What rotating-blade aircraft did Leonardo da Vinci describe in a 1489 design?

Leonardo da Vinci described an aerial screw, an early rotating-blade aircraft concept, in a design from 1489.

The drawing shows a large helical rotor made from a reed framework covered with linen. Leonardo reasoned that the rotating screw could “screw” upward through the air in a manner analogous to a screw moving through a solid material. The machine was intended to be powered by people turning a central mechanism.

The aerial screw was not a working helicopter. Renaissance materials and human muscle power could not provide the thrust needed to lift the structure and its operators. Modern helicopters use powered rotors, aerodynamic airfoils, and carefully controlled lift rather than a cloth-covered spiral surface.

The design is still historically significant because it anticipated the general principle of vertical flight. It is commonly called Leonardo’s helicopter, although “aerial screw” is the more precise name for his proposal.