.
10.
Finish WLB with a sanding block.
11.
Carve WLB to airfoil contour.
12.
Hold the cores together at the center joint. If there is any mismatch in the airfoil shape, sand as required to make them fit
smoothly together. Done this way, little matching will be required after planking. Refer to the dihedral view on the plan.
Check out the cores as shown there before proceeding. Do not cover the cores until you are certain they match properly.
NOTE: If you plan to have retract gears, turn to the section called "Retracts" and install the gear mounts in the wing at this
time. Then preceed with step 13.
13.
a. Sig Core Bond is recommended for applying the wing skins. This is a
special adhesive, light and strong, that is ideal for use with foam. As
experienced modelers have found, many foam wing glues contain very
volatile solvents. When using these glues, if the wing skin is put on before
the glue is absolutely dry, the still evaporating solvents are trapped in the
assembly and quickly attack and destroy part of the foam core, ruining the
wing. Sig Core Bond doesn't cause this type of damage so it is ideal for
beginners at foam wing sheeting in addition to being a superior adhesive. If
directions on the can and these instructions are followed, it will result in a
perfect wing sheeting job.
b. Shorten the bristles of an ordinary 2" house paint brush to about 1-1/2" in
length. This stiffens the brush and makes it easier to spread the glue
evenly.
c. Apply a thin, even, full coverage coat of Core Bond to both sides of the
foam cores. Avoid heavy spots. These are inclined to skin over, leaving wet
spots underneath that won't stick down properly after the wings are
skinned. Stand the cores on end to dry. (The cores should be coated first
because they take slightly longer to dry than the wing skins.)
d. Coat the wing skins with Core Bond.
e. Allow the cores and skins to dry completely. This generally takes about one
hour. In conditions of high humidity it may take somewhat longer. It is best
to join the parts as soon as they are dry, since if they are allowed to lay
around for a long period, they will not stick together as well.
THE SECRET OF A
PERFECT FOAM WING
It's a simple matter of a FLAT table.
Most tables are not flat, as can be
seen by checking them with a good
straightedge. If a foam core is covered
on a bowed or twisted surface, then
the wing will be bowed or twisted. And
a table that checks out true but is
flexible and will yield as you press on
it will also spoil a wing. The ideal
working surface is a sheet of plate
glass. Or, it is possible to find a thick
piece of plywood that is perfectly true.
Like balsa blocks, foam blocks
sometimes have built-in internal
stresses and the core bows slightly
when cut out of the block. Skinning on
a flat surface, in the sequence shown
in the pictures, will correct minor
bows.
Incidently, the washout in the King
Kobra wing is cut right into the foam
core. The tip section is higher at the
trailing edge compared to the center
section trailing edge. The washout will
take care of itself. No blocking up or
other steps are required of the builder.
Proceed with wing construction as if it
were a standard wing.
14.
Hold the trailing edge of the foam core in position just above the wing skin and
lower the edge only onto the skin. Make sure it is properly aligned before contact
is made because it cannot be removed and repositioned after contact is made.
Press down along the trailing edge to make sure it is making good contact and is
flat against the table.
