ENGINE CONTROL SYS

Question 1

What type of engine do we have?

Answer 1

T700-GE-401C front drive turboshaft engine

Question 2

How can ambient air be heated via the anti-ice system in the inlet cowling?

Answer 2

air can be heated via the inlet anti-ice valve or via the inlet surface which is perforated with small slits to allow 5th stage bleed air to heat the inlet surface

Question 3

What type of compressor do we have?

Answer 3

5-stage axial, single-stage centrifugal

Question 4

What type of combustion chamber do we have? How many ignitors and fuel injectors?

Answer 4

flow-through annular combustion chamber with 2 igniter, 12 fuel injectors, and 1 exciter

Question 5

What type of turbines do we have?

Answer 5

dual stage coaxial turbines (Np lives inside Ng)

Question 6

Where is TGT measured?

Answer 6

between the Ng and Np turbines using 7 thermocouples

Question 7

What does the Ng turbine drive?

Answer 7

the compressor and the accessory gear box

Question 8

What does the Np turbine drive?

Answer 8

the power turbine drive shaft

The power turbine drive shaft extends through the front of the engine and connects to the high speed shaft which connects to the input modules

Question 9

Explain the breakdown of airflow in the engine. (Think %)

Answer 9

30% of the total airflow through the engine is used for combustion

70% is used for:
compressor inlet air temperature (T2)
compressor discharge air pressure (P3)
combustion and turbine cooling
engine oil seal pressurization

Question 10

Name the five major components of the engine control system.

Answer 10

HMU, ODV, EDECU, engine-driven alternator, fuel flow control valves

Question 11

Name the three inputs to the HMU.

Answer 11

1. Mechanical (PAS / LDS)
2. Electrical (torque motor servo to trim Ng speed)
3. T2, P3, Ng (control variable geometry vane and anti-ice valve position during start)

Question 12

Name the functions of the HMU. (RANFAN)

Answer 12

R - rapid engine transient response through collective compensation. (LDS)
A - automatic fuel scheduling for engine start (PAS)
N - Ng overspeed protection (110+/-2%)
F - flameout and compressor stall protection (variable geometry vane)
A - acceleration limiting
N - Ng governing (T2, P3, Ng to sked fuel flow)

Question 13

What does the variable geometry vane servo do?

Answer 13

using fuel tapped from the HMU, the servo opens the anti-ice / start bleed valve preventing compressor instability

the valve opens at 88% Ng and closes at 90% or 94% with OAT > 15C

Question 14

What is the relationship between the torque motor servo and the metering valve?

Answer 14

the metering valve schedules engine fuel flow commensurate to the current power demand

the torque motor servo trims fuel flow by the the metering valve in response to the EDECU

Question 15

What does the linear variable displacement transducer (LVDT) do?

Answer 15

provides a feedback signal to the EDECU to null the torque motor servo input therefore stabilizing the metering valve and preventing engine oscillation/hunting

Question 16

What does EDECU stand for?

Answer 16

enhanced digital electronic control unit

Question 17

What inputs does the EDECU take from the cockpit?

Answer 17

engine speed trim switch
contingency power switch
engine overspeed test A/B

Question 18

What inputs does the EDECU take from the helo?

Answer 18

torque from the other EDECU
Np demand
400-Hz backup power
HMU (via LVDT)

Question 19

Name the functions of the EDECU. (4N CHEF TASTED)

Answer 19

N - Np governing
N - Np overspeed protection
N - Np overspeed test
N - Ng decay relight feature

C - Contingency power
H - Hot start prevention
E - Engine load sharing
F - Fault diagnostic system

T - TGT limiting
A - Auto-ignition system
S - Cockpit Signals
T - Transient droop improvement
E - Engine speed trim
D - EDECU lockout

Question 20

Np governing

Answer 20

Np sensor located on left side of the power turbine sends signal to EDECU

actual vs. a reference Np is compared to compute a speed error

Question 21

Np overspeed protection

Answer 21

when Np > 120%, a signal is sent from EDECU to ODV, diverting fuel to the inlet of the HMU therefore causing a flameout

Question 22

Np overspeed test

Answer 22

activated via A/B, pressed together Np overspeed limit is re-referenced to 96%

Question 23

Ng decay relight feature

Answer 23

if the engine flames out and exceeds Ng deceleration rate, the auto-ignition system will turn on igniters for 5 seconds in an attempt to relight the engine

this feature is disabled below 62% Ng

Question 24

Contingency power: Manual, Auto, Dual-Eng

Answer 24

Manual - switch allows TGT up to 903C, max contingency range power limiter will prevent further fuel flow at 891+/-10C

Automatic - enabled in OEI conditions when torque of one engine < 50%, TGT limit reset from 866+/-10C to 891+/-10C (light will not illuminate)

Dual-engine auto - TGT up to 891+/-10C if the following exists: 1) Np < 96% 2) >3% droop between reference and actual Np 3) >5%/sec. Np droop with Np < Np reference

Question 25

Hot start prevention

Answer 25

detects a hot start when TGT > 900C with Ng < 60% and Np < 50%, fuel flow is stopped.

fuel restored when TGT < 300C or after 25 seconds.

Question 26

Engine load sharing

Answer 26

torque matching system will increase torque of the lower Q engine

Question 27

Fault diagnostic system

Answer 27

displays fault codes on startup/shutdown, can be suppressed with A/B

Question 28

TGT limiting

Answer 28

fuel flow stopped at 866+/-10C so that TGT does not exceed 878C.

Np/Nr will droop and Ng governing will be sacrificed to protect against an overtemp.

Question 29

Auto-ignition system

Answer 29

triggered at Np = 120%, overspeed valve in the ODV opened to reroute fuel to HMU

when Np < 120%, valve closes and turns on igniters on a 5 sec. time to relight the engine. this will continue until Np/Nr are controlled

Question 30

Cockpit signals

Answer 30

Np, TGT, and Q signals are sent to the cockpit display

Question 31

Transient droop improvement

Answer 31

uses anticipator signals from the TDI Nr sensor and collective position

fuel flow increased via torque motor servo at low torque settings when collective demand increases rapidly

Question 32

Engine speed trim

Answer 32

increase/decrease switch controls Np of both engines simultaneously between 96-101%

Question 33

EDECU lockout (what do you lose and retain?)

Answer 33

Np and Ng with PAS and LDS positions only, torque motor servo is disabled (loss of TGT limiting, Np governing, and load sharing)

Np overspeed protection retained

Question 34

Where does the engine anti-ice valve live in the engine?

Answer 34

Within the swirl vanes in the IPS

Question 35

What does the inlet particle separator (IPS) consist of?

Answer 35

Swirl vanes which impart rotation to airflow and throws particles outward to the collection scroll. The dirty air in the collection scroll is thrown overboard with the blower assembly. Clean air is sent through the deswirl vanes with remove rotation and provide smooth airflow to the compressor.

Question 36

Name the four main functions of the ODV.
“Provides, Purges, Traps, Returns”

Answer 36

1. Provides main fuel flow to the 12 fuel injectors during engine start and operation.
2. Purges the main fuel manifold overboard, after engine shutdown, to prevent coking of the fuel injectors.
3. Traps fuel upstream, which keeps the fuel/oil heat exchanger full, so that system priming is not required prior to the next start.
4. Returns fuel back to the HMU if the Np overspeed is energized or if the EDECU hot start preventer is activated.