Leonardo da Vinci designed the aerial screw as a flying machine with a large helical rotor.
Leonardo sketched the design around 1489–1490 in the Codex Atlanticus. Its linen-covered, reed-framed helix was intended to push against the air and lift the craft, somewhat like a screw advancing through a solid material.
The aerial screw is often described as an early helicopter concept, but it was never built or tested by Leonardo. The design also lacked a practical engine and a reliable way to control flight. Modern reconstructions show that the original concept would not have flown as drawn.
It is sometimes incorrectly called the first helicopter. Helicopters use powered rotors, but Leonardo’s sketch was a theoretical Renaissance design rather than a functioning aircraft. The separate ornithopter concept used flapping wings, while the aerial screw relied on rotary motion.