Placing the Bell P39 Aircobra.

[tcolvin]

This aircraft was rejected by the RAF without reference to the Army because of an irrelevant lack of performance at altitude.
It was fitted with a cannon with a low muzzle velocity suitable for knocking down bombers but unsuitable for killing tanks.
The engine was mid-mounted and therefore less vulnerable to ground fire.
The Russians fell in love with it. The British Army never knew it. The USAAF were ambivalent.
What were the pluses and minuses of a unique design?

[Kutscha]

The engine was mid-mounted and therefore less vulnerable to ground fire.

The engine was still liquid cooled.

What the Brits thought they ordered was not what they got.

"Bell Aircraft executives later sheepishly admitted that their performance figures had been based on the unarmed and unequipped XP-39 prototype, which weighed a ton less than the armed and equipped P-39C."

[Steve49]

Ordered by the French and taken over by the UK, its initial shortcomings as a fighter are discused at some length in W. Wolf's '13th Fighter Command in WWII'. Many were later reclaimed by the AAC and being the only aircraft available were used as fighters during operations over New Guinea and Guadalcanal, during which they performed poorly. Later used in the ground attack role 'its low-altitude performance, good protective armor plate, and a heavy armament' made it a 'superlative attack aircraft' and it gained much praise.

However this was in the face of limited ground defences, whether its would have been able to survive any better than over Allied aircraft, with its liquid cooled engine, in the face of flak defences found in Western Europe is another question.

Regards,

Steve

[tcolvin]

2 TAF's CAS aircraft, Typhoon and Spitfire, were both liquid cooled with the engine in the most exposed position.
The only air-cooled CAS plane IIRC was the P-47 Thunderbolt.

[Kutscha]

Oh deary me. The A-36, with its engine stuck out the front, flew 23,373 missions and lost 177 a/c to all enemy causes. Gee, that is 132 missions per loss.

Now what is all this babbling about engines out front being most exposed?

[Graham Boak]

Originally Posted by tcolvin

2 TAF's CAS aircraft, Typhoon and Spitfire, were both liquid cooled with the engine in the most exposed position.
The only air-cooled CAS plane IIRC was the P-47 Thunderbolt.

Indeed, and this was their greatest weakness. The P-39 would have been no better, and of poorer performance. You are however forgetting the ground-attack missions carried out by the USN, USMC, and the Japanese Army and Navy. All used radial engines. As did the Russian Su 2, and the unsuccessful Su 6, regarded as superior to the Il 2 but by then there was no point in stopping production. The Italians also used radial engines for ground-attack missions, as did the French. And Swedish, Romanian...... The RAF used liquid-cooled engines in the role because they were the best engines it had available at the time of placing its wartime types into mass production. Had Fedden not spent so much time on the sleeve-valve, then perhaps a poppet-valve Hercules or Centaurus could have been available much sooner, and the story completely different.

You also say "This aircraft (P-39) was rejected by the RAF without reference to the Army because of an irrelevant lack of performance at altitude." But there as nothing irrelevant to the RAF about a lack of performance at high altitude. They already had two superior types with better low-altitude performance, the Typhoon and the Mustang. The RAF just didn't need the P-39, and at that stage wasn't desperate enough to take anything that could fly.

It is certainly interesting to consider just what it was about the Soviet operations that brought out the best points of the P-39. Partially it has to be a criticism of their own types, particularly their robustness and weak armament. One key point seems to be the lack of significant medium-altitude bomber operations, either as subjects of attack or requiring defense. If you only meet the enemy, or protect your friends, at low level then a lack of performance at higher levels becomes irrelevant. The agility of the P-39 would come into its own, and you don't need great speed to run down a Stuka or an Fw 189.

[Kutscha]

Had Fedden not spent so much time on the sleeve-valve, then perhaps a poppet-valve Hercules or Centaurus could have been available much sooner, and the story completely different.

Both the Hurc and Centaurus were sleeve valves. Are you saying they could have been re-designed with poppets?

The Soviets did not leave the P-39s stock (as shipped from the USA).

[Franek Grabowski]

P-400 ordered by French? I understand this was a purely British order. Also, it is worth to note the reason behind rejecting by the RAF. Hardly pressed by Soviet demands for Hurricanes and Spitfires,the latter being in short supply, the RAF decided to send Hurricanes to North Africa and then to supply Soviets with American aircraft available. There was a substantial fear of sending new types to North Africa because of critical situation there and a rather poor maintenance and recovery there. Otherwise P-400 would likely see a more active service.

[Kutscha]

France was sufficiently interested that they ordered 200 Model 14s on October 8, 1939.

After these four missions, the RAF Airacobras were taken off operations because of difficulties encountered with the compass. The compass was too close to the guns in the nose, and when the guns were fired, the compass got thrown out of alignment. Deviations of anything from 7 degrees to 165 degrees were recorded. Without a reliable compass, pilots tend to get themselves lost.

In spite of the problems with the compass and the need for flame dampers for the exhaust and flash suppressors for the nose guns, the RAF concluded that the Airacobra would make an excellent day fighter at altitudes below 20,000 feet and was well suited for the ground-attack role. However, before these plans could be implemented, a decision was made to divert the bulk of the British Airacobra contract to Russia.

[bearoutwest]

Let’s not get caught up with the myth about the Airacobra being USED as a great ground attack aircraft – it wasn’t, though it may have had some potential.

In reality, the Russians used it as a fighter for interception, for fighter sweeps, etc at low to medium altitudes. Any ground attack role was purely incidental based on short term requirements for battlefield use, not as an intended full-time role. The 37mm cannon was not designed with anti-tank armour piercing ammunition in mind. The Russians found it marvellous as much for it’s relatively advanced (for them in 1942-43) radio gear as much as any firepower or flight-characteristics. It’s a big advantage to send your fighters off on an intercept mission, and then be able to redirect them mid-flight.

The USAAF in North Africa and Italy used them as tactical reconnaissance due to their relatively high low-level speed. The French and Italian Co-Belligerent Air Forces were given hand-me-downs and were used predominantly ground attack role in Italy due partly to the reduced level of air opposition, and because these now tired and run-down P-39s were probably not the best aircraft to take on Bf109s and Fw190s in air combat.

The RAF flew 4 (or was it 6) sorties in their Airacobras before “retiring” them. These were low-level intruder (Rhubarb) missions, which were fighter sweeps against targets of opportunity, not necessarily ground attack. However, 6 sorties is not really enough to make a judgement on any possible future use.

The USAAF in the Pacific used the P-39/P-400s for whatever use was required on the day – intercept, recce, troop support, bomber escort, strategic bombing. In the early days of the Pacific war, there was basically insufficient resources to designate any fighter capable aeroplane to a specific role. So the Airacobra was no more a ground support aircraft than was a USN/USMC Wildcat. In late 1943-1944, the P-39 squadrons retired their aircraft and replaced them directly with P-38s, P-47s, P-51, etc. There was no planned widescale redesignation of P-39 squadrons for the ground attack role.

Historically, the P-39/P-400/Airacobra was a fighter primarily and used as such where-ever deployed in large numbers. Any ground pounding was a secondary task.

This is not to say that it did not have some potential as a tactical support/assault aircraft. It’s load carrying capacity was reasonable, and it was reasonably fast down low. The 37mm cannon would have made mince-meat out of soft-skinned targets. It would have been easier to retrofit armour in the nose cavity without an engine to get in the way, but the centre of gravity shift with this modification may have effected flight characteristics. Fore-aft CG balance was always an issue under certain loadings. A weak point may have been the fuel tankage in the wings.

...geoff