Leonardo da Vinci designed the aerial screw as a proposed flying machine in 1489.
His drawing shows a large helical surface wrapped around a central mast. Leonardo reasoned that, if the screw turned quickly enough, its linen-covered surface might push against the air and lift the structure, much as a screw advances through water.
The design was an idea rather than a tested aircraft. It had no practical engine, and the materials and power available in Renaissance Italy could not have made it fly. Modern historians often describe it as an early conceptual ancestor of the helicopter, not as a working helicopter.
The aerial screw is also commonly confused with Leonardo's bird-inspired ornithopter designs. The screw uses rotary lift, while an ornithopter depends on flapping wings. Later helicopter development required lightweight engines, rigid rotors, and aerodynamic knowledge unavailable to Leonardo.