posted 06-14- 07:37 AM               

quote:

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Originally posted by Razer:
P-400 was a variant of the P-39 that was lend-leased to britain and russia but no one liked them and they sent a lot back so we sent them to our boys in the pacific.

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Close... The P-39 was originally supposed to be a bomber-destroyer, that's why it had the 37mm cannon, and it would have likely been excellent in that role. In order to get the performance out of it they used a turbosupercharger and the plane was one of the fastest out there.

However as the plane was coming to completion the USAAF decided it had enough interceptors and what it was lacking was ground attack aircraft. It ordered the A-24 (the Dauntless) to fill the Stuka role and then changed the P-39's to remove the supercharger and was going to use them in the sort-a Hs 129 role.

Of course as soon as they removed the turbo (replaced with a very simple supercharger) the high-alt performance went to nothing, but that was OK for the ground attack role.

But then they sent them to England and Pac and told people to use them as fighters. Of course, they did poorly. However the Sovs got them and used them for ground attack, and there they did very well indeed. The Sovs loved the plane and took all they could get, including the follow-on P-63.

I think P-400 actually refers only to a specific model, the P-39C, or the Airacobra I as the Brits called them. It seems the later Q's and N's were called P-39's by everyone.

posted 06-14- 09:12 AM            

"THE BELL XP-39 AIRACOBRA

The Bell XP-39

How America's Best Pre-War Single Engine Fighter
Was Ruined By The Air Corps

The story of the Bell P-39 is one that causes you to stop and think of what might have been, as opposed to what actually was.
Having gone down in aviation history as the "Iron Dog", the Airacobra had from its inception, the potential to be the world's finest
fighter aircraft at the beginning of America's involvement in WWII. That it instead became one of the wars most loathsome fighters,
easily conceals the real potential the prototype.

Bell's XP-39 prototype was rolled out for the world to see on April 6, 1939 at Wright Field. Essentially designed around the new
Oldsmobile 37mm cannon (not unlike the A-10 Warthog), the XP-39 was the second design which incorporated the 37mm to come
from Bell. Their original concept had placed the cannon behind a front mounted engine, pushing the cockpit too far to the rear of
the fuselage to be practical.

Bell's chief engineer, Robert Woods, went back to work and conceived an aircraft with a mid engine location, which allowed the
plane's nose to be dedicated to a very heavy ( by late 1930's standards ) battery of weapons. This rather unusual engine placement
was not unique. A mid-engine concept had been tried by Koolhoven of Holland with limited success due to a poor choice of
powerplant and inadequate technology. Their FK-55 fighter did not live up to expectations. The general concept, however, was not
without merit.

Woods' design employed the new Allison V1710 engine, rated at 1,150 hp with the new B-5 turbosupercharger. Installation of the
Turbosupercharged Allison promised excellent high altitude performance. This provided for a critical altitude of 20,000 feet, about
the same as the XP-38. Expectations were fully met and justified when, on April 6, the XP-39 attained a speed of 390 mph. Later
flights produced speeds that flirted with 400 mph (398 mph was reported). Bell's little fighter also displayed a remarkable rate of
climb, reaching 20,000 feet in 5 minutes flat! This odd looking aircraft created no small stir in the aviation community. Nothing flying
in Europe could match the overall level of performance displayed by the XP-39. At least nothing having the potential for production.
It should be noted that the prototype was unarmed and was not fitted with armor plate nor self-sealing fuel tanks (the last two items
were not part of the USAAC specification).

Despite the superlative performance of the new Bell fighter, there were design flaws. An undersized vertical stabilizer led to
problems with directional stability. Woods' also made a poor choice in airfoil section for the wing. These problems could have been
overcome, and in fact, the vertical stabilizer was later redesigned to resemble that of the Curtiss P-36/P-40. Airfoil section design
was not addressed until the P-63 Kingcobra, where a laminar flow wing was employed.

After the initial test flight, the XP-39 was turned over to the engineers at Wright Field. And here is where the P-39 was generally
undone.

At the time the Bell was being evaluated, the AAF was deep into "streamlining" as a way to improve aircraft performance. This is
somewhat understandable, due to the relatively low powered aircraft engines of the 1930's. By reducing drag, especially parasite
drag, the engineering minds at Wright Field found that significant increases in performance could be attained. This was all well and
good. Unfortunately, they carried it too far as it related to the XP-39. NACA engineers decided that the Bell's turbosupercharger
inlet created too much drag. Certainly the inlet generated no greater drag than did the Prestone inlets on the Lockheed XP-38.
Nonetheless, they were insistent, the inlet scoop had to go. They 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. This effectively eliminated decent high altitude performance. Thanks to these changes,
the Airacobra had it's center of gravity shifted further aft, exacerbating its already marginal stability. All said and done, the people at
Wright Field had reversed the old cliche, and created a sow's ear out of a silk purse.

Certainly Larry Bell and Bob Woods were outraged at the butchered result. Unfortunately, there was very little they could afford to
do about it. Bell Aircraft was at the edge of bankruptcy. Having only produced 15 total flyable aircraft, of any type, Bell was deep in
debt. Neither Bell nor Woods were willing to go to the mat for their beautiful fighter. To preserve the company's financial viability,
they would have to take it on the chin. Their pressing need was to get an order and establish some inward cash flow.

Fortunately, Bell sold the French on the P-39 and received 2 million dollars in advance on an eleven million dollar order. Later that
same year (1940), Bell received orders for just under 1,000 P-39Cs and Ds from the USAAF. These were equipped with self-sealing
fuel tanks and additional armor, the weight of which, only further degraded performance. Without the turbosupercharger, or even a
gear driven two speed, two stage supercharger, the Airacobra was not capable of taking on modern fighter aircraft at anything
above 10,000 feet. It should also be noted that the early versions of the Allison V1710 engine never produced anything close to
their advertised power rating without a turbosupercharger pressurizing the intake system.

Overall handling had degraded to a point where some claimed (without a grain of truth) that if the pilot simply sneezed, the plane
would spin. Some Brits flat out refused to fly the plane, one pilot saying it was more dangerous to RAF pilots than the Luftwaffe.
Such extreme examples of exaggeration followed the P-39 throughout its service life.

Adding to the general unhappiness with the airplane, the 37mm Colt M4 cannon frequently jammed after only firing a few rounds.
The balance of the guns, 2 .50 cal. M2 and 4 .30 cal. Brownings were inadequate by 1942 standards. One of the problems pointed
out by the British was the cockpit being filled with cordite fumes after firing the guns. They also found that firing the guns would
knock the magnetic compass out of whack. The RAF did admit that at low level they found the Airacobra to be a match for the
Bf-109E. Unfortunately, the RAF needed a high altitude fighter. Besides, the Luftwaffe was now getting newer and far better
performing fighters.

Because the Russians were seemingly satisfied with the P-39 is not indicative of the aircraft's performance as much as the
Russian's 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 marginal level of 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.

Bell P-39s served in North Africa and Italy with the USAAF and several other Allies including the Free French and Italians. Airacobra
service in the Pacific has been the subject of many books and articles. In a single sentence; the "Iron Dog" was replaced as
quickly as possible.

Taken as a whole, the P-39 was a dismal failure of the AAF's engineering and procurement establishment to identify and develop
the better attributes of an advanced and promising fighter aircraft. This was the same establishment that prevented Lockheed from
installing Merlin engines in the P-38 as early as 1941. Had the USAAC (Air Corps) not stripped the turbosupercharger from the
XP-39, the United States may have entered the war with a competitive single engine fighter plane already in service. Indeed, it was
not until the advent of the Bell P-63 that the level of performance finally matched that of the Bell XP-39 of 1939. Of course, by that
time, the P-63 was already outclassed by the P-38, P-47 and P-51. Indeed, the P-63 was too little too late. In large part, it was the Air
Corps myopic vision of the future of aerial warfare that caused it to be so."

posted 06-15- 01:21 AM               

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