The Bell P-76 was a single-engine fighter aircraft prototype – an improved version of the Bell P-39 Airacobra, designed during World War II. The design, which was initially designated XP-39E, never entered production

On 26 February 1941 the United States Army Air Corps (USAAC) placed a contract with Bell for two prototypes (41-19501 and 41-19502) that were intended to be a major improvement on preceding P-39s. In particular, the XP-39E was intended to address the poor high-altitude performance of the Airacobra.

The performance issues of previous P-39 variants were to be addressed by incorporating a new wing design with a lower wing loading, a more powerful engine and redesigning the tailfin. The wing span was increased to 35 ft 10 in (10.9 m) and the total wing area to 236 ft² (21.9 m²), was to be wider and thicker, with a symmetrical airfoil; the section chosen was NACA 0018 at the wing-root tapering to an NACA 23009 at the tip. (While the new wing was sometimes referred to as having a laminar flow profile, that was not technically the case.)^[1] The greater internal dimensions of the wing allowed an increase in the fuel capacity to 150 US gallons (568 L).^[2] The engine bay was modified to accept a more powerful engine in lieu of the Allison V-1710. Its origins lay in a 1941 project to equip three P-39Ds (41-19501, 41-19502 and 42-7164) with the Continental V-1430-1 liquid-cooled supercharged engine. The resultant XP-39E had a symmetrical airfoil wing with square wingtips, an elongated fuselage to accommodate the larger engine, and revised air intakes and radiators. In addition, each of the three prototypes featured a different, redesigned version of the P-39 tailfin.

Since the Continental engine was not available at rollout, the prototypes flew with a new variant of the V-1710, the Allison V-1710-E9. This version, which had the military designation of V-1710-47, used a two-stage mechanical supercharger to increase the engine power at altitude. (After the Continental V-1430 failed to live up to its potential, a later version of the V-1710, the Allison V-1710-93, was used in the XP-63A.)^[2]

The prototypes performed well and 4,000 P-39Es were ordered for the USAAF. However, the order was postponed to permit Bell to manufacture the Boeing B-29 Superfortress, under license. Many elements of the P-39E were subsequently incorporated in the P-63 Kingcobra, a parallel program to develop an enlarged version of the Airacobra; the XP-63 first flew in December 1942. While the P-39E was retrospectively redesignated P-76, it never entered production.

General characteristics

• Crew: 1
• Length: 31 ft 11 in (9.7 m)
• Wingspan: 35 ft 10 in (10.9 m)
• Wing area: 236 sq ft (21.9 m²)
• Empty weight: 6,936 lb (3,150 kg)
• Max takeoff weight: 8,918 lb (4,050 kg)
• Powerplant: 1 × Continental I-1430-1 , 2,100 hp (1,600 kW)

Performance

• Maximum speed: 386 mph (620 km/h, 335 kn) at 21,680 ft (6,600 m)
• Rate of climb: 2,150 ft/min (11 m/s)

Armament

• Guns:
  
  • 1× 37 mm (1.46 in) Oldsmobile T9 cannon, 30 rounds
  • 2× 0.50 in (12.7 mm) M2 Browning machine guns, 200 rounds per gun
  • 4× 0.30 in (7.62 mm) M1919 machine guns, 1,000 rounds per gun
• Bombs: 500 lb (227 kg) externally

Related development

• Bell P-39 Airacobra
• Bell P-63 Kingcobra

Related lists

• List of military aircraft of the United States