Building an Air Dam


I'm trying to improve the aerodynamics of the midget so I can get more driving range out of my batteries. The front bumper of the newer midgets makes for an easy placement of an air dam. Air dams are supposed to keep air from going under the car and creating drag from passing over the typically rough underside. Midget’s have a clean underside when compared to most cars, but I decided to try making an air dam anyway.

The early test results don’t show any real change in drag. At 60 mph there might be a 2% improvement. With this little change I will probably end up taking this off. I’m putting this information on the site anyway. Someone following in my footsteps will know not to expect too much, or try something different than what I did. The air dam ended up at 5.5 inches from the road, so someone might try moving it closer. It is possible that it’s effects can’t be observed at 60 mph. At higher speeds it might have more effect.

The underside of the front bumper provides a horizontal surface across the front of the car and attaching an air dam to it is relatively easy.

Front of the Car

The rubber portion of the bumper is held onto a steel beam with a cap strip. This strip is curved the same way as the bumper is. When I took the steel out of the front bumper for weight reduction, I removed this cap strip.

Bottom of Bumper

To make the actual air dam I was going to use a material called Coroplast. This material is corrugated plastic 4mm thick. To hold it to the bumper I decided to make a downward vertical surface that I would clamp the plastic to. I welded a 1 ¼ inch wide soft steel strip to the cap strip I showed in the above picture. The cap strip would be mounted to the underside of the bumper and provide the correct curvature for the soft steel strip and my Coroplast air dam.

Support Frame1

Support Frame3

Support Frame4

From the above pictures you can see I tack welded the steel strip to the cap strip about every 4 inches. I left some of the steep strip go past the end of cap strip so I could curve the air dam when it got to the edge of the car. You’ll see in the later pictures.

Coroplast comes in 4ft by 8ft sheets. If you can find a local source that carries it in that size, you’ve probably found the cheapest source. My local Home Depot has 30” pieces that cost way more than I’d like to pay, but they are right there. My small sheet cost over $8.00. For those of you who haven’t seen this stuff, I took a close up shot so you could have an idea of what it is. It is great material for all sorts of custom projects. It’s tough and very light and cheap if you can find the larger sheets.

Coroplast Sheet

Coroplast Closeup

I cut the coroplast with an exacto knife. I made it so it would hang down below the bumper by 8 inches. This would match the height of my lowest point in the frame. Because I needed to bend this around at the edges of the car, I made the ribs hang vertically. If they were placed the other way I wouldn’t be able to get a decent curvature. This direction also creates the stiffness in the vertical direction, which is needed as well. I used a clamping strip to hold the coroplast to the vertical steel strip. I made the clamping strip out of window screen frame. It is very light and because it is a box beam, stiff as well. It is also very cheap, $2.70 for 7 feet. I drilled large holes to allow the head of the screw to pass through the first side and clamp using the backside. This maintains the integrity of the beam section without crushing it if I clamped the screws too tight.

Screen Frame

coroplast mounted to frame1

coroplast mounted to frame2

coroplast mounted to frame4

With the coroplast attached to my frame I was almost done. The frame was stiff enough that I could attach it to the bumper with only 2 screws, one at each end. I used ¼ bolts up through the thick rubber material in the same holes that the rivets went through when there was a steel beam in the bumber. To keep the air dam from being pushed back into the car, I cut to size and inserted a foam stiffener between the car’s frame and the back of the air dam. It was held in place with duct tape for the initial test runs. It will be glued in place for the final installation.

Almost Finished2

Almost Finished2

Rear Support Foam in Place2

In order to make the coroplast go around the corners on the end of the air dam I had to slit the outer surface in a vertical fashion. In the true final product will have some form of covering over this to smooth it out so it looks better than now.


Almost Finished4

Almost Finished5

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