Two early rotor-wing hybrids, the XV-1 (right) had small fixed wings so that the rotors provided little lift during cruise. The X-100 (left) was an early tilt-rotor design.
XV-1 was unloaded-rotor type which, after vertical takeoff, transitioned to fixed-wing flight with rotor free-wheeling as it went to minimum-drag profile in flat pitch. Engine drove pusher propeller and also provided pressurized air to 170-lb-thrust McDonnell pressure jet engines mounted at tip of each of three rotor blades. Pressurized air fed through hollow rotor blades, mixed with regular fuel, and ignited to produce thrust. Engines had been developed on McDonnell's previous helicopter, "Little Henry" (XH-20) and were very effective. XV-1's biggest advantage was ease and safety with which it could switch from one mode of flight to the other. Reached speeds of 200 mph and was quite maneuverable, requiring no special techniques. Like all VTOLs, consumed inordinate amounts of fuel and was relatively short-ranged. Program abandoned 1957 primarily because XV-1 underpowered for military tasks. Summer 55, set a speed record for helicopters of about 200 mph. Record, however, later rescinded because XV-1 was no longer recognized as helicopter. Length 26 ft; height 10 ft; weight 4277 lbs empty, 5505 lbs gross; top speed 200 mph.