[aerohead]

Originally Posted by ERTW

Kamperbob, you are correct. I wanted to investigate the prismatic shape because firstly I don't see anybody using the revolved shape. The template works for a revolved shape, or even a high aspect ratio wing. However, cars are narrow boxes. Flow around such a body is very different. That's why I'm modeling a prism. Perhaps Aerohead can comment.

You could argue that the box fish is the slipperiest shape found in nature. Boxes are also much more pragmatic than footballs; they offer more usable space and are easier to build than compound curves.

Aerohead, I put the template up against a 2010 GMC Sierra, and found that it only goes out to 45%. What is the minimum Cd at that point?

My template approximation is good to about 60%. The zebra stripes should be concentric circles - as they are at the peak. You can see the broad space and the reverse stripe on the tail which confirms a discontinuity.

At 45% you'd be in between Cd 0.209,and 0.177.