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Hi Wyatt,
Ok. Well, I do not think its only surface area. Ther aero guys seperate the two - one called form drag, the other parasitic (surface? ) drag.
To see the difference. Make a rigid hemispherical shell, and tie strings to it with cup up and down. Then time the drop with the same weight and see if you get the same fall times.
I am pretty sure the cup down orietation will fall more slowly. It has greater form drag. A simple model is that the air goes in, and them comes out. So, that in effect doubles the surface area. But in reality a buble forms, and some air is trapped going around in a circle inside the the shell. The ratio between the circular air flowing volume, and the overflow volume does not neccassarily need to be 2. But its greater than 1, and that is why the parashell falls more slowly cup down.
The reason the difference is so great in a parashell is that all the drag is associated with the parashell, and nothing else. In a car there are other issues.
Which brings up the idea of another experiment. Get a half cylinder shell (PVC tubing cut in half) the same height as the the grill work. And do a coast down test with the cylinder open end forward, versus rearward over the grill work.
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