What kind of machine did Leonardo da Vinci sketch to imitate a bird's flapping flight?

Leonardo da Vinci sketched an ornithopter to imitate a bird's flapping flight. An ornithopter is an aircraft designed to generate lift through the movement of wings rather than through fixed wings alone.

Leonardo studied birds, bats, and the movement of their wings in detail. His flying-machine drawings include frames, wings, straps, and mechanical arrangements in which a human pilot would supply power by moving arms or legs. Some designs used wings modeled more closely on bats than on birds.

The major difficulty was power. Human muscles cannot produce enough sustained energy to lift a person with flapping wings of the required size, so Leonardo's proposed machines were not practical aircraft. He nevertheless recognized important aerodynamic questions involving lift, drag, balance, and wing structure.

An ornithopter is not the same as a glider, which relies on fixed wings and forward motion, or a helicopter, which uses rotating blades. Leonardo's work is significant as an early systematic attempt to study powered flight by biological analogy.