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State of the art Automatic Start Sequencer and Governor
A fully automatic start sequencer and governor was developed which takes care of all critical engine
parameters during start - up. It was designed to minimize the workload of the pilot and maximize safety.
Some of the features of the ECU are listed below:
Specifically designed for the Solar T-62T-32 engines
Controls all the engine systems and monitors its functions
Includes governor (RPM stability appr. +-0.5% no-load / full-load), startup sequencer, safety monitoring systems
Optional 12V back-up battery can be attached so the engine will be kept running if main power fails. The backup battery
is recharged during normal operation
Operates from 12V to 28V, maximum current consumption during startup 25A, during normal operation approx. 5A; during
starter engagement supply voltages as low as 4V will be tolerated
Internal, electronic RPM preset pot to eliminate long, RFI-sensitive and safety-critical wires as well as failure-prone
mechanical pots
Control panel is equipped with three back-lit LCDs to show preset RPM percentage, actual engine RPM percentage and EGT
in degrees celsius (can be modified to display farenheit), one momentary "start engine" switch and an ultrabright two-colour LED indicator to indicate engine status
Connections for rpm trim up, rpm trim down and "kill engine" momentary switches
Up to four auxiliary inputs for pressure or temperature switches or chip detectors (to be software configured if required)
RFI insensitive optocouplers on all external connections
Hermetically sealed aluminium enclosure, Cannon MIL style connector
ECUs will be pre-adjusted to work directly, without additional adjustment, on any stock T-62T-32 engine with an aftermarket
12V starter (original starters will also work if a 24V power system or external 24V supply is used)
Using SMT throughout the circuitry for much improved susceptibility to vibration
The software so far implements many features of which a few are highlighted below:
Startup sequence improved so the main fuel valve will be opened only if there’s an EGT reading higher than 100°C and
not only based on the RPM schedule as specified by Solar. This prevents the engine from being flooded with fuel in case of
a delayed light-off. It will also keep the start fuel pressure high for good atomization until the engine actually lights
off. This improves cold climate startups considerably
Engine acceleration and clutch engagement controlled by an EGT schedule. If the temperatures during engine acceleration
(between 40% idle and 80% start fuel valve disengagement RPM) should approach the limit of 600°C, further increase of RPM
preset will be inhibited. If EGT increases further, the ECU will actually decrease RPM preset to bring temperatures down
again. If all this won’t help, the engine will be shut down to prevent it from damage.
This shutdown feature is only enabled during startup and acceleration. Ιn “Run Mode”, i.e. the helicopter is potentially
flying, the pilot is responsible to decide about engine health. The electronics will only light a warning signal if there’s
a malfunction detected. This may leave the pilot valuable time with engine power available, even if the engine later may be
a smoking heap of melted metal...
During “Run Mode”, there’s one single situation that indicates for an engine shutdown, that’s too high or erroneous
engine RPM. As per the Solar specifications, the limit is set to 110% rated speed. If, for some reason, the engine will
reach that speed, then the governor isn’t in control of the engine anymore, either due to mechanical or (rarely) due to
electrical failure of a component. The result of a run-away situation is much more dangerous than a forced autorotation. If
the engine accelerates without limit, the rotor system of the helicopter may be overloaded and fail or the turbine rotor may
explode and cause severe damage to components in its neighborhood, potentially making an autorotation impossible. A failure
of the engine RPM pickup will have the same result because the engine cannot be controlled anymore if there isn’t a
reference signal available.
If the engine is operating in “Run Mode” and the ECU senses a fast decrease of RPM or EGT, it will energize the ignition
exciter. In case the change of RPM or EGT was caused by a flameout, there’s a good chance that the engine will relight and
return to normal operation. Even though I never witnessed a T-62T-32 with a properly adjusted fuel control unit (FCU) to
flame out, this may give the pilot some additional peace of mind...