Leonardo da Vinci proposed a helicopter-like aircraft with a large helical rotor called the aerial screw.
Leonardo drew the aerial screw around 1489–1490 in his Codex Atlanticus. His design used a linen-covered helical surface wound around a light frame. He reasoned that the screw could rise if turned rapidly, much as a screw advances through a solid material.
The drawing is often described as an early helicopter concept, but it was not a practical helicopter in the modern engineering sense. Leonardo did not provide a workable engine, lightweight structural materials, or a complete method for producing enough power. The machine would probably have been too heavy for its proposed human-powered operation.
People sometimes call it the first helicopter, but that claim needs qualification: it was an important conceptual predecessor, not a flown aircraft. Modern helicopters use powered rotating blades that generate lift through aerodynamic airfoils, a principle Leonardo’s sketch did not fully develop.