aerohead -
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Originally Posted by aerohead
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.
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I was working on a version of the "tear-drop line" for Xringer's CRV, but you can see I may be off a bit on how I aligned the tear :
However, the alignment may not be too important because the angle all along the "trail" of the tear (comet?) is almost the same. The hard-to-see trailing red line is about 10.5 degrees below 0 degrees horizontal.
Xringer -
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You are so right about the lack of taper on the CRV. It's way too boxy.
That's the main reason I found the improvements being used on trucks so interesting.
If this stuff doesn't contribute anything to the MPG or causes drag, I should be able to see the effect on the MPG after a while.
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I agree with your logic on using trucks as your inspiration. To me, the truck solutions make sense for Scion XBs, Jeeps, and "boxy-shaped" SUVs.
CarloSW2