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Composite-ARF Yak 55 (2.1m/83")
Horizontal Stabs
The stabs are 95% factory-finished
and the hinging is completed, using
4 large Robert hinge-points in each
elevator - so you only need to install
servos, horns and linkages. The
fibreglass tube inside the fuselage
that accepts the carbon stab spar,
and the holes for the anti-rotation
pins are also jig-installed at the fac-
tory, so the alignment and inci-
dences are already perfectly set. Please double-
check now that the 6mm fibreglass anti-rotation
pins are securely glued into the root ribs.
Insert the 14mm Ø carbon tube spar in the fuse-
lage sleeve, and slide on both stabs. Check the
fit between the root ribs and fuselage, and if nec-
essary you can sand the roots of the stabs
slightly for a perfect fit. The carbon tube may
need to be shortened a little to 275mm long.
Due to manufacturing tolerances it is possible
that the carbon tube may be a little tight, or loose
in the fibreglass tube in the fuselage. If it is a
slightly tight you can sand the outside of the car-
bon with 600 grit - and if it is a little loose you
can either spray a few coats of clear coat on it,
or even cover it in one layer of clear tape.
Servos: The elevators can travel more than 45
degrees, and if you are going to use the maxi-
mum throw for 3D manoeuvres, we strongly rec-
ommend
hi-torque
JR8411/8511/8611 or Futaba S9351. It is not
just that the torque of a standard servo is not
enough - it is also the play in the gears which
could cause problems centering, and it might
result in high speed flutter.
IMPORTANT -
Servo Output arms:
To obtain large elevator throws of around 45°
you will need to use servo arms of 30mm (1.25") length, and it is very important that these are
capable of handling the stresses placed on the splines by high-power digital servos, which can
strip the plastic splines out of low quality/soft plastic arms - resulting in flutter.
We highly recommend that you use full metal arms, but high-quality rigid reinforced plastic arms
(like the grey Dubro types shown here) can also be used with care.
The elevator servos are installed, inverted, in the plywood root rib as shown - with the servo out-
put shaft towards the leading edge of the stabs. The cutouts in the root ribs are milled for stan-
digital
servos
like
techsupport@composite-arf.com
(above) Completed stab servo & linkage, also
showing the position of the M3 stab securing
bolt, recessed into the bottom of the stab.
Note positions of clevises on the horns for the
maximum mechanical advantage.
(below) You should use a 30mm long high-
quality reinforced plastic or metal servo arm
on powerful digital servos.
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