Turbomeca Lecture - Part 4-Engine Control

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2ndnd _{level Specializing}_{level Specializing}

Master Course in Rotary Wing Technologies

Edition 2014-2015

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installation within rotorcraft

Part 4 :

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Tu Turbrbomomececaa cocoururse se Effective slide : 28 Effective slide : 28

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Turboshaft Control System Turboshaft Control System Introduction

Introduction



 From From the the very very beginning beginning of of TURBOMECA TURBOMECA turboshafts, turboshafts, control control systemsystem

skills are as important as bare

skills are as important as bare engine skillsengine skills

ARTO

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Introduction



 From From the the very very beginning beginning of of TURBOMECA TURBOMECA turboshafts, turboshafts, control control systemsystem

skills are as important as bare

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Introduction



Control system is a strategic component for helicopterControl system is a strategic component for helicopter

tur

turbosboshafhaftt appappliclicatiationon

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 Enhances the engine performance and its operabilityEnhances the engine performance and its operability

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 Directly acts on the helicopter handling Directly acts on the helicopter handling qualities and on qualities and on the performance ofthe performance of NR speed control

NR speed control

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 Contributes to the pilot workload reduction and to the aircraft safetyContributes to the pilot workload reduction and to the aircraft safety

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 Embeds monitoring and diagnosis functionsEmbeds monitoring and diagnosis functions

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 Counts for 15 thru 20% of engine production cost and has become Counts for 15 thru 20% of engine production cost and has become a majora major technical and economical issue

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Control System – General presentation Vocabulary NR rotor speed T1, P0 Combustion chamber Gas generator Free turbine CH or WF N2 P3 _Torque Collective pitch XPC T45 N1 N2 Engine Control system MGB N1

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Turboshaft Control System

TURBOMECA architectures history

 Hydromecanical control

 All the functions are achieved by flyweights, hydraulic spool/sleeve, pneumatic bellows…

 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 in a protected range

 Dual channel FADEC

 Redundancy of critical electronic and electrical functions

 Auxiliary backup mode is available for single engine applications

1990’s design

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Control System– Architectures Hydromecanical Fuel Control

Rotor Combustion chamber Gas generator Power turbine Main Gear Box Fuel flow N2 N1 P3 Collective pitch N1 N2 HMU (governor) P0

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Control System– Architectures FADEC control T1, P0 Combustion chamber Gas generator Power turbine Fuel Flow _N2 P3 Torque Collectif pitch data T45 N1 N2 EECU + Fuel system BTP N1 Pilot commands (Stop, Idle, Flight…)

Helicopter Engine

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Control System– Architectures Dual channel FADEC control

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Control System– Architectures Dual channel FADEC control

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Control System– Architectures Fuel system

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Control System– Architectures Metering unit

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Control system - Architectures Fuel system manifold control

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Control System– Architectures FADEC control

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Control System – General presentation Control 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"

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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

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Control System – General presentation Overspeed protection

In case of overspeed due to system or mechanical failure, an independent

subsystem detects the overspeed condition and energizes the fuel shut-off valve

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Control system- Control laws

N2 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 > TRQr N2 increases N2 decreasesTRQ < TRQr TRQ = TRQr N2 constant TRQ = TRQr N2 constant N2 Pitch decrease N2 XPC TRQr TRQ TRQ = TRQr N2 constant TRQ = TRQr N2 constant TRQ > TRQr N2 increases TRQ < TRQr N2 decreases Pitch increase

• helicopter inertias (rotors, MGB) + free turbine inertia of the engine(s)

• inertia of inertial flywheel + inertia of the engine free turbine on test bed

Resistive torque (TRQr): • on the helicopter, this is a

function of collective pitch XPC • on the engine test bed, this is a

function of the brake valve position

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Control system- Control laws Speed control loops

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Control system- Control laws Fuel control and limitations

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Control system- Control laws Starting control

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Control system- Control laws Acceleration limitations

Example of limits used during a pitch increase

N2 N1* N1L* Anti-surge protection Over-torque Protection Maximum N1 protection (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 N2 speed increases, the acceleration "breaks off" in order to limit over-torque and yaw kicks

N2 N1

Over-torque

Control system- Control laws Overtorque limitation

Example of over-torque limitation

N1*

N1L*

N2 N1

Engine torque Over-torque

Without over-torque protection _{With over-torque protection} Goal :

• Protect helicopter main gear box against overtorque

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Control system- Control laws Deceleration limitation

Example of limits used during a pitch decrease

N1* N1L* Anti-flame-out protection Minimum N1 protection N2

Goal : best balance between :

• quick response to prevent N2/NR overshoot • mandatory flame-out free deceleration

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- - - accel trajectory with power off-take

- - - accel trajectory without power off-take

Working line with power off-take

Surge line

Working line without power off-take N1initial N1final WF/P3 limit line Air Flow P/P

Surge protection by WF/P3 limitation

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Current fuel demand WF/P3 fuel limit

Surge

Surge protection by WF/P3 limitation

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Control system- Control laws Starting control Example of a start-up WFstart* Preset fuel flow

The pilot orders the start-up: the starting

accessories are

commanded (starter, start electrovalve, on/off electro-valve, igniters). T45 N1 Combustion chamber ignition End of start-up: starting

accessories cut off and the engine switches to control mode T45 protection T45 maximum

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Control System – Control Laws

Rotor speed control – Torsional stability

Tail rotor Main rotor

blades

Main rotor hub

and MGB Engine 2

Engine 1

Main rotor lag mode

Return torque

Torsion stiffness

Blade

Rotor hub Blade lag axis

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Control System – Control Laws

Rotor speed control – Torsional stability

The control system and the engine can excite the helicopter modes. To avoid this

phenomenon, 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