What flying-machine concept did Leonardo da Vinci call an “air screw”?

Leonardo da Vinci’s “air screw” is widely regarded as an early helicopter concept.

The design appears in his notebooks and uses a large helical surface made from reeds, linen, and wire. Leonardo reasoned that the screw could rise if it rotated rapidly enough to push against the air, much as a screw advances through a solid material.

The machine was not a functioning helicopter. Leonardo had no engine light or powerful enough to drive the mechanism, and the proposed structure would not have produced practical flight as drawn. Its importance lies in identifying the basic idea of rotary lift centuries before powered helicopters were developed.

The air screw is sometimes called a helicopter in popular accounts, but “helicopter” is a modern label. The word itself was coined in the nineteenth century. Modern helicopters use powered rotors, aerodynamic blades, and control systems that Leonardo’s sketch did not include.