USAAF # AN 01-240JA-1
a. AIRPLANE.- The XF-11 is a reconnaissance-photographic, twin-boom, high wing monoplane manufactured by Hughes Aircraft Company. Equal pressurization is maintained in the pilot's and photographer's compartments located in the fuselage. The crew of two, pilot and relief pilot-navigator, may change places during flight. The relief pilot also performs the duty of photographer. The recommended maximum gross weight for the take-off is 58,300 pounds. The fighter version of XF-11 was the XP-73 and the attack variant was designated the A-37.
b. POWER PLANTS.- The airplane is powered by two Pratt & Whitney Model R-4360-31 radial air-cooled, 28 cylinder engines. The cylinders are arranged in four radial rows of seven cylinders in each row. Seven magnetos are mounted on each engine to furnish the ignition. An injection type carburetor, and two single stage single speed turbo-superchargers are installed on each engine.
c. PROPELLERS.- A Hamilton-Standard eight blade, counter-rotation, super-hydromatic propeller is used on each engine. The propellers are of the constant speed, full feathering, reversable pitch type.
d. FLIGHT CONTROLS
AILERONS-SPOILERS AND TRIM TAB.- The ailerons and spoilers are mechanically synchronized. Conventional operation of the ailerons in the "UP" position for the left or right wing automatically actuate the spoilers.
XF-11 in test flight without counter-rotating propellers
XF-11 with installation of counter-rotating propellers
The plane which would become the F-11 began in 1939 under the Hughes Aircraft experimental model designation DX-2. Hughes originally proposed it as a bomber, but his true interest seems to have been the idea of constructing a large airplane by using the Duramold process. This process had been developed and patented by Colonel V. E. Clark, the Army's chief aeronautical engineer during the First World War. Duramold involved molding resin-impregnated plywood into desired shapes and contours under high heat and pressure. Duramold wooden structures demonstrated it had the strength and rigidity comparable to metal, if not superior in some respects.
In 1941, the United States was not yet involved in World War II, but the USAAF was building its strength in the expectation of war. Meanwhile, the DX-2 project had evolved into a large two-seat fighter design which interested the US Army Air Forces because aluminum was becoming scarce because of Word War II. In October 1941, after examining the DX-2, the USAAF Materiel Command at Wright Field, Ohio, decided against the Hughes proposal because it couldn't envision aviation future by reintroducing the past of wooden airplanes.
After the United Stated entered the war, USAAF headquarters in Washington urged the Materiel Command to reconsider the project. On 25 May 1942, the Hughes 'Duramold' airplane was ordered under the experimental attack designation XA-37. Subsequently, the project was briefly considered for deployment as a night fighter under the experimental fighter designation XP-73. Howard Hughes, however, decided not to 'sell' the airplane to the USAAF until it made its first flight. This event transpired 11 months later, on 20 June 1943, with Hughes at the controls. It was 43 feet long, with a wing span of 60 feet and a gross weight of just under 29,000 pounds. Power was supplied by two Pratt & Whitney R-2800 Double Wasp engines rated at 2000 hp each.
The DX-2 (prototype of the XA-37) was estimated to have a top speed of 435 mph, but this is unknown, because Hughes himself was the only test pilot of the airplane, and the only time someone was in the cockpit with Hughes during a high-speed test flight, Hughes held his hand over the airspeed indictor.
The secrecy surrounding the development of the DX-2 exceeded that of a military program. All of the flying was done as a secret Hughes Aircraft facility at Harper's Dry Lake in the Mojave Desert, by Hughes himself. Furthermore, he wouldn't permit any photographs to be taken of the airplane.
The story of the Hughes DX-2 ended mysteriously on 11 November 1943 when a fire struck the hanger that contained the wooden aircraft, destroying both, along with any hope that the A-37 attack series ever coming into existence. There were rumors of arson and some political finger-pointing at Howard Hughes. However, it remains unclear what motive he would have had for destroying the mysterious airplane.
Colonel Elliot Roosevelt, the son of the President, convinced USAAF chief General Henry 'Hap' Arnold that a DX-2-based aircraft would make an ideal high altitude reconnaissance aircraft because of its speed and light weight. This USAAF had observed, and used, the Royal Air Force's deHavilland Mosquito, a high altitude reconnaissance aircraft made of wood. Hughes had completed design studies for such an aircraft under his own D-5 designation.
Despite the continued reluctance of the Materiel Command, General Hap Arnold compelled them to issue a purchase order offering in October 1943, to pay $56.6 million for 100 D-5s, which would be given the USAAF designation F-11. Ironically, the compromise was that the F-11 would be based on the design of the DX-2, but it would have to be metal, not wood.
Please note: that the 'F' series of designations stood for 'photographic reconnaissance' prior to 1948. For example, the photographic reconnaissance versions of P-38 Lightning, the P-51 Mustang and the DH-98 Mosquito were known as F-5, F-6 and F-8 respectively. After 1948, the F designations were assigned to fighters, and the recon aircraft were given 'R for reconnaissance' prefixes. Also of importance here is that the F-11 was the first of the series to be designed from the beginning as a high performance reconnaissance aircraft. All the others -- F-1 through F-10 -- were modified versions of some other type of aircraft.
The contract called for a first delivery date of March 1945. There were many problems inherent in the development of so unique a plane as the F-11, including re-engineering the design to metal, but the project was proceeding reasonably well with the first prototype being 80 percent completed. In May 1944, 21 Hughes engineers, including the F-11 project engineer, quit their jobs. From this point on, the F-11 continuously faced delays and chronic labor shortages. The first set of wings did not reach the Culver City, California, final production site from a subcontractor until 10 April 1945, a month after the scheduled delivery of the first airplane. The first of the two Pratt & Whitney R-4360 engines with their eight-bladed contra-rotating propellers wasn't available until September, the month after the war ended.
Unknown to Hughes or Roosevelt, Republic Aircraft started design work in 1943 on their own long-range reconnaissance aircraft, the Republic XF-12. The aircraft used four R-4360 Wasp-Major engines and had a range of 4,100 miles. In March 1944, the USAAF ordered two prototypes.The aircraft flew in 1946 but retired in 1952 due to obsolescence with the arrival of jets.