Quote:
Originally Posted by BabyDiesel
I agree Chaz, but I would be more aggressive and make the top more "Kamm-back-y". Instead of making it as a typical cover with the back edge sloping front to rear, go the opposite way. If I had Wi-Fi, I'd draw a mock up of what I'm suggesting.
And rounding out the edges as you get closer to the rear helps Cd, but makes the construction a bit harder.
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I'd be interested to see an A-B-A test of the taller, more gently curved topper that follows that damn template exactly versus the 12° average slope version suggested by that one engineering thesis. I may or may not get around to that. It would be kinda neat if OP and I went with somewhat opposing designs to compare. Definitely slope the rear backwards not forwards though, I agree, and leave an overhang to get that hard edge around the convex section for the fluid tail like aerohead always talks about.
How critical is it to round the joint between the sides and top? It makes sense if the goal is to create an elliptical curve on the backside to induce the "Morelli's Fluid Tail" smoke-ring effect, but it doesn't apply as much if you intend to get the rear edge height close enough to the height of the tailgate. But I also wonder if a hard edge on those "shoulders" to ease construction and purposefully induce flow separation there like the kammbacks' rears (except on top) would be somewhat helpful too. I think it's likely there's a minimum radius for those shoulders below which you're better off with a hard edge. Though as always I'd love for someone to question and point out if/how I'm wrong. Crosswinds may play into it too. (I asked aerohead but he's only on his computer on Saturday mornings haha.)
Attached images are of a quick model from a 3d sketch I made a couple weeks ago in Autodesk Inventor (which for this I prefer over Solidworks). This represents the laziest possible geometry for the aerocap: I lofted the curve of the rear window down a straight 12° slope then trimmed it up. That would require zero heat-forming of the polycarb, just cutting shapes out of a single 4'x8' sheet and solvent/heat welding them together, and bolting them down such that the top section has that longitudinal curve that follows the window curve (which, if I choose to follow it, means I can't have any transverse curvature). Frame discussion in other posts. Sorry for the derail. Again, I'm very curious about your other planned mods!