What rotary-wing concept did Leonardo da Vinci call an aerial screw?

Leonardo da Vinci called his rotary-wing concept an aerial screw.

Drawn around 1489, the aerial screw is one of Leonardo's best-known experiments in flight. The design shows a large helical surface wrapped around a central mast. Leonardo reasoned that, if the screw were turned rapidly, its surface might bite into the air and lift the structure upward.

The idea resembles a modern helicopter rotor in its proposed use, but the mechanism is not the same. Leonardo's drawing does not provide a practical engine, lightweight materials, or a tested control system. A team of people was apparently expected to turn the device's central mechanism, making sustained flight highly unlikely.

The aerial screw is also frequently called a “helicopter” in popular accounts, but that label is retrospective. The modern helicopter developed much later through advances in engines, aerodynamics, and rotor control. Leonardo's concept remains important as an early documented rotary-wing idea.