Motor Ignition System
The ignition unit is normally fixed to the motordome, as
close to the engine as possible - because of the length of
the HT leads that connect to the spark plug(s). Mount it on
a foam pad and secure with cable-ties, or use sheetmetal
screws into small plywood pads with rubber grommets for
vibration isolation. Don’t forget that the ignition unit also
gets warm during use, so it is wise to put it in a location
where there is some cooling airflow.
Use a very small cable tie, ‘safety clip’, or a length of heat-
shrink tubing to securely connect the plug and socket from
the motor pick-up to the ignition unit.
Fuel Tank
The fuel tank is held to the tank base with 3 large cable-ties
(photo on page 29 and P23). Drill a hole in the motor fire-
wall if necessary for the fuel feed tube from the tank to the
carburettor, and protect it where it passes through the hole
using a rubber grommet or similar. Fix the tubing securely
to the underside of the top of the motordome with a couple
of cable-ties or equivalent, to make sure that it cannot come
in contact with the headers or hot exhausts.
Fit the correct stopper to the fuel tank for the fuel type used.
(If using Dubro tank the gasoline stopper has a small ‘O’ moulded in the top of it). We use the
excellent ‘Tygon’ brand of fuel tubing for all our aerobatic models. It is totally gasoline and
kerosene-proof, and does not go hard and crack with age. Secure the feed tube inside the tank
to the clunk with a small cable tie. If the tube is even a little loose on the brass tubes though the
stopper, you can be sure it will come off at just the wrong moment and your engine will quit !
Therefore please solder some small rings onto both ends of the brass tubing (easily made from
the soft wire of a paperclip wrapped around a small screwdriver, or short lengths of brass tube)
and also secure with a fuel-line clamp or cable-tie. Don’t miss this small detail - it could cost you
your plane !
We use the normal 3 tube plumbing system, one from the clunk to feed the motor, one out of the
bottom of the plane (vent/overflow - leave open) and one at the top for filling (close for flight).
If you want to fit a smoke system the smoke tank can be fitted alongside the fuel tank but you
will need to make an extra platform for it. Follow the manufacturers instructions for fitting the
smoke system.
Final Check
Now check that you have fixed all components securely. Keep in mind that all the components
inside the aircraft are loaded with the same G’s as the wing and the wing spar during aerobatic
maneouvers. Check engine, cowling, wing and stab mounts carefully again.
-
Are all extension leads, cables & fuel tubes securely fixed to the side of the fuselage
and cannot come loose when subjected to high ‘G’ forces during flight.
Composite-ARF Extra 300SX
(2.6m span)
33
(below) Secure the connectors
between the motor & ignition unit.
(below) Fit barbs to all brass tubes
and fuel connections for safety.
Easily made from a paper-clip, sol-
dered onto the brass tubes.