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Re: Closed compartments
I read Martin's post and agree with all of it, as many of us will. My post
here is more for the newbies who haven't gotten to the point of glassing their
wings. Any and all comments from anybody/everybody more experienced would be
>1) The micro slurry used to coat the foam core prior to doing the
>fiberglass lay-up is:
>a) not mixed properly (too dry or the epoxy resin mix itself is bad),
Boy! Knowing that you are about to put acres of slurry on REALLY makes adding
too much balloon to the mix a great temptation. I helped David Doshey lay up
his wings and I think we were right on the good side of too dry. When it gets
to the point of peanut butter, I think that a little more epoxy needs to be
added. One can tell when things are too dry as the slurry will not stick to
the foam. I opted to go a little wetter to make sure that adhesion would be
>b) not applied properly (do not ensure even coating and filling of all
>the small pockets in the foam.
Once again, too dry will make this a real problem as the slurry will not flow
into the pores of the foam. After the slurry is applied, let things sit for
about 1/2 hour to give the epolite a chance to begin melting the foam. This is
part of the process needed to form a good bond between the glass and foam.
>2) Poor technique in the application of the fiberglass cloth and epoxy
>resin to the prepared surface.
Not pulling the lengthwise fibers in the tri-ax to help the glass lay down is
a big cause of problems here. This takes about 2 hours of back and forth
pulling and results in 1). frustration as the tri-ax drapes and contorts into
all kinds of shapes as it settles down, 2). A stronger wing, 3). blisters on
your middles two fingers. I unfortunately had several lengthwise bubbles form
in the curing process. Murphy's law sez that this will happen when you are
asleep because the last thing that you do after a long day of glassing is
baby-sit this mess!
Several things can be done to prevent this. On David's wings, we covered the
entire surface of the wing with thin, plastic sheeting and formed a "poor
man's vacuum bag." This worked really well and resulted in a pair of wings
that did not have any visible flaws. The drawback? It adds about 2 hours of
additional work in an already long day. Covering the most troublesome areas of
the wing/canard could be a compromise. The area that bubbles will have the
best chance of forming will be in the area of the foam/spar joint. This is
particularly so in the wing as the section thickness' are very different. I
had a problem in this area and sought Mark Machado's advise. Taper the foam
back much further than what the manual calls for. This area is going to be
filled with alpha anyway. After the glass is laid out and slurried, cover the
spar area with plastic sheeting and weigh the sheeting down with magazines.
They are heavy enough to help prevent air from creeping back into the glass
from outside and "form fit" the wing well enough to keep the glass from
raising if it has taken a "memory" from tri-ax pulling.
Even then, air bubbles may creep into the mix as Martin alludes to. Unless a
true vacuum bag assembly is used, I think that the eventuality of air is
always possible. When that happens, get out your 1/8" drill bit, drill a
series of holes along the ridge of the air pocket about every 1/2 to 1 inch.
Mix some wet slurry and use a hypo needle to inject the slurry into the
bubble. Hopefully this will cause the glass to adhere to the foam and prevent
the delamination problems that started this thread.
>Even the best, most experienced fiberglass people have less than
>desirable results on occasion. (Eh, Alan?) Ambient conditions, such as
>temperature and humidity, all play a part in the results of any glass
>lay-up. It is experience and vigilance in inspecting post cured lay-ups
>that prevents any delamination.
Thanks, Martin! I gotta get my sleep after a wing lay up. This thing could be
worse than getting up for 3:30 am feeding of a baby!!! Anybody wanna job
working the graveyard shift at Alexander Aircraft works? ;<)
First coat of 545 primer to the left wing and canard last night---Whoo whoo!