An ornithopter is a Leonardo da Vinci aircraft concept designed to fly by flapping wings like a bird.
Leonardo studied birds extensively and drew several machines with wings intended to move through mechanical action. Some designs used a human operator's arms or legs to power the wing motion, while others explored different arrangements of frames, membranes, and linkages. His notebooks contain many observations about bird flight and air resistance.
The word ornithopter means a machine that flies by the motion of its wings. Leonardo's designs were not successful aircraft because human muscle power was insufficient to lift the proposed structures and operate their wings effectively. He did, however, investigate principles that later became important to aviation, including balance, drag, and the relationship between wing shape and movement.
Modern ornithopters exist as small experimental machines and radio-controlled aircraft. They are different from airplanes, whose fixed wings generate lift while propellers or jets provide forward thrust. Leonardo's ornithopters belong to the earliest systematic European studies of mechanical flight.