Leonardo da Vinci based his helical flying-machine design on an aerial screw.
Leonardo sketched the aerial screw in a manuscript now associated with the Codex Atlanticus, probably around 1489. The drawing shows a large helical sail or screw mounted around a central mast. Leonardo reasoned that, if the screw rotated rapidly, its surface might press against the air and lift the machine.
The concept resembles a helicopter rotor, but it was not a practical helicopter. The proposed frame was large, and the materials and human power available in Renaissance Italy could not have produced enough thrust. Modern historians therefore usually describe it as an important conceptual forerunner rather than a working aircraft.
The aerial screw is often called a “helicopter” in popular accounts, but that label can suggest a closer mechanical match than the design actually provides. Unlike a modern helicopter, Leonardo’s sketch did not include an engine, powered rotor system, or a method for controlling flight. Its importance lies in applying a screw principle to vertical lift.