Great Planes Piper J-3 Cub 60 Kit - GPMA0162 - Manual (Page 19)

D D 14. Accurately cut both front spars, both main spars,
the balsa bottom sheet and trailing edge.
D D 3. Replace the sheet on the wing and mark the rear
edge of the sheet so it ends about 1/16" ahead of the aft
edge of the forward spar. Trim the rear of the sheet to
this mark.
D D 15. From the excess 1/2" x 1/2" main spar, cut off a
1" piece to be used later for the receiver hatch block.
D D 4. Before attempting to bend the sheet so it may
reach the outer wing tip, the sheet must be thoroughly
wetted from R8 outward. Use a spray bottle or a sponge
to liberally apply water to the tip area of the sheet outboard
of rib R8. Some experienced modelers add alcohol or
ammonia to the water in order to help penetrate the wood
fibers. About a 50/50 mix w i l l do the job. Carefully "work"
the sheet with your fingers by bending and twisting it in the
direction required to meet the wing tip. Replace the sheet
on the wing and test bending the sheet into position. Don't
force the sheet - add more water if necessary.
D D 1. Use a T-bar sander or flat sanding block with 150-
grit sandpaper to carefully sand the top edges of the ribs to
smoothly blend them to the main spar. Remove any glue
bumps or other irregularities.
D D 2. Custom fit a 3/32" x 2-3/4" x 42" balsa wing LE
sheet. Use a straightedge to true the front edge of the
sheet and cut a slight bevel to match the angle of the
slanted leading edge.
D D 5. When you position the sheet on the wing and
attempt to bend it down toward the wing tip, you will notice
that as the sheet bends, it also naturally twists rearward.
However, in this area the sheet is supposed to maintain a
straight line parallel to the spar. Trim a "curved wedge"
from the sheet starting at rib R8. Trim and test fit the sheet
until it conforms to the desired straight line.
OUTER WING TIP
D D 6. To provide gluing surfaces for the sheeting, carve
a bevel on both sides of the tip where the top and bottom
sheet will join the tip.
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