Hi Winkosmosis,
You mean surface area. Because a parachute actually has less frontal area than that of a flat sheet of the same surface area, and less drag too.
A half sphere has 2*pi*r^2 area. Its frontal area is that of a circle, or pi*r^2. So, it has twice the surface areas as frontal area.
Cd of a domed parachute is 1.5. Cd of a rigid square plate is 1.0. For the same frontal area, the flat plate has 1/1.5 = 2/3s the drag. But for the same surface area the rigid square has 2/1.5 , or 1 1/3 times the drag of the domed parachute. This is probably why DaVinci tried to make a stretched square fabric parachute originally. Fabric was probably pretty expensive back then.
Which jives with my previous email, and causes a discrepancy to the parachutes work by surface area theory. Identical surface area devices have different drags. Parachues work by form drag. Identical frontal areas devices have different drags too. The form is important to the true drag.
Check out:
Parachute Design
Wyatt,
By saying that its only surface area, your in effect telling motorcyle guys that they would get the same drag reduction on their bikes if they mount their shells backwards (driver side towards the foward direction).
Now, given, this drag difference is small compared to that of an overall car. But mounting the grill block behind the grill, will have more drag. One can always paint the coroplass black, and on the road nobody will notice the difference. And if you start to overheat, its much easier to remove! And, if there is any defect in mounting the coroplas, it does not get blown back into the thin radiator fins, but just falls sideways.