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Old 07-08-2008, 01:06 PM   #1 (permalink)
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Kamm/Korff discrepancy

When I did the installment on aftbody"quotes" I wanted to give you "all the gory details",spoken from the horses mouth.When I got up to 1963,I included a quote from Walter H. Korff,one of my hero's.although something stuck in my craw for what he was saying.Since that post,I dug a little deeper and found the reference Korff used and while not untrue,if not taken in an EXACT context,it will throw you completely off the globe! -------------------------------------------------The source is Hoerner,it's from 1951,and here's the deal: Given that a car is operated in traffic,goes up and down driveways,and must fit inside a parking garage,one would consider giving it a "resricted- length." For a "restricted-length" vehicle,a chopped-off rear will have a lower drag than a than a radius'd rear.Hoerner recommends that you chop the rear at 50 % of frontal area.--------------------------------------------What Korff said,and I'll repeat the quote"this blunt...aft portion will have no more drag than a full length streamlined body that curves down to the bellypan." I believe what Korff means to say,is that a restricted length body,curving down steeper than the prescribed aerodynamic pathway will tolerate,will have separated flow,so allow it to follow the prescribed pathway until you achieve 50% frontal area,then just chop it off.When he uses the term "streamlined" I believe he is using it in the context of styling,not true aerodynamics.----------------------------------- The fact is,that if a "full length streamlined body" continued out to where it intersected the line of the belly pan,that the vehicle would experience an additional 50% drag deduction.This would be physically impossible to achieve at 50% frontal area chop.

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Old 07-08-2008, 05:19 PM   #2 (permalink)
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Hoerner summed up our big problem. Vehicles have to be driven in the real world with traffic and inclines.

If I were to make a 10 degree slope boattail for my truck it would have to be as long as the rest of the truck. Ergo, you gotta chop it somewhere.
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Old 07-08-2008, 05:57 PM   #3 (permalink)
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length

Quote:
Originally Posted by Big Dave View Post
Hoerner summed up our big problem. Vehicles have to be driven in the real world with traffic and inclines.

If I were to make a 10 degree slope boattail for my truck it would have to be as long as the rest of the truck. Ergo, you gotta chop it somewhere.
Yeah,I'm not immune from this myself.I take the boat-tail off the T-100 when in urban duty.I'm trying to de-program my brain,and see if my single braincell can manage some creative solution to the length issue.There's an additional 25% mpg hiding behind most vehicles.If you could tap it.I've seen 50 mpg pulling a trailer behind the CRX at 3,300-lbs gross.The trailer had no under carriage streamlining,and it lacked the full gap sealers envisioned for the project.The 1-wheel trailer promised better mpg,but results were marred by two fried vacuum lines behind the carb (didn't know it at the time of testing).She averaged 48 mpg with the leaks and at speeds as high as 85 mph and Vail Pass,Colorado @ 10,600 feet.The inflated tail was good for 30 mpg with half-tonneau in the T-100.That is something which could possibly address the length issue,as it stows itself below 45 mph.I'll keep chipping away at it and until some breakthrough occurs,I'll be in the "it's too damn long"camp.

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