Which Leonardo da Vinci design used a helical screw to suggest a helicopter?

Leonardo da Vinci’s design that used a helical screw to suggest a helicopter was the aerial screw.

Leonardo drew the concept around 1489–1490 in the manuscript known as the Codex Atlanticus. His drawing shows a large spiral rotor made from linen stiffened with reeds. Leonardo wrote that, if the screw were properly made and rapidly rotated, it could rise through the air.

The aerial screw is often described as an ancestor of the modern helicopter, but it was not a working helicopter. Leonardo did not have an engine light or powerful enough to turn the rotor, and the design’s weight and aerodynamic limitations would have prevented practical flight with the materials shown.

The idea is also sometimes confused with Leonardo’s ornithopter designs, which imitate the flapping motion of birds. The aerial screw instead relies on rotary motion and is one of the clearest examples of Leonardo imagining vertical flight centuries before powered helicopters became possible.