The Vought V-173 "Flying Pancake" designed by Charles H. Zimmerman was an American experimental test aircraft built as part of the Vought XF5U "Flying Flapjack" World War II United States Navy fighter aircraft program. The first flight of the V-173 was on 23 November 1942 with Vought Chief Test Pilot Boone Guyton at the controls. The aircraft's most significant problem concerned its complicated gearbox that routed power from the engines to its two long propeller shafts. The gearbox produced unacceptable amounts of vibration in ground testing, delaying the aircraft's first test flight for months. Flight testing of the V-173 went on through 1942 and 1943 with 190 flights, resulting in reports of UFOs from surprised Connecticut locals. Charles Lindbergh piloted the V-173 during this time and found it surprisingly easy to handle and exhibiting impressive low-speed capabilities.

Both aircraft featured an unorthodox "all-wing" design consisting of a flat, somewhat disk-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.