What object did Leonardo da Vinci design as a helical aerial machine?

Leonardo da Vinci designed an aerial screw as a helical machine intended to rise into the air.

His drawing, usually dated to about 1489, shows a large spiral surface wrapped around a central mast. Leonardo reasoned that if the spiral could rotate rapidly, it might screw itself upward through the air, much as a screw advances through a solid material.

The concept is often described as an ancestor of the helicopter, but it was not a working helicopter. Leonardo did not provide a practical engine, lightweight frame, or sufficiently effective rotor system. The proposed machine would also have been far too heavy for the human-powered mechanisms available in his era.

The aerial screw remains important because it shows Leonardo thinking about vertical flight. Its rotating helical principle differs from the bird-inspired flapping machines in his other studies.