Sikorsky S-72

The Sikorsky S-72 was an experimental compound helicopter that Sikorsky developed as the Rotor Systems Research Aircraft for NASA and the US Army, a testbed for rotor and propulsion systems at high speed. Sikorsky won the contract for two aircraft in January 1974, and the aircraft were modified S-67 Blackhawks with the rotor and gearbox of the S-61. It could be fitted with wings and General Electric TF34 turbofans to study compound configurations at speeds up to 300 knots, and could even fly as a fixed-wing aircraft without a main rotor. The joint NASA and Army project began in December 1970 and the first flight was on 12 October 1976.