Last night’s Mythbusters (Oct 21) tested the hypothesis that a dirty car gets better mileage than a clean one. It doesn’t.
However, the crew then built a car with a (golfball-like) dimpled surface. It was a lovely thing to see. They covered a car with about 1" of clay, and tested it with a smooth surface and with dimples.
The smooth clay car (with a running start) got mpg equal to a normal painted vehicle. The textured car did 11% better.
Approximately 26mpg vs 29mpg.
Eleven percent is a major improvement, and I’m sure the texture could be fine-tuned for better results.
I think I’ve read about WW2 fighter aircraft with textured surfaces, but a quick google didn’t turn up anything.
My General Question is "Why aren’t we seeing hybrid cars, race cars, and aircraft with textured sheet metal?