Engine/Engine Control Flashcards
Engine Type/Sections
T700-401C – front-drive turboshaft
inlet, compressor, combustor, turbine, exhaust
Inlet Section
Inlet cowling, swirl frame, front frame, main frame, accessory section, scroll case, and waterwash manifold.
Inlet fairing perforated to allow 5th stage bleed air to heat surface from inlet anti-ice valve.
Intake air passes through swirl vanes–hollow for 5th stage bleed air from engine anti-ice valve
Inlet Particle Separator
Prevents foreign particles from entering compressor. Throws particles outward to collection scroll before dumping overboard
Sends air to deswirl vanes removing rotation for smooth airflow to compressor
Compressor Section
5 stage axial, 1 stage centrifugal rotor/stator assembly
Combustion Section
flow-through, annular combustion chamber with 2 igniters and 12 fuel injectors receiving fuel from ODV
Gas-Generator Turbine
Ng turbine drives compressor and AGB
2 stage air-cooled, axial design
Power Turbine
Coaxial design, turning inside the Ng turbine shaft.
Extends though front connecting to high speed shaft which connects to input module.
TGT sensed between Ng and Np shafts
Airflow
Approx 30% of air used for combustion.
Remaining 70% used for:
- T2 - Compressor inlet temp
- P3 - Compressor discharge pressure
- Combustor and turbine cooling
- Engine oil seal pressurization
Accessory Section
AGB driven by rotor vai a radial drive shaft from Ng
Rear face: starter, HMU, IPS blower, and ODV
Front face: alternator and engine-driven fuel boost pump
Face port: oil cooler, fuel filter, and oil filter
Engine Control Basic Operation
HMU provides gas generator control while DECU trims the HMU to satisfy the requirements of the power turbine load and reduce pilot workload.
HMU provides functions esseential to safe engine operation, while the DECU performs a fine trim to reduce pilot workload
PCL-Power Available Spindle (PAS)
OFF - PAS mechanically shuts off fuel at shutoff valve
IDLE - HMU auto controls start sequence fuel flow allowing self-sustaining combustion
FLY - sets max level of power that could be supplied if demanded; allows Ng to reach a setting providing intermediate power–collective input adjusts available Ng to a power level equal to rotor load demand power.
- Fail safe to high power: in case of electrical failure, does not cause power limiting and can be manually retarded to desireable level
- Power avail with OEI: if failure of one engine, remaining eng can increase power up to its limi (c-power) to carry load at given LDS setting
LOCKOUT - manually control Np/Ng
Load Demand System (LDS)
With PCL in FLY, HMU responds to collective position through the LDS to auto control engine speed and provide required power.
In LOCKOUT, engine still vary power in response to collective position.
Engine Driven Fuel Boost Pump
- Provide reliable suction feed from the aircraft fuel tank to the engine, minimizing vulnerability and fire hazard in the event of damaged fuel lines
- Provide discharge pressure to satisfy min inlet pressure requirement of HMU or high-pressure pump.
Fuel Filter
Does not filter water
Has bypass
Hydromechanical Control Unit (HMU)
After center of the AGB
Fuel enters high-pressure eng-driven pump, pumped through metering valve and shutoff valve, then through external line to oil-fuel heat exchanger.
Some fuel tapped off for:
- Positioning metering valve to ensure proper fuel flow to engine.
- Positioning a servo piston that actuates the variable geometry vane servo and start bleed valve.
- Amplifying T2, P3, Ng signals to influence fuel flow and variable geometry servo position (reduce chance of compressor stall)
Inputs to HMU
2 mechanical, 1 electrical
- LDS - directly coordinates Ng sppeds to approx power requried by rotors based on collective position.
- PCL - position of PCL manipulates the PAS at the HMU setting desired power setting.
a. Fuel shutoff
b. Setting engine start fuel flow with auto accel to ground idle.
c. Setting permissible Ng up to max.
d. Fuel priming.
e. DECU LOCKOUT - DECU - (electrical) actuates torque motor servo in HMU to precisely trim Ng speed for power turbine control and load sharing.
HMU Operation
DECU signals via torque motor servo trim fuel flow via metering valve.
HMU sends signal back to DECU via Linear Variable Displacement Transducer (LVDT) to null torque motor servo input stabilizing metering valve preventing engine oscillation/hunting–excess fuel routed back to pump inlet.
HMU Provides (RAGGAF)
- Rapid engine transient response through collective compensation.
- Auto fuel scheduling for engine start
- Ng Overspeed protection - 110+/-2%; secures fuel flow to engine until below value
- Ng governing - receives T2, P3, Ng inputs used to schedule fuel flow for min, max and variable geometry vane control.
- Accel limiting - Ng governor ensure PCL movement won’t damage engine; no inadvertent shutdown during movement
- Flameout and compressor stall protection - adjusts variable geometry vane position and opens anti-ice/start bleed valve to prevent compressor instability
Overspeed Drain Valve
- Provides fuel flow to 12 fuel injectors during engine start and operation.
- Purges main fuel manifold overboard, after engine shutdown, to prevent coking of fuel injectors
- Traps fuel upstream which keeps the fuel/oil heat exchanger full to prevent need for priming.
- Returns fuel back to HMU if Np overspeed energized or DECU hot start preventer activated.
Types of Limiting
Engine limiting - i.e. TGT-limiting, HMU fuel flow limiting (increasing torque further causes drooping)
-Protects engine components by reaching max possible output based on ambient conditions and collective setting
Parameter limiting
-Reaching a max prescribed value in chapter 4
Alternator
Provides ac power to ignitor assembly, DECU and Ng signal to vertical instruments
DECU Operation (4NCHEFTASTED)
- Np governing - (left) provides Np signal to DECU; compared to reference signal
- Np overspeed protection - (right) actuated 120% Np; diverts fuel to inlet of HMU causing flameout
* WARNING* A popped No1 or No2 ENG OVSP cb shall not be reset in flight. Resetting a popped cb may initiate an engine overspeed signal and result in engine failure. - Np overspeed test - re-references limit to 96%; if Np decrease when A/B individual, opposite test switch may be faulty.
- Ng decay relight - if specified Ng decel rate exceeded, auto-ignition turns on igniters for 5 sec; disabled below 62% Ng
- C-Power - increases TGT limit to 903C; CRP limiter prevent further fuel flow at 891+/-10C
- Hot Start Prevention - when TGT exceeds 900C with Ng below 60% and Np below 50%, auto stops fuel flow tripping ODV; flow restored when TGT <300C or after 25 sec; disable by pressing A/B for duration of start
- Engine Load Sharing - torque signals compared via DECUs; error signal if one less than other and increases power on the lower engine
- Fault Diagnostics - codes displayed on torque indicator after shutdown; 4 sec on, 2 sec off; supress with either A/B button
- TGT Limiting - 851C DECU prevents fuel flow; IRP limiter prevents this at 839+/-10C; if power applied causes droop and Np governing sacrificed to protect engine against overtemp
- Auto-ignition - Np overspeed reroutes fuel to HMU inlet; when Np drops below 120%, closes valve and turns on igniters for 5 sec; continues cycling until Np/Nr controlled (may experience yaw kicks)
- Signals - provides Np, TGT and Torque signals to Data Concentrator for cockpit display
- Transient Droop Improvement - initiate power turbine acceleration early via anticipator signals from TDI Nr sensor (left access module) and collective position sensor in mixing unit; circuits in DECU increase fuel flow to engine via HMU torque motor servo at low torque settings when collective demand increased rapidly or in event of rapid Nr decay.
- Engine Speed Trim - INCR/DECR controls Np both engines simultaneously between 96-101%
- DECU LOCKOUT - PCL manually controls Np/Ng via PAS/LDS positions; disables torque motor servo deactivating TGT limiting, Np governing, and load sharing; retains Np overspeed protection
EDECU/CEDECU
Additional features:
1. TGT Limiting - MRP limiter reduces fuel flow 866+/-10*C
- Auto C-Power - when torque from one engine below 50%, other eng auto sets TGT limiter from 866+/-10C to 891+/-10C; indications will not illuminate
Ignition Sytem
Electrical power to ignition excited from alternator during start or whenever auto-ignition feature activated
Np/Torque Sensing
2 Np sensors on top of exhaust frame
Np shaft equiped with 2 pairs of teeth inducing electrical pulses on the sensor permiting measurement of torsion or twist of the shaft (proportional to output torque)
Left - Np signal to DECU and cockpit vertical instrument
Right - feeds torque computation circuit and Np overspeed protection
Ng Sensing
Alternator provides Ng signal to vertical instruments
TGT Sensing
7 thermocouples joined in parallel and provide average output to DECU.
Biased -71*C by DECU
If DECU not powered by alternator or airframe power, through ENG OVSP cb, -71*C bias will be absent.
HMU Fuel Flow Limiting
- Under certain combinations of PA and temp with a high power setting from collective, the max fuel flow provided by the fuel pump is limited by physical size of the fuel lines within HMU and ODV
DECU - not likely to occur because limited by IRP
(C)EDECU - may occur with C-power ON or OFF (prior to IRP TGT limiter of the (C)EDECU which is higher than DECU)
- HMU protects compressor section by limiting fuel flow as a function of Ng and ambient temp. Engine Pressure Ratio (EPR) limiting and is associated with Ng limiting (happens in cold ambient temps at any PA)
