What shape did Leonardo da Vinci use for his proposed aerial screw?

Leonardo da Vinci used a helical screw shape for his proposed aerial screw.

The design, sketched around 1489, consists of a large spiral surface mounted on a vertical shaft. Leonardo suggested that turning the shaft could make the screw “drill” upward through the air, an idea often compared with the operating principle of a helicopter rotor.

The aerial screw was not a helicopter in the modern engineering sense. Leonardo did not provide a practical engine, lightweight materials, or a complete control system capable of lifting the proposed machine.

Its importance lies in the early recognition that a rotating helical surface might generate upward motion. Modern helicopters use powered rotors with airfoils, not a fabric-covered spiral screw.