I photographed this 1931 Pitcairn-Cierva PCA-2 Autogiro “Miss Champion” in the EAA museum at Oshkosh during a trip for the 2024 EAA AirVenture.
The autogiro, the direct predecessor of the helicopter, used large unpowered rotor blades to provide lift through autorotation, much like a maple tree “helicopter” seed as it spins to the ground. Instead of falling to the ground like a seed, however, the autogiro could keep flying because it was pulled through the air by an engine-driven propeller, much like a conventional airplane. The spinning rotor blades, acting like the wings of an airplane, permitted very slow flight and nearly vertical landings.