Hughes XV-9A was an experimental American high-speed research helicopter developed in the 1960s to test "hot cycle" propulsion, a system that eliminated the need for a heavy gearbox and tail rotor. First flown on November 5, 1964, the aircraft proved the feasibility of the concept but was ultimately cancelled due to high noise levels and excessive fuel consumption Design and Propulsion The XV-9A, also known as the Hughes Model 385, used a unique tip-jet propulsion system to drive its three-blade