What flying-machine design did Leonardo da Vinci model on a helical screw?

Leonardo da Vinci’s helical flying-machine design is called the aerial screw.

Leonardo drew the aerial screw around 1489, presenting a large helical surface mounted on a central structure. His notes suggested that rotating the screw could make it rise through the air, an idea frequently compared with the principle of a helicopter rotor. The proposed machine was far larger than a practical hand-powered aircraft.

The aerial screw is best understood as a visionary mechanical study rather than a working helicopter. Its linen-covered helical surface and supporting framework would have been heavy, and Renaissance power sources could not provide the required lift and rotation.

People sometimes call it the first helicopter, but that label is only an analogy. Modern helicopters use powered rotors that generate lift through aerodynamic blades. Leonardo’s drawing anticipated a broad idea about vertical flight without supplying a workable modern rotor system.