On Dec 15, 12:42 pm, wrote:
Hey guys. I've got a question regarding wing "waviness". I've got an
LS1f with very good gelcoat condition. However, if I look down the
wing long-ways, just above the leading edge I can see what looks like
a series of 4"-6" diameter lumps (for lack of a better term). They're
somewhat regularly spaced along the full length of both wings and are
parallel to the leading edge. They are very, very subtle, and you
can't really see them without looking from the correct angle to use
the glossy reflection. They're very similar on both wings and are in
the 4"-8" range up from the leading edge. I've done some "tap tests"
to see if I could detect delamination, but the wing surface is
consistently solid all over. I'm thinking this might be gelcoat "sag"
and/or just improper sanding during the last refinish. Do refinishers
have rigs to "rotate" the wings (on the spar) as they're spraying? It
almost seems like after spraying the top of the wings, they were
rotated to a position where this point of the wing was the lowest
allowing sag there. Anyone have any thoughts or comments as to what
this might be? Besides these defects, the rest of the wing surfaces
are consistently smooth and uniform.

The description of the wing refinish in the log indicates the
following:

- acrylic enamel (from previous refinish) and factory gel coat removed
via sanding
- primed with Simtec primer
- sanded with 100 grit
- primed again with Simtec primer
- sanded with 120 grit
- series of coats of Simtec white to thickness of 6-8 mils
- sanded with 180 grit
- series of coats of Simtec white to thickness of 8 mils
- wet sanded with 1000 grit
- wet sanded with 1200 grit
- wet sanded with 1500 grit
- power buffer with 3M finesse #1
- power buffer with 3M finesse #2

There's nothing in the log that refers to profiling or shaping. Only
"sanding" and "polishing". If any attempts were done to shape and/or
profile, do you think that would have been logged along with the rest
of the description? There's two and a half pages devoted to this
refinish job, so it's not like he left much out.

The ship flies beautifully, and sure seems to have good legs relative
to it's published performance numbers. I don't think these surface
defects are pronounced enough to be having any large effect on
performance, but I haven't tried any serious attempts at performance
testing either. At this time I guess I'm more interested in knowing
what they are. Although there will probably come a time when I'd like
to remedy it for the performance improvements if there are any to be
had.

Thanks,
Dave

Dave,

Just speculating here, but either something's missing from the logs,
your transcription of the logs is off, or ... well... something
doesn't quite make sense.

After spraying with the Simtec sandable primer, it sounds like the
refinisher sanded with 120 grit. Sounds a bit coarse to me, but
okay. Assuming it was sanded with a machined-flat bar, the wing was
probably pretty smooth at that point. Next was a coat of the white
Simtec followed by a 180 grit sanding. Okey doke. Still pretty
smooth. Next is multiple build coats of white but no sanding below
1,000 grit? Unless this guy (gal) was the best spray artist known to
man (or at least known to glider refinishing), there are bound to be
some waves introduced with multiple coats. I've never heard of
anyone NOT doing another pass with 200 grit or at least 400 grit
(followed by 600, 800) to smooth stuff out. Assuming the wing was
resting trailing edge down, I can easily see where you would get
exactly the kind of sag/ build-up you describe.

Maybe JJ or someone who did/does this for a living can chime in, but
I've never seen it done the way you describe.

BTW, if you really wanna see how bad the bumps are try this: Thin
some colored dope down to a fairly runny consistency and wipe it over
the suspect area with a paper towel. Take a piece of thin plastic
sheet and form it to the curve of the wing. Run it spanwise trying to
hold firm but consistent pressure (like you're screeding grout across
a tile). You'll be able to see the high spot/ low spot due to the
contrast.

That's my non-professional assessment.

P3