Great Planes Piper J-3 Cub 20 Kit - GPMA0158 - Manual (Page 16)

D 3. After the epoxy on the dihedral brace has cured, trial
fit the brace between the main spars. The dihedral brace
should fit snugly between the main spars without forcing
them apart. Sand the dihedral brace as necessary, being
careful not to change the angle of the brace.
D 4. 30-minute epoxy must be used for this step. Place
waxed paper on your work surface and mix up at least
1/2oz. of 30-minute epoxy. Apply the epoxy to all mating
surfaces of the forward and aft spar joiner, leading edge
joiner, main spars, dihedral brace and trailing edge.
Slide all the parts together and wipe off any excess epoxy
with a paper towel. Lay one wing panel flat on the work
table and block up the other wing panel 15/16" at rib R5.
Carefully align the spars and trailing edges of the panels,
being careful not to build in a twist. Clamp everything
together and wipe off any excess epoxy. Remove any
epoxy that squeezes into the dowel hole of the forward spar
joiner. Allow the epoxy to fully cure before removing the
clamps and disturbing the wing.
D 5. Remove the wing from the building board and take off
all of the clamps. Sand off any excess epoxy that may
interfere with final assembly (wing sheeting, shear webs).
D 6. Add the four remaining 1/16" balsa vertical grain
shear webs - one in front and one behind the joiners
between ribs R2 and R3. Important: the bottom center
sheeting does not cover the main spar but butts up against
the spar joiners in front of, and behind the spar. Therefore,
the 1/16" shear webs must be positioned so that they are
about 1/16" lower than the edge of the spar joiners.
D 7. Without gluing, install both 3/32" die-cut balsa sub
ribs 1A and 1B between ribs R2. Place the aileron servo
tray in the notches in ribs 1B to produce the proper spacing
between the ribs. Note: Keep the plywood aileron servo
tray doublers you removed from the center of the aileron
servo tray. They will be used during radio installation. Also,
check that the 1B ribs are centered vertically in the slots in
the TE and 1/16" below the main spar and spar joiners.
Glue ribs 1A, 1B and the aileron servo tray in position with
thin CA. Turn the wing over a apply a fillet with thick CA at
the joints of the 1B ribs, the aft spar joiner and the aileron
servo tray.
D 8. Round off one end of the 1/4" hardwood wing dowel
and slightly chamfer the other end of the dowel. Remove
any hardened epoxy that may be remaining in the hole in
the forward spar joiner with a round file. Install the dowel
with 6-minute epoxy. Wipe off any excess epoxy around the
front of the dowel with alcohol and a paper towel.
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