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Goofball Answer:

Mallori,

I'm not so sure how airplanes fly, which is precisely why I jump out of them. I mean, how can something heavier than air possibly remain airborne? It would be ridiculous to stay inside one of those airplane thingies. Ridiculous.

Actually, the way an airplane flies is almost identical to the way my parachute flies, so let me give your question a whirl.

When we discuss airplanes flying, we concern ourselves with four primary things:

1. Weight
2. Lift
3. Thrust
4. Drag

Weight is the name of the force—directed toward the ground—equal to the weight of the airplane, its fuel, passengers, cargo, and boring magazine selection. Lift is the name we give to the force lifting the airplane up against the force of its weight. Thrust is the name of the force driving the airplane forward through the air (and across the ground while it's still on the runway). Thrust is most often provided by a propeller or jet engine. Drag is the name of the force described by the airplane's wind resistance.

I scribbled on this picture to show the direction in which these forces act on the airplane. Weight, thrust, and drag are all pretty easy to understand. It's lift that perplexes most people when thinking about flying. So to keep it simple, I'll just focus on how airplanes create lift...

Daniel Bernoulli, a Swiss mathematician who tinkered with mathematical equations for mechanical issues, figured out that fluids decrease in pressure when they increase in speed. Thus: more speed, less pressure. And: less speed, more pressure.

Daniel died in 1782, so he never got to see an airplane fly. But 120 years or so later, a few people had figured out that air behaved a lot like fluids—which is to say air also drops in pressure when it is traveling faster. Some time around 1903 The Wright Brothers stopped playing around with bicycles long enough to design a fancy airplane wing. The wing was shaped specifically to mess with the way air flowed over its surfaces. The brothers designed their wing so air traveling over the top of the wing would have to briefly travel a wee bit faster than air below the wing. Because the air on top of the wing had to move a little faster, it also lost some pressure.

Therefore, as an airplane moves through the air, the air directly above the wing is at a lower pressure than the air below the wing. The high-pressure air below the wing "pushes" up against the wings and creates lift. The faster the airplane is traveling, the greater this difference in pressure becomes, and the greater the resulting lift.

So to fly, an airplane begins rolling along the ground through the air. The plane increases speed creating a difference in air pressure between the tops and bottoms of its wings. Once the airplane is moving fast enough along the ground, the lift generated by the wings will be a force greater than the force of the airplane's weight. At this point, the airplane begins to fly. To stay flying, the airplane must obviously keep moving forward through the air. If the wings do not move through the air at sufficient speed, or do not move through the air at the right angle (to take advantage of their special shape), the wings stop producing lift and the wing is said to "stall". Stalls are bad.

On this picture I scribbled some lines to show how the air moves around an airplane wing as it flies. You can see how the path the air takes around the wing is different on the top and the bottom. This difference creates lift. And that's pretty cool.

So, are you ready to buy a magic backpack full of specially shaped nylon? They're a lot of fun. And when the nylon comes out of the backpack and inflates, it takes on the same basic shape as an airplane wing. But we skydivers don't have engines, so we rely on gravity to pull us down and the angle of the parachute to drive us forward. This forward movement creates the airflow over the wing, which creates lift. And because we don't have an engine to continuously move us forward, we only get one chance to land our nylon aircraft.

Mallori, do you know anyone who has botched up his one chance to land his nylon aircraft???

~ topher