What flying-machine concept did Leonardo da Vinci design as a spiral air screw?

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

Leonardo sketched the aerial screw around 1489, during his studies of flight and the movement of air. The design used a large helical surface, or screw, intended to rotate and lift the machine upward. Its shape is often compared with the rotor of a modern helicopter.

The aerial screw was a theoretical design rather than a proven aircraft. Leonardo had no lightweight engine capable of turning the mechanism, and the proposed materials would have made the machine too heavy for human-powered flight. Modern experiments have built models inspired by the drawing, but these are reconstructions, not evidence that Leonardo flew one.

It is commonly called a “helicopter” in popular summaries, but “aerial screw” is the more historically precise name for Leonardo’s concept. The sketch belongs to his broader investigation of birds, air resistance, wings, and mechanical force.