Quote:
Originally Posted by JohnForde
Thank you everybody!
I appreciate the 'rounding' idea, but I need access to the door.
Here is an idea. Increase door angles to 16 degrees. That leaves an aperture or wake area 36" wide. Tuft test.
Then fabricate a detachable cone as shown. 100% polycarbonate Twinwall. Under 10 lbs.
Length is now 108" behind bumper but I can move the tail lights easily to within 48" of the rear tip. Aperture is rounded and now 12" W & 36" Tall.
Fine for highway. Very tricky in a parking lot.
Still square to 66" behind bumper but rounding the final 44" or so.
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* On a simple, prismatic, 'saloon/ sedan' fastback test model, Rolf Buchheim et al., of Volkswagen, went as steep as 16-degrees top slope, on a car with an aft-body length equal to around 20% of total length.
* With your 70-inch tail, you were at 19.4% body length. But Zevo isn't a 'saloon' body. It's 'taller' than it is 'wide', requiring a different solution.
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* We have no empirical test data for any vehicle which is analogous to Zevo.
* No investigator has tested a 'rounded-roof' vehicle, with a 'sharp-edged' tail extension.
* So we're in un-charted waters, data wise.
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* When Dr. Hermann Burst designed the 'duckbill' rear spoiler for the Porsche 911 Carrera RS 2.7, his original 'solution' was to add a Kammback, following the exact contour of what the aerodynamic streamlining template, part-c has. 'Porsche' forbid it, and after surrendering to the Paris Dressmakers, he ended up constructing the rear spoiler, of which, it's upper termination point ( it's tearing edge ) is 'exactly' where the 'Kammback' contour would have been.
* When you examine the truncated boat tail on NASA's Ford Econoline-based 'Project Shoebox', you see them doing basically the same thing.
* Same for Lawrence Livermore's 11-degree, 'straight' tail. That tail constituted 5.8% of total body length.
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If you've got the stomach for it, run a range of angles, record tuft orientations, and get your pressure coefficients recorded.
I'm inclined to think that the 'smaller' angles will be your 'friend.'
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The 'value' of the rear 'aperture' area, is completely predicated upon fully-attached flow, and it's attendant pressure recovery, for the entire length of whatever you build.
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Transitioning, from square-edges, back to rounded edges, while within an environment of increasing pressure may provide little probability for mended flow.
Paul Jaray would transition from 'round' to 'square', and then back to 'round, but he'd never do it 'in' the aft-body. His would be at the 'beginning' ( the 'cuff' ) of the aft-body, and increase, incrementally, with distance as it grew nearer and nearer to the trailing edges.
And, if a 'radius' is too daunting, a 45-degree 'chamfer' is the next best thing.