What did Leonardo da Vinci call his 1489 rotating flying-machine concept?

Leonardo da Vinci called his 1489 rotating flying-machine concept an aerial screw.

The aerial screw is drawn as a large helical rotor supported by a frame. Leonardo proposed that the rotating surface could “screw” upward through the air, much as a screw moves through a solid material. The surviving sketch is one of his best-known studies of vertical flight.

The design is frequently described as a helicopter precursor, but it was not a helicopter in the modern engineering sense. Leonardo did not have an engine light and powerful enough to turn the rotor, and the proposed structure was too heavy for practical flight. The drawing therefore represents an important conceptual step rather than a working aircraft.

Its spiral shape is also unlike the powered rotors used by helicopters. Modern helicopters generate lift with rotating airfoils, while Leonardo’s design relied on a helical surface. The comparison is useful historically, but calling it a completed helicopter would be inaccurate.