the back of the fin and glue the fin post in with
slow epoxy and micro-balloons mix. Tape rudder
in position with a 1mm spacer on top (see
photo), and clamp fin to fin post until cured.
Servo:
The rudder is a huge surface on the
Extra which definitely needs a hi-torque power
servo, and we highly recommend the digital
JR/Graupner 8411 for this important surface.
The servo is mounted in a CNC milled compos-
ite balsa plate, with the milled 3mm plywood
reinforcement underneath, in the fuselage under
the canopy area. Glue the ply plate to the bottom
of the balsa with CA and mount the servo with
the 2.9Ø x 13mm screws provided,
not
the stan-
dard ones that come with the servo. The com-
posite balsa rails are glued into the milled slots
under the front and back of the plate with CA.
Rough up the fuselage sides before gluing the
complete assembly into place with 30 min. epoxy, and then rein-
force these important joints with the glassfibre tape provided in the
kit, and 24hr laminating epoxy (see photo).
Note
: Fit the wings to the fuselage before gluing in the rudder
servo mounting plate - so that you can-
not accidentally deform the fuselage.
We have left the milled balsa parts for
the rudder mount a bit long, so you can
chose the position to suit your motor,
and help to set the correct C of Gravity.
If you are using a lightweight set-up,
like a glow engine (or the Plettenberg
electric motor and LiPo cells) then you should move the rudder servo mounting plate as far for-
ward as possible, so that the front of the plate at the position of the rear wing anti-rotation pins.
The top of the rudder mounting plate should be 88 - 90mm above the fuselage floor. Do
not
mount it lower, or the rudder closed-loop cables may touch the elevator servos. With servo
mounted as shown, the slots (40mm x 3mm) for the cable exits need to be approx. 380mm (15”)
from the back of the fin, and approx. 65mm above the chine (angled corner) of the fuselage.
Rough sand the top surface of a standard 25mm (1”) Ø plastic output disc with 60 grit, or
Permagrit, and the bottom of the phenolic rudder servo arm. Centre the servo using your R/C
and glue the phenolic horn in place perpendicular to the servo. Then remove the assembly and
secure the phenolic arm to the disc with 3 of the 2.2Ø x 10mm sheetmetal screws supplied.
Make up the closed loop wires for the rudder from the hardware supplied, with a loop at the front
that goes over the hooks on the output arms, and a quick-link with turnbuckle and locknut at the
rudder end. For security pass the closed loop cable through the supplied ‘crimping tubes’ 3 times
before squashing flat with large pliers (see photo). Make sure that the wires are tight, and check
and adjust after the first few flights as the cables straighten out. Even a small amount of slop will
prevent your Extra from perfect tracking.
Composite-ARF Extra 330L
(2 x 2m)
17
