Leonardo da Vinci designed the aerial screw as a flying machine with a helical rotor and a central mast.
Leonardo recorded the design in a manuscript generally dated to about 1489. The machine has often been compared with a modern helicopter because its rotating spiral surface was intended to lift the craft vertically. Leonardo reasoned that a screw-shaped surface could move through the air in a way similar to a screw moving through a solid material.
The aerial screw was never demonstrated as a working aircraft. Its proposed rotor was far too large and heavy for the materials and power sources available in Renaissance Europe. It is therefore better described as an early theoretical helicopter concept than as an actual helicopter. It is also distinct from Leonardo’s ornithopter, which depended on flapping wings rather than a rotating screw.