McDonnell XP-67

The McDonnell XP-67 was a prototype for a twin engine, long range, single-place fighter for the U.S. Army Air Corps with a pressurized cockpit. Two Continental XI-1430-1 engines powered the aircraft. The engines were fitted with turbo-superchargers and drove four bladed propellers and used the exhaust to augment thrust. The armament proposed were six 37 mm M-4 cannon.

Based upon interest in an earlier McDonnell study for a long-range fighter, the A.A.C. issued an order for two prototype airplanes on July 29, 1941 designating them XP-67. The aircraft was unique in that the design team sought to maintain true aerofoil sections throughout the entire fighter including the center fuselage and merging the rear portions of the engine nacelles with the wing. A number of armament configurations were considered including six 0.5 inch machine guns, four 20 mm cannon, and even a 75 mm cannon before the configuration of six 37 mm cannon was chosen.

The first XP-67 was ready for ground trials on December 1, 1943 although it was not yet complete for flight. The aircraft was fitted at this time with XI-1430-17/19 engines and General Electric D-23 turbo-superchargers. On December 8, however, the aircraft was damaged by fires in both engine nacelles, caused by a malfunction of the exhaust manifold slip rings. But, by January 6, 1944 the damage was repaired and the XP-67 made its first flight. The flight, however, ended after six minutes due to difficulties with the experimental engines. After a number of modifications were made to the engine installations two test flights were accomplished. On the fourth flight the engine bearings burned out when the engines were unintentionally overspeeded.

As a result of wind tunnel tests the tail-plane was raised a foot while the aircraft waited for replacement engines. On March 23, 1944 flight trials restarted and continued for several months. After five test flights by A.A.F. pilots found the aircraft cockpit layout fair and ground handling satisfactory, but that the aircraft appeared underpowered with long take-offs, poor initial rate of climb, and slow acceleration. Other flight characteristics were good, such as light stick forces, effective control at all speeds with flight stable longitudinally, but a tendency to “Dutch roll.”

Additional changes were made to the XP-67 as flight trials continued, but as official flight trials were to begin in September 1944, the aircraft was irreparably damaged by fire. With slow progress on completing the second prototype, the fire damage to the first prototype, and other performance related issues when combined led to termination of the contract.

Specifications (XP-67)

General characteristics

• Crew: one, pilot
• Length: m (44 ft 9 in)
• Wingspan: m (55 ft)
• Height: m (15 ft 9 in)
• Wing area: m² (414 ft²)
• Empty: kg (17,745 lb)
• Loaded: kg (22,114 lb)
• Maximum takeoff: kg (25,400 lb)
• Powerplant: Two Continental XI-1430-17/19 twelve cylinder inverted vee, liquid-cooled engines, kW (1,350 hp)

Performance

• Maximum speed: km/h (405 mi/h at 25,000 ft)
• Range: km (2,385 statute miles)
• Service ceiling: m (37,400 ft)
• Maximum rate of climb: m/min (2,600 ft/min)
• Wing loading: kg/m² ( lb/ft²)
• Power/mass:

Armament (Proposed)

• Six 37 mm M-4 cannon

References

• William Green (1961). War Planes of the Second World War - Fighters, (Vol 4). London: MacDonald