What rotary flying device did Leonardo da Vinci sketch in the 1480s?

Leonardo da Vinci sketched an aerial screw as a proposed rotary flying device in the 1480s.

The design appears in Leonardo's notes from about 1489 and is often recognized as an early helicopter-like concept. It shows a large helical surface made from reeds and linen, mounted around a central structure. Leonardo reasoned that rotating the screw could push against the air and raise the machine.

The aerial screw was not a helicopter in the modern engineering sense. It had no engine, and the human power available in the proposed arrangement could not have produced enough lift to fly a full-sized machine. The sketch is therefore best understood as a theoretical study of rotary lift.

The design is often compared with later helicopters because both use rotating lifting surfaces. However, modern helicopter rotors are shaped airfoils and are driven by engines. Leonardo's aerial screw used a continuous helical surface, making it historically important as an imaginative precursor rather than a working aircraft.