Leonardo da Vinci designed the aerial screw as a flying-machine concept with a rotating helical rotor.
Leonardo sketched the device around 1489 in his Codex Atlanticus. Its linen-covered, reed-and-wire structure was intended to push against the air as the rotor turned, somewhat like a modern helicopter rotor.
The aerial screw is often called a helicopter prototype, but it was not a working helicopter. Leonardo had no lightweight engine capable of supplying the necessary sustained power, and the design also lacked a practical method for controlling flight.
The idea reflects Leonardo’s study of birds, air resistance, screws, and mechanical lifting. Modern helicopters use powered rotors, but their aerodynamics and control systems are much more advanced than Leonardo’s concept. The design is also sometimes confused with his ornithopter, which used flapping wings rather than a helical rotor.