Hughes XF-11
The Hughes XF-11 was a twin-engined photographic reconnaissance prototype built by Hughes Aircraft Company for the United States Army Air Forces. Developed from the secretive D-2, it was designed for 400 mph at high altitude, but it was not completed until after the Second World War had ended. The first prototype crashed on its maiden flight in July 1946, critically injuring Howard Hughes; the second flew in 1947, was tested by the Air Force as the XR-11, and was scrapped in 1949. No example survives.
Why It Mattered
The XF-11 was Hughes Aircraft Company's attempt to give the United States Army Air Forces a purpose-built photographic reconnaissance aircraft, developed from Howard Hughes's secretive D-2 project. The design target was a speed of 400 mph at high altitude. It was built for the same Army Air Forces objective as the Republic XF-12 Rainbow. Aerospace historian Richard P. Hallion has called it a very highly developed, well-thought-out design. Yet only two prototypes were completed, the first was destroyed on its maiden flight, and the type never entered service.
Design Notes
The XF-11 took the D-2's basic concept and rebuilt it in metal, larger and more powerful. Each of its two turbo-supercharged Pratt & Whitney R-4360-31 radials drove a pair of four-bladed contra-rotating propellers, 14 feet across. The wing spanned 101 feet 4 inches, and at a gross weight of 58,315 pounds it was a large aircraft for a twin-engined type. Contra-rotating propellers were a contract requirement, imposed on the competing XF-12 as well. The second prototype replaced the contra-rotating installation with conventional four-blade propellers.
Operational History
In 1943 Hughes won a contract for two prototypes and 98 production aircraft. Development ran late, and the XF-11 was not completed until the war had ended. The production order was cancelled at the war's end, leaving only the two prototypes to finish. Howard Hughes personally made the official first flight on 7 July 1946, from the company airfield at Culver City. An oil leak caused the right rear propeller to reverse pitch, the engine lost power, and the aircraft crashed in Beverly Hills, damaging houses. Hughes was the only person injured, and he was pulled from the wreckage in critical condition. Investigators traced the failure to a loss of hydraulic fluid in the right propeller's pitch-change mechanism. Wright Field nevertheless understood the crash as pilot error, while Hughes successfully sued the propeller's maker, Hamilton Standard, over the malfunction. The second prototype, fitted with standard propellers, made its first flight on 5 April 1947, with Hughes test pilot Peter Forney at the controls. Smithsonian Magazine records that Hughes himself flew the airplane nine months after the accident. The programme was controversial from the beginning, and the United States Senate investigated the XF-11 and the Hughes H-4 Hercules flying boat.
Afterlife
After its early flights, the surviving prototype passed into the hands of the Army Air Forces. In July 1948 a new designation system renamed it the XR-11. In 1947 and 1948, the Air Materiel Command at Wright Field subjected it to rigorous tests. Defense Media Network reports that no fault was ever found in the design, but the Air Force decided to move on. The aircraft was scrapped in 1949; with the first prototype destroyed in the 1946 crash, no XF-11 survives.