Which Leonardo da Vinci design is known as the aerial screw?

Leonardo da Vinci’s flying-machine concept known as the aerial screw is often considered an early helicopter idea. He sketched it around 1489, showing a large helical surface intended to rise by turning through the air.

Leonardo’s notes suggested that a linen-covered frame might act like a screw in a solid material. The machine was probably intended to be powered by people turning a central mechanism, although the drawing does not provide a complete practical engine or control system.

The aerial screw would not have flown with the materials and power sources available in Renaissance Italy. Its large rotor concept nevertheless resembles the basic lifting principle of a helicopter, in which rotating blades push air downward to generate upward force.

The design is sometimes called a helicopter prototype, but that label needs care. It was a conceptual sketch, not a working aircraft, and its operation differs substantially from modern rotorcraft.