Leonardo da Vinci based one flying-machine design on the motion of a bird’s wings: the ornithopter.
An ornithopter is an aircraft intended to fly by flapping wings rather than by using fixed wings, propellers, or jet engines. Leonardo studied birds and bats and filled notebooks with observations about wing structure, airflow, balance, and muscular effort. His proposed machines included wings operated by a pilot’s arms and legs.
Leonardo’s ornithopter was never demonstrated as a successful human-carrying aircraft. Human muscles cannot provide enough sustained power for a practical flapping-wing machine of that scale. The design is nevertheless important because it shows Leonardo applying anatomical observation and mechanical analysis to aviation. It is sometimes confused with his aerial screw, which used a rotating helical surface instead of flapping wings. Modern ornithopters, including small robotic aircraft, continue to explore the same basic principle.