What aircraft-like device did Leonardo da Vinci call an aerial screw?

Leonardo da Vinci’s aircraft-like aerial screw is commonly regarded as an early helicopter concept.

Leonardo sketched the aerial screw in a manuscript dated to about 1489. The machine featured a large helical rotor made from reeds, linen, and wire, with a platform and supporting structure beneath it. His notes suggested that rotating the screw could make it rise by pressing against the air, an idea analogous to a screw advancing through a solid material.

The aerial screw was not a practical helicopter and was never demonstrated as a powered aircraft. Its proposed human-powered mechanism could not have supplied enough energy for sustained flight. The design is still historically important because it shows Leonardo reasoning about vertical lift centuries before powered helicopters became possible. It should not be confused with his ornithopter, which sought lift through flapping wings.