What spiral-shaped aerial machine did Leonardo da Vinci design in the 1480s?

Leonardo da Vinci designed an aerial screw, a spiral-shaped flying-machine concept, in the 1480s.

The drawing appears in the Codex Atlanticus and shows a large helical surface wrapped around a central mast. Leonardo reasoned that the screw might rise by pressing against the air, in a way analogous to a screw moving through a solid material. The concept is often described as an early helicopter idea.

The aerial screw was not a working helicopter. Its proposed linen-covered reed frame was too large and heavy, and the design lacked a suitable power source. Modern helicopters use powered rotors with carefully shaped blades, whereas Leonardo’s machine depended on a broad spiral surface and human effort.