What flying-machine design did Leonardo da Vinci model on bird flight?

Leonardo da Vinci’s bird-inspired flying-machine design was an ornithopter. An ornithopter is an aircraft intended to fly by flapping wings, rather than by using fixed wings or a rotor.

Leonardo studied birds extensively and filled notebooks with sketches of wings, feathers, joints and air currents. His proposed machine used a human pilot’s muscular power to move large wings, although a person could not realistically generate enough energy for sustained flight. The design therefore remained theoretical.

The word ornithopter comes from Greek roots meaning “bird” and “wing.” Modern ornithopters are usually small radio-controlled aircraft or experimental machines. Leonardo’s drawings are historically important because they show an attempt to apply anatomical observation and mechanical engineering to aviation centuries before powered airplanes became practical.