Leonardo da Vinci's ornithopter was a winged machine modeled on the flapping motion of birds and bats. The word ornithopter means a machine that flies by means of wings flapping like those of a bird.
Leonardo filled notebooks with studies of bird flight, wing structure, air resistance, and the muscles needed to move wings. His proposed human-powered machines generally placed the pilot inside a frame connected to large wings. The pilot would use pedals, levers, or other mechanisms to flap them.
The design is often confused with Leonardo's glider concepts. A glider uses fixed wings and gains lift by moving through the air, while an ornithopter depends on flapping wings. Leonardo understood that human muscles could not easily provide the power required for a large flapping aircraft, which made practical success unlikely.
No Leonardo ornithopter is known to have flown. His work was nevertheless important in the history of flight because it treated flying as a mechanical and biological problem. His observations of birds helped establish ideas later used by aerodynamic engineers.