Hands-on Activity Windy Tunnel

Learning Objectives

After this activity students, should be able to:

• Use computer software (available on the internet) to model the lift on an airplane wing.
• Explain the variables that affect lift.
• Solve linear math equations with known and unknown variables.
• Describe a real-world application of Bernoulli's principle.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• computer with Internet access
• 2 pencils
• Worksheet 1: Virtual Wind Tunnel
• Math Worksheet 2: Windy Tunnel: What Does It Mean? (for advanced math)

Worksheets and Attachments

Introduction/Motivation

If you arm wrestle someone---who wins? Well of course, the person who exerts the most force wins! But, if both "wrestlers" push with the same force, their arms do not move. Lift on airplane wings is somewhat similar. As air flows over the top and bottom of the wing the pressure and velocity of the air change. These changes create lift. But on a symmetric wing, the changes on the top half match the bottom half. If the forces on the top and bottom of the wing are the same, no lift results. Because the cambered airfoil (the curve in the wing) is not symmetric, the forces on the top and bottom are different—in this case, lift is generated.

Can you ever have lift on a symmetric airfoil? Yes, if you raised the nose of the airplane. Doing this places the wing at an angle. Engineers call this the angle of attack. Now the forces on the top and bottom of the wing are different, and create lift.

The greater the angle of attack, the more lift; however, this only works up to a certain angle. If the angle is too high, the air will not flow smoothly over the airfoil and no lift can be created; in this case, the wing stalls, which means it loses lift.

Engineers often use wind tunnels to see how the air is flowing and if it flows smoothly over a wing. They do this by filling a wind tunnel's air chamber with smoke and watching as the (smoky) air blows over a model wing. This process also helps them determine how much drag an airfoil has by the size of the wake (an area where the airflow is not smooth at the trailing edge of the airfoil). They can also observe stall when the air has separated from the wing and starts to flow towards the front of the airfoil.

Now try out the virtual wind tunnel yourself!

Procedure

Background on Wind Tunnels

If you were to slice apart a wing from its leading (front) edge to its trailing edge (back), the "cutaway" illustrated in the Figure 1 is what you would see. Aeronautical engineers call this an airfoil.

The top and bottom halves of the first airfoil are identical—this is referred to as symmetric. The airfoil on the right is not symmetric: its top and bottom halves are different. The difference in the bottom from the top means this airfoil is cambered.

Four Forces of Flight

The four forces of flight are lift, weight, thrust and drag. Lift and weight are opposites and counteract one another. Likewise, thrust and drag counteract each another.

How Does the Bernoulli Principle Create Lift?

The top of a plane's wing is longer than the bottom because it is curved (see Figure 2). This means air travels faster over the top of the wing than under it. As a result, the air moving over the top has less time to push on the wing, creating less air pressure than air passing below the wing. In Figure 2, the air moving under the wing moves slower and exerts more pressure/force on the wing than does the air moving over the wing. Since more force exists under the wing than above it, the net result is that the wing rises up, creating lift. This principle forms the basis of winged flight.

Flaps are located the front and back edges of airplane wings. During takeoff and landing, pilots extend the 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 (puts back in) the flaps. Engineers continuously test their airplane wing designs to determine the lift, and in so doing, they consider the following:

• The amount of air diverted by the wing is proportional to the speed of the wing and the air density.
• The vertical velocity of the diverted air is proportional to the speed of the wing and the angle of attack.
• The lift is proportional to the amount of air diverted times the vertical velocity of the air.
• The power needed for lift is proportional to the lift times the vertical velocity of the air.

Before the Activity

• Make copies of the worksheets.
• Bring up on the computers the virtual wind tunnel website at: http://wayback.archive.org/web/20120502104554/http://www.swe.org/iac/LP/wind_tunnel.html. UPDATE: Since this activity was first published, its online virtual wind tunnel resource (by Society of Women Engineers, swe.org) has gone away. It can, however, still be accessed via the Internet Archive Wayback Machine at http://wayback.archive.org/web/20120524022956/http://www.swe.org/iac/LP/wind_tunnel.html.

With the Students

1. Discuss Bernoulli's principle and introduce the concept of lift, as provided in the Introduction/Motivation and Background sections.
2. Explain the difference between a symmetric and cambered (asymmetric) airplane wing.
3. Direct students' attention to Worksheet 1 and the virtual wind tunnel website . Have students read the background information silently to themselves. After 10 minutes, discuss the reading as a class.
4. Divide the class into student pairs.
5. Be sure to model the process. Students may find it difficult to grasp how the model runs. The model depicts velocity lines flowing over different wing types. Velocity lines that are close together above the wing demonstrate lift; lines that are the same distance apart above and below the wing demonstrate no lift.

Instructions for Virtual Wind Tunnel

1. Pick an Airfoil Shape from column #1.
2. Pick an Angle of Attack from column #2.
3. Click "Run Tunnel."
4. Close the window when you are done with this activity.
5. Have students complete the worksheet. Be sure they try several models to decide which causes the most or least lift.
6. Be sure to model the process. Students may find it difficult to turn the English sentences into math equations. The worksheet walks students through the process step-by-step.
7. Discuss with students that the phrase "proportional to something " means "equal to some number multiplied by something." More specifically, we can say "is proportional to" means K times something where K is the constant of proportionality.
8. Assign Math Worksheet 2 for students to complete as homework. (The worksheet may be too difficult lower grades.)

Assessment

Pre-Activity Assessment

Discussion Question/Answer: Ask students questions and have them raise their hands to respond. Write their answers on the board

• If you arm wrestle someone, who wins? (Well of course, the person who exerts the most force wins!)
• What happens if both "wrestlers" push with the same force? (Their arms do not move.)
• How does this relate to lift? (Lift occurs when the force under a plane is greater than the force pushing down on the plane [weight]. This is similar to arm wrestling since the person who exerts the most force pushes the other arm in that direction.)
• Describe the force of lift and how it affects airplane flight. (Expect that students understand Bernoulli's Principle and can explain that lift is caused when air is pushing harder from below a wing than from above a wing.)

Activity Embedded Assessment

Worksheet 1: Have the students record their activitiy observations and comments on their Worksheet 1: Virtual Windy Tunnel. After students have finished their worksheets, have them compare answers with their peers. Then discuss as a class.

Post-Activity Assessment

Worksheet 2: Assign students to complete Math Worksheet 2: Windy Tunnel: What Does It Mean? as homework. Review their answers to gauge their comprehension of the subject.

Figure Drawing/Race: Draw an airfoil on the classroom board or overhead projector (see Figure 1 for example airfoils). Have two students come to the board and race who can draw the top or the bottom of the airfoil the fastest. The student who "wins" completes the drawing (gets to the end of the airfoil) first. Which student was the fastest? Will that airfoil create lift or not?

Troubleshooting Tips

• Make sure students understand the instructions.
• Make sure all computers are open to the virtual wind tunnel website.
• Be sure to have students read the background information or review it as a class.

Activity Extensions

A great teacher demo on lift is to throw a Frisbee. The shape of the top of the Frisbee is smooth and air flows over the top faster, creating less pressure. It takes longer for air to flow over the bottom of a Frisbee, thus creating a higher-pressure area that lifts the Frisbee up into the air.

Have students compare airfoil shapes with the wing shapes on different airplanes. Why do different planes have different wing shapes?

Have students research the work of aerospace engineers and how they use lift/drag in their designs.

Activity Scaling

For lower grades: Read the wind tunnel instructions together, ask a class, and ask for questions after they have been read. While the math worksheet may be too difficult, you can walk through the steps of creating a math equation as a class.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and the National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the DOE or NSF, and you should not assume endorsement by the federal government.