Which Leonardo da Vinci design imitated bird flight by using flapping wings?

Leonardo da Vinci’s ornithopter design imitated bird flight by using flapping wings.

An ornithopter is an aircraft intended to fly through the motion of wings that flap rather than rotate like helicopter blades. Leonardo studied birds extensively and produced several flying-machine sketches based on their anatomy and wing movements. His designs included mechanisms intended to transmit the pilot’s effort to the wings.

Leonardo’s ornithopters were never proven capable of carrying a person into sustained flight. Human muscles cannot deliver the same power-to-weight performance as many flying birds, and the proposed structures would have been too heavy or mechanically inefficient.

The term ornithopter applies to a whole class of aircraft, not only Leonardo’s drawings. This distinguishes it from the aerial screw, which used a rotating helical surface, and from the parachute, which addressed safe descent rather than powered flight.