Pat,
You'll probably get as many answers as there are people, but I think all
would agree, any depression will show. And we all would agree, it really
doesn't affect the flying characteristics, only the aesthetics.
I used the 3M rigid board with 80 grit. Buy extra paper. On an
ES wing I used a new sheet each time I did a wing. The paper gets old
quickly and you tend to rub the primer, not cut through it. With fresh
paper you don't push as hard and you won't warp the rigid board.
Keep the board along the length of the wing. All Lancair wings are
linear from root to tip. So at the leading edge you're parallel to the
leading edge, working in a "fan pattern" you described to the trailing
edge. I went diagonally at approximately 45 degrees upper left to lower
right the full length of the wing and then upper right to lower left all the way
back. So the board is always straight down the wing, and the motion is
always a 45 degree angle. Roll the rigid board over the leading edge by
moving at a 45 degree angle. That way you won't cause any flat
spots.
I sanded like that until I had removed all the guide coat OR saw the skin
showing through. Resist the temptation to give a couple extra passes to
try to get the last bit of guide coat off in one area. The primers sands
much faster than the fiberglass, so you will create an uneven surface is the
skin is showing. Also resist the temptation to push really hard in one
area to get the last bit of guide coat. If you push hard you'll warp the
3M board and create a depression. If it's low, it's low!
When I finished sanding I still had a few spots that were low, I re-primed
by hitting the low spots first, then another light coat over the whole wing,
then over the low spots again. Be sure to let the primer flash off between
coats or it may stay soft underneath.
When to use micro or another filler? When to use primer? Again,
you'll have as many opinions as builders. Micro is good to contour,
especially on the fuselage over seams, etc. It's almost too much on a
pre-molded Lancair wing. I used micro to fill the obvious low spots on my
wings before I primed. Don't try to get the micro perfect, you'll sand the
skin too much trying the feather it out perfectly. The micro will get you
close enough for the primer to do the rest of the work. I used some
lightweight body filler very sparingly where the micro was too much and the
primer wasn't enough. Sometimes trying to do a really low spot with primer
can be tedious to say the least.
Some guys will recommend a really long sanding board, but I personally
think the 3M board will bridge the low areas adequately and give an overall
smooth surface.
Going from 80 grit to 220 for the painter is also critical. Don't
just buzz the surface with a 6" DA. You could mess up your nice straight
wing that way. At this point you aren't trying to get rid of low spots,
they're gone, you just don't want to put any new ones in!
A year went by between my 80 "fly in primer" paint job to my final prep for
painting. I did another primer coat, but I treated that coat like it was
real paint, really smooth, two even coats. I guide coated again. I
didn't use the 3M long board, but I used an 18" rigid board, still on the 45
degree angle and started with 120. Then to 220. I changed diagonals,
one direction for the 120, the other for the 220. That's a good way to
make sure you are getting rid of the 120 scratches with the 220. It took
very little sanding to get rid of the guide coat and have a very smooth
wing. This step is more about spotting the tiny flaws than about
getting the wing straight. You'll see the tiny nick in the trailing edge,
or the pinhole you didn't see before.
One trick is to really take a good look at your wing when the primer is
still wet and shiny. You can spot any waves really easily with the
temporary glossy paint job. You shouldn't have any, but it's nice to know
before you put on the real paint.
My painter uses a single stage glossy paint for the base coat. He
says it covers better, and it's a last chance to check for
flaws. He scuffs it before he paints the accent colors (with base coat)
and before he clear coats. In the past, he has gone back and fixed some
minor body work flaws and repainted with the glossy white. After the clear
coat, you can't see where it's been touched up.
Mike Easley
ES