Bell 33 / 41 / XP-39E / P-63 Kingcobra
At a fairly early stage in the development of the Bell P-39 Airacobra, work had been carried out to enhance the performance of this aircraft by the introduction of aerodynamic improvements. A line of investigation resulted in a USAAF contract for two "XP-63" prototypes awarded in June 1941. Three experimental aircraft were built, each utilising the basic fuselage of the P-39D, to which were added a new laminar-flow wing with square wingtips and a revised tail unit. In fact, each of the three XP-39Es, as these aircraft were designated, had a different tail unit. It was planned originally to power the prototypes with the Continental Aviation and Engineering Corporation’s IV-1430 12-cylinder inverted-vee piston-engine, which had demonstrated a power output in excess of 1491 kW (2,000 hp). However, Allison V-1710 engines of little more than half of that power output were installed.
As it emerged, the P-63 was similar enough to the P-39Q to be mistaken for it, the P-63A being a low-wing aircraft with tricycle landing gear, mid-mounted Allison engine, car doors on each side of the cockpit, and armament consisting of a 37 millimeter cannon firing through the prop hub, two 12.7 millimeter Brownings on top of the nose, and a single 12.7 millimeter Browning in a fairing under each wing, for a total of five guns.
The P-63 was a generally new design, featuring little parts commonality with the P-39. The P-63 was slightly longer than the P-39, with the most distinctive recognition feature being that the trailing edge of the rudder on the P-63 was straight, while it was rounded on the P-39; the P-63's tailfin was also taller. Another distinctive recognition feature was a four-bladed prop.
Other changes were subtler. The wingspan and wing area were increased, and the wing featured the new "laminar" airfoil configuration established by NACA. More importantly, the P-63 was powered by an Allison V-1710-93 engine with a second supercharger stage -- not a turbocharger, giving it good high altitude performance.
Bell was distracted by producing the P-39 in volume, and the initial XP-63 design turned out to be badly overweight, demanding a redesign. The same basic fuselage design and engine (with two superchargers) was fitted into an enlarged airframe - essentially based on the XP-39E with a laminar flow wing, improved supercharger and new Continental I-1430 engine. Three prototypes were ordered, two with Allison V-1710-47 engines and one with a Packard V-1650 Merlin. The Packard-engined XP-63 was never built. The prototype was powered by an Allison V-1710-93 engine and a four-bladed propeller. Armament remained as the P-39Q model design with a 37mm nose cannons, 12.7mm heavy machine guns in the engine cowl and an additional 2 x 12.7mm heavy machine guns under the wings in pods. The designation was set as Bell Model 33, or P-63 Kingcobra. The first XP-63 (serial number 41-19511) flew on 7 December 1942, though the aircraft was lost in a crash a few weeks later.
The second prototype (serial number 41-19512) took to the air on 5 February 1943, but was lost in a crash in May. Both powered by the 988-kW (1,325-hp) Allison V-1710-47 engine. Fortunately for the program, a third prototype had been ordered in mid-1942. The third prototype, the XP-63A, first flown on 26 April 1943 and powered by a V-1710-93 engine with a war emergency rating of 1119kW (1,500 hp). It was planned subsequently to flight-test this prototype with a Packard-Merlin V-1650-5 engine installed, under the designation XP-63B, but this did not happen.
The type was ordered into production, with the first "P-63A Kingcobra" machines rolled out in October. Some 4,000 aircraft were to be built at Bell’s Marietta, Ohio, facility but were cancelled only three months later.
A total of 50 initial production P-63A-1 machines was built. They were followed by improved subvariants:
The "P-63A-5" was much the same as the P-63A-1 but featured some minor detail changes and new radios. 20 were built.
The "P-63A-6" added a stores attachment under each wing for an external tank or bomb. 130 were built.
The "P-63A-7" was a minor change on the P-63A-6, featuring a modified tailplane with wider span, revised mountings for the nose machine guns, and other fixes. 150 were built.
The "P-63A-8" featured an Allison engine with water-methanol injection, which permitted several minutes of combat power under redline operation, further improving the P-63's performance. Ammunition supply for the wing guns was cut from 250 to 200 rounds per gun. 200 were built.
The "P-63A-9" was similar to the P-63A-8, but featured more cockpit armour. 445 were built.
The "P-63A-10" replaced the old M4 37 millimeter cannon with the improved M10 model, and also raised the cannon's ammunition supply from 30 rounds to 58 rounds; the small ammunition supply for the cannon had been a persistent pilot complaint. In addition, the P-63A-10 featured an N-9 lead-computing gunsight. 730 were built.
Initial deliveries of the P-63A began in October 1943, and by the time production ended in 1945 more than 3,300 Kingcobras had been built in several versions. By far the majority, something in excess of 2,400, were supplied to the USSR under lend-lease, and about 300 went to the Free French Armée de l’Air. Very few of the total production of P-63 close-support fighters/ fighter-bombers were delivered to the USAAF, and so far as is known no Kingcobras were used operationally by that service. Honduras became another primary operator.
The Soviet Union operated the P-39 and, with input from Soviet test pilot Andrey G. Kochetkov, the P-63 Kingcobra was modified for the better and ultimately shipped to the Soviet Union from Nome, Alaska, to be used solely against Japanese forces in the East. Despite this "agreement" on the part of the Soviets, P-63 air groups were set up in the West to battle the Germans. The P-63 excelled in the ground attack role, and as tank busters. Soviet use of the P-63 amounted to over 72% of all Kingcobras produced, making them the primary operator of the aircraft.
Equipment of production batches varied considerably, resulting in many sub-types. The first production P-63A-ls had V-1710-93 engines, a nose-mounted 37-mm M4 cannon and two 12.7-mm (0.5-in) machine-guns in underwing fairings; other sub-types had two additional 12.7-mm (0.5-in) guns mounted in the fuselage nose. P-63A-ls and P63A-5s could accommodate a 284-litre (75-US gal) or 662-litre (175-US gal) drop tank, or a 237-kg (522-lb) bomb beneath the wing centre-section; P-63A-6s had underwing racks for two similar bombs or additional fuel; and P-63A-10s could mount three air-to-surface rockets beneath each wing. The weight of defensive armour, intended primarily to give protection from ground weapons, increased progressively from 39.8 kg (87.7 lb) on the P-63A-1 to 107.2 kg (236.3 lb) on the P-63A-10.
A "P-63B" variant with a Rolls-Royce Merlin engine was considered but never built, and so the next Kingcobra variant was the "P-63C". The P-63A was succeeded on the production line by the P-63C with the improved V-1710-117 engine, this offering with water injection an emergency war rating of 1342 kW (1,800 hp), wingspan clipped by 25 centimeters (10 inches) and, after early production at least, a prominent ventral fin to improve yaw stability; it is unclear if the fin helped reduce the aircraft's propensity to spin.
The "P-63C-1" was the initial production subvariant, with 215 built; they were followed by 1,012 "P-63C-5" machines with minor improvements. 200 more P-63C-1 machines were manufactured as "RP-63C-2" Pinball targets, for a total of 215 + 1,012 + 200 = 1,427 P-63C machines built.
Only one "P-63D" - technically a "P-63D-1" - was built. It was similar to the P-63A-10, with no ventral fin, but featured a bubble canopy and the carburetor intake moved back, presumably to allow the canopy to be slid back to open. The wingspan was increased over that of the P-63A, to 11.94 meters (39 feet 2 inches); the P-63D was powered by an Allison V-1710-109. The aircraft was lost in a crash due to an engine fire that claimed the life of pilot Bob Borchardt.
The P-63D was followed by the "P-63E", which was along the lines of the P-63C-10, with the ventral fin and the M10 cannon, but with the wider wingspan, stepped-back carburetor intake, and V-1710-109 engine of the P-63D. It retained the old car-door cockpit scheme; it featured more fuel capacity and a new Aeroproducts propeller.
Thirteen of the P-63E (or Bell Model 41), all that had been produced of 2,930 on order when contracts were cancelled at the war’s end, and which were generally similar to the P-63D except for a reversion to the standard cockpit canopy. The P-63E was similar to the D-model but sported the original automotive-style doors of the P-39 Airacobra and P-63A and P-63C Kingcobras. The underside fin was extended some and a new propeller were fitted though only 13 examples of this Kingcobra made it out the door. The E-model exhibited a top speed of 408 miles per hour, a cruising speed of 280 miles per hour, a range of 450 miles and a service ceiling of 43,000 feet.
There were two P-63F-1 built on an experimental basis. A version of the P-63E with a V-1710-135 engine and modified tail surfaces and substantially taller tailfin.
The XP-63H was a single conversion attempt based on a modified P-63E and featuring a new engine.
One other unusual version of the Kingcobra was built extensively (in excess of 300) for use by the USAAF in a training programme involving the use of live ammunition. Developed from the P-63A, all armour and armament was removed, and the external surface of the wings, fuselage and tail unit were protected externally by the addition of a duralumin alloy skin weighing some 680kg (1,500 lb). Other protection included the installation of bulletproof glass in windscreen and cockpit side and upper windows, the provision of a steel grille over the engine air intake and steel guards for the exhaust stacks, and the use of a propeller with thick-walled hollow blades All of these precautions were to make possible for the aircraft to be flown as a target that could withstand, without significant damage, the impact of frangible bullets. When a hit was made by an attacking aircraft a red light blinked to confirm the accuracy of the weapon being fired against it.
The first five of these target aircraft were designated RP-63A-11; the 95 RP-63A-12s which followed had increased fuel tankage; the next production version, with the V-1710-117 engine, became designated RP-63C (200 built). The final production version of the Kingcobra was the "RP-63G" Pinball target, with 32 built, for a total of 100 + 200 + 32 = 332 Pinballs. The RP-63G had the V-1710-135 engine. RP-63A/C's were based on five P-63A completed production models modified for the role while at least 95 other A-models were modified as such while still on the production lines. Although never flown as pilotless drone aircraft, the designations of these three versions were changed subsequently to QF-63A, QF-63C and QF-63G respectively.The Pinballs remained in service after the war, but were generally retired in 1947.
Bell considered but never built a trainer version, though the company did add a secondary cockpit on the rear fuselage to one P-63A and two P-63Es, the rear cockpit being used to seat an observer to keep an eye on trials aircraft. The Soviets did perform at least three conversions of P-63As to "TP-63A" trainer configuration, with a configuration along the lines of that of the TP-39 trainers.
Two P-63C production models were converted into L-39 test aircraft for swept wing and wind tunnel evaluation.
At the time of their production, a single P-63 cost American tax payers $48,000 to produce. A total of 3,303 were built.
A P-63A was converted in 1945 as a test-bed for a V-tail.
The XP-63N was a 1948 RP-63G conversion for V-tail testing.
The Soviets were the primary users of the P-63, obtaining about 2,400, air ferried by the Siberia route. P-63s shipped to the USSR never saw combat against the Nazi Reich; the Soviets had plenty of fighter aircraft at the time, and being intent on performing a thorough evaluation of the Kingcobra before putting it into service, it was not available to frontline units before the Nazi surrender in May 1945. Some Red Air Force pilots recollected seeing P-63s in service against the Germans, but no records confirm this.
The P-63 did see action in the brief Soviet campaign against the Japanese before Japan's surrender in August 1945, primarily being used for escort and ground attack.
After the war, the P-63 remained in first-line Red Air Force service. It was seen as very useful in helping pilots convert to new jet fighters as they came into service, since the jets generally had tricycle landing gear. The Kingcobra lingered on the flightlines into the early 1950s. There are tales that US pilots encountered them during the war in Korea, but no documentation confirms that notion.
The only other serious export user of the Kingcobra was the French Armee de l'Aire, which received 114 P-63Cs at the end of World War II. They served in combat as ground-attack aircraft in the French war in Indochina, being finally retired in 1951 in favour of US-supplied Grumman F8F Bearcat piston fighters. Some P-63s lingered in liaison and other secondary roles for a few years after that.
The Kingcobra was out of military service by the mid-1950s, but a few surplus P-63s did have a new career as air racers in the postwar period. A number of Kingcobras survive as museum displays, while a few remain flying as airshow "warbirds".
Including the Pinballs, a total of 50 + 20 + 130 + 150 + 200 + 445 + 730 + 5 + 95 = 1,825 P-63A machines was built.
Engine: Allison V-1710
Engine: 988-kW (1,325-hp) Allison V-1710-47
Engine: Rolls-Royce Merlin V-1710- 93 1119kW (1,500 hp)
Initial production machines
Engine: one 988-kW (1,325-hp) Allison V-1710-93 inline piston
Maximum speed 660 km/h (410 mph) at 7620m (25,000ft)
Cruising speed 608 km/h (378 mph)
Service ceiling 13110m (43,000 ft)
Range maximum weapon load and internal fuel 724 km (450 miles)
Ferry range maximum internal and external fuel 3541 km (2,200 miles)
Empty weight: 2892 kg (6,375 lb)
Maximum take-off 4763 kg (10,500 lb)
Wing span 11.68m (38ft 4in)
Length 9.96m (32ft 8in)
Height 3.84m (l2ft 7in)
Wing area 23.04sq.m (248 sq ft)
Armament: one 37-mm M4 cannon, two wing-mounted and two nose-mounted 12.7-mm (0.5-in) mg, plus up to three 237-kg (522-lb) bombs.
Wingspan: 11.68 m / 38 ft 4 in
Wing area: 23.04 sqm / 248 sq. ft
Length: 9.96 m / 32 ft 8 in
Height: 3.84 m / 12 feet 7 in
Empty weight: 2,892 kg / 6,375 lb
MTO weight: 4,763 kg / 10,000 lb
Max speed at altitude: 660 KPH / 410 MPH / 355 KT
Service ceiling: 13,100 m / 43,000 ft
Range: 725 km / 450 MI / 390 NMI
Engine: Allison V-1710-93
Armament: nose-mounted 37-mm M4 cannon and two 12.7-mm (0.5-in) machine-guns in underwing fairings; other sub-types had two additional 12.7-mm (0.5-in) guns mounted in the fuselage nose.
284-litre (75-US gal) or 662-litre (175-US gal) drop tank, or a 237-kg (522-lb) bomb beneath the wing centre-section
284-litre (75-US gal) or 662-litre (175-US gal) drop tank, or a 237-kg (522-lb) bomb beneath the wing centre-section
284-litre (75-US gal) or 662-litre (175-US gal) drop tank, or a 237-kg (522-lb) bomb beneath the wing centre-section, underwing racks for two similar bombs or additional fuel
Three air-to-surface rockets beneath each wing.
Ventral fin, clipped wings.
Engine: Allison V-1710-117/E21, 1342 kW (1,800 hp) / 1100 hp @ 25,000 ft.
Length: 32.81ft (10m)
Width: 38.39ft (11.70m)
Height: 12.47ft (3.80m)
Empty Weight: 6,834lbs (3,100kg)
Maximum Take-Off Weight: 8,818lbs (4,000kg)
Maximum Speed: 410mph (660kmh; 356kts)
Maximum Range: 450miles (725km)
Rate-of-Climb: 2,500ft/min (762m/min)
Service Ceiling: 42,979ft (13,100m)
1 x 37mm cannon in propeller hub
4 x 12.7mm machine guns (2 x in nose; 2 x in wing assembly).
Number built: 1227
Bubble canopy, wide wing
Engine: Allison 109/E22, 1100 hp @ 28,000 ft.
Number built: 1
P-63E / Bell Model 41
Like P-63D but with old cockpit scheme.
Engine: Allison 109/E22, 1100 hp @ 28,000 ft
Experimental machine with tall tailfin, etc.
Engine: Allison V-1710-135
Initial Pinball targets.
RP-63A-11 / QF-63A
RP-63A-12 / QF-63C
RP-63C / QF-63G
Engine: Allison V-1710-117
Final production Pinball machine.
Engine: Allison V-1710-135