XP-39 II - The Groundhog Day Thread

[pbehn]

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.

 

[Dash119]

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?

 

[pbehn]

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.

 

[buffnut453]

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.

 

[pbehn]

You say tomayto, I say tomahto.

Chucklehead is understood on both sides of the pond, unless you are in Glasgow or Newcastle of course.

 

[P-39 Expert]

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.

 

[P-39 Expert]

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.



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.



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.



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.View attachment 601399

Here's a photo of the arrangement. Don't think the 37mm horsecollar magazine fits in there, but a 20mm belt feed might.

 

[XBe02Drvr]

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.

 

[P-39 Expert]

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?

 

[fubar57]

Many get shot down without realizing the opponent was there

 

[GregP]

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.

 

[P-39 Expert]

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

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?

 

[MIflyer]

 

[pbehn]

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.

 

[SaparotRob]

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.

 

[GregP]

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.

 

[FLYBOYJ]

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.

 

[MIflyer]

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.

 

[XBe02Drvr]

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.

 

[nuuumannn]

EIGHTY pages! Dammit, got a bit of catching up to do on the Lancaster nuclear bomber thread...