----- Original Message -----
From: Fred Fillinger <fillinger@ameritech.net>
Subject: Re: Wing Filling
> Nigel Graham wrote:
>
> > All filler continues to shrink for some months after initial cure. I
> > have seen some beautifully finished wings where the spar and ribs
show
> > through after six months to a year.
>
> I wonder if what was being observed was polyester Bondo, not epoxy
> fillers.
To my knowledge, nobody has ever filled a (an?) Europa wing with
bondo - certainly none that have left the ground ;-)
> Or possibly Europa's fluffy stuff, which when mixed very dry, seems
> more absorbent, creates some long-term effect vis-a-vis some finish
> coatings. In which case waiting 6+ months won't work!
Two of the Europa examples cited had show quality Schwarblac gel coat
finish over (factory recommended) Ampreg 20/filler/colloidal-silica mix.
The wings were built and finished by one of the most
accomplished glass glider repairers in the UK. The subsequent (small)
shrinkage was perhaps more visible due to the high quality surface
finish. (This in now way implies criticism oh his work)
In a professional aircraft finishing/painting organization, is simply
not possible to fill six months before finishing/painting. Jobs have to
be cycled as quickly as possible. The risk of some degree of shrinkage
is accepted.
In a home-build environment, no such pressure exists. The length of
build is sufficient to allow other build tasks to be scheduled in
between filling and finishing without impacting overall build time.
> The mfr of SuperFil states clearly it does not shrink........
And, as the old joke goes, the manufactures of the Titanic claimed it
was unsinkable!
Less facetiously, I chose SuperFill because of the qualities you quote
and I have to say I found it a joy to work with.
>I can't believe would be visible.
Depends on surface finish. The higher the finish quality, the more
observable any discrepancy will be.
> The post also suggested an 80" sanding spline. On the Mk 1 wings
> especially, this will necessarily require more filler.................
The amount of filler required is inversely proportional to the accuracy
of the core/spar build. On a wing with no intended dihedral, the
straighter the alignment, the less filler needed. If your wing core is
flat/straight, the length of spline will have no affect on filler
quantity. An 80 inch + spline will always span at least two 40 inch
spaced reference profile strips in the technique quoted, preventing
"rocking" and results in a very flat finish with minimum filler, mine
was almost transparent in places after light finishing.
> Once the wing is installed, it will no longer be exactly
> flat under the 80" spline, a sad fact I noticed after screwing around
> trying to get a straight surface under a 72" straight-edge.
Accepted completely. They'll droop down on the ground, flap up in flight
and (tend to) go their own ways during rolling. But we don't worry
about that. We attempt to build a perfect wing in the static (supported)
condition. I bonded all of the wing "jig blocks" to my 4.5 metre work
bench to form a "reference plane" and built /filled the wing on that.
> I can't recommend it.
I can recommend it.
The argument is purely academic. I have also seen some absolute "dogs"
with undulating wing surfaces and paint jobs that resemble sand paper
........and they seem to fly just as well! Testament to the strength of
the design.
Regards,
Nigel
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