On Jan 28, 9:30*am, Derek Copeland wrote:

Why not just make a one design, mass produced 15m glider (preferably with
optional plug in 18m tips)...

Root bending moment scales something like exponentially with span,
regardless of whether the span is part of the orignial wing or added
later. So if you want to add 3m of span, you'd better design the wing
structure for it from the get-go.

We've already seen that even in what passes for mass production in the
glider world that the per-unit cost and price of a 15m ship are great
enough to severely limit the potential market, driving down production
rates and driving up per-unit costs. This is driven to some degree by
the complexity of the aircraft and the materials that go into it. It
is driven by a greater degree by the cost of the tooling, the amount
of floor space and volume it occupies, and by business expenses
relating to maintaining, heating, and lighting commensurate shop
space, and by wages and other labor costs. Big gliders require big
tools, and big tools require big shops, and the bigness seems to scale
with something like the square or the cube of the span.

The only thing I'm bringing to the party with my own 15m/18m design is
to keep overhead down to the barest of minimums and to offload a bunch
of the more labor intensive tasks of assembly, fitting, and finishing
to individual kit builders. The RV series of homebuilt airplanes
suggests that there is a great deal of manufacturing capacity
available in that market.

My interest in smaller gliders is chiefly in that they would fit into
smaller shops and smaller garages, opening up more potential market
for kit sailplanes. I also think that the potential kit market might
be more receptive to simplifications such as 90-degree landing flaps
instead of airbrakes as we saw with the Schreder HP kits and the
Monerai.

Thanks, Bob K.