An airfoil is any surface designed to obtain a reaction from the air through which it moves. For example, wings, ailerons, elevators, stabilizers, propeller blades, and helicopter rotors are all airfoils. In the following experiment we will investigate the application of Bernoulli's principle to airfoil.

Materials:

Procedure:

1. Make an airfoil (wing) by placing one end of a strip of paper between the pages of a book so that the other end hangs over the top.
2. Move the book swiftly through the air, or blow across the top of the strip of paper. It flutters upward.
3. Hold the book in the breeze of an electric fan so the air blows over the top of the paper. Take the strip of paper out of the book. Grasp one end of the paper and set it against your chin, just below your mouth. Hold it in place with your thumb and blow over the top of the strip. The paper rises.
4. Try the same thing after you have fastened a paper clip on the end of the strip. See how many paper clips you can lift in this way. It doesn't matter whether you move the air over the strip of paper by blowing or whether you move the paper rapidly through the air-- either way it rises.

Here are some additional activities and ideas to discuss in your group: • Use a graphics software (e.g., PhotoShop) to draw a cross sectional view of the above airfoil.
• Illustrate the flow around the airfoil. What is the relationship between pressure and velocity above/below the airfoil?
• How is this airfoil similar to the venturi tube?
• How is this similar to an aircraft wing?
• What happens if you change the shape of the airfoil in the above experiment? Is there a way to find out the effect of this change in shape?
• Prepare a presentation to the other teams in the class to explain what you discovered from this experiment.

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Additional Information about the application of Bernoulli's principle to aircraft.

Bernoulli's principle states that an increase in the velocity of any fluid is always accompanied by a decrease in pressure. Air is a fluid. If you can cause the air to move rapidly on one side of a surface, the pressure on that side of the surface is less than that on its other side. Look at the following figures:   Bernoulli's principle works with an airplane wing. In motion, air hits the leading edge (front edge) of the wing. Some of the air moves under the wing, and some of it goes over the top. The air moving over the top of the curved wing must travel farther to reach the back of the wing; consequently it must travel faster than the air moving under the wing, to reach the trailing edge (back edge) at the same time. Therefore the air pressure on the top of the wing is less than that on the bottom of the wing. This combination of pressure decrease above the airfoil and increase below the airfoil produces lift.

Here is a link to a useful source for more details about airfoils.

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Here is a fascinating experiment to explore Wing Design and Aspect Ratio

An examination of the shape of an aircraft wing discloses that it has been designed to create a pressure difference. Search the following list of resources to find various types of aircraft wings.

• How are they different and how are they similar (e.g., how are Stealth's wings different from a Boeing 747 or an F-16)
• Prepare a brief report examining the shape of two of your favorite aircraft's wings. Include pictures of the wings. You may want to publish your report along with the pictures you found on the Web as an html document.