Quote:
Originally Posted by freebeard
...85" inches across the flats? x.25 would be 21". Or it could be more complicated, the distance on the diagonal is 85x1.42...
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No idea what all ^that^ means.
Van is 85" tall from ground to rooftop. That's H. 2H = D so D = 170" and Mair's graph shows .25 on a scale of L/D (x axis) as the point of greatest cod reduction/length of tail so .25 x D = L. 170/4 = 42.5. That's L, length of tail, which should return greatest gain in reduction of cod for its length. An approximation and WAG to be sure, but best I've got for now.
I've got no room for anything further back than 33" or so. I'll build what I can fit and know there's more to be had with a longer tail. If instead of 42.5 I'd found something like 32" I'd feel better and if I'd found that gains peaked at 18" I'd just build to that length and stop.
A 15° line drops 11.375" over a run of 42.5" and my roofline is about 10.5" above the tops of my rear windows so the tail's top side shouldn't be intrusive at all. With tinted windows I bet painting the flap's inner edges black would make that 7/8" of overlap totally unnoticeable.