Turbomeca Lecture - Part 4-Engine Control

7/23/2019 Turbomeca Lecture - Part 4-Engine Control

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2nd

level SpecializingMaster Course in Rotary Wing Technologies

Edition 2014-2015

2014

Turboshaft engine and its

installation within rotorcraftPart 4 :Turboshaft Control System

Turbomeca courseEffective slide : 28


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Ce document et les informations quil contient sont la proprit de Turbomeca. Ils ne doivent pas tre copis ni communiqus un tiers sans lautorisation pralable et crite de Turbomeca.

Turboshaft Control SystemIntroduction

From the very beginning of TURBOMECA turboshafts, control systemskills are as important as bare engine skills

ARTOUSTE Fuel Control Unit (1951)


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Turboshaft Control SystemIntroduction

Control system is a strategic component for helicopterturboshaft application

Enhances the engine performance and its operability

Directly acts on the helicopter handling qualities and on the performance ofNR speed control

Contributes to the pilot workload reduction and to the aircraft safety

Embeds monitoring and diagnosis functions

Counts for 15 thru 20% of engine production cost and has become a major

technical and economical issue


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Control System General presentationVocabulary

NR rotor speed

T1, P0

Combustionchamber

Gas generatorFreeturbine

CH or WF N2P3 Torque

Collectivepitch XPC

T45

N1

N2

Engine Controlsystem

MGB

N1


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Turboshaft Control SystemTURBOMECA architectures history

Hydromecanical control

All the functions are achieved by flyweights, hydraulic spool/sleeve, pneumaticbellows

Single channel FADEC with backup manual fuel control protected mode

Single channel FADEC controls a stepper motor driving the fuel metering valve

Fail freeze failure mode with auxiliary backup allowing manual fuel flow change ina protected range

Dual channel FADEC Redundancy of critical electronic and electrical functions

Auxiliary backup mode is available for single engine applications

1990s design

2000s design


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Control System ArchitecturesHydromecanical Fuel Control

Rotor

Combustionchamber

Gas generatorPowerturbine

MainGearBox

Fuelflow

N2N1P3

Collectivepitch

N1

N2

HMU

(governor)

P0


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Control System ArchitecturesFADEC control

T1, P0

Combustionchamber

Gas generator

Powerturbine

Fuel Flow N2P3

Torque

Collectifpitch data

T45

N1

N2

EECU

+Fuel system

BTP

N1

Pilot commands(Stop, Idle, Flight)

HelicopterEngine


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Control System ArchitecturesDual channel FADEC control


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Control System ArchitecturesDual channel FADEC control

C l S A hi


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Control System ArchitecturesFuel system

C t l S t A hit t


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Control System ArchitecturesMetering unit

Failure mode fail freeze thanks to stepper motor technology : enginepower remains constant in case of electronic or electric failure

C t l t A hit t


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Control system - ArchitecturesFuel system manifold control

Control S stem Architect res


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Control System ArchitecturesFADEC control

Control System General presentation


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Control System General presentationControl system functions

The control system provides the following functions:

Fuel pumping

Fuel filtering

Fuel metering to the start injectors and the main injectors

Fuel shut-off

Electrical self-sufficiency of the control system, thanks to an alternator

Automatic starting without "over-temperature"

Automatic in-flight re-start



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Automatic N2 control in flight mode

Acceleration control (anti-surge protection systems)

Deceleration control (anti-flame-out protection systems)

Temperature limits

Torque limits

N2 overspeed protection (not systematic)

N1 overspeed protection (not systematic)

OEI detection and management of emergency ratings (for twin engines)

OEI training mode (TRAINING) (for twin engines)



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Indications to the helicopter cockpit

Engine maintenance assistance:

engine power check

Available T45 marging to deliver the required power Available N1 marging to deliver the required power

automatic counting of N1 and N2 cycles

creep counting

failure detection

failure recording failure context recording

emergency rating usage counters



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Control System General presentationOverspeed protection

In case of overspeed due to system or mechanical failure, an independentsubsystem detects the overspeed condition and energizes the fuel shut-offvalve

Control system- Control laws


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Control system- Control lawsN2 and NR control during pilot manoeuvre

Torque engine Torque resistive= inertia x dN2

dt

Torque engine Torque resistive= inertia x dN2

dt

XPC

TRQr

TRQ

TRQ > TRQrN2 increases

TRQ < TRQrN2 decreases

TRQ = TRQrN2 constant


N2

Pitch decrease

N2

XPC

TRQr

TRQ



TRQ > TRQrN2 increases

TRQ < TRQrN2 decreases

Pitch increase

helicopter inertias (rotors, MGB) + freeturbine inertia of the engine(s)

inertia of inertial flywheel + inertia of theengine free turbine on test bedResistive torque (TRQr):

on the helicopter, this is afunction of collective pitch XPC

on the engine test bed, this is a

function of the brake valveposition



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Control system- Control lawsSpeed control loops



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Control system Control lawsFuel control and limitations



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Control system Control lawsStarting control



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Control system Control lawsAcceleration limitations

Example of limits used during a pitch increase

N2

N1*

N1L*

Anti-surgeprotection

Over-torqueProtection

Maximum N1protection(thermal)

Goal : best balance between : quick response to prevent N2/NR undershoot

mandatory surge free compressor acceleration



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N1*

N1L*

Over-torque Protection when the N2speed increases, the acceleration

"breaks off" in order to limit over-torque and yaw kicks

N2

N1

Over-torque

Control system Control lawsOvertorque limitation

Example of over-torque limitation

N1*

N1L*

N2

N1

Engine torque

Over-torque

Without over-torque protection With over-torque protectionGoal : Protect helicopter main gear box against overtorque

Prevent yaw jerk in reaction to too high dNR/dt

Engine torque Engine torque



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Co t o syste Co t o a sDeceleration limitation

Example of limits used during a pitch decrease

N1* N1L*

Anti-flame-out

protection

Minimum N1protection

N2

Goal : best balance between : quick response to prevent N2/NR overshoot

mandatory flame-out free deceleration



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- - - accel trajectory with poweroff-take

- - - accel trajectory without

power off-take

Working line with power off-take

Surge line

Working line without poweroff-take

N1initial

N1final

WF/P3 limit line

Air Flow

P/P

ySurge protection by WF/P3 limitation

Benefit : adaptive surge margin control vs power extraction on gas generator shaft



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Current fuel demand

WF/P3 fuel limit

Surge

ySurge protection by WF/P3 limitation

Benefit : ability to get out from an unexpected surge event



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yStarting control

Example of a start-up

WFstart*

Preset fuelflow

The pilot orders the start-up: the startingaccessories are

commanded (starter, startelectrovalve, on/off electro-valve, igniters).

T45

N1

Combustionchamber ignition

End of start-up:startingaccessories cut offand the engine

switches to controlmode

T45protection

T45maximum

Control System Control Laws


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yRotor speed control Torsional stability

Tail rotor

Main rotor

blades

Main rotor huband MGB

Engine 2

Engine 1

Main rotor lag mode

Return torque

Torsionstiffness

Blade

Rotor hub

Blade lag axis

Helicopter drive train very different from an inertial load

Control System Control Laws


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Rotor speed control Torsional stability

The control system and the engine can excite the helicopter modes. To avoid thisphenomenon, the engine manufacturer generally adds corrective devices in the control loop

Tail rotor

frequency

Main rotor

frequency

Inertial mode :

depends on the

rotating parts

inertias

Example of helicopter linear model

Control System Control laws


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Rotor speed control Torsional stability

The control law correction aims to damp the helicopters modes peeks below -6dB, but withcorrect phase and gain margins conservation (ARP704 norm).

The main challenge is to damp the modes with a minimal alteration the low frequenciesband (conservation of N2/NR control loop time response)

Documents

Turbomeca Lecture - Part 4-Engine Control