Leonardo da Vinci studied an ornithopter, an aircraft designed to fly by flapping wings like a bird.
The word ornithopter comes from Greek roots meaning bird and wing. Leonardo filled notebooks with observations of birds, their wing movements, balance, and the role of air currents. He then adapted those observations into mechanical designs with large wings operated by human power.
Leonardo's ornithopters were never successfully flown. A human pilot could not produce enough continuous power to flap wings of the required size, and the proposed mechanisms would have been heavy. Leonardo eventually paid more attention to gliding and the behavior of air than to simply copying bird anatomy.
An ornithopter differs from a helicopter, whose rotor spins, and from a glider, whose wings remain fixed. Modern ornithopters exist as small experimental aircraft and model machines, but Leonardo's designs were conceptual studies rather than working aircraft.