Flying machines with flapping wings
In one of the early phases of his research, Leonardo envisaged complex flying machines with flapping wings. The machine is operated by the muscular force of the prone pilot, who activates the wings by moving his arms and legs. In another project, the pilot is upright and moves the craft with his arms, legs, and head. Leonardo also contemplated the use of a spring motor that could be rewound in flight. He planned test flights and designed crash safety systems using inflated animal skins and shock absorbers.
The Codex on the Flight of Birds, written in about 1506, marks the start of a second research phase. Once Leonardo realized the inadequacy of human power, he turned his attention to the flight of birds. He observed that birds rely less on their wing beat than on exploiting air currents and wind. He therefore examined how birds, when struck by air currents, manage to keep their balance by moving their wings and tails. At the same time, he made an anatomical study of bird wings, demonstrating that the bastard wing acts as a brake. These investigations led Leonardo to substitute sail-flight projects for flapping-wing machines. Leonardo studied mechanical wings that could mimic the complex motions of bird wings.
Air and wind
Aerology and meteorology were an integral part of Leonardo's research on flight. He designed anemometers and hygroscopes to measure air resistance in flight. Leonardo compares air to water, and flight to swimming. As in swimming, a body that flies by flapping its wings moves forward by exerting a contrary thrust. In one of the flying machines, the pilot is housed in a boat-shaped hull. For Leonardo, the flying fish, which can both swim and fly, offers living proof of the analogy that links all living beings together.