rately mark the position of the quick-link hole in the horn.
Drill 1.5mm diameter and glue in a short piece of 1.5mm Ø
wire with a drop of thin CA.
Fit the control horn to the other elevator in the same man-
ner, adjusting the milled slot as needed to make sure that it
lines up with the servo output arm, and using the template
to make sure that the hole in the arm for the clevise is in
exactly the same position as the 1st horn. This method
makes sure that both surfaces have identical control move-
ments, and a similar method is also used for the aileron
horns.
Servo choice:
The elevators can travel more than 50
degrees, and it is up to you whether you want to use this
throw or not. The throw defines the kind of servo. If you are
going to use the maximum throw for 3D manoeuvres, we
definitely recommend digital servos like JR8411. It is not
just that the torque of a standard servo is not enough - it is
the play in the gears which could cause problems center-
ing, and high speed flutter might be the result.
When using the powerful digital servos and larger throws
we highly recommend that you use our Composite-ARF
phenolic servo arms, designed for this kind of aircraft and
included in the kit. These must be fixed to the standard (25 mm/1” Ø) plastic output arms sup-
plied with the servo with 2 small sheet-metal screws each. Rough up the bottom surface of the
C-ARF servo arm and the top surface of the standard servo arm. With servos installed, centre
the standard servo arms (using your R/C) at 90° to the btm. surface of the stabs.
Then glue the phenolic C-ARF arms in place with a couple of drops of thick CA, making sure they
are centred on the servo arm bolt in the shaft and also at 90° to the stab surface. Finally remove
them from the servo and secure the phenolic arms to the standard plastic arms with at least 2 of
the very small (2.2mm Ø x10) sheet metal screws provided in the kit. Make up the linkages from
the 80mm long M3 threaded rods, with 2 quicklinks and 2 x M3 locknuts for each stab. Don’t for-
get to ‘Loctite’ the quick-link and lock-nut on one end of each linkage. Do
NOT
use ball-links on
the servo arms or the control-surface horns, because they will twist the servo arm/horn and
cause flutter. This is a solid experience and you should consider it a
FACT
.
The last job is to fit the M3 stab retaining bolts. Inside the stabs and you will see the small square
plywood reinforcement plates between the spar sleeve and the bottom surface of the stab. Mark
the bottom of both stabs in the centre of this plywood. Install the aluminium tube into 1 stab, and
drill a 2.4mm hole right through the stab surface, the plywood plate, sleeve and into the 20mm
aluminium tube. Thread the hole with an M3 tap and secure it with an M3 x 16 bolt. To be really
safe, you can glue an M3 blind nut inside the stab spar tube, with some 30 minute epoxy/micro-
balloons. Wax or oil the bolt first! Fit both stabs to the fuselage, check that they fit tightly to the
fuselage at the roots, and then drill the hole in the other stab and spar tube, thread as before,
and secure with another bolt. Counterbore the holes in the bottom surface of the stabs for the
boltheads so that they fit flush.
Note:
Try to always leave the stab tube fixed into one stab, and never remove that one bolt, as
it is very difficult to find the right position for the stab tube again if it is removed from both stabs.
Composite-ARF Yak-55 SP
(2.6m span)
20
(above) Shows C-ARF servo arm
glued and screwed onto standard
25mm diameter servo output arm.
(below) M3 blind nut glued into
the 20mm Ø elevator spar tube
with epoxy and milled fibre.
