Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (2 Viewers)

The issue with the P-400 is that it didnt go anywhere near 400 so questioning test data on this aircraft has been done from the start. If it could climb to 25,000ft in exactly the same time as a Spitfire Mk I it wouldnt have been the disappointment that it actually was.

Yes it is from Wiki.

For the P-400

British expectations had been set by performance figures established by the unarmed and unarmored XP-39 prototype. The British production contract stated that a maximum speed of 394 mph (634 km/h) +/- 4% was required at rated altitude.[41]​ In acceptance testing, actual production aircraft were found to be capable of only 371 mph (597 km/h) at 14,090 ft (4,290 m). To enable the aircraft to make the guarantee speed, a variety of drag-reduction modifications were developed by Bell. The areas of the elevator and rudder were reduced by 14.2% and 25.2% respectively. Modified fillets were installed in the tail area. The canopy glass was faired to its frame with putty. The gun access doors on the wing had been seen to bulge in flight, so they were replaced with thicker aluminum sheet. Similarly, the landing gear doors deflected open by as much as two inches at maximum speed, so a stronger linkage was installed to hold them flush. The cooling air exit from the oil and coolant radiators was reduced in area to match the exit velocity to the local flow. New engine exhaust stacks, deflected to match the local flow and with nozzles to increase thrust augmentation, were installed. The machine gun ports were faired over, the antenna mast was removed, a single-piece engine cowling was installed and an exhaust stack fairing was added.

The airframe was painted with 20 coats of primer, with extensive sanding between coats. Standard camouflage was applied and sanded to remove the edges between the colors. Additionally, about 200 lb (91 kg) of weight was removed, making it lighter than normal (7,466 lb (3,387 kg) gross).[42]​ After these modifications, the second production aircraft (serial AH 571) reached a speed of 391 mph (629 km/h) at 14,400 ft (4,400 m) in flight test. As this speed was within 1% of the guarantee, the aircraft was declared to have satisfied contractual obligations.[41]​ Despite the success of these modifications, none were applied to other production P-39s. Later testing of a standard production P-400 by the British Aeroplane and Armament Experimental Establishment (A&AEE) revealed a top speed of only 359 mph (578 km/h).

Shortround6 said:

You know, even in New Guinea the US pilots might have like to have a radio. Just maybe they would like to talk to the other plane or to their base? Wing waggling as a form of communication is rather over rated.
This was the radio the US used in some of it's P-39s.

File:SCR-522 Data.png - RadioNerds

radionerds.com

About 90lbs

The weight charts in the P-39D-1/D-2 manual specify the radios by model number.

This has been gone over in some of the previous posts.
The IFF weighed around 45lbs How much is the actual unit and how much is in "electrical" and how much is in "furnishings" I don't know.

I Have no idea why but in AHT the P-400 has 205lbs of "armament provisions" but a P-39D-2 with the same 20mm cannon, the same two .50 cal machine guns and the same four .30 cal wing guns has 147lbs of "armament provisions". How you came up with 50lbs of it for the wing guns I don't know.
There are a few other spots where you seem to pick and choose your weights.

BTW your 7011lb P-39 won't get far because you forgot to put 2 gallons of oil (15lbs) into the reduction gear box behind the prop. No, it is not included in the empty weight but it is included in the tactical empty weight in the pilots manual.

As far a seeing what a 7075lb P-39 would do..........ROFLMAO.

It is a 6689lb P-39 and it won't even make level speed without failing to meet both coolant and oil temperature requirements.
level speed is usually much easier to cool than climbing because you have a lot more air going through the cooling system per minute.
No surprise it fails to meet cooling requirements when climbing. This is for both oil and coolant.
Perhaps the "D"s got better cooling? or a more positive method of controlling the exit flap/s?

This is one reason the argument goes circular. You ignore contradictory information (like the radios) and come up with your own, most favorable numbers. The only way to come up with 11lbs for gun sight and oxygen in your example is to use the gun sight from the P-400 and the oxygen weight number from the P-39D-2. The numbers for the D-2 are only 13lbs so it makes no practical difference. But why juggle the numbers to begin with?

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Yes, all this has been discussed many times. But this is the P-39 thread where we're allowed to discuss the P-39, right?

Radio (voice) included in empty weight. 35lbs.

IFF listed in AHT as 110lbs for the P-400. If it only weighed 45lbs then the P-400 would be lighter by 65lbs, right?

"Armament Provisions" weights are different for different models. I take this to mean gun mounts, chargers, heaters, ammunition boxes etc. 50lbs is my estimate based on percentage weight of the 30cals to total weight of the guns.

Reduction gear oil is included in total weight of oil 71lbs.

As we have discussed many times before, the 6689lb weight is the average weight of this plane during a flight due to fuel burn. Most all of the Wright Field tests for all the WW2 AAF fighters listed a weight that was less than the published gross weight from the Weight and balance Chart in the pilot's manual. British used 95% of gross weight as test weight. 6689lbs + 64gal = 7075lbs. 6689lbs divided by 95% = 7041lbs, within 34lbs of published gross weight.

Regarding engine cooling, most of the early AAF models (P-38F/G, P-47D, P-51A/B) didn't meet cooling requirements as noted in the Wright Field tests either, just like the P-39. This was common until development of automatic cooling flaps in 1944. P-39 never got these.

Yes I used the oxygen weight from the D model which saved 22lbs. P-400s at Guadalcanal had oxygen system not compatible to Marine system, so I used the AAF system. All other weights are for the P-400.

This 7100lb P-400 (or P-39) was an armored warplane with self sealing fuel tanks and cannon/heavy machine gun centerline armament.

Climb and ceiling from the tests would have been further improved in mid-42 when the 5 minute limit (3000rpm combat power) was increased to 15min. Engine power was reduced to 2600rpm (normal power) after 5min at 16750'. I estimate climb would have improved to approximately 2600fpm at 20000' and ceiling to approximately 37000' at full 3000rpm. Compare this to the 1942 A6M2 which climbed at 1800fpm at 20000' or the not yet available F4U, F6F, P-38F, or P-47D which climbed at around 2000fpm at 20000'. The 1943 FW190 also climbed at about 2000fpm at 20000'. Remember this test was in mid 1941 with the early 1150hp -35 engine. By fall of 1942 the uprated -85 engine was available for the M/N/Q models and no weight reduction was needed, although deleting the 30cal wing guns would have been nice.

I've posted all this many times before and it is all based on factual information. The 1942 P-39s were grossly overweight for their engine power. Eliminating the 30cal wing guns and a piece of redundant armor plate would have improved performance tremendously and could have been done at forward bases.

P-39 Expert said:

Eliminating the 30cal wing guns and a piece of redundant armor plate would have improved performance tremendously and could have been done at forward bases.

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And the guns were removed for some airframes but the performance increase wasn't "tremendous". If the performance improvement had been "tremendous" then surely it would have been implemented on all P-39s in combat theatres, with requirements passed to the manufacturer to stop building airframes with wing guns?

Also, if a "tremendous" performance increase was so readily available, why did the AAF get rid of the P-39 as quickly as it did?

Note the use of steel.

P-39 Expert said:

Yes, all this has been discussed many times. But this is the P-39 thread where we're allowed to discuss the P-39, right?

Radio (voice) included in empty weight. 35lbs.

IFF listed in AHT as 110lbs for the P-400. If it only weighed 45lbs then the P-400 would be lighter by 65lbs, right?

I've posted all this many times before and it is all based on factual information. The 1942 P-39s were grossly overweight for their engine power. Eliminating the 30cal wing guns and a piece of redundant armor plate would have improved performance tremendously and could have been done at forward bases.

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You have posted this many times as you have posted it all many times, and many times you have been told you are wrong. Was the Mustang MkI and P-51A lighter than a P-39? 50% of a P51A fuel load is almost the same as 100% of a P-39s. Did the British take Mgs off the Mustang Mk I or swap them for 4 cannon? When the P-51B was being designed they added even more fuel added more oil and probably added oxygen, plus later gyro stabilised gunsights etc etc etc.

The 1942 P-39 was just obsolete for use in the ETO, the Mustang MkI wasnt, using the same engine and it almost always carried a camera and obviously had IFF.

Milosh said:

http://www.wwiiaircraftperformance.org/P-39/P-39C_Chart-Bell_Aircraft-1400.jpg

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That's an interesting graph...but I have huge questions over its accuracy. It claims that the P-39C had a ceiling of approx 37,500 ft and can reach 30,000ft in less than 12 minutes. However, the tabular data on this page (P-39 Performance Tests) lists the absolute ceiling for the P-39C as 34,150ft and time to 30K in 18.4 mins. These figures seem much more realistic than the chart MIlosh posted...but why the discrepancy since both were apparently created by Wright Field test pilots?

The performance characteristics for the P-39D-1 listed in this table:


The P-39D-1 can't reach 31,000ft as a service ceiling and takes 25.7 minutes to get there. Even the later N and Q models take more than 25 mins to reach service ceiling.

P-39 Expert said:

IFF listed in AHT as 110lbs for the P-400.

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Pretty sure AHT does not list the IFF, specifically, at 110 pounds. Rather some communication systems.

Unfortunately my copy is not available to me at this time.

Can't answer but the graph is from the test,

WAR DEPARTMENT

AIR CORPS, MATERIEL DIVISION

Wright Field, Dayton, Ohio

July 17, 1941

MEMORANDUM REPORT ON
Pursuit Single Engine P-39C, A.C. No. 40-2988

So...

Earlier, SR6 mentioned that the P-39 originally had 1,000 rpg for the .30 cals giving fifty (50) seconds of firing time.

Which got me thinking, if facing down the light, rather flammable IJA/IJN fighters and bombers, what if you ditched the entire nose armament and kept only the 4 .30's in the wings with a hefty amount of incendiary/tracers laced into those 1,000 rounds per gun?

Granted the .30 wasn't a giant killer but against the right targets that tended to flame easily and with almost a minute of firing time perhaps worth a try? If I'm full of it let me know, it just seems like a mod that would work in a specific area (SWPA) vs. a specific enemy (IJA & IJN).

Of course as I write this I realize the removal of all that weight in the nose is going to be problematic at best. Replace with ballast? And if so, you've gained nothing in weight reduction so maybe I just killed a lot of electrons for nothing with this post.

Be easy on me with critique, I'm very sensitive...

buffnut453 said:

That's an interesting graph...but I have huge questions over its accuracy. It claims that the P-39C had a ceiling of approx 37,500 ft and can reach 30,000ft in less than 12 minutes. However, the tabular data on this page (P-39 Performance Tests) lists the absolute ceiling for the P-39C as 34,150ft and time to 30K in 18.4 mins. These figures seem much more realistic than the chart MIlosh posted...but why the discrepancy since both were apparently created by Wright Field test pilots?

The performance characteristics for the P-39D-1 listed in this table:

http://www.wwiiaircraftperformance.org/P-39/P-39_Aircraft_Performance_Characteristics.jpg

The P-39D-1 can't reach 31,000ft as a service ceiling and takes 25.7 minutes to get there. Even the later N and Q models take more than 25 mins to reach service ceiling.

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Bolded by me.

In response to the bold text, I see this at the top of the chart:



So was that a USAAF test or a Bell corporate test?

P-39 Expert said:

Radio (voice) included in empty weight. 35lbs.

IFF listed in AHT as 110lbs for the P-400. If it only weighed 45lbs then the P-400 would be lighter by 65lbs, right?

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AHT says in the table.
"Misc. equip (radio)"
If it says IFF somewhere else please point it out.
The radio was included in the empty weight of the P-39C as per the Manual.
It was NOT included in the empty weight of the P-39D-1 and P-39D-2 as per the manual.
By the time you get to the P-39N the radios (included is the IFF) are back to being in the empty weight. They are the same radios as used in the P-39Ds. They are listed by type/model number. This probably one of the reasons the P-39N was about 100lbs heavier empty than the P-39D?

Make sure you are comparing like to like.

P-39 Expert said:

"Armament Provisions" weights are different for different models. I take this to mean gun mounts, chargers, heaters, ammunition boxes etc. 50lbs is my estimate based on percentage weight of the 30cals to total weight of the guns.

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So you used a WAG to come up with your number.
You could have just used the armament provision number for the P-39D-2

P-39 Expert said:

As we have discussed many times before, the 6689lb weight is the average weight of this plane during a flight due to fuel burn. Most all of the Wright Field tests for all the WW2 AAF fighters listed a weight that was less than the published gross weight from the Weight and balance Chart in the pilot's manual. British used 95% of gross weight as test weight. 6689lbs + 64gal = 7075lbs. 6689lbs divided by 95% = 7041lbs, within 34lbs of published gross weight.

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Funny thing about that.
In the Manual for the P-39C the performance number page (page 22) says the level speeds were with a design gross weight of 662lbs. an obvious typo.
The climb data (IAS as various altitudes, no climb rate given) was for a design gross weight of 6662lbs.
The landing and take-off distances are given for a design weight of 6662lbs.
the weight chart comes up with a weight of 6684lbs with 104 gallons of fuel. There are no self sealing tank liners or tanks. full fuel is 170 gallons.
Things change with time. This was common practice in the late 30s or 1940 (?)
The P-36 and early P-40 performance specifications also use a limited fuel load. The performance numbers are done with 105 gallons in the case of the P-36 with a 57 gallon overload tank available
see http://www.wwiiaircraftperformance.org/P-36/P-36_Operation_and_Flight_Instruction.pdf
The P-40 numbers are really strange.
see; http://www.wwiiaircraftperformance.org/P-40/P-40_Official_Summary_of_Characteristics.pdf
normal fuel is 120 gallons, max is 181 gallons.
Performance numbers are for 120 gallons. at a design weight of 6787lbs

So, in this case the P-39C was tested at about 27lbs over it's "design" gross weight. Which is close enough, maybe they couldn't find a test pilot that weighed 160lbs in flight suit and with parachute.

P-39 Expert said:

Reduction gear oil is included in total weight of oil 71lbs.

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If it is you are going to run out of oil before you run out of gas. P-39N carried 62lbs of oil including the gear box oil for it's 87 gallons of fuel. The P-39Ds carried 88lbs of oil including the gear box oil, Both could and did carry more oil when the drop tank was fitted. The P-39C carried 7.4 gallons in the main tank/engine (55lbs) with 15lbs for the gear box on a separate line. The tank could hold 12.1 gallons. Again the "normal" fuel load for the P-39C was 104 gallons.
Perhaps planes in combat zones carried an extra gallon or two just for "insurance"?
I know I would try to, especially if the engine was somewhat worn.

P-39 Expert said:

Regarding engine cooling, most of the early AAF models (P-38F/G, P-47D, P-51A/B) didn't meet cooling requirements as noted in the Wright Field tests either, just like the P-39. This was common until development of automatic cooling flaps in 1944. P-39 never got these.

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Apparently the P-39C had semi automatic cooling flaps. At high speed the airflow pushed them shut.
There is also a difference between a plane that has trouble cooling in a long hard climb and one that overheats in high speed level flight.

Peter Gunn said:

Bolded by me.

In response to the bold text, I see this at the top of the chart:

View attachment 631726

So was that a USAAF test or a Bell corporate test?

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Great question...and I know where I'd wager my money.

The climb rate data in that graph are also hugely optimistic. Again, for comparison purposes (altitude: graph climb rate (normal power)/tabular climb rate)

Sea Level: 4200/3720
5000': 4100/3720
10,000': 3975/3720
13,050': 3850/3040
16,750': 3550/2360
20,000': 2200/1350
25,000': 1600/975
30,000': 1050/440

If we look at the military power climb rates above 20,000' then the figures are even higher in the graph:

25,000': 2200 fpm
30,000': 1550 fpm

The graph even claims a climb rate of 400fpm (normal)/750fpm (military) at 35,000'.

These figures are simply fantastical. There is no way any P-39 ever reached these levels of performance. The must be from estimated data or must include some other factor that wasn't present in production airframes.

Peter Gunn said:

Bolded by me.

In response to the bold text, I see this at the top of the chart:

View attachment 631726

So was that a USAAF test or a Bell corporate test?

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Also check out the date - created 10/29/39 and checked 2/7/40. The P-39C first flew in January 1941. The graph is entirely estimated data and of no relevance to the real airframe as delivered.

Peter Gunn said:

Bolded by me.

In response to the bold text, I see this at the top of the chart:

View attachment 631726

So was that a USAAF test or a Bell corporate test?

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Look at the dates in upper left corner.
10/29/39
and checked 2/10/40
The first YP_39 didn't fly until 9/13/40
7 months after the chart was "checked"
the first P-39C didn't fly until Jan 1941. 11 months after the chart was "checked"

The whole thing is calculated estimates.

Buffnut beat me to it.

Shortround6 said:

Buffnut beat me to it.

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That's unusual!

This is what Bell was selling to the French and British.

Note that this was page 31 of a report.

Maybe the French (and later the British) thought that they could add some weight and still have a good performing plane???

Also please note the engine in the chart was supposed to give 1150hp from sea level to 15,000ft.
A fantasy engine for the Aircobra until late 1942.

My Lord, he's turned you all into P-39 experts.

Expert
/ˈekˌspərt/

noun
Person from out of town with a brief case

SaparotRob said:

My Lord, he's turned you all into P-39 experts.

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Well, everyone has a talent for SOMETHING.

The exception is we're realistic "experts" who rely on pesky things like "data" and "facts".