Short Wings Gliders

Darryl Ramm wrote:
On Feb 1, 2:06*pm, (Michel Talon) wrote:
Bob Kuykendall wrote:
No, not true. As I've written elsewhere the manufacturing cost seems
to scale exponentially with span.

I don't pretend to be as knowledgeable as you about gliders, but
i know that exp(15/14) is not very different from 15/14.

One has to chase economies elsewhere.

One must chase economies everywhere.

Mostly in the hourly cost of manpower, e.g. by building in China,
not paying horrendous fees to some university departments to do the
computations when it is certainly possible to get them for free,
and so on. Probably everything else is negligible.

--

Michel TALON

Not so fast, if you want to argue with pseudo-math lets get it right.
15/14 is ~1.071, e^1.071 is 2.91 which *is* very different. But what
you should be asking is what is e^15/e^14 which is a ratio of 2.72,
since Bob said the cost scales exponentially with span, not

I expressed myself very poorly, my idea was that the increase in cost is
exp(15/14) *compared to* the case where there is no increase, exp(14/14)
so the net increase is exp(1/14) which is very close to 1/14 (the second
order term being 1/2 (1/14)^2, negligible). Hence, even if the increase
in cost is exponential, you will pay (15/14) x (cost of a 14 m glider)
for a 15 m glider. The factor 2.7.. = exp(1) above is bogus.


exponentially with the span ratio. Not that 2.7 is far from 2.9, but
at different span ratios the difference in calculations becomes, ah
exponential. Not that this means anything, since Bob was just likely
making a point with a hyperbole.

I agree completely with that. But i remark that the cost of gliders has
indeed increased exponentially the last twenty years, for reasons which
have nothing to do with concrete factors, but everything to do with
hourly cost of workers, and total lack of will of controlling the costs.
The glider factories seem to think that glider buyers are like Ferrari
buyers, who will accept to pay any price for their toys. The problem
with that is the category of people interested in flying has no
intersection with the category of people interested in showing their
external signs of richness to bimbos.



I'm curious who pays "horrendous fees" to universities. My impression
is many European manufactures get pretty sweet deals via relationships
with different University research groups and Akafliegs.

A closely previous post mentioned that Schleicher was paying heavy fees
to Delft University to get his computations done. Compare this to the
Pegase which was computed at ONERA for free. I have the impression that
the Pegase was the last glider whose aim was allowing a lot of people to
fly. And incidentally, it shows that one can build a 15m glider of
reasonable simplicity, with performances not that different from the more
complex ASW 20, easier to fly, and much cheaper. The LS4 also fits the
bill, but already in its time it was 3/2 more expensive.



Darryl


--

Michel TALON