Leonardo da Vinci studied an ornithopter, a machine intended to fly by flapping wings like a bird.
The word ornithopter combines Greek terms associated with bird and wing. Leonardo's notebooks contain detailed observations of birds, wing structure, air movement, and human flight. His proposed machines used articulated wings and mechanical systems rather than the fixed wings of a glider or the buoyancy of a balloon.
Leonardo understood that human muscles alone would not easily power wings large enough for sustained flight. Some designs therefore explored mechanical assistance, although none was successfully tested as a practical aircraft. His work was valuable because it treated flight as a problem of anatomy, mechanics, and aerodynamics.
An ornithopter is not the same as Leonardo's aerial screw. The aerial screw aimed to rise through a rotating helical surface, while the ornithopter aimed to generate lift through repeated wingbeats.