Helicopter Test and Evaluation (Aiaa Education Series)

385 Pages·2002·2.11 MB·English

by  Alastair K. Cooke

Helicopter Test
and Evaluation

HELICOPTER TEST
AND EVALUATION
Alastair K. Cooke
BTech, BEng, MSc, PhD, CEng, MRAeS, MIMechE
Eric W. H. Fitzpatrick
MRAeS, Test Pilot
©QinetiQLimited2002 Firstpublished2002byBlackwellScienceLtd
BlackwellScienceLtd,aBlackwellPublishing LibraryofCongress
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EditorialOffices: Cooke,AlastairK.
OsneyMead,OxfordOX20EL,UK Helicoptertestandevaluation/AlastairK.
Tel:ò44(0)1865206206 Cooke,EricW.H.Fitzpatrick.
BlackwellScience,Inc.,350MainStreet, p.cm.
Malden,MA02148-5018,USA Includesbibliographicalreferencesandindex.
Tel:ò17813888250 ISBN0-632-05247-3(Hardcover)
BlackwellScienceAsiaPtyLtd,54University 1. Helicopter–Flighttesting.
Street,CarltonSouth,Melbourne,Victoria 2. Helicopters–Aerodynamics.
3053,Australia I. Fitzpatrick,EricW.H. II. Title.
Tel:ò61(0)393470300 TL716.5.C662002
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Contents
Preface vii
Abbreviations x
Notation xiii
Chapter1 TheFlightTestProcess 1
1.1 Introduction 1
1.2 Flighttestplanning 1
1.3 Conductingthetrial 5
1.4 Post-trialsactions 6
Chapter2 PerformanceTheory 8
2.1 Introduction 8
2.2 Axialflight:momentumtheory 8
2.3 Axialflight:bladeelementtheory 11
2.4 Non-dimensionalcoefficients 14
2.5 Axialflight:improvedtheoreticalestimates 16
2.6 Axialflight:verticaldescentsandthevortex-ringstate 20
2.7 Horizontalflight:momentumtheory 22
2.8 Horizontalflight:bladeelementtheory 26
2.9 Horizontalflight:improvedtheoreticalestimates 29
2.10 Tailrotorpower 34
2.11 Powereddescents 36
2.12 Autorotation 44
2.13 Autorotativeperformance 51
2.14 Flarecharacteristicsandengine-offlandings 54
2.15 Theavoidcurve 60
Chapter3 PerformanceTesting 65
3.1 Introduction 65
3.2 Non-dimensionalparameters 65
3.3 Performancetestplanning 68
3.4 Levelflightperformancetesting 71
3.5 Verticalperformancetesting 87
3.6 Climbperformancetesting 106
3.7 Determinationofperformancelimitedparameters 115
v
vi Contents
Chapter4 StabilityandControlTheory 119
4.1 Introduction 119
4.2 Aero-derivativesforrotorcraft 120
4.3 Equationsofmotionforarigidairframe 125
4.4 Equationsofflappingmotion 128
4.5 Flapdynamics 132
4.6 Rotorcontributionstostaticanddynamicstability 146
4.7 Longitudinalstaticstability 150
4.8 Manoeuvrestability 152
4.9 Longitudinaldynamicstabilityandcontrolresponse 153
4.10 Lateral/directionalstaticstability 163
4.11 Lateral/directionaldynamicstabilityandcontrolresponse 167
Chapter5 StabilityandControlTesting 179
5.1 Assessingflightcontrolmechanicalcharacteristics 179
5.2 Assessingstaticstability 185
5.3 Manoeuvrestabilitytesting 194
5.4 Documentingdynamicstabilitycharacteristics 198
5.5 Timedomainmethodsforcontrolresponsetesting 202
5.6 Frequencydomainmethodsforcontrolresponseassessment 211
5.7 Missiontaskmethods 220
Chapter6 HelicopterSystems 231
6.1 Introduction 231
6.2 Airdatasystems 231
6.3 Enginecontrolandrotorgoverningsystems 239
6.4 Flightcontrolsystems 261
6.5 Automaticflightcontrolsystems 264
Chapter7 SystemsTesting 295
7.1 Methodology 295
7.2 Cockpits 298
7.3 Pressureerrormeasurement 310
7.4 Engineandrotorgoverning 319
7.5 EffectofAFCSonhandlingqualitiestesting 329
7.6 Failuretesting 338
References 357
Index 361
Preface
The authors of this book have been employed at the Empire Test Pilots’ School
(ETPS), part of QinetiQ, for the past ten years instructing student test pilots and
flighttestengineersonhelicoptertesting.AlastairCookehasamastersdegreeinflight
dynamicsfromCranfieldUniversityandgraduatedasaflighttestengineerfromETPS
in 1989. Eric Fitzpatrick is a former military helicopter pilot and instructor who
graduatedasatestpilotfromETPSin1986.
Thisbookhasbeenproducedusingtheexperienceoftheauthorsinflighttestand
flight test training gained over a combined period of 25 years in the field. Much of
the material has its origin in the training notes produced by ETPS. These have been
developed over a period of over forty years since the start of specific training for
helicoptertestpilots.Thebookhasbeendesignedtoappealtoprofessionalsworking
in the area of rotorcraft test and evaluation but it is hoped that it will also prove
usefultoawideraudience.Inourexperience,wehavefoundthathelicopterpilotsare
generally not well informed about the process that has led to their aircraft entering
service,noraboutwhyithascertainlimitationsimposedonit.Wehopethisbookwill
provide pilots with this information as well as being a useful text for practising
engineers and technologists. The rotor theory presented is more extensive than is
found in most aeronautical degree courses and so the book should prove useful to
graduatesspecializinginrotorcrafttechnology.Perhapsuniquely,thisworkapproaches
thisimportantsubjectfromboththetheoreticalandpracticalviewpoints.
Foreachtopicthetheoryisexplainedbrieflyandisthenfollowedbydetailsofthe
practicalaspectsoftestingahelicopter.Thesedetailsincludethesafetyconsiderations
relatedtotheanticipatedtests,planningtheteststhemselves,and,whereappropriate,
the most efficient way to conduct individual flights. Following a description of each
type of test, typical results are examined and an explanation given as to why they
would be important to the clearance process. Whenever possible examples of actual
test results have been presented and used in the subsequent discussion. The book is
splitintofourmainsections:
Ω Introduction: covering a methodology for testing and general aspects of test
programmes.
Ω Performance: in this section level flight, vertical and climb/descent performance
is addressed. The planning of performance trials is covered together with the
methodsforairbornedatagatheringandanalysisofresults.
Ω Handling qualities: this is a major section and covers the basics of helicopter
stabilityandcontroltesting.Alsoincludedarefrequencydomainmethodsandthe
useofmissiontaskelements.
Ω Systems:inthissectionthemajorsystemsrequiredtoenableahelicoptertoflyare
vii
viii Preface
covered.Thisincludesassessmentofthecockpit,airdatasystems,enginecontrol
systems,andautomaticflightcontrolsystems.Alsoaddressedinthissectionisthe
testingofsystemfailures.
Althoughhighlyspecialized,thetopicofhelicoptertestingisstillvastandnosingletext
couldhopetocovereverything.Theauthorshaveattempted,therefore,toconcentrate
on the most important aspects using their own knowledge of the subject as a guide.
Inevitably,anumberofimportantareashavenotbeencovered;forexample,ithasnot
beenpossibletoincludeinformationonspecialistareassuchasunderslungloadtrials,
deck operation trials or armament testing. The amount of information on systems
testingtoincludeinthebookwasadifficultdecisionduetotheplethoraofsystemsthat
canbefittedtoamodernrotorcraft.Consequently,itwasdecidedtodetailthegeneral
methodologyusedinthistypeoftestingandthentoconcentrateonsystemswhichare
intrinsictotheoperationofallhelicopters.Thus,ithasnotbeenpossibletoincludethe
testingofhydraulics,electricsandlubricationsystems.Similarlythetestingofanumber
ofcockpitsystemssuchaspilotingvisionaids,navigationsystems,weapons,andmission
displayswereconsideredtobebeyondthescopeofthisbook.Finally,itwasnotpossible
toincludesometypesoftestingwhichoftenplayalargepartinthelifeofatestpilot
suchasenvironmentaltrials,notablycoldweatherandicing.Despitetheseomissions,it
isbelievedthatthebookcoversalltheessentialareasofrotorcrafttestingandwillprove
usefultoalargepartofthehelicoptercommunity.Astheauthors’backgroundhasbeen
in military test and evaluation this has clearly influenced the subject matter that has
been presented. However, most of the information given in the book can be applied,
withonlyminormodification,tothetestingofcivilrotorcraft.
BeforeclosingwewouldliketoacknowledgethehelpofMrMikeCookofCranfield
University,MrMarkRootsofQinetiQLtdandMissJuliaBurdenofBlackwellPub-
lishinginhelpingusdevelopourmanuscriptforpublication.
AlastairCookeandEricFitzpatrick
ETPS,QinetiQLtd
MODBoscombeDown
Copyrightacknowledgements
Thefollowingorganizationsaregratefullyacknowledgedforgrantingpermissionsfor
theuseofcopyrightmaterial.
The UK MOD for the cover photograph. NASA for Figure 3.37 and the AHS for
Figures3.18,3.20and3.22.
Theexamplehelicopter
On several occasions throughout this book quantitative calculations have been made
tosupportthetheoreticaltrendsbeingdiscussed.Wherepossiblethecalculationshave
been made using the same baseline data, referred to as the example helicopter. The
Preface ix
detailsofthishelicopter,whichislooselybasedontheWestlandLynx,aresummarized
below:
Mainrotor
Radius 6.5m Bladechord 0.4m
Standardrotorspeed 35rad/s Numberofblades 4
Liftcurveslope 0.1/º Twist 10º
Profiledragcoefficient 0.008or0.01
Tailrotor
Tailarm 7.5m Radius 1.1m
Bladechord 0.2m Standardrotorspeed 165rad/s
Numberofblades 4 Profiledragcoefficient 0.010
Fuselagefrontaldragarea 2m2
Fuselageverticaldragarea 8m2
Mass(unlessotherwiseindicated) 5000kg