NATOPS Chapter 2 Engine Control System HSM-50

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

HMU vs EDECU functions

Answer 3

HMU provides gas generator control

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

Question 4

What do you lose and retain in lockout?

Answer 4

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

Question 5

How far can you move PCL with rotor brake applied?

Answer 5

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

Question 6

Collective is to __ as PCL is to ___

Answer 6

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

Question 7

Where is engine driven fuel boost pump mounted?

Answer 7

Fwd side of AGB

Question 8

2 Purposes of the Engine Driven Fuel Boost Pump

Answer 8

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 9

Does the Engine Fuel Filter filter water?

Answer 9

No; solids only

Question 10

Activation of #1/#2 FUEL FLTR BYPASS

Answer 10

After electrical switch senses pressure difference

Question 11

HMU receives filtered fuel through

Answer 11

Cored passage

Question 12

HMU stands for

Answer 12

Hydromechanical Control Unit

Question 13

HMU contains

Answer 13

Fuel stuff:High px fuel pump, Ng gov, metering valve, shutoff valve

Control stuff: LVDT, torque motor servo

Anti ice stuff: variable geometry vane servo

And this: vapor vent

Question 14

First mechanical input to HMU

Answer 14

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

Question 15

Second mechanical input to HMU

Answer 15

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

Question 16

Electrical Signal to HMU

Answer 16

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

Question 17

HMU responds to PCL for

Answer 17

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 18

3 signals HMU responds to and what for

Answer 18

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 19

Fuel flow through HMU

Answer 19

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 20

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

Answer 20

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

Question 21

What is lockout actually doing?

Answer 21

disabling the torque motor servo

Question 22

Failure to clear EDECU fault codes will prevent

Answer 22

AFCS Ground Checks & Blade fold

Question 23

EDECU Functions

Answer 23

4N CHEF TASTEE

Np governing
Np overspeed
Np overspeed test
Ng decay relight feature

C Power (MAD: Manual, Automatic, Dual Engine Auto)
Hot Start Prevention
Engine Load Sharing
Fault diagnostic System

TGT Limiting
Auto ignition system
Signals (Cockpit)
Transient Droop Improvement
EDECU Lockout
Engine Speed Trim

Question 24

Never reset a popped ENG OVSP CB because

Answer 24

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

Question 25

TGT Limiting

Answer 25

Reaching either MRP or CRP functions w/in the EDECU

Fuel flow limited at 878C

Droops Nr at 866 ± 10C

Question 26

Ng decay relight feature

Answer 26

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

Auto relight comes on for 5 sec

Disabled below 62%

Question 27

Manual C power

Answer 27

TGT can increase to 903

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

Question 28

Auto C power

Answer 28

enabled in OEI conditions

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

Question 29

Dual Auto C power

Answer 29

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 30

Np Overspeed Test

Description and what to do for flameouts

Answer 30

Rereferences Np Governer from 120% to 96%

Successful test: Ng decreases w/ both buttons pressed

If 1 button is pressed and Ng decreases: indicates a failed button

If engine flames out after a test:

Do a normal start of the engine
Bring opposite engine to Idle
Retest the engine that flamed out

If it relights: Fly-Fly good to go

If it flames out again: advance opposite PCL to Fly
Have Mx Check (can only retry once)

Question 31

Important EDECU Fault Codes

Answer 31

15: EDECU failure (will cause high side if you start up)

35: CEDECU installed w/ correct software

If you need to clear code: do EDECU fault code clearing procedure

Question 32

What does a CEDECU provide that an EDECU does not

Answer 32

Discrete Application Selection Plug (specific software for the Romeo instead of the other A/C series) (35% displayed as EDECU code)