|First flight||7 December 1942|
|Primary users||United States Army Air Forces
Soviet Air Force
French Air Force
|Bell P-39 Airacobra|
The Bell P-63 Kingcobra is an American fighter aircraft developed by Bell Aircraft in World War II from the Bell P-39 Airacobra in an attempt to correct that aircraft's deficiencies. Although the P-63 was not accepted for combat use by the United States Army Air Forces, it was adopted by the Soviet Air Force.
While the P-39 had originally been introduced as an interceptor, later in its development it was decided to reduce the cost and complexity of the engine by removing the turbocharger. High-altitude performance suffered dramatically as a result, and Bell proposed an experimental series to test out a variety of solutions.
The resulting XP-39E featured two primary changes from the earlier P-39D from which it was developed. One was a redesigned wing. The root airfoil, a NACA 0015 on other models of the P-39, was changed to a NACA 0018, to gain internal volume. The other was a switch to the Continental I-1430 engine, which featured an improved overall design developed from the hyper engine efforts, as well as an improved supercharger.
Three prototypes were ordered in April 1941 with serials 41-19501, 41-19502 and 42-7164. The I-1430 was having continued development problems and could not be delivered in time, so it was replaced by an Allison V-1710-47, similar to that powering the P-39. Each prototypes tested different wing and tail configurations: 41-19501 had a rounded vertical tail, but squared-off tailplane tips; 41-19502, a squared-off fin and rudder and large wing fillets; and 42-7164 had all its flight surfaces squared off. The XP-39E proved faster than standard Airacobra, reaching a maximum speed of 386 mph (621 km/h) at 21,680 ft (6,610 m) during tests. However, the XP-39E was considered inferior to the stock P-39 Airacobra in all other respects, so it was not ordered into production.
Although the XP-39E proved disappointing, the USAAF was nevertheless interested in an even larger aircraft based on the same basic layout. Even before its first flight, the USAAF placed an order on 27 June 1941 for two prototypes of an enlarged version powered by the same V-1710-47. The new design was given the designation XP-63 and serials were 41-19511 and 41-19512. A third prototype was also ordered, 42-78015, using the Packard V-1650, the U.S.-built version of the Rolls-Royce Merlin engine.
The XP-87897 was larger in all dimensions than the Airacobra. The wing was redesigned again, this time with new NACA laminar flow airfoils, 66(215)-116 a=0.6 at the root and a NACA 66(215)-216 a=0.6 at the tip. The wing taper ratio was approximately 2:1, span was 38 ft 4 in (11.68 m), and wing area was 248 sq ft (23.0 m2). The engine was fitted with a second remotely mounted supercharger, supplementing the normal single-stage supercharger. At higher altitudes, when additional boost was required, a hydraulic clutch would engage the second supercharger, adding 10,000 ft (3,000 m) to the service ceiling. A larger four-bladed propeller was also standardized. A persistent complaint against the Airacobra was that its nose armament was not easily accessible for ground maintenance, and in order to cure this problem, the XP-63 airframe was fitted with larger cowling panels.
In September 1942, even before the prototype flew, the USAAF ordered it into production as the P-63A (Model 33). The P-63A's armament was to be the same as the current P-39Q, a single 37 mm (1.46 in) M4 cannon firing through the propeller hub, two synchronized 0.50 in (12.7 mm) machine guns in the cowl, and two 0.50 in (12.7 mm) machine guns in underwing gondolas.
The first prototype, 41-19511, flew for the first time on 7 December 1942. It was destroyed on 28 January 1943 when its landing gear failed to extend. The second prototype, 41-19512, followed on 5 February 1943. It, too, was destroyed, this time due to an engine failure. The Merlin-engined 42-78015 (as Merlins were primarily needed for the P-51 Mustang) was delivered with another Allison instead, a -93, which had a war emergency rating of 1,500 hp (1,120 kW) at sea level, making this prototype one of the fastest Kingcobras built, attaining 421 mph (678 km/h) at 24,100 ft (7,300 m).
Deliveries of production P-63As began in October 1943. The USAAF concluded the Kingcobra was inferior to the Mustang, and declined to order larger quantities. American allies, particularly the Soviet Union, had a great need for fighter aircraft, however, and the Soviets were already the largest users of the Airacobra. Therefore, the Kingcobra was ordered into production to be delivered under Lend-Lease. In February 1944, the Soviet government sent a highly experienced test pilot, Andrey G. Kochetkov, and an aviation engineer, Fyodor P. Suprun, to the Bell factories to participate in the development of the first production variant, the P-63A. Initially ignored by Bell engineers, Kochetkov's expert testing of the machine's spin characteristics (which led to airframe buckling) eventually led to a significant Soviet role in the development. After flat spin recovery proved impossible, and upon Kochetkov's making a final recommendation that pilots should bail out upon entering such a spin, he received a commendation from the Irving Parachute Company. The Kingcobra's maximum aft CG was moved forward to facilitate recovery from spins.
P-63A-8, SN 269261, was extensively tested at TsAGI in what was then the world's largest wind tunnel. Soviet input was significant. With the Soviet Union being the largest buyer of the aircraft, Bell was quick to implement their suggestions. The vast majority of the changes in the A sub-variants were a direct result of Soviet input, e.g. increased pilot armor and fuselage hardpoint on the A-5, underwing hardpoints and extra fuel tanks on the A-6, etc. The Soviet Union even experimented with ski landing gear for the P-63A-6, but this never reached production. Most significantly, Soviet input resulted in moving the main cannon forward, favorably changing the center of gravity, and increasing its ammo load from 30 to 58 rounds for the A-9 variant. The P-63 had an impressive roll rate, besting the Americans' P-47, P-40, and P-51--and the Japanese Navy's Kawanishi N1K2 Shiden-Kai fighter--with a rate of 110° per second at 275 mph (443 km/h).
Two war surplus P-63Cs were modified by Bell under Navy contract for flight testing of low-speed and stall characteristics of high-speed wing designs. The aircraft received new wings with adjustable leading edge slats, trailing edge flaps and a pronounced sweep of 35 degrees. The wings had no wheel wells; only the nose gear was retractable. L-39-1 first flew 23 April 1946, demonstrating a need for extra tail surface and rear fuselage length to balance the aircraft in flight--the wing repositioning reduced empennage effectiveness and moved the center of lift aft. A lighter three-bladed propeller from a P-39Q-10 was mounted and the necessary changes to the empennage were made. L-39-2 incorporated these adjustments from the start. L-39-1 later went to NACA at Langley for wind tunnel testing, where much valuable data were gathered. L-39-2 also served as a testbed for the Bell X-2 40-degree wing design.
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The first version to be supplied in quantity to the Soviet Union was the P-63A-7 with a higher vertical tail, and reinforced wings and fuselage. The fuselage proved to need strengthening, consequently in October 1944, a reinforcement kit for operational P-63s was developed.
Air Transport Command ferry pilots, including U.S. women pilots of the WASP program, picked up the planes at the Bell factory at Niagara Falls, New York, and flew them to Great Falls, Montana and then onward via the Northwest Staging Route through Canada to Alaska, where Soviet ferry pilots, many of them women, would take delivery of the aircraft at Nome  and fly them to the Soviet Union over the Bering Strait via the Alaska-Siberia route (ALSIB). A total of 2,397 (2,672, according to other sources) such aircraft were delivered to USSR, out of the overall 3,303 production aircraft (72.6%).
By a 1943 agreement, P-63s were disallowed for Soviet use against Germany and were supposed to be concentrated in the Soviet Far East for an eventual attack on Japan. However, there are many unconfirmed reports from both the Soviet and German side that P-63s did indeed see service against the Luftwaffe. Most notably, one of Pokryshkin's pilots reports in his memoirs published in the 1990s that the entire 4th Guards Fighter Aviation Regiment (4 GvIAP) was secretly converted to P-63s in 1944, while officially still flying P-39s. One account states they were in action at Königsberg, in Poland and in the final assault on Berlin. There are German reports of P-63s shot down by both fighters and flak. Hans Rudel, highest decorated pilot of the Luftwaffe, states in his memoirs, "We often encounter American types of aircraft, especially Airacobras, Kingcobras and Bostons." This was in the Courland front towards the end of the war.  Nevertheless, all Soviet records show nothing but P-39s used against Germany.
In general, official Soviet histories played down the role of Lend-Lease supplied aircraft in favor of local designs, but it is known that the P-63 was a successful fighter aircraft in Soviet service. A common Western misconception is that the Bell fighters were used as ground attack aircraft.
One of the enduring myths regarding the P-39/P-63 in Soviet use is that because of its armament, in particular the 37mm nose cannon, it excelled as a ground-attack aircraft, even a 'tank buster'. In translating and preparing this manuscript for publication, I have had the opportunity to peruse several Russian-language sources. Mentions of the employment of this aircraft in the ground-attack role are so rare in these sources as to be exceptional ... The 'tank buster' myth has its roots in the misunderstanding of the general wartime role of the Red Air Force and in the imprecise translation of specific Russian-Language terms that describe this role. The specific Russian-Language term most often used to describe the mission and role of the Airacobra-equipped Red Air Force fighter units, in this manuscript and other Russian-language sources , is prikrytiye sukhoputnykh voysk [coverage of ground forces]... Frequent misunderstanding in this country as to the combat role of the P-39 in Soviet use is based in part on imprecise translation of the term prikrytiye sukhoputnykh voysk to 'ground support'. The latter term as it is understood by many Western military historians and readers, suggests the attacking of ground targets in support of ground troops, also called 'close air support'. Did a Soviet Airacobra pilot ever strafe a German tank? Undoubtedly. But this was never a primary mission or strong suit for this aircraft.-- Soviet Army Colonel Dmitriy Loza
The Soviets developed successful group aerial fighting tactics for the Bell fighters and scored a surprising number of aerial victories over a variety of German aircraft. Low ceilings, short missions, good radios, a sealed and warm cockpit and ruggedness contributed to their effectiveness. To pilots who had once flown the tricky Polikarpov I-16, the aerodynamic quirks of the mid-engined aircraft were unimportant. In the Far East, P-63 and P-39 aircraft were used in the Soviet invasion of Manchukuo and northern Korea. In the Pacific theatre, the Kingcobras flew escort, close air support and ground attack missions. The Soviet P-63s achieved their first air victory on 15 August 1945, when Lejtenant I. F. Miroshnichenko from 17th IAP/190 IAD, shot down a Nakajima Ki-43 Hayabusa IJAAS fighter off the coast of North Korea.
Sufficient aircraft continued in use after the war for them to be given the NATO reporting name of Fred. By 9 May 1945, operational units had still 1,148 Kingcobras on strength. On 8 October 1950, two USAF F-80Cs from the 49th Fighter Group breached the USSR's border and attacked Sukhaya Rechka airfield 19 mi (31 km) south-west of Vladivostok and 62 mi (100 km) from the Soviet-Korean border, making two strafing runs before returning to their home base. Although Soviet sources claim the attack was intentional, the pilots claimed it was a result of a navigational error. The airfield belonged to the Air Forces of the Pacific Fleet (VVS TOF), but it was occupied by the 821st Fighter Aviation Regiment (821 IAP) of the 190th Fighter Aviation Division (190 IAD). Mostly aircraft of the 1st Squadron of 821 IAP were hit with 12 P-63s damaged, one P-63 burned to the ground while the other damaged aircraft were able to be repaired. No human losses were suffered.
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In 1945, 114 later models were delivered to the French Air Force (Armée de l'Air), but they arrived too late to see service in World War II. They however saw service during the First Indochina War before being replaced in 1951.
Initially the French Kingcobras were deployed to Algeria. Fighter squadron (Groupe de Chasse) 2/6 "Travail", previously equipped with P-39 Airacobras, received their Kingcobras on 18 July at Casablanca; the pilots were surprised by the higher landing speed of their new aircraft. The Kingcobra were scrambled to Indochina when the insurgency broke. Only 60 Kingcobras were operational in Indochina in January 1950, mainly because the Americans refused to supply spare parts. Starting in February 1951, the squadrons equipped with Kingcobra started to receive Grumman F8F Bearcats as replacements. Most Kingcobras were mothballed by July. The last flight of a Kingcobra in Indochina took place on September 6, 1951.
Its main use in American service was the unusual one of a manned flying target for gunnery practice. The aircraft was generally painted bright orange to increase its visibility. All armament and the regular armor was removed from these RP-63 aircraft, and over a ton of armored sheet metal was applied to the aircraft. This was fitted with sensors that would detect hits, and these hits were signaled by illuminating a light in the propeller hub where the cannon would have been. This earned the aircraft the unofficial nickname of Pinball. Special frangible rounds made of a lead/Bakelite combination were developed that would disintegrate upon impact. These were known as the "Cartridge, Caliber .30, Frangible, Ball, M22". In 1990, veteran Pinball pilot, Ivan L. Hickman, wrote Operation Pinball about the training flights.
British engineers, like the Americans, had a growing interest during World War II in the application of laminar flow airfoils. In an effort to learn more about the practical application of laminar flow airfoils, in 1945 the Royal Aircraft Establishment (RAE) undertook a flight test program with one of the two P-63As that the United Kingdom had received.[page needed] The aircraft was equipped with a wake rake array mounted outboard, behind the wing, to allow the momentum deficit, and thus section drag, to be measured.
The RAE first tested it in an "as delivered" configuration. The wing airfoil was designed to support laminar flow to 60% of chord. In the "as delivered" configuration, a profile drag was measured which was representative of the wing section with boundary layer transition at the leading edge (0% laminar flow). Reducing the surface roughness reduced the drag at low lift coefficients to a level representative of laminar flow to 35% of chord. Measurements were made of the surface waviness. This showed peak wave amplitudes, above the mean, of approximately 0.011 inches over a two-inch span. The standard waviness criteria shows the critical wave height to be 0.0053 inches for this application. To reduce the waviness, RAE personnel stripped the wing to bare metal. The wing was then sprayed with two coats of primer paint and a coat of paint type filler. After the paint was dry, it was sanded in a chordwise direction, using sanding blocks, whose curvature matched the local surface curvature. This was repeated several times. Surface waviness was then measured and found to be no more than 0.005 inches. In flight, this configuration was found to have a profile drag representative of boundary layer transition at 60% of chord. This gave researchers an idea of what level of wing surface quality was required to actually get the benefits of laminar flow airfoils.
Numerous surplus P-63s ended up on the air racing circuit in the immediate postwar era. Charles Tucker purchased two P-63s from the disposal facility at Kingman, Arizona just after the war. He entered one of them, the Tucker Special as Race 28 with the name Flying Red Horse emblazoned on the nose (civilian register N62995) in the 1946 Thompson Trophy race. He had clipped the wing by 12 ft 9 in (3.89 m) in an attempt to improve its speed, reducing the span to 25 ft 9 in (7.85 m). The second one (44-4126 (XN63231 Race 30) was intended for the 1946 Bendix cross country race. It was initially fitted with two wingtip drop tanks. In 1947, the drop tanks were removed and the wings were clipped to 28 ft 6 in (8.69 m)
Two other significant racers were flown later. Tipsy Miss, John Sandberg's clipped-wingtip P-63 unlimited racer, was identified as "Race 28," and painted in bright orange, white and black race numbers with a chrome spinner. Later sold to a European pilot, this P-63 was destroyed in a fatal accident in 1990Crazy Horse Campgrounds was the most radically modified P-63 Kingcobra ever. Larry Haven's "Race 90" clipped-wing unlimited racer had a tiny bubble canopy installed; it appeared in all silver (unpolished aluminum) finish with a white rudder and black trim. The aircraft later crashed into the ocean on a test flight in 1972.
Data from Jane's Fighting Aircraft of World War II