The P-63 Kingcobra was the result of an attempt on the part of the Bell Aircraft Corporation to correct some of the deficiencies of the earlier P-39 Airacobra. Although the Kingcobra had a superficial resemblance to the P-39 which preceeded, it was, in fact, a completely new design and no parts of the two aircraft were interchangeable.
Of the several USAAF single-seat fighter designs which reached the preliminary flight test stage immediately after Pearl Harbor, only the Bell P-63 Kingcobra succeeding in going into large-scale production and operational service before the end of the war. Although the Kingcobra met the requirements for which it was designed, these requirements were actually already outdated by the time they were framed. The P-63 was, in fact, fated never to enter combat wearing the colors of the nation which created it. Those Kingcobras which did participate in combat did so while serving with foreign air forces. Of the 3303 Kingcobras built, 2421 were supplied to the USSR under Lend-Lease and 114 went to the French. Of the remaining Kingcobras which stayed in the USA, 332 were converted as armored target aircraft.
The history of the Kingcobra actually begins back before Pearl Harbor. Even before the USA entered World War 2, the USAAC had come to the conclusion that the Airacobra had too poor a high-altitude performance to make it an effective interceptor. The deficiencies of the Airacobra were not due to any intrinsic flaw in the basic design, but were caused primarily by low engine power at high altitudes due to the unfortunate initial decision to omit the two-stage turbosupercharger.
In February of 1941, the Bell Aircraft Corporation proposed to cure some of Airacobra's performance problems by mating the basic P-39D fuselage to an uprated engine and a laminar flow wing. In order to test this concept, three prototypes were ordered in April of 1941 under the designation XP-39E. Serials were 41-19501, 41-19502, and 42-7164.
The engine for these three planes was originally intended to have been the experimental Continental V-1430-1, but this engine ran into protracted development problems and a decision was made to switch over to the 1350 hp Allison V-1710-47 liquid-cooled V-12 engine. As compared to the Airacobra, the wingspan and gross wing area were increased to 35 feet 10 inches and 236 square feet respectively.
Each of these three aircraft tested different wing and tail configurations. XP-39E Number one had a rounded vertical tail, but the tailplane had squared-off tips. XP-39E number two had a squared-off fin and rudder and had large wing fillets. XP-39E number three had all its flight surfaces squared off. The XP-39E proved to be faster than the standard Airacobra--a maximum speed of 386 mph being attained at 21,680 feet during tests. However, the XP-39E was considered to be inferior to the stock P-39 Airacobra in all other respects, so it was not ordered into production.
Even before its first flight, the USAAF considered the XP-39E project as showing sufficient promise that on June 27, 1941 they placed an order for two prototypes of an enlarged version powered by the same Allison V-1710-47 engine. The designation was XP-63 (company designation was Model 24) and USAAF serials were 41-19511 and 41-19512.
The XP-63 was larger in all dimensions than the Airacobra. The wings were of a NACA laminar flow design that reduced drag by a significant amount and increased the overall span by 4 feet 4 inches to 38 feet 4 inches. In pursuit of a better high-altitude performance, the Allison V-1710-47 engine was fitted with a second hydraulic turbosupercharger supplementing the normal single-stage supercharger, effectively adding 10,000 feet to the service ceiling. A four-bladed propeller was standardized. A persistent complaint against the Airacobra was that its nose armament wasn't easily accessible for ground maintenance, and in order to cure this problem the XP-63 airframe was fitted with larger cowling panels.
In September of 1942, even before the first flight of the prototype, the aircraft was ordered into production by the USAAF as the P-63A (Model 33). The P-63A's armament was to be the same as that of the P-39Q--a single 37-mm cannon firing through the propeller hub, two 0.50-inch machine guns in the upper nose, and two 0.50-inch machine guns in underwing gondolas.
The XP-63 Ser No. 41-19511 flew for the first time on December 7, 1942. This was the first anniversary of Pearl Harbor, and the significance of that date was not lost on anyone. The XP-63 was fitted with a 37-mm hub cannon and two nose 0.50-inch machine guns (the underwing guns were not fitted). Weights were 6054 pounds empty, 7525 pounds gross, and 10,000 pounds maximum takeoff. Dimensions were wingspan 38 feet 4 inches, length 32 feet 8 inches, height 11 feet 5 inches, and wing area 248 square feet. As anticipated, the XP-63 exhibited a performance that was much better than that of the P-39. A speed of 407 mph was attained at sea level during early testing.
On January 28, 1943, the XP-63 prototype was lost in an unfortunate accident. Test pilot Jack Woolams was just about to bring the XP-63 in for a landing after a routine test flight when he found that the landing gear wouldn't extend. He circled the airfield for several hours to burn off excess fuel. By the time he was ready to attempt a belly landing, the sun had set. Woolams mistook the runway side lights for end lights and put the XP-63 down in a field of small trees. Woolams walked away from the accident, but the XP-63 was damaged beyond repair. The wreck was later shipped to Wright Field for ground-based gun firing tests.
The second prototype (41-19512) flew for the first time on February 5, 1943. It did not have much better luck. During a test flight on May 25, 1943, the Allison engine threw a rod at altitude, and the cockpit filled up with smoke. Test pilot G. E. "Gus" Lundquist was forced to parachute to safety, and 41-19512 was destroyed in the ensuing crash.