Leonardo da Vinci studied ornithopters, aircraft concepts intended to fly by flapping wings like birds or bats.
His drawings show several arrangements of wings, frames, and control systems. Some concepts placed the pilot inside a machine and imagined human muscles powering the wing movement through pedals, levers, or cranks. Leonardo carefully observed birds and investigated lift, balance, and the mechanics of flight.
The best-known designs were theoretical studies rather than successful aircraft. Human power is not sufficient to flap wings large enough to lift a person using the mechanisms Leonardo proposed. His work nevertheless helped develop the vocabulary of flight engineering by treating air as a physical medium that could support a machine.
An ornithopter differs from a glider, which has fixed wings, and from a helicopter, which uses rotating blades. Leonardo also drew fixed-wing and rotor-like ideas, so not every flying-machine sketch should be called an ornithopter.