What spiral-shaped aircraft concept did Leonardo da Vinci sketch in the 1480s?

Leonardo da Vinci sketched an aerial screw as a spiral-shaped aircraft concept in the 1480s.

The design appears in the Codex Atlanticus and consists of a large helical surface wrapped around a central mast. Leonardo reasoned that if the spiral were turned rapidly, it might screw itself upward through the air. The idea resembles the principle of a modern helicopter rotor, although the proposed mechanism and materials could not have produced practical flight.

The aerial screw is often described as a precursor to the helicopter, not as an actual helicopter. It had no engine capable of supplying the necessary power, and its heavy linen-and-reed structure would have created major engineering problems.

Leonardo also investigated flapping-wing machines. Those sketches belong to the ornithopter tradition and should not be confused with the rotating aerial screw.