Which Leonardo da Vinci design featured wings that flapped like a bird's?

Leonardo da Vinci's ornithopter design featured wings intended to flap like a bird's.

An ornithopter is an aircraft that gains thrust from flapping wings. Leonardo studied birds and bats and produced several flying-machine sketches, including designs with large wings, a pilot position, and mechanical systems for moving the wings. He hoped that careful observation of nature could reveal principles useful for human flight.

His ornithopters were never practical aircraft. A human pilot could not generate enough power through the proposed pedals, levers, or crank mechanisms to create sustained flight. The machines also lacked the lightweight engines and aerodynamic understanding later needed for powered aviation.

The word ornithopter comes from Greek roots meaning bird and wing. Unlike a glider, which relies on fixed wings, an ornithopter depends on repeated wingbeats. Leonardo's work therefore belongs to the long history of bio-inspired flight concepts, even though no Leonardo aircraft actually flew.