What flapping-wing aircraft did Leonardo da Vinci study?

Leonardo da Vinci studied an ornithopter, an aircraft designed to fly by flapping wings like a bird.

His notebooks contain observations of birds and sketches of wing mechanisms intended to translate human or mechanical motion into flight. Leonardo examined anatomy, balance, air resistance, and the movement of wings, trying to understand how a flying machine might generate lift. His proposals were not powered aircraft in the modern engineering sense, and no evidence shows that one achieved sustained flight.

An ornithopter is defined by its flapping wings, not by the appearance of the machine. That distinguishes it from a glider, which relies on fixed wings, and from the helical rotor machine often associated with another of Leonardo’s famous sketches. The latter is commonly called a helicopter concept, while an ornithopter imitates the active wingbeat of birds or insects.

Leonardo’s studies helped connect artistic observation with mechanical experimentation, even though powered human flight remained centuries away.