What flying-machine concept did Leonardo da Vinci model on a screw?

Leonardo da Vinci’s screw-based flying-machine concept was called the aerial screw.

Leonardo sketched the device around 1489. Its design used a helical surface made from linen stretched over a reed frame, with a central mast and rotating mechanism. Leonardo appears to have believed that rotating the screw could make it rise through the air.

The aerial screw is frequently described as a distant precursor to the helicopter, but it was not a practical helicopter and was never demonstrated as a successful powered aircraft. Its proposed lifting principle also differs from the aerodynamic rotors used by modern helicopters.

The idea is sometimes incorrectly called Leonardo’s helicopter. “Aerial screw” is the more precise historical name for the sketch and its concept.