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All Together Now: With mounted
ailerons and sealed gaps, it is nearly time to join the wing halves.
Trial-fit the servo into each wing half. Lightly sand the wood edges
until it fits. Remove the servo.
Find the wing spar you made at the
beginning of the building process. Draw a centerline on the spar; it
should match the "V" of the spar. Insert the spar in both wing halves.
Lightly sand the spar if required, but a snug—not tight—fit is
desirable. Keep the sanding to a minimum. The centerline should match
the center rib on both sides.
Trial-fit all spar and wing halves
together. The wing's LEs and TEs should align with minor hand
adjustment. If one LE is more than 1/16 inch forward of the other, the
spar was not laminated straight. A new spar will have to be made, so
make sure it is straight during construction.
If all pieces line up,
separate them for one final step. Using a 1/2-inch chisel blade, gently
raise all of the overlapping covering material from inside each wing half's center-section. Use a sharp #11 modeling blade to cut away the
excess covering.
Even though the plastic covering is thin, two layers
will separate the center wood ribs, weakening the all-important center
joint. Covering removal allows full wood-to-wood contact, providing a
strong center bond.
A photo shows everything you will need to assemble
the wing halves. The blue tape is 3MŐs low-tack Painters Masking Tape.
The low tack protects the covering during removal. Since this tape is
slightly "stretchy," it applies a pulling force when properly applied.
Do not join the wing halves if flaperons are to be used. If flaperons
are not in this aircraft's future, use an epoxy brush to liberally coat
the inside of each spar box with 30-minute epoxy. Brush epoxy onto all
sides of one spar half. Slide it into a spar box until the centerline
matches the wing rib. Brush 30- or 12-minute epoxy (your choice) onto
the same center rib.
Good advice is to coat the entire center rib except
the outer 1/16-inch edge. Epoxy will flow to this area when the halves
are joined but will not seep out.
The clock is ticking, so this is not a
good break time. Brush 30-minute epoxy onto the remaining open spar-box
surfaces and onto all sides of the protruding spar. Do not apply epoxy
to the uncoated center rib.
Join the wing halves and use short pieces of
tape to hold them together. Adhere one side first, and then pull gently
on the tape and affix its other side. This pulls the halves together.
Apply tape to both sides of the wing. Doing all of this over a piece of
waxed paper prevents you from gluing the wing to the building surface.
The metal sanding block is not just for sanding; it is used as a stand
to prop up the "high" wing caused by the wing's dihedral. Once the wing
is joined, hold half against the surface and slide the stand under the
high wing until it just touches the wing's underside. Make sure the
stand is perpendicular to the wingspan.
Click on photo to view large image with caption
Apply a clamp to the rear of the
wing to make sure TEs align. Check the front LEs to make sure they match
perfectly. They should at this point. Any mismatch causes a "warped"
wing effect that will be difficult to trim away.
Use 12-minute epoxy on
the center rib in case there is a slight LE mismatch. It is possible to
correct such a misalignment by holding the alignment in place for a
short time. I can hold on for the remaining five minutes required for
12-minute epoxy to harden. I can't do that for 30-40 minutes! Once the
overlapping covering is removed from the center ribs, 12-minute epoxy
has more than enough penetration and bond strength to do the job.
Once
the wing cures, install the center aileron servo. Most ARF trainers use
a plywood tray to mount the servo. However, the wing's dihedral prevents
the tray from seating flat on the wing. Use the chisel blade or a
high-speed hobby drill to gently remove some of the center bulge.
If you
use the chisel blade, cut only away from yourself and only toward the
aileron opening. Keep your other hand away from the chisel's path, in
case it should slip from the wood. Trust me on this or make a
reservation at your local ER.
Use five-minute epoxy to glue the
aileron-servo tray in place. Mount the servo using the screws provided
with the radio system. You may have to trim the center ribs to clear the servo's wire.
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