Leonardo da Vinci sketched ornithopters, aircraft intended to fly by flapping wings like birds.
Leonardo studied bird anatomy, wing movement, and the relationship between weight and lift. His ornithopter drawings show human-powered machines with large wings and mechanical systems intended to transmit the pilot's effort to those wings. The designs reflect his belief that careful observation of nature could guide engineering.
No Leonardo ornithopter is known to have achieved powered flight. Human muscles cannot easily provide the sustained power needed for a large man-carrying flapping aircraft, and the proposed mechanisms would also have been heavy. An ornithopter differs from a glider, which remains aloft with fixed wings, and from a helicopter, which uses rotating blades.