Quadrotors

1963 experimental tiltrotor aircraft by Curtiss-Wright

experimental helicopter/airship by Piasecki Aircraft

proposed four-rotor derivative of the V-22 Osprey

1958 quadrotor helicopter prototype model by Curtiss-Wright

Human powered helicopter built for the Igor I. Sikorsky Human Powered Helicopter Competition

experimental gyroplane family

type of aircraft

Unmanned aerial vehicle