Leonardo da Vinci designed ornithopters, human-powered flying machines with flapping wings inspired by birds.
The word ornithopter refers to any aircraft that flies by flapping wings, rather than by fixed wings or rotary blades. Leonardo studied birds, bats, and the mechanics of flight in numerous notebooks, then translated those observations into machine designs. His sketches include wing structures, harnesses, and mechanisms intended to transmit a pilot's movement to the wings.
Leonardo understood several important aerodynamic problems, including the need for a strong but lightweight frame and the difficulty of generating enough power. Human beings cannot flap wings with the force and endurance required for sustained powered flight, so his ornithopters were not practical aircraft.
The designs nevertheless mattered historically because they treated flight as a problem of anatomy, mechanics, and air movement rather than pure fantasy. Modern experimental ornithopters use motors or other external power sources. Leonardo's machines are therefore examples of early biomimetic engineering: technology modeled on observed natural forms.