What rotor-based flying machine did Leonardo da Vinci call an aerial screw?

Leonardo da Vinci called his rotor-based flying machine an aerial screw.

Leonardo sketched the aerial screw around 1489. The machine had a large helical surface wrapped around a central mast, with a frame intended to rotate the structure. His notes suggested that if the screw-shaped rotor were turned quickly enough, it could rise by pushing against the air.

The design is often described as a helicopter ancestor, but it was not a helicopter in the modern engineering sense. Leonardo had no lightweight engine capable of supplying the required power, and the proposed materials and human-powered mechanism would not have produced practical flight. The drawing is better understood as an early exploration of vertical lift.

The aerial screw must also be distinguished from Leonardo’s flapping-wing ornithopter. The ornithopter copied bird motion, whereas the aerial screw used rotary motion. Modern helicopters use powered rotors with carefully shaped blades, control systems, and engines, technologies unavailable in Renaissance Italy.