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
