What Leonardo da Vinci design is a precursor to the modern helicopter?

Leonardo da Vinci’s aerial screw is often identified as a precursor to the modern helicopter.

The design appears in Leonardo’s flight studies from about 1489–1490. A spiral surface wrapped around a central shaft was supposed to rotate and rise through the air. Leonardo’s reasoning anticipated the idea that a rotating lifting surface could generate upward force.

Calling it a helicopter is an anachronism: the helicopter depends on powered rotors, engines, and aerodynamic principles developed centuries later. The aerial screw also lacked a practical power source and would probably have been too heavy. Nevertheless, it is a clear early attempt to solve vertical flight directly, unlike Leonardo’s gliding and flapping-wing proposals.