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Composite-ARF Yak-55 SP (2.6m span)
The split joint at the bottom of the cowling is reinforced with
the CNC milled plywood parts supplied. Prepare all the
mating surfaces carefully with some rough sandpaper and
clean off the dust with alcohol. Tack glue the plywood parts
in place with CA as shown, and add the small triangular
pieces at the front and back to hold them at 90° to the cowl-
ing. Wax the threads of two M3 bolts and fit through the
holes in one side and CA the bolt heads in place.
Remove the cowling and secure the plywood parts with
some fibreglass cloth and slow epoxy on both sides, mak-
ing sure that the glue goes into the milled slots in the ply-
wood parts. Also secure the heads of the 2 bolts with some
epoxy thickened with microballoons at the same time.
When cured refit the cowling and check for a perfect joint
line at the bottom. Then drill two 3 mm Ø holes from the
underside through the cowl and fuselage - about 8mm from
the back edge of the cowling. Wax two M3 bolts and fit into
the holes with two M3 blind nuts on the inside of the fuse-
lage. Secure the blind nuts to the inside of the fuselage with
a drop of thick CA, then remove the M3 bolts and secure
the blind nuts properly with 30 min epoxy and microbal-
loons. Note that the Blind nuts are fitted inverted, with the
spikes pointing upwards !
For flying the cowling is held together using the 2 strong
steel paper clamps (supplied) as shown in the photo. This
system makes it very quick and easy to remove the cowl-
ing for motor or exhaust system access if needed, and has
been proven with many hundreds of our Yak 55's.
The 6 vacuum-formed grilles (louvres) for the cowling come
pre-painted in a single colour and trimmed approx. to size
from the factory. However you need to cut out the vertical
face behind each angled blade on the louvres - easily done
with a very sharp X-Acto knife in a couple of hours. It is
important not to forget this as it allows the cooling air to
escape from the cowl.
Mask each of the 6 pre-cut openings in the fuselage
about 5mm (1/4") outside the cut-out, with tape as
shown, and scuff up the exposed surface with coarse
sandpaper. Prepare the bottom surface of the grilles in
the same way and glue them in place with slow CA.
The last photo below shows the completed cowling
and grilles, and you can also see the position of the dual Rx
battery switches. The Ignition battery switch is on the other
side of the fuselage in a similar position. 'Powerswitches'
were used for both Rx batteries and ignition switches, and
are available as an optional items from C-ARF., and highly
recommended.
techsupport@composite-arf.com
(above) Parts for the cowling joint.
(below) The milled plywood parts
are glued into the cowling, and the
two M3 bolts are glued into one
side only. Secure the plywood
parts with small pieces of glassfibre
cloth and epoxy. The spring clamps
hold the parts together for flying.
(above) Finally the cowling is
retained with two M3 bolts from
the underside, into Blind nuts
glued onto the inside of the fuse-
lage with epoxy & micro-balloons.
15
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