Science in Your Airplane Seat

Activities you can do at home


Why are airplane wings shaped the way they are? What can pretzels tell you about flying? Find out on your next airplane trip.

In the terminal or while waiting for takeoff

Wing Shape

Look at the wings of an airplane from the side and notice their shape. How would you describe it? Which edge of the wing is pointy? Which is rounded? Why do you think they are shaped this way?
During takeoff and landing, watch the wing. Notice the flaps that move. How do they change the shape of the wing? Why do you think these changes are made?

What's Going On?

The cross section of most airplane wings is shaped something like a teardrop on its side - the front edge is thick and round, the back edge is thin. The thicker front edge forces air to speed up as it moves up and over the wing. As the air speeds up, it pushes on the wing less than the air below the wing. The "pushier" air below the wing helps lift the plane into the air. During takeoff and landing, the pilot extends flaps on the back edge of the wing. The flaps increase the curve of the wing, which maintain the lift at slower speeds. After takeoff, the pilot retracts the flaps.

In the Airport

Wind

Look for a windsock on the airfield. Is it limp or full of air? Can you tell which direction the wind is coming from? Notice the direction of your plane as it takes off. How does this compare to the direction of the windsock?

What's Going On?

A windsock is pushed in the direction the wind is blowing. As the wind blows faster, the windsock fills up more. Airplanes usually take off and land into the wind. This increases the speed of the air flowing over the wings, which increases the lift. (See Wing Shape for more information about lift.)

Before and during the flight.

In-Flight Physics

Before the plane begins moving, tie one end of a string to a small weight (such as a key or pencil) and tape the other to the drawing [at right]. Watch the string as the plane begins to speed up (accelerate) down the runway. Try to mark where the string swings. As the plane lifts off the ground, look straight at the paper and notice where the string is hanging. Mark this point on the paper. (If the weight is wobbling, touch it gently to steady it.) Mark the string's position a few minutes later, while the plane is still climbing. Mark it again after the pilot announces that the plane is at its cruising altitude. As the plane is landing, but before it touches the runway, mark the string's position one last time.
  • tape
  • string
  • key or small weight
  • pencil or pen

What's Going On?

The string is measuring the plane's tilt and/or its change in speed (also called acceleration). During a test flight of this activity, the string swung between 15 and 20 degrees toward the back of the plane as it took off. During most of the climb, the string held steady at 10 degrees, and for the rest of the flight it stayed right around zero degrees. As the plane was landing, the string swung about 10 degrees toward the front of the plane.

Explore More

Mark the string's angle as the plane turns on the runway, then again as it turns in flight. On the ground, planes can't tilt as they turn on runways. In the air, though, planes tilt into the turn just as you do when you make a tight turn on your bicycle. (See Obey the Law for more information.)
If you test tilt and acceleration at home, you'll see that both can produce the same results but for different reasons.

In the air

Obey the Law

Settle back into your seat and close your eyes. Do you feel like you are moving? What clues do you feel? Can you tell how fast you are moving? Repeat this activity if the plane turns to approach the airport. Do you feel differently now? Why? Compare how you feel to when you are in a turning car or on a bicycle pedaling around a curve. What is different or similar? While the plane is descending, repeat the activity. Compare how you feel to when the plane was cruising and turning. What feels different?

What's Going On?

The observations you make during this activity show one of the laws of motion: A force is needed to change the speed or direction of an object. For example, if you're moving in a straight line at a constant speed_such as when the plane is cruising_you won't be able to feel the motion because nothing is forcing you to change your speed or direction. However, you should feel a change in motion if you are in a plane that is speeding up or slowing down. You may also notice when the plane is turning, but maybe not. Planes make turns that are perfectly banked or coordinated_they tilt at an angle, into the turn. You do this on a bicycle too. But if you are in a car that is turning on a flat surface (such as a parking lot), you'll feel "pushed" to the outside of the turn.

As soon as you get on the plane.

Puffy Pretzels and Popping Ears

Ask for a bag of pretzels or peanuts before the plane takes off. Look at the bag carefully_notice its size, its shape, if you can squish it_but Do Not Open It! Put the bag away in a safe place during takeoff.
As the plane takes off, notice how your ears feel. Do they feel differently once the plane begins to fly level? What do you think is happening inside your ears?
When the pilot announces that the plane has reached its cruising altitude, look at the snack bag again. Describe its size and shape; notice if you can squish it. Has anything changed? Why? Put the bag away again until the plane begins to land.
As the plane begins to land, take out the snack bag and watch for any changes. Also, notice how your ears feel. When do you first feel pressure inside your ears? What do you think is happening? How do you think the air pressure in the plane compares to the air pressure in your house?

What's Going On?

Air pressure goes down as you go higher in altitude. If you were outside the airplane when it is flying at 30,000 feet, you'd hardly be able to breathe because the air pressure is so low. You can breathe easily in a plane because the cabin is pressurized_the air in it is kept at near-normal pressure. The plane's air pressure is actually slightly less than normal. You feel this slight change as the plane takes off and lands.
The snack bag probably looked a lot puffier once the plane was in the air. The pretzels were packed with normal air pressure, so air presses on the inside and outside of the bag equally. During flight, as the cabin pressure drops, the pressure inside the bag pushes the bag outward. As the plane lands, the air pressure outside the bag increases and pushes on the bag, so it may seem to deflate.
Your eardrums behave like the snack bag. On the ground, your ears are filled with normal air pressure, so air presses on both sides of the eardrum equally. As the air pressure inside the plane drops, the pressure inside your ears pushes the eardrums outward. This can make your ears hurt and distort your hearing. You can relieve this pressure by helping some of the air inside your ear escape through an opening into your throat. (This is called equalizing.) The safest way to equalize your ears is by chewing gum or swallowing. When you have a cold, you may have difficulty equalizing because the opening might be blocked. If this happens, ask a flight attendant for help.

What Wasn't Going On?

The amount of air inside the bag doesn't change during any part of this activity_only the pressure of the air around it.

But My Pretzels Didn't Puff Up!

If your snack bag seemed to stay the same during the entire flight, the snack might have been packed in a high-altitude city such as Denver or Salt Lake City. How might this make a difference?


Produced by the National Air and Space Museum's Educational Services Department to accompany HOW THINGS FLY, an interactive gallery. HOW THINGS FLY is made possible through the generous funding of the Boeing Company and a grant from the National Aeronautics and Space Administration, with additional support from the National Science Foundation, The Smithsonian Institution Special Exhibition Fund, and the James Smithson Society. ©1996, National Air and Space Museum, Smithsonian Institution.

(Rev. 10/04/96)