Quote:
Originally Posted by AeroMcAeroFace
Wasn't the top speed as a claim of drag reduction to sub 0.2 shown to be not true by both Julian and R.H Barnard?
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Interesting story behind that.
First, when Aerohead offered pics/description of his truck for inclusion in my book, there was lots of back and forth emails as I kept questioning his claims. (I didn't then know Aerohead from bar of soap, but it was pretty obvious some of what he was claiming was highly doubtful.) Therefore, I didn't run any of his claimed drag coefficients in the description of his truck in my book.
One thing that raised red flags was his new/old top speeds, that didn't seem to match the claimed improvement in drag. Using Aerohead's figures, I did some calculations (page 21 - I didn't mention Aerohead, but that's the data I was using) and they showed his new claimed Cd was not right. On the basis of the top speeds he then gave me (I see Aerohead uses completely different speeds in his post above, but anyway...) it appeared to be a change in Cd from 0.44 to 0.37.
However, when Dr Wolf of Porsche read my book after publication, he said he had a much more accurate way of calculating changes in top speed with changes in Cd, and gave me a new equation to use. When I apply that equation to Aerohead's original new/old top speeds, I get 0.33 - so better than I originally calculated.
And if the correct figure is 0.33, that's an excellent reduction from the starting point (well the originally quoted one, anyway) of 0.44. Based on all I have researched about reducing drag, and looking at the pics of the truck, I'd also say that's possible.
But a claimed Cd of 0.195? That was always ridiculous.