BASIC HELICOPTER AERODYNAMICS Aerospace Series List BasicHelicopterAerodynamics,Third SeddonandNewman August2011 Edition AdvancedControlofAircraft,Rocketsand Tewari July2011 Spacecraft CooperativePathPlanningofUnmanned Tsourdosetal. November2010 AerialVehicles PrinciplesofFlightforPilots Swatton October2010 AirTravelandHealth:ASystems Seabridgeetal. September2010 Perspective DesignandAnalysisofComposite Kassapoglou September2010 Structures:Withapplicationsto AerospaceStructures UnmannedAircraftSystems:UAVS Austin April2010 Design,DevelopmentandDeployment IntroductiontoAntennaPlacementand Macnamara April2010 Installations PrinciplesofFlightSimulation Allerton October2009 AircraftFuelSystems Langtonetal. May2009 TheGlobalAirlineIndustry Belobaba April2009 ComputationalModellingandSimulation Diston April2009 ofAircraftandtheEnvironment: Volume1–PlatformKinematicsand SyntheticEnvironment HandbookofSpaceTechnology Ley,WittmannandHallmann April2009 AircraftPerformanceTheoryandPractice Swatton August2008 forPilots SurrogateModellinginEngineering Forrester,Sobester August2008 Design:APracticalGuide andKeane AircraftSystems,ThirdEdition MoirandSeabridge March2008 IntroductiontoAircraftAeroelasticity WrightandCooper December2007 AndLoads StabilityandControlofAircraftSystems Langton September2006 MilitaryAvionicsSystems MoirandSeabridge February2006 DesignandDevelopmentofAircraft MoirandSeabridge June2004 Systems AircraftLoadingandStructuralLayout Howe May2004 AircraftDisplaySystems Jukes December2003 CivilAvionicsSystems MoirandSeabridge December2002 BASIC HELICOPTER AERODYNAMICS Third Edition John Seddon Formerly ofthe Ministry ofDefence, UK Simon Newman Aeronautics and Astronautics, University ofSouthampton, UK (cid:1)2011JohnWiley&Sons,Ltd Registeredoffice JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester,WestSussex,PO198SQ,UnitedKingdom Fordetailsofourglobaleditorialoffices,forcustomerservicesandforinformationabouthowtoapplyforpermission toreusethecopyrightmaterialinthisbookpleaseseeourwebsiteatwww.wiley.com. TherightoftheauthortobeidentifiedastheauthorofthisworkhasbeenassertedinaccordancewiththeCopyright, DesignsandPatentsAct1988. Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmitted,inany formorbyanymeans,electronic,mechanical,photocopying,recordingorotherwise,exceptaspermittedbytheUK Copyright,DesignsandPatentsAct1988,withoutthepriorpermissionofthepublisher. Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappearsinprintmaynotbe availableinelectronicbooks. Designationsusedbycompaniestodistinguishtheirproductsareoftenclaimedastrademarks.Allbrandnamesand productnamesusedinthisbookaretradenames,servicemarks,trademarksorregisteredtrademarksoftheirrespective owners.Thepublisherisnotassociatedwithanyproductorvendormentionedinthisbook.Thispublicationis designedtoprovideaccurateandauthoritativeinformationinregardtothesubjectmattercovered.Itissoldonthe understandingthatthepublisherisnotengagedinrenderingprofessionalservices.Ifprofessionaladviceorotherexpert assistanceisrequired,theservicesofacompetentprofessionalshouldbesought. LibraryofCongressCataloging-in-PublicationData Seddon,JohnM. Basichelicopteraerodynamics/JohnSeddon,SimonNewman.–3rded. p.cm. Includesbibliographicalreferencesandindex. ISBN978-0-470-66501-5(hardback) 1. Helicopters–Aerodynamics.I. Newman,Simon,1947-II. Title. TL716.S432011 629.133’352–dc22 2011010960 AcataloguerecordforthisbookisavailablefromtheBritishLibrary. PrintISBN:9780470665015 ePDFISBN:9781119994107 oBookISBN:9781119994114 ePubISBN:9781119972723 MobiISBN:9781119972730 Setin10/12ptTimesbyThomsonDigital,Noida,India To Stella, for everything Contents About the Authors xi Series Preface xiii Prefaceto First Edition xv Prefaceto Second Edition xvii Prefaceto Third Edition xix Notation xxiii Units xxvii Abbreviations xxix 1 Introduction 1 1.1 LookingBack 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-warYears 7 1.1.6 The Helicopter from an Engineering Viewpoint 13 1.2 Book Presentation 22 Reference 22 2 Rotor inVertical Flight: Momentum Theoryand Wake Analysis 23 2.1 MomentumTheory for Hover 23 2.2 Non-dimensionalization 25 2.3 Figure ofMerit 26 2.4 Axial Flight 29 2.5 MomentumTheory for Vertical Climb 29 2.6 Modellingthe Streamtube 34 2.7 Descent 37 2.8 WindTunnel Test Results 45 2.9 CompleteInduced-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 MomentumTheory 52 2.11 Complexity ofReal Wake 53 viii Contents 2.12 Wake Analysis Methods 55 2.13 GroundEffect 58 2.14 Brownout 60 References 61 3 Rotor inVertical Flight: Blade ElementTheory 63 3.1 Basic Method 63 3.2 Thrust Approximations 68 3.3 Non-uniformInflow 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 TheEdgewise Rotor 79 4.2 Flapping Motion 85 4.3 Rotor Control 88 4.4 Equivalence ofFlappingand Feathering 94 4.4.1 Blade Sailing 95 4.4.2 Lagging Motion 95 4.4.3 Coriolis Acceleration 95 4.4.4 LagFrequency 98 4.4.5 Blade Flexibility 99 4.4.6 Ground Resonance 99 References 109 5 Rotor Aerodynamics in Forward Flight 111 5.1 MomentumTheory 111 5.2 DescendingForward Flight 115 5.3 Wake Analysis 120 5.3.1 Geometry ofthe Rotor Flow 120 5.4 Blade Element Theory 125 5.4.1 Factors Involved 125 5.4.2 Thrust 128 5.4.3 In-PlaneH-force 130 5.4.4 Torqueand 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 TipShapes 144 Contents ix 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 ofDownwash 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 AerodynamicDesignProcess 173 References 177 7 Performance 179 7.1 Introduction 179 7.2 Hoverand Vertical Flight 180 7.3 Forward LevelFlight 183 7.4 Climb in Forward Flight 184 7.4.1 Optimum Speeds 186 7.5 MaximumLevelSpeed 187 7.6 Rotor Limits Envelope 187 7.7 Accurate Performance Prediction 188 7.8 AWorldSpeed Record 189 7.9 Speculationon the Really Low-DragHelicopter 191 7.10 An Exercisein High-Altitude Operation 193 7.11 Shipborne Operation 195 References 200 8 Trim, Stabilityand Control 201 8.1 Trim 201 8.2 Treatment ofStability and Control 204 8.3 Static Stability 205 8.3.1 Incidence Disturbance 206 8.3.2 Forward SpeedDisturbance 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 ofHover 208 8.5 Hingeless Rotor 209 8.6 Control 209 8.7 Autostabilization 211 References 213 x Contents 9 APersonalLook atthe Future 215 References 222 Appendix: Performance and Mission Calculation 223 A.1 Introduction 223 A.2 Glossaryof Terms 224 A.3 OverallAircraft 224 A.3.1 Main Rotor 225 A.3.2 Tail Rotor 227 A.3.3 Complete Aircraft 228 A.3.4 Example ofParameter Values 228 A.4 Calculation ofEngine Fuel Consumption 229 A.5 Engine Limits 230 A.5.1 Maximum Continuous PowerRating 231 A.5.2 Take-Off or 1 Hour PowerRating 231 A.5.3 Maximum Contingency or 21/ MinutePowerRating 231 2 A.5.4 Emergency or 1/ MinutePowerRating 231 2 A.6 Calculation ofthe Performance ofa Helicopter 231 A.6.1 Influence ofWind 236 A.7 Mission Analysis 237 A.7.1 Calculation Method 238 A.7.2 AtmosphericParameters 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 ofMission Calculations 244 A.12 Westland Lynx– Searchand Rescue 245 A.12.1 Description ofthe Mission 245 A.12.2 Fuel Consumption 246 Index 249