Leonardo da Vinci’s bird-inspired flying-machine design was an ornithopter.
An ornithopter is an aircraft intended to fly by flapping its wings, rather than by using fixed wings, rotors, or lighter-than-air gas. Leonardo studied birds and bats extensively and filled notebooks with observations about wing movement, balance, and air resistance.
His proposed machines generally used a human operator to power or control the wings. They were never demonstrated as successful aircraft, partly because human muscles cannot provide enough sustained power for a machine of the proposed size.
Leonardo’s ornithopter is often confused with his aerial screw. The ornithopter depends on flapping wings, while the aerial screw is a separate vertical-flight concept with a helical rotor-like surface. Neither design became a working aircraft during Leonardo’s lifetime, but both influenced later discussions of flight.