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Old 12-06-2008, 03:54 PM   #4 (permalink)
aerohead
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half or full

Quote:
Originally Posted by basjoos View Post
The Cd would go up because you'd have quadrupled the size of the recirculation eddy trailing the car.

When I first built my prototype boattail, it was cut off at the point where the back edge of my hatch glazing is now, then later I added a tail cone to complete the boattail (see pics in my Photobucket site). I got a noticeable increase in coasting performance when I went from the partial to the full boattail. There's a reason you don't see subsonic aircraft flying around with kammbacked boattails, its called increased drag.
basjoos,
I've been going over the old German stuff and it's in agreement with everything you say.And I was surprised that there is a certain degree of ledgerdermain with respect to the claims by the "experts" with respect to cropped posteriors on cars.---------------- With Jaray's and Lay's research,along with Dornier,Messerschmitt,etc.,full drag reduction does not occur until the full boattail is achieved.---------- Even when Korff eludes to Dornier's aircraft fuselage being truncated for the rear gunner's turret,we're only talking about 2 % of the tail length being compromised before extreme drag increase occurs!-------------------- Sure,there are practical limits to the length of a car,and Kamm openly admits that his 50-% tail- "Kammback" was to address "length" issues not"drag" ,but in purely aerodynamic terms,whether practical or not,its incorrect and untrue to say that a 50 % crop is as low drag as a full tail.The science simply does not support the claim!------------------------ Not to go off-topic,but if people expect to ever achieve high levels of fuel economy,they are seriously going to have to re-consider how they think about what cars should look like.---------------------- Thanks for all you do,and for remaining a constant source of inspiration for an old tin-knocker like me and so many others.It makes it easier for me when I know there are a few out there that "get it" and are willing to apply themselves,sometimes amidst an environment of zero encouragement and support.My hats off to you!
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