The fastest and most accurate way to sheet a model aircraft is to use 'skins',
either the store-bought, extremely thin, plywood variety (known as veneer in
the woodworking trades) or balsa skins which have been built up from individual
balsa sheets.
Sheeting an open-bay (built-up) airframe with veneers is extremely difficult
because the thin wood flexes very easily and many times the completed model has a
wash-board appearance.
Sheeting with built-up balsa skins works much better and is very much more forgiving.
Making a skin :
Cover the work surface with waxed paper.
Lay the balsa sheets on the waxed paper butted edge to edge and with the ends aligned.
Tape the layer of sheets together by running masking tape across the sheets (not
along the butted edges) as if you were trying to make a hinge. Use a strip of
masking tape every six inches or so. Make sure there are no gaps and that the
individual balsa sheets aren't bowing, buckling, or warping (because if they are
they're not square).
Flip the taped assembly over on the waxed paper.
Flex the first taped joint open and apply a _thin_ line of glue between the two edges.
Flex the joint closed (lay it back down flat) and wipe off the excess glue.
Continue working across the assembly until all butted sheet edges have been glued.
Wipe off all excess glue, flip the assembly over again, and wipe that side clean.
Lay a sheet of waxed paper on the upper surface, cover with flat sheet stock of some
sort, and weight it with whatever is handy. I use some scrap oak boards and two or
three gallon jugs filled with water. You don't need immense pressure, just enough
to keep the glued-up assembly flat while the glue cures.
When the glue has fully cured sand both sides with a long bar sander.
Cut the sheet as needed and apply to the model.
You can use whatever adhesive you like to apply the skin, but make sure to apply it
evenly to the structure and clamp it in position while the adhesive cures.
I prefer Titebond ®because it allows time to reposition the skin if
needed. I also use a set of webbed straps to 'clamp' the skin to the model (gently,
but firmly !).
Adhesives for making balsa skins :
Nothing works better than aliphatic resin (ordinary white or yellow carpenter's
glue).
Cyanoacrylate (CA) is far too hard when cured and not sandable. If you use CA you _will_
have ridges in the finished skin; you'll have a washboard. CA simply does not sand
as quickly as balsa no matter what the CA manufacturers claim.
Do not use polyurethane expanding foam adhesives, e.g. "Gorilla Glue" ®, because the
expanding foam can force the individual sheets apart - resulting in a warped, twisted
skin.
Titebond is an excellent general purpose wood glue and you can get it just about
anywhere; I buy it in gallon jugs at The BORG. Titebond II ®costs a good bit more
(it's _hobby money_ we're spending here, right ?) and the major difference between
the two is that Titebond II is intended for exterior applications where water
resistance is important. Titebond II doesn't offer any extra performance for model
uses.
Check the balsa sheet stock before you start :
Lay several sheets on the building surface, edge to edge. Using light pressure,
push the edges together. If there are any gaps you need to square the sheets. If
there are no gaps >anywhere<, the sheets can be used as is (not likely, but
accidents do happen !).
Squaring balsa sheets :
Using an accurate metal straightedge, trim one edge of a sheet straight.
Square both ends of the sheet to the trimmed edge.
Cut the other edge of the sheet parallel with the trimmed edge and square with the
trimmed ends.
It's a finicky thing, so take your time.
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