Wren 44 TurboProp Users Manual. Copyright Wren Turbines Ltd February 2008 Page 11
Data Terminal
The ecu is accessed from the outside world by a port with a telephone style
socket connector and a hand-held unit called the Data Terminal.
This terminal is primarily a display for the engine but is also used to input
settings from buttons on its front panel. The terminal’s functions are
described in more detail later.
RPM Pickup
Mounted on the front of the engine, under the FOD screen is a hall-type
magnetic rpm sensor. It picks up a signal from a small magnet fitted into
the compressor nut one the end of the shaft of the engine. The signal
terminates in a servo-type plug which plugs into the rpm input on the
ECU.
The pickup is sensitive to stray magnetic and electrical noise so be careful
about routing cables close to it. The starter and glow plug cables are
tightly twisted to reduce their stray signal for this reason – do not untwist
them.
Temperature probe.
The temperature probe is a standard
miniature industrial thermocouple which is positioned in the
interstage casting via the engine bulkead and senses the
exhaust temperature of the engine and feeds this
information back to the ECU.
Temperature information is used to detect sufficient pre-heating at the engine start phase and correct
operation during normal running. On shutdown, the temp’ probe indicates to the ECU when the engine has
cooled sufficiently during the cool-down phase. It is secured on the front of the engine and connects to the
ECU via a small servo-type plug with a special green cable. It is attached to the engine and should not be
moved from this position.
Fuel Pump.
The fuel pump is one of two special
gear type pumps especially made for the Wren 44
and turbo-prop. They have very small gears to allow
a wide range of control for the engine and
must not
be substituted for anything else. Almost all other
turbine fuel pumps are much too large and are
therefore not suitable for this application and result in
loss of control on this engine. Be very careful whenever disconnecting or connecting it
to ensure there are no small slices of pipe left at the inlet or outlet.
When people say that “cleanliness is next to godliness” they are referring to small turbine fuel pumps. Treat
this component with total reverence and keep it spotless. Always carefully blank off the pipes
with clean
blanks
, when moving it about. The smallest particle can spoil the operation of this pump so only allow clean
fully filtered
fuel into it. Connect to a fuel tank by a single direct pipe with no connectors, fuelling valves,
stoppers etc between it and the fuel pickup. The pickup should be a quality felt type clunk or propietry pickup
with fine filtering qualities.
ALWAYS
carefully filter the fuel going into the tank, don’t rely on the pickup to stop particles getting in. If a
tank gets badly contaminated then discard it – this engine is far too costly to risk a dirty tank. Be careful also
to ensure any tank vents cannot suck grit into the tank. A filter on the air vent is not going too far to keep the
fuel pump in tip-top condition.
Propane Valve
This valve is a specially made brass body valve used to switch the propane gas on and off
during the start phase. It has an “in” and “out” (marked by an arrow). The valve is powered
by the propane outlet on the ECU and care should be taken to ensure it is plugged into the
correct ECU socket. The valve coil is rated at 5v and may be tested with a 5v supply where
a solid click can be heard. If it malfunctions the valve is not user serviceable and must be
replaced. It is identical to the fuel valve in construction. Note – the “F” on the side of the
valve base indicates the direction of “Flow” and not “Fuel”.
