Leonardo da Vinci studied ornithopters, aircraft intended to fly by flapping wings.
The word ornithopter comes from Greek roots meaning “bird” and “wing.” Leonardo examined bird anatomy, wing movement, balance, and air resistance in numerous notebooks. His proposed machines generally used a human operator to power or control wings made from wood, cloth, and other lightweight materials.
Leonardo understood that birds generate lift and propulsion through coordinated wing movements, but human muscles cannot provide enough power for a practical flapping aircraft of the type he sketched. His studies therefore remained designs and mechanical investigations rather than successful aircraft.
An ornithopter is different from Leonardo’s aerial screw. The ornithopter depends on flapping wings, while the aerial screw depends on a rotating helical surface. Modern ornithopters do exist as small experimental or model aircraft, but Leonardo’s large human-powered versions were never proven to fly.