50+:1 15m sailplanes

"Jim Phoenix" wrote in message
om...
Interesting.

I recall a technical discussion a long time ago asking whether there
was a
"natural best wingspan" imposed by the nature of soaring weather. The
question was this: "Ignoring competition classes, is there a single
best
wingspan that is suited for the widest range of soaring conditions? The
answers converged around 18 meters. Larger spans were considered too
slow
in strong conditions and smaller spans suffered in weak conditions.
It's
interesting that the "most cost effective wingspan" is about the same.

This makes me wonder if eventually the 18 meter class will become
dominant.
It also makes me wonder if the selection of 15 meters for the two most
popular classes was an error.

Bill Daniels

If this was true, why do the 25m gliders win the Open class
competitions? Why aren't the LS8-18's and V2C's etc. cleaning up on
the ASH-25's?

Maybe I'm missing something... but maybe not - didn't a Ventus win
open in SA recently (I could be mistaken).

Jim

Hi, Jim.

I like big gliders too.

I don't think these guys were talking about existing gliders. They were
just asking, if you designed a glider for speed, what wingspan would you
choose, ignoring all else? The consensus was 18 meters.

With carbon rods, you could probably build a 60 meter glider but would it go
fast? Probably not. There is likely to be an upper limit imposed by
soarable meteorological conditions. There may also be a sweet spot
somewhere around 18 meters. If that turned out to be the case, and it was
also the most "cost effective span", the 18 meter class would be a "natural
class". I find that a pleasing thought.

Bill Daniels
Nimbus 2C

Earlier, "Bill Daniels" wrote:

With carbon rods, you could probably build a 60 meter glider...

Now, let's hang on for a second while I use that as an excuse to
hijack this thread.

As strong as those pultruded rods and strips are, they offer only a
20% or so increase in stiffness (per weight or per volume) over wet
layups of dry carbon tape. For gliders, and especially for long-winged
gliders, the structural design is bounded by stiffness, not strength.
As such, pultruded carbon rods buy you only a relatively modest
premium over more conventional arrangements of carbon materials.

It's the stiffness, in both bending and in torsion, that keeps gliders
from fluttering themselves to pieces. It's also the stiffness that
keeps exterior finishes like gelcoat happy.

The reason I so dearly love those pultruded rods and strips is that
they represent an extremely effectively packaged solution for the
low-tech glider builder like me. I don't need any expensive autoclaves
or fiber alignment equipment or resin calibration/saturation stuff. I
just grab a bunch of pultruded strip off the spool and go with it.

As for 60-meter gliders (that's just under 197 feet for us
metrically-challenged folks), I happen to believe that they're
possible, but not very probable. But I see the limitations as being
more operational than meterological. There are few places to launch or
land one of them, let alone a contest full of them.

Personally, I think that 15 meter ships are close enough to the sweet
spot for all practical purposes. They fit easily in trailers, hangars,
fields, and launch grids. The pieces are relatively light. And 18
meters is only a wingtip-change away.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com