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Originally Posted by kach22i
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I just wanted to mention that the square-edged roof model airflow is not applicable to a rounded-roof contour as on the Beetle.
In Hucho's 2nd Edition,Chapter 4,Pg 154,Fig. 4.60,'Effect of rear end height z on drag,' an image from Buchheim et al. is shown for a rounded rear end contour of 30% 'Template' aft-body.
Minimum drag occurs when the 27.5-degree roofline is pushed upward to include an exit tangent angle of 13-degrees.Cd is cut 0.075.
On the New Beetle,the rear slope at the top of Ernie's wing is 37-degrees.Ernie;s wing relaxes that angle to 19-degrees.
From Buchheim's research,it would suggest that for the lowest drag,you would continue to extend the wing further back until it intersected the 13-degree line,as the Beetle is also a 30% aft-body car.