they were a little heavier as far as I remember.

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## PAT303 (Nov 11, 2020)

BiffF15 said:


> P39 Expert,
> 
> Your ability to repeat something, while faced with information that refutes it, is truly something to see.
> 
> ...



I think this is the only thing we can all agree on, well almost all of us.

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## XBe02Drvr (Nov 11, 2020)

PAT303 said:


> I think this is the only thing we can all agree on, well almost all of us.


All but one, maybe.


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## nuuumannn (Nov 11, 2020)

PAT303 said:


> I think this is the only thing we can all agree on, well almost all of us.



I'm getting thread envy over here...

The Lancaster as a potential nuclear bomber in 1945

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## GregP (Nov 11, 2020)

Hi P-39 Expert. Post #1616! You hit the nail on the head! EXACTLY.

Except for the propeller, there was little aerodynamic difference, yet the climb rate is 37% higher for the P-39C and that is impossible if both planes were making 1,150 hp as stated in the reports. It just won't happen that way. EXACTLY my point.

Since the climb difference was noted, then either the P-39C was making more hp (extra MAP that, handily, is unreported) than indicated, or the P-39D was making less hp (my assumed rated power rather than military power) than indicated, or the pilot mis-timed it. Let's give the test driver the benefit of the doubt and say he timed it correctly. If so, then I am left with the first sentence of this paragraph, without the assumption that the pilot mis-timed it.

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## wuzak (Nov 11, 2020)

P-39 Expert said:


> *All those differences were internal. They had no aerodynamic effect whatsoever. The only difference in the two planes was weight.*



The guns in the wing would have some effect.

The fuselage was longer, which would have had some effect, albeit small.

And then there was the different propeller - not sure how different they were, so hard to know what effect that would have.




P-39 Expert said:


> *Same engine, same power below 10000'. Above 10000' the P-39C horsepower was actually slightly less.*



Why would that be? They are the same engine, right?

One would expect that the P-39C, being faster than the P-39D, would have greater ram effect and therefore a higher critical altitude. Assuming the same engine and rating.

We don't know what actual power the two planes had, the power numbers having been taken from two different charts. The charts also are unlikely to include ram effect.


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## windhund116 (Nov 11, 2020)

GregP said:


> Hi Stig1207. What book did Claringbould write? I ask becasue:
> 
> 1) I have the Statistical Digest of World War II. The total victorie are shown, but not by model of aircraft.
> 2) I have Naval Aviation Combat Statistics for WWII. The Navy didn't fly P-39s, so it is of no help.
> ...



I think Stig1207 meant this book. _P-39/P-400 Airacobra versus A6M2/3 Zero-Sen. New Guinea 1942_. Michael John Claringbould. Osprey Publishing, 2018. ISBN 978-1472823663.

Amazon link.

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## GregP (Nov 11, 2020)

Looks like a decent book ... we'll see.


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## MIflyer (Nov 11, 2020)

Well, some models of the P-39 had significantly better performance than did others.

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## GregP (Nov 11, 2020)

Wherever did you find THAT, Miflyer? Never saw that one before!

Those sure are BIG cannons in the wings! What are they, 15" inch Bazookas?

And it still has a big pushbutton on the nose, too! Or it that a nipple and it needs a bra?

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## BiffF15 (Nov 11, 2020)

GregP said:


> Wherever did you find THAT, Miflyer? Never saw that one before!
> 
> Those sure are BIG cannons in the wings! What are they, 15" inch Bazookas?
> 
> And it still has a big pushbutton on the nose, too! Or it that a nipple and it needs a bra?



It gets cold at altitude...

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## GregP (Nov 11, 2020)

Perhaps it would have made a good "American Meteor."

Wonder if it would have faster or slower than the F.9/40?





The cockpit on the P-39 jet is farther back than on the F.9/40, so it should be more streamlined, right? After all, the Gee Bee was fast:





But, the P-39 jet doesn't have that innovative, Mach-capable cruciform tail. Maybe it wouldn't need a jack under the wing trailing edge to stop it from falling back on the tail, though. The aerogodamnics might be tricky, too.


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## vikingBerserker (Nov 11, 2020)

Looking for that I came across a Soviet copy that was to have mated two together ala F-82. The Belyayex OI-2

Powered by 2 x 1,800 hp engines and armed with 2 x 23mm in the hubs, 4 x .50 cals in the left fuselage and 4 x 30 cal in the center wing and up to 1,100 lbs of bombs


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## GregP (Nov 11, 2020)

Vikes, Picture? Maybe this?




or this:





Well, at least it follows the rule: If it is wierd, it is British; if it is ugly, it is French; it it is weird AND ugly, it is Russian.

Not that the U.S.A didn't have wierd and ugly airplanes:





We DID! It has a face that would make a train want to take a dirt road on a rainy night. Note the not-quite-fully-enclosed nosewheel. That is so it can double as a big wheelbarrow?

Whoever designed that should be slapped, hard ... sort of like Moe slaps Curly:

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## vikingBerserker (Nov 11, 2020)

Only a silhouette:





The Bell P-39 Airacobra & P-63 Kingcobra


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## Stig1207 (Nov 12, 2020)

GregP said:


> Hi Stig1207. What book did Claringbould write? I ask becasue:
> 
> 1) I have the Statistical Digest of World War II. The total victories are shown, but not by model of aircraft.
> 2) I have Naval Aviation Combat Statistics for WWII. The Navy didn't fly P-39s, so it is of no help.
> ...



The link windhund116 provided; originally referenced by jmcalli2, to which I replied here #1025. Can't blame you for having missed or forgotten it, it's some 30 pages back!

1. There is this Warbirds and Airshows, but the victories by model given here don't really agree with the Statistical Digest, see USAAF figher victories. Ray Wagner provided stats by model for the ETO and MTO, which do agree with the Statistical Digest and at the same time noted that stats by model for the theatres vs Japan do not exist. Unfortunately, his website is no longer available, but Eagledad at one time posted an attachment on this site with the numbers in them.

4. I have downloaded your file, it's good work by you, my own Excel skills are rather limited. You could possibly match the aircraft with the claims by trawling through this site ww2.dk, but that too would be a major undertaking.

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## GregP (Nov 12, 2020)

Thanks, Stig1207. Nice sites. Unfortunately, it seems that Tony Wood's site is no longer up.

I can find Jan Safarik's site, and Tony seems to be his main source.

It DOES take some Excel time to turn that data into useful tables! I have a lot, but getting it all cross referenced so it is useful takes a LOT of time and effort. And I'm missing some rather vital data I'll likely never find. If it hasn't surfaced by now, it may never surface.

Even the Maxwell AFB site had been down more than 10 years ... at least for victory credits. And ... if you can get them, they are missing some data.

Cheers.


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## buffnut453 (Nov 12, 2020)

GregP said:


> Not that the U.S.A didn't have wierd and ugly airplanes:
> View attachment 601586
> 
> 
> We DID! It has a face that would make a train want to take a dirt road on a rainy night. Note the not-quite-fully-enclosed nosewheel. That is so it can double as a big wheelbarrow?



The fellas in the cockpit are all looking towards the camera...it's almost as if they're saying "Can we come out now? We PROMISE to be good!!!" 

Actually, as ugly as that aircraft is, I'm surprised the aircrew don't have paper bags over their faces to hide their embarrassment.

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## Stig1207 (Nov 12, 2020)

GregP said:


> Thanks, Stig1207. Nice sites. Unfortunately, it seems that Tony Wood's site is no longer up.
> 
> I can find Jan Safarik's site, and Tony seems to be his main source.
> 
> ...



Try this for Tony Wood #17


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## XBe02Drvr (Nov 12, 2020)

GregP said:


> Perhaps it would have made a good "American Meteor."
> 
> Wonder if it would have faster or slower than the F.9/40?


"Does it have roundels?"
"No, star and bar."
"Ergo, overweight and underspeed, old chap!"

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## MIflyer (Nov 12, 2020)

I found that jet P-39 in an article on the P-59. That was the first design..

Now, if you really want an innovative design for a version of the P-39, look at this night fighter modification. Who needs that old cannon?

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## Peter Gunn (Nov 12, 2020)

buffnut453 said:


> And that's another reason to disengage from the fight.
> 
> Did you see what I did there?
> 
> Ok...I'll get my coat!


In the "Likes" bar we need one of these -->

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## Peter Gunn (Nov 12, 2020)

MIflyer said:


> I found that jet P-39 in an article on the P-59. That was the first design..
> 
> Now, if you really want an innovative design for a version of the P-39, look at this night fighter modification. Who needs that old cannon?
> 
> View attachment 601608


Is this a "Just for the hell of it" experiment? What could they possibly think this would accomplish?


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## special ed (Nov 12, 2020)

It would most definitely out climb the meteor at all altitudes. And be faster without the radio.


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## MIflyer (Nov 12, 2020)

It's pretty obvious that if Larry Bell thought that P-39's could be sold as washing machines or refrigerators that we would have versions addressing those missions as well.

Pity that poor radar operator. Barf city! And I wondered how the guy in the nose of the Droopsnoot or ECM versions of the P-38 felt.


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## vikingBerserker (Nov 12, 2020)

Not a bad design, the exhaust stacks would be out of the way but I dont think that's a very comfortable position to be in on extended flights.


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## BiffF15 (Nov 12, 2020)

vikingBerserker said:


> Not a nad design, the exhaust stacks would be out of the way but I dont think that's a very comfortable position to be in on extended flights.



Well it didn't hold much gas (not going to be stuck in there for long), part of it's better performance. Just like the 109 & 190.

Cheers,
Biff


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## XBe02Drvr (Nov 12, 2020)

MIflyer said:


> Now, if you really want an innovative design for a version of the P-39, look at this night fighter modification. Who needs that old cannon?


With the droopsnooter and electronics out front as ballast, you can play schrage musik from behind the engine. Just remember to jettison your radar operator as you approach the end of your symphony to stay in CG!

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## XBe02Drvr (Nov 12, 2020)

MIflyer said:


> Pity that poor radar operator. Barf city! And I wondered how the guy in the nose of the Droopsnoot or ECM versions of the P-38 felt.


Especially since he'd have to pull the hood closed inside the glass nose when stalking a target to keep scope glow from alerting enemy gunners. Better have stomach acid resistant electronics! The "hell hole" for sure.


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## GregP (Nov 12, 2020)

Maybe they could figure out a way so the two guys could change seats and wouldn't be so bored with mundane missions. At least dual controls (sidestick, anyone?).

I'm still trying to figure out how a radar, a seat, and a guy in front are as heavy as a 37 mm cannon and two 50-cal MG with ammunition. Maybe they only let fat guys be radar operators to keep the airplane within CG limits.

I've also seen the inside of the nose with the driveshaft in there. Ain't much room for your necessary parts with the shatf running right up the middle, and you'd better pray it never has a bearing failure!

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## XBe02Drvr (Nov 12, 2020)

GregP said:


> I'm still trying to figure out how a radar, a seat, and a guy in front are as heavy as a 37 mm cannon and two 50-cal MG with ammunition.


If you ever saw my uncle's ham radio transmitter, a WWII airborne HF unit "tweaked" to 1KW, you wouldn't wonder. It could have served as a storm anchor for USS Enterprise.

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## vikingBerserker (Nov 12, 2020)

I think it would have been better having him behind the pilot, back to back.


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## P-39 Expert (Nov 12, 2020)

vikingBerserker said:


> I think it would have been better having him behind the pilot, back to back.


Finally something we can agree on, this POS was DOA.


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## BiffF15 (Nov 12, 2020)

vikingBerserker said:


> I think it would have been better having him behind the pilot, back to back.



AKA He-219 IIRC...

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## GrauGeist (Nov 12, 2020)

BiffF15 said:


> AKA He-219 IIRC...


Yep, back-to-back layout.


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## vikingBerserker (Nov 12, 2020)

Or take the Russian twin fuselage idea and put him in the other one.


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## glennasher (Nov 12, 2020)

vikingBerserker said:


> Or take the Russian twin fuselage idea and put him in the other one.




Just like they did the F-82................ Oh wait, F-82? Hell, if we've got the F-82, what do we need this thing for????

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## MIflyer (Nov 12, 2020)

Well, take a look at the electronics under the canopy and above the engine and then also in the regular radio compartment just ahead of the tail. CG would not be a problem. As for guns. the four .30 cal in the wings would have to do the job - but then again the Blenheim fighter had that same armament.

They did build a two seat radar equipped P-51D and tried it out in the ETO - but not for night fighting.


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## vikingBerserker (Nov 12, 2020)

glennasher said:


> Just like they did the F-82................ Oh wait, F-82? Hell, if we've got the F-82, what do we need this thing for????



But 3 years ealier


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## XBe02Drvr (Nov 12, 2020)

vikingBerserker said:


> I think it would have been better having him behind the pilot, back to back.


...straddling the engine, with the electronics in his lap to keep his essential bits warm!

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## eagledad (Nov 12, 2020)

Response to 1640

Attached are 2 files, Ray Wagner's ETO/MTO numbers and a revised set of victories that was posted on the net.

Eagledad

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## pbehn (Nov 12, 2020)

XBe02Drvr said:


> ...straddling the engine, with the electronics in his lap to keep his essential bits warm!


If you put the engines in the wings, have the crew side by side but slightly offset, swap the engines for Merlins and make it out of wood you will have a great P-39 night fighter, I am now glad I thought about it, why didn't anyone else? Hardly any work involved, it took less than a minute to type.

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## GregP (Nov 13, 2020)

I always wondered where the numbers from the internet came from since I can find the internet numbers, but not any documents that support those numbers.


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## MIflyer (Nov 13, 2020)

pbehn said:


> Hardly any work involved, it took less than a minute to type.



That's the way things work at the Pentagon.

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## Juha3 (Nov 13, 2020)

On the use of 7.62 mm (0.300) mgs in the Soviet Airacobras

On June 4, 1944, the famous 16 GvIAP, one of the most famous VVS KA Fighter Regiments and definitely the most famous P-39 unit

_Mission #2 between 16:25-17:30 (Moscow time), 10 Aerocobras in the Larga area between 1500-2500 m. (Klubov, Ivankov, Trofimov, Ketov, Ivashko, Berezhkin, Sukhov, Dushanin, Glinka, Vahnenko) Combat with 15 Ju 88, 14 Me 109, 12 Fw 190. Capt. Klubov downed an Me 109 at Redich (Dedich?), while Ivashko at Bogonos. 1 Ju 88 and 3 Fw 190s (by Glinka, Trofimov, …) were also claimed.* Consumed ammo: 129 37mm, 940 12.7mm, 6529 7.62mm rounds. *On the other hand 3 soviet Aerocobras were damaged:_

_Mission #3 between 18:20-19:15 (Moscow time), 8 Aerocobras in the Larga area. (Starchikov, Novikov, Torbeev, Statsenko, Ivanov, Onishenkov, Nikitin, Belozerov) Combat with 6 Fw 190, 4 Bf 109 at 2500 m. St.Lt. Nikolaii Alexeevich Starchikov downed a Fw 190, which fell at Movileni(?)–SE, 3 km. St.Lt. Grigorii Grigorevich Statsenko got damaged, but hit another one. *Consumed ammo:* *95 37mm, 950 12.7mm and 1400 7.62mm rounds. *No soviet losses!_

So they still had their .300 mgs installed. Klubov (31+3 victories) was still flying P-39N-1 at that time, Glinka is either Dmitri (50+0) or his brother Boris (27+2). Probably at least one of those flying Mission #3 and who had fired flew in a P-39Q with 0.5 gun gondolas installed because of the difference in the ratio of 37 mm ammo used to .5 ammo used
between Mission #2 and Mission #3.

Suorce:
Hartmann: claims vs. victories - Page 14 - Luftwaffe and Allied Air Forces Discussion Forum
HGabor 13th November 2020 02:55 Re: Hartmann: claims vs. victories

PS. Looking the ammo consumption data more carefully, it seems that at least a couple P-39s participating the Mission#3 did not have their wing mgs installed.

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## GregP (Nov 13, 2020)

Here's a little spreadsheet study I did a few years back.

I tried to list the individual victories for the top German aces. Depending on where you look, there are discrepancies in victory tallies. But then, you all KNOW that anyway.

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## Stig1207 (Nov 14, 2020)

GregP said:


> I always wondered where the numbers from the internet came from since I can find the internet numbers, but not any documents that support those numbers.



The attachments Eagledad posted are from Ray Wagner's American Combat Aircraft and the other I believe is from William Wolf's Victory Roll. It would be interesting where the authors got there statistics.

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## GregP (Nov 14, 2020)

Hi Stig1207.

I have Ray Wagner's book and have come across the other numbers on the net, but never knew where they came from.

Seems to me that if someone is going to go to all the trouble to accumulate the numbers shown, they'd include other numbers, too, such as sorties, losses, etc ... not just victories. Maybe I'm too much an engineer.

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## windhund116 (Nov 15, 2020)

I just received Michael Claringbould's new book on the New Guinea air battles WW2. 1942-44. Seems like a good book on specific types and pilots. 

Pacific Adversaries.

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## GregP (Nov 15, 2020)

Thanks Windhund!

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## windhund116 (Nov 15, 2020)

Welcome! Claringbould writes very good books. I like his style and Bruce Gamble trilogy about Rabaul --- re: this era and theater of the SWPA. 

Rabaul trilogy.

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## Stig1207 (Nov 16, 2020)

GregP said:


> Hi Stig1207.
> 
> I have Ray Wagner's book and have come across the other numbers on the net, but never knew where they came from.
> 
> Seems to me that if someone is going to go to all the trouble to accumulate the numbers shown, they'd include other numbers, too, such as sorties, losses, etc ... not just victories. Maybe I'm too much an engineer.



Which raises the question: where did Wagner get those stats? I have taken the liberty of adding the total stats for fighters in the ETO and MTO from USAAF Statistical Digest, to the attachment provided by Eagledad. The numbers are so close that they suggest a common source, but the breakdown by type of fighter is not in the Digest.

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## GregP (Nov 16, 2020)

Hi Stig. I've been chasing the numbers like these for some 40+ years, and it's tough to find data. Well, at least for me.

Some have pointed mne at sources that, for the life of me, I can't find, no matter how I look for them.

Almost seems like a deliberate attempt at NOT saving any reliable data by governments. They have data about bullets expended. Why not about kills, losses, sorties, etc by airplane model? It HAS to be in the combat reports when they save ANY data.


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## buffnut453 (Nov 16, 2020)

GregP said:


> Hi Stig. I've been chasing the numbers like these for some 40+ years, and it's tough to find data. Well, at least for me.
> 
> Some have pointed mne at sources that, for the life of me, I can't find, no matter how I look for them.
> 
> Almost seems like a deliberate attempt at NOT saving any reliable data by governments. They have data about bullets expended. Why not about kills, losses, sorties, etc by airplane model? It HAS to be in the combat reports when they save ANY data.



The problem is that, in certain theatres, the information was simply lost. Any campaigns where friendly airfields were overrun would result in lost records (e.g. France in 1940, Greece in 1940-41, Malaya/Singapore/NEI/Burma/Philippines in 1941-42 etc.). Also, the further forward the operating base, the more likely it is that record-keeping fell down the priority list of "things to do". Even high-intensity operations from relatively safe operating bases could lead to records being kept in a rather haphazard manner.

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## GregP (Nov 16, 2020)

Granted what you said above. But the existing records don't seem to track things that every commander would want to know, other than gasoline, ammunition, and airplanes on hand. Seems to me any self-respecting commander would want to know how his people are fairing at their jobs, and would track losses, accidents, victories, ran out of fuel, etc. How else can you create a "report card" for your unit and keep track of who is doing well versus who is not doing so well?

As a supervisor of electronic test, I needed to know how my department was doing and had to report on it at least 3 times per year and anytime something expensive happened. In the USAF in the mid-1970's I was a sergeant and had to report on things regularly. Included in these reports was data. There is nothing remotely so disturbing as systematic lack of information to someone in charge, expecially since they are responsible. 

Ask the Captain of the Exxon Valdiz, who was running his ship quite shorthanded, his radar had been out for over a year (Exxon would not repair it), the coast guard failed to report to ships that they were no longer tracking ships in the channel, and it was very widely reported that Capatain Hazelwood had been drinking even though it was established in the trial clearly that he had not. Think he wanted more information? I'd say. His career has never recovered even though he still has a Master's license.

A WWII commander would have known everything about his unit, and the records that DO exist should be pretty clear.

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## buffnut453 (Nov 16, 2020)

And exactly how long was a commanding officer in charge of a squadron during WW2? Months, maybe? He would see how the unit operated based on observation during combat and would make adjustments to training and leadership as he saw fit, or as forced upon him by circumstances (e.g. receiving a batch of sub-standard new pilots or losing a key flight leader due to death, injury or posting). 

Most squadron commanders weren't in place long enough to focus on long-term trends. They simply made decisions necessary to get the job done based on what they observed. Frankly, they didn't have time to pore over statistical charts. They were too busy fighting a war.

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## GregP (Nov 16, 2020)

Decent points, buffnut. 

And I wsan't thinking of statistical charts. I was thinking of necessary data:

Available food & resupply date, clothes & necessities, ammunition, spare parts & tools& utensils (like litchen), kills, losses, accidents in several categories, aborts for mechanical that weren't verified, mechanical state of your assigned airplanes in general, and replacement personnel lead time as a bare minimum. If you don't know about any one of them, then you may not stay operational and you may not know who is doing well and who isn't.


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## buffnut453 (Nov 16, 2020)

I understand, and my use of the word "statistics" wasn't very apt...but my general point remains that full documentation is nice if you have the luxury to maintain it. 4

The RAF Operations Records Books for many units that operated in Malaya, Singapore and Burma, which would normally provide details of sorties flown, losses to all causes, and kills, were destroyed or abandoned in February 1942, thus the ORBs for 67, 243, 488 and 21 Sqns all peter out at the end of December 1941. There are no records for January-February which, for most of the units, was the primary period of fighting. I did manage to find a few combat reports for 67 Sqn over Burma in December 1941, and even one or two for 21 Sqn RAAF over northern Malaya earlier in the month. However, all other combat reports are lost to the mists of time. 

I'm sure each day that the Squadron COs and Flight Commanders had a pretty good handle on the number of available aircraft because it would be reported to them verbally by the engineering staff. There were also returns on availability that flowed up to HQ, and some of those have survived. However, the availability numbers never reflect the true number of airframes still in use by the units because it doesn't include those machines undergoing maintenance/repair that, ultimately, were returned to operational status. 

Bottom line is that people aren't going to sit in offices typing up reports if they're being shot at. They have far more important things to worry about. Equally, the Daily States chalkboard would be of much more practical use than any amount of paper files.


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## GregP (Nov 16, 2020)

Office work and mission plans rarely if ever survive enemy contact since the enemy VERY rarely does what you THINK they will do.

Understand that well.  Cheers.


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## BiffF15 (Nov 16, 2020)

GregP said:


> Decent points, buffnut.
> 
> And I wsan't thinking of statistical charts. I was thinking of necessary data:
> 
> Available food & resupply date, clothes & necessities, ammunition, spare parts & tools& utensils (like litchen), kills, losses, accidents in several categories, aborts for mechanical that weren't verified, mechanical state of your assigned airplanes in general, and replacement personnel lead time as a bare minimum. If you don't know about any one of them, then you may not stay operational and you may not know who is doing well and who isn't.



Greg,

You are in my opinion correct on what commanders should know. However, you are very data oriented, being an engineer that's understandable! However, you have to understand that not everyone is like that, or has time for detailed data collection. I've got ten planes, eleven pilots, and need to fly an 8 ship mission. Do I have enough flight leaders, a mission commander, and supervision? Yes, I can fly the mission. No, adjust and get them airborne. Maintenance what are you short of, or projected to be short of and lets get that lead turned. Bodies, planes, equipment in, bodies, planes equipment out. In Europe there were civilians you could bring into the squadron to help, in the Pacific not so much. Add attrition at all levels, rapid turnover, squadron movement, fog of war, etc., and the gators closet to the canoe got handled, and the ones further away would get dealt with when they get closer.

It certainly makes analysis 75 years later a PITA!

Cheers,
Biff


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## nuuumannn (Nov 16, 2020)

XBe02Drvr said:


> "Does it have roundels?"
> "No, star and bar."
> "Ergo, overweight and underspeed, old chap!"



Upvoted for the use of the word "ergo"!

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## GregP (Nov 16, 2020)

Hi Biff,

Offhand, I'd say that if the CO only thought that far ahead, then the unit wasn't going to be very effective for long. Yes, there are last-second detail changes and unforeseen events to handle (I've done that many times, as have you, I'm quite sure ... I bet you've flown an F-15 that wasn't 100% mission-capable, too), but parts, replacements, food and other necessary items don't come in overnight, so you HAVE to anticipate your needs or you'll run out of something vital. Want your morale to drop out of sight? Just forget food and/or toilet paper! Or the mail! The troops ain't gonna' be happy!

I'm assuming that the CO was expected to send in his list of needs and wants. He gets what he needs and as much of what he wants as they can spare ... assuming the supply boat isn't sunk or the supply train isn't blown up.


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## Stig1207 (Nov 17, 2020)

Greg, Buff
I think this a case of you both being right; administrative requirements to ensure operational ability vs what's practical and possible out in the field when it gets real.

However, the information that did get passed through to the relevant authorities, was collected and collated into the document that is USAAF Statistical Digest, which (along with the USN statistics) is unique; a similar overview is not available publicly for other of the Airforces. It is a little strange then, when those statistics vary compared to other sources, eg. USAF85.


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## GregP (Nov 17, 2020)

Running the unit was tough, and I'm fully aware that saving data wasn't an objective. I just think that someone must have written down what ws going on, if only to give the CO a report. I'm sure a lot got lost, but I have trouble finding almost ANY data about regular things that most units cared about, like kills, all types of losses, sorties, etc. I think there should at lest be some good data somewhere about it.

Biff is right, of course, they were trying to fight a war, first and foremost.

I'm just thinking that SOMEONE was tracking this stuff at headquarters. Yet we only seem to have USAAF Report # 85, and it is nowhere close to being able to import for analysis. If you want to use report 85, you have to enter it yourself. It seems to me that SOMEONE in the military would be interested in the history of the biggest aerial war ever fought. But, since we are in sequester, even the Maxwell AFB database had been down for about 10 years. The data are there, but we don't have much access. The Navy likely has the data, too, but won't release it just like they maintain that they own all the crashed Navy airplanes in the ocean.

It's frustrating, but it is what it is.

Cheers.

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## XBe02Drvr (Nov 17, 2020)

GregP said:


> It seems to me that SOMEONE in the military would be interested in the history of the biggest aerial war ever fought. But, since we are in sequester, even the Maxwell AFB database had been down for about 10 years. The data are there, but we don't have much access. The Navy likely has the data, too, but won't release it just like they maintain that they own all the crashed Navy airplanes in the ocean.


You don't suppose they're comfortable with the publically accepted narrative as it stands, and don't feel the need to have their applecart upset by those pesky historians and revisionists?


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## SaparotRob (Nov 17, 2020)

The truth is out there.

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## buffnut453 (Nov 17, 2020)

SaparotRob said:


> The truth is out there.



Sometimes. Sometimes not.

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## GregP (Nov 17, 2020)

Well, offhand, I'd say there isn't a lot of official interest in releasing data that people interested in aerial warfare during WWII want to see. It could be that they just want to piss us off, but that seems highly unlikely. Much more likely is that it takes money and time (manpower) to dig into this stuff and nobody wants to pay for it. Truth be know, taxpayers wouldn't likely approve of the expense, either. Just look at the AHFRA site that had been down for 10 years. They HAVE the data and just won't even put it on a server! That seem like a slap in the face beause it was THERE back in 2009 or so. Searchable.

So, it's left for interested parties like us to dig out. I'm just not really sure where to start digging. Where would we find the data? Data that we could trust.

Maybe we should have a sticky thread where we can post links and references to places and documents where we have found data on WWII. I have a great start on it, bit am not really sure where to go from here. Where did Ray Wagner get his data for the ETO/MTO in his 1960's book "American Combat Planes?" We shopuld be able to find THAT data, anyway. He did.

And I surely didn't mean to argue with Biff about it. It's just that I've been looking for the data for more than 35 years. off and on, and it seems as if though there should be a better way to go about it than my route ...

Cheers anyway!

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## glennasher (Nov 17, 2020)

Since this is a groundhog thread, I thought I'd show the one outside the house this afternoon.

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## Snautzer01 (Nov 17, 2020)

It is missing its armour.

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## buffnut453 (Nov 17, 2020)

Snautzer01 said:


> It is missing its armour.



Wait for it to start tumbling, then.

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## Dash119 (Nov 17, 2020)

buffnut453 said:


> Wait for it to start tumbling, then.



I don't know, maybe they moved the radio forward to correct the CG...

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## glennasher (Nov 17, 2020)

Snautzer01 said:


> It is missing its armour.




They did that so it could climb higher and faster...........................


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## buffnut453 (Nov 17, 2020)

glennasher said:


> They did that so it could climb higher and faster...........................



Just means they have further to tumble...faster.

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## SaparotRob (Nov 17, 2020)

There’s plenty of life in this thread.

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## vikingBerserker (Nov 17, 2020)

So.........................what color should we paint the ground hog?

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## buffnut453 (Nov 17, 2020)

vikingBerserker said:


> So.........................what color should we paint the ground hog?



That rather depends on whether you want to build an early- or mid-war groundhog, and whether you're looking at a standard daytime pursuit groundhog or the specialized night intruder groundhog.

Bear in mind that lend-lease groundhogs given to the Brit's had standard RAF camo using U.S. equivalent paints. However, their service was short-lived because the Brits didn't like the groundhog, finding it neither useful for hunting nor as a decent Sunday roast (tastes too much like chicken).

Finally, don't forget that, later in the war, groundhogs started leaving the factory unpainted to reduce drag and eliminate the weight of the paint.

So...you takes your groundhog and makes your choice!

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## Airframes (Nov 17, 2020)

anyone got any colour pics for a groundhog I'm building .......................

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## buffnut453 (Nov 17, 2020)

Airframes said:


> anyone got any colour pics for a groundhog I'm building .......................



Post #1693. There's even a colour video clip at post #1695, but it's a bit brief. Sadly no special markings are visible on any of the groundhogs shown.


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## Dash119 (Nov 17, 2020)

Airframes said:


> anyone got any colour pics for a groundhog I'm building .......................


The 'C' model, or the slower climbing, overweight but aerodynamically identical 'D' model...

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## buffnut453 (Nov 17, 2020)

My wife just told me I need to get out more...so I'm off to take the groundhog for a walk.

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## Airframes (Nov 17, 2020)

Socially distancing, of course ................

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## buffnut453 (Nov 17, 2020)

Well, of course...6 ft for COVID and an extra 10 ft in case the groundhog starts tumbling. Standard safety protocols.

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## buffnut453 (Nov 17, 2020)

I'm lucky enough to own a Packard-built groundhog which is far superior to the original Rolls Royce groundhogs.

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## Airframes (Nov 17, 2020)

But I always understood that the initial acceleration wasn't as good as the Rolls version - but they did come with a great socket set, in a handsome wooden case !

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## GregP (Nov 17, 2020)

Here's their squadron emblem.






It's from the old Groundhog-in-the-Ring squadron of WWI. Mascot was Eddie Rickenbarker ...

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## buffnut453 (Nov 17, 2020)

Airframes said:


> But I always understood that the initial acceleration wasn't as good as the Rolls version - but they did come with a great socket set, in a handsome wooden case !



Yeah, but the Packard is much smoother and sounds better. Plus it was specially redesigned for faster production.


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## GregP (Nov 17, 2020)

... faster production, does that mean they eat faster?


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## buffnut453 (Nov 17, 2020)

Yeah, quite a bit, actually. So much so that it presented CofG problems during longer meals.

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## Airframes (Nov 17, 2020)

And I believe the Daimler-Benzackard was even better, capable of well over 450 mph at 30,000 feet, and only burning five Imp Gallons per hour, with a plug change only required after 200 hours .............

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## buffnut453 (Nov 17, 2020)

Well, that goes without saying. Any groundhog with black crosses on it is automatically better than any Allied groundhog.

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## GrauGeist (Nov 17, 2020)

Just curious, on that particular model, are it's incisors 37mm or 20mm - hard to see in the photo...

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## windhund116 (Nov 17, 2020)

Snautzer01 said:


> It is missing its armour.



Center-of-gravity modification.

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## windhund116 (Nov 17, 2020)

buffnut453 said:


> And exactly how long was a commanding officer in charge of a squadron during WW2?  Months, maybe? He would see how the unit operated based on observation during combat and would make adjustments to training and leadership as he saw fit, or as forced upon him by circumstances (e.g. receiving a batch of sub-standard new pilots or losing a key flight leader due to death, injury or posting).
> 
> Most squadron commanders weren't in place long enough to focus on long-term trends. They simply made decisions necessary to get the job done based on what they observed. Frankly, they didn't have time to pore over statistical charts. They were too busy fighting a war.



In case you didn't see this from the _Bail out of B-24 thread_, an old family friend was a CO of an 8AF Heavies unit. He trained the unit in the US. Went over to England with the unit. Then, came home with same unit, after the war ended. According to records, he is the only CO to accomplish this, with any 8AF Heavies, in WW2. 

Rackheath Aggies.

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## BiffF15 (Nov 17, 2020)

buffnut453 said:


> Yeah, but the Packard is much smoother and sounds better. Plus it was specially redesigned for faster production.



Faster production, or REPROduction?...

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## Snautzer01 (Nov 18, 2020)

vikingBerserker said:


> So.........................what color should we paint the ground hog?




Pre war livery

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## windhund116 (Nov 18, 2020)

Hey!!! No make fun of me!

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## Marcel (Nov 18, 2020)

I’m guessing the British groundhog was rather flimsy?

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## windhund116 (Nov 18, 2020)

Wasn't the P39 a more-or-less "stop-gap" fighter, as used in the early stages of the SWPA? At least, until more advanced fighters could be employed?


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## windhund116 (Nov 18, 2020)

Were Ki-44 (Tojo) Sentai ever placed in New Guinea or Rabaul?

Thanks!


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## Snautzer01 (Nov 18, 2020)

Marcel said:


> I’m guessing the British groundhog was rather flimsy?




No underpowered for its weight. (Early production with out blower below)

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## buffnut453 (Nov 18, 2020)

That appearance is unlikely to result in reproduction.

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## Marcel (Nov 18, 2020)

Snautzer01 said:


> No underpowered for its weight. (Early production with out blower below)
> 
> View attachment 602224


I thought that was a french ground hog

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## Snautzer01 (Nov 18, 2020)

Marcel said:


> I thought that was a french ground hog


Licence build. You can tell the difference by taking a close look a the cockpit canopy.

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## Snautzer01 (Nov 18, 2020)

The japanese copied the design but it was not liked very well.


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## Snautzer01 (Nov 18, 2020)

The Germans also copied it but it was over designed and as a lot of their stuff to late to make an impact.
Below the late 44 version with smoke apparatus.

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## special ed (Nov 18, 2020)

I thought I had learned not to drink coffee at the computer.

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## Peter Gunn (Nov 18, 2020)

special ed said:


> I thought I had learned not to drink coffee at the computer.


I thought that was scotch you're not supposed to drink at the computer.

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## Peter Gunn (Nov 18, 2020)

windhund116 said:


> Wasn't the P39 a more-or-less "stop-gap" fighter, as used in the early stages of the SWPA? At least, until more advanced fighters could be employed?


Yes but what's that got to do with Groundhogs?

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## pbehn (Nov 18, 2020)

Later American groundhogs were fitted with an internal nut supply in each front paw, had a spare nut sack in its stomach and could carry three years supply of nuts in bags made of disposable brown paper. They could walk further than any other groundhog without stopping.

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## windhund116 (Nov 18, 2020)

pbehn said:


> Later American groundhogs were fitted with an internal nut supply in each front paw, had a spare nut sack in its stomach and could carry three years supply of nuts in bags made of disposable brown paper. They could walk further than any other groundhog without stopping.



Didn't this upset the center-of-gravity?

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## Marcel (Nov 18, 2020)

pbehn said:


> Later American groundhogs were fitted with an internal nut supply in each front paw, had a spare nut sack in its stomach and could carry three years supply of nuts in bags made of disposable brown paper. They could walk further than any other groundhog without stopping.


I think this answer is totally NUTS!

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## buffnut453 (Nov 18, 2020)

windhund116 said:


> Didn't this upset the center-of-gravity?



Yes, and the extra weight reduced climbing performance.

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## pbehn (Nov 18, 2020)

windhund116 said:


> Didn't this upset the center-of-gravity?


Only on the first few days of the holiday, dancing and other means of showing off were restricted until all bags and additional nut sacks were emptied.


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## pbehn (Nov 18, 2020)

Marcel said:


> I’m guessing the British groundhog was rather flimsy?


British groundhogs would never travel so stayed at home aggressively attacking anything trying to steal its nuts.

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## Airframes (Nov 18, 2020)

There may be a kernel of truth in that, although we'd need to shell out more than just peanuts to confirm it, and I hazel a guess we never would .............

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## SaparotRob (Nov 18, 2020)

Peter Gunn said:


> I thought that was scotch you're not supposed to drink at the computer.


It’s not just for breakfast anymore.

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## SaparotRob (Nov 18, 2020)

Were Allied nutsacks self sealing?


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## GrauGeist (Nov 18, 2020)

windhund116 said:


> Wasn't the P39 a more-or-less "stop-gap" fighter, as used in the early stages of the SWPA? At least, until more advanced fighters could be employed?





windhund116 said:


> Were Ki-44 (Tojo) Sentai ever placed in New Guinea or Rabaul?
> 
> Thanks!


The P-39, much like the F4F, was a type caught in a unique situation. A prewar design that had to adapt and make due until newer types could take the lead.

As for IJA aircraft of the 7th Air Division operating in the New Guinea area, there were no KI-44s. Only KI-43s, KI-61s and KI-45s.

Great questions, maybe we should have a thread just for that discussion.

Oh...wait...nevermind

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## buffnut453 (Nov 18, 2020)

SaparotRob said:


> Were Allied nutsacks self sealing?



Not at the outbreak of hostilities but the Allies learned very quickly and, by the summer of 1940, it was acknowledged that any groundhog destined for RAF service required self-sealing nutsacks.

On the Axis side of things, Germany was in-step with Britain regarding self-sealing nutsacks. However, the Japanese sacrificed nutsack protection on their groundhogs in favour of improved speed and climbing performance. That approach worked fine until the middle of 1942 but thereafter it proved to be a disastrous approach as the Japanese air arms lost increasing numbers of groundhogs because they either ran out of nuts due to damaged nutsacks or their nuts exploded due to Allied fire.

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## vikingBerserker (Nov 18, 2020)

Dear Diary,

Today I learned information about the following topics on the P-39 Thread:
1 - P-39
2 - Guns people own
3 - Scotch
4 - Groundhogs (both aerodynamic properties and CG)

I wonder if it makes a difference if it's African or European?

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## Marcel (Nov 18, 2020)

vikingBerserker said:


> Dear Diary,
> 
> Today I earned information about the following topics on the P-39 Thread:
> 1 - P-39
> ...


You’re forgetting nutsacks.

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## Airframes (Nov 18, 2020)

There is a current shortage of nutsacks as, due to the Covid pandemic, they are being adapted for use as face masks by many people across the world.
However, an as yet unsubstantiated report has hinted that a hitherto unknown supply of genuine, 1944 vintage, un-issued nutssacks has been discovered, in crates buried "somewhere in Burma", although it is not known if these are of the self-sealing variety.

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## GregP (Nov 18, 2020)

P-39s gathered in "towns," "clans," and "coteries." They kept morale up with social mixing and grooming, which was good becasue the landing gear needed con stant grooming.

Once the P-39 went from 1,200 hp to 1,325 hp, it could carry an astounding assorment of nutsacks, mostly centerline. If it didn't start eating the nutsacks from the aft end forward, it would wind up out of CG and would just sit on it's tail and not go anywhere until it crashed or was eaten by a German Hawk.


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## SaparotRob (Nov 18, 2020)

GregP said:


> P-39s gathered in "towns," "clans," and "coteries." They kept morale up with social mixing and grooming, which was good becasue the landing gear needed con stant grooming.
> 
> Once the P-39 went from 1,200 hp to 1,325 hp, it could carry an astounding assorment of nutsacks, mostly centerline. If it didn't start eating the nutsacks from the aft end forward, it would wind up out of CG and would just sit on it's tail and not go anywhere until it crashed or was eaten by a German Hawk.


Does the Planes Of Fame Museum in Chino, California, have any groundhogs in its collection?

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## Dash119 (Nov 18, 2020)

SaparotRob said:


> Does the Planes Of Fame Museum in Chino, California, have any groundhogs in its collection?


Edward T. Maloney had tremendous foresight, but even he didn't foresee the need to preserve the veteran groundhogs...

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## GregP (Nov 18, 2020)

Our P-39 came from a South Pacific island and, instead of digging a burrow, it sat on its wheels in the dirt for 30+ years or more, and the corrosion means it will never fly again unless some rich benefactor donates a truckload of money so the wing spar can be replaced. So, ours IS a groundhog. Maybe COULD fly again, but likely never will. Not sure of ours was in the Prairie Dog-in-the-Ring squadron, but I think not. If it had been, it would be more dignified.

I think ours was in a redneck clan that was on New Guinea and was recovered in the 1970's by David Tallichet's team.

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## windhund116 (Nov 18, 2020)

GrauGeist said:


> The P-39, much like the F4F, was a type caught in a unique situation. A prewar design that had to adapt and make due until newer types could take the lead.
> 
> As for IJA aircraft of the 7th Air Division operating in the New Guinea area, there were no KI-44s. Only KI-43s, KI-61s and KI-45s.
> 
> ...



Was it newly developed Navy air tactics or the Wildcat's toughness versus the Airacobra which lead the F4F to have a 5:1 plus kill ratio over the Japanese? From sources I've read, the P39 kill ratio was closer to 1:1 against the Japanese.

Thanks!


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## nuuumannn (Nov 18, 2020)

buffnut453 said:


> That approach worked fine until the middle of 1942 but thereafter it proved to be a disastrous approach as the Japanese air arms lost increasing numbers of groundhogs because they either ran out of nuts due to damaged nutsacks or their nuts exploded due to Allied fire.



Nonetheless, right until the end of the war, Allied groundhogs were advised never to dog fight Japanese ones, particularly if they exposed their nutsacks at low speed, regardless of how under armoured they were...

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## windhund116 (Nov 19, 2020)



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## P-39 Expert (Nov 19, 2020)

windhund116 said:


> Was it newly developed Navy air tactics or the Wildcat's toughness versus the Airacobra which lead the F4F to have a 5:1 plus kill ratio over the Japanese? From sources I've read, the P39 kill ratio was closer to 1:1 against the Japanese.
> 
> Thanks!



Attached is a performance chart for the F4F-4 with P-39K performance in red. Keep in mind that the Wildcat climb data is at combat power while the P-39K is at normal power (2600rpm) above 12500'. The blue dots are climb rates for the P-39K at combat power (3000rpm). 

My opinion of the combat record of the two planes in 1942 can be summarized as follows:

1. Training: Navy pilots graduated flight school with 600hrs flight time, AAF pilots 200hrs. Obviously this evened out as both groups gained combat experience.
2. Tactics: Navy discipline was probably better, hit and run only, no dogfighting since they were normally aboard ship.
3. Equipment: F4F-4s seldom carried drop tanks while P-39s almost always carried a drop tank which limited their climb and ceiling. Weight reduction would have helped.
4. Mission: Very similar fighter missions, escorting medium altitude bombers and defending their carrier/airbase against attack. The AAF had to contend with more high altitude bombers (G4M) at 18000'-22000' while the Navy carrier pilots intercepted mostly low altitude dive bombers and torpedo planes. At Guadalcanal both services mission was almost identical. Both planes performed ground strafing missions, but P-39s were also tasked with more ground attack missions including level and dive bombing. They effectively performed both missions while the Navy used SBDs and TBFs for bombing.

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## Peter Gunn (Nov 19, 2020)

windhund116 said:


> Was it newly developed Navy air tactics or the Wildcat's toughness versus the Airacobra which lead the F4F to have a 5:1 plus kill ratio over the Japanese? From sources I've read, the P39 kill ratio was closer to 1:1 against the Japanese.
> 
> Thanks!


I was under the impression that when all was said and done after much research, the F4F was closer to 1:1 not 5:1 but I could be mistaken.

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## Peter Gunn (Nov 19, 2020)

SaparotRob said:


> Does the Planes Of Fame Museum in Chino, California, have any groundhogs in its collection?


Upon first reading this one, you came close to owing me a new keyboard...

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## MIflyer (Nov 19, 2020)

The FM-2 had a very high kill ratio, some say the best of any.

Note that on the occasions when the F6F shot down seven on one mission the kills were all bombers that were not doing much maneuvering. The F6F pilot had to just bore in and not be disturbed by the rear gunner. I think they junked the Hellcat when they got it back on the carrier.


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## SaparotRob (Nov 19, 2020)

Peter Gunn said:


> Upon first reading this one, you came close to owing me a new keyboard...


I hope you didn’t spill any scotch.


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## P-39 Expert (Nov 19, 2020)

SaparotRob said:


> Does the Planes Of Fame Museum in Chino, California, have any groundhogs in its collection?


Not that I know of, but the Commemorative Air Force, San Marcos, TX branch has one.

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## windhund116 (Nov 19, 2020)

SaparotRob said:


> Does the Planes Of Fame Museum in Chino, California, have any groundhogs in its collection?



You mean you didn't stop in at the *Groundhogs of Fame Museum*? It's just a little further south in Corona. Next to Rosie's Queen of Corona cantina, where me and Julio used to hang out.

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## buffnut453 (Nov 19, 2020)

windhund116 said:


> Next to Rosie's Queen of Corona cantina, where me and Julio used to hang out.



Is that down by the schoolyard?

I'll get my coat!

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## Airframes (Nov 19, 2020)

The cantina is now closed - it has a virus.
I'll get my coat too ...................

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## buffnut453 (Nov 19, 2020)

Airframes said:


> The cantina is now closed - it has a virus.
> I'll get my coat too ...................



You bring your groundhog and I'll bring mine.


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## Airframes (Nov 19, 2020)

Sorry, mine is shielding, due to the virus ............


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## fubar57 (Nov 19, 2020)

This thread has improved vastly over the past few days

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## buffnut453 (Nov 19, 2020)

Airframes said:


> Sorry, mine is shielding, due to the virus ............



I guess yours doesn't have the virus-repelling, self-sealing nutsacks, huh? You need to splash out and get the upgrade. It's worth every penny and really improves performance and safety of your groundhog.


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## GregP (Nov 19, 2020)

I'm not entirely sure we want perverted, self-sealing nutsacks down by the schoolyard. There might be a law against it.

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## fubar57 (Nov 19, 2020)

This is what happens to a pigeon when you expend it’s nose ammo. I guess you have to click on the photo to get the video going....I guess 


​

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## Dash119 (Nov 19, 2020)

fubar57 said:


> This is what happens to a pigeon when you expend it’s nose ammo
> View attachment 602310
> ​


It is quite obvious from this photo that they failed to move the radio forward from the tail section to correct the CG...

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## Airframes (Nov 19, 2020)

That looks coo-cool.
I've got me coat............................

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## fubar57 (Nov 19, 2020)

When I was growing up on the farm, amongst other breeds, I had Tumblers (backwards) and Rollers (forwards). Once they started to interbreed they turned into complete retards.

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## buffnut453 (Nov 19, 2020)

Is it a stealth pigeon? I can't see the photo. Maybe a groundhog stole it?


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## GregP (Nov 19, 2020)

Who knew the "P" in P-39 stood for Pigeon? That almost looks like a Pugachev Cobra maneuver.

A combat pigeon? With 20 mm feet?


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## buffnut453 (Nov 19, 2020)

Hey...I can see the pigeon on my phone. Maybe the groundhog brought it back. 

Definitely an aft CofG problem there, methinks, based on the video!


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## special ed (Nov 19, 2020)

When you take the radio out of a homing pigeon, that's what happens.


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## GregP (Nov 19, 2020)

A lamechevek?

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## glennasher (Nov 19, 2020)

He's back in the back yard..........................................................


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## buffnut453 (Nov 19, 2020)

Certainly appears to be struggling to gain altitude...barely looks like he's off the ground at all. Maybe if we removed about 836lb of excess weight, maybe we could turn it into an interceptor. Perhaps we should have an entire thread revolving around that single data point?

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## P-39 Expert (Nov 19, 2020)

buffnut453 said:


> Certainly appears to be struggling to gain altitude...barely looks like he's off the ground at all. Maybe if we removed about 836lb of excess weight, maybe we could turn it into an interceptor. Perhaps we should have an entire thread revolving around that single data point?


Gonna be hard to take 836lbs out of that.

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## buffnut453 (Nov 19, 2020)

P-39 Expert said:


> Gonna be hard to take 836lbs out of that.



Depends on how many nutsacks he has.


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## P-39 Expert (Nov 19, 2020)

fubar57 said:


> This is what happens to a pigeon when you expend it’s nose ammo. I guess you have to click on the photo to get the video going....I guess
> 
> 
> ​



Looks like he was under complete control at all times.

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## GregP (Nov 19, 2020)

Would be a task to remove 8.63 pounds ... if you did, all you'd have left is a Chipmonk, which is a decent trainer, but far from a fighter.

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## buffnut453 (Nov 19, 2020)

Those pesky decimal points...I knew I was missing something.

Maybe the groundhog took it.

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## GregP (Nov 19, 2020)

I've been robbed!


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## windhund116 (Nov 19, 2020)

And who can forget that famous movie _*Groundhog Down*_? From the bestseller by Joe Beaver?

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## GregP (Nov 19, 2020)

He might make a decent Frisbee ... wonder what the record is for the longest groundhog toss?


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## FLYBOYJ (Nov 19, 2020)

GregP said:


> He might make a decent Frisbee ... wonder what the record is for the longest groundhog toss?



go to 1:17

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## GregP (Nov 20, 2020)

Where do you FIND this stuff?

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## Peter Gunn (Nov 20, 2020)

buffnut453 said:


> You bring your groundhog and I'll bring mine.



...



Airframes said:


> Sorry, mine is shielding, due to the virus ............



...



buffnut453 said:


> I guess yours doesn't have the virus-repelling, self-sealing nutsacks, huh? You need to splash out and get the upgrade. It's worth every penny and really improves performance and safety of your groundhog.



Uh... do you two need a room?

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## Just Schmidt (Nov 20, 2020)

buffnut453 said:


> Certainly appears to be struggling to gain altitude...barely looks like he's off the ground at all. Maybe if we removed about 836lb of excess weight, maybe we could turn it into an interceptor. Perhaps we should have an entire thread revolving around that single data point?



It's entirely safe to fly it as long as it dosn't leave the ground.

However, if we get rid of those useless nuts, and move the lungs to its mouth, it'll leave even a squirrel behind in a climb.


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## XBe02Drvr (Nov 20, 2020)

Peter Gunn said:


> ...
> 
> 
> 
> ...


More like a dog (oops I meant gopher) fight ring!


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## windhund116 (Nov 20, 2020)

Groundhogs favorite group. The Almond Brothers.

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## Airframes (Nov 20, 2020)

What's got a hazel nut in every bite ?
Groundhog sh*t !!!


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## buffnut453 (Nov 20, 2020)

Peter Gunn said:


> ...
> 
> 
> 
> ...



Hey...what 2 grown men do with their groundhogs in their private time is nobody else's business. This is the 2020s after all! 

Personally, I think you're suffering from groundhog envy!


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## buffnut453 (Nov 20, 2020)

FLYBOYJ said:


> go to 1:17




See? Groundhogs can fly! It's all down to the propulsive force applied.

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## windhund116 (Nov 20, 2020)

FLYBOYJ said:


> go to 1:17




I'm wondering if the extra armor around the nutsack affected the groundhog's trajectory over that car? Should be some wind tunnel test results on the Net, somewhere. No?


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## buffnut453 (Nov 20, 2020)

It probably had self-sealing nutsacks because there was no sign of nut explosion.


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## GregP (Nov 20, 2020)

Maybe it was a zombie groundhog with zombie nutsacks. Unfortunately, they prey on regular nutsacks.


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## Airframes (Nov 20, 2020)

I wonder if that particular 'hog heard the music playing over the PA system at the track - I think it was the Nutcracker Suite ...........

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## XBe02Drvr (Nov 20, 2020)

buffnut453 said:


> See? Groundhogs can fly! It's all down to the propulsive force applied.


Net effective thrust, not rated horsepower. Got to factor in the propulsive efficiency percentage.


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## GregP (Nov 20, 2020)

Propulsive efficiency? Is that the exit velocity of groundhog farts? Or maybe if you light them with a match?

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## buffnut453 (Nov 20, 2020)

GregP said:


> Propulsive efficiency? Is that the exit velocity of groundhog farts? Or maybe if you light them with a match?



That's another reason why you need the self-sealing nutsack upgrade for your groundhog.

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## nuuumannn (Nov 20, 2020)

fubar57 said:


> This thread has improved vastly over the past few days



Well, now that the Lancaster one's been shut down, we gotta go _somewhere_ to get down with the brown...

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## fubar57 (Nov 20, 2020)

Two groundhogs arguing about weight removal and both claiming victory

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## XBe02Drvr (Nov 20, 2020)

buffnut453 said:


> That's another reason why you need the self-sealing nutsack upgrade for your groundhog.


Not just that. Also need variable geometry exhaust nozzles to be competitive in the GTO (Groundhog Theater of Operations)!


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## nuuumannn (Nov 20, 2020)

XBe02Drvr said:


> Not just that. Also need variable geometry exhaust nozzles to be competitive in the GTO (Groundhog Theater of Operations)!



What about the impact of laminar flow nutsacks? Or the Meredith effect on groundhog performance, particularly at altitude?


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## XBe02Drvr (Nov 20, 2020)

nuuumannn said:


> What about the impact of laminar flow nutsacks? Or the Meredith effect on groundhog performance, particularly at altitude?


The only Meredith I ever knew had no lift effect whatsoever! Zero camber laminar flow = zero lift. Zero AoA flat plate = drag only, no lift.


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## GrauGeist (Nov 21, 2020)

nuuumannn said:


> Well, now that the Lancaster one's been shut down, we gotta go _somewhere_ to get down with the brown...


Is it too soon to start the "Stirling as potential atomic bomber" thread?

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## Marcel (Nov 21, 2020)

GrauGeist said:


> Is it too soon to start the "Stirling as potential atomic bomber" thread?


I think the spitfire is way better at that.

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## XBe02Drvr (Nov 21, 2020)

Marcel said:


> I think the spitfire is way better at that.


_Fat Man and the Spitfire, _by Edsel T Ford. Sounds like a blockbuster novel! Where do I submit my bid for the screen rights?

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## GrauGeist (Nov 21, 2020)

Marcel said:


> I think the spitfire is way better at that.


I had suggested the P-39, but there were Cog issues that needed to be worked out

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## nuuumannn (Nov 21, 2020)

GrauGeist said:


> I had suggested the P-39, but there were Cog issues that needed to be worked out



_"The P-39 as a Potential Nuclear Bomber"_?

We need someone to lead though, any ideas?

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## nuuumannn (Nov 21, 2020)

XBe02Drvr said:


> The only Meredith I ever knew had no lift effect whatsoever!



Well, that's no good for our groundhog, better remove something to change the CofG...

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## GrauGeist (Nov 21, 2020)

nuuumannn said:


> _"The P-39 as a Potential Nuclear Bomber"_?
> 
> We need someone to lead though, any ideas?


Well...not me, my theories of the B-29 being the best candidate for the job were dismissed in another thread.

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## GrauGeist (Nov 21, 2020)

Marcel said:


> I think the spitfire is way better at that.


Won't work unless you get rid if the roundels - major drag penalty, you know.

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## Marcel (Nov 21, 2020)

GrauGeist said:


> Well...not me, my theories of the B-29 being the best candidate for the job were dismissed in another thread.


Come on Dave, you know as well as I do that the BF109 (which is just a spitfire without roundels) is a better nuclear bomber than the B29. Especially when you pair it with a ground hog ( sorry, Ein Waldmurmeltier).

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## XBe02Drvr (Nov 21, 2020)

nuuumannn said:


> Well, that's no good for our groundhog, better remove something to change the CofG...


What's to remove? Both "airfoils" were flat as boards. No camber, no lift. Nutsack dragging.


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## Airframes (Nov 21, 2020)

Hmm. We may have accidentally found the perfect role for the P-39.
Remove the rear-mounted engine, and the front - mounted armament. Replace these with a "nuke" and a rudimentary guidance system, and hang the whole lot beneath a A.W. Whitley, to be dropped and glide to the target.
Of course, the Whitley would need some modification to allow it to fulfil the mission; probably longer wings, a deeper fuselage, four engines etc, which would also help it to "escape" the target area, with the aid of range-extending, self-sealing, flash-protected nutsacks, especially as the P-39 would probably take some time to get to the detonation point (if it hadn't already stalled and plumetted vertically earthwards).
Sounds like a reasonable use of what was otherwise a collection of aluminium and other metals, all joined together and flying in close formation ..........

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## Peter Gunn (Nov 23, 2020)

buffnut453 said:


> Hey...what 2 grown men do with their groundhogs in their private time is nobody else's business. This is the 2020s after all!
> 
> *Personally, I think you're suffering from groundhog envy!*


I think not:

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## SaparotRob (Nov 23, 2020)

Peter Gunn said:


> I think not:
> 
> View attachment 602797


You see them too!


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## windhund116 (Nov 23, 2020)

fubar57 said:


> Two groundhogs arguing about weight removal and both claiming victory
> 
> View attachment 602481​


 
NEVER attempt to dogfight hogfight the Reisen!

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## buffnut453 (Nov 23, 2020)

Peter Gunn said:


> I think not:
> 
> View attachment 602797



You're not fooling me with that one. That's the box art for the 1979 re-pop of the old 1/48 Monogram Groundhog released to coincide with the re-make of the classic Japanese monster movie G'hogzilla. 

The old Monogram kit was pretty neat and quite well detailed for its day. It even included extra parts so you could model your groundhog with the Silverplate modifications for the nuclear mission. 

Interesting factoid: had the U.S. Boeing Super-Groundhog failed, consideration was being given to use British Avro Groundhogs instead. There's some debate about whether the British groundhogs had the range or altitude to actually complete the nuclear drop successfully, although the former problem could have been overcome using air-to-air nutsack replenishment which was a proven technology as early as 1935.

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## glennasher (Nov 23, 2020)

[QUOTE="buffnut453, post: 1598502, member: 11447"

Interesting factoid: had the U.S. Boeing Super-Groundhog failed, consideration was being given to use British Avro Groundhogs instead. There's some debate about whether the British groundhogs had the range or altitude to actually complete the nuclear drop successfully, although the former problem could have been overcome using air-to-air nutsack replenishment which was a proven technology as early as 1935.[/QUOTE]


Yes, but what about the COG issues?

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## buffnut453 (Nov 23, 2020)

glennasher said:


> [QUOTE="buffnut453, post: 1598502, member: 11447"
> 
> Interesting factoid: had the U.S. Boeing Super-Groundhog failed, consideration was being given to use British Avro Groundhogs instead. There's some debate about whether the British groundhogs had the range or altitude to actually complete the nuclear drop successfully, although the former problem could have been overcome using air-to-air nutsack replenishment which was a proven technology as early as 1935.




Yes, but what about the COG issues? [/QUOTE]

I think they fixed those...but I can't remember if they moved the radio forward, removed the IFF, futzed around with the nose armour, or swapped out the cannon for 50 cals. Regardless, the changes resulted in a massive increase in rate of climb.

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## SaparotRob (Nov 23, 2020)

glennasher said:


> [QUOTE="buffnut453, post: 1598502, member: 11447"
> 
> Interesting factoid: had the U.S. Boeing Super-Groundhog failed, consideration was being given to use British Avro Groundhogs instead. There's some debate about whether the British groundhogs had the range or altitude to actually complete the nuclear drop successfully, although the former problem could have been overcome using air-to-air nutsack replenishment which was a proven technology as early as 1935.




Yes, but what about the COG issues? [/QUOTE]
Someone must have a spreadsheet here.

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## SaparotRob (Nov 23, 2020)

SaparotRob said:


> Yes, but what about the COG issues?


Someone must have a spreadsheet here.[/QUOTE]
This is what happens with fat finger syndrome.


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## rochie (Nov 23, 2020)

GrauGeist said:


> Won't work unless you get rid if the roundels - major drag penalty, you know.


That Spitfire in LW colours you posted a while ago could've carried little boy under each wing !

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## warbird51 (Nov 23, 2020)

Actually, there was a proposal to mount tandem V-1701-E11s in a P-39 in February, 1942. That would have solved the cg problem!

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## warbird51 (Nov 24, 2020)

Here you go


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## GregP (Nov 24, 2020)

Here is a P-40 with twin Allisons:






Maybe they could do that with a P-39 and change the CG issues.

But what O what could you ever do about the VISIBILITY from the cockpit? The enemy can sneak up on this thing from ANYWHERE except directly in front of the nose or straight above the cockpit, and he can sneak up from in front if he is at lower altitude. The pilot has a GREAT view of cowlings and exhausts. I bet he was deaf in one flight!

In hindsight, it makes you wonder why this was ever attempted. Perhaps some crew chief lost a bet or ir was a commie plot of some sort. We should have supplied these to Germany free of charge. Send German pilot prisoners home in one ...

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## fubar57 (Nov 24, 2020)

How many groundhogs would that hold?

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## GregP (Nov 25, 2020)

Eleventy three groundhogs. That data from Junior Samples of Hee Haw, serial number BR549.

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## GrauGeist (Nov 25, 2020)

In case anyone is wondering about that "modified" P-40C, it's real.
From Joe Baugher:
"41-13456 - modified in 1942 to become a mock-up of an undesignated twin-engined fighter. W/o 18 Feb 1943 at Craig Field, AL; Condemned Feb 27, 1943."


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## XBe02Drvr (Nov 25, 2020)

warbird51 said:


> That would have solved the cg problem!


Don't think so. Look at the drawing. Change from tail heavy to nose heavy. Unless, of course, you do a P47 and fill all that suddenly empty space back there with turbochargers and intercoolers.


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## Peter Gunn (Nov 25, 2020)

GrauGeist said:


> In case anyone is wondering about that "modified" P-40C, it's real.
> From Joe Baugher:
> " *SNIP* Condemned Feb 27, 1943."


The best thing that could have happened to it.

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## wuzak (Nov 25, 2020)

warbird51 said:


> Actually, there was a proposal to mount tandem V-1701-E11s in a P-39 in February, 1942. That would have solved the cg problem!





warbird51 said:


> Here you go



But they would have to use wing mounted guns and couldn't have the 37mm cannon that shoots flat out to 400 yards.

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## Peter Gunn (Nov 25, 2020)

buffnut453 said:


> You're not fooling me with that one. That's the box art for the 1979 re-pop of the old 1/48 Monogram Groundhog released to coincide with the re-make of the classic Japanese monster movie G'hogzilla.
> 
> The old Monogram kit was pretty neat and quite well detailed for its day. It even included extra parts so you could model your groundhog with the Silverplate modifications for the nuclear mission.
> 
> Interesting factoid: had the U.S. Boeing Super-Groundhog failed, consideration was being given to use British Avro Groundhogs instead. There's some debate about whether the British groundhogs had the range or altitude to actually complete the nuclear drop successfully, although the former problem could have been overcome using air-to-air nutsack replenishment which was a proven technology as early as 1935.


*NOW* who's trying to hide their Groundhog envy?

Nice try but it doesn't wash, we all know the box art was taken from the real photo of Groundhog Boeing 44-5499's historic August 1945 mission, no nutsack replenishment needed. Also no thinking person that had authority was seriously considering the Avro Groundhog, it's a myth.

As a side note, I tried to build the 1/48 Monogram kit as a younger me, but my cat had romantic "tendencies" towards it so I had to cease and desist the build.

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## windhund116 (Nov 25, 2020)

Early squirrel operated reconnaissance drone.

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## XBe02Drvr (Nov 25, 2020)

windhund116 said:


> Early squirrel operated reconnaissance drone.
> 
> View attachment 603005


CG out of limits forward. Rejected for service use due to squirrelly behavior at the stall and on landing. Only a lightweight surgically neutered squirrel can fly it safely. Standard heavy nutsack groundhogs incompatible.

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## GrauGeist (Nov 25, 2020)

windhund116 said:


> Early squirrel operated reconnaissance drone.
> 
> View attachment 603005


But could it nuke Japan?


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## windhund116 (Nov 25, 2020)

Demonstration by test pilot W.E. Coyote of center-of-gravity fail.

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## SaparotRob (Nov 25, 2020)

windhund116 said:


> Demonstration by test pilot W.E. Coyote of center-of-gravity fail.
> 
> View attachment 603008


COG too far aft?

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## Dash119 (Nov 25, 2020)

SaparotRob said:


> COG too far aft?


He forgot to move the radio forward...

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## SaparotRob (Nov 25, 2020)

Oh. Thanks. I never get this stuff right.


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## buffnut453 (Nov 25, 2020)

Dash119 said:


> He forgot to move the radio forward...



Nah...he removed his nose armour.


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## GregP (Nov 25, 2020)

Nah...he removed his nose armour.

Buffnut, could you expand on that?

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## buffnut453 (Nov 25, 2020)

GregP said:


> Nah...he removed his nose armour.
> 
> Buffnut, could you expand on that?



By removing armour from the forward area of the system, he forced the CofG to move aft, causing instability. Here's an image of a correctly-configured Wile E Coyote with nose armour in place:

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## Dash119 (Nov 25, 2020)

buffnut453 said:


> By removing armour from the forward area of the system, he forced the CofG to move aft, causing instability. Here's an image of a correctly-configured Wile E Coyote with nose armour in place:
> View attachment 603029


Of course, anyone who has been following along would know he had removed the nose armor. If I had any intelligence, it would it would insulted by such comments.

But as I pointed out, all he had to do to correct that issue was to move the radio forward.

Oh, and delete the IFF unit in the tail...

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## GregP (Nov 25, 2020)

Don't forget deleting the 30-cal MG ... AND their ammunition and mounting hardware.


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## Dash119 (Nov 25, 2020)

GregP said:


> Don't forget deleting the 30-cal MG ... AND their ammunition and mounting hardware.


Sorry, but that will not affect Mr. Coyote's CofG nearly as much as moving the radio. It will however contribute to a nearly 1000 fpm increase in the rate of climb at all altitudes...

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## Dash119 (Nov 25, 2020)

Prior to the second flight, you can see Mr. Coyote has realized his mistake and is removing the IFF...






Photo courtesy the Internet
via Acme Rocket, LLC.
a division of Bell Aircraft...

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## Airframes (Nov 25, 2020)

I read somewhere that, after that flight, with the IFF removed, M. Coyote replaced the IFF, as he'd been told (in jest, but he believed it) that IFF stood for "It Flies Faster".
With the IFF now replaced, but unfortunately wrongly located, and not properly secured , the craft certainly _*did*_ fly faster - in a vertical dive, straight into the nutsack replacement storage facility located on he edge of the desert airstrip. This resulted in a severe shortage of nutsacks, particularly those allocated for fitment to Groundhogs, and was a key factor in the short and inglorious service life of the Grrounhog.

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## vikingBerserker (Nov 25, 2020)

Well, don't forget the X-15 Cruise Basselope........ The CG was almost perfect!

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## Dash119 (Nov 25, 2020)

vikingBerserker said:


> Well, don't forget the X-15 Cruise Basselope........ The CG was almost perfect!
> 
> View attachment 603044


Clearly a viable alternative to the B-29 for the Hiroshima and Nagasaki missions. Oh, wait...


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## GregP (Nov 25, 2020)



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## windhund116 (Nov 25, 2020)

ACME the manufacturer of that prototype rocket, built many useful wartime products. Constantly tweaking the engineering envelope. Searching for the perfect CG!!!

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## windhund116 (Nov 26, 2020)




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## SaparotRob (Dec 2, 2020)

Hey, where did everybody go?


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## windhund116 (Dec 2, 2020)

Saw their shadows?

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## P-39 Expert (Dec 2, 2020)

SaparotRob said:


> Hey, where did everybody go?


Seriously? You want more of this?

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## Airframes (Dec 2, 2020)

We apologise for our extended absence - as it's Groundhog hunting season, a number of members have been fully engaged in this pursuit. We would like to reassure readers that no forum members were injured or maltreated during, or after, these events, and normal service will be resumed a soon as possible.

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## buffnut453 (Dec 2, 2020)

Hey...we're all back here again. It's GROUNDHOG DAY!!!!

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## Marcel (Dec 2, 2020)

buffnut453 said:


> Hey...we're all back here again. It's GROUNDHOG DAY!!!!


I'm not, I was just attacked by a groundhog.


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## SaparotRob (Dec 2, 2020)

P-39 Expert said:


> Seriously? You want more of this?


Yes Sir!


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## Airframes (Dec 2, 2020)

You're lucky Marcel. 
Had you been in my town, it might have been a Hippocroccofroghog ( which are all female ), a close relation to the dreaded Hippocroccofrog ( also all female ), but smaller, and not _*quite*_ as dangerous.
If you are unfortunate enough to see a Hippocroccofrog ( and this town is full of them ! ), the normal initial reaction ( until one becomes accustomed to the sight ) is instant retching and vomiting, followed by slow dissolving of the retina, vertigo, dribbling, and finally, insanity, sometimes followed by a merciful death.
However, the Hippocroccofroghog normally just induces retching, and puts one off one's beer for around a week - which, of course, is bad enough !

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## buffnut453 (Dec 2, 2020)

Hippocroccofrogs are NOTHING. It's the Kangarillapigs you need to watch out for....those things are DANGEROUS!!!


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## GrauGeist (Dec 2, 2020)

Which leads us to the Speed of Dark and could the P-39 exceed it?


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## Airframes (Dec 2, 2020)

Nah, it only just reached the Speed of Standing Still............................


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## Dash119 (Dec 2, 2020)

GrauGeist said:


> Which leads us to the Speed of Dark and could the P-39 exceed it?


Which model, the 'C' or the needlessly overweight 'D'? Straight and level, or in a climb?

For those of us who have been following along, these are critical distinctions...

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## buffnut453 (Dec 2, 2020)

Hmmmm...if a groundhog exceeds the speed of dark, does it mean it can't see a shadow? 

The question remains whether it's the C- or D-model groundhog that is capable of those speeds. My money's with the C but I'm still worried about CofG and the risk of tumbling groundhogs.

Does the "seeing shadows" indicator of groundhog speed perhaps suggest a conspiracy that there is more than one Punxsatawny Phil and, worse, that they are of different variants?


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## glennasher (Dec 2, 2020)

buffnut453 said:


> Hmmmm...if a groundhog exceeds the speed of dark, does it mean it can't see a shadow?
> 
> The question remains whether it's the C- or D-model groundhog that is capable of those speeds. My money's with the C but I'm still worried about CofG and the risk of tumbling groundhogs.
> 
> Does the "seeing shadows" indicator of groundhog speed perhaps suggest a conspiracy that there is more than one Punxsatawny Phil and, worse, that they are of different variants?


There are all kinds of groundhog variants, the Eastern (Marmota Monax) and the yellow-bellied marmots of the American West, there's a European variant, and a Himalayan variant, and those are just the ones I can think of, off the top of my head. All of those variants can have different colored fur, and some can be quite heavy, while the yellow-bellied Western ones are relatively smaller than the Eastern variants (American). I've always been interested in the groundhogs, even if their COGs are "off". They are all fun to shoot, and I've devoted quite a bit of time doing that. I have yet to shoot one out of a tree, although I know they climb them often enough. I've seen them sunning themselves on top of fenceposts a time or two, but they bailed quicker than I could get them shot. Groundhogs are fun.

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## nuuumannn (Dec 2, 2020)

Peter Gunn said:


> Also no thinking person that had authority was seriously considering the Avro Groundhog, it's a myth.



Hey, there's something in this, we should start a thread on it...

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## SaparotRob (Dec 2, 2020)

... and we’re back.

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## buffnut453 (Dec 3, 2020)

Some of us just can't stop ourselves...

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## GrauGeist (Dec 3, 2020)

SaparotRob said:


> ... and we’re back.


You're welcome

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## Marcel (Dec 3, 2020)

glennasher said:


> There are all kinds of groundhog variants, the Eastern (Marmota Monax) and the yellow-bellied marmots of the American West, there's a European variant, and a Himalayan variant, and those are just the ones I can think of, off the top of my head. All of those variants can have different colored fur, and some can be quite heavy, while the yellow-bellied Western ones are relatively smaller than the Eastern variants (American). I've always been interested in the groundhogs, even if their COGs are "off". They are all fun to shoot, and I've devoted quite a bit of time doing that. I have yet to shoot one out of a tree, although I know they climb them often enough. I've seen them sunning themselves on top of fenceposts a time or two, but they bailed quicker than I could get them shot. Groundhogs are fun.


All nice and fine, but will you be careful with their nutsacks?


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## Marcel (Dec 3, 2020)

GrauGeist said:


> Which leads us to the Speed of Dark and could the P-39 exceed it?


Just noticed, 

 Geedee
removed the first post of that. Why would he do that?


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## buffnut453 (Dec 3, 2020)

Marcel said:


> Just noticed,
> 
> Geedee
> removed the first post of that. Why would he do that?



Maybe he's in on the Great Punxsatawny Phil Conspiracy and is hiding the evidence. I demand a recount!!!


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## Peter Gunn (Dec 3, 2020)

buffnut453 said:


> Maybe he's in on the Great Punxsatawny Phil Conspiracy and is hiding the evidence. I demand a recount!!!


A recount from the Grassy Knoll.

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## Peter Gunn (Dec 3, 2020)

nuuumannn said:


> Hey, there's something in this, we should start a thread on it...


Totally agree, perhaps the title can be something like:
"Did the Avro Groundhog have the Nutsack to pull off the Atomic Mission?"

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## buffnut453 (Dec 3, 2020)

Peter Gunn said:


> Totally agree, perhaps the title can be something like:
> "Did the Avro Groundhog have the Nutsack to pull off the Atomic Mission?"



Well, it rather depends on whether we're talking internal or external nutsacks. The latter are higher drag but the the poor groundhog may lack the internal capacity or fortitude for the former.

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## windhund116 (Dec 3, 2020)

buffnut453 said:


> Well, it rather depends on whether we're talking internal or external nutsacks. The latter are higher drag but the the poor groundhog may lack the internal capacity or fortitude for the former.



It's the main reason they went to triple-staged super-turbocharging, with Nitrous Oxide boost! To overcome heavier external nutsacks.


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## buffnut453 (Dec 3, 2020)

windhund116 said:


> It's the main reason they went to triple-staged super-turbocharging, with Nitrous Oxide boost! To overcome heavier external nutsacks.



Hmmm...I thought they just removed the nose armour and relocated the radio.


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## Dash119 (Dec 3, 2020)

buffnut453 said:


> Hmmm...I thought they just removed the nose armour and relocated the radio.


Everyone seems to forget... They also removed the IFF from the tail.

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## nuuumannn (Dec 3, 2020)

Peter Gunn said:


> Totally agree, perhaps the title can be something like:
> "Did the Avro Groundhog have the Nutsack to pull off the Atomic Mission?"



Colombian commentator celebrates GOAL - YouTube

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## Simon Thomas (Dec 4, 2020)

I liked the silverplated nutsacks, as it significantly reduced the likelihood of the groundhog's rear end catching fire.

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## glennasher (Dec 4, 2020)

Here he is, attempting to rotate, but I don't know if his nutsack is effecting his COG or not, I would think so, unless he forgot to remove his IFF.


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## Marcel (Dec 5, 2020)

The advantage of external nutsacks is that they are air cooled.

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## buffnut453 (Dec 5, 2020)

Marcel said:


> The advantage of external nutsacks is that they are air cooled.



Yes...overheating nutsacks caused no end of problems and discomfort.

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## Reluctant Poster (Dec 5, 2020)

buffnut453 said:


> Yes...overheating nutsacks caused no end of problems and discomfort.


Having grown up where it reaches minus 40 I would be more concerned about over cooling. At 20,00 feet it gets cold enough to freeze the proverbial brass monkey.

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## buffnut453 (Dec 5, 2020)

Reluctant Poster said:


> Having grown up where it reaches minus 40 I would be more concerned about over cooling. At 20,00 feet it gets cold enough to freeze the proverbial brass monkey.



This is the groundhog thread. If you want to start a monkey thread (brass or otherwise) be my guest.

That said, we all know that monkeys were highly capable weapon systems that had none of the tumbling or altitude limitations of the groundhog. Overall, a far superior platform that tended to invoke dread in its adversaries. 

Below are photographs from the various flight trials of the MkI, MkII and MkIII monkey with the differing wing forms that were unique to each variant:

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## SaparotRob (Dec 5, 2020)

Did the VVS receive flying monkeys lend-lease?

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## buffnut453 (Dec 5, 2020)

SaparotRob said:


> Did the VVS receive flying monkeys lend-lease?



Yes, but they only equipped one squadron associated with the Night Witches and, like the latter, it had a female CO seen here mission planning with one of her flight commanders:

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## SaparotRob (Dec 5, 2020)

Man, I set that one up for you!

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## SaparotRob (Dec 5, 2020)

And the kicker is you’d have to be an aviation buff to get it.

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## buffnut453 (Dec 5, 2020)

It's what I do....I'm here all week!

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## GregP (Dec 7, 2020)

Didn't the Japanese try to attack the U.S.A. by spreading Anthrax with flying monkeys?

They WOULD have used Samurai Kamakaze groundhogs, but there was no way to transport them across the Pacific Ocean in such a way as to leave them combat ready when they got there. Groundhogs do NOT do well at sea, and their nutsacks shrink more than can be tolerated. All they wanted to do when they got to the U.S.A. was kiss the ground.

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## XBe02Drvr (Dec 7, 2020)

GregP said:


> They WOULD have used Samurai Kamakaze groundhogs, but there was no way to transport them across the Pacific Ocean in such a way as to leave them combat ready when they got there. Groundhogs do NOT do well at sea, and their nutsacks shrink more than can be tolerated. All they wanted to do when they got to the U.S.A. was kiss the ground.
> 
> View attachment 604164
> View attachment 604165


Wait - didn't the Japanese have long range sea otters with groundhog hangars behind their conning towers? In the stormy north Pacific, the ride is much less nutsack-shrinking two hundred feet down. A fleet of these could have devastated the west coast. Good thing they didn't think of it!

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## vikingBerserker (Dec 7, 2020)

That makes sense, I know they tried in the North Atlantic but the nutsack shrinkage would not allow any payload to be carried.

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## buffnut453 (Dec 7, 2020)

XBe02Drvr said:


> Wait - didn't the Japanese have long range sea otters with groundhog hangars behind their conning towers? In the stormy north Pacific, the ride is much less nutsack-shrinking two hundred feet down. A fleet of these could have devastated the west coast. Good thing they didn't think of it!



No, no, NO!!! The Japanese used inflatable groundhogs with underslung nutsacks which relied on high-altitude jetstreams to carry the groundhog over US territory. Accuracy was atrocious and the weapon system had virtually no impact on the war.

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## GregP (Dec 7, 2020)

Except we STILL have groundhogs with nutsacks ... even COVID couldn't erradicate them.


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## XBe02Drvr (Dec 8, 2020)

buffnut453 said:


> No, no, NO!!! The Japanese used inflatable groundhogs with underslung nutsacks which relied on high-altitude jetstreams to carry the groundhog over US territory. Accuracy was atrocious and the weapon system had virtually no impact on the war.


What is this...
I-400-class submarine - Wikipedia
...if not a long range sea otter? Huh?

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## SaparotRob (Dec 8, 2020)

He’s got you there, Buffnut.

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## buffnut453 (Dec 8, 2020)

XBe02Drvr said:


> What is this...
> I-400-class submarine - Wikipedia
> ...if not a long range sea otter? Huh?



That's NOT a sea otter....THIS is a sea otter:







Note the size of the available deck space, clearly illustrated by the cargo. There is NO WAY any sea otter can carry a fully-laden groundhog, of either African or European variants. I acknowledge that the Far Eastern groundhog is typically slightly smaller than other variants but it's still WAAAYYYY too big to be accommodated on a sea otter. 

And just for reference, here's a French sea otter, which can be easily distinguished from other nationalities:







You guys are AMATEURS!!!!

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## buffnut453 (Dec 8, 2020)

SaparotRob said:


> He’s got you there, Buffnut.



I think not!

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## Snautzer01 (Dec 8, 2020)

Ok the french sea otter made my day. Thanks, but it is missing something. What could it be? Must be white i think.

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## SaparotRob (Dec 8, 2020)

What color white?

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## SaparotRob (Dec 8, 2020)

buffnut453 said:


> I think not!


I think not too. Thinking is overrated.

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## Airframes (Dec 8, 2020)

Blanc lumiere Francais, of course !

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## SaparotRob (Dec 8, 2020)

I should have remembered that.


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## Airframes (Dec 8, 2020)

D'accord.

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## SaparotRob (Dec 8, 2020)

No, I have d’Mazda.

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## SaparotRob (Dec 8, 2020)

..and it was built in Hiroshima.


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## Airframes (Dec 9, 2020)

And it got glowing reviews .............

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## PAT303 (Dec 19, 2020)

Hey mods would you all get upset if I posted a heap of dribble just to get this thread to 100 pages, I'm only asking because everyone has spent so much time and effort on an endless loop of wash rinse and repeat for 96 pages trying to explain why the P39 was never a front line worthy aircraft and I feel making it to triple figures will be a small reward for all their effort.


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## fubar57 (Dec 19, 2020)

Just


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## fubar57 (Dec 19, 2020)

Do


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## fubar57 (Dec 19, 2020)

This

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## GrauGeist (Dec 20, 2020)

Or...let it quietly fade into obscurity, to take it's place among classic threads that too, ran well past it's "best used by" date...

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## PAT303 (Dec 20, 2020)

fubar57 said:


> This



fubar, thanks for the laugh.


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## warbird51 (Dec 20, 2020)

I’ve been thinking about the front armor......


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## GrauGeist (Dec 20, 2020)

warbird51 said:


> I’ve been thinking about the front armor......


Did it look something like this?

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## Dash119 (Dec 20, 2020)

GrauGeist said:


> Did it look something like this?
> 
> View attachment 605734


Oh ye of the quiet death...


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## buffnut453 (Dec 20, 2020)

Maybe turning the groundhog into a newt will improve it's rate of climb and ceiling?


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## Dash119 (Dec 20, 2020)

buffnut453 said:


> Maybe turning the groundhog into a newt will improve it's rate of climb and ceiling?


Well aren't newts amphibious? That means the navy could also consider the fighter to end all fighters...


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## buffnut453 (Dec 20, 2020)

Dash119 said:


> Well aren't newts amphibious? That means the navy could also consider the fighter to end all fighters...



Yup...I think I'm on to something here. A newt has smaller frontal area so less form drag, plus replacing all that draggy fur with a slippery skin will further improve performance. Granted, the newt's smaller overall size will limit load carrying capacity so we may need to remove the wing guns....but they aren't really needed anyway.


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## Dash119 (Dec 20, 2020)

buffnut453 said:


> Yup...I think I'm on to something here. A newt has smaller frontal area so less form drag, plus replacing all that draggy fur with a slippery skin will further improve performance. Granted, the newt's smaller overall size will limit load carrying capacity so we may need to remove the wing guns....but they aren't really needed anyway.


Wait, if it floats isn't it a witch? What is the climb rate and ceiling of a witch?


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## GrauGeist (Dec 20, 2020)

The Holy Hand Grenade of Antioch shall prevail in the advent of the arrival of a worthy (or scary) adversary.


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## Dash119 (Dec 20, 2020)

GrauGeist said:


> The Holy Hand Grenade of Antioch shall prevail in the advent of the arrival of a worthy (or scary) adversary.


Oh, so now you are bringing rabbits into the mix... Well they do have tremendous rates of production, perhaps they could overwhelm with quantity.

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## GrauGeist (Dec 20, 2020)

Rabbits of the large variety would be far more worthy in armed confrontation than a ground hog.
One must always keep in mind that the rabbit is not to be taken lightly.


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## Dash119 (Dec 20, 2020)

GrauGeist said:


> Rabbits of the large variety would be far more worthy in armed confrontation than a ground hog.
> One must always keep in mind that the rabbit is not to be taken lightly.


They have very sharp teeth, so we could probably remove the front armor and move the radio forward...


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## P-39 Expert (Dec 20, 2020)

GrauGeist said:


> Did it look something like this?
> 
> View attachment 605734


And they are on horseback.


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## GrauGeist (Dec 20, 2020)

Dash119 said:


> They have very sharp teeth, so we could probably remove the front armor and move the radio forward...


Nay, preserve the front armour as it is most nessecary.
Throw the radio at it and run away.


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## Dash119 (Dec 20, 2020)

GrauGeist said:


> Nay, preserve the front armour as it is most nessecary.
> Throw the radio at it and run away.


Ah yes, the Brave Sir Robin strategy.


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## GrauGeist (Dec 20, 2020)

Dash119 said:


> Ah yes, the Brave Sir Robin strategy.


Indeed.


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## Ascent (Dec 20, 2020)

This is a silly place

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## Airframes (Dec 20, 2020)

Yeah and verily, for tis the season of silliness. Let the thread be silly, for silliness be eth the end all, and ................ Oh, hello Nurse !


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## warbird51 (Dec 20, 2020)

GrauGeist said:


> Rabbits of the large variety would be far more worthy in armed confrontation than a ground hog.
> One must always keep in mind that the rabbit is not to be taken lightly.



a great idea, however there are some flaws. The production rate of the rabbits would be such that you could supply more rabbits to our lend lease partners to assist in fighting. However, when the rabbits were entering the ‘field of battle’ , if they saw any female rabbits, they would remember their favorite slogan of “make love, not war” and would desert the field of battle at a most inopportune time. It would not matter if you removed the armor, IFF, radios and wing guns, if they were ‘attacking’ in the other direction .


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## Airframes (Dec 20, 2020)

Would these rabbits be the long-tailed or bob-tailed version ?


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## buffnut453 (Dec 20, 2020)

Ascent said:


> This is a silly place



Talk about blinding flash of the obvious!

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## GrauGeist (Dec 20, 2020)

Airframes said:


> Would these rabbits be the long-tailed or bob-tailed version ?


It would seem to me, that the long-tailed version would have more stability - that is, as long as it maintained the proper CoG.
We can see how well this worked with the Me410, Meteor T.7 and flying squirrels.

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## fubar57 (Dec 20, 2020)

I had surgery last week and while waiting to be put under I noticed how bare the operating room looked. I asked the surgeon if I was getting one of these and the entire staff looked at me as if my IQ was kinda questionable

​


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## buffnut453 (Dec 20, 2020)

GrauGeist said:


> It would seem to me, that the long-tailed version would have more stability - that is, as long as it maintained the proper CoG.
> We can see how well this worked with the Me410, Meteor T.7 and flying squirrels.



Yes, but the longer tail means you need more weight up front...so definitely need that nose armour. Plus you definitely want to move the radio and IFF forward as much as possible.


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## GregP (Dec 20, 2020)

If there are big ears up forward, it means a loss of yaw stabiliity that could be compensated for by longer claws on the rear paws.


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## buffnut453 (Dec 20, 2020)

GregP said:


> If there are big ears up forward, it means a loss of yaw stability that could be compensated for by longer claws on the rear paws.



Are we talking rabbits or newts? Last time I checked, big ears up forward were not available as a standard fit on newts. Of course, the wonders worked by the maintenance crews, I'm sure they could have fitted the ears to newts. I'm pretty sure it wasn't a difficult modification that probably could have been done at squadron level.

Then again, a google search for newts with rabbit ears came up with this...so perhaps they were available as a standard fit:


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## SaparotRob (Dec 20, 2020)

Could the larger ears increase fuel supply, or perhaps an increase in armament?


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## special ed (Dec 20, 2020)

I understand Hugh Hefner used to have a squadron of Bunnies available.

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## Dash119 (Dec 20, 2020)

special ed said:


> I understand Hugh Hefner used to have a squadron of Bunnies available.


Yes, but from what I have "read", most of those bunnies had a CofG that was quite forward and high...

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## special ed (Dec 20, 2020)

I notice the quotes, so not first hand (so to speak) knowledge.

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## warbird51 (Dec 20, 2020)

Dash119 said:


> Yes, but from what I have "read", most of those bunnies had a CofG that was quite forward and high...



That is what got me into “bunny” watching in the first place😎

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## special ed (Dec 20, 2020)

I suspect a bird in hand is about the same as a bunny in hand.


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## Dash119 (Dec 20, 2020)

special ed said:


> I suspect a bird in hand is about the same as a bunny in hand.


If we are talking about payload capacity, it would depend on which type of bird, African or European swallow...

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## GregP (Dec 20, 2020)

I am reminded of W. C. Fields who once said, "two women at 19 each are better than one woman at 38!"

Jessica Rabbit, not a bunny, but ...

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## P-39 Expert (Dec 21, 2020)

GregP said:


> If there are big ears up forward, it means a loss of yaw stabiliity that could be compensated for by longer claws on the rear paws.


So, departing briefly from the animal kingdom, would you agree that a P-39D that weighs the same as a P-39C would climb at the same rate?


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## Snautzer01 (Dec 21, 2020)

No, because a groundhog is heavier then a squirle. Both usa and european ones.
Now one could argue about the nuts it could carry but that would only bring beans to a breakfast.


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## GregP (Dec 21, 2020)

P-39 Expert, not according to the tests we saw ... I still wonder about those tests. One engine was sour or one was a "good" one, or they didn't use book power, or ... hey, we went over that more than 50 pages back. There's more to the tests we have seen than is recorded in them. Thet were NOT recorded in enough detail or perhaps even correctly. I doubt we'll ever know the exact nature of the test differences. 

I can speculate, sure, but that's all it would be ... speculation. I'd rather not at this juncture. Suffice to say a stock P-39 is quite sprightly at lower altitudes.

Cheers.


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## Snautzer01 (Dec 21, 2020)

I say humbug. There is only one test of nut comperison but i was told by one called Nigel that the it was not a fair test.
Now we all know Nigel so there you go.


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## buffnut453 (Dec 21, 2020)

I thought we were "only making plans for Nigel."

Let's see how many admit to remembering THAT!

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## GrauGeist (Dec 22, 2020)

P-39 Expert said:


> So, departing briefly from the animal kingdom, would you agree that a P-39D that weighs the same as a P-39C would climb at the same rate?


Here's a serious point to consider:
Tests are tests - period.
They take one off the assembly line and put it through it's paces, recording data, listing this and that and it becomes a "pseudo benchmark".
No one took the time to record what the weather was that day, hot and humid? Cold and windy? These can affect stats.
Was the test pilot aggressive like a combat pilot? Was the test pilot familiar with the aircraft enough to know the right settings to get the most out of that particular machine?

Then on to the the real world - how will that stellar crate perform after being shot up and patched a few times?
What's the hours on the engine?
Does it have a new wing or tail cannibalized from a wreck?
Has it had a couple hard landings (which can have an effect on handling)?
Is the climate hot and humid or is it freezing temps - these extremes will have a profound effect on performance.
Are it's wheel wells packed solid with mud?
Does it have a tropical filter on the intake and is it clogged with Coral dust or Saharan sand?

There are SO many variables and combinations of variables that no two aircraft are going to perform the same out on the front lines and rest assured, they will be nothing like the clean, shiny new test aircraft back home.
Using test data for a particular type is good for having a basic idea of the type's performance perimeter, but one should never assume this is what's going to happen once it gets out to the front line.

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## P-39 Expert (Dec 22, 2020)

GregP said:


> P-39 Expert, not according to the tests we saw ... I still wonder about those tests. One engine was sour or one was a "good" one, or they didn't use book power, or ... hey, we went over that more than 50 pages back. There's more to the tests we have seen than is recorded in them. Thet were NOT recorded in enough detail or perhaps even correctly. I doubt we'll ever know the exact nature of the test differences.
> 
> I can speculate, sure, but that's all it would be ... speculation. I'd rather not at this juncture. Suffice to say a stock P-39 is quite sprightly at lower altitudes.
> 
> Cheers.


So again, which one had the good one and which one had the bad one?


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## PAT303 (Dec 22, 2020)

99, come on, we can do it.

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## PAT303 (Dec 22, 2020)

One last push


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## PAT303 (Dec 22, 2020)

The last hurdle


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## DerAdlerIstGelandet (Dec 22, 2020)

Get ready...


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## DerAdlerIstGelandet (Dec 22, 2020)

Almost...


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## DerAdlerIstGelandet (Dec 22, 2020)

Let


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## DerAdlerIstGelandet (Dec 22, 2020)

The


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## DerAdlerIstGelandet (Dec 22, 2020)

Countdown


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## DerAdlerIstGelandet (Dec 22, 2020)

Begin


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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)




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## DerAdlerIstGelandet (Dec 22, 2020)



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## DerAdlerIstGelandet (Dec 22, 2020)



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## P-39 Expert (Dec 22, 2020)

GrauGeist said:


> Here's a serious point to consider:
> Tests are tests - period.
> They take one off the assembly line and put it through it's paces, recording data, listing this and that and it becomes a "pseudo benchmark".
> No one took the time to record what the weather was that day, hot and humid? Cold and windy? These can affect stats.
> ...



Please expand above.


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## GrauGeist (Dec 22, 2020)

P-39 Expert said:


> Please expand above.


How many test aircraft flew into combat?


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## GregP (Dec 22, 2020)

How many, indeed.

I think we're all done expanding P-39 Expert. It's sort of like a car wreck where your wife starts the car, puts it in gear, looks backwards from the garage, runs through the front wall becasue she wasn't in reverse, runs over the swing set, bounces off a tree, goes through the hedge, and then loses control of the car.

You've had all the explanations many times over and can't seem to get them from the screen to your fingers when you type.

But, hey, Happy Holidays all the same. Cheers. Perhaps a hot toddie or some really good eggnog will help. Or is that a really good groundhog? Almost anything can be improved by the addition of bacon. Have some. Ham even helps.

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## buffnut453 (Dec 22, 2020)

GregP said:


> I think we're all done expanding P-39 Expert. It's sort of like a car wreck where your wife starts the car, puts it in gear, looks backwards from the garage, runs through the front wall becasue she wasn't in reverse, runs over the swing set, bounces off a tree, goes through the hedge, and then loses control of the car.



I don't care, so long as she misses the groundhog!

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## P-39 Expert (Dec 22, 2020)

GregP said:


> How many, indeed.
> 
> I think we're all done expanding P-39 Expert. It's sort of like a car wreck where your wife starts the car, puts it in gear, looks backwards from the garage, runs through the front wall becasue she wasn't in reverse, runs over the swing set, bounces off a tree, goes through the hedge, and then loses control of the car.
> 
> ...


Well, tests don't mean anything and weight doesn't affect climb. Right. I'll stick with my position. You have a Merry Christmas and a Happy New Year. I'll buy the first round.


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## P-39 Expert (Dec 22, 2020)

GrauGeist said:


> How many test aircraft flew into combat?


I would think that virtually all of them flew into combat. The AAF didn't just discard a plane just because it was used in a test.


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## PAT303 (Dec 22, 2020)

You guys crack me up, okay mods, trying to make a silk purse out of a sows ear has run it's course, thanks for the ride.


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## SaparotRob (Dec 22, 2020)

C’mon, just 11 more. Okay?


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## buffnut453 (Dec 22, 2020)

One.


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## buffnut453 (Dec 22, 2020)

Two.


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## buffnut453 (Dec 22, 2020)

Three.


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## buffnut453 (Dec 22, 2020)

Four.


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## buffnut453 (Dec 22, 2020)

Five.


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## buffnut453 (Dec 22, 2020)

Six.


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## buffnut453 (Dec 22, 2020)

Seven.


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## buffnut453 (Dec 22, 2020)

Eight.


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## buffnut453 (Dec 22, 2020)

Nine.


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## buffnut453 (Dec 22, 2020)

Ten.


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## buffnut453 (Dec 22, 2020)

Eleven....AAAAANNDD you're welcome!

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## GregP (Dec 22, 2020)

That makes it eleventy three?

Honestly, I'd be happy to talk about the P-39 or any other airplane, but I'm afraid to open the door to the P-39 again since no amount of reasoning seems to "take."

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## BiffF15 (Dec 22, 2020)

GregP said:


> How many, indeed.
> 
> I think we're all done expanding P-39 Expert. It's sort of like a car wreck where your wife starts the car, puts it in gear, looks backwards from the garage, runs through the front wall becasue she wasn't in reverse, runs over the swing set, bounces off a tree, goes through the hedge, and then loses control of the car.
> 
> ...





GregP said:


> But, hey, Happy Holidays all the same. Cheers. Perhaps a hot toddie or some really good eggnog will help. Or is that a really good groundhog? *Almost anything can be improved by the addition of bacon. *Have some. Ham even helps.



This is our Bacon and he wishes everyone a Merry Christmas and a Happy New Year!

PS: His name really is Bacon.

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## buffnut453 (Dec 23, 2020)

I'll bet he's faster than a groundhog.

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## GrauGeist (Dec 23, 2020)

buffnut453 said:


> I'll bet he's faster than a groundhog.


But not a flying squirrel


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## buffnut453 (Dec 23, 2020)

GrauGeist said:


> But not a flying squirrel



What about a sea otter?

Sorry...just can't help myself (then again, methinks I'm not alone in suffering that trait!)

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## BiffF15 (Dec 23, 2020)

buffnut453 said:


> I'll bet he's faster than a groundhog.



He might be, but not by much. CG issues, along with over weight and not mentally armed / armored to do battle beyond our front door step. Like the P-39 he has his optimum operating window. His is looking out the glass beside the door, barking at any real or perceived intruder.

His redeeming characteristic is personality. He's a total lovebug. However, Jason from Friday the 13th, along with hockey mask and bloody dripping axe could show up at our door, and my dog would be excited beyond belief to welcome him in.

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## Snautzer01 (Dec 23, 2020)

Now look what i have made.

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## buffnut453 (Dec 23, 2020)

I'm confused...am I seeing a Soviet P-39 pilot diving into the heat of battle while simultaneously wondering what Santa will bring him for Christmas? 

I think I need to lie down!

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## Snautzer01 (Dec 23, 2020)

Its a NORAD thing. Just lie down and it will come good.


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## GregP (Dec 23, 2020)

What's "Ho, ho, ho" in Russian?

If he can make an unaerodynamic Reindeer fly, bullets should be NOTHING, but this pilot might get a lump of coal in his stocking ... assuming he has an extra one to hang up, that is.


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## Dimlee (Dec 26, 2020)

buffnut453 said:


> I'm confused...am I seeing a Soviet P-39 pilot diving into the heat of battle while simultaneously wondering what Santa will bring him for Christmas?
> 
> I think I need to lie down!



Njet. Not wondering but attacking and not Santa but Joulupukki flight. The incident happened before the Moscow armistice, when Finns were still at war. This historical photo reveals some interesting details. Six raindeer... I did not know that Me 323 was in the Finnish service.

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## Just Schmidt (Dec 27, 2020)

buffnut453 said:


> I'm confused...am I seeing a Soviet P-39 pilot diving into the heat of battle while simultaneously wondering what Santa will bring him for Christmas?
> 
> I think I need to lie down!



From the square looking tip of the tail I think that may a P 63, though I'm not entirely sure it should look that square.

I'm nearly afraid to ask, but is there a P 63 expert on the forum?


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## GregP (Dec 27, 2020)

Well, if you're going to nit-pick, I should chime in about the incorrect shape of the island in the river ... I seem to recall it being more narrow than depicted ... of course, it might be due to the rectangle around the airborne target ...


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## GrauGeist (Dec 27, 2020)

And Santa's team had eight Reindeer, not six - nine if you include Rudolph...

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## Airframes (Dec 27, 2020)

And Santa was wearing an oxygen mask at the time ....................


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## buffnut453 (Dec 27, 2020)

No, silly, it's not an oxygen mask. It's a COVID mask. Santa doesnt want to be a super spreader.

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## Airframes (Dec 27, 2020)

No, no, no - the Covid mask was over the top of the oxygen mask, as he was being ultra cautious !


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## Snautzer01 (Dec 27, 2020)

GregP said:


> What's "Ho, ho, ho" in Russian?
> 
> .



Probably like this: Ho, Ho Cyka Blyat, Ho .

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## GrauGeist (Dec 27, 2020)

GregP said:


> What's "Ho, ho, ho" in Russian?


Xo Xo Xo

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## jmcalli2 (Jan 4, 2021)

Snautzer01 said:


> Now look what i have made.
> 
> View attachment 606119

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## jmcalli2 (Jan 4, 2021)

I'll just leave this here:

http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2990_PHQ-M-19-1297-A.pdf


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## XBe02Drvr (Jan 5, 2021)

jmcalli2 said:


> I'll just leave this here:
> 
> http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2990_PHQ-M-19-1297-A.pdf


Nice hotrod! In no way relevant to a combat airplane. No cannon, no wing guns; a toothless tiger, but it would make an awesome dragster.

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## P-39 Expert (Jan 5, 2021)

jmcalli2 said:


> I'll just leave this here:
> 
> http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2990_PHQ-M-19-1297-A.pdf


This was a P-39C modified like the P-400 serial AH 571 that made 391mph in the performance acceptance tests for the British. Slightly different tail, glazed finish, etc. but with experimental 9.6 supercharger gears in a standard -35 engine (normally 8.8 gears). Too bad this engine (as the -59 and -61) wouldn't pass the 150 hour tests, would have been a quick and easy way to add 3000ft of critical altitude almost immediately and get P-39N performance a year earlier. The 9.6 gears had to be widened to improve durability and that modification set the engine back a year to fall 1942. I think going to the aluminum intake manifold without the backfire screens may have enabled the -59/-61 engines to pass the 150 hour test without having to widen the gears, but who knows.

Honestly I don't think the aerodynamic modifications (different tail, glazing etc) were really necessary. The standard P-39C test in July 1941 in wwiiaircraftperformance indicated a top speed of 379mph and the 9.6 gears added 20-25mph so that's about 400mph right there. The P-39C weighed only 7075lbs gross without self sealing fuel tanks and armor plate, but a standard P-39D with the tanks and armor only weighed an additional 75-100lbs without the .30cal wing guns and the 100lb nose armor plate. Oh well.

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## Snautzer01 (Jan 5, 2021)



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## windhund116 (Jan 5, 2021)

jmcalli2 said:


> View attachment 607596
> View attachment 607597
> View attachment 607598
> View attachment 607599



F104 "Widowmaker." Was the crash due to The Cat in the Hat's navigation error?

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## jmcalli2 (Jan 5, 2021)

XBe02Drvr said:


> Nice hotrod! In no way relevant to a combat airplane. No cannon, no wing guns; a toothless tiger, but it would make an awesome dragster.



Perhaps not "toothless" in that the C model had all the machine guns in the nose: 2 x .30cal and 2 x .50cal. No mention as to them or their openings being taped or not.




Just interesting that the changes could make such a difference. Makes me wonder if the early P-39s were a little 'loose' on their production tolerances; panels not fitting correctly, etc. Perhaps Bell had a 'production learning curve' before they got it right.
That would add to the explanation for the difference between the prototypes and production early planes, and why the N & Q models were able to approach 400mph, 30+ more than the D models.

Just a thought.

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## jmcalli2 (Jan 5, 2021)

P-39 Expert said:


> This was a P-39C modified like the P-400 serial AH 571 that made 391mph in the performance acceptance tests for the British. Slightly different tail, glazed finish, etc. but with experimental 9.6 supercharger gears in a standard -35 engine (normally 8.8 gears). Too bad this engine (as the -59 and -61) wouldn't pass the 150 hour tests, would have been a quick and easy way to add 3000ft of critical altitude almost immediately and get P-39N performance a year earlier. The 9.6 gears had to be widened to improve durability and that modification set the engine back a year to fall 1942. I think going to the aluminum intake manifold without the backfire screens may have enabled the -59/-61 engines to pass the 150 hour test without having to widen the gears, but who knows.
> 
> Honestly I don't think the aerodynamic modifications (different tail, glazing etc) were really necessary. The standard P-39C test in July 1941 in wwiiaircraftperformance indicated a top speed of 379mph and the 9.6 gears added 20-25mph so that's about 400mph right there. The P-39C weighed only 7075lbs gross without self sealing fuel tanks and armor plate, but a standard P-39D with the tanks and armor only weighed an additional 75-100lbs without the .30cal wing guns and the 100lb nose armor plate. Oh well.



File it next to the P-38K.


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## jmcalli2 (Jan 5, 2021)

windhund116 said:


> F104 "Widowmaker." Was the crash due to The Cat in the Hat's navigation error?



No.

Santa had one too many Hos and didn't have his IFF on...

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## XBe02Drvr (Jan 5, 2021)

jmcalli2 said:


> Just interesting that the changes could make such a difference. Makes me wonder if the early P-39s were a little 'loose' on their production tolerances; panels not fitting correctly, etc. Perhaps Bell had a 'production learning curve' before they got it right.





jmcalli2 said:


> Just a thought.


Smoothness matters! Bigtime. A high performance sailplane can lose two to five points off its glide ratio just by flying through a swarm of insects and contaminating its leading edges. If you're going to fly a Mooney or an Aerostar or MU2 in winter, you need to polish every last vestige of frost from your airfoils. (Don't forget the props!)
Just for giggles, we went out and "tufted" the Mooney one day with six inch lengths of yarn, then went out and practiced slow flight and stalls, first with "clean" wings, then with mud splattered on the leading edges and first third of the top surfaces, and baked in the sun. "Whoa, Nellie!" Noticeable difference in cruise speed, and airflow started detaching from the wing surface at significantly lower angles of attack. She never attained enough AoA to trigger the stall warning, and the stall was abrupt and never symmetrical. We kept higher than normal speed in the landing pattern, and landed flat and fast. Things to remember if you ever encounter inflight icing in a Mooney, a Comanche, or any other "slippery" airplane.
BTW, *everybody *has a "production learning curve". It goes with the territory. At GE, every time we had to build a new assembly, the first batch of 50 would have a 10%-25% QA rejection rate. And then a bunch more would fail their initial fire test, sometimes spectacularly. The worst were "brass retrieval" type Vulcan ammo drums and feed mechanisms.

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## jmcalli2 (Jan 5, 2021)

XBe02Drvr said:


> Smoothness matters! Bigtime. A high performance sailplane can lose two to five points off its glide ratio just by flying through a swarm of insects and contaminating its leading edges. If you're going to fly a Mooney or an Aerostar or MU2 in winter, you need to polish every last vestige of frost from your airfoils. (Don't forget the props!)
> Just for giggles, we went out and "tufted" the Mooney one day with six inch lengths of yarn, then went out and practiced slow flight and stalls, first with "clean" wings, then with mud splattered on the leading edges and first third of the top surfaces, and baked in the sun. "Whoa, Nellie!" Noticeable difference in cruise speed, and airflow started detaching from the wing surface at significantly lower angles of attack. She never attained enough AoA to trigger the stall warning, and the stall was abrupt and never symmetrical. We kept higher than normal speed in the landing pattern, and landed flat and fast. Things to remember if you ever encounter inflight icing in a Mooney, a Comanche, or any other "slippery" airplane.
> BTW, *everybody *has a "production learning curve". It goes with the territory. At GE, every time we had to build a new assembly, the first batch of 50 would have a 10%-25% QA rejection rate. And then a bunch more would fail their initial fire test, sometimes spectacularly. The worst were "brass retrieval" type Vulcan ammo drums and feed mechanisms.



Great info!

Bell's learning curve may have been steeper, since they had only produced the XFM-1 before the P-39. 
They learned well, considering the company went from inception in 1935 to the X-1 in 1946.

Just curious; did you work at the GE plant in Schenectady or Syracuse?


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## P-39 Expert (Jan 5, 2021)

jmcalli2 said:


> Perhaps not "toothless" in that the C model had all the machine guns in the nose: 2 x .30cal and 2 x .50cal. No mention as to them or their openings being taped or not.
> View attachment 607661
> 
> Just interesting that the changes could make such a difference. Makes me wonder if the early P-39s were a little 'loose' on their production tolerances; panels not fitting correctly, etc. Perhaps Bell had a 'production learning curve' before they got it right.
> ...


That's great performance! But that's just a projection, not an actual test. It's dated 10/28/39 and the P-39C didn't start production until early 1941.


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## P-39 Expert (Jan 5, 2021)

jmcalli2 said:


> Perhaps not "toothless" in that the C model had all the machine guns in the nose: 2 x .30cal and 2 x .50cal. No mention as to them or their openings being taped or not.
> View attachment 607661
> 
> Just interesting that the changes could make such a difference. Makes me wonder if the early P-39s were a little 'loose' on their production tolerances; panels not fitting correctly, etc. Perhaps Bell had a 'production learning curve' before they got it right.
> ...


That's great performance! But that's just a projection, not an actual test. It's dated 10/28/39 and the P-39C didn't start production until early 1941.


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## jmcalli2 (Jan 5, 2021)

P-39 Expert said:


> That's great performance! But that's just a projection, not an actual test. It's dated 10/28/39 and the P-39C didn't start production until early 1941.



Good catch! I read it as 1940.
Looking more closely I see that this was the Bell model 12; the P-39C was the model 13. This would put the aircraft as the XP-39 or perhaps the projection of the XP-39B, since the only P-39 flying in October 1939 was the XP-39!


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## GrauGeist (Jan 5, 2021)

jmcalli2 said:


> Bell's learning curve may have been steeper, since they had only produced the XFM-1 before the P-39.
> They learned well, considering the company went from inception in 1935 to the X-1 in 1946.


Bell and his cheif engineers were no strangers to aircraft design and production.
Bell himself was well involved in the industry, last working for Fleet/Consolidated before founding Bell Aircraft.


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## jmcalli2 (Jan 5, 2021)

GrauGeist said:


> Bell and his cheif engineers were no strangers to aircraft design and production.
> Bell himself was well involved in the industry, last working for Fleet/Consolidated before founding Bell Aircraft.



Bell had industry experience, but they didn't have an experienced factory staff. And understanding a business is not the same as running one; there is a learning curve there in everything from hiring to marketing to quality control to anticipating industry direction.
Bell didn't have to learn everything from scratch, but he had to build the company from scratch, except for the building. Consolidated left that and Bell grabbed it.
An illustration: Curtiss delivered 1,200+ P-36/P-40s in 1940. Bell delivered 926 P-39s in 1941 (plus 13 prototypes in 1940).
As both companies ramped up production, Curtiss went to 2,200+ in '41, 4,400+ in '42, and 4,200+ in '43. Bell increased more slowly at first, 926 in '41, 1,973 in '42, then passed Curtiss with 4,900+ in '43. In addition, Bell was able to develop a significantly better fighter using the same basic configuration, the P-63, while Curtiss never did find an acceptable P-40 follow-on. Lessons well learned and applied.

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## GregP (Jan 5, 2021)

The chart above is dated 10/29/39. The XP-39B was first flown 25 Nov 39. So, at the time this chart was made, the only flying P-39 was the XP-39. Perhaps the XP-39 was NOT flying at the time since it well might have been being modified into the XP-39B at the time of this chart. On wwIIaircraftperformance, the P-39 reports START with the YP-39, not the XP-39. The chart was made from Tables VI and VII of the XP-39 test report. Since I don't have that report, I have no idea wheter the data were projected or were as-tested. From discussions we had more than 60 pages back, I'm going to assume the data were projected, not as-tested.

Looks like a hot rod on paper but ... hey ... the Douglas X-3 Stiletto looked pretty fast on paper, too. It wasn't when actually flying in real air. It was much more of a, "Hey, look what we made, and it FLIES!" Turned out to be decidedly subsonic unless it was in a 25°+ dive.

Methinks the P-39 chart above is projected, not tested.


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## jmcalli2 (Jan 5, 2021)

GregP said:


> The chart above is dated 10/29/39. The XP-39B was first flown 25 Nov 39. So, at the time this chart was made, the only flying P-39 was the XP-39. Perhaps the XP-39 was NOT flying at the time since it well might have been being modified into the XP-39B at the time of this chart. On wwIIaircraftperformance, the P-39 reports START with the YP-39, not the XP-39. The chart was made from Tables VI and VII of the XP-39 test report. Since I don't have that report, I have no idea wheter the data were projected or were as-tested. From discussions we had more than 60 pages back, I'm going to assume the data were projected, not as-tested.
> 
> Looks like a hot rod on paper but ... hey ... the Douglas X-3 Stiletto looked pretty fast on paper, too. It wasn't when actually flying in real air. It was much more of a, "Hey, look what we made, and it FLIES!" Turned out to be decidedly subsonic unless it was in a 25°+ dive.
> 
> Methinks the P-39 chart above is projected, not tested.



See post #2,033


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## GregP (Jan 5, 2021)

Post 2033 doesn't say the chart is projected performance. That's the point I was trying to make, not the XP-39 part.

I have never found an actual XP-39 test flight report that is from that time, but I have a book that clearly state 390 mph for the XP-39 from 1946. It also says the gross weight was 6,204 lbs.

Who knows, maybe the test flight report will show up at some future date. I'm not expecting it, though. Cheers.

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## P-39 Expert (Jan 5, 2021)

jmcalli2 said:


> See post #2,033


This chart may not be too far off depending on the weight. The power is listed as 1150hp at 15000' which is just about what Allison projected in fall of '41. Allison thought they could just plug in the 9.6 supercharger gears but turned out they wouldn't take the additional MP and had to be redesigned/widened. This projected C model probably weighed 5800lbs with the cannon and twin .50s. That's about a ton lighter than production P-39s. A 5800lb P-39 with 9.6 supercharger gears would probably perform like that chart says.

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## jmcalli2 (Jan 5, 2021)

GregP said:


> Post 2033 doesn't say the chart is projected performance. That's the point I was trying to make, not the XP-39 part.
> 
> I have never found an actual XP-39 test flight report that is from that time, but I have a book that clearly state 390 mph for the XP-39 from 1946. It also says the gross weight was 6,204 lbs.
> 
> Who knows, maybe the test flight report will show up at some future date. I'm not expecting it, though. Cheers.



Yeah, I've seen the 390mph figure repeated on many sources, but no primary source of origin for it.

What is odd for a projected graph is the line labeled "Actual Time To Climb Curve" and a dashed line that I assume is the projected time to climb. Also, the abrupt 'switch' from "Military Power" to "Normal Power" at around 19,000 feet on the Rate Of Climb curve as indicated by the switch of solid and dashed lines.
This chart is "Figure 8" of some report. Also of interest would be "Tables VI and VII."

I also wonder who "Asey" (Casey?) and "Robinson" were.

If someone could find Bell report "12Y005" we'd know. Maybe.


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## GrauGeist (Jan 5, 2021)

jmcalli2 said:


> Bell had industry experience, but they didn't have an experienced factory staff. And understanding a business is not the same as running one; there is a learning curve there in everything from hiring to marketing to quality control to anticipating industry direction.
> Bell didn't have to learn everything from scratch, but he had to build the company from scratch, except for the building. Consolidated left that and Bell grabbed it.
> An illustration: Curtiss delivered 1,200+ P-36/P-40s in 1940. Bell delivered 926 P-39s in 1941 (plus 13 prototypes in 1940).
> As both companies ramped up production, Curtiss went to 2,200+ in '41, 4,400+ in '42, and 4,200+ in '43. Bell increased more slowly at first, 926 in '41, 1,973 in '42, then passed Curtiss with 4,900+ in '43. In addition, Bell was able to develop a significantly better fighter using the same basic configuration, the P-63, while Curtiss never did find an acceptable P-40 follow-on. Lessons well learned and applied.


Curtiss had other aircraft being produced (C-46, SB2C, CW-22, AT-9, O-52, SC and the ill-fated SO3C) so their manufacturing capacity was stretched thin (which is why North American was aproached by the BPC to build them Hawk 81s).
All told, Curtiss produced close to 14,000 P-40 types which is a bit more than Bell's P-39 numbers, which was less than 10,000.
Which is impressive, considering that the Hawk 81 was a follow-on to the Hawk 75. The fact that Curtiss couldn't develop the P-40 any further (not for the lack of trying, however) is not surprising, since the airframe was a mid-30's design.


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## GregP (Jan 5, 2021)

As someone formerly in the Defense Industry, Casey is the person who produced the chart, and Robinson is the person who checked that the chart was drawn correctly from the data supplied. Drawing "checkers" sometimes find errors and it gets corrected when found, if the error is actual.

Hi P-39 Expert,

The chart is, in fact, pretty far off, regardless of weight. It was established more than 60 pages ago that the drag coefficient of the XP-39 as it was built and before being modified into the XP-39B, would not allow 390 mph at either 1,050 or 1,150 hp. This chart of what is certain to be projected performace will not resurrect the debate and result in a different analysis if the analysis is done correctly since it was done correctly the first time. Time doesn't change the outcome when the facts are correct.


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## P-39 Expert (Jan 5, 2021)

jmcalli2 said:


> Yeah, I've seen the 390mph figure repeated on many sources, but no primary source of origin for it.
> 
> What is odd for a projected graph is the line labeled "Actual Time To Climb Curve" and a dashed line that I assume is the projected time to climb. Also, the abrupt 'switch' from "Military Power" to "Normal Power" at around 19,000 feet on the Rate Of Climb curve as indicated by the switch of solid and dashed lines.
> This chart is "Figure 8" of some report. Also of interest would be "Tables VI and VII."
> ...


The Allison (as with other American aircraft engines at the time) had a 5 minute limit for military power, so the pilot had to reduce to normal power at the five minute mark of his climb. The five minute limit was increased to 15 minutes in mid 1942. The dashed line above 19000ft represents the climb rate at military power which was available if the pilot hadn't just used up his five minutes. IOW pilot is cruising along above 19000ft and spots an enemy and goes to military (combat) power and can climb at the dashed line rate. I didn't explain that very well, hope it made some sense.

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## jmcalli2 (Jan 5, 2021)

GregP said:


> As someone formerly in the Defense Industry, Casey is the person who produced the chart, and Robinson is the person who checked that the chart was drawn correctly from the data supplied. Drawing "checkers" sometimes find errors and it gets corrected when found, if the error is actual.



That I know, but it does not tell us WHO those men were, only WHAT their jobs were.

The question is, what the chart is supposed to communicate. Rehashing what was in "several pages ago" does not contribute to finding out what it was for or what the other 30 pages of the report it was a part of said.


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## jmcalli2 (Jan 5, 2021)

P-39 Expert said:


> The Allison (as with other American aircraft engines at the time) had a 5 minute limit for military power, so the pilot had to reduce to normal power at the five minute mark of his climb. The five minute limit was increased to 15 minutes in mid 1942. The dashed line above 19000ft represents the climb rate at military power which was available if the pilot hadn't just used up his five minutes. IOW pilot is cruising along above 19000ft and spots an enemy and goes to military (combat) power and can climb at the dashed line rate. I didn't explain that very well, hope it made some sense.



I think you explained it pretty well, thanks.


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## XBe02Drvr (Jan 5, 2021)

jmcalli2 said:


> Just curious; did you work at the GE plant in Schenectady or Syracuse?


Neither. In the 50s through the 80s GE Armament Division was housed in the former Bell Aircraft Lakeside Plant in Burlington VT, conveniently within commuting distance of the VT National Guard Underhill Artillery Range. I believe it's now in Siberacuse.
"Sunshine everywhere else, it's cloudy in Syracuse. Cloudy everywhere else, it's raining in Syracuse. Raining everywhere else, it's snowing in Syracuse. Snowing everywhere else, it's an effing blizzard in Siberacuse!"
"Indefinite, sky obscured, estimated ceiling two hundred broken, three hundred overcast, visibility one half mile in snow and blowing snow, wind two zero zero at two five, gusts four zero, altimeter two niner eight two. Expect ILS Runway two eight. Two eight RVR eighteen hundred, variable sixteen hundred. Braking action poor."
"Metro Air two five one four, cleared to land two eight, best speed to the runway, jets to follow. Plan exit taxiway Bravo, Charlie and Delta unavailable. Piedmont two four three, you're overtaking traffic ahead, expedite your speed reduction to one six zero, be ready for a go around or delayed landing clearance.... Metro, thanks for Bravo, hold short of the parallel, Ground point nine. Piedmont two four three cleared to land two eight. Roll it on down to Foxtrot, Charlie and Delta closed for snow removal."

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## jmcalli2 (Jan 5, 2021)

XBe02Drvr said:


> Neither. In the 50s through the 80s GE Armament Division was housed in the former Bell Aircraft Lakeside Plant in Burlington VT, conveniently within commuting distance of the VT National Guard Underhill Artillery Range. I believe it's now in Siberacuse.
> "Sunshine everywhere else, it's cloudy in Syracuse. Cloudy everywhere else, it's raining in Syracuse. Raining everywhere else, it's snowing in Syracuse. Snowing everywhere else, it's an effing blizzard in Siberacuse!"
> "Indefinite, sky obscured, estimated ceiling two hundred broken, three hundred overcast, visibility one half mile in snow and blowing snow, wind two zero zero at two five, gusts four zero, altimeter two niner eight two. Expect ILS Runway two eight right, departures two eight left. Two eight right RVR eighteen hundred, variable sixteen hundred. Braking action poor."
> "Metro Air two five one four, cleared to land two eight right, best speed to the runway, jets to follow. Plan exit taxiway Bravo. Piedmont two four three, expedite speed reduction to one six zero, be ready for a go around or delayed landing clearance. Metro, thanks for Bravo, hold short of the parallel, Ground point nine. Piedmont two four three cleared to land two eight right. Roll it on down to Foxtrot, Charlie and Delta closed for snow removal."



Cool.

I just asked because I grew up in Syracuse, my Mom worked at GE making TVs in the '60s. That Syracuse GE facility, actually in Liverpool NY, is Lockheed-Martin now, recently got a big sonar contract. Could still be some GE there too.

I worked in the Albany area for a time, passed through the huge Schenectady GE campus there quite often.
Along with the Watervliet Arsenal, I drove past that about every day for a year. Interesting place.

I've been to Burlington a few times. Lovely town.

One of my first jobs in the early 80s had me going around the SAC base at Griffiss AFB in Rome. B-52s and F-106s. Saw a Navy T-2 Buckeye parked in front of the tower once. Very interesting place.

BTW, Syracuse is 40 inches short of their usual snowfall for this time of year. The Lake Effect seems to have moved South about 70 miles; Binghamton is 28 inches above their usual snowfall right now.

Worst thing about flying (commercial) out of SYR is they don't remember how to de-ice more than one plane at a time until mid January.

Stay safe, and thanks for the info!


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## jmcalli2 (Jan 5, 2021)

jmcalli2 said:


> View attachment 607596
> View attachment 607597
> View attachment 607598
> View attachment 607599



These pics were sent to me in late December 2004-5 or so by my mentor and good friend. He was a retired USMC Captain with a Marine Corps sense of humor.


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## XBe02Drvr (Jan 6, 2021)

jmcalli2 said:


> That Syracuse GE facility, actually in Liverpool NY, is Lockheed-Martin now


GE Armament was sold to Lockheed-Martin sometime in the mid 90s.



jmcalli2 said:


> I've been to Burlington a few times. Lovely town.


"Ithaca North"



jmcalli2 said:


> One of my first jobs in the early 80s had me going around the SAC base at Griffiss AFB in Rome. B-52s and F-106s.


Got my A&P at Riverside School of Aeronautics in Marcy NY, just west of Utica and just inside the outer marker for the long runway at Griffiss. Frequent aluminum overcasts accompanied with seismic tremors and rolling thunder. If a 106 got a waveoff on final, he'd light his burner right over us for the go around. If a BUFF did same, we'd have a virtual earthquake. They were Ds, no whiny turbofans here!



jmcalli2 said:


> BTW, Syracuse is 40 inches short of their usual snowfall for this time of year. The Lake Effect seems to have moved South about 70 miles; Binghamton is 28 inches above their usual snowfall right now.


I've been watching this on radar on my cellphone. Airmass flow seems to be more east-west nowadays with less NW-SE component than I remember. Watertown and Fort Drum are getting the snow dumps Syracuse and Utica used to get, and ELM, ITH, BGM are catching it from Lake Erie, which used to dump on the northern tier of PA. Used to do overnights in ITH. BTV on steroids, AND it has the renowned Moosewood Restaurant.


jmcalli2 said:


> Worst thing about flying (commercial) out of SYR is they don't remember how to de-ice more than one plane at a time until mid January.


Some things are eternal.
Thanks for the stroll down Memory Lane. Stay safe!

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## P-39 Expert (Jan 6, 2021)

GregP said:


> As someone formerly in the Defense Industry, Casey is the person who produced the chart, and Robinson is the person who checked that the chart was drawn correctly from the data supplied. Drawing "checkers" sometimes find errors and it gets corrected when found, if the error is actual.
> 
> Hi P-39 Expert,
> 
> The chart is, in fact, pretty far off, regardless of weight. It was established more than 60 pages ago that the drag coefficient of the XP-39 as it was built and before being modified into the XP-39B, would not allow 390 mph at either 1,050 or 1,150 hp. This chart of what is certain to be projected performace will not resurrect the debate and result in a different analysis if the analysis is done correctly since it was done correctly the first time. Time doesn't change the outcome when the facts are correct.


Agree that the P-39C chart was a projection and not actual, but the attached P-39N chart was actual and it shows 390+mph at 15000ft. At a much heavier weight.


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## jmcalli2 (Jan 6, 2021)

XBe02Drvr said:


> GE Armament was sold to Lockheed-Martin sometime in the mid 90s.
> 
> 
> "Ithaca North"
> ...



Used to watch the B-52s do touch & goes when I drove a truck. 
Also remember driving up around Gouverneur/Massena/Malone when the snow banks were higher than the telephone poles.
Here's a cute site for snow: GoldenSnowball.com

Once mourned '78 we drove (North of Rome or South of Oneonta, can't remember) by some unusual sights: first a F-80 upside down on a pylon about ten feet above the ground, then a F-89 the same way, then a F-84F, then a F-102 and finally a F-100. All were at least a mile apart in the middle of nowhere (we were killing time, taking the scenic route). Finally we saw an olive drab truck with a half dozen soldier types around it about 200 yards up a side road. We turned towards them to ask about the planes, but they energetically waved us off.

My guess is it was a radar test range of some sort. Why the planes were all mounted upside down I can't figure.

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## GregP (Jan 6, 2021)

Hi P-39 Expert. You are comapring apples to orange.

The XP-39 had a V-1710-35 with a turbocharger unit. It was rated at 1,150 hp and 3,000 rpm @ 44" MAP at altitude. After the turbo was deleted, the V-1710-35 made 1,050 hp and 3,000 rpm @ 44" MAP at about 9,500 feet. It never hit 390 mph, ever, in level flight.

The P-39N had a V-1710-85 (E19) engine. It developed 1,410 hp at 3,000 rpm @ 57" MAP. Add 360+ hp to a 360 - 370 mph airplane and you will get a speed increase. The P-39N test on wwiiaircraftperformance shows 398.5 mph at 9,700 feet; 1,420 hp; 3,000 rpm, 59.8" MAP, which is war emergency power plus another 1.5" MAP; at 7,274 lbs. It had 9.6 : 1 supercharger gears, so the service celing was a bit lower than the 8.8 or 8.1 gear units. The -85 was really just a -83 engine driving through 2.23 : 1 reduction unit rather than the 2.00 : 1 unit the -83 used.

The P-39N was a very different animal than the XP-39 chart shown a few pages above, and it has decent performance. But, by then, the reputation of the P-39 had been established and pretty much nobody in the USAAF wanted it. Most went to the Soviet Union (4,746 P-39s in total) since they mostly got the P-39N and Q models. After being left exposed to winter and harsh conditions in Soviet Service, I seriously doubt many would get the same performance at the same power levels, but the Soviets were not much concerned with the engines since they didn't pay for them, so they likely COULD get the test performance and more at 75 - 80" MAP.

By that time, the U.S.A. wasn't really sending out new P-39 units to war. We were supplying replacement aircraft and trying to re-equip as was possible. Let's recall that the Pacific was not the theater of priority until Germany was defeated.

Bottom line: The performance of a shiny new P-39N does not mean the XP-39 suddenly got better.

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## soulezoo (Jan 6, 2021)

jmcalli2 said:


> Cool.
> 
> I just asked because I grew up in Syracuse, my Mom worked at GE making TVs in the '60s. That Syracuse GE facility, actually in Liverpool NY, is Lockheed-Martin now, recently got a big sonar contract. Could still be some GE there too.
> 
> ...



I have family in Binghamton and can confirm about the snow.

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## jmcalli2 (Jan 6, 2021)

GregP said:


> Hi P-39 Expert. You are comapring apples to orange.
> 
> The XP-39 had a V-1710-35 with a turbocharger unit. It was rated at 1,150 hp and 3,000 rpm @ 44" MAP at altitude. After the turbo was deleted, the V-1710-35 made 1,050 hp and 3,000 rpm @ 44" MAP at about 9,500 feet. It never hit 390 mph, ever, in level flight.
> 
> ...



Small point: the XP-39 didn't fly without the turbo, the XP-39B did.

You are correct about the Soviets not caring about the longevity of the engines; they saw training a replacement pilot as more expensive than replacing an engine.

For overboost, I refer to what the British did with the Mustang I & IA, found near the bottom of this page:

E-GEH-16

My guess would be the Soviets did pretty much the same thing with their P-39s.
I'd love to see the climb rate for a P-39N at 72" Hg of boost.

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## jmcalli2 (Jan 6, 2021)

soulezoo said:


> I have family in Binghamton and can confirm about the snow.



Hope they're away from the rivers. Some springs those floods are brutal.


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## jmcalli2 (Jan 6, 2021)

A little more 'food for discussion.'

Note: there are typos in the report: paragraph B. 1. b. "P-39D" should read "P-38D;" in paragraph B. 3. e. "P-39D" should;d read P-39C." Reading the entire report makes this clear.

it is an interesting report.

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## GregP (Jan 6, 2021)

Where did you find the typos?


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## jmcalli2 (Jan 6, 2021)

GregP said:


> Where did you find the typos?



In the report.

When you read it, you'll see the ONLY P-38 was the P-38D model and the ONLY P-39 was the P-39C model. The paragraph B. 3. e. (P-39 vs Spitfire) also reverts to "P-39C" later in the paragraph, further illustrating the typo.

Paragraph B. 1. b. only makes sense if you change "P-39D" to "P-38D" given the context of the report.

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## XBe02Drvr (Jan 7, 2021)

jmcalli2 said:


> Once mourned '78 we drove (North of Rome





jmcalli2 said:


> some unusual sights: first a F-80 upside down on a pylon about ten feet above the ground, then a F-89 the same way, then a F-84F, then a F-102 and finally a F-100. All were at least a mile apart in the middle of nowhere


Rome Air Development Center, based out of Griffis, had responsibility for evaluation of antenna radiation and reception patterns for communications and ECM equipment. You missed the best exhibit of them all, a B52 inverted on a pylon and its vertical stabilizer on a hilltop south of Griffis, right near the revolutionary war Oriskany battlefield site, but visible only from the air.


jmcalli2 said:


> Also remember driving up around Gouverneur/Massena/Malone when the snow banks were higher than the telephone poles.


We used to do PLB, MSS, OGS, ART, and on to SYR, BGM, AVP, and EWR, then back again. On a low IFR heavy snow day, it was a serious workout. When we got back to PLB, it was on to BTV, then ALB or BOS for a long layover overnight. Well earned.

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## SaparotRob (Jan 7, 2021)

XBe02Drvr said:


> Rome Air Development Center, based out of Griffis, had responsibility for evaluation of antenna radiation and reception patterns for communications and ECM equipment. You missed the best exhibit of them all, a B52 inverted on a pylon and its vertical stabilizer on a hilltop south of Griffis, right near a revolutionary war battlefield site, but visible only from the air.
> 
> We used to do PLB, MSS, OGS, ART, and on to SYR, BGM, AVP, and EWR, then back again. On a low IFR heavy snow day, it was a serious workout. When we got back to PLB, it was on to BTV, then ALB or BOS for a long layover overnight. Well earned.


I LOVE aviation gibberish!

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## buffnut453 (Jan 7, 2021)

SaparotRob said:


> I LOVE aviation gibberish!



That's not gibberish...it's gobbledygook!!!! Sheesh...don't you even know basic aviation terminology?

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## jmcalli2 (Jan 7, 2021)

SaparotRob said:


> I LOVE aviation gibberish!


PLB = Clinton County Airport (Plattsburgh, NY)
MSS = Massena Airport
OGS = Ogdensburgh Airport
ART = Watertown Airport
SYR = Syracuse Airport
BGM = Binghamton Airport
AVP = Wilkes-Barre Airport
EWR = Newark Airport
BTV = Burlington Airport
ALB = Albany Airport
BOS = Logan Airport (Boston)

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## SaparotRob (Jan 7, 2021)

jmcalli2 said:


> PLB = Clinton County Airport (Plattsburgh, NY)
> MSS = Massena Airport
> OGS = Ogdensburgh Airport
> ART = Watertown Airport
> ...


Kind of takes the mystery out of it.

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## GregP (Jan 7, 2021)

Which airport is WTF?


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## GrauGeist (Jan 7, 2021)

What's odd, is that there were lea


GregP said:


> Which airport is WTF?


Only one local, that I can think of, is AVX - if that's not a WTF, I don't know what is.


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## jmcalli2 (Jan 7, 2021)

SaparotRob said:


> Kind of takes the mystery out of it.



The past ten years I traveled 3 weeks a month for work. Hit 1.1 million miles with Delta. Got to work in all 50 States and Puerto Rico. Learned lots of airport codes planning those flights & drives.

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## jmcalli2 (Jan 7, 2021)

GregP said:


> Which airport is WTF?



Way Too Far.

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## SaparotRob (Jan 7, 2021)

I’ve flown Delta many times and it was always a good experience, except for the LAG part.

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## Milosh (Jan 8, 2021)

*Prefix code* 

_W – Maritime Southeast Asia (except the Philippines)_


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## XBe02Drvr (Jan 8, 2021)

GregP said:


> Which airport is WTF?


The story goes that when Wichita Falls applied for an airport code back in the 1950s, they innocently requested WTF. The CAA responded "Denied". No explanation, no comment, which was most unusual in those days.

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## GregP (Jan 8, 2021)

My favorite is DUA .... Don't Use Abbreviations.

Once, as test manager for a company, we were working with Lockheed martin on a Space Shuttle component and we had a femal engineer from Lockheed Martin attend one of our test meetings. We were discussing environment testing and there are a lot of abbreviations for environmental testing. We were testing for temperature, altitude, humidity, blowing dust, blowing sand, shock, vibration, gunshock, etc. It is pretty standard in the busineed to called temperature, altitude, and humidity with the abbreviaiton T, A, and H.

We were having some issues with temperature and altitude test results, and spent an hour or so discussing T & A, which SHOULD have been obvious since we discussed temperature and altitude. After about 45 minutes, the female engineer was looking a bit angry and demanded to know exactly what T & A was supposed to be. After all of us males looked at her like she was from another planet for about 10 seconds, then we all burst out laughing and explained it was temperature and altitude. She broke up laughing and we went on with the meeting after a few minutes of amusement. We apologized for causing her grief and mentioned that we had all been using these abbreviations for 20 years. After that, I composed a list of environmental test abbreviations that I sent out to the participants before any meeting where we expected women to attend. It bled over into other test subject as well since almost all had a long list of abbreviations.

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## jmcalli2 (Jan 8, 2021)

XBe02Drvr said:


> The story goes that when Wichita Falls applied for an airport code back in the 1950s, they innocently requested WTF. The CAA responded "Denied". No explanation, no comment, which was most unusual in those days.



Years after Curtiss flew the XP-51 "Ascender"...


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## Dash119 (Jan 8, 2021)

jmcalli2 said:


> Years after Curtiss flew the XP-51 "Ascender"...


It was the XP-55 "Ascender"...

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## GrauGeist (Jan 8, 2021)

AKA "Ass-Ender"


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## jmcalli2 (Jan 8, 2021)

Dash119 said:


> It was the XP-55 "Ascender"...



I blame fat fingers...


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## Dash119 (Jan 8, 2021)

jmcalli2 said:


> I blame fat fingers...


When this type of thing happens to me, it's almost always a loose nut on the keyboard...

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## jmcalli2 (Jan 8, 2021)

Dash119 said:


> When this type of thing happens to me, it's almost always a loose nut on the keyboard...



With me it was a case of thinking 55 and typing 51.

I try to avoid loose nuts as much as I can.


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## GregP (Jan 8, 2021)

Tight ones hurt!


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## jmcalli2 (Jan 8, 2021)

GregP said:


> Tight ones hurt!



Loose nuts lead to loose screws.


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## GregP (Jan 9, 2021)

So THAT's why they call them "loose?"

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## XBe02Drvr (Jan 9, 2021)

jmcalli2 said:


> Loose nuts lead to loose screws.


And those lead to unintended heirs.

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## jmcalli2 (Jan 9, 2021)

GregP said:


> So THAT's why they call them "loose?"


No.

That's way they call them fast.


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## jmcalli2 (Jan 9, 2021)

XBe02Drvr said:


> And those lead to unintended heirs.


Heir today, gone tomorrow.

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## P-39 Expert (Jan 10, 2021)

jmcalli2 said:


> In the report.
> 
> When you read it, you'll see the ONLY P-38 was the P-38D model and the ONLY P-39 was the P-39C model. The paragraph B. 3. e. (P-39 vs Spitfire) also reverts to "P-39C" later in the paragraph, further illustrating the typo.
> 
> Paragraph B. 1. b. only makes sense if you change "P-39D" to "P-38D" given the context of the report.


Those may not have been typos. The report is dated October 1941. Both the P-39C and the D would have been available, along with the P-38D. The P-38E only began production in September '41 so may not have been available, the F model began production in March '42 so it was definitely not available.


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## jmcalli2 (Jan 10, 2021)

P-39 Expert said:


> Those may not have been typos. The report is dated October 1941. Both the P-39C and the D would have been available, along with the P-38D. The P-38E only began production in September '41 so may not have been available, the F model began production in March '42 so it was definitely not available.



Read the report.


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## P-39 Expert (Jan 10, 2021)

GregP said:


> Hi P-39 Expert. You are comapring apples to orange.
> 
> The XP-39 had a V-1710-35 with a turbocharger unit. It was rated at 1,150 hp and 3,000 rpm @ 44" MAP at altitude. After the turbo was deleted, the V-1710-35 made 1,050 hp and 3,000 rpm @ 44" MAP at about 9,500 feet. It never hit 390 mph, ever, in level flight. *Agree. Except the 1050HP V-1710 was a -33, a derated -35 made for the YP-39 because the -35 hadn't passed the 150 hour test. The -35 that went into the P-39D/D-1/F/P-400 was rated at 1150HP at 12000ft. *
> 
> ...


Please see above.


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## Airframes (Jan 10, 2021)

Tighter nutsacks required ..................


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## jmcalli2 (Jan 10, 2021)

P-39 Expert said:


> Please see above.



I came across this earlier today:

LiTOT: P-39 index


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## GregP (Jan 10, 2021)

So, where exactly did that pic come from? I've seen the pic before, but never that caption.


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## P-39 Expert (Jan 10, 2021)

GregP said:


> So, where exactly did that pic come from? I've seen the pic before, but never that caption.


Definitely the turbo XP-39, scoop for the intercooler and no armament.


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## jmcalli2 (Jan 10, 2021)

GregP said:


> So, where exactly did that pic come from? I've seen the pic before, but never that caption.



The link above the pic.

Here it is again:

LiTOT: P-39 index

Look for the link, "XP-39 seen on the ground from 11 o'clock" near the bottom of the page.

General contents for that site: 

LiTOT: Content

I had forgotten about the site. Glad I re-found it. A lot of information on many types there.


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## ddwhitney (Jan 14, 2021)

The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.

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## jmcalli2 (Jan 14, 2021)

ddwhitney said:


> The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
> The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.
> View attachment 608920



Gee, it looks like NACA was full of it.

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## P-39 Expert (Jan 15, 2021)

ddwhitney said:


> The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
> The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.
> View attachment 608920


AAF had to remove the turbo if they were going to get a plane in production by 1941. Which they did and produced a good airplane, except that they let the weight get too high.

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## tyrodtom (Jan 15, 2021)

jmcalli2 said:


> Gee, it looks like NACA was full of it.


The full size wind tunnel at Langley Field was limited to 125 mph, so those are estimates.
Plus was EVERY modification suggested by those wind tunnels test ever applied to a real P-39 ?


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## GregP (Jan 15, 2021)

No.


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## SaparotRob (Jan 15, 2021)

Please expand above.


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## pbehn (Jan 15, 2021)

P-39 Expert said:


> AAF had to remove the turbo if they were going to get a plane in production by 1941. Which they did and produced a good airplane, except that they let the weight get too high.


You cant really complain about the weight increase when it was caused by stuff needed by a war plane. They all increased in weight.


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## P-39 Expert (Jan 15, 2021)

pbehn said:


> You cant really complain about the weight increase when it was caused by stuff needed by a war plane. They all increased in weight.


They could have been a lot more judicious about what they put into the plane in the early models D/F/K/L/P-400. The later models with the uprated engine were fine as they were. The basic airframe was light enough. They didn't need the .30cal wing guns, after all they had a 37mm cannon and two .50cal MGs. And the 100lb nose armor plate was redundant, no other planes had their nose reduction gear armored. Those items total around 300-500lbs, depending on the amount of .30cal ammunition carried. A fully equipped P-39D without those items weighed about 7150lbs versus up to 7850lbs normal gross weight. Russians deleted the wing guns and the IFF radio and did really well with it.


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## pbehn (Jan 15, 2021)

P-39 Expert said:


> They could have been a lot more judicious about what they put into the plane. The basic airframe was light enough. They didn't need the .30cal wing guns, after all they had a 37mm cannon and two .50cal MGs. And the 100lb nose armor plate was redundant, no other planes had their nose reduction gear armored. Those items total around 300-500lbs, depending on the amount of .30cal ammunition carried. A fully equipped P-39D without those items weighed about 7150lbs versus up to 7850lbs normal gross weight. Russians deleted the wing guns and the IFF radio and did really well with it.


But that was the "thing" and we have been through it before. Whatever the theoretical advantages of a mid engine design the practical disadvantages were against it. The Spitfire and Hurricane just had to put the stuff in. There are few sleeker designs than the early Bf109s but by the end of the war they were like a soccer player who took up steroids and bodybuilding with lumps bumps and blisters all over the place.

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## GregP (Jan 15, 2021)

Without that armor, the CG would be farther aft, and aft CG was already a problem. It would take some thinking that I'm pretty sure they DID.

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## P-39 Expert (Jan 16, 2021)

GregP said:


> Without that armor, the CG would be farther aft, and aft CG was already a problem. It would take some thinking that I'm pretty sure they DID.


We've spent pages on this already, nose armor can be deleted by making other internal adjustments such as moving the radio up from the tail cone to above the engine. Bell stated that nose armor was not needed. They were able to reballast for different nose cannons that differed in weight by 140lbs. More heresay beating a dead horse.


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## GrauGeist (Jan 16, 2021)

P-39 Expert said:


> We've spent pages on this already, nose armor can be deleted by making other internal adjustments such as moving the radio up from the tail cone to above the engine. Bell stated that nose armor was not needed. They were able to reballast for different nose cannons that differed in weight by 140lbs. More heresay beating a dead horse.


So, 75 years after the fact, we need to ask why they didn't do it?
Were they just complete dumbasses or what?

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## wuzak (Jan 16, 2021)

P-39 Expert said:


> They could have been a lot more judicious about what they put into the plane in the early models D/F/K/L/P-400. The later models with the uprated engine were fine as they were. The basic airframe was light enough. They didn't need the .30cal wing guns, after all they had a 37mm cannon and two .50cal MGs. And the 100lb nose armor plate was redundant, no other planes had their nose reduction gear armored. Those items total around 300-500lbs, depending on the amount of .30cal ammunition carried. A fully equipped P-39D without those items weighed about 7150lbs versus up to 7850lbs normal gross weight. Russians deleted the wing guns and the IFF radio and did really well with it.



Déjà vu


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## P-39 Expert (Jan 16, 2021)

GrauGeist said:


> So, 75 years after the fact, we need to ask why they didn't do it?
> Were they just complete dumbasses or what?


I don't know why they didn't eliminate those unnecessary/redundant items. All the other countries were very careful to control the weight of their planes, but the AAF and Navy seemed to try and cram as much crap into their planes as they could.

Now in the case of the P-39, only the early models were too heavy, the later M/N/Q models with the uprated engines were okay. But the P-40 weighed 8400lbs with a 1150hp engine (7.3lbs/HP) and the F4F Wildcat weighed 7975lbs with a 1200hp engine (6.6lbs/HP). Both suffered performance penalties because of the excess weight. Later model Hellcats and Corsairs were in the 6lbs/HP range and had much better performance. But 1942 was fought with P-39s, P-40s and F4Fs and they paid the weight penalty. Defense of Port Moresby NG began about April and Coral Sea was in May, so the the AAF and USN had until December/Feb before the P-38 and Corsair got into combat. The AAF did lighten some P-39Ks at Guadalcanal in September and increased rate of climb substantially but little is written about that. We have benefit of hindsight but the last half of '42 was a very busy time for the AAF and USN.


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## wuzak (Jan 16, 2021)

P-39 Expert said:


> I don't know why they didn't eliminate those unnecessary/redundant items. All the other countries were very careful to control the weight of their planes, but the AAF and Navy seemed to try and cram as much crap into their planes as they could.



Unnecessary items such as IFF?


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## P-39 Expert (Jan 16, 2021)

wuzak said:


> Unnecessary items such as IFF?


IFF is redundant if there is no radar at your base. In 1942 Port Moresby didn't have radar until October and Guadalcanal until September. PM had Australian radar but it was too far away to do any good. IFF is also redundant in every plane on a mission. A 16 plane squadron mission didn't need every plane in the squadron to have an IFF set. 

The Russians had American lend lease radar from May 1943 but removed the IFF set (along with the .30cal wing guns) as standard procedure anyway.

USN planes probably need a set on every plane given their unique situation. Each aircraft carrier had radar and needed to account for each plane sent out.


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## jmcalli2 (Jan 16, 2021)

tyrodtom said:


> The full size wind tunnel at Langley Field was limited to 125 mph, so those are estimates.
> Plus was EVERY modification suggested by those wind tunnels test ever applied to a real P-39 ?



I find it interesting the Kelly Johnson pretty much refused the NACA recommendations for the P-38. 

As far as I can tell, the NACA changes were all applied. One I question is placing the induction air intake behind the cockpit canopy. Again, compare to the P-38 where it is placed in clean air. I suspect being so close to the canopy negated ram effect; the P-63D with the bubble canopy pushed the intake significantly further back (to give the canopy room to slide) and that was significantly faster than P-63Es with the same wing & engine. That makes more sense to me now with the 125 limit of the wind tunnel. Thanks for that info!

The turbo in the XP-39 was located where the radiator was placed in the production models. The installation problems went to intercooler intakes. The only operational experience the AAF had with turbos was the P-30/PB-2. They didn't fly them high very often because of crew discomfort and expense; I believe that reinforces the idea that the turbo was killed because making it work would have taken too long.

Bottom line is I don't know of ANY combat equipped aircraft that could hit the 400+ mph at 15,000 ft prediction the NACA gave for the P-39 with their modifications with a single 1,050hp engine. 1,050hp at 20,000 ft, maybe. There is that much less air resistance up there.

This, - CRGIS review - used to be a good NACA wind tunnel reference site, but it is currently down for 'review.'

I also remember a NACA report on the drag of various single engine WWII planes, P-39, P-40, P-43, P-35, F4F, SBD I think, all in one report. I can't find it now; it most likely was in the NACA link above.


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## P-39 Expert (Jan 16, 2021)

P-39 had the least drag of any American WW2 fighter except the P-51 according to AHT.


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## Milosh (Jan 16, 2021)

jmcalli2 said:


> he only operational experience the AAF had with turbos was the P-30/PB-2.



Ah, B-17 iirc.


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## jmcalli2 (Jan 16, 2021)

Milosh said:


> Ah, B-17 iirc.




The first B-17 with turbos, the YB-17A, first flew with turbos on 29 April 1938.
The XP-39 made it's first flight on 6 April 1938.


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## GrauGeist (Jan 16, 2021)

The Bell YFM-1 had turbosupercharged Allison V-1710-9 engines - first flew in '37.


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## Glider (Jan 16, 2021)

P-39 Expert said:


> IFF is redundant if there is no radar at your base. In 1942 Port Moresby didn't have radar until October and Guadalcanal until September. PM had Australian radar but it was too far away to do any good. IFF is also redundant in every plane on a mission. A 16 plane squadron mission didn't need every plane in the squadron to have an IFF set.
> 
> The Russians had American lend lease radar from May 1943 but removed the IFF set (along with the .30cal wing guns) as standard procedure anyway.
> 
> USN planes probably need a set on every plane given their unique situation. Each aircraft carrier had radar and needed to account for each plane sent out.



I admit to finding the idea that not every aircraft in a squadron needed an IFF set somewhat bemusing. Almost every time a squadron went into combat they got split up. How many times have you heard of an aircraft getting a bearing home by using it's IFF set. I can imagine them drawing lots before take off because everyone would want the one with IFF.


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## Glider (Jan 16, 2021)

P-39 Expert said:


> Bell stated that nose armor was not needed.


Clearly the people who went into combat decided they did need the armour. In fact, all the airforces of all nations, who went to war decided that they needed armour.


> They were able to reballast for different nose cannons that differed in weight by 140lbs.


If they had such flexibility why didn't they make changes to make the aircraft safer or at least more flexible from a COG position.


> More heresay beating a dead horse.



More practical experience beating a theoretical argument.

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## Reluctant Poster (Jan 16, 2021)

GrauGeist said:


> The Bell YFM-1 had turbosupercharged Allison V-1710-9 engines - first flew in '37.


As did the XP-37. The P-30 first flew in 1934. 60 of them were built.


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## Milosh (Jan 16, 2021)

jmcalli2 said:


> The first B-17 with turbos, the YB-17A, first flew with turbos on 29 April 1938.
> The XP-39 made it's first flight on 6 April 1938.


A 14th Y1B-17 (_37-369_), originally constructed for ground testing of the airframe's strength, was upgraded and fitted with exhaust-driven General Electric turbochargers. *Scheduled to fly in 1937, it encountered problems with the turbochargers*, and its first flight was delayed until 29 April 1938.


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## BiffF15 (Jan 16, 2021)

I have what must be a morbid fascination with this thread. It's like I can't look away from a traffic accident as it unfolds.

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## MiTasol (Jan 16, 2021)

P-39 Expert said:


> Russians deleted the wing guns and the IFF radio and did really well with it.



*But they kept the nose armor plate *because they knew removing that would make the aircraft highly unstable once all or most of the ammunition was expended

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## jmcalli2 (Jan 16, 2021)

GrauGeist said:


> The Bell YFM-1 had turbosupercharged Allison V-1710-9 engines - first flew in '37.



True, and I considered including that aircraft with the P-30 in my post. 

The XFM-1 first flew in September 1937, but the contract for 13 YFM-1s wasn't issued until May 1938. The first YFM-1 flew in September 1939 and was delivered to the AAF in February 1940.
The XP-39B flew in November 1939.

An interesting side note is that the USAAC dealt with underperforming prototypes in exactly the opposite way: for the B-17 they added turbos, but for the P-39 they removed the turbo.
Ain't bureaucracy grand.


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## jmcalli2 (Jan 16, 2021)

Milosh said:


> A 14th Y1B-17 (_37-369_), originally constructed for ground testing of the airframe's strength, was upgraded and fitted with exhaust-driven General Electric turbochargers. *Scheduled to fly in 1937, it encountered problems with the turbochargers*, and its first flight was delayed until 29 April 1938.




Not much experience if it's not flying.


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## glennasher (Jan 16, 2021)

Glider said:


> I admit to finding the idea that not every aircraft in a squadron needed an IFF set somewhat bemusing. Almost every time a squadron went into combat they got split up. How many times have you heard of an aircraft getting a bearing home by using it's IFF set. I can imagine them drawing lots before take off because everyone would want the one with IFF.




Yes, indeed, if you took out the IFFs of all the squadron except one, what happens if that unlucky soul gets shot down? Just because the Russians did it, doesn't make it a great idea............... They had a very different and distinct set of circumstances compared to what the USAAF was doing over Europe and the SW Pacific area, so much so, that they were fighting a completely different war.

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## FLYBOYJ (Jan 16, 2021)

P-39 Expert said:


> IFF is also redundant in every plane on a mission. A 16 plane squadron mission didn't need every plane in the squadron to have an IFF set.


Can you validate that statement based on some operational or historical reference?


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## wuzak (Jan 16, 2021)

P-39 Expert said:


> IFF is redundant if there is no radar at your base. In 1942 Port Moresby didn't have radar until October and Guadalcanal until September. PM had Australian radar but it was too far away to do any good. IFF is also redundant in every plane on a mission. A 16 plane squadron mission didn't need every plane in the squadron to have an IFF set.



So when the bases did get radar you would re-install the IFF, losing the small performance from removing it?

As others have said, if your aircraft doesn't have IFF and you are separated from your squadron, you are suddenly a bogey that needs to be dealt with.

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## PAT303 (Jan 16, 2021)

BiffF15 said:


> I have what must be a morbid fascination with this thread. It's like I can't look away from a traffic accident as it unfolds.



There are fanboys for aircraft, cars, V8 engines and many can be very passionate about their favorite choice but then you have people that take it to another level, to the point of fanaticism despite all the facts put to them, that describes this thread

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## SaparotRob (Jan 16, 2021)

It’s still kind of comforting. Like watching re-runs of an old TV show.

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## GrauGeist (Jan 16, 2021)

Look at the Ad at the bottom of the screenshot taken just now!

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## tyrodtom (Jan 16, 2021)

Google " The summer it rained airplanes / the long hunt " .


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## Marcel (Jan 17, 2021)

This thread is like Covid. P39 is popping up everywhere. I hope the vaccin will work better than the groundhog-antidote here.

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## Snautzer01 (Jan 17, 2021)



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## Marcel (Jan 17, 2021)

Agreed. People can complain to me by PM...

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