|Maiden flight||6 January 1944|
|Status||Cancelled 13 September 1944|
|Primary user||U.S. Army Air Force|
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.
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 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 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.
Upon return to the factory the cooling ducts were reworked and the tailplanes raised a foot. Then followed more flight tests 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.
- Crew: one, pilot
- Length: 44 ft 9 in (13.64 m)
- Wingspan: 55 ft (16.76 m)
- Height: 15 ft 9 in (4.80 m)
- Wing area: 414 ft² (38.50 m²)
- Empty weight: 17,745 lb (8,050 kg)
- Loaded weight: 22,114 lb (10,030 kg)
- Max takeoff weight: 25,400 lb (11,520 kg)
- Powerplant: 2× Continental XI-1430-17/19 twelve cylinder inverted vee liquid-cooled engine, 1,350 hp (1,000 kW) each
- Maximum speed: 405 mi/h at 25,000 ft (650 km/h)
- Range: 2,385 statute miles (3,840 km)
- Service ceiling: 37,400 ft (11,400 m)
- Rate of climb: 2,600 ft/min (13 m/s)
- Wing loading: 53.4 lb/ft² (260 kg/m²)
- Power/mass: 0.06 hp/lb (0.09 kW/kg)
- Six 37 mm M-4 cannon
- William Green (1961). War Planes of the Second World War - Fighters, (Vol 4). London: MacDonald
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