* Your fabrication looks 'good to go' for testing. I like to think that the tape will be good for 63-mph.
* I looked at P. W. Bearman's Windsor body testing from 1984. At a 15-degree rear slope, vortex-drag had increased by 300% compared to zero-slope.It would continue to grow to 900% by 32.5-degrees slope, where it finally 'burst', creating an all-squareback wake, as if it had no slope.
* On the Ahmed body, drag minimum occurred at a slope of 9-degrees.
* Clarkson University reported 10-degrees for their 'sweet spot '.
* And the Lawrence Livermore Lab. 11-degrees closely-matched NASA's Ford Econoline-based 'Shoebox's curved boat tail's lead-in' contour, even though it was 'curved.
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The 'empirical testing results' of actual aft-body contours appears to corroborate the historical strictures of Professor Hermann Schlicting's 'Boundary-Layer Theory '. Dr. Wolf-Heinrich Hucho studied under Professor Schlicting, and he emphasized that all of these 'historical' trends, observed for well over a century now, should be used to inform the direction of our own research.
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I think the takeaway for us is that:
* Just as has been said by all the 'pros', the surface of body must always 'live' within a few degrees of the local streamline.
* If the body cross-section varies to 'quickly', we'll introduce a super-deceleration of the boundary-layer.
* This super-deceleration will introduce the 'adverse pressure gradient' responsible for flow reversion, eddy-rollup, separation, and turbulence.
* Once separation/turbulence has occurred, any hope of additional pressure recovery is lost forever.
* Base pressure will be 'low'.
* Pressure drag will be 'high'.
* Total drag will be 'high'.
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For simple, prismatic boat tails, with no curvature, the pressure regimes which remain within the 'Goldilocks' zone of attached flow, appear to reside inside the range of 10-degrees-to-11-degrees.
What John Forde's R&D may provide us for the very first time in aerodynamic history is, how far can we 'stretch' that zone by introducing vortex generators into the calculus.
