Mark the position against
the outer edges of the
hatches where the servo
arms will be, and file
3mm wide x 20mm long
slots in the skin for them
as shown. Now you can
glue the mounts into the
wing, with the servos in
place, checking that the
servo arms are centred in
the slots, and parallel
with the wing roots. Use
a 30 minute epoxy and
micro-balloons mixture,
and make sure that they
are properly glued to the skin and to the back of
the wing spar in front of the servo pockets. When
the glue has cured, remove the servos and add
glue to any parts that are not properly bonded,
making sure that they are well fixed to the spar.
The linkages should be in line with the airflow
(parallel to the wing root), and in practice that is
close enough to the (ideal) 90 degrees to the
elevon hinge-line that it works fine. Tape the
elevons into the neutral position. Carefully mark
the line (on masking tape) of the linkage, exactly
in line with the servo arms. The control horns are
made from the 35mm lengths of M3 threaded rod,
and there are small plywood blocks installed in-
side the elevons for the horns during manufac-
ture. Drill right thru' the elevons on the marked line, exactly 10mm behind the leading edge, using
a sharp Ø 2.2 or 2.3mm drill. Use a 90° square to keep the drill perpendicular to the bottom sur-
face of the elevators. The holes should be just behind, or against, the balsa elevon L.E. spars.
Thread these holes, right thru' the elevons, using an M3 tap. Sand both ends of the threaded rods
flat, and screw on the plastic adapters provided. Screw them into the tapped holes until the upper
end is flush with the top outer surface of the elevons. The M3 rods are finally secured in place by
applying glue through the open (root) end of the elevons. Apply one drop of thick CA and, when
cured, add a little 30 minute epoxy and micro-balloons mixture.
Make up the linkages using M2 or 2 x 56 clevises and threaded rods. The clevises will need to be
in the servo horn hole approx. 13mm from the servo centre, and the clevise on the elevon horn as
far out as possible - to maximise the mechanical advantage, whilst still obtaining the necessary
maximum elevator throws of 10mm ‘up’. The servo hatches can be held closed with strips of clear
tape. Some small scraps of very thin ply or fibreglass sheet glued inside the corners of the servo
pockets keep the hatches flush with the wing skin.
IMPORTANT
: Do NOT use ball-joints or ball-links on the plastic horn adapters, or plastic servo
arms. They will cause twisting, and almost certain flutter !
Fox Composites Co., Ltd.
13
(above) Completed elevon servo installa-
tion, elevon horn and linkage.
(below) Elastic hinged servo hatches are se-
cured with clear tape for flight.
