Hughes XF-11

The second XF-11 prototype in flight.

The Hughes XF-11 was a prototype military reconnaissance aircraft designed by millionaire Howard Hughes for the United States Army. It was a tricycle-gear, twin-engine, twin-fuselage, twin-boom, all-metal monoplane with a pressurized central crew nacelle. In general appearance, it was similar to the Lockheed P-38 Lightning made famous in World War II, though the XF-11's wing had a much larger span and much higher aspect ratio.

Experimental propeller design

Hughes checking the first XF-11 prototype (with the original twin propeller design).

The XF-11 used Pratt & Whitney R-4360-31 28-cylinder radial engines with twin four-bladed, controllable-pitch propellers at the front of each engine. The propeller design was very unusual in that the front and rear propellers on each engine were counter-rotating, which can increase a propeller-driven aircraft's performance and stability, but which can also add much mechanical complexity.

The aircraft was designed to be very fast and have a long range. The Army originally ordered 100 of them for the purposes of photo reconnaissance. The order was cancelled following the end of World War II, leaving Hughes with two prototypes.

Prototypes

The first prototype crashed on July 7, 1946, on its maiden flight. An oil leak caused the right engine propeller controls to lose their effectiveness and the rear propeller subsequently reversed its pitch, distorting much of that engine's thrust which made the aircraft yaw hard to the right and extraordinarily difficult to control. Hughes elected to make an emergency landing on the Los Angeles Country Club's golf course, but about 300 yards short of the course, the aircraft suddenly lost altitude and clipped three houses. The third house was completely destroyed by the fire resulting from the crash and Hughes was nearly killed. [1]

The second prototype was fitted with conventional propellers and flown on April 5, 1947, after Hughes had recuperated from his injuries. This test flight was uneventful and the aircraft proved to be stable and controllable at high speed. However, it was lacking in low-speed stability and the Air Force instead chose the Boeing RB-50 which had similar long-range photo-reconnaissance capability and was available for much less.

Specifications (XF-11)

General characteristics

* Crew: two; pilot and navigator/photographer
* Length: 65 ft 5 in (19.94 m)
* Wingspan: 101 ft 4 in (30.89 m)
* Height: 23 ft 2 in (7.06 m)
* Wing area: 983 ft² (91.3 m²)
* Empty: 37,100 lb (16,800 kg)
* Loaded: lb ( kg)
* Maximum takeoff: 58,300 lb (26,400 kg)
* Powerplant: 2x Pratt & Whitney R-4360-31 radials, 3,000 hp (2,240 kW) each

Performance

* Maximum speed: 450 mph (720 km/h)
* Range: 5,000 miles (8,000 km)
* Service ceiling: 44,000 ft (13,415 m)
* Rate of climb: ft/min ( m/min)
* Wing loading: lb/ft² ( kg/m²)
* Power/Mass: hp/lb ( kW/kg)

Hughes XF-11: Encyclopedia BETA