At 18:43 08 December 2016, J. Nieuwenhuize wrote:
Op dinsdag 6 december 2016 11:58:23 UTC+1 schreef Ross:
I tend to disagree with most of that.
UD is difficult on complex shapes yes, but what is complex about a
wing?
=
It is basically straight. If you can laminate it with wet laminate, you
can=
do it with prepreg.
=20

Not really. Wing skins need 45/-45 fibers. Easy enough to put in a single
t=
apered wing, but multiple tapers, fairings or wing tips are pretty
awkward
=
for either prepregs or thick BIAX/TRIAX.
Fuselage is worse.

Don't see the issue with postcure. No need for it to be done in the
mold
=
with Prepreg. We were postcuring suspension to 180-220 deg C out of the
mol=
d and had no issues. They were cured at 130 to start with.
As far as thermal expansion goes, why not make your molds out of
tooling
=
prepreg? Works like a charm, and if you have a decent glider you will
make
=
plenty of gliders out of the mold and you will always have the same
shape.
=
Beats having to rework your molds every couple of years
Pretty expensive to make such a mold since you need a plug that can
withsta=
nd that temperature too. Solid aluminium requires major adjustment
(thermal=
expansion during cure), inconel is $$$.
That's one of the biggest advantages of infusion. Cure at 30C or so, join
p=
arts etc and pull from the molds. Then, with a very slow ramp-up
(5C/hour)=
you can postcure to 100-120C and you have a plane that can be painted
any
=
color and won't need rework for spar bumps and other annoying issues.

I definitely would not take Ros's recommendation of co curing the wing
skins
and spars in one operation . This is just what SH got badly wrong on the
Discus wings when they tried to co cure the caps to the wing skins but
found
they couldn't ensure a satisfactory bond to the spar web when they bonded
the skins together;- was it 70 odd wings sets scraped?

As for a partial cure on a wing cover, remove from mould and final cure at

high temperature, I'm very dubious. In order to assemble the wing skins
together to get the right twist and fit the wing skins must be held to a
high
level of precision. Added to this an individual wing skin is an unbalanced

layup I.e two thick 45's, foam, and one thin bid so its ripe for thermal
distortion. However when the top skin and bottom skins are bonded it
becomes balanced across the wing section. As for the justification that it

works on a 30 (or so) cm part therefore it must work on an 8m I will make
no
further comment.

Yes of course it's possible to build a wing in pre-preg but why? The mould
has
to be made from a more expensive material, more expensive energy is
required to heat it to higher temperature and more expensive manhour time
is required to do all the inter leafing so as to avoid the wrinkling.

Fraser