The Science of Flight

"How can I possibly gain flying speed? Why did I ever think that air could carry such a weight? Why have I placed such reliance on a sheet of paper's curves?"--Charles Lindberg

The year was 1927. Charles Lindberg was taking off from New York in his specially designed plane called the Spirit of St. Louis. Of course Lindberg knew the answers to his own questions.

His plane's wings were modeled after the shape of birds' wings. Air moving over these carefully designed wings created lift which got his plane into the air.

Within minutes, Lindberg's heavy plane lumbered down the runway. He was on his way to becoming the first person to fly solo and non-stop across the Atlantic.

Lindberg knew flight is made possible (or impossible) by four forces:

Weight

A real downer, caused by gravity, pulls everything toward the ground.

Lift

An upbeat kind of force, caused by air moving over the wings, acts upward against weight.

Drag

A backward force, caused by air resistance, acts in the opposite direction to motion.

Thrust

A very forward force, caused by an engine, overcomes the force of drag.

These four forces act in combination to decide if you can sit back and enjoy the flight or if you should be looking for a parachute.

Basically, if the plane is moving forward, it means that thrust is overcoming drag. If the plane is climbing, the force of lift is greater than the force of weight. If the plane is descending (hopefully near an airport), weight is greater than lift.

We just found out that lift makes flight possible. And we know that air moving over the wings causes lift. But how? To explain this one, we need to introduce air pressure and a Swiss mathematician named Daniel Bernoulli (pronounced Ber-noo-lee).

Air has pressure--it's always pushing against things. But in 1738, Bernoulli found that when a gas (like air) moves, it exerts less pressure. According to Bernoulli's principle, the faster air moves, the less pressure it exerts.

Normally air moves along smoothly in streams. Air flow is disturbed, however, when a wing moves through it. Air divides and flows around the wing.

The top surface of the wing is curved--air travelling over it has farther to travel to reach the trailing edge of the wing. To travel across the wing in the same amount of time, air moving across the top of the wing has to go faster. Because it's moving faster, the air on top of the wing exerts less pressure on the wing than the air below the wing. In other words, air below the wing pushes up more than air above the wing pushes down. This difference in pressure results in an upward force called lift. And presto, lift gets things flying.

Let's review: big engines get a plane moving, air flowing over the wings creates differences in air pressure which creates lift, and since lift makes flight possible...well, you get the picture.

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