What energy source did Leonardo da Vinci propose for his flying screw?

Leonardo da Vinci proposed human muscle power as the energy source for his flying screw.

Leonardo’s aerial-screw sketch, made around 1489, shows a helical surface wrapped around a mast. He reasoned that if the screw rotated rapidly, its spiral form might press against the air and rise, an idea often compared with the principle of a modern helicopter rotor. His notes indicate that people would turn the mechanism through a system of bars or other mechanical supports.

This was a conceptual study, not a demonstrated aircraft. Human muscles cannot provide enough continuous power for a machine of the design’s likely mass, and the sketch does not provide the aerodynamic details needed for stable, controlled flight. The idea also lacked a modern engine and rotor-control system.

The aerial screw is therefore best understood as an early speculation about vertical flight. It is distinct from Leonardo’s flapping-wing ornithopters, which imitated birds rather than using a rotating helical surface.