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2TORIAL
Learn2 Understand How Airplanes Work (continued)
Step 2: Understand lift

Believe it or not, wings actually harness the principles of "flow" and "spread" to create enough force to pull hundreds of tons of metal off the ground.

Let's look at the typical wing of a plane:

According to the flow principle, we know that air flowing past the wing follows the contours of the wing itself. However, the air flowing over the curved top of the wing has a farther distance to travel than air moving along the flat bottom of the wing. As a result, the air at the top of the wing actually moves faster than the air at the bottom.

Now we must introduce one more principle of fluid dynamics: The faster a fluid flows, the lower its pressure. That means the air at the bottom of the wing has a higher pressure than the air at the top of the wing.

We already know that air at a higher pressure pushes with greater force than air at a lower pressure (remember "spread"?). Thus, the high pressure air below the wing is actually pushing against the wing with more force than the low pressure air above the wing is pushing.

The difference between these two forces is what we call "lift"--the force that lifts the plane off the ground and keeps it there. In order for a plane to fly, the lift must be greater than the weight of the plane.

To achieve enough lift, the air must be flowing at a very high velocity past the wing. After all, you've never seen a jet tooling along at 20 miles an hour. (How fast you need to go depends on the plane's size, but most passenger planes must be traveling faster than 100 miles an hour to achieve take-off. A Boeing 747 needs to be going about 180 miles per hour.)

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2TORIAL STEPS
Introduction
Step 1: Understand the basics of fluid dynamics
Step 2: Understand lift
Step 3: Understand propellers and jet engines
Step 4: Understand how planes are steered

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