Oh BMatthews, what have I done to deserve this. All I wanted was support your point of pretty rearward balance, and I just thought I take it to both extremes - no tail (and sweep) at all and really big undercambered tail.

I'm the last one suggesting the "lifting stabilizer", on the contrary. You really don't seem to remember our discussions five years ago (e.g. my earlier post in the same thread). All I was saying is that the undercambered airfoils of freeflight wings have a strong down-pitching moment and that way contribute to the rear balance. Yes, they do, just try a moment plan or use a NP calculator which takes moment into account. Of course NP doesn't shift, but balance does if you change airfoil moment, or incidences/decalage change noticeably. And a big stab, say 33% of wing area, with cambered airfoil contributes noticeably to the overall down-pitching moment and the rear balance position. Thats all.

And the flying plank is an academic example, meaning that even a configuration without any stabilizing measures can be stable. The interesting point is that the balance has to be behind 25%, not ahead. The diagram shows that a balance at 28% makes for about 7 or 8 degrees AoA. (Not 6 degrees, that's only where the moment starts to become noticeable.) That's pretty much but not quite stalled, and it's an academic example. It works for thicker airfoils as well because they as well have a moment at higher AoAs. They tried it in the 1930s as a small test glider in a hall, it has whiskers, I don't have to do it again.

As a funny aside, I even tried such balsa chuckies following a book about the basics of model flying. Not only conventional tail, but also swept flying wing, flying disk, and flying plank. And indeed all except the plank had some form of decalage or reflex, the plank going to show the extreme case. Alas, that was only 50 years ago. :-)