bination, having plenty of power - and a weight reduction of
about 800 grams over the DA-100 version. Full details of
this installation are also described below. All photos of the
3W motor are shown mounted on the 300SX (Patty
Wagstaff scheme). Any similar 75 - 85cc single-cylinder
motor could also be used, for example the ZDZ 80 or the
EVO80.
The only major engine mounting difference between the
300SX and the 330L is that the firewall on the 300SX is
approx. 30mm further back from the front of the cowl, to
allow for longer motors, and that the complete motor-
dome is an integral part of the fuselage molding - which
saves weight, increases rigidity and ensures that the
alignment of the firewall is more accurate.
The front face of the molded motor-dome/firewall on the
300SX is set at 0 degrees downthrust, and has 2.5
degrees of sidethrust built in to to it. Therefore you only
need to secure your motor parallel to the firewall, and so
that the spinner is central with the cowling, and your
thrustlines will automatically be very close to optimum. At
most you will need to add a couple of washers behind the
motor standoffs to have a perfect thrustline set-up.
Whichever motor you are using the vertical location of the
centre of the motor on the firewall can be set as follows:
Lay a steel straight-edge on top of of the fuselage (on the
joint seam) as shown in photo P13. The offset between the
radiused part at the front top of the cowl and the straight
edge is 20mm (photo right). The top of the spinner should
be about 5mm below the top of radiused part of the top of the cowl. Therefore, if you are using
a 120mm (4.75”) diameter spinner the horizontal centreline that the engine should be mounted
on is 85mm (half of 120 + 5 + 20mm) below this straight-edge. Of course, if your spinner is Ø
125mm, then this centreline will be 2.5mm lower, etc., pro-rata. Mark the horizontal centreline
(for your choice of spinner diameter) on tape on the front of the firewall now, making sure that
the line is horizontal by eyeing thru’ the steel ruler and the
wing tube.
The side-to-side location of the centre of your motor is also
easily set. It is 8mm to the (pilots) left of the central seam
of the motor-dome. (see photo right). With the motor
mounted centred on these 2 lines, with 4 equal length
standoffs, the centre of the spinner will be centred on the
front of the cowling.
3W 80cc Xi.
For this set-up we used a C-ARF 120mm diameter carbon
spinner (# 810103), a Greve tuned pipe (# 910200), with
a custom welded manifold and a Mejzlik 27 x 10 carbon 2-
blade prop.
Composite-ARF Extra 300SX
(2.6m span)
24
(above) The top of the spinner
should be 5mm below the
radiused front edge of the cowl,
which is 20mm below the straight
edge laid flat on the fuselage.
(below) The side-to-side centre of
the motor should be 8mm to the
pilots left of the motordome seam.
The cutout shown here is for the
rear-mounted 3W carburettor.
(above) The 3W 80cc Xi motor,
attached to 6mm carbon/plywood
plate, with 30mm long aluminum
stand-offs - also showing throttle
and choke linkages.
20mm
