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Old 05-20-2011, 05:33 PM   #162 (permalink)
aerohead
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Nasa

Quote:
Originally Posted by orbywan View Post
Thanks for info aerohead. My RV, and especially Randy's RV, I think will benefit from aerodynamic studies on semis, since the 'taller than wider' shapes are similar. My RV is also 8 feet wide, so the ideal length for a boat tail 'template' design would be about 14.5 feet long, according to the width X 1.8 equation. Looking at the curve of the template, I'm surprised it's not longer than that. I think for practicality's sake, though, this one will have to be 6 to 8 feet long.

The info from the link to the NASA/Dryden project that wyatt posted in his email above, notes that leaving off the last four feet or so of the pointed tail in their van project only resulted in a net gain of 0.004 drag, so I'm hoping the shorter length won't be too detrimental.

Doing a full belly pan on my RV is going to be a pain in the neck, but if the truncated boat tail yields sufficient gains I'm game.
orbywan,that's correct.The last bit of boat-tail creates a virtual tail( phantom tail )when chopped off.Air skipping over the small wake as if it were a solid cone.
For the 'Template',when doing a car:
* @ 100% = Cd 0.13 ( with no wheel fairings )
* @ 90% = Cd 0.13
* @ 80% = Cd 0.133
* @ 70% = Cd 0.14
So you can see that,and as others have published,there is little benefit doing the entire tail.
I chose 75 % for the Prius tadpole.
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