In 1799, Sir George Cayley (1773-1857) designed an airplane that incorporated a fixed wing, a separate propulsion mechanism, and a tail for stability. His design was revolutionary because he was the first to break lift and propulsion into two parts. He understood that the wings would not generate the power by flapping or some other means. Instead, Cayley envisioned a power source that was independent of the wings. He also introduced the concept of camber – curvature – of the wing.
Cayley engraved his design on a coin – known as Cayley’s Coin. On one side of the coin he engraved a picture of his flying machine. On the other he engraved a diagram of the four forces of flight at work. The forces were lift, weight, drag, and thrust. Thrust and drag work in opposition to one another as thrust moves an object forward and drag works to slow that movement. Lift and weight work in opposition to each other as lift brings an object aloft while weight is the force of gravity pulling that object toward the earth.
Sir George Cayley was the first to understand and articulate that an object will remain in the air only when all four forces – lift, weight, drag, and thrust – are in balance.
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