I also sat in the Diana-1 and it fit me fine, I'm 5"10. I actually
like the side stick, though I haven't flown one. As to the structural
integrity of lighter frames - if it's lighter, it'll take less energy
to push/pull it and otherwise less force will be applied to it. Look
how robust model a/c are. They seem more crash worthy than the real
ones. So I don't readily accept that argument off hand. Lighter might
actually be stronger as it would also have less kinetic energy to move/
absorb and thus need less energy (and incur less structural stress) to
stop/move it. Of course I could be wrong on that, but I think there is
something to it.

I think there is an exponential factor here - the heavier the plane's
structure is, the stronger the wing has to be, making it heavier
still, etc...and true in reverse.

Imagine if a structure like Diana-2 were also made of prepegs? Would
it be lighter still by a significant amount? It already weighs less
than 200Kgs. I think there is a lot of improvement coming, mostly by
making the sailplanes lighter and increasing their aspect ratio for
the same wing span.

I would love to see an 18M Diana-3. Any news on something like that?