Leonardo da Vinci sketched an aerial screw as a spiral-bladed device intended to lift into the air.
The design appears in Leonardo's Codex Atlanticus and is usually dated to around 1489. It shows a large helical surface, probably made from a reed framework covered with linen, turning around a central shaft. Leonardo reasoned that the spiral could push against the air much as a screw moves through water.
The aerial screw is often called a helicopter ancestor, but it was not a practical helicopter. Leonardo did not have an engine light and powerful enough to turn it, and the proposed structure would have been very heavy. Modern reconstructions generally treat it as an important conceptual step rather than a successful aircraft.
It is also easy to confuse the aerial screw with Leonardo's parachute and ornithopter. The screw was meant to rise by rotating a helical surface; the parachute was intended to slow a descent; and the ornithopter imitated bird flight with flapping wings. These sketches show Leonardo exploring several different solutions to human flight.