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Originally Posted by BabyDiesel
Aerohead, I found the scholarly article that mentions the C-130 fuselage. They were working with scale models - http://enu.kz/repository/2009/AIAA-2009-90.pdf
From Kosin & Lehmann's phantom tail research, my math showed that 70% of the original length gave a 12.12% increase in drag. I'm trying to figure out how exactly Hoerner, 1951 got the Cd of 0.158 with what appears to be only ~40% of the tail cutoff, when it takes 70% of the tail to be cutoff to equal a Cd of 0.169 in Kosin & Lehmann's data?
It seems that the more "aggressive" contour receives a greater drag penalty with a truncated tail than the less aggressive contour. The more aggressive contour is better for street driven vehicles due to length. Would there be a happy medium between these, or is the Aero Template the best to use for our daily drivers? |
You might need to help me out with images.
One thing to bear in mind,is that the Lehmann/Kosen streamlined body is of larger fineness ratio with Cd 0.066,whereas Hoerner might have been using a 2.1:1 streamlined body of Cd 0.04 in free flight.
In ground proximity,as half bodies,the longer body could have no lower drag than Cd 0.132,while Hoerner's would be Cd0.08,due to the 'ideal' pressure drag/friction drag bias of the shorter body.
When wheels are added it alters the drag/length relationship.
The drag trend of the truncation should behave the same as a function body length,but the dissimilar surface friction qualities and overall drag differences of the two bodies aggravates the comparison,not to mention the effects of the wheels.
As to the 'happy medium',Kamm and Fachsenfeld advocated a streamlined body which was truncated at a 'practical' length (where wake = 50% frontal area).This would allow for moving in traffic,as well as parking and driveway ramps.
Then Fachsenfeld came up with the idea for the extensible tail which would only deploy on the highway.
It just comes down to how much length you can live with,or add when needed.
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The 'template' is primarily for aft-body streamlining.Since it is based upon the lowest drag streamlined body which also respects down-slope, in-slope ,and up-slope contours incapable of producing separation it's a safe bet for modding.
23-degrees is the absolute maximum tangent angle which can sustain attached flow according to PhD Rolf Buchheim et al,from VW research.
Here is their profile
I'm playing safe at 22-degrees,according to Mair's research.It can't fail.
Again,just chop off as much tail as you like.