Quote:
Originally Posted by Xringer
Question: Are boat-tails and kamm-backs *both* legitimate solutions to aero design problems? Which one gives you a better solution?
I think that some may consider the $$cost vs gain as a factor in the "better solution"..
The Wake board and Frame extension ideas have been wind-tunnel tested,
because they were VERY cheap to install on 16 wheelers.
(Of course, an expensive full boat-tail is going to be way better).
My aim is to try out that cheap, quick and easy stuff to see what might work..
It's a crap shoot. But, if something quick-n-easy actually works, that would save a lot of people a lot of work and maybe some gas money..
One more step in trying to save the planet.. LOL! 
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Xringer,the boattail is merely an extension of a Kamm roofline which has attached flow.--------------------------- If you want a sense of what it will do,take a look at cfg83's Saturn,under MetroMPG's aero template/teardrop.Where the roofline begins to fall away,is the beginning of the Kamm roofline.From that point,to the end of the teardrop is the potential for drag reduction.If you divide that length into 10 equal segments,each segment is good for a 10% reduction in wake area,a 10% drag reduction,and a 5% increase in mpg (HWY).--------------------------- As you can see on the Saturn,the roofline allows for some drag reduction by the end of the roof and sides.Your CRV doesn't have as much taper,so your wake is basically as big as your frontal area.------------------------ The longer you make the tail,the greater the drag reduction,as you convert air velocity back to static pressure.That's really all there is to aerodynamics!-------------------- So basically,you can compare the length of your extension and new wake area,to the CRV's original wake.For every 10% reduction you pick up 5% better mpg.---------------------------------- Theoretically,if you had a lightweight tadpole trailer,with gap-fillers between the CRV and the trailer,which extended out the full length of the teardrop,you'd have a 100% drag reduction,and pick up 50% better mpg on the highway.So say your pulling 30-mpg on a good day,you'd be looking at 45-mpg at a steady 55-mph.