Leonardo da Vinci called his spiral flying-machine concept the aerial screw.
The design appears in Leonardo’s notes from around 1489 and consists of a large helical surface wrapped around a central mast. He reasoned that if the screw could be rapidly rotated, its spiral surface might push against the air and lift the machine.
The aerial screw was not a working helicopter. Leonardo lacked a sufficiently light engine and suitable materials, and the design would probably have required more power than human operators could provide. Modern commentators nevertheless regard it as an early conceptual ancestor of the helicopter.
The aerial screw is sometimes confused with Leonardo’s bird-inspired ornithopter. The two ideas differ: the ornithopter depends on flapping wings, while the aerial screw depends on rotary motion and a helical rotor.