Fast Fact:
Indy cars produce so much downforce at race speeds that they would be capable of driving upside down on an inverted track!
Objective:
The students will investigate how the shape of a race cars wings affect the flow of air over the car.
In the Film:
At the Cranfield wind tunnel testing center, a car is studied for aerodynamic performance. It is tested with a smoke stream and with ultraviolet dye, which provides engineers with a map of the cars aerodynamic flow. We see the engineers attempt, through trial and error, to find the best design to increase the speed of the car.
Background:
Racer Jim Hall is considered to be the father of racing aerodynamics. His novel approach used air forces to improve performance. His experiments eventually led to the use of small wings to create downforce. Downforce is similar to lift on planes, only in the opposite direction. It is used to force a cars wheels to stay in contact with the track.
Materials:
A large electric fan with a variable speed control, paper, a straw, string, tape or a stapler.
To Do:
Have the students bend a sheet of paper in half widthwise and staple the top and bottom together without making a crease. Following the illustration (figure 1), have them make a hole through both layers near the rounded end. Pass a straw through the holes. Pass a string through the straw, and hold the string taut and verticle. Tell them to place the paper in front of the fan and watch what happens. Encourage them to experiment by tilting the string forward, backward and sideways. Have the students consider why the wing moves as it does. Suggest that they draw how the air passes over the wing. How should a wing be shaped and which way should it be tilted on a race car?
Whats Going On?
When the paper wing is hung from the straw it sags enough to round the top surface more than the bottom. When air goes over the rounded part of the paper (the wing), it creates a low-pressure area because the air has to travel further over the top than it does over the bottom. The relatively high-pressure area below the wing generates lift. When the string is tilted backward, the angle at which the air strikes the wing creates even higher pressure under the wing, generating more lift. Compared with an airplane wing, the wing on an Indy car is upside down. The net effect is lift in reverse, which is called downforce.
Taking It Further:
1. Ask the students to place cardboard side pieces across the ends of the wing as shown in the illustration (figure 2). How does this effect the stability and lifting power of the wing? How can this be used to increase the stability of a race car?
2. Have the students place wheels on the side pieces and put the wing on a board in front of the fan. The board represents the ground. Does the wind pick up the wing or push it toward the ground? Have them turn the wing over and try again!
3. Suggest that the students do research on aerodynamics. What are they and why are they important? How do the wings on cars differ in effect from the wings on airplanes? Give the students time to revise their designs from Activity 1 in terms of aerodynamic features. Hold another race event.
