What did Leonardo da Vinci call his 1489 device with a helical rotor?

Leonardo da Vinci called his 1489 helical-rotor concept an aerial screw. The drawing shows a large spiral surface wrapped around a central axis, intended to rise by pushing against the air when rotated.

Leonardo compared the principle to a screw moving through a solid material. His notes proposed a machine roughly 5 meters wide, with a reed-and-cane frame covered by linen stiffened with starch. The design also included a platform and a rotating mechanism, but it did not contain an engine capable of supplying enough power.

The aerial screw is commonly described as a conceptual ancestor of the helicopter, not as a working helicopter. Modern helicopters use powered rotors and aerodynamic blades rather than Leonardo's continuous helical surface. Leonardo's study nevertheless anticipated the important idea that a rotating lifting surface could support vertical flight.