Carf-Models Composite-ARF Yak-55 SP Instruction Manual page 22

Composite-ARF Yak-55 SP (2.6m span)
Horizontal Stabs
The stabs are 99% finished at the factory, and only need
the servos, horns and linkages installing. Insert the 20mm
aluminium tube spar into the fuselage sleeve, and install
both stabs to check the fit between the root ribs and the
fuselage. You might need to sand the root of the stabs
slightly to make a perfect joint, and if the spar tube is too
long you can shorten it a little.
Attach the elevators to each stab using the 4mm Ø alumini-
um tubes provided. Be careful inserting the tubes, and if
they are a bit stiff, then use a little grease on the wire. Don't
use too much force, otherwise the phenolic plates inside
might break loose. Leave the tubes a bit long during
assembly, and cut them to length later. During final assem-
bly, retain the ends of the tubes with a small piece of clear
tape at the root and tip ends.
Fit the servos into the root ribs (with servo output shaft at
the front) and screw in place using the 2.8mmØ x 14mm
screws we supply in the kit, not the standard screws that
come with the servos. Because of the thin profile you must
install the servo arms through the slots in the bottom of the
stab, and you will need to make the slots 1mm wider when
using the C-ARF phenolic servo arms. You can extend the
slots forwards to get the maximum throws if needed.
The slots are already milled in the elevators for the eleva-
tor horns, but may be adjusted a little if required. It is impor-
tant that they line up with the output arm on the servo so
that there is no twisting moment. Trial fit one horn in the
milled slot, so that the hole for the clevise is between 22 -
24mm from the bottom surface of the elevator, and exactly
perpendicular to the hinge axis (the centre of the aluminium
hinge tube). Adjust slots as needed. Put a layer of clear
tape over the area of the milled slot, wax it carefully, and
then cut through the tape with a very sharp knife to allow
the horns to be glued into the slots. This stops the glue get-
ting on the surface of the elevator.
Mark the part of the horn that will be glued inside the eleva-
tor, and then remove it and scuff up both sides with coarse
(60 grit) sandpaper or a Permagrit tool. Glue the horn in
place with slow epoxy (minimum 30 min. cure) mixed with
milled fibreglass, or a filled thixotropic epoxy (eg:
Loctite/Hysol 9462 or BVM Aeropoxy). Check that horn is at
90° to the surface of the elevator, and in line with servo out-
put phenolic arm, and wipe excess glue off before cure.
When the 1st control horn is fixed, make the horn alignment
template from thin scrap plywood (see photo) and accu-
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Finished in 2.5 hours
(above) Completed stabs showing
linkage, sleeve for aluminium spar
tube and front anti-rotation pin.
(above) JR8411 servo fitted into
stab with phenolic C-ARF horn.
(below) Note the position of the
counterbored hole for the stab
retaining bolt, secured with clear
tape before flying.
(below) Elevator horn alignment
template made from scrap ply-
wood. Line is hinge axis. Use for
both elevators to ensure same
throws. (2.6m Extra shown)
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