The Drag-Reducing "Wing" on the VW Beetle—How It Works
Most cars have very low aerodynamic drag. But some cars, and ALL trucks have high drag. We apply airfoil principles to improve drag for cars and trucks. An airfoil (like an aircraft wing) has very low drag. It looks like this:
Automobile drag occurs mostly at the rear. The rear part of a car should have a shape similar to an airfoil for low drag:
A well-designed car has a drag coefficient, Cd, between 0.25 and 0.30. By comparison, the regular VW Beetle has unusually high drag, Cd = 0.38. We added a shelf to the back of the Beetle like this:
And, finally, winglets were added on the ends of the shelf to give it strength and to further lower drag in a way reminiscent of airplane wings, like this:
The drag reducer lowers the Beetle's drag to about Cd = 0.28. Handling at high speed and in windy conditions is greatly improved (as you would expect with a wing or spoiler). Fuel economy is increased by 5% to 8% depending on speed.
Our modified car is a 2003 Beetle TDI diesel. On the trip to Alaska, the mileage averaged 57 miles per gallon. On our test track* we get 60 mpg at 65 miles per hour.
* Our test track is the straight portion of I-80 from west of Salt Lake City to the Nevada border. If you drop by for a visit, you can come along on one our test runs.