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Old 07-16-2011, 03:47 PM   #23 (permalink)
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Originally Posted by orbywan View Post
I should have tested it before and after with the A/C fairing but according to the tell tails the air is flowing perfectly over the rear upper section, in spite of the steep angle. I think the A/C fairing is mostly responsible for that.

If you can figure out a way to Kamm the back, I'd love to see the results mileage-wise. I've never seen it done on a 5th wheel before. Never saw it done on an RV before either. To be honest I didn't think it would make such a big difference, but I kept looking at the huge abrupt drop off (for the air) area at the back and figured if it worked for NASA (referring to the Dryden AFB tests), I'll give it a shot. Completing the belly pan is next.
I don't know if a 1970 VW Westfalia Campmobile qualifies as an RV,but the 18-inch boat tail,with Breer/Fachsenfeld/Kamm-chop that I put on it in 1980 was good for almost 4 mpg by itself.
The radiused tail of the VW allowed more lead in curvature,so in essence,the virtual boat tail was more like 2-feet in length.
The tail curved into a maximum 20-degree angle,top and sides.No bottom.
With spare tire cover( on nose),full bellypan,rear wheel skirts,and tail,the van was capable of as high as 35 mpg @ 55 mph,up from 27 mpg.
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