McDonnell XP-67
The McDonnell XP-67 was a prototype for a twin-engine, long range, single-place fighter aircraft for the U.S. Army Air Corps with a pressurized cockpit. Two Continental XI-1430-1 engines provided power, and were fitted with turbosuperchargers. The engines were of an X-configuration, and drove four-bladed propellers, using the exhaust to augment thrust. The armament proposed was six 37 mm M4 cannon. Although the design represented an advanced concept, numerous problems handicapped the project and led to its cancellation.
Design and development
Based upon interest in an earlier McDonnell study for a long-range fighter, the USAAC issued an order for two prototype airplanes on 29 July 1941, designating them XP-67. The aircraft was unusual 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 50-caliber machine guns, four 20 mm cannon, and even a 75 mm cannon before the configuration of six 37 mm cannon was chosen.
Testing
The first XP-67 was ready for ground trials on 1 December 1943 although it was not yet ready for flight. The aircraft was fitted at this time with XI-1430-17/19 engines and General Electric D-23 turbo-superchargers. On 8 December, however, the aircraft was damaged by fires in both engine nacelles, caused by a malfunction of the exhaust manifold slip rings. By 6 January 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 tailplanes were raised 12 inches while the aircraft waited for replacement engines. On 23 March 1944 flight trials restarted and continued for several months. After five test flights by USAAF pilots found the aircraft cockpit layout fair and ground handling satisfactory, but that the aircraft appeared underpowered with long takeoffs, 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 was prevalent.
Upon return to the factory the cooling ducts were also reworked. More flight tests then followed before AAF pilots finally got to fly the plane on 11 May 1944. During the following flights, several problems were cured, but engine related ones never were satisfactorily corrected. The biggest problem was engine overheating which led to a fire in the right nacelle on 6 September 1944. The ensuing fire caused major damage and on 13 September, McDonnell and the USAAF agreed to terminate the contract. The second airframe was never completed.
Specifications (XP-67)
General characteristics
- Crew: one, pilot
Performance
Armament
- Six 37 mm M-4 cannon
References
- Green, William. War Planes of the Second World War - Fighters (Vol 4). London: MacDonald, 1961.
External links
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