Andreas Maurer wrote:

I fail completely to understand why a smaller span (and crippled
performance) should lower production costs significantly. Why no
outgrown glider with up-to-date performance?

Changing wing span to, say, 14 meters will cost about 5 points of L/D,
and I doubt that it will save more than $500 (slightly less material
needed, and three man-hours saved for finish).

There's design, and then there is design for manufacture. If you look at
models for manufacturing costs of things, airplanes included, the
biggest factors are the choice of materials, the mass of whatever it is
you are making, and the complexity. The big things that affect
complexity are parts count and the ease/difficulty of working with the
material. Drops in parts count can have *big* impact on touch labor.
Think fixed wheels, for example.

After that, there are big learning curves for how many you make, with
the cost per unit dropping significantly. Aerospace thingies typically
have about an 80% learning curve, which means each time you double the
number of things you make, you drop the cost of manufacture by 80%. So
if it costs $10K to make the 20th plane, it will cost $8K to make 40th.
That's not saying the manufacture will pass on the savings, of course.

There are probably enough gliders out there against which to do build a
semblance of a cost models for gliders.