I don't entirely agree. On sailplanes there's been done a lot of research on the same subject. Low-pressure flow, even more so the flow on the top of a wing is very sensitive. The basics are known. Sure, we can improve the details, but the big picture will always be draggy with a low-wing, since you can't fix the big issue (having most "sensitive" flow in a disturbed area).Generally I feel that almost every attempt at doing a low wing has been done by designing the structure first and then trying to figure out the aerodynamics after. Most times in small planes all the fattest parts line up and create a sort of mess where the bulk of the low pressure peaks are. Sacrificing or deleting pressure gradients in one area to pull hard to evacuate another area longitudinally has not ever really been examined. I think there is room to follow behind Mike Arnold and to try to understand such phenomena.
Sure. But the extra momentum around that tail boom (=extra drag) is tiny because it's so small. That's what planes like the SB14 are about. Once flow gets turbulent, minimize wetted area.And so it goes. There are only two choices of shapes to look at and move around.... convex and concave. Most simple concave blends have not worked. So that leaves the other or combinations of the two changing along a longitudinal line. The other one is to shed off into the free flow. If separated flow starts but doesn't have any real wetted area to follow then it is minimized. How much of the large tailboom of some of the competition sailplanes are in the turbulent zone? For what distance after separation? 3-4 meters?
But way better is to maximize laminar flow given the almost order of magnitude difference in drag.
Admittedly that's terribly hard to do though..