Bell XP-77

https://en.wikipedia.org/wiki/Bell_XP-77

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 canceled 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 Bell trademark that
bestowed good ground handling. A sleek bubble canopy also provided all-round
visibility (except forward due to the extended nose); a key requirement for a
fighter.

While originally conceived using an air-cooled 500 hp 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 (much like the larger caliber 37 mm moteur-canon of the SPAD
S.XII) and two 0.5 inch Browning machine guns, with the option of either a 300
lb bomb or 325 lb 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 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.


Role
Fighter aircraft

Manufacturer
Bell Aircraft Corporation

First flight
1 April 1944

Retired
December 1944

Primary user
U.S. Army Air Forces

Number built
2 prototypes

Testing

The XP-77 project continued to suffer numerous delays, many related to
correction of the excess weight issues. A change in subcontractor for the wing
assembly also caused headaches as the first subcontractor refused to release
necessary parts. Concerns over structural integrity relating to the glue and its
binding properties were also difficult to resolve. With the anticipation that
contract costs would soon be exceeded, and no hope that the supercharged engine
would become available, the USAAF would only continue the project as an
experiment to evaluate the use of wooden construction and materials in combat
aircraft. The first XP-77 flew 1 April 1944 at Wright Field but the flight tests
revealed vibration problems due to directly mounting the engine to the airframe,
without vibration isolation. The long nose and rear-mounted cockpit also
inhibited visibility relative to operational aircraft of the time.

The XP-77 proved to be difficult to fly and despite flying without guns or
armor, it did not come up to the expected performance estimates mainly because
it was woefully underpowered. Further trials were conducted at the USAAF Proving
Ground at Eglin Field with the second aircraft, which was destroyed when it
entered an inverted spin while attempting an Immelmann, and the pilot bailed
out. The development was terminated in December 1944.

Specifications (Bell XP-77)

General characteristics
Crew: 1 pilot
Length: 22 ft 10 in (6.96 m)
Wingspan: 27 ft 6 in (8.38 m)
Height: 8 ft 2 in (2.49 m)
Wing area: 100 sq?ft (9.3 m²)
Empty weight: 2,855 lb (1,295 kg)
Max. takeoff weight: 4,028 lb (1,827 kg)
Powerplant: 1 × Ranger V-770-7 inverted V12 engine, 520 hp (388 kW)

Performance
Maximum speed: 330 mph (290 knots, 530 km/h)
Range: 550 mi (480 nmi, 890 km)
Service ceiling: 30,100 ft (9,180 m)
Rate of climb: 3,600 ft/min (1,097 m/min)
Wing loading: 40.28 lb/sq?ft (196.5 kg/m²)
Power/mass: .13 hp/lb (213 W/kg)

Armament

Guns:
1× 20 mm (0.787 in) Hispano-Suiza HS.404 cannon, firing through the propeller.
2× .50 in (12.7 mm) M2 machine guns with 200 rounds each.

Bombs:
1× 300 lb (136 kg) bomb or
1× 325 lb (147 kg) depth charge




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