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Old 06-02-2018, 12:32 PM   #721 (permalink)
aerohead
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22-degrees

Quote:
Originally Posted by Tesla View Post
I have re-done the equation with the specs from post 517 (3-Wheeler) just to explore those specs further, although it does come up with a 2.5:1 Aspect ratio, there are other issues which make it less than ideal.
I have made the x & y grid lines the same as the template so it's just a matter of lining up the height and length markers to compare, the overlay is below:



I think there's probably enough detail in the overlay to explain itself, particularly comparing the angles which start gentle but then accelerate to 27 degrees at the 80% mark, which breaks the 22 degree rule. Although the Aspect ratio is 2.5:1, the issue is that 1/3rd was in the fore body, which leaves the tail with a 1.67 tail ratio.
In Hucho's book he shared a metric researched by Buchheim et al.,in which they reported that we could take the rear down-slope to a maximum 23-degrees without inviting flow separation.
Buchheim's lowest drag body was the VW 'Flow',at Cd o.14 as a long tail.
If you look at his graphic for this car,I came up with 22.5-degrees maximum angle by just laying a protractor to the drawing.
So it looks like we get a little wiggle room without degrading performance.
Again,great work! Thanks so much!

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