Which Leonardo da Vinci design is often called a prototype helicopter?

Leonardo da Vinci’s aerial screw is often called a prototype helicopter. His drawing shows a large helical rotor made from reed, linen, and wire, with a platform and several people turning a central mechanism.

Leonardo developed the concept around 1489. He proposed that the rotating screw might “screw” itself upward through the air, much as Archimedes’ screw moves through water. The design is one of his best-known studies of vertical flight, even though it could not have lifted its own weight with the materials and power available in Renaissance Italy.

The aerial screw was not a working helicopter and did not directly produce modern rotorcraft. Successful helicopters required lightweight engines, suitable rotors, and control systems developed much later. The first sustained, controlled helicopter flights occurred in the twentieth century.

It is also easy to confuse this design with Leonardo’s ornithopters. The distinction is mechanical: an ornithopter flaps wings, while the aerial screw relies on a rotating helical surface.