The bird-inspired flying-machine type Leonardo da Vinci repeatedly studied was the ornithopter.
An ornithopter is a machine intended to fly by flapping wings, imitating the motion of birds or bats. Leonardo made numerous sketches and notes about such machines during the late fifteenth and early sixteenth centuries. His studies examined wing structure, muscles, balance, and the behavior of air.
Leonardo’s ornithopter drawings included large wings operated by a person using pedals, levers, and other mechanical linkages. The machines were ingenious mechanical studies, but human muscles could not supply enough power to lift the proposed structure and pilot. Unlike modern aircraft, they also lacked an engine and a reliable control system.
Leonardo’s work is sometimes called a design for “the first airplane,” but that label is misleading. His flapping machines belong to the ornithopter tradition, while modern airplanes use fixed wings and powered forward motion to generate lift.