The Bell XP-77 development was initiated by the United States Army Air Forces during World War II to produce a simplified lightweight fighter aircraft using non-strategic materials.
Despite being innovative, the diminutive prototype proved tricky to handle and the project was cancelled when the XP-77 did not deliver its projected performance.
The Tri-4, Company designations, later changed to D-6 Project with the Bell Aircraft Corporation was initiated in October 1941.
Originally a design study to meet the USAAF specifications for a very light interceptor, the XP-77 was intended to be a small, light fighter much in the mold of the 1930s Thompson Trophy air racers.
On 16 May 1942, the USAAF recommended the construction and testing of 25 XP-77s.
The aircraft featured a single engine, low-wing monoplane with mainly wood construction, equipped with tricycle landing gear, a typical Bell feature that bestowed good ground handling.
A bubble canopy also provided fair visibility except in the forward-downward direction due to the extended nose.
While originally conceived using an air-cooled 500 hp (370 kW) Ranger XV-770-9 12-cylinder engine with a supercharger, the prototypes were delivered with the non-supercharged XV-770-7 engine due to engine development delays.
With the anticipated delivery time of the original engine delayed for one and a half years, Bell proposed that seven XP-77s be built using the seven XV-770-7 engines then available.
The planned armament was one Hispano 20 mm cannon firing through the propeller hub and two 0.5 inch (12.7 mm) M2 Browning machine guns, with the option of either a 300 lb (140 kg) bomb or 325 lb (147 kg) depth charge with the deletion of the cannon armament.
The mock-up inspection on 21–22 September 1942 produced some concerns from both the manufacturer and the USAAF inspection team.
Weight had crept up beyond the 3,700 lb (1,700 kg) design limit but delays in the program were experienced when the company resorted to sub contracting the wooden construction while the ongoing production at the Bell facilities did not allow for the XP-77 to take priority for research and development.
Bell asked and received permission to reduce the production run of aircraft to two prototypes.
22 ft 10 in (6.96 m)
27 ft 6 in (8.38 m)
8 ft 2 in (2.49 m)
100 sq ft (9.3 m2)
2,855 lb (1,295 kg)
Max take-off weight
4,028 lb (1,827 kg)
1 × Ranger V-770-7 inverted V12 engine,
520 hp (388 kW)
330 mph (530 km/h, 290 kn)
550 mi (890 km, 480 nmi)
30,100 ft (9,180 m)
Rate of climb
3,600 ft/min (18.3 m/s)
40.28 lb/sq ft (196.5 kg/m2)
13 hp/lb (213 W/kg)
1 × 20 mm (0.787 in) Hispano-Suiza HS.404 cannon, firing through the propeller hub.
2 × .50 in (12.7 mm) M2 machine guns with 200 rounds each.