Wren 44 TurboProp Users Manual. Copyright Wren Turbines Ltd February 2008 Page 26
Fuel Tank Clunk Pickup
A felt-type clunk is supplied for you to use for your fuel tank in case
you need it.
A washer needs to be fitted before the felt part to stop it sliding onto
the part where the tube goes on.
UAT/Hopper Tank
If you plan to fit a UAT (Ultimate Air Trap from BVM Models) or a hopper tank then position this
close to the tank outlet and plumb in using the largest tube that can be fitted. A length of 3.1mm
(1/8”) soft yellow Tygon tube is included in the package and this is ideal. This allows the greatest
flow possible and minimises the chances of pulling a vacuum or starting an air leak into the fuel
system. Note – it is possible for air leaks to appear that are so small as to not let fuel out and
leave a trace, but still cause troubles.
Making an airtight joint to the fuel pump
Make a similar secure connection between the UAT/hopper to the fuel pump and similarly keep
this pipe run as short as you can. If the Tygon is not such a firm fit onto the pump then push on a
12mm (½”) length of 4mm tube onto the barb first and then push the Tygon on over this – this
should be really tight and very leak free. Just adding a tie-wrap onto a loose pipe will not make a
secure joint as it forces the tube into a “D” shape and air can leak in through the corners of the
“D” – use the short length of 4mm tube, it works every time. If later you need to remake the joint
simply cut the last bit off the Tygon and refit it onto a fresh end to keep it tight.
Fuel pump to fuel valve and engine
The outlet of the fuel pump feeds the fuel valve directly - note the direction arrow on the valve.
The outlet of the fuel valve feeds the engine fuel filter. This pipe run can be some distance
without causing any problems as it is a pressure line. As before, if you have to remake any of
these connections then it is a good idea to cut the last bit cleanly and remake the join. Keep all
your pipes a little on the long side to enable you to do this.
ECU (Engine Control Unit)
Next, connect the propane and fuel valves to the ECU. The propane valve
is plugged into the top connector and the fuel valve connects to the one
below (see left). The green temperature probe cable (thermocouple) and
RPM pickup are next to be inserted. Make sure that the colouring of the
wires matches the picture on the ECU. It is very important that these are
connected correctly in order for the ECU to function correctly.
The fuel pump and starter need to be joined to the ECU via their Multiplex
connectors, these can only be connected in the correct order but you can
check the wire colouring against the picture on the ECU.
Connect the signal lead from the ECU to the
throttle channel on your receiver.
If required, the solenoid, RPM pickup and
thermocouple wires can be extended with a
standard servo extension lead. Those for JR radios are compatible
with the ECUs connections.
NOTE: The wires leading to the pump, glowplug and starter are
twisted together in order to reduce interference; do not attempt to untwist them.
