Right: Align and
temporarily glue the
fuselage halves with
Using a Dremel tool, grind evenly
spaced, shallow grooves around
the fuselage to embed carbon tow.
Epoxy the tow into the
grooves and blot away
the excess epoxy.
Firmly wrap the area
with electrical tape.
by Gordon Buckland
W ho hasn’t dropped a wing on landing or landed out and treed your composite model,
snapping the boom? My experience is
that most mishaps where the model
is substantially damaged seem to also break the boom
generally midway between the wing’s TE and the stabilizers.
Being so far behind the CG, it is important that the least
amount of weight is added during the repair or your model
is going to be compromised in performance and will need
added nose weight to compensate.
Let’s discuss a repair procedure that is adequately strong,
yet adds less than 3/4 ounce to the model’s overall weight.
The first step is to assess whether the stabilizer and rudder
pushrods need to be replaced. I typically remove the old
ones and replace them in any case, because the originals are
often .050-inch stainless steel hypodermic tubing and they
get bent during crashes. New hypodermic-tube pushrods can
be obtained from Graves RC (see “Sources”).
I use .050 x .030 x 60-inch tubing. Disconnect the clevis
at the servo end and either cut or de-solder the clevis end
to allow you to remove the pushrods from the rear of the
fuselage. Fold your rudder back against the fin and tape it
there so you can remove an inch of the balsa rudder post in
the back of the fin to gain access to the stabilizer bellcrank.
Unhitch the clevis and remove the stabilizer pushrod.
Inspect the pushrod outer sleeves and replace them with
new ones available from CST-The Composites Store if your
new pushrods don’t slide freely through when the broken
fuselage is aligned.
The first step is to accurately align the two broken
fuselage halves and temporarily bond them in place with
thick CA. I use Zap thick-viscosity glue.
Attach the wing’s center section to the fuselage and
suspend it above a bench or table with a box under each
side so the wing is parallel with the bench surface and the
towhook is not touching down. Attach the stabilizers and
set the rear piece up with the correct
thickness spacers over your bench so
you can align the two halves.
Tack the break with thick CA on
the top and then, using a straightedge
to check alignment, tack the bottom.
Before tacking on the side, use the straightedge to ensure the
center seam is aligned and double check it by measuring from
the ends of the center section to the tips of the stabilizers.
After you are sure the two halves are perfectly aligned,
thoroughly glue the broken area with CA and spray it with
accelerator before dismantling the model from your fixtures.
107 Model Aviation MAY 2014