XP-39 II - The Groundhog Day Thread

[Juha3]

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

 

[DerAdlerIstGelandet]

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.

 

[P-39 Expert]

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.

 

[DerAdlerIstGelandet]

Somebody just say okay I agree with you and I will go away.

 

[rochie]

no, Karl dont do it ........

 

[buffnut453]

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.

 

[P-39 Expert]

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.

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.

 

[buffnut453]

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?

 

[Ivan1GFP]

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.

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.

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.

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.....

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.

 

[GregP]

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.

 

[Ivan1GFP]

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.

 

[GregP]

They had a good-running Zero for the 1944 Fighter Conference. The Planes of Fame is still flying it, and it STILL runs good.

 

[Ivan1GFP]

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.

 

[GregP]

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!

 

[Ivan1GFP]

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.

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.

 

[Ivan1GFP]

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.

Happy Haloween.

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.

 

[Peter Gunn]

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.

 

[fubar57]

The SB2C-1 replaced its single .50 Mg with twin .30s in the observers position

 

[glennasher]

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.

 

[GregP]

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.