Quote:
Originally Posted by Xist
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Here's the easy way to see if "building up the roof" will have an advantage. Both pictures have the same streamline template which tells you how much of a drag reduction you'll see at certain sections. Now see if you've slided the template far enough forward to offset the increased frontal area, for the same length of boat tail behind the car. The math is there for you to find out.
My reasoning:
"Building up the roof" is a compromise to shortening the length of the boat tail. Say you have two cars with the same frontal area and a 100% complete boat tail. But one starts it's taper at the top of the windshield, and the other 6 feet back of a flat roof. Shouldn't both have within <1% the same cda of each other? So building the roof will increase the cda, but give you a more compact boat tail. Shortening the boat tail is "mostly" the whole point of starting the taper as far forward as you can.