What rotating flying-machine concept did Leonardo da Vinci call an aerial screw?

Leonardo da Vinci’s aerial screw was a rotating flying-machine concept with a helical, screw-like rotor.

Leonardo drew the design in the Codex Atlanticus, generally dated to around 1489. The machine featured a large spiral surface made from reed, linen, and wire. Leonardo reasoned that rotating this helical structure could “screw” upward through the air, much as a screw moves through a material.

The aerial screw is often described as a distant conceptual ancestor of the helicopter, but it was not a working helicopter. Leonardo did not provide a practical engine capable of turning the rotor, and the materials and aerodynamic arrangement would not have produced efficient modern vertical flight.

The idea is important because it shows Leonardo thinking about lift from rotating surfaces rather than only flapping wings. It is also frequently confused with a propeller: a propeller pushes air backward to create forward motion, while the aerial screw was intended to generate upward movement.