Avrocar, with distinctive "flying saucer" shape, designed as a VTOL aircraft for DoD. At the time, concept considered promising way to incorporate VTOL capability into high-speed design. Annular nozzle equipped with some rather ingenious flow control mechanisms intended to produce lifting thrust during cruise and control moments during all phases of flight. Air for annular jet pumped by centrally mounted 5 ft diameter turbo rotor driven by exhaust of the 3 engines. In forward flight, body of the Avrocar intended to develop aerodynamic lift. Avrocar designed to have max speed of 300 mph at high altitude and range of 1,000 mi. 2 pilots sat in bubble- enclosed cockpits. Avrocar found to have narrow flight envelope in tests at NASA Ames Research Center and in flight tests by USAF. Was unstable and never operated at a height of over 4 ft. Work abandoned on concept due to limited flight success, existence of major mechanical problems caused by structural fatigue, and possible disenchantment over potential of unique flying saucer design.