In college, I wanted to do something interesting for my senior project. I decided I wanted to look at different types of air foil shapes to replace the standard wings that have been used in oval racing. My goal was to find a design that was much more efficient at producing downforce. I tested 4 different wing configurations at 3 different speeds from 0 to 112 ft/s (77 mph). Here is a link to my full report (PDF).
This is a video of the car being tested from 0 to 80 mph. There is an airspeed indicator in the upper right of the screen. As it reaches 80 mph you can see how much the wing bends down from the force of the air. It also starts to flutter at those high speeds (its hard to see, but its starts shaking at about 60 mph)
Car ready to be tested in tunnel
This shows the setup used to measure the loads. There is one load cell for the front end of the car and one load cell for the rear of the car. There is a force trasducer to also measure drag. The load cells and force transducers work by measuring resistance in a strain gauge located in the load cells and force transducers. A voltage is applied to the strain gauge and current and resistance is measured. As a load is applied the length of the conductor changes and its resistance changes. The changes in resistance are measured and then the actual load applied can be calculated. I could only measure half the downforce applied to the rear end because I only had one force transducer. The graphs shown below only represent half the total downforce on the rear axle. It was unfortunate to have many problems with getting accurate data from the front force transducer. I was unable to get any data loads from the front axle of the car. I would have liked to compare the front to rear downforce.
Traditional wing and spoiler installed
Anderson airfoil cross section
NACA 9509 airfoil
NACA 9509 airfoil cross section
This is the shape of the wing with zero windspeed.
Severe wing deformation at 80 mph
Drag vs. Speed.
Downforce vs. Speed. You can see that the baseline body (no spoiler or wing) actually creates lift. This can be terribly bad at high speeds. Even using a spoiler reduces lift significantly. Also, you can see the standard wings downforce falls off dramatically above 50 mph. This is because of the deformation that is caused from the high speed. The lexan material is not able to keep the wings shape and causes it to lose its effectiveness.
This is a link to the facilties I used at Iowa State. I used the Bill James Wind Tunnel. Its an open circuit tunnel for aerodynamic testing (3.0 ft wide by 2.5 ft high section) with 180 mph wind speed capability.