Sikorsky XV-2

The Sikorsky XV-2, company model S-57, was a planned experimental stoppable rotor aircraft, a convertiplane studied in a joint research programme of the United States Air Force and the United States Army. It was meant to take off and land like a helicopter and then cruise faster like an aeroplane. A single-blade, single-rotor system with a counterweight, driven by tip jets, would hover and fly slowly, and then retract into the upper fuselage when stopped so that the aircraft flew on delta wings with a single jet engine that was to be thrust-vectored for steering and anti-torque control. A prototype was given serial number 53-4403, but the programme was cancelled before construction began.