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In early 1935, executives with the Bell aircraft company were present at a demonstration of the American Armaments Corporation’s T9 37-mm cannon. Impressed by what they had seen the Bell execs instigated a design of a fighter aircraft which would include a T9 cannon firing through the propeller hub, as well as two .50-in machine-guns mounted in the fuselage nose and synchronized to fire between the rotating propeller blades.
The decision to place the cannon firing through the propeller hub meant the engine had to be mounted within the fuselage, directly above the rear half of the low-set monoplane wing. The engine position over the planes center of gravity itself is what prompted the designers to introduce a try-cycle type landing gear. The design concept proved attractive enough to the Army Air corps to win an order for a single prototype to be completed by October 7, 1937. The XP-39 flew for the first time on April 6th 1938 and 12 months later, after extensive evaluation, 12 YP-39s were ordered for a wider service test, plus a single YP-39A without a turbo charger for the Allison V-1710 engine.
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After service evaluations, certain modifications were recommended for the model such as the introduction of fairing doors for the main wheel units; a lower canopy profile, resetting of the engine air intake and coolant radiators, and the deletion of the turbo charger.
Maximum speed: 376 mph.
Cruising speed: 250 mph.
Range: 650 miles
Service Ceiling: 35,000 ft.
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The original prototype, modified to include these modifications flew under the designation YP-39B. As a result of the improved performance of the aircraft the turbocharger was deleted from all future models and 13 pre-production prototypes were completed to XP-39B standard. (Two additional .30-in machine guns were added in the fuselage nose) With the initial designation P-45, the new fighter was ordered into production on August 10, 1939, the first contract was for 80 aircraft. Before the first of them was delivered the designation reverted back to P-39. The first 20 aircraft completed to XP-39B standard were designated P-39C, but the remaining 60 received each two more .30-cal. machine guns, self sealing fuel tanks, and provisions for either a 500 lb bomb or 75 gallon fuel drop tanks: it was these changes that brought the designation to P-39D.
Listen to the P-39 Aircraft flying
The first large order for 369 P-39Ds was placed in September 1940, and the initial deliveries of these began several months later. A total of 675 aircraft ordered by a British purchasing commission were exported to Great Britain arriving in April of 1941. These differed only in armament as the 37-mm cannon was replaces with a 20-mm, and the six-.30-cal. Machine guns were replaced by 0.303-in caliber. In September that year No. 601 squadron exchanged its Hawker Hurricanes for these new aircraft. Immediately they were introduced into service, the full implication of the decision to delete the turbo charger was appreciated for the first time, for the aircraft had an inadequate rate of climb and its high altitude performance was completely unacceptable for deployment in the European theatre. Only about 80 of the total order entered service with the RAF, equipping only No. 601 Squadron, which exchanged them for Super Marine Spitfires in March of 1942. A total of 250 aircraft were supplied to Russia, 200 to the USAAF in Britain and the remainder back to the USAAF in America.
These ex-British Air Cobras were designated P-400s in the USAAF service. Constructed in large numbers, a total of 9.558 Air Cobras were built before production ended. There were no major design changes in the several variants that followed. The P-39F, of which 229 were built, succeeded the P-39D into production. The P-39J, of which 25 were built, had a different version of the Allison V-1710 engine. The P-39K (210 built) and the P-39L (250 built) differed in detail equipment and amore powerful V-1710-63 engine. The P-39M (240 built) had the lower powered V-1710-83 engine and a larger diameter propeller.
The final production P-39N and Q were built in larger number s to supply Russia under Lend-Lease. Although deletion of the turbo charger limited the potential of the Air Cobra as a fighter, it was used with a great degree of success in North Africa in late 1942 in the ground attack role and was deployed widely in the Pacific theatre by the USAAF. Until 1944 when more powerful and deadlier fighters began to enter service the P-39 together with the P-40 represented the main first-line equipment of the USAAF’s fighter squadrons.
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Aircraft
