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I'm not on the scaling bus. Just want to state that.
But, there is something that I don't quite have a grasp on. I posted in another thread, but it was a bit of tangent there. What I don't think I have ever seen is a "template" that describes what the minimum rear "tail" needs to look like to achieve attached flow. This shape is NOT ideal relative to drag, but should have much less drag than say a flat rear like a semi trailer, or even a hemisphere. We see this over and over, less than ideal shapes making good aero numbers. From the Dryden van, to Trailer Tails, to Joe Schmoe's kammback, to the latest hybrid car, etc. We hear a lot about attached flow and tuft testing here as being a reasonable metric. Just what shape do we need to get that? (And just how good is it?)
The Dryden van is a good example. It has a boattail. Does it match the template? No. We can conclude from that it could have been better. OK, got that. But there were tuft tests done that showed it achieved what looked like attached flow. And was A LOT better than no tail, or rounded rear edges.
(And on the 25% - 75% "fits" above. Doing the same for the plan view would find a closer fit. Everyone seems so stuck on the side view....)
Tim
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