Leonardo da Vinci designed an ornithopter, an aircraft intended to fly with birdlike wings operated by human muscles.
Leonardo studied birds and bats extensively because he believed their flight could reveal principles useful for human aviation. His notebooks contain several flapping-wing machines, including designs with wings, frames, pedals and levers. In these concepts, a pilot would lie or stand inside the structure and use body power to move the wings.
An ornithopter is defined by its flapping wings, rather than by an engine, propeller or fixed wing. Leonardo's designs were ingenious mechanical studies, but the available materials and human muscle power could not produce enough lift for sustained flight. No surviving evidence shows that he built a successful full-scale flying machine.
Leonardo's work helped organize observations about lift, drag and wing movement, even though powered flight remained impossible for him. Modern ornithopters have been built as small mechanical or remote-controlled aircraft, and some have flown using engines or electric motors.