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View Full Version : America's Best Pre-War Fighter, the P-39, ruined by the AAF



arcadeace
01-02-2004, 06:56 AM
http://www.onpoi.net/ah/pics/users/ah_222_1073051313.jpg
The initial design employed the new Allison V1710 engine, rated at 1,150 hp with the new B-5 turbosupercharger. The prototype was unarmed and not fitted with armor plate nor self-sealing fuel tanks. Flights produced speeds that flirted with 400 mph and reaching 20,000 feet in 5 minutes flat! In 1939, nothing having the potential for production in Europe could match the overall level of performance displayed by the XP-39. It had an undersized vertical stabilizer and a poor choice in airfoil section for the wing but these problems could have been overcome at that time.

The AAF was deep into "streamlining" to improve performance, largely due to lower powered engines of the 1930's. The engineering minds at Wright Field carried it too far: they were insistent the inlet scoop had to go; reduced the height of the canopy; chopped 2 feet off the wing span and lengthened the fuselage by over a foot. A less powerful Allison with only a single stage mechanical supercharger replaced the turbosupercharged engine. It's center of gravity shifted further aft, exacerbating its marginal stability. When production models were equipped with self-sealing fuel tanks and additional armor, performance degraded further. The Airacobra was not capable of taking on modern fighter aircraft at anything above 10,000 feet.

Because the Russians were seemingly satisfied with the P-39 is not indicative of the aircraft's performance as much as their desperate need for combat aircraft. Moreover, the air war on the eastern front was fought largely below 20,000 feet, and more often than not, well below that. At these heights, the P-39 possessed some capability. Credit must be given to those Soviet pilots who, despite the severe limits of the aircraft, used them very effectively against the Luftwaffe's superior Bf 109s and Focke Wulf 190s.

http://home.att.net/~C.C.Jordan/XP-39.html

arcadeace
01-02-2004, 06:56 AM
http://www.onpoi.net/ah/pics/users/ah_222_1073051313.jpg
The initial design employed the new Allison V1710 engine, rated at 1,150 hp with the new B-5 turbosupercharger. The prototype was unarmed and not fitted with armor plate nor self-sealing fuel tanks. Flights produced speeds that flirted with 400 mph and reaching 20,000 feet in 5 minutes flat! In 1939, nothing having the potential for production in Europe could match the overall level of performance displayed by the XP-39. It had an undersized vertical stabilizer and a poor choice in airfoil section for the wing but these problems could have been overcome at that time.

The AAF was deep into "streamlining" to improve performance, largely due to lower powered engines of the 1930's. The engineering minds at Wright Field carried it too far: they were insistent the inlet scoop had to go; reduced the height of the canopy; chopped 2 feet off the wing span and lengthened the fuselage by over a foot. A less powerful Allison with only a single stage mechanical supercharger replaced the turbosupercharged engine. It's center of gravity shifted further aft, exacerbating its marginal stability. When production models were equipped with self-sealing fuel tanks and additional armor, performance degraded further. The Airacobra was not capable of taking on modern fighter aircraft at anything above 10,000 feet.

Because the Russians were seemingly satisfied with the P-39 is not indicative of the aircraft's performance as much as their desperate need for combat aircraft. Moreover, the air war on the eastern front was fought largely below 20,000 feet, and more often than not, well below that. At these heights, the P-39 possessed some capability. Credit must be given to those Soviet pilots who, despite the severe limits of the aircraft, used them very effectively against the Luftwaffe's superior Bf 109s and Focke Wulf 190s.

http://home.att.net/~C.C.Jordan/XP-39.html

VW-IceFire
01-02-2004, 08:04 AM
These documents often seem to forget that Bell modified the P-39 later by Soviet request and that in addition to that, there was numerous field modifications made to the P-39 to make it more capable.

Low altitude was ok by them (not good for a Western Front fighter) and with the necessary modifications the center of balance was shifted back to something more acceptable. It was a quirky fighter but everything I've read has said that the VVS made it much better as they figured out what problems the fighter did have.

It had great low altitude climb and good manuverability provided that the center of balance wasn't too dangerously positioned.

- IceFire
http://home.cogeco.ca/~cczerneda/sigs/spit-sig.jpg

TX-Zen
01-02-2004, 08:09 AM
Interesting information, thanks!

TX-Zen
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Bogun
01-02-2004, 08:35 AM
It is worth to notice that turbocharger technology for airplane engines were not perfected for another three-four years (or even later) and there were some justifications for AAF decisions. Just look at all the problems with P-38 turbochargers which led to dismissal of the plane from ETO. All American planes with turbochargers had their share of problems initially. Russians, Germans (and British, I think) never managed to make them reliable enough to consider operational use during the war.
Practice of announcing inflated performance numbers of the stripped down planes by manufacturers was the practice which cause a lot of confusion for all the nations, not just Bell in US.
And inability of P-39 to perform at high altitude was irrelevant on the Easter Front where all sides were seldom flying above 5000m. To understand the differences between conditions existing on the West and on the East is a crucial for understanding of the nature of the dissimilar threats Germans had to counter during the war.

Regards,

<b>AKA_Bogun</b>
http://www.akawardogs.com/

http://img5.photobucket.com/albums/v22/Bogun/Sevastopol.jpg

arcadeace
01-02-2004, 09:30 AM
Your info is appreciated. I've read others here making claims on Soviet modifications and this article, apparently from a reputable site implied, if not stated there weren't any. And I have no knowledge on the AAF and contemporary realities influencing their decisions; interesting details which were not included.

S!

http://www.onpoi.net/ah/pics/users/ah_222_1072923641.jpg

StellarRat
01-02-2004, 12:47 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Bogun:
Russians, Germans (and British, I think) never managed to make them reliable enough to consider operational use during the war.<HR></BLOCKQUOTE>
I thought the 109 and 190 both used turbochargers throughout the war. ?? http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

DaBallz
01-02-2004, 03:19 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by StellarRat:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Bogun:
Russians, Germans (and British, I think) never managed to make them reliable enough to consider operational use during the war.<HR></BLOCKQUOTE>
I thought the 109 and 190 both used turbochargers throughout the war. ?? http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif<HR></BLOCKQUOTE>

Only the United stated made large scale use of turbo superchargers in combat aircraft. The only turbo equipped German combat plane I am aware of was the Ju-86P high altitude Diesel powered reconasance plane.

Turbo superchargers were highly developed by 1941 and as reliable as the engines they were attached to, roughly 400 hours life span.

A turbo in the 1940's was not used for boost in the modern way of thinking, but was used for altitude compensation. An engine saw the same carb inlet pressure at its critical altitude as it did at sea level. Critical altitude was usually around 25,000'

The P-39 was in fact ruined by the changes, I know of NO American pilots that liked it. Later marks such as the P-39N were much better but by then the "Iron Dog" was so much hated and mis trusted that few were not given to the Soviets.

Da

StellarRat
01-02-2004, 03:48 PM
You're right. They were supercharged, not turbo-supercharged. That is slightly different, but they both do the same thing, provide over-pressure for high altitude flight.

DaBallz
01-02-2004, 03:59 PM
arcadeace, when posting copied information you
should post the credit. I have read that information before
I believe at Joe Baughers web site.

Gear drive was the most common way of driving a supercharger.
Turbosuperchargers were exhaust driven via a turbine.

Jets are little more than a turbosupercharger
with a combustion chamber where the piston
engine normally is.

Da

Platypus_1.JaVA
01-02-2004, 04:12 PM
Let's face the fact, The americans screwd-up the P-39 http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

1 Judge not, that ye be not judged.
2 For with what judgment ye judge,
ye shall be judged: and with what
measure ye mete, it shall be measured
to you again.

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Huckebein_FW
01-02-2004, 04:14 PM
DaBallz, Germany had a operational turbosupercharged engine from '43, the BMW801TJ. It was mounted on T and S models of Ju88, 188, 388, high speed high altitude bomber and recce aircraft. It was evaluated by the americans that found it very reliable though very compact.

here you can see the turbo intake and intercooler:

http://www.warbirdsresourcegroup.org/LRG/images/lrg0660.jpg

http://cip.physik.uni-wuerzburg.de/~vernalek/Ju388/Standlauf.jpg

http://home.comcast.net/~bogdandone/me262_steinhoff.jpg

[This message was edited by Huckebein_FW on Fri January 02 2004 at 03:24 PM.]

DaBallz
01-02-2004, 04:46 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Huckebein_FW:
DaBallz, Germany had a operational turbosupercharged engine from '43, the BMW801TJ. It was mounted on T and S models of Ju88, 188, 388, high speed high altitude bomber and recce aircraft. It was evaluated by the americans that found it very reliable though very compact.


I believe you, but I see no turbos, do you have a photo of another view?

I have also found little reference to this engine on line, and none saying it was turbosupercharged. Again, I am not doubting you, but I would love to see some data.

Germany's turbosupercharger program was quite advanced before WWII and led to the Jet program. I can see no reason why the Germans largely abandoned the turbo program, except possibly the lack of high temprature alloys essential in making them reliable.

Da

here you can see the turbo intake and intercooler:

http://www.warbirdsresourcegroup.org/LRG/images/lrg0660.jpg

http://cip.physik.uni-wuerzburg.de/~vernalek/Ju388/Standlauf.jpg

http://home.comcast.net/~bogdandone/me262_steinhoff.jpg

[This message was edited by Huckebein_FW on Fri January 02 2004 at 03:24 PM.]<HR></BLOCKQUOTE>

Huckebein_FW
01-02-2004, 04:53 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by DaBallz:
I believe you, but I see no turbos, do you have a photo of another view?

I have also found little reference to this engine on line, and none saying it was turbosupercharged. Again, I am not doubting you, but I would love to see some data.

Germany's turbosupercharger program was quite advanced before WWII and led to the Jet program. I can see no reason why the Germans largely abandoned the turbo program, except possibly the lack of high temprature alloys essential in making them reliable.

Da
<HR></BLOCKQUOTE>

Read DESCRIPTION here:
http://cip.physik.uni-wuerzburg.de/~vernalek/T2-Report.html

http://home.comcast.net/~bogdandone/me262_steinhoff.jpg