make up the linkage from the M3 clevises, 45mm long
threaded rod and nuts provided - and connect the linkage
from the servo arm to the control surface horn while the
glue is curing to help maintain perfect alignment. When
cured, remove the plastic parcel tape and make a plywood
template, as shown right, so that you can copy the position
for gluing in the inboard horn on the other aileron.
The 2 outer control surface horns are completed using the
same method, first finishing one, and then using a template
to glue in the other one. However, the distance between the
clevise holes in the phenolic horns to the hinge axis line (
top
surface of the wing) should be the same for the inner and
outer horns. However, because the wing/aileron is
6mm
(1/4”) thinner
at the position of the outer horns, these outer
horns must project of the aileron
6mm more
than the inner
horns. This is to ensure that the aileron servo throws are
similar and that the servos don’t ‘fight’ against each other.
Because of the difference between the inner and outer
horns, the easiest method is to make the template for the
inner horns and glue them both in place first, and then drill
another hole in the same template
6mm
higher, exactly on
a line drawn on the template that is perpendicular to the
hinge axis - and use this for the outer horns.
Note:
There are a few early slightly different versions of the
300SX wings which do not have a balsa sub-rib outboard of
the outer aileron servo position. Although this rib is not
structurally necessary, if your wings do not have this rib it is
a good idea to glue a 70mm (3”) long piece of 3mm balsa
immediately outside the servo cutout between the top and
bottom wing skins to prevent damage to the wing in the
case of flutter.
Sand the inside surfaces of the wing, cut a piece of scrap 3mm balsa, with the
grain vertically
,
and glue inside the wing with 30 minute epoxy and micro-balloons mixture against the edge of
the plywood hatch reinforcement. This part is shown with an ‘arrow’ in the photo right.
Engine and Exhaust Installation
We strongly advise you to complete the motor and exhaust installation before the fuel tank base
and rudder servo tray are permanently installed, as it provides much easier access.
The most commonly installed motor in our 2.6m Extras seems to be the DA-100, very often with
a pair of MTW TD75k canisters - and we have shown photos of the installation of this popular
set-up below. However, please note that all of those photos show the installation in one of our
original 2.6m Extra 330L’s (Futaba scheme), but it is almost identical - so please don’t get con-
fused !
For the 300SX prototype we chose to use a single-cylinder 3W 80cc Xi, and single ‘Greve’ tuned
pipe set-up, to show a lightweight and lower cost option. This has proved to be a very nice com-
Composite-ARF Extra 300SX
(2.6m span)
23
(above) The aileron horn template
used to position the inner horns
for gluing in place. The line is per-
pendicular to the hinge axis.
(below) Same template, with an
extra hole drilled exactly 6mm
higher, for installing outer horns.
