Leonardo da Vinci’s aerial screw used a helical surface to imitate the screw-like action of a helicopter.
Leonardo sketched the aerial screw in 1489. The design consisted of a large spiral made from reed, linen, and wire, mounted on a central platform. He reasoned that if the spiral rotated rapidly, its surface could push against the air and lift the structure.
The drawing is often called a helicopter ancestor, but it was not a helicopter in the modern sense. It had no engine, and the human power available in the fifteenth century could not have spun the large screw fast enough for practical flight. The concept nevertheless anticipated the importance of rotating airfoils.
Leonardo’s aerial screw also differs from his ornithopter studies. An ornithopter depends on flapping wings modeled on birds, while the aerial screw relies on rotation and a helical lifting surface.