Leonardo da Vinci designed an aerial screw with a helical rotor intended to rise vertically.
The drawing, usually dated to around 1489, shows a large spiral surface wrapped around a central mast. Leonardo reasoned that if the screw were turned rapidly, its helical surface might push against the air and lift the machine. The idea resembles the basic visual form of a modern helicopter rotor, although the proposed mechanism was very different.
Leonardo’s aerial screw was a theoretical design, not a functioning helicopter. The materials and human-powered drive available in the Renaissance could not provide enough lift, and the craft lacked the control systems needed for safe flight. The air would also pass through the open structure rather than behave like a solid medium.
The design is sometimes called a proto-helicopter, but that label can overstate its similarity to powered helicopters. Its importance is that Leonardo explored vertical lift independently of birdlike flapping wings.