|The second Hughes XF-11 during a 1947 test flight|
|First flight||7 July 1946|
|Primary user||United States Army Air Force|
|Developed from||Hughes D-2|
The Hughes XF-11 was a prototype military reconnaissance aircraft, designed and flown by Howard Hughes and built by Hughes Aircraft for the United States Army Air Forces. Although 100 F-11s were ordered in 1943, only two prototypes and a mockup were completed. During the first XF-11 flight in 1946, Howard Hughes crashed the aircraft in Beverly Hills, California. The production aircraft had been canceled in May 1945, but the second prototype was completed and successfully flown in 1947. The program was extremely controversial from the beginning, leading the U.S. Senate to investigate the F-11 and the Hughes H-4 Hercules flying boat in 1947–1948.
Design and development
While Hughes had designed its predecessors to be fighter variants, the F-11 was intended to meet the same operational objective as the Republic XF-12 Rainbow. Specifications called for a fast, long-range, high-altitude photographic reconnaissance aircraft. A highly modified version of the earlier private-venture Hughes D-2 project, in configuration the aircraft resembled the World War II Lockheed P-38 Lightning, but was much larger and heavier. It was a tricycle-gear, twin-engine, twin-boom all-metal monoplane with a pressurized central crew nacelle, with a much larger span and much higher aspect ratio than the P-38's wing.
The XF-11 used Pratt & Whitney R-4360-31 28-cylinder radial engines. Each engine drove a pair of contra-rotating four-bladed, controllable-pitch propellers, which can increase performance and stability, at the cost of increased mechanical complexity. Due to constant problems with the contra-rotating propulsion system, the second prototype had regular single four-bladed propellers.
On the urgent recommendation of Colonel Elliott Roosevelt, who led a team surveying several reconnaissance aircraft proposals in September 1943, General Henry "Hap" Arnold, chief of the U.S. Army Air Forces, ordered 100 F-11s for delivery beginning in 1944. In this, Arnold overrode the strenuous objections of the USAAF Materiel Command, which held that Hughes did not have the industrial capacity or proven track record to deliver on his promises. (Materiel Command did succeed in mandating that the F-11 be made of aluminum, unlike its wooden D-2 predecessor.) Arnold made the decision "much against my better judgment and the advice of my staff" after consultations with the White House. The order was canceled on 29 May 1945, but Hughes was allowed to complete and deliver the two prototypes.
Numerous difficulties of both a technical and managerial nature accompanied the program from the beginning. From 1946-1948, the Senate subcommittee to investigate the Defense Program, popularly known as the Truman Committee and then the Brewster Committee, investigated the F-11 and H-4 programs, leading to the famous Hughes-Roosevelt hearings in August 1947. The program cost the federal government $22 million.
Hughes did not follow the agreed testing program and communications protocol, and remained airborne almost twice as long as planned. An hour into the flight (after onboard recording cameras had run out of film), a leak caused the right-hand propeller controls to lose their effectiveness and the rear propeller subsequently reversed its pitch, disrupting that engine's thrust, which caused the aircraft to yaw hard to the right. The USAAF account said that, "It appeared that loss of hydraulic fluid caused failure of the pitch change mechanism of right rear propeller. Mr. Hughes maintained full power of right engine and reduced that of left engine instead of trying to fly with right propeller windmilling without power. It was Wright Field's understanding that the crash was attributed to pilot error."
Rather than feathering the propeller, Hughes performed improvised troubleshooting (including raising and lowering the gear) during which he flew away from his factory runway. Constantly losing altitude, he finally attempted to reach the golf course of the Los Angeles Country Club, but about 300 yards short of the course, the aircraft suddenly lost altitude and clipped three houses. The third house was destroyed by fire, and Hughes was nearly killed. The crash is dramatized in the 2004 film The Aviator.
The second prototype was fitted with conventional propellers and flown by Hughes on 5 April 1947, after he had recuperated from his injuries. Initially, the USAAF had insisted that Hughes not be allowed to fly the aircraft, but after a personal appeal to Generals Ira Eaker and Carl Spaatz, he was allowed to do so against posting of $5 million in security.
This test flight was uneventful, and the aircraft proved stable and controllable at high speed. It lacked low-speed stability, however, as the ailerons were ineffective at low altitudes. When the US Army Air Forces (USAAF) evaluated it against the XF-12, testing revealed the XF-11 was harder to fly and maintain, and projected that it would to be twice as expensive to build. A small production order of 98 for the Republic F-12 had been issued, but the USAAF soon chose the RB-50 Superfortress, and Northrop F-15 Reporter instead, both of which had similar long-range photo-reconnaissance capability and were available at a much lower cost.
The F-12 production order was canceled. When the United States Air Force was created as a separate service in September 1947, the XF-11 was redesignated the XR-11. The surviving XR-11 prototype arrived at Eglin Field, Florida, in December 1948 from Wright Field, Ohio, to undergo operational suitability testing through July 1949 but a production contract for 98 was canceled. The airframe was transferred to Sheppard AFB, Texas, on 26 July 1949 for use as a ground maintenance trainer by the 3750th Technical Training Wing, and was dropped from the USAF inventory in November 1949.
Data from Jane's all the World's Aircraft 1947
- Crew: 2, pilot and navigator/photographer
- Length: 65 ft 3 in (19.9 m)
- Wingspan: 101 ft 5 in (30.9 m)
- Wing area: 983 sq ft (91.3 m2)
- Empty weight: 37,100 lb (16,828 kg)
- Gross weight: 47,500 lb (21,546 kg) (4,000 mi (3,500 nmi; 6,400 km) range)
- Max takeoff weight: 58,315 lb (26,451 kg) (5,000 mi (4,300 nmi; 8,000 km) range)
- Powerplant: 2 × Pratt & Whitney R-4360-31 Wasp Major 28-cyl. air-cooled radial piston engines, 3,000 hp (2,200 kW) each
- Propellers: 8-bladed Hamilton Standard Hydromatic contra-rotating propellers
- Maximum speed: 450 mph (724 km/h; 391 kn) at 33,000 ft (10,000 m); 295 mph (256 kn; 475 km/h) at sea level
- Service ceiling: 42,000 ft (13,000 m)
- Rate of climb: 1,000 ft/min (5.1 m/s)
- Time to altitude: 33,000 ft (10,000 m) in 17.4 minutes
- Wing loading: 59.3 lb/sq ft (290 kg/m2) (5,000 mi (4,300 nmi; 8,000 km) range)
Aircraft of comparable role, configuration and era
- Parker, Dana T. Building Victory: Aircraft Manufacturing in the Los Angeles Area in World War II, pp. 49-51, Cypress, CA, 2013. ISBN 978-0-9897906-0-4.
- Winchester 2005, p. 222.
- Hansen 2012, p. 541.
- Hansen 2012, pp. 530–536.
- "Crash of the XF-11." check-six.com. Retrieved: 16 June 2010.
- Winchester 2005, p. 223.
- USAAF Materiel Command to Gen. Spaatz, 16 August 1946, at F-11 project file at Air Force Historical Research Agency
- Hansen 2012, p. 562, quoting Eaker's Nov. 1947 testimony to the Senate.
- Fort Walton, Florida, "New Ship At Eglin", Playground News, 30 December 1948, Vol. 3, No. 48, p. 1.
- Francillon, René J., "McDonnell Douglas Aircraft Since 1920, Vol. II", Naval Institute Press, Annapolis, Maryland, 1979, 1990, Library of Congress card number 88-61447, ISBN 1-55750-550-0, p. 76.
- Francillon, René J., "McDonnell Douglas Aircraft Since 1920, Vol. II", Naval Institute Press, Annapolis, Maryland, 1979, 1990, Library of Congress card number 88-61447, ISBN 1-55750-550-0, p. 77.
- Bridgman, Leonard, ed. (1947). Jane's all the World's Aircraft 1947. London: Sampson Low, Marston & Co. p. 172c.
- Barton, Charles. "Howard Hughes and the 10,000 ft. Split-S." Air Classics, Vol. 18, no. 8, August 1982.
- Hansen, Chris. Enfant Terrible: The Times and Schemes of General Elliott Roosevelt. Tucson, Arizona: Able Baker Press, 2012. ISBN 978-0-61566-892-5.
- Winchester, Jim. "Hughes XF-11." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc., 2005. ISBN 978-1-84013-809-2.
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