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Guess where we went this weekend?

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I don't know. Outer space?

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Funny, Dr. D. We went to the National Air and Space Museum.

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Oh, did you see the Wright Brothers plane?

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Yeah, it was so cool.

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Well, did you know that after the last flight, a gust of wind threw up and sent the Wright Brothers flyer tumbling across the sand?

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Is that why the Wright flyer never flew again?

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That's right, because it was damaged.

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Today, planes are built much differently.

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When we went to the museum, we learned about the four forces of flight.

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What are the four forces of flight?

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Let's see. There's lift, that pushes a plane upward.

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And weight, which is Earth's gravity pulling down on a plane.

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Then thrust, which is the power to push a plane through the air.

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Oh yeah, and drag.

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Why do you think it is important that we must understand all four forces?

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I'm not sure. I would guess you have to have all of them to make a plane fly.

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Yes, they're all connected to each other.

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For example, changing the thrust also affects the lift and the drag.

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We must first examine them individually before we can see how they're related to each other.

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Can we start with the force of lift?

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Sure. What part of the plane do you think provides the lift?

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I would say the wings.

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That's right. The wings are designed to push air downward.

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The air flowing over top of the wing and the air flowing underneath the wing are both bent downward.

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These fan blades are just like a wing.

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Look at the blades. See how they're angled?

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Yes, why is that?

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Well, the blades are angled upward from the direction of motion.

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This angle allows the blades to push the air downward.

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How do airplane wings compare to fan blades?

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As the fan blades spin, they cut through the air like an airplane wing.

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Take a look at this airplane that I got many years ago.

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Notice how the wing is slanted upward with the front edge higher than the back edge.

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Turn on the fan now and see what happens.

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Those fan blades are pushing a lot of air.

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How can we increase the air pushed down by the fan?

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It could spin faster.

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Indeed. A faster spinning fan blade is like an airplane wing flying through the air faster, pushing more air down.

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Why does a wing need to push air down?

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It's what provides lift.

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I don't get it. How does pushing air down create lift?

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Mr. Isaac Newton said, for every action there is an equal and opposite reaction.

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It's called his third law.

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So that means when the wing pushes the air downward, the air is pushing up on the wing?

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Correct again.

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Let's try an experiment.

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Tip the fan up like this and put it on these skates.

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Now the fan is going to push the air this way. That's the action.

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And the air is going to push the fan the other way. That's the reaction.

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All right.

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Wow.

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I bet the problem with our airplane last year was that we didn't have an angle on the wing.

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If we don't have an angle on the wing, we can't push the air downward and get an upward lift.

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We need to angle the wing up, and it would work better.

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I can't believe that the air will push up on this model plane and give it lift,

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but it's hard to believe that air can push up and give lift to something as big as those passengers.

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They do weigh a lot more, but I guess their wings are a lot bigger.

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Well, it's almost like magic, but it's real science.

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To really understand lift, you need to visit a wind tunnel.

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Why don't you contact Luther Jenkins over at NASA?

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Wow, this is really neat.

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Have you ever seen a wind tunnel?

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I've never been in a wind tunnel, but I've seen them on TV.

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Well, this is one of 30 wind tunnels we have here at NASA.

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We found at the National Air and Space Museum that the Wright Brothers built their own wind tunnel in 1901.

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They collected data from that wind tunnel and put it in a successful ladder.

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That's absolutely correct.

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What do you use wind tunnels for?

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Well, like the Wright Brothers, we use wind tunnels to examine how the air flows over different objects,

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like planes, cars, wings, and even tires.

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This helps us understand how they will perform and gives us insight into how the air flows over different objects.

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This helps us understand how they will perform and gives us insight so that we can develop new designs.

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Is there anything you can show me?

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Well, Dr. D showed you how the angle of a wing actually deflects the air downward to create lift.

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I'm going to show you how the air flows over a wing.

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This is a different way of looking at the concept of lift.

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Come with me.

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Okay.

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What do you mean to show me how the air goes over the top of the wings?

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We can see air?

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No, you really can't, so we use smoke to visualize the air.

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Can you see how the smoke particles that strike the front edge of the wing,

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some travel over the upper surface and some travel over the lower surface?

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It looks like the smoke is going faster over the top of the wings.

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You're right.

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The curvature of the upper surface actually causes the smoke particles to speed up

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or travel faster over the upper surface.

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The force applied by these faster moving particles on the upper surface

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is lower than the force that is applied on the lower surface by the slower moving particles.

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The difference in forces actually creates a lift and causes the plane to stay in the sky.

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That's weird.

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I wonder how big airplanes stay in the air.

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I mean, they're so large.

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That's true.

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They are very big, but they also have large wings,

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and the air has more surface area over which to travel.

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That generates more lift and allows them to stay in the sky.

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Why is it important to test airplane wings?

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Well, we test airplane wings so engineers know which ones to use

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for their particular design or application.

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That saves time and money.

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That was so cool.

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I think it was so interesting seeing how the smoke went over the wings.

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Well, I hope it helps.

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I'm sure you'd do well in the contest.

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Thanks.