Leonardo da Vinci sketched an aerial screw as a proposed flying machine with a rotating helical sail.
His drawing, made around 1489, shows a large spiral surface mounted on a framework. Leonardo reasoned that the spiral could move upward by “screwing” through the air, much as a screw moves through a solid material. The concept is often compared with the modern helicopter, although it could not have flown as drawn.
The aerial screw was a theoretical design rather than a working aircraft. Its heavy materials and lack of a suitable power source made human-powered flight impractical in the fifteenth century. Modern experiments have built small models to explore the idea, but these do not make Leonardo’s original machine a functioning helicopter.
The aerial screw is sometimes called Leonardo’s helicopter, but that name is a modern comparison, not the design’s historical title. Leonardo’s notebooks contain several other flight studies, including a parachute and flapping-wing machines.