About the Authors xi
Series Preface xiii
Preface to First Edition xv
Preface to Second Edition xvii
Preface to Third Edition xix
Notation xxiii
Units xxvii
Abbreviations xxix
1 Introduction 1
1.1 Looking Back 1
1.1.1 Early Years 1
1.1.2 First World War Era 3
1.1.3 Inter-war Years 3
1.1.4 Second World War Era 6
1.1.5 Post-war Years 7
1.1.6 The Helicopter from an Engineering Viewpoint 13
1.2 Book Presentation 22
Reference 22
2 Rotor in Vertical Flight: Momentum Theory and Wake Analysis 23
2.1 Momentum Theory for Hover 23
2.2 Non-dimensionalization 25
2.3 Figure of Merit 26
2.4 Axial Flight 29
2.5 Momentum Theory for Vertical Climb 29
2.6 Modelling the Streamtube 34
2.7 Descent 37
2.8 Wind Tunnel Test Results 45
2.9 Complete Induced-Velocity Curve 49
2.9.1 Basic Envelope 49
2.9.2 Autorotation 51
2.9.3 Ideal Autorotation 52
2.10 Summary Remarks on Momentum Theory 52
2.11 Complexity of Real Wake 53
2.12 Wake Analysis Methods 55
2.13 Ground Effect 58
2.14 Brownout 60
References 61
3 Rotor in Vertical Flight: Blade Element Theory 63
3.1 Basic Method 63
3.2 Thrust Approximations 68
3.3 Non-uniform Inflow 70
3.3.1 Constant Downwash 71
3.4 Ideal Twist 71
3.5 Blade Mean Lift Coefficient 73
3.6 Power Approximations 74
3.7 Tip Loss 76
3.8 Example of Hover Characteristics 78
Reference 78
4 Rotor Mechanisms for Forward Flight 79
4.1 The Edgewise Rotor 79
4.2 Flapping Motion 85
4.3 Rotor Control 88
4.4 Equivalence of Flapping and Feathering 94
4.4.1 Blade Sailing 95
4.4.2 Lagging Motion 95
4.4.3 Coriolis Acceleration 95
4.4.4 Lag Frequency 98
4.4.5 Blade Flexibility 99
4.4.6 Ground Resonance 99
References 109
5 Rotor Aerodynamics in Forward Flight 111
5.1 Momentum Theory 111
5.2 Descending Forward Flight 115
5.3 Wake Analysis 120
5.3.1 Geometry of the Rotor Flow 120
5.4 Blade Element Theory 125
5.4.1 Factors Involved 125
5.4.2 Thrust 128
5.4.3 In-Plane H-force 130
5.4.4 Torque and Power 131
5.4.5 Flapping Coefficients 133
5.4.6 Typical Numerical Values 136
References 138
6 Aerodynamic Design 139
6.1 Introductory 139
6.2 Blade Section Design 139
6.3 Blade Tip Shapes 144
6.3.1 Rectangular 144
6.3.2 Swept 144
6.3.3 Advanced Planforms 146
6.4 Tail Rotors 148
6.4.1 Propeller Moment 151
6.4.2 Precession – Yaw Agility 155
6.4.3 Calculation of Downwash 160
6.4.4 Yaw Acceleration 162
6.4.5 Example – Sea King 164
6.5 Parasite Drag 165
6.6 Rear Fuselage Upsweep 168
6.7 Higher Harmonic Control 172
6.8 Aerodynamic Design Process 173
References 177
7 Performance 179
7.1 Introduction 179
7.2 Hover and Vertical Flight 180
7.3 Forward Level Flight 183
7.4 Climb in Forward Flight 184
7.4.1 Optimum Speeds 186
7.5 Maximum Level Speed 187
7.6 Rotor Limits Envelope 187
7.7 Accurate Performance Prediction 188
7.8 AWorld Speed Record 189
7.9 Speculation on the Really Low-Drag Helicopter 191
7.10 An Exercise in High-Altitude Operation 193
7.11 Shipborne Operation 195
References 200
8 Trim, Stability and Control 201
8.1 Trim 201
8.2 Treatment of Stability and Control 204
8.3 Static Stability 205
8.3.1 Incidence Disturbance 206
8.3.2 Forward Speed Disturbance 207
8.3.3 Angular Velocity (Pitch or Roll Rate) Disturbance 207
8.3.4 Sideslip Disturbance 207
8.3.5 Yawing Disturbance 207
8.3.6 General Conclusion 207
8.4 Dynamic Stability 208
8.4.1 Analytical Process 208
8.4.2 Special Case of Hover 208
8.5 Hingeless Rotor 209
8.6 Control 209
8.7 Autostabilization 211
References 213
9 A Personal Look at the Future 215
References 222
Appendix: Performance and Mission Calculation 223
A.1 Introduction 223
A.2 Glossary of Terms 224
A.3 Overall Aircraft 224
A.3.1 Main Rotor 225
A.3.2 Tail Rotor 227
A.3.3 Complete Aircraft 228
A.3.4 Example of Parameter Values 228
A.4 Calculation of Engine Fuel Consumption 229
A.5 Engine Limits 230
A.5.1 Maximum Continuous Power Rating 231
A.5.2 Take-Off or 1 Hour Power Rating 231
A.5.3 Maximum Contingency or 21/2 Minute Power Rating 231
A.5.4 Emergency or 1/2 Minute Power Rating 231
A.6 Calculation of the Performance of a Helicopter 231
A.6.1 Influence of Wind 236
A.7 Mission Analysis 237
A.7.1 Calculation Method 238
A.7.2 Atmospheric Parameters 238
A.7.3 Downwash Calculation 239
A.8 Helicopter Power 240
A.9 Fuel Flow 242
A.10 Mission Leg 242
A.11 Examples of Mission Calculations 244
A.12 Westland Lynx – Search and Rescue 245
A.12.1 Description of the Mission 245
A.12.2 Fuel Consumption 246
Index 249
