Autogiro

autogiro, also spelled autogyro, rotary-wing aircraft, superseded after World War II by the more efficient helicopter. It employed a propeller for forward motion and a freely rotating, unmotorized rotor for lift. In searching for an aircraft that could be slowed down in flight and landed vertically, experimenters built many prototypes that were difficult to control in flight.

By 1923 the Spaniard Juan de la Cierva had discovered how to articulate (hinge) the rotor blades at the hub, thus allowing them to respond differentially to the aerodynamic and centrifugal forces involved in rotation. This made autogiro flight possible for the first time and led to later development of the helicopter. An autogiro had to taxi for takeoff, and it required a forward airspeed in order to drive its rotor. By contrast, a helicopter, with its engine-driven rotor, is capable of both vertical takeoff and landing.

The gyroglider is an unpowered autogiro designed to glide freely on the rotary wings after release from towing.