.
32. Carefully sand the entire wing half until all joints are smooth. Use a large sanding block to avoid sanding down anyone area
too much.
33.
Use a deep blade razor saw (such as an X-Acto No. 236) to cut through the top and bottom main wing spars and the
temporary balsa spacers at the wing joint.
CAUTION: BE VERY CAREFUL NOT TO CUT OR EVEN NICK THE ALUMINUM JOINER SPARDURING THIS STEP.
Even a very small nick in the joiner at this spot may become the starting point for a stress crack that could lead to a
structural failure of the spar.
You may now loosen the set screws in the wing joiner channels and remove the outer panel from the center section half.
Reassemble the wing parts to check for smooth operation of the joiner assemblies. Any binding or misalignment must be
corrected before proceeding.
34.
Repeat Steps 8 through 33 for the opposite wing half.
BUILDER'S TIP:
Although it's not
shown on the plans, we recommend
that you install scrap pieces of lite-ply
above and below the front wing joiner
channel and joiner spar. This will
prevent any possible movement of the
aluminum parts.
Completing The Wing Center Section
The center section may at first appear to be overly complex or "overbuilt". You should remember, though, that it not only has
to withstand the airloads from its nine·foot wing, it must also bear the brunt of the landing loads. Many of the following steps
are required to make the landing gear attachment as safe, strong, and scale as possible.
35.
a. Sand the inboard and outboard ends of the center section halves bringing the spars, leading edges, and trailing
edges flush with the end ribs. Trial fit the center section halves together with the die-cut 5/32" plywood DB-1 and DB-
2 dihedral braces. The center ribs should meet flush when the dihedral braces are clamped in place temporarily. The
long dihedral braces will automatically set the proper dihedral.
b. Use slow-drying epoxy glue to join the two center section halves, DB-I, and DB-2. Hold everything in place with
clamps until dry. Try for good joints and don't be stingy with the glue during this step! Before it dries, double check
that the two halves are aligned perfectly with each other.
36.
a. Glue the SW-2shear webs to the back of the spar and dihedral braces to finish "boxing off" the spar.
b. Add the 1/8" sq. balsa spacers to the top spar at the W-1 ribs.
37.
Install the top center sheeting using pieces cut from the 3/32"x3"x30" balsa sheet provided (don't sheet the bottom yet).
38.
a. Use a razor saw to cut a 3/32" wide slot in the center ribs, just forward of the rear spars, to accept the die-cut plywood
DB-4 dihedral brace.
b. Trial fit DB-4 and trim to size, if necessary. Epoxy DB-4 to the rear spars and the ribs, again using clamps to hold it in
place until dry.
Summary of Contents for SIGRC61
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