What spiral aircraft concept did Leonardo da Vinci draw in the Codex Atlanticus?

Leonardo da Vinci’s spiral aircraft concept in the Codex Atlanticus was the aerial screw.

Leonardo drew the aerial screw around 1489, presenting a machine with a helical surface intended to “screw” upward through the air. The design is frequently described as an early conceptual ancestor of the helicopter, although it could not have lifted itself with the materials and power available in Renaissance Italy.

The drawing shows a large frame, a central mast, and a linen-covered helical structure. Leonardo’s idea depended on rotating the screw rapidly enough to generate upward force. Modern reconstructions have demonstrated the design’s visual and mechanical interest, but they do not turn the sketch into a working Renaissance helicopter.

The aerial screw is sometimes incorrectly called the first helicopter. It was instead a speculative flight machine that anticipated the principle of a rotating lifting surface. Leonardo’s notebooks contain several other aviation studies, including gliders, parachutes, and flapping-wing mechanisms.