The Vought XF5U "Flying Flapjack" was an experimental U.S. Navy fighter aircraft designed by Charles H. Zimmerman for Vought during World War II. This unorthodox design consisted of a flat, somewhat disc-shaped body (resembling a flying flapjack/pancake, hence its nickname) serving as the lifting surface.[1] Two piston engines buried in the body drove propellers located on the leading edge, at the wingtips.

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A developed version of the original V-173 prototype, the XF5U-1 was a larger aircraft. Of all-metal construction, it was almost five times heavier, with two 1,400 hp (1,193 kW) Pratt & Whitney R-2000 radial engines. The configuration was designed to create a low aspect ratio aircraft with low takeoff and landing speeds but high top speed. The aircraft was designed to keep the low stall speed and high angle of attack from the V-173 prototype while providing for better pilot visibility, cockpit comfort, less vibration, and provisions to install armament. This included a cockpit redesign moving the cockpit from the leading edge of the wing to a nose nacelle that extended further in front of the leading edge.

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The XF5U design was promising: specifications given at the time promised great maneuverability and speeds up to 452 mph (727 km/h).[6] However, it came at the time when the United States Navy was switching from propeller driven to jet propelled aircraft. By 1946, the XF5U-1 project was already long over its expected development time, and well over budget.[2] With jet aircraft coming into service, the Navy finally canceled the project on 17 March 1947, and the prototype aircraft (V-173) was transferred to the Smithsonian Museum for display. Although two aircraft were constructed, a lone XF5U-1 underwent ground runs but never overcame vibration problems. Taxi trials at Vought's Connecticut factory culminated in short "hops" that were not true flights.[7][8] The only completed XF5U-1 proved to be so structurally solid that it had to be destroyed with a wrecking ball.