Quote:
Originally Posted by vteco
For me the interesting take-away from that study is that, with regard to the cabin top, a long exit angle and a short entry angle, with a strong bias for location of maximum thickness at about 30% aft of the front of the cabin top approximately mirrors the configuration of conventional airfoils.
As a guess, their model would show improvements, if instead of the simple prismatic shape, they tried a smoothed foil of about the same proportions with thickness at about 30% of chord.
I think, the incidence probably would be critical to shaping the flow over the tailgate in a real truck, and that would probably vary for different trucks, with the heights of the cabin-top, and the tailgate, and the distance between them.
Also, of course if there was a partial or full tonneau.
Lots of variables, no definite statements... this is the postulation part. No certainties.
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1) 30% is close to the recommended ' 1/3rd-'chord'' of ' ichtyoid / fusiform ' bodies ( penguin, raptors, dolphin, shark, embryos, seal, tuna, etc.)
2) Dr. Hucho's pick for low drag was a streamline body of revolution, with a fineness ratio of length / width = 2.5:1, @ Cd 0.04.
3) When you examine this shape in mirror image ground reflection ( The 'road' bifurcates the 'teardrop' longitudinally ) leaving streamline 'half-bodies' both, 'above' and 'below' ground. You'll see that the 'forebody/aft-body demarcation occurs at one-third body length from the nose.
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If you parked the pickup next to a shallow pool of placid water and stood back, behind the pool, you'd see the 'phantom' truck 'under the ground. And technically, lowest drag would occur when the 'mirror-image' satisfied the 2.5:1 ratio.
Any shorter, and more drag.
Any longer, and more drag.