Leonardo da Vinci’s 1485 spiral-rotor flying-machine concept is called the aerial screw.
Leonardo sketched the design in the Codex Atlanticus. It resembles a large helical screw, with a linen-covered framework intended to rotate and push against the air. He reasoned that the device could rise if its screw surface moved rapidly enough.
The aerial screw is often described as an early helicopter concept, but it was not a practical helicopter and was never built by Leonardo. Its mechanism lacked a suitable lightweight engine and a proven method of generating enough continuous power.
The design is also commonly confused with Leonardo’s ornithopter, which imitates the flapping motion of bird wings. The aerial screw instead uses rotary motion, making it a distinct idea in the history of flight.