Which Leonardo da Vinci machine used a spiral cylinder to compress and move air?

Leonardo da Vinci’s helical air screw was a machine concept using a spiral cylinder to compress and move air.

Leonardo drew the aerial screw in 1489, describing a linen-covered helical structure supported by a reed framework. He reasoned that turning the screw could make it rise by acting on the air, an idea that resembles the principle of a modern rotorcraft. The drawing is famous as an early helicopter-like concept, but it is distinct from Leonardo’s other air-moving designs.

The proposed machine was not tested as a practical aircraft in Leonardo’s lifetime. Its linen surface, scale, and human-powered operation would have created serious engineering limitations. Modern historians generally treat it as an important conceptual study rather than a functioning helicopter.

The aerial screw is also called the “helicopter” or “air screw” in popular accounts. That terminology can cause confusion because the modern helicopter uses rotating blades that generate lift, while Leonardo’s design used a continuous helical surface.