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Originally Posted by eco_generator
So leading edge is vastly important if you are starting with a completely flat face...
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That is my understanding.
Unlike most passenger cars and trucks today that early 60s semi tractor trailer example had high initial Cd (0.88) due to poor onset. I expect quantitative analysis (CFD, wind tunnel smoke) would show a lot of bow splash from initially stingy/small leading edge radii and turbulence from a large gap between the tractor and trailer. Cd reduced a lot by addressing those problem areas with modest treatments.
Quote:
Originally Posted by aerohead
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After initial gains the difference between modest and massive rounding of trailer front edges (shadowed by the tractor) provided marginal return.
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Originally Posted by aerohead
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Radical front redesign of the tractor was needed to further reduce the Cd to 0.46.
Quote:
Originally Posted by aerohead
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Much better ... and yet still worse than most passenger vehicles. because the large flat rear of the trailer acts like a drag chute. Hoerner showed this. Clean onset creates good attachment. Which also increases base drag. And thereby limits return on front investment. A boat tail is all the more important for a holistic solution and ultimate aero slippery.
Phil, thanks again for sharing all this research!
