On 2/11/2011 8:08 AM, Walt Connelly wrote:
I see planes that are "refinished" in polyurethane. Is this different
from GelCoat? I have looked at ships whose gelcoat is horrible and
understand that it can cost in excess of 20K dollars to refinish
properly. Is PU more durable than Gelcoat? Is one better than the
other? The glass vs aluminum thing has me leaning toward aluminum big
time. I don't ever expect to be competing seriously in cross country
competition so a bird for local fun might be adequate.

Walt,

At the risk of telling you stuff you already know, plastic gliders are
generally built 'from the outside in', & their smooth external finish
(assuming good gelcoat) comes from female molds into which gelcoat is
generally sprayed prior to the skin layers & epoxy going in. So THE
fundamental role of gelcoat is to ensure the weave of the outermost cloth
layer isn't visible when the cured structure is popped from the mold.

Another role of gelcoat is UV protection. (If sprayed gelcoat was not used,
something else would have to be.)

It's this latter which most (at least non-racer sort of) folks 'in the know'
probably worry about when loooking at a glider with cracked/chipped gelcoat,
though some undoubtedly obsess over 'lost L/D'. (As the late Dick Johnson used
to say: "Air has fingers, but no eyes.")

FWIW, you'll likely encounter a *lot* of 'FUD' (Fear. Uncertainty, Doubt.)
when it comes to gelcoat opinionating. I'd encourage you - regardless of what
sort of ship/structure you opt for in the near future - to continue the
process of self-education, and strongly suggest you relentlessly include the
'Why do you say that?' tool in your questioning kit. The answers will help you
distinguish between 'FUD-based' answers and genuine 'knowledge-based' ones.
(Most owners of any sort of glider have done this at some level prior to
purchasing - perhaps plastic owners more so simply because of the relentless
conservative streak often found in pilots. By 'conservative' I mean a general
reluctance to opt for anything perceived as 'out of mainstream thought.')

FWIW, I consider myself lucky in that my introduction to the sport was via a
superb engineer (who performed major aerodynamic and structural modifications
to fiberglass gliders) who approached plastic gliders from an engineering
perspective, and was willing to answer - or point me in the direction of
answers to - every question I threw at him. Since then (early 1970's), I've
seen a lot of people throw a lot of FUD-based money toward gliders that -
structurally speaking - didn't need it. I suppose one could rationalize that
it made them feel better, and in that sense it wasn't wasted money, but...

In any event, every structural material used in gliders has its own pros &
cons, and you've already heard of some via RAS. It's a start!

Regards,
Bob W.