Wren Turbines 75 Manual page 8

Failsafe function.
The ecu contains a failsafe function that will stop the engine in the event of loss of radio link or continued
radio interference that masks the normal signal, but will allow the engine to continue to operate in the case
of short glitches. The system works with PCM, PPM and IPD systems.
PPM systems.
In case of loss of radio link, corrupted or signal pulses outside the programmed window of operation, for the
first 0.5 secs the FADEC will do nothing and keep the engine at its last valid setting. If during this time the
radio link is recovered or signal pulse-width returns to within the programmed window, control is returned.
If after this 0.5secs the signal still is missing or bad, the FADEC will command the engine to "idle", and
keep it at idle for a further 1.5secs. After this 1.5secs (total 0.5+1.5secs=2secs) the FADEC will
command the engine to shutdown.
If the signal returns during this 2s, the FADEC will take this signal as good and reset the 2secs timer
and engine control will return.
PCM/IPD systems.
The user should program the "failsafe" function of the radio to send a signal lower than the normal "stop"
signal (ie if normal "stop" is –100%, then program the failsafe to output –125%).
When the receiver enters into "failsafe" mode, it will issue a signal to the FADEC of -125% that is
outside the valid command window, (between STOP (-100%) and Full power (+100%) . In this case
the FADEC will follow same procedure as described in PPM mode and shutdown the engine after 2s
of failsafe. In this event the FADEC will record the cause of shutdown as a "Failsafe" shutdown.
If the failsafe setting is programmed on the TX to the same point as the "STOP" command, the
system will act exactly the same, except that the FADEC will record in its memory that the cause of
the last shutdown was "User-Off". This could make it more difficult to troubleshoot a in-flight shutdown.
This system allows the engine to fly through minor interuptions of signal or glitches, thus avoiding the
engine shutting off unnecessarily, while maintaining the safety of automatic shutdown in cases of loss
or corruption of radio link.
IMPORTANT - ALWAYS PROGRAMME THE FAILSAFE TO SHUT OFF THE ENGINE.
NEVER FLY A TURBINE AIRCRAFT WITH THE FAILSAFE SET TO "HOLD".
Checking operation of the gas (propane) start.
The gas required is from a gas canister available from hardware stores (screw-top variety) and will
ideally be 30% propane 70% butane, the higher propane mix means less gas needed and quicker
starting. Other suitable types are those sold for the "Taymar" and similar blowtorches but check
carefully the propane content. Do your gas filling outside in open air away from sources of ignition, no
smoking etc.
The gas tap supplied should be screwed onto the canister (ensure tap is off first) and checked to
ensure there are no leaks.
If you are using off-board gas then simply plug the quick release into the matching female connector. If
this is the first time then do a quick visual check to ensure you have connected the quick release
female either direct to the engine or through pipework to the gas solenoid, if fitted.
If you are using onboard gas then again ensure all the pipework to the engine is
complete and the flow restrictor is set to no more than 1-1/2 turns out. Direction of
flow is in to solenoid first, then to bottom of flow control valve, then out the side to
engine (see left). Keep your your fire extinguisher close whenever filling the gas
tank. Connect the gas canister to the quick-release coupling and invert the cylinder
so the valve is at the bottom, and open the valve. Liquid gas will be seen to travel
down the tube to the tank. Disconnect the tank when the flow ceases.
The tank does not need to be any more than about 1/3
not attempt to fill more than this as it is unnecessary and will not aid gas supply.
WREN 75 - High Performance Gas Turbine Engine
rd
full for several successful starts. Do
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