Vought XF5U The Vought XF5U " Flying Flapjack " was an experimental U . S . Navy fighter aircraft designed by Charles H . Zimmerman during World War II . This unorthodox design consisted of a flat , somewhat disc - shaped body ( hence its name ) serving as the lifting surface . Two piston engines buried in the body drove propellers located on the leading edge at the wingtips . Design and development . 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 , 600 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 . Normally , a wing with such a low aspect ratio will suffer from very poor performance due to the degree of induced drag created at the wingtips , as the higher pressure air below spills around the wingtip to the lower - pressure region above . In a conventional aircraft , these wingtip vortices carry a lot of energy with them and hence create drag . The usual approach to reducing these vortices is to build a wing with a high aspect ratio , i . e . one that is long and narrow . However , such wings compromise the maneuverability and roll rate of the aircraft , or present a structural challenge in building them stiff enough . The XF5U attempted to overcome the tip vortex problem using the propellers to actively cancel the drag - causing tip vortices . The propellers are arranged to rotate in the opposite direction to the tip vortices , with the aim of retaining the higher - pressure air below the wing . With this source of drag eliminated , the aircraft would fly with a much smaller wing area , and the small wing would yield high maneuverability with greater structural strength . The propellers envisioned for the completed fighter were to have a built - in cyclic movement like a helicopter ' s main rotor , with a very limited ability to tilt up and down to aid the aircraft in maneuvering . An ejection seat was fitted to allow the pilot to clear the massive propellers in the event of an in - flight emergency . Although the prototype was unarmed , a combination of machine guns and cannons would have been installed under the nose . Testing and evaluation . The XF5U design was promising : specifications given at the time promised great maneuverability and speeds up to 550 mph ( 885 km / h ) . 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 . 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 . The only completed XF5U - 1 proved to be so structurally solid that it had to be destroyed by a wrecking ball .