Quote:
Originally Posted by jray3
How much of a penalty from ideal airflow would a triangular trailer tail extract?
(ok- found it here http://ecomodder.com/forum/showthrea...tml#post294074
with a similar example dropping Cd from 0.25 to 0.214)
My enclosed car hauling trailer has a drop-down ramp, but I use long extensions to get the low-riding car in and out. I'd rather rebuild the ramp to be longer, and extend the roofline down at approx 12 degrees till they meet, forming a 'triangular prism' tailcone. Not a pyramid, as the apex will be just as wide as the base. This approach maintains overhead clearance while coming up the ramp and entering the trailer. Actually, I could make the end of the ramp about 20" narrower than the hinged end, to match the floor width between the wheelwells. That would provide perhaps 10-15 degrees of taper on the tailcone sidewalls. |
In 1933 Walter Lay,at University of Michigan did wind tunnel research on a car model with a prismatic tail.
*The roofline curved as with Mair's boat tail,then descending into a constant 18-degree slope out to a point.
*The sides had initial curvature as above,blending into a constant 12-degree angle.
*The side/roof intersection was radius'd with the minimum,around 5% of the vehicles width.
*There was no up-swept 'diffuser.'
Lay measured Cd 0.12 for the smooth model.Kamm and Fachsenfeld reproduced the model and got the same results in the late '30s.
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A tail based upon something like this would be a lot easier to fabricate than the ideal compound curves.
As with Kamm and Fachsenfeld,you'd just decide how much length you could live with,and then just slice off the rest so to speak.
*It's extremely important to have the initial curvature,as NASA did with their Dryden Research Center truck studies.