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Old 06-29-2013, 02:55 PM   #44 (permalink)
aerohead
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such thing

Quote:
Originally Posted by ennored View Post
Thanks once again Phil.

So, there's really no such thing as a "less than optimum" tail, other than a truncated ideal tail.

Not quite clear why the Dryden van works as well as it does, I'll have to accept "it just does" for now.

Looking at some percent drag reduction vs. percent of tail stuff, the Dryden van could have gotten to where it was (with 04" and 80" tails) with about an 18" (~15%) truncated template tail. A tail that short would only have drawn in 1". Could that really have worked? Wow...
All we have to go on is what made it into publication.There may be proprietary designs awaiting Patent Office Gazette publication which awaits access to our eyes.
Other than that,we can only infer or deduce potential design performance based upon data which exists in the public domain.
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If you're doing an 18-wheeler,and we already know that rounded edges give 11% lower drag than square edges,then we can lean on HVAC technology,creating a boat tail as an inside-out square-to-round duct transition exo-plenum.
Throwing in Mair's careful curvilinear profile,we protect the boundary layer against the too-sudden pressure rise which would force the air down an up-escalator,or downhill skiing into an uphill avalanche,forcing the turbulence we must absolutely avoid if we're to ever reach low drag.
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Again,the Cd will be totally dependent upon the length.The aft-body is responsible for a 566% drag reduction on the body.If you're looking for the Lost Dutchman Mine,this is it!
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