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

[greybeard]

Hello!
I was intrigued by reading of this interview with Golodnikov, especially by his mention about true performances of German fighters (color plus some correction of the text by me):

"A. S. Nikolay Gerasimovich, if you look at any reference book, the superiority in speed of German aircraft [like] the Bf-109G and FW-190 is indisputable. Minimum 20-25 kilometers at low altitudes and up to 80-100 kilometers at high altitudes. And you say ours did not lag behind?

N. G. No, some difference in speed always exists. At low altitudes we were a bit faster, at high altitudes they were. The difference was on the order of 10-20 km. But this difference was not so great that it ensured overwhelming superiority. In combat it was practically not discernible.

A. S. Nikolay Gerasimovich, sometime relatively long ago I was speaking with a pilot, a frontline veteran. Right after the war they flew in captured aircraft. And no matter how hard they tried, they were unable to attain the speeds the Germans had written in their specifications. The shortfall in speed was significant. In the end, they prevailed upon a German, a high-level specialist, and asked him, "Why this shortfall in speed? Are we using the engine's capability incorrectly?" His response was that they would never achieve the target speed, because the German specifications showed the theoretical speed, and they were attempting to attain that speed on their instruments.

Nikolay Gerasimovich, in your view, is this possible?

N. G. Of course. We had a group of specialists with us from NII VVS. They were examining specifications and were looking at speed. "What speed is indicated at 7,000 meters? 780? Take away 100. And what about 3,000 meters? 700? Reduce it 70 km." This is how they calculated the instrumented speed and, characteristically, almost always hit their target. Perhaps they knew something about our focus on speed."

I wonder what they mean for "theoretical speed": didn't Germans actually test in flight their planes? And what is this "instrument speed" they speak of?

I would be glad to know your opinion. Cheers,
GB

 

[MIflyer]

I recall reading of one German pilot saying, "The P-39 performed like the 109 at low altitudes."

And in the book "P-39 Aces of WWII" the author points out that in reality P-39 versus Zero losses in the Pacific were about equal. He also points out that when the Soviets got in later aircraft such as the LA-5, Yak-3, and Yak-9 they did not use them to replace P-39's but kept the Airacobras in front line air superiority service.

 

[pbehn]

The war in the east was always on a land front, this may have been static or fluid but it was over land, apart from N Africa the majority of conflicts in the west had a water barrier until 1944. The P 39 may have been disadvantaged at high altitude, but the fight was at the front was on the ground where the two sides armies were in conflict . After D Day the fight in the east and west was pretty much the same on the front. The Typhoon and Tempest were disadvantaged at altitude but that was of no consequence because to take the fight up to high altitude needs strategic bombers or recon aircraft.

 

[FLYBOYJ]

I recall reading of one German pilot saying, "The P-39 performed like the 109 at low altitudes."

And in the book "P-39 Aces of WWII" the author points out that in reality P-39 versus Zero losses in the Pacific were about equal. He also points out that when the Soviets got in later aircraft such as the LA-5, Yak-3, and Yak-9 they did not use them to replace P-39's but kept the Airacobras in front line air superiority service.

There were few old discussions on this. There is no doubt the Zero had the definite advantage over the P-39 over New Guinea, but if you look at the combat record of say the 8th FG, the P-39's combat record wasn't as dismal as portrayed by some historians.

 

[MIflyer]

One thing I've wondered about is just how much difference there was between the P-39D and the P-400. The P-400 had the RAF oxygen system that was incompatible with the US equipment and the 20MM gun, which probably was actually better than the 37MM for air to air combat. It also had the SCR-283 radio rather than the much better 274-N. But the P-39D-1 was simply a P-400 brought up to P-39 standards, but retaining the 20MM gun. Other than that I see no reason to suspect a real difference in the performance of the two types. But the conditions on Guadalcanal were a lot worse than on New Guinea and the maintenance no doubt suffered.

 

[Denniss]

P-39 was a fine aircraft at low level.
One should not forget that the soviets tended to improve the P-39 by saving weight, removing wing cannon and sometimes even armor plates and other stuff.
The weight savings should have helped with maneuverability and speed/acceleration

 

[XBe02Drvr]

I wonder what they mean for "theoretical speed": didn't Germans actually test in flight theirSS planes? And what is this "instrument speed" they speak of?

Sounds to me like a loosely translated reference to speed under optimum conditions as opposed to indicated airspeed under real world conditions. Perhaps akin to the difference in SAE vs DIN horsepower ratings back in the musclecar days. SAE measured the output of the raw engine block, with all accessory functions such as coolant circulation, electrical generation, and carburetion provided by the test rig, while DIN measured horsepower delivered to a transmission by a fully assembled engine as it would be installed in a car. Make sense?
I think the "theoretical" speeds might have been measured speeds of (perhaps prototype) thoroughly instrument test aircraft corrected for temperature pressure and altitude. The indicated airspeed of a frontline aircraft in combat trim would obviously be much lower.
Cheers,
Wes

 

[MIflyer]

Well, the P-39 did not have any "Wing Cannons" to delete. But ever since reading Caiden's "Rugged, Ragged Warriors" I have wondered if you could strip a P-39 down a bit to yield a better air to air fighter. They did that with a P-40 in India with a degree of success in intercepting Japanese Dinah recon aircraft.

Take a look at the P-39 Design Analysis. The 37MM gun was not all that useful in air to air combat. It had a rate of fire described as similar to that of a "Roman Candle" which was supposed to be 135 rounds a minute; at 300 mph the airplane would have moved 200 ft between rounds. Even more importantly, the 37MM trajectory was significantly different from that of the .50 cal and .30 cal guns, so it usually was a matter of deciding which gun you wanted to hit the target with.

So let's get rid of the 37MM and replace it with another .50 cal. The 37MM weighs 238 lb and its 30 rounds of ammo weighs 60 lb, for a total of 298 lb saved. One .50 cal gun weighs 80 lb and 400 rounds of ammo for it weighs 129 lb (the two .50 cal guns already there have 200 rpg). So, swapping out the 37MM for a .50 saves 89 lb.

Next let's get rid of the four .30 cal guns in the wings. That saves 92 lb for the 4 guns and 78 lb for the 1200 rounds of ammo. By the way supposedly the P-39 could hold 2000 rounds of .30 cal ammo but they probably did not load all of it. We get rid of another 170 lb, for a total reduction of 259 lb, which is not really very much.

The total weight of armor plate for the airplane is given as 202 lb. I read somewhere that one unit in the Pacific made a big improvement in the P-39 by removing the armor on the belly protecting the radiator. If you are planning on air-to-air work that belly armor is not very useful, but I'm sure it was useful for strafing.

So if you get rid of, say, half the armor and you have stripped the airplane down to three .50 cal guns, it is 359 lb lighter. That does not sound like very much to me. No wonder they never seemed to try it. It appears that the P-39Q-20 without the two underwing .50 cal guns was about 260 lb lighter than the other Q models. The P-39N-0-BE model had four fuel cells removed to reduce the max fuel load by 28 gal, which reduced the max gross weight from 9100 to 8750 lb. So if a 350 lb weight reduction was worth doing then maybe 359 lb would be worth doing.

 

[XBe02Drvr]

So if a 350 lb weight reduction was worth doing then maybe 359 lb would be worth doing.

WHOA!! So far all this weight you've removed seems to be forward of the center of lift. Don't forget this is a rear engine plane with a hint of a tail heaviness problem. If you don't compensate by moving some heavy objects forward, you're going to have a right squirrelly bastard on your hands with some nasty slow flight and stall behaviors and a penchant for unrecoverable flat spins. This wheel has been invented before!
Cheers,
Wes

 

[tomo pauk]

Well, the P-39 did not have any "Wing Cannons" to delete. But ever since reading Caiden's "Rugged, Ragged Warriors" I have wondered if you could strip a P-39 down a bit to yield a better air to air fighter. They did that with a P-40 in India with a degree of success in intercepting Japanese Dinah recon aircraft.

Take a look at the P-39 Design Analysis. The 37MM gun was not all that useful in air to air combat. It had a rate of fire described as similar to that of a "Roman Candle" which was supposed to be 135 rounds a minute; at 300 mph the airplane would have moved 200 ft between rounds. Even more importantly, the 37MM trajectory was significantly different from that of the .50 cal and .30 cal guns, so it usually was a matter of deciding which gun you wanted to hit the target with.

So let's get rid of the 37MM and replace it with another .50 cal. The 37MM weighs 238 lb and its 30 rounds of ammo weighs 60 lb, for a total of 298 lb saved. One .50 cal gun weighs 80 lb and 400 rounds of ammo for it weighs 129 lb (the two .50 cal guns already there have 200 rpg). So, swapping out the 37MM for a .50 saves 89 lb.

Next let's get rid of the four .30 cal guns in the wings. That saves 92 lb for the 4 guns and 78 lb for the 1200 rounds of ammo. By the way supposedly the P-39 could hold 2000 rounds of .30 cal ammo but they probably did not load all of it. We get rid of another 170 lb, for a total reduction of 259 lb, which is not really very much.

The total weight of armor plate for the airplane is given as 202 lb. I read somewhere that one unit in the Pacific made a big improvement in the P-39 by removing the armor on the belly protecting the radiator. If you are planning on air-to-air work that belly armor is not very useful, but I'm sure it was useful for strafing.

So if you get rid of, say, half the armor and you have stripped the airplane down to three .50 cal guns, it is 359 lb lighter. That does not sound like very much to me. No wonder they never seemed to try it. It appears that the P-39Q-20 without the two underwing .50 cal guns was about 260 lb lighter than the other Q models. The P-39N-0-BE model had four fuel cells removed to reduce the max fuel load by 28 gal, which reduced the max gross weight from 9100 to 8750 lb. So if a 350 lb weight reduction was worth doing then maybe 359 lb would be worth doing.

There was no belly armor on the P-39.
In order to compensate for lighter front end, remove the rearmost armor plate (the one behind the oil tank) and replace it with aluminium type. Keep the number of radios to one. Less gun & spent cartridge openings = less drag, so indeed remove the wing guns. Keep the fuel tankage, radius is is already short for Pacific.

WHOA!! So far all this weight you've removed seems to be forward of the center of lift. Don't forget this is a rear engine plane with a hint of a tail heaviness problem. If you don't compensate by moving some heavy objects forward, you're going to have a right squirrelly bastard on your hands with some nasty slow flight and stall behaviors and a penchant for unrecoverable flat spins. This wheel has been invented before!
Cheers,
Wes

Wing gus are as close to the centre of lift as possible.

 

[MIflyer]

Yes, it goes without saying that clearly the CG would have to be addressed, as the P-39 without either ammo or suitable ballast in the forward compartment displayed some unpleasant handling characteristics. I'd consider moving the aircraft battery forward, perhaps even to the nose compartment which is probably the most common approach; the battery weighed 76 lb, so it was a pretty substantial influence.

As for "no belly armor" I guess that WWII fighter pilot did not know what he was talking about. Maybe he meant the armor behind the engine.

 

[FLYBOYJ]

Keep in mind the P-39 also had 2 CG datum points

 

[XBe02Drvr]

Keep in mind the P-39 also had 2 CG datum points

Explain please? That's a new one on me. Thanks.

 

[FLYBOYJ]

Explain please? That's a new one on me. Thanks.

It had a vertical and horizontal C/G, just like a helicopter. I'll try to find the W&B form

 

[FLYBOYJ]

P20A P-39Q pilot manual

 

[swampyankee]

The more I keep learning about how US aircraft like the P-39 and P-40 performed in Europe, the more it's apparent that these aircraft have been maligned.

 

[pbehn]

The more I keep learning about how US aircraft like the P-39 and P-40 performed in Europe, the more it's apparent that these aircraft have been maligned.

I don't know why, for me, their performance is respected for what they were, some habitually compare them to a P 51 which was from a different era doing a different job.

 

[Greg Boeser]

Some of the problem with the P-39 in North Africa is it was recognized as obsolete and the pilots flew them accordingly.
In the Pacific, the P-39 was rated better than the P-40 by those who flew them, but we are comparing P-40E to P-39D in Pacific vs P-40F vs P-39D in North Africa. The Merlin did give the P-40 an advantage over the P-39.

 

[DKoor]

From the moment I've heard about the type, I've read mostly positive things about it.
Granted it were Soviet experiences with the type... there is a good book about their experiences "Attack of the Airacobras", some very good read.
I may be 'pushing it' a bit if I say that if the game "IL-2 Sturmovik" is ANYTHING to go by, P-39 was truly fearsome weapon if piloted by a grizzled veteran.
Even when confronted by some of the era best aircraft such as Bf-109 and FW-190. Also, curiously I've seen several VVS pilot opinions where they regard 109 as a bit more capable plane that 190. That may be due to nature of Eastern Front warfare and many other things.

To return to "IL-2 Sturmovik"... I've flown/played that game for years and can say without any doubt that (in-game) P-39 is very capable plane, at least on Eastern front scenarios... when you mix it up with enemy fighters the way you shouldn't (flashy dogfights), and you gain upper hand they usually tend to shallow dive away. P-39 can follow them without problem and shot them down. Same thing if they try high speed maneuvers during dive... Cobra is quite fast in such type fights, more capable than early/mid-war Lavochkin and Yak types which often lose their opponents during hi-speed shallow dives. Also that NS-37 nose cannon... lower rate of fire, but I guess once pilot gets some experience under his belt shouldn't be an issue (when compared to the higher rof 20mm cannons). One shot can cripple bomber, and is usually insta-kill vs fighter.
So it is not a surprise to me when I see how several of the highest scoring Soviets flew this type.

Cobra was not so popular on the far East fronts... but then again I guess nothing really was truly popular (allied side) there in those days vs Zero until Hellcat arrived and gained upper hand in performance. At least in pilot's eyes. Because let's face it, if pilot go into actual combat he is not really interested in any kind of equal fights or proving himself in lesser types, what pilots really wanted is a truly superior type which could regularly bring success in combat..

 

[FLYBOYJ]

From the moment I've heard about the type, I've read mostly positive things about it.
Granted it were Soviet experiences with the type... there is a good book about their experiences "Attack of the Airacobras", some very good read.
I may be 'pushing it' a bit if I say that if the game "IL-2 Sturmovik" is ANYTHING to go by, P-39 was truly fearsome weapon if piloted by a grizzled veteran.
Even when confronted by some of the era best aircraft such as Bf-109 and FW-190. Also, curiously I've seen several VVS pilot opinions where they regard 109 as a bit more capable plane that 190. That may be due to nature of Eastern Front warfare and many other things.

To return to "IL-2 Sturmovik"... I've flown/played that game for years and can say without any doubt that (in-game) P-39 is very capable plane, at least on Eastern front scenarios... when you mix it up with enemy fighters the way you shouldn't (flashy dogfights), and you gain upper hand they usually tend to shallow dive away. P-39 can follow them without problem and shot them down. Same thing if they try high speed maneuvers during dive... Cobra is quite fast in such type fights, more capable than early/mid-war Lavochkin and Yak types which often lose their opponents during hi-speed shallow dives. Also that NS-37 nose cannon... lower rate of fire, but I guess once pilot gets some experience under his belt shouldn't be an issue (when compared to the higher rof 20mm cannons). One shot can cripple bomber, and is usually insta-kill vs fighter.
So it is not a surprise to me when I see how several of the highest scoring Soviets flew this type.

Cobra was not so popular on the far East fronts... but then again I guess nothing really was truly popular (allied side) there in those days vs Zero until Hellcat arrived and gained upper hand in performance. At least in pilot's eyes. Because let's face it, if pilot go into actual combat he is not really interested in any kind of equal fights or proving himself in lesser types, what pilots really wanted is a truly superior type which could regularly bring success in combat..

Please don't compare historical aircraft performance to a game. Unless you're prepared to make comparisons in full motion simulators that could simulate actual G loading as well as other external stimuli encountered while in combat, or fly the real thing, you're basically guessing