Engine Control
The engine control system is a completely automatic digital engine control that requires minimum human intervention to reduce pilot workload, with automatic backup to increase safety.
It provides control of the engine power for all phases of engine operation, from startup to shutdown through all flight regimes. It is a dual channel Full Authority Digital Engine Control (FADEC) with automatic backup.
It consists of the components that follow:
Engine Control Unit (ECU)
Auxiliary Control Unit (ACU)
Pilot throttle switch
Engine switch
Fly/idle relay
Crank relay
Start relay
Fuel low relay
XOP low relay
XOT hot relay
Engine mounted controls and sensors
ECU maintenance connector
Copilot throttle switch, if installed.
Engine Control Unit (ECU)
The ECU is a dual channel digital engine control unit, or FADEC, that monitors engine parameters from multiple engine mounted sensors, mode selection from the throttle and the ENGINE switch, and power demand from the collective control position.
It computes the data and controls the fuel metering needle inside the Hydro-Mechanical Unit (HMU).
It consists of the channel A, channel B, and circuits that are shared by the two channels, all in one Line Replaceable Unit (LRU).
It is located on the shelf above the baggage compartment.
Auxiliary Control Unit (ACU)
The ACU is a solid state and discrete control unit that provides automatic backup when the actuator of the fuel metering needle fails.
Under these circumstances, the ECU uses the discrete components of the ACU to control a bypass valve inside the HMU.
The ACU is located on the bulkhead behind the passenger headrest.
Pilot THROTTLE switch
The pilot THROTTLE switch is a Double Poles, Single Throw (DPST) rocker switch that lets the pilot control the engine power.
It is located on the pilot collective stick.
Copilot THROTTLE switch
The copilot THROTTLE switch lets you operate the engine from the copilot position when the dual controls kit is installed. It is located on the copilot collective stick.
Engine switch
The engine switch is a 3-position rotary selector switch that lets the pilot control the operation of the engine.
It is located on the miscellaneous control panel.
Relay Panel
Fuel low relay
The fuel low relay is a DPDT relay that gives the fuel low indication to the ECU while isolating the ECU connections from the helicopter ground potential. It is located on the relay panel.
XOT hot relay
The XOT hot relay is a DPDT relay that gives the transmission oil temperature hot indication to the ECU while isolating the ECU connections from the helicopter ground potential. It is located on the relay panel.
XOP low relay
The XOP low relay is a DPDT relay that gives the transmission oil pressure low indication to the ECU while isolating the ECU connections from the helicopter ground potential. It is located on the relay panel.
Idle/fly relay
The idle/fly relay is a Double Pole, Double Throw (DPDT) relay that controls the modes of operation of the ECU. It is located on the relay panel.
Start relay
The start relay is a three poles, double throw relay that controls the starter and the fuel prime pump. It is located on the relay panel.
Crank relay
The start relay is a three poles, double throw relay that controls the starter and the fuel prime pump. It is located on the relay panel.
ECU maintenance connector
The ECU maintenance connector gives access to the ECU internal memory to upload software and to download maintenance data. It is located on the relay panel.
Engine Mounted Sensors
The engine mounted sensors let the ECU monitor the operation of the engine. They also provide backup electrical power to the ECU.
The ECU monitors the following engine mounted sensors:
Engine Torque (Q)
Measured Gas Temperature (MGT)
Gas Producer (NG) Speed
Power Turbine (NP) Speed
Engine oil pressure and temperature
Fuel pressure and temperature
Fuel pressure after the filter to determine clogging
Position of the fuel metering needle
Neutral position of the bypass valve
Compressor Discharge Air (P3)
Ambient temperature
Engine Torque (Q)
Engine torque (Q) is measured using specific components and sensors. This process involves the engine oil pump pressure, a torquemeter piston arrangement connected to the intermediate gear of the reduction gear system, and a torquemeter transmitter. As the engine's power demand fluctuates, the helical teeth of the intermediate gear trigger a reaction against the torquemeter piston, thereby altering the modulated oil pressure supplied to the torquemeter transmitter. The torquemeter transmitter measures the modulated pressure and delivers an electrical signal to the ECU. The ECU channel in charge (channel A or channel B) provides a torque signal through its ARINC-429 bus connection to the indicating/recording system. Refer to Engine Torque (Q) Indication.
Measured Gas Temperature (MGT)
The engine Measured Gas Temperature (MGT) measurement involves a specialized harness housing four double thermocouples. The thermocouple probes are positioned in the gas flow at the gas generator turbine outlet in order to measure the gas temperature. The result is two pairs of independent temperature inputs. These inputs are then directed to a MGT junction box, ensuring separation and integrity of data.
Redundancy and Control: To further elevate reliability, both MGT signals proceed to ECU channels A and B. Each ECU channel undertakes a continuous verification process, assessing the validity of the MGT signals. Upon validation, the signal values are subjected to averaging. The ECU channel in charge (channel A or channel B) then provides the averaged signal through its ARINC-429 bus connection to the indicating/recording system. Refer to Measured Gas Temperature (MGT) Indication.
Gas Producer (NG) Speed
NG speed is measured using a dual-channel, 3-phase alternator. This device serves a dual purpose: providing power to the ECU and generating the NG acquisition signal. ECU channels A and B work together with the alternator's voltage frequency to measure gas generator speed. The ECU channel in charge (channel A or channel B) provides the signal through its ARINC-429 bus connection to the indicating/recording system. Refer to Gas producer (NG) Indication.
Power Turbine (NP) Speed
Two separate NP magnetic speed sensors are situated on the forward side of the engine gearbox at the NP intermediate gear shaft to measure Power Turbine (NP) speed. As the NP intermediate gear shaft rotates, it generates an alternating voltage in these sensors, with the voltage frequency reflecting the shaft's rotational speed. Dedicated speed sensors on Channel A and B acquire the NP speed signal, with continuous checks by the ECU to ensure accuracy and validity. The ECU channel in charge (channel A or channel B) provides the signal through its ARINC-429 bus connection to the indicating/recording system. Refer to Gas Producer (NG) indication.
Engine Oil Pressure and Temperature
The oil pressure and temperature transmitter provides an indication of oil pressure and oil temperature on the indicating/recording system. The oil pressure and temperature is located on the engine on the front left-hand side of the lubrication device.
The transmitter measures the oil pressure and temperature downstream of the filter and transmits the pressure and temperature signals to the ECU, which then sends them to the indicating/recording system for display on the Engine Indication System (EIS) strip. Refer to engine oil pressure and temperature indication.
Engine Mounted Controls
The engine mounted controls let the ECU control the operation of the engine.
The ECU also controls the following engine mounted actuators:
Pump and Metering Unit Assembly
Fuel Valves Assembly
Fuel Injection System
Combustion Chamber Drain Valve
The Arrius 2R engine fuel system is designed to supply, distribute, control, meter and inject fuel. All the system components are located on the engine, except for the ECU, fuel storage (cell) and the priming pump. The engine fuel system is comprised of the fuel pump and metering assembly, fuel valves assembly and fuel injection system. Fuel is drawn from the airframe fuel system by the priming pump to the low pressure liquid ring fuel pump located inside the pump and metering assembly. Once the engine reaches 50% NG, the priming pump is disabled and the low pressure pump continues to provide adequate suction. The low pressure fuel pump then supplies a pressure head to the fuel filter, and from the fuel filter fuel flows to a high pressure gear pump downstream which applies the proper pressure to the fuel metering unit controlled by the ECU. The metering unit than allows metered fuel flow to the fuel valves assembly which distributes the fuel to the fuel nozzles where fuel is atomized and sprayed into the combustion chamber for stable and efficient combustion. Engine Control > Power Control > Engine Mounted Control - Fuel Pump and Metering Unit The Fuel Pump and Metering Assembly is mounted on the left front upper face of the reduction gearbox casing and secured by mounting bolts.
Fuel Pump and Metering Unit Assembly
Pumps
A Low Pressure (LP) pump and High Pressure (HP) pump that are mounted on the same shaft supply fuel under determined conditions of pressure and flow rate to the engine. The LP pump is a liquid ring pump. It is fitted with an ejector that taps part of the fuel from the LP pump outlet and loops it back to the LP pump inlet to improve suction efficiency. The impeller is driven at a speed proportional to NG by the pump assembly’s internal drive shaft. This internal drive shaft also drives the gear of the HP pump. A seal prevents any leaks between the LP fuel pump and the HP fuel pump. The HP pump is a spur-gear pump. It has a driven gear and a drive gear driven at a speed proportional to NG. The shaft is fitted with seals to prevent fuel leakage. There is also a drain between the two seals to evacuate fuel or oil if a leak were to occur. A pressure-relief valve is incorporated to return any excess fuel to the HP pump inlet in the event of an overpressure in the fuel system.
Start Purge Valve
The start-purge valve is a ball valve controlled by a piston and spring. It permits the purge of air from the fuel system during engine start. It is located between the LP pump and the fuel filter. Fuel Filter - located between the LP and the HP fuel pumps, a 20-micron fiberglass filter is utilized to retain any particles in the fuel to protect the fuel metering components. The fuel filter assembly incorporates a bypass valve that will open when the pressure difference across the filter exceeds 21.8 PSID (150 kPa). The valve ensures that fuel continues to flow to the metering unit in the event the filter becomes clogged. It is housed in the body of the fuel filter blockage indicator.
Fuel Filter Monitoring
Level 1 (Maintenance) - In the event that the pressure drops below the FADEC ECU Level 1 fuel filter pre-clogging threshold (i.e. less filter blockage than Level 2), the ECU will request that the Integrated Avionics System (IAS) activate the FUEL FILTER CAS message when the state of the engine is at IDLE or STOP. The CAS message will remain activated.
Level 2 (Warning) - If the pressure drop reaches the FADEC ECU Level 2 fuel filter pre-clogging threshold (partially blocked), the ECU will request that the IAS activate the FUEL FILTER CAS message and an audible tone will sound. Once activated, the CAS message is latched “ON” and will remain activated. The FUEL PRESS (CAS) message and audio tone displays when the FADEC ECU low fuel pressure warning becomes active. The warning level is a variable threshold based on ECU monitored fuel pressure, fuel temperature and atmospheric pressure. In such an event, prepare for a possible engine failure.
Visual Blockage Indicator - located on the filter body, the blockage indicator will display a red pop up indicator when the pressure difference exceeds 21.8 PSID (150 kPa) indicating that the bypass valve is open allowing unfiltered fuel to the metering unit. Maintenance action is required. The pop up red indicator can be reset after removal of the cover and pushing it back into the housing.
Metering Unit
The Fuel Metering Unit Assembly is a hydromechanical unit located downstream of the pump-filter assembly that controls the fuel flow in response to signals from the ECU. The mtering unit consist of the following:
Constant Delta P Valve: The constant delta pressure valve returns the excess fuel to the HP pump inlet and maintains a constant pressure across the metering needle. Therefore, fuel flow is only a function of metering needle position, unaffected by change of delta pressure.
Auxiliary Constant Delta P Valve: In the event the Constant Delta P Valve diaphragm should fail the Auxiliary Delta P Valve will take over and return the excess fuel to the HP pump inlet and maintain a constant pressure across the metering needle.
Neutral Position Switch: This switch determines if the auxiliary metering valve is in the neutral position.
Auxiliary Metering Valve: The Auxiliary Metering Valve is controlled by the Auxiliary Control Unit (ACU) when the ECU determines that both stepper motors in channel A and channel B are malfunctioning.
Dual stepper motor: The Dual stepper motor is a dual channel motor with two separate windings on a single shaft. The stepper motor is driven by Channel A or Channel B as commanded by the ECU. At any given instant, only one channel is in control. The motor rotates and drives the metering needle as commanded by the ECU and will either decrease or increase the fuel flow by means of a rack and pinion mechanism. Metering Needle Position Transmitter - located on the same rack and pinion system as the stepper motor, the resolver provides a signal to the ECU providing a metering needle position.
Metering Needle: The metering needle meters the flow of fuel in response to ECU demands. The fuel is then sent to the fuel valves assembly.
Fuel Valves Assembly
Fuel Valves Assembly controls the fuel flow to the injection system. It consist of the:
Stop electro-valve
The stop electro-valve is a bi-stable type which includes a solenoid with two coils and a two position valve (open and closed). When start is selected, the opening coil of the stop-electro valve is electrically supplied. The stop electro-valve opens allowing fuel to flow to the pressurizing valve.
Pressurising valve
The pressurizing valve ensures priority of fuel flow to the start injectors. It is a differential valve which is spring loaded closed (setting: approximately 1000 kPa (145 PSI). When the fuel pressure is sufficient, the pressurizing valve opens and supplies fuel to the main injectors.
Preference injector valve
When conducting the FOPS test you are checking to see that the preference valve is working properly. If it is, the preference injector will have enough fuel pressure for a proper spray to keep the flame lit. If the valve does not close, like it should, the fuel pressure will go to all the injectors causing a pressure drop across all of them. This will cause the injectors to drool instead of spray so the flame will go out.
The preference injector valve closes fuel supply to the nine main injectors during a rapid fuel decrease (fuel flow lower than approximately 25 LPH (6.6 GPH). However, the flow is maintained to the preference injector to avoid engine flame-out.
Start electro-valve
The start electro-valve allow the start injectors to either be supplied with fuel or ventilated with P3 air. It is a 3-way, mono-stable valve. It consists of a solenoid which controls a double valve. During start the start electro-valve also opens and supplies fuel to the start injectors. As the engine reaches self-sustaining speed (approximately 50% NG), electrical power to the start electro-valve is cut and there is no fuel supply to the start injectors and at this point P3 air pressure ventilates the start injectors through a restrictor to prevent carbonization of residual fuel that might cause injector blockage (ventilation is continuous during engine operation).
Fuel injection system
The fuel injection system is located downstream of the fuel valves assembly, on the engine around the rear part of the combustion chamber casing. It sprays fuel into the combustion chamber providing stable and efficient fuel combustion.
The fuel injection system consists of the following:
Starter injectors
The starter injectors spray fuel into the combustion chamber during engine start and are located at the 1 and 9 o’ clock positions of the combustion chamber casing as viewed from the rear.
Main injectors
Ten pre-vaporizing type injectors are mounted on 2 half-manifolds at the rear of the combustion chamber casing with one of the ten being a preference injector. The right half-manifold supplies 4 injectors and the left half manifold supplies 5 injectors. The 2 half-manifold unions are secured to the preference injector valve outlet, located at the rear of the valve assembly. The left half-manifold inlet union is secured to the right half-manifold inlet union by means of two bolts.
Preference injectors
The preference injector is supplied by the preference injector supply pipe. The injectors are integral with the manifolds. The preference injector supply pipe is a rigid pipe which supplies fuel to the preference injector located at the rear upper part of the combustion chamber casing. The preference injector is integral with the pipe and is identical to the 9 other main injectors.
During operation, the fuel is supplied by the valve assembly to the injectors which spray fuel into the pre-vaporizing tubes. In each tube the primary air is mixed with the fuel. The vapor exiting from the two outlets of each tube is ignited.
Combustion chamber drain valve
The combustion chamber drain valve drains any unburned fuel remaining in the combustion chamber. It is located at the lowest part of the combustion chamber. It is a piston type valve that closes at approximately 65% NG speed. The valve has two positions: open and closed. As the engine starts the combustion chamber pressure begins to rise and causes the valve to close. When the engine is stopped the valve is held open by the spring action and drains any unused fuel to prevent any starting problems (e.g. starting over-temperature).
Operation
The ECU is energized with 28 VDC from the MAIN bus and can be isolated with the ECU CH A circuit breaker and the ECU CH B circuit breaker. The ACU is energized with 28 VDC from the MAIN bus and can be isolated with the ACU MODE circuit breaker and the ACU NEUT circuit breaker. The ENG IGN/VLV circuit breaker provides 28 VDC from the MAIN bus to the engine mounted ignition unit through the ignition relay, and to the engine mounted ON/OFF electro-valve through the start relay. The ECU RLYS circuit breaker provides 28 VDC from the MAIN bus to the idle/fly relay, fuel low relay, XOP low relay, and XOT hot relay.
Engine Control Unit (ECU)
Each channel is alternatively in command of the engine controls, changing at every start. The ECU monitors each channel, its sensors, and its actuators, for consistency of data between the two channels, and to detect eventual failures. Depending on the severity of the detected failure, the ECU uses backup laws to simulate the failed sensor, switches to the operable channel, or enables the ACU to allow the helicopter to continue to fly safely. Channel A of the ECU sends information to the Primary Flight Display (PFD) and to the integrated avionics unit (GIA) through an ARINC 429 data bus. Refer to central display system and general computers. "Channel B of the ECU sends information to the Multi-Function Display (MFD) and to the integrated avionics unit (GIA) through an ARINC 429 data bus. Refer to central display system. The two channels of the ECU receive information from the integrated avionics unit (GIA) through dedicated ARINC 429 data busses.
Monitoring
The ECU monitors the following engine mounted sensors "Collective pitch position The ECU reads the voltages of potentiometers inside the collective transducer, which are proportional to the position of the collective control.
The collective transducer connection are required to reference the inputs of the ECU to ground." "Relays The fuel level sensor, transmission oil temperature switch, and transmission oil pressure switch control the fuel low relay, XOP low relay, and XOT hot relay, respectively.
The relays, when energized, apply the COMMON connection of the ECU to its FUEL LOW, TRANSMISSION OIL PRESSURE LOW, and TRANSMISSION OIL TEMPERATURE HOT connections, respectively. This effectively isolates the ECU connections from the helicopter ground potential.
Processing
Both channels of the ECU process the data concurrently. They are continuously compared for discrepancies.
One channel is in command of the fuel flow through the fuel metering needle.
Single Channel Failure
When the ECU detects that the channel in command cannot control the fuel flow, it switches to the other channel.
Auxiliary Control Unit (ACU)
When the ECU detects that either channel cannot control the fuel flow, the following occurs:
The ECU keeps the drive signal to the fuel metering needle actuator constant.
The ECU enables the ACU through the HMU AUX CTRL SYSTEM ENABLE to HMU AUX CTRL ENABLE connection.
The ACU signals the integrated avionics unit (GIA) through the HMU ENABLE to HMU ENABLE connection. This causes the CAS caution message HMU AUX CTRL to show on the PFD.
The ECU uses the FUEL INCREASE, FUEL DECREASE, OUTPUT VOLTAGE DMD 1, and OUTPUT VOLTAGE DMD 2 connections to the LP8, LP4, LP1, and LP10 connections of the ACU, respectively, to control the backup electrical actuator.
The ACU drives the backup electrical actuator through the INC and DEC connections.
Dual Channel Failure
When both channels of the ECU fail, the following occurs:
The ECU signals the integrated avionics unit (GIA) through the PAN3 to ECU FAILED connection. This causes the Caution Alerting System (CAS) warning message ECU FAILED to show on the PFD. Refer to central warning system.
The fuel metering needle is frozen in the position it was in before the failure. Note - it is not possible to control fuel flow other than to shut off the fuel supply." "If, during normal operation, the ECU detects, through an HMU mounted neutral position switch, that the position of the bypass valve is not centered, the following occurs:
The ECU sends the command to the ACU to center the bypass valve through the NEUTRAL POSITION RECOVERY DMD to NEUT POS RECOVERY connection.
The ACU uses the < CN INC and > CN DEC connections to determine the direction to drive the backup electrical actuator.
The COMMON connection of the ACU supplies the power to the backup electrical actuator for the < CN INC and > CN DEC connections.
The neutral position switch tells the ECU that the bypass valve has returned to center.
The ECU then disables the NEUTRAL POSITION RECOVERY DMD.
Engine Switch
The engine switch on the miscellaneous control panel tells the ECU the mode of operation selected for the engine as follows:
OFF position:
The COMMON connection of the ECU is supplied to the engine switch.
The OFF actuator of the ON/OFF electro-valve is supplied with power through the engine switch, shutting off the fuel supply.
The engine spool is down, if it was operating.
START/RUN position:
The COMMON connection of the ECU is supplied to its IDLE connection through the engine switch and the energized idle/fly relay.
The power to the OFF actuator of the ON/OFF electro-valve is removed.
The ECU initiates the start sequence by energizing the start relay.
Power is supplied to the ON actuator of the ON/OFF electro-valve through the start relay letting the fuel flow to the engine.
A ground is applied to the EPSU through the start relay telling it to engage the starter to crank the engine.
When energized by the ECU during the start sequence, the ignition relay provides power to the ignition unit.
When the ECU sees that the engine is operating properly, it finishes the start sequence by de-energizing the start relay and the ignition relay.
The engine continues to operate as long as fuel is supplied. The operator must push the engine switch to return it to the OFF position to shut down the engine.
CRANK position:
The COMMON connection of the ECU is still supplied to its STOP connection through the engine switch, preventing the initiation of the start sequence.
The OFF actuator of the ON/OFF electro-valve is still supplied with power through the engine switch. The engine is not supplied with fuel.
A ground is applied to the EPSU through the engine switch and the start relay, telling the EPSU to engage the starter.
The CRANK position of the engine switch is spring loaded. Releasing the engine switch returns it to the OFF position.
THROTTLE Switch (IDLE)
The pilot THROTTLE switch, on the pilot collective, controls the engine operation as follows:
When it is set to IDLE - closed:
The pilot THROTTLE switch applies a ground to the integrated avionics unit (GIA).
The pilot THROTTLE switch applies the ground from the copilot jumper, or from the copilot THROTTLE switch, if installed, to the idle/fly relay.
The COMMON connection of the ECU is supplied to its (IDLE) connection through the engine switch and the energized idle/fly relay.
The ECU mode of operation is IDLE.
When it is set to FLY - opened:
The ground to the PILOT FLY connection of the integrated avionics unit (GIA) is removed by the pilot switch.
The ground from the copilot jumper is removed by pilot switch and the idle/fly relay is de-energized.
The COMMON connection of the ECU is supplied to its DIN10 (FLIGHT) connection through the engine switch the de-energized idle/fly relay.
The ECU mode of operation is FLIGHT.
The ECU can now command the engine to produce sufficient power for flight.
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