Leonardo da Vinci's winged machine designed for human flight is commonly called an ornithopter. The word refers to an aircraft that flies by flapping wings, imitating the movement of birds or bats. Leonardo produced several studies of such machines during his investigations of flight in the late fifteenth and early sixteenth centuries.
His drawings explored large wings, mechanical linkages, and ways a pilot might use leg and arm power to move them. Leonardo carefully observed birds, especially their gliding, balancing, and wing movements. He correctly recognized that human muscles alone would not provide the same power-to-weight ratio as a bird, but he continued to examine mechanical possibilities.
Leonardo's ornithopter was a design concept, not a documented successful aircraft. It is often confused with his separate aerial-screw design, which is more closely associated with a helicopter-like lifting concept. Modern aircraft called ornithopters have flown, but they use improved materials, engines, or remote control rather than relying on Leonardo's original mechanism.