The Hughes XF-11 was a prototype for a two-seat, twin-engine reconnaissance airplane with a relatively small, pressurized, central crew compartment and twin tails on long, slender booms. The crew of two including a pilot and a relief-pilot/navigator could change places during flight. The relief pilot also performed the duty of photographer. The 67-foot-long airplane had a maximum takeoff gross weight of 58,300 pounds and a 101-foot wingspan.

The XF-11 was powered by two Pratt & Whitney R-4360-31 radial air-cooled, 28 cylinder engines. The cylinders were arranged in four radial rows of seven cylinders in each row. Seven magnetos were mounted on each engine to furnish the ignition. An injection type carburetor, and two single stage single speed turbo-superchargers were installed on each engine.

Each engine powered a set of Hamilton-Standard eight-blade, counter-rotating, superhydromatic propellers. The propellers were of the constant speed, full feathering, reversible-pitch type.

The XF-11 was an all-metal monoplane with tricycle landing gear. The ailerons and spoilers were mechanically synchronized. Conventional operation of the ailerons in the "UP" position for the left or right wing automatically actuated the spoilers.

The XF-11 evolved from an earlier Hughes project called the D-2. The D-2 had a similar configuration, but was constructed primarily of Duramold, a resin-impregnated plywood molded under heat and high pressure. It was powered by two 2800-hp Pratt & Whitney R-2800-49 radial engines driving three-bladed propellers.

The D-2 was designed for breaking speed records, but with the onset of the war in Europe in 1939 Hughes offered the design to the U.S. Army Air Corps with the hope of winning a military contract for a pursuit aircraft.

Army officials approved the project, but in May 1940 Hughes began to change his concept of the airplane's mission. For a while, it was improbably considered as a bomber, but it could not carry a significant payload. Hughes also recommended the D-2 for the bomber escort role, but it was not sufficiently maneuverable.

A RARE SHOT OF THE FIRST XF-11 WITH ITS DISTINCTIVE COUNTER-ROTATING PROPELLERS IS SEEN HERE ON THE RAMP AT HUGHES CULVER CITY AIRCRAFT FACILITY

In 1942, Lt. Gen. H.H. "Hap" Arnold approved procurement of the D-2 for testing at Wright Field. Hughes, however, wanted to test it himself first. The major subassemblies of the D-2 were constructed at the Hughes plant in Culver City and trucked to a hangar at Harper Dry Lake in the Mojave Desert for final assembly.

Initial ground trials in the spring of 1942 resulted in short hops above the runway and indicated some aileron instability and control problems. Hughes made some changes and the D-2 made its first real flight on 20 June 1943. Howard Hughes himself piloted that flight and a second one on the same day. He noted some additional controllability problems and grounded the airplane subject to modification.

An increase in wingspan failed to solve the problem. Hughes concluded that major changes would be required. While the D-2 was undergoing modifications at Harper Lake, the Army requested it be flown to Bolling Field, D.C. for inspection. Although the airplane was in no condition to be flown and the design remained unproven, Hughes proposed that the Army purchase three different production variants with various roles. Army officials were unimpressed and recommended in August 1943 that development of the airplane be discontinued.

Hughes continued to work on his own, modifying the airplane into a new configuration called the D-5. In November 1944, with work still not yet completed, the D-2/D-5 was lost in a mysterious fire. Hughes claimed that a lightning bolt struck the hangar at Harper Lake, setting it ablaze.

Hughes now set his sights on the all-metal XF-11. He reached an agreement with Army officials at Wright Field, Ohio, to build two experimental prototypes and 98 production airframes.