Wind Above My Wings

There is a popular song titled "Wind Beneath My Wings." For those of us who fly, there should be another titled "Wind Above My Wings," for that is what makes an aircraft fly. An eighteenth-century Swiss scientist called Bernoulli discovered that when the flow of a fluid substance (air or water, for example) is forced through a tube with a constriction in it, the speed of the flow increases, and the pressure of the substance decreases. The Wright brothers capitalized on that discovery several centuries later, and built the first powered flying machine. The secret was in the shape of the wing, which was curved over the top, forcing air into an arc to follow the wing's shape, and back to meet the air traveling a shorter distance more slowly under the wing. The air on top of a wing has to speed up, is compressed, and its pressure decreases, creating a vacuum above the wing which lifts the aircraft. A small increase in air pressure under the wing contributes to the total lifting force. The brothers tinkered with wing shapes in a wind tunnel until their design could produce a strong enough vacuum to lift the weight of the Wright Flyer.

All modern aircraft are built around Bernoulli's principle, also called a venturi. An airplane's propeller, wings, fuselage, and tail create venturis; a helicopter's rotors create venturis; the carburetors in small aircraft engines are built with internal venturis. Mother Nature creates her own powerful venturis when wind blows through a mountain pass, ocean air spins into a hurricane, or a river rushes into a narrow canyon. Flight in a small airplane or glider requires acute awareness of, and careful management of Bernoulli's Principle.

When a pilot activates the starter on a small airplane's engine, air is sucked into the cylinders as intake and exhaust valves open and close. This in turn pulls air through the carburetor and intake manifold. Fuel is sucked into the system because of the low pressure created in the carburetor venturi, enters the cylinders, and spark plugs ignite the mixture causing small explosions that force the pistons to move. With the engine running, the propeller spins. It's shape echoes that of the airplane's wing, with low pressure forming on the curved front of the blades. The force created is called thrust, and it pulls the airplane forward. Add power, spinning the blades faster, and eventually the airplane is moving fast enough for the air going over the wings to produce lift equal to the airplane's weight. Voila! We fly, and given enough excess thrust, we climb into the wild blue yonder.

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