What flying-machine design did Leonardo da Vinci call an “aerial screw”?

Leonardo da Vinci’s “aerial screw” was an early helicopter concept.

Leonardo drew the aerial screw in the Codex Atlanticus around 1489. The design showed a large helical rotor made from reeds, linen, and a starch-like coating. Leonardo reasoned that turning the screw could make it rise by pushing against the air.

The design was not a working helicopter. Its proposed materials and human-powered mechanism could not provide enough lift, and Leonardo did not build a full-scale flying machine. Modern helicopters use powered rotors shaped according to aerodynamic principles that were not yet understood in Renaissance Europe.

The aerial screw is often called a helicopter because its basic idea resembles a vertical-lift rotorcraft. However, the word “helicopter” was coined centuries later, and Leonardo’s drawing was a speculative invention rather than a tested aircraft.