Leonardo da Vinci sketched an ornithopter as an aircraft with wings modeled on a bat's anatomy.
An ornithopter is a machine intended to fly by flapping wings rather than using propellers, jets, or a fixed wing. Leonardo studied birds and bats carefully, especially their wing joints, feathers, and control surfaces. His notebooks contain several ideas for human-powered flying machines, including designs in which a pilot would move large wings through mechanical linkages.
These sketches were theoretical designs, not successful aircraft. A human could not generate enough power with the proposed body-powered mechanisms to sustain flight. Leonardo nevertheless recognized important aerodynamic problems, including weight, balance, lift, and the need for a strong but light frame.
An ornithopter is often confused with Leonardo's aerial screw, which used a helical rotor concept rather than flapping wings. The word itself comes from Greek roots meaning “bird” and “wing,” and modern experimental ornithopters use motors or remote control.