What rotating aerial device did Leonardo da Vinci call an aerial screw?

Leonardo da Vinci designed a rotating aerial device known as the aerial screw.

The aerial screw was a large helical structure covered with a material such as linen. Leonardo reasoned that if the screw rotated rapidly, its spiral surface might press against the air and lift the machine upward. The concept was recorded in a notebook entry dated 1489.

The device is frequently described as an early helicopter or helicopter prototype, but it was not a helicopter in the modern engineering sense. Leonardo had no lightweight engine capable of supplying the necessary power, and the design was never demonstrated as a practical aircraft.

Its historical importance is conceptual. The aerial screw anticipated the idea of rotary-wing lift, while modern helicopters use powered rotors with carefully shaped blades and control systems. Leonardo’s other flight studies focused on flapping wings and parachute descent.