Leonardo da Vinci’s aerial screw was a rotating-screw machine intended to rise through the air.
Leonardo sketched the design in 1489. It had a large helical surface made from linen held on a framework of reeds. His notes suggested that if the screw rotated rapidly, the helical surface would bite into the air and lift the machine upward.
The aerial screw is often described as a forerunner of the helicopter, but it was not a functioning helicopter. The proposed human-powered mechanism could not produce enough lift with the materials and power available in the fifteenth century. Modern helicopters use powered rotors with carefully shaped blades rather than one large fabric screw.
The idea still matters in aviation history because Leonardo recognized that a rotating lifting surface could provide vertical flight. The sketch is sometimes incorrectly called the first helicopter; more accurately, it was an early conceptual study of rotary-wing flight.