Originally Posted by Doctor DEF
The drag coefficient of a flat plate inclined at 30 degrees or so (like a windshield) is about .9 for speeds that RV's travel at. The area (reference area or the projected area of the windshield) of a medium sized windshield is about 6 ft. X 2 ft. or 12 square feet.
Those numbers look like they're for a typical car windshield, not a motorhome. Motorhomes typically have vertical, or almost vertical, front caps, not slanted at 30 degrees, and the windshield is typically about 1/2 the total front cap area - considerably more than 6' X 2'.