Engine Control System Flashcards
System purpose
Maintaining constant Np/Nr
Major components of the Engine Control System
HMU ODV EDECU Engine-driven Alternator Series of fuel flow control valves
System is governed through
Interaction of DECU and HMU
HMU vs EDECU functions
HMU provides gas generator control
DECU trims HMU to satisfy requirements of power turbine load and reduce pilot workload
PCL positions
OFF - IDLE - FLY - LOCKOUT
Off - PAS mechanically shuts off fuel at shutoff valve within HMU
Idle - HMU auto controls start sequence fuel flow allowing engine to get to self sustaining combustion
Fly - provides max level of power if necessary
Lockout - PCL manually controls Ng and Np
What do you lose and retain in lockout?
Retain - Np overspeed system via manual connection between DECU and ODV
Lose - TGT limiting, Np governing, load sharing
How far can you move PCL with rotor brake applied?
IDLE; solenoid activates locking device that prevents it from moving further
Collective is to __ as PCL is to ___
Load Demand Spindle (LDS); Power Available Spindle (PAS)
Where is engine driven fuel boost pump mounted?
Fwd side of AGB
2 Purposes of the Engine Driven Fuel Boost Pump
- Provide reliable suction feed from fuel tank to engine (minimize vulnerability/fire hazard if fuel lines damaged)
- Provide discharge pressure to satisfy minimum inlet px req of HMU or high px fuel pump
Does the Engine Fuel Filter filter water?
No; solids only
Activation of #1/#2 FUEL FLTR BYPASS
Afte electrical switch senses pressure difference
HMU receives filtered fuel through
Cored passage
HMU stands for
Hydromechanical Control Unit
HMU contains
High px fuel pump, Ng gov, metering valve, LVDT, torque motor servo, variable geometry vane servo, viper vent, shutoff valve
Inputs to HMU
2 mechanical, one electrical
First mechanical input to HMU
from LDS; directly coordinates Ng speeds to approx power required by rotor system based on collective position
Second mechanical input to HMU
through PCL; PCL position manipulates PAS at HMU to set desired power setting
Electrical Signal to HMU
from DECU; actuates torque motor servo in HMU to precisely trim Ng speed for power turbine control and load sharing
HMU responds to PCL for
- Fuel Shutoff
- Setting engine start fuel flow with automatic acceleration to ground idle
- Setting permissible Ng up to maximum
- Fuel priming
- DECU override capability (LOCKOUT)
3 signals HMU responds to and what for
T2, P3, Ng; signals aid HMU in controlling variable stator vanes and anti-ice/start bleed valve position during engine start and normal ops, reducing chance of compressor stall
Fuel flow through HMU
fuel flows to HMU via cored passage –> high px engine-driven pump –> metering valve and shutoff valve –> external line to oil to fuel heat exchanger; some fuel goes to metering valve, servo piston, and various signals (T2, P3, Ng). see 2-8
Why actual level of engine power is normally more than req by helo
- Fail safe to high power - prevent being power limited if have engine electrical failure
What is lockout actually doing?
disabling the torque motor servo
Failure to clear EDECU fault codes will prevent
AFCS Ground Checks & Blade fold
EDECU Functions
4xN CHEF LATTE MAD
Np governing
Np overspeed
Np overspeed test
Ng decay relight feature
Cockpit Signals
Hot Start Prevention
Engine Load Sharing
Fault diagnostic System
Lockout Auto ignition system Transient Droop Improvement TGT Limiting Engine Speed Trim
Manual C power
Auto C power
Dual auto C power
Never reset a popped ENG OVSP CB because
it may initiate engine overspeed signal and cause the engine to fail
TGT Limiting
866 ± 10°
Np/Nr will droop if power is demanded beyond that
Ng decay relight feature
If an engine flames out and Ng decay exceeds a certain rate
Auto relight comes on for 5 sec
Disabled below 62%
Manual C power
TGT can increase to 903
max CRP limiter will prevent further increase in fuel flow to engine at 891 ± 10
Auto C power
enabled in OEI conditions
when tq from oen engine <50%, opposite engine EDECU will auto reset TGT limiter to 891±10°
Dual Auto C power
bring TGT limit to 891±10°
To activate, one or more must exist:
- Np drops below 96%
- Greater than 3% droop between reference Np and actual Np
- Greater than 5% per second Np droop rate exists with Np less than or equal to Np ref set point
Control parameters of EDECU?
Np sensing, Np overspeed and tq sensing, TGT monitoring
EDECU receives these inputs from the cockpit
- Engine speed trim switch
- C power switch
- Engine over speed TEST A and B
