Engine Control System

Question 1

System purpose

Answer 1

Maintaining constant Np/Nr

Question 2

Major components of the Engine Control System

Answer 2

HMU
ODV
EDECU
Engine-driven Alternator
Series of fuel flow control valves

Question 3

System is governed through

Answer 3

Interaction of DECU and HMU

Question 4

HMU vs EDECU functions

Answer 4

HMU provides gas generator control

DECU trims HMU to satisfy requirements of power turbine load and reduce pilot workload

Question 5

PCL positions

OFF - IDLE - FLY - LOCKOUT

Answer 5

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

Question 6

What do you lose and retain in lockout?

Answer 6

Retain - Np overspeed system via manual connection between DECU and ODV
Lose - TGT limiting, Np governing, load sharing

Question 7

How far can you move PCL with rotor brake applied?

Answer 7

IDLE; solenoid activates locking device that prevents it from moving further

Question 8

Collective is to __ as PCL is to ___

Answer 8

Load Demand Spindle (LDS); Power Available Spindle (PAS)

Question 9

Where is engine driven fuel boost pump mounted?

Answer 9

Fwd side of AGB

Question 10

2 Purposes of the Engine Driven Fuel Boost Pump

Answer 10

1. Provide reliable suction feed from fuel tank to engine (minimize vulnerability/fire hazard if fuel lines damaged)
2. Provide discharge pressure to satisfy minimum inlet px req of HMU or high px fuel pump

Question 11

Does the Engine Fuel Filter filter water?

Answer 11

No; solids only

Question 12

Activation of #1/#2 FUEL FLTR BYPASS

Answer 12

Afte electrical switch senses pressure difference

Question 13

HMU receives filtered fuel through

Answer 13

Cored passage

Question 14

HMU stands for

Answer 14

Hydromechanical Control Unit

Question 15

HMU contains

Answer 15

High px fuel pump, Ng gov, metering valve, LVDT, torque motor servo, variable geometry vane servo, viper vent, shutoff valve

Question 16

Inputs to HMU

Answer 16

2 mechanical, one electrical

Question 17

First mechanical input to HMU

Answer 17

from LDS; directly coordinates Ng speeds to approx power required by rotor system based on collective position

Question 18

Second mechanical input to HMU

Answer 18

through PCL; PCL position manipulates PAS at HMU to set desired power setting

Question 19

Electrical Signal to HMU

Answer 19

from DECU; actuates torque motor servo in HMU to precisely trim Ng speed for power turbine control and load sharing

Question 20

HMU responds to PCL for

Answer 20

1. Fuel Shutoff
2. Setting engine start fuel flow with automatic acceleration to ground idle
3. Setting permissible Ng up to maximum
4. Fuel priming
5. DECU override capability (LOCKOUT)

Question 21

3 signals HMU responds to and what for

Answer 21

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

Question 22

Fuel flow through HMU

Answer 22

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

Question 23

Why actual level of engine power is normally more than req by helo

Answer 23

1. Fail safe to high power - prevent being power limited if have engine electrical failure

Question 24

What is lockout actually doing?

Answer 24

disabling the torque motor servo

Question 25

Failure to clear EDECU fault codes will prevent

Answer 25

AFCS Ground Checks & Blade fold

Question 26

EDECU Functions

Answer 26

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

Question 27

Never reset a popped ENG OVSP CB because

Answer 27

it may initiate engine overspeed signal and cause the engine to fail

Question 28

TGT Limiting

Answer 28

866 ± 10°

Np/Nr will droop if power is demanded beyond that

Question 29

Ng decay relight feature

Answer 29

If an engine flames out and Ng decay exceeds a certain rate

Auto relight comes on for 5 sec

Disabled below 62%

Question 30

Manual C power

Answer 30

TGT can increase to 903

max CRP limiter will prevent further increase in fuel flow to engine at 891 ± 10

Question 31

Auto C power

Answer 31

enabled in OEI conditions

when tq from oen engine <50%, opposite engine EDECU will auto reset TGT limiter to 891±10°

Question 32

Dual Auto C power

Answer 32

bring TGT limit to 891±10°

To activate, one or more must exist:

1. Np drops below 96%
2. Greater than 3% droop between reference Np and actual Np
3. Greater than 5% per second Np droop rate exists with Np less than or equal to Np ref set point

Question 33

Control parameters of EDECU?

Answer 33

Np sensing, Np overspeed and tq sensing, TGT monitoring

Question 34

EDECU receives these inputs from the cockpit

Answer 34

1. Engine speed trim switch
2. C power switch
3. Engine over speed TEST A and B