Introduction ix

Notations and Acronyms xiii

Chapter 1. General Considerations 1

1.1. Power transmission in aircraft 1

1.1.1. Needs and requirements for secondary power and power flows 1

1.1.2. Actuation functions 2

1.1.3. Actuation needs and constraints 5

1.2. Primary and secondary power transmission functions for actuators 8

1.2.1. Primary functions 10

1.2.2. Secondary functions 12

1.2.3. Signal approach and power approach 13

1.2.4. Types of actuators 14

1.3. Hydraulic power actuation 16

1.3.1. Units and reference values 16

1.3.2. Energy transport by a liquid 18

1.3.3. Historical evolution of power and pressure use 22

1.3.4. Potential advantages and disadvantages of hydraulic technology 27

1.3.5. Overall hydraulic circuit architecture 31

Chapter 2. Reliability  33

2.1. Risks and risk acceptance 33

2.2. Response to failure 36

2.2.1. Resistance to failure 37

2.2.2. Tolerance to failure 38

2.2.3. Examples 40

2.3. Redundancy 40

2.3.1. Static redundancy 44

2.3.2. Dynamic redundancy 48

2.4. Feared events and failure rates in actuation 51

2.5. Fundamentals of reliability calculation 52

2.5.1. Variables used in reliability calculation 52

2.5.2. Generic failure rate models 55

2.5.3. Reliability of element associations 57

2.6. Short glossary of technical terms pertaining to reliability 60

Chapter 3. Hydraulic Fluid and its Conditioning 63

3.1. Needs and constraints 63

3.1.1. Opportunities and constraints in hydrostatic power transmission 63

3.1.2. Actual hydraulic fluid 64

3.1.3. Physical properties 66

3.2. Fluid conditioning 68

3.2.1. Fluid in sufficient quantity 68

3.2.2. Pressurization and charging 70

3.2.3. Filtration 73

3.2.4. Thermal management 76

3.2.5. External leakage collection 81

3.3. Monitoring and maintaining the fluid in working conditions 81

3.3.1. Fluid quantity 82

3.3.2. Cleanliness 82

3.3.3. Pressurization – depressurization 83

3.3.4. Examples 83

3.4. Energy phenomena caused by the fluid 84

3.4.1. Hydraulic resistance 84

3.4.2. Hydraulic capacitance 84

3.4.3. Hydraulic inertia 87

3.4.4. Speed of sound in the hydraulic fluid 87

Chapter 4. Hydromechanical Power Transformation  89

4.1. Hydromechanical power transformation  89

4.2. Functional perspective 94

4.3. Technological shortcomings 95

4.3.1. Energy losses 96

4.3.2. Compressibility of the hydraulic fluid 97

4.3.3. Wall deformation 97

4.3.4. Pulsations 97

4.3.5. Drainage 99

4.4. Pump driving 100

4.4.1. Driving performed by main engines: Engine Driven Pump (EDP)  100

4.4.2. Driving performed by an electric motor: Electro Mechanical Pump (EMP) or Alternative Current Motor Pump (ACMP)  102

4.4.3. Driving performed by a hydraulic motor: Power Transfer Unit (PTU) 102

4.4.4. Dynamic air driving: Ram Air Turbine (RAT) or Air Driven Pump (ADP) 104

4.4.5. Driving performed by a gas turbine: Solid Propellant Gas Generator (SPGG) or Monofuel Emergency Power Unit (MEPU) 104

4.4.6. Fluid supply under pressure 105

Chapter 5. Power Metering in Hydraulics 107

5.1. Power metering principles 107

5.2. Power-on-Demand 110

5.2.1. Metering by pump drive adjustment 110

5.2.2. Metering by displacement adjustment 111

5.3. Metering by hydraulic restriction 114

5.3.1. Functional configuration 115

5.3.2. Types of distribution 120

5.4. Impact of restriction configuration and properties on the metering function 122

5.4.1. Fixed hydraulic restriction 122

5.4.2. Variable hydraulic restriction 125

5.5. Servovalves 139

5.5.1. Architecture 139

5.5.2. Incremental improvements of servovalve performances  143

5.5.3. Power supply of the electromagnetic motor 145

5.5.4. Concepts of pilot stages 145

5.5.5. Direct drive valve 151

Chapter 6. Power Management in Hydraulics 157

6.1. Power distribution 157

6.2. Providing power 157

6.2.1. Transporting fluid 157

6.2.2. Isolating 162

6.2.3. Sequencing user power supplies 165

6.2.4. Merging sources 165

6.2.5. Sharing sources 166

6.2.6. Storing/restoring energy 168

6.2.7. Adjusting the pressure level 171

6.3. Protecting 172

6.3.1. Protecting against overpressure/overload 173

6.3.2. Protecting against cavitation and desorption 176

6.3.3. Protecting against over-consumptions 178

6.4. Managing the load 180

6.4.1. Locking the load in position 180

6.4.2. Ensuring irreversibility 181

6.4.3. Releasing the load 182

6.4.4. Damping the load 183

Chapter 7. Architectures and Geometric Integration of Hydraulically-supplied Actuators 189

7.1. Introduction 189

7.2. Arrangement of actuation functions 190

7.3. Architecture and routing of hydraulic power networks 191

7.3.1. Architecture 191

7.3.2. Routing 193

7.4. Integration of components and equipment 193

7.4.1. In-line integration 194

7.4.2. Manifold integration 194

7.4.3. Sub-system integration 197

7.5. Integration of actuators in the airframe  200

7.5.1. Controls 200

7.5.2. Structural integration 203

Bibliography 209

Index 219

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