Erik mann wrote:

I wonder about this cost issue. Having done some re-profiling and
re-finishing myself, I have to believe that the decrement in labor and
materials involved in a 2 meter reduction in span is insignifiant.
For instance, once you have the 600 grit on the sanding bar and you're
moving right along, the last one meter of a given wing is lost in the
overall effort of setup and cleanup. Although the materials are
clearly incremental, the percentage of material is certainly less than
10 percent since the surface area of the last two meters is likely
less than 10 percent of a modern wing (e.g. 115ft2 for a modern glass
bird vs about 15 ft2 for the outboard 1 meter on each side [3 feet x 2
feet mean chord]). So, maybe we could optimistically see a 5-7%
reduction in per unit construction cost. Throw in tooling and
development costs, and what's the real savings? That's at least how I
would view the numbers if I were setting up shop...

Compare the 113 sq ft, 15 M, 513 pound LS4 with the 82 sq ft, 12.6 M,
290 pound AC4 Russia: that's a 27% reduction in wing area and a 43%
reduction in weight! The fuselage is smaller, too, but not as much a
reduction as the wing. That seems to me a significant reduction in
finishing is possible, and also in the construction. Of course, an
obvious difference in materials cost (these are both fiberglass gliders).

But, since
the homebuilders movement is pretty much moribund except for a few
hearty soles, what's the magic about 13M?

Nothing magic about the 13 meters, except it's big enough that I think a
modern design can match the LS4 in performance (it IS a 24 year old
design, after all!), which has become the de facto "minimum acceptable
performance" for the more vocal on the newsgroup.

We know it no longer requires 15 meters to match LS4 performance. 13
meters seems likely to achieve that, and the overall size is enough
smaller to make real cost reduction possible.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA