Bell/Boeing V-22 Osprey: Multi Service Tilt-rotor

130 Pages·2004·123.83 MB·English

by  Bill Norton

el Boeing
Y - 2 2 O s p r e y
Tiltrotor Tactical Transport
Bill Norton
Bell Boeing
V·22 Osprey
Tiltrotor Tactical Transport
Bill Norton
An imprint of
Ian Allan Publishing
BellBoeingV·22Osprey Contents
©2004WilliamJNorton
ISBN1857801652
PublishedbyMidlandPublishing Introduction 3
4WatlingDrive,Hinckley,LE103EY,England Abbreviationsand Designations 4
Tel:[phone] Fax:[phone]
E-mail:[email protected] Chapters
1 Origination 5
MidlandPublishingandAerofaxareimprintsof Designconceptandlayout
IanAllanPublishingLtd ©2004MidlandPublishingandJayMiller 2 Background 13
3 Birth andHiatus 23
Worldwidedistribution(exceptNorthAmerica): EditedbyJayMiller
4 StartingAgain 51
MidlandCountiesPublications
5 ProductionandService 75
4WatlingDrive,Hinckley,LE103EY,England PrintedinEnglandby
Telephone:[phone] Fax:[phone] IanAllanPrintingLtd 6 TheFuture 81
E-mail:[email protected] RiverdeneBusinessPark,MoleseyRoad,
7 OspreyDescribed 89
www.midlandcountiessuperstore:com Hersham,Surrey,KT124RG
8 V-22Specifications&Performance. 110
NorthAmericantradedistribution: Allrightsreserved.Nopartofthispublication 9 TiltrotorGallery 112
SpecialtyPressPublishers&WholesalersInc. maybereproduced,storedinaretrievalsystem,
39966GrandAvenue,NorthBranch,MN55056 transmittedinanyformorbyanymeans,
Tel:[phone] Fax:[phone] electronic,mechanicalorphoto-copied,
Tollfreetelephone:8008954585 recordedorotherwise,withoutthewritten
www.specialtypress.com permissionofthepublishers.
Titlepage:ThefirstV-22,BuNo163911duringthe
courseofitssecondflightatBellHelicopter
Textron'sArlingtonMunicipalAirportFacility
inTexas.JayMiller
Below:FreshfromBoeing'sRidleyTownship,
Pennsylvaniaproductionfacility,afuselagefor Facingpage:ThedeckcrewoftheUSStwoJima
anewV-22,BuNo165943(aircraft44),sitsat havepositionedaircraft10(BuNo164942)witha
BellHelicopterTextron'sV-22facilityinAmarillo, tugpreparatorytoatestflightinJanuaryof
TexasduringSeptemberof2003awaitingfinal 2003.NoteuniquetailmarkingsforthisEMD
assembly.JayMiller aircraft.NAVAIR
__--ll
3
4 Introduction
5
3
3
,1
5
,1
,9
o
2
,
a
AttimeofwritingtheUSMarineCorpsMV-22B providemorethanenoughfascinating aviation Acknowledgements
Ospreytiltrotoraircrafthadyettoenterfull-rate history to fill this volume. A review of tiltrotor Manyindividualsgavegenerouslyoftheirtime
productionordeployment.Thiswasthestatus flight technology offers aview into one ofthe andcollectedmaterialstohelpmakethisbook
following nearly two decades of development fewVSTOLapproachestobetakensofaralong possible. At Bell Helicopter Textron this
andflighttestthatsawmarkedchangestothe the development path. The technology is not included RoyHopkinsII, ChuckJacobus, Bob
vehicle, vacillations in Congressional and new, and a look at the predecessor vehicles Leder, Bob McClure, and DickPeasley. Ofthe
Administration support despite steadfast reveals the long development path leading to Boeing Company thanks go to Phil Dunford,
USMC dedication to the machine, and three the Osprey. The struggle to realize a military Doug Kinneard, JimJagodzinski, Bill Leonard,
fatal accidents, Opinions about the Osprey application through multiple programs and theotherBill Norton, and MartyShubert. From
throughout the aviation field was similarly conceptual designs emphasizes the vagaries the US Navythe author is grateful for support
divided betweenthosewhosawthetiltrotoras oftheUSDepartmentofDefenseweaponsys from Ward Carroll, Gidge Dady, and Linda
an aeronautical advance that would surely tem acquisition process. The development of Drew.MarineswhoassistedincludeLieutenant
comewith sacrificesintreasureand lives, and the V-22 itself, marked by drawn-out sched Colonel'Curly'CulpandMajorChrisSeymour.
thosewhosawacomplex,expensiveanddan ules, up-and-down budgets, industryteaming, From the US Air Force debt is owed to lieu
gerous craft unsuitable for military employ crisesandtriumphs,isremarkableinthatitpro tenantColonel Tom Currie, MajorTom Good
ment. The controversy recalled the furor over duced avehicle ofsuch capability. So poten nough, Major Greg Weber, and John Haire.
theintroductionoftheAV-8AHarrierintoUSMC tiallysignificantistheOspreyinmilitaryaviation Marty Maisel, formerly of NASA Ames, was
service decades before. Both offered highly that it has spawned the US Air Force CV-22B especially helpful. Thanks also to retired Bell
desirableVerticalorShortTakeoffandLanding special operationsvariant, concepts offollow test pilot Ned Gilliand. Jay Miller and the
(VSTOL) enhancements to the Marines' arse ondesigns, experimentaluninhabited airvehi archivistsatthe JayMillerCollection provided
nal in fUlfilling their challenging mission. Yet, cles, and made possible a long-dreamed of indispensablehelp.Aspecialthankstothelate
both aircraft represented newtechnology that civiltiltrotor.Inshort,thesignificantandalready John Schneider, formerly of Boeing Vertol,
was met with a mixture of suspicion and the considerable history ofthe V-22 Osprey more Michael Hirschberg ofVertiflite magazine, and
needtolearnthebestmeansofoperation and thanjustifiesabookonthesubject. Ken Katz.
employment. If the history of the Osprey continues, this
Although the history ofthe Osprey may be bookcan be updated inthefuture. Feedback,
short- provided itcontinues intofull-rate pro research material, andadditional photographs Bill Norton
duction and service - the story of its lineage, arewelcome.Contacttheauthoratwilliamnor January2004
development, flight test, and characteristics [email protected].
V-22Osprey 3
Abbreviations and Designations
A Amperage GTA groundtestarticle NBC nuclear,biologicalandchemical
AC alternatingcurrent GW grossweight nm nauticalmile
ale aircraft helo helicopter No number
AEW airborneearlywarning HF highfrequency NOE Nap-of-the-Earth
AFB AirForceBase HIFR HoverIn-FlightRefueling NORM normal
AFCS AutomaticFlightControlSystem hp horsepower Nr rotorspeed
AFFTC AirForceFlightTestCenter HROD highrateofdescent NVG nightvisiongoggles
AFSOC AirForceSpecialOperationsCommand hrs hours " OAT outsideairtemperature
amp amperage HSD HorizontalSituationDisplay OBOGS On-BoardOxygenGeneratingSystem
AMT AirManeuverTransport HSX HelicopterSeaeXperimental OGE outofgroundeffect
AOA angleofattack HUD head-updisplay OLC OpposedLateralCyclic
APLN airplanemode H-V height-velocity OPEVAL operationalevaluation
APU auxiliarypowerunit H/WOG Hoist/WinchOperator'sGrip OT operationaltest
AR aerialrefueling HX HelicoptereXperimental Pax PatuxentRiverNAS
ASW anti-submarinewarfare HXM HelicoptereXperimentalMarines PFCS primaryflightcontrolsystem
ATV AirTestVehicle Hz Hertz PRGB proprotorgearbox
aux auxiliary ICDS interconnecteddriveshaft PRTV ProductionRepresentativeTestVehicles
AVSS ActiveVibrationSuppressionSystem ICS inter-communicationsystem psf poundspersquarefoot
BFWS bladefold/wingstow IFF IdentificationFriendorFoe psi poundspersquareinch
bhp brakehorsepower IGE ingroundeffect PU/SS pitch-upwithsideslip
BIT built-intest IMC instrumentmeteorologicalconditions P&W Pratt&Whitney
BuNo BureauNumber in inches P'I preplannedproductimprovement
C Centigrade IOC initialoperationalcapability QTR QuadTiltRotor
cal caliber IOT&E InitialOperationalTestandEvaluation RADALT radaraltimeter
CAP CompositeAircraftProgram IPS IceProtectionSystem RAF RoyalAirForce
CAT cabinauxtanks IR infrared RAM reliability,availabilityandmaintainability
CDU/EICAS ControlDisplayUnit/Engine,Instruments, IRS InfraredSuppressor rev revolution
CrewAlertingSystem IT integratedtesting RFP requestforproposal
CFB CanadianForcesBase In IntegratedTestTeam RM&A reliability,maintainabilityandavailability
cg centerofgravity JSOR JointServicesOperationalRequirements rpm revolutionsperminute
c/n constructionnumber JTAG JointTechnologyAssessmentGroup RSI RadarSignalIndicator
COD carrieronboarddelivery JVX JointservicesadvancedVerticalliftaircraft R&D researchanddevelopment
COEA OperationalEffectivenessAnalysis (eXperimental) SAR searchandrescue
CFG constantfrequencygenerators kg kilogram SATCOM satellitecommunications
em centimeter km kilometer SCAS StabilityandControlAugmentationSystem
CMDS countermeasuresdispensingsystem kts knots SCP setclearanceplane
CONV conversionmode kVA kilovolt-amps SOC shaftdrivencompressor
CSAR combatsearchandrescue kW kilo-Watts sec seconds
CSMU CrashSurvivableMemoryUnit Ib pounds SEMA SpecialElectronicMissionAircraft
DC directcurrent LCD liquidcrystaldisplay SEO singleengineoperating
DMS DigitalMapSystem LOS LaserDetectorSet sfc specificfuelconsumption
DoD DepartmentofDefense LHA AmphibiousAssaultShip(GeneralPurpose) shp shafthorsepower
DoN DepartmentoftheNavy LHD AmphibiousAssaultShip(Multi-purpose) SIRFC SuiteofRadioFrequency
DT developmenttest LPD AmphibiousTransportsDock Countermeasures
DU DisplayUnit LPI lowprobabilityofintercept SOCOM SpecialOperationsCommand
EAPS EngineAirParticleSeparator LRIP low-rateinitialproduction SOF specialoperationsforces
ECL EngineConditionLever LSD DockLandingShips SPECOPS specialoperations
ECS environmentalcontrolsystem It liters STA statictestarticles
ECU EnvironmentalControlUnit LTM LateralTranslationMode STO shorttakeoff
EMC electromagneticcompatibility LWINS LightWeightInertiaiNaVigationSystem STOL shorttakeoffandlanding
EMD EngineeringandManufacturing LZ landingzone TA terrain-avoidance
Development m meters TAGB tilt-axisgearbox
EW electronicwarfare MAn Multi-missionAdvancedTacticalTerminal TCL thrustcontrollever
F Fahrenheit MAW MarineAirWing TF terrainfollowing
FADEC FUll-AuthorityDigitalElectronicControl max maximum TF/TA terrainfollowing/terrain-avoidance
FBW fly-by-wire MC MissionComputers TARA TiltRotorResearchAircraft
FCC flightcontrolcomputers MCAS MarineCorpsAirStation UAV uninhabitedairvehicle
FD FlightDirector MDL missiondataloader UHF ultra-highfrequency
FUR Forward-LookingInfrared MFD multi-functiondisplay US UnitedStates
fit flight MFS MannedFlightSimulator USAF UnitedStatesAirForce
FM frequencymodulated mi statutemile USCG UnitedStatesCoastGuard
FMU FuelManagementUnit min minimum USgal USgallons
FOV fieldofview MLR Medium-LiftReplacement USMC UnitedStatesMarineCorps
fpm feetperminute mm millimeter USN UnitedStatesNavy
fps feetpersecond MMR multi-moderadar VAC voltsalternatingcurrent
FRP full-rateproduction MOn Multi-serviceOperationalTestTeam VERTREP verticalresupply
FS federalstandard mps meterspersecond VFG variablefrequencygenerators
FSD Full-ScaleDevelopment MTE ModernTechnologyDemonstratorEngine VHF veryhighfrequency
ft feet MWGB midwinggearbox V/HXM HelicoptereXperimentalMarines
FTR FutureTransportRotorcraft MWS MissileWarningSystem VRS vortexringstate
FY FiscalYear NAS NavalAirStation VSS vibrationsuppressionsystem
G accelerationduetogravity NASA NationalAeronauticsandSpace VSLED Vibration,StructuralLife,
GAO GeneralAccountingOffice Administration andEngineDiagnostic
GFE governmentfurnishedequipment nav navigation VSTOL VerticalorShortTakeoffandLanding,
GRDP groundrefuel/defuelpanel NAVAIR NavalAirSystemsCommand VSTOLmode
4 V-22Osprey
ChapterOne
Origination
The military helicopter's ability to takeoff and surfaceisavailable,suchanaircraftcould per Above:TheV·22ismuchlikeanyotherlarge
land vertically is oftremendous tactical utility, form ashorttakeoffand landing (STOL) when rotorcraft,althoughwithtwinlateraltandem
rotors.Notetheslighttoe·outofthenacelles.
anditisanindispensableassetin modernwar verticaltakeoffisprecludedbyweightorambi
RonCulp
fare. However, the comparatively lowairspeed entconditions. TheVSTOLaircrafthavesafety
andaltitudeatwhichthehelicoptercommonly advantagesoverthe airplanesuchaseliminat
flies makes it more vulnerable to enemy fire ing or reducing high-speed ground rolls for rotor system and, where present, atail rotor.
than airplanes. The helicopteristypicallycon takeoff and landing, and executing off-field Airplane flight control relies on deflecting sur
strainedto aserviceceiling ofaround 10,000 emergencylandingsintoaconfinedspace.On faces against the passing air mass, requiring
20,OOOft (3,050-6,1OOm), usually preventing it theotherhand,VSTOLaircraftfrequentlyhave forward velocity. AVSTOLaircraft cannot use
from flying above weather. In fact, the all little powermarginand anenginefailurewhile airplane controls in hover andthe slow-speed
around performance ofthe helicopter is com in hoveror slowflight, evenforamulti-engine endofconversionandreconversion.Arotoror
monly less than fixed-wing, conventional machine, can mean an immediate descent at someothersource ofadequatecontrol power
takeoffandlandingairplanesofsimilarweight. perhapshighsinkrate.This,however,isacom mustbeavailable.
The tail rotor on single-rotor helicopters is a Il)only accepted characteristic of most heli Over decades nations and corporations
markeddrainonenginepower,addstoaircraft copters. have invested considerablyinVSTOL. Afasci
dragandnoise,andisanever-presenthazard. ManyapproachestoachievingVSTOLflight nating assortment of these machines have
Thehelicopterreachedthepracticallimitsofits have been explored. The general design been built and tested, employing Virtually all
capabilities decades ago in terms of size, requirement is a vertical component of conceivableapproachestoVSTOLflight.Inthe
speedandrange. Becauseoftherotoraerody thrust/liftgreaterthantheweightoftheaircraft US, each armed service operates transport
namics, a practical limit of 200kts is general to permit vertical takeoff and hover. Normal helicopters for aerial assault, search and res
acknowledgedforrotorwingaircraft. propulsivethrustmustthenbeavailableforfor cue,andvertical replenishment. All soughtthe
One answer to the helicopter's limitations wardflight. Theconversion betweenverticalto potential benefits of a VSTOL transport.
has been to combine the speed, range, forward flight must smoothly transition Through these decades only a few military
endurance, payload, maneuverability, and betweenthetwothrust/liftgenerationandvec designs,thetri-serviceLTV-Hiller-RyanXC-142
superior survivability of the airplane with the toringschemes.Anadequatemeansofattitude being one, came even close to production
vertical lift capabilities of a helicopter. The control from hover, through conversion at low before being ultimately jUdged unsuitable.
resultistheVerticalorShortTakeoffandLand speed, and atcruise airspeedsisalso manda Designs to fill other combat and support mis
ing (VSTOL) aircraft. Ifeven aminimal runway tory. Helicopters do allthis with an articulated sionsthatwould benefitfromVSTOLhavealso
V-22Osprey 5
metwithlimitedsuccess.Throughouttheworld upto'recirculate',interactingwithaircraftaero Above:Thismontageshowsthetiltrotorconcept
onlythe Harrier 'jump jet' fighter-bomber, first dynamics.Itmayspoilliftinhover(called'suck fromhelicoptermodefortakeoffandlandingat
therightside,conversiontoforwardflightinthe
flown in 1960, and the later Yakovlev Yak-38 down')andcancarrygroundmaterialaloftthat
middlewithforwardtiltingofthetwinproprotors,
naval fighter have seen production. However, can damage the airframe and engine. If the
andhigh-speedairplanemodeattheleftwiththe
only the Harrier can be considered truly suc ground plume is hot, as from a vertically ori proprotorsservingaspropellers.BellHelicopter
cessful. Admittedly, these specialized aircraft ented engine exhaust, the recirculate air
are inferiorto comparablewarplanes in nearly ingested into the engine(s) ('reingestion') will Belowleft:Thisgeneralizeddiagramcompares
theV-22'sspeed-altitudeflightenvelopewiththat
allrespectssavefortheirVSTOLcapability.Yet produce a reduction in thrust. The high tem
ofacommontacticaltransporthelicopterand
theyrepresentusefulsystemsinamixofmod peraturescan alsohavedetrimentaleffectson
airplane,theSikorskyH-60andLockheedC-130.
ernaircombatweapons. other aircraft components. The generation of Thetiltrotornicelyencompasseshelicopter
Therearedecisive reasons whyVSTOLhas highvelocityairiscommonlyaccompanied by andairplanecapabilities.Author'scollection
almost always proven disappointing. The very high noise levels; annoying and possibly
Belowright:Ashorttakeoff(STO)hasthe
weightandcostpenaltiesareusuallytoogreat, hazardous to personnel and aircraft structure
nacellesatabout60°andthepilotsrotateat
resulting inexpensive machineswith marginal given longexposure.
theappropriateairspeed.NAVAIR
performancewhen compared with helicopters Achieving VSTOLisamatterofengineering
andfixed-wingaircraft.Thelargeexcesspower and performance tradeoffs, and the tiltrotor
required for hover has required a high thrust generally sacrifices less for its benefit than lage naturally cancel the opposing rotor
to-weightratio.Thepropulsionsystemhasfre other VSTOL concepts. The best use of the torquestoeliminatethetailrotor. Hoverperfor
quently represented a disproportionate per tiltrotor has generally appeared to be as a mance is not as great as a helicopter with its
centage of the vehicle's empty weight for a medium-lift transport where moderately high larger rotor diameter, but this sacrifice is
reduction in range and payload, plus adding cruiseairspeedsarerequired,yetalsoneeding acceptedforthecomparativelyhighcruiseair
considerably to the machine's cost, complex tomakeseveralstopswithbrieflowspeedand speed. ForAPLN,flightcontrolsurfacesonthe
ity, and maintenance demands. Hover perfor hoveringoperations. wing andtailtakeeffectasairspeed increases
mancehasgenerallybeenpoor,characterized followingconversion.
byveryhighfuelconsumption.Theconversion TheTiltrotor The maximum speed ofthetiltrotoris much
from vertical to forward flight and back again Mosttiltrotordesigns havethe proprotors and greaterthanacomparablehelicopter,andwith
hasalso been achallenging stabilityand con engines together in rotating wingtip nacelles. similarly improved endurance. The tradeoff is
trolproblem,complicated byanarrowconver The basicscheme isthatthe aircrafttakes off typicallyslowercruisespeedsthananairplane
sion corridor for some configurations. The asahelicopter(referredtoas'helicoptermode' ofcomparableweightandpower.InVSTOLthe
conversioncorridoristherange ofacceptable orVSTOL) with thetworotors/nacellesvertical airspeed upper limits are still defined by rotor
thrust vector angle as a function of airspeed. or90°.Thesearethenrotatedforwardto0°for overstress and retreating blade stall. In APLN
Operational problems have also been conversion to high-speed wing-borne flight thelowspeedlimitsaresetbywingstall,withthe
endemic to many VSTOL designs. Many are ('airplanemode',APLN).Hence,the'proprotor' propellerwashoverthewinghelpingtoreduce
characterized by high velocity columns ofair, blades and hub serve dual use as helicopter this speed. The prop slipstream also helps to
called downwash, hitting the surface beneath rotors and airplane propellers. The counter ensure adequate flow into the engine intake
the aircraftduringvertical takeoffand landing. rotating proprotors on either side ofthe fuse- evenatextremeattitudesand lowairspeed.
This can cause surface erosion with high
energy bits potentially striking and damaging
the aircraft or nearby personnel and equip
ment.Thisairwillspreadoutalongtheground
asaground plumeorgroundwashasanother
potentialhazard.Additionally,thisaircanrising
V-22 Performance
30,000
25,000
ALTITUDE
(FEET)
200 300
AIRSPEED(KNOTS)
6 V-22Osprey
Above:Amodestforwardtiltofthenacellesand simultaneouslyfor disk liftvariation to change theaircrafttoaccelerateanddecelerate.
ashortgroundrollallowstakeoffatgross altitudeorhover, butpoweronlyinAPlN.The In some areas of the airspeed and nacelle
weightsorambientconditionsthatwould
TCl commands symmetric rotor or mast angleconversion corridorthechoiceofcontrol
precludeaverticaltakeoff.RonCulp
torquein bothVSTOlandAPlN. technique can be uncertain. The 30° nacelle
Belowright:Thevalueoftheleveldeckangle As the aircraft accelerates through high setting atthe lower end ofthe acceptable air
possiblewiththetiltrotorduringtransitionto speed conversion, the controls change their speed for that angle is one such ambiguous
forwardflightisgraphicallyillustratedhere. functionsandthepilot'scontrolstrategyhasto condition in then V-22, and accompanied by
Aircraft10,duringits'returntoflight'on29May
progressively change to resemble that of a airframe buffet. However, pilots aretrained to
2003,convertseffortlesslywhiletheSH-60
conventional fixed-wing aircraft. In APlN the use a few nacelle settings and certain air
safetychasehelicopterbeyondassumesa
markednose-downattitudetokeepup- the rudder pedals produce yaw while the stick speeds during transition to help avoid confu
rotorsofthetwoaircraftnearlyparallel.Navy becomes aclimb, diveand roll rate controller, sion.Thetiltrotor normally spendslittletime in
movingtheailerons/flaperonsandanelevator. transition.
TheTClinput(power)isusedasasimplethrot The conversion is begun at an airspeed at
The cockpit controls serve common func tletosetthelongitudinalthrustwhilelongitudi which thewing is gaining in liftasthe rotor lift
tions regardless of flight mode. In hover and nalstickisusedto managetheaircraftenergy decreases with tilt angle. This airspeed must
lowspeed flight, with the nacelles tilted near statebyincreasingordecreasingtheflightpath alsobesuchthatthewing andtail control sur
vertical, the collective (or thrust control lever, angle at relatively constantspeed, orallowing facesaresufficientlyeffectivetocontroltheair-
Tel) and cyclic (stick) provided familiar heli
copter functions, and the proprotors employ
helicoptercontrolmechanization. lateralcyclic
for roll and translation (sideward flight) com
mandschangeinproprotorbladepitchangles
astheycomearoundinrotation.Thisproduces
eitherasidewaystiltingoftherotordisksdueto
asymmetrical proprotor lift, or differential col
lectivepitch (uniformbutopposedbladeangle
changeoneachproprotorfordifferentiallift),or
amix of both side-to-side. Pitch control from
longitudinalcyclicdisplacementgivesforeand
afttilting ofthe rotordisks. Forrearwardtrans
lation, aftcyclic also bringsthe elevator upto
keepthetailfrom dropping dueto airflow pro
ducingadowntailload.Ineitheraxisthecyclic
produces increasing rate depending uponthe
magnitude of displacement. Directional (yaw)
controlwithpedalsusesdifferentialcyclicpitch
therotor disks tilting differentiallyforward and
aftto produce aflat rotation aboutthevertical
axis. In VSTOL the TCl commands proprotor
collective (uniform) pitch and engine power
V-22Osprey 7
Bothpages:Thisseriesofdrawingsandnotes
illustrateshowthetiltrotoriscontrolledinflight
A
• throughthepilotthrustcontrollever,cyclic
Helicopter Airplane (stick)anddirectionalpedals.A.ThrustControl
(power);B.ForwardCyclic;C.AftCyclic;D•
LateralCyclic(right);E.Pedal(left)
BellHelicopter
to anywing, arefrom high-pressureaironthe
bottom flowing up around the wingtip to the
low-pressure region atopthe wing and gener
atedrag.Theproprotorscounterofthisflowfor
ThrusVpowerlevercontrols ThrusUpowerlevercontrols
proprotorcollectivepilchand bladepitchandenginethrottle reduced drag.
throttles Actsasairspeedcontrol The proprotor blades must be designed to
Actsasaltitudecontrol
operateefficientlyas helicopterrotors and air
plane airscrew. This challenging requirement
hasyielded short and broad blades with con
siderabletwist- 47.5°ontheV-22versus8°for
atypical helicopter. A measure ofthis is disk
B loading,oraircraftweightdividedbytheareaof
Helicopter Airplane the circle(s) formed by the rotor diameter. A
Elevator
typical disk loading forthe medium liftV-22 is
Forwardlongitudinal
cyclicpitch 20psf(99kg/m')versusatypical6psf(27kg/m')
forthecomparableCH-46and1Opsf(50kg/m')
forthe heavy liftCH-53D. The helicopter's low
diskloadingismoreefficientinhoverandgen
erates a comparatively mild downwash. High
diskloadingmeansmorepowerrequiredtolift
thesameaircraft,equatingtomoreweightand
high fuel consumption in hover, and greater
Proprotordiscstiltforward Elevatordeflectsdownward downwash velocity. Consequently,the tiltrotor
Aircraftassumesnose-downattitude Aircraftassumesnose-downattitude normallyrequiresmorepowerforhover,trans
Airspeedincreases Altitudedecreases lation andforward flight in VSTOLthan aheli
Airspeedincreases copter, but less than many other VSTOL
designs. Plus, the tiltrotor possesses greater
rotor drag in edge-wise flight. However, high
disk loading is preferablefor cruise flight with
thebladesworkingaspropellers.Here,too,the
c
designisnotidealandtherotationratemustbe
reduced in APLN for improved proprotor effi
Helicopter Airplane
I ciency. However, tiltrotor hover efficiency is
Aftlongitudinal
cyclicpilch much better than almost all other VSTOL
designs. The presenceofthe wingtip nacelles
Elevator
also contributes considerable drag during
translation and conversion. So, a helicopter
performs betterthan the tiltrotor in hover and
translation, butcannotflyasfastincruise.The
airplane performs better in cruise, but cannot
Proprotordiscstiltaft Elevatordeflectsupward takeoffvertically. Thetiltrotoristhe epitome of
Aircraftassumesnose-upattitude Aircraftassumesnose-upaltitude engineeringcompromise.
Airspeeddecreases Altitudeincreases
Along-standing challenge intiltrotor design
Angleofattack(AOA)ismonitored
andlimited hasbeenavoidingrotor,pylon(combinedtilting
Airspeeddecreases nacelleandpowertransmission gearbox),and
structuralinstabilities.Theelasticresponsesof
the structure and rotor dynamics can interact
craft as the proprotor hub controls become yawing forcestoo greatfor conventional rotor withtheaerodynamicforcestoproducestruc
ineffectiveastiltangledecreases.Intermediate hubsorairplaneflightcontrolsurfacestoover tural oscillations that can grow to destructive
proprotor positions ('conversion mode', come.Thismeansitisbestthatatransmission magnitude.Allthesefactorschangewithflight
CONY)allowsforveryshortrollingtakeoffsand interconnect drive shaftthrough the wing join condition, fuel weight in the wing, nacelle
landingswithagreaterpayloadthanforaverti the engines, or at least the proprotors. like angle, blade flapping, and rpm, making for a
cal takeoff, provided ground clearanceforthe wise, the rotors or engines/rotor combination complex design problem. The tiltrotor wing is
rotorsismaintained.Thesystemcan alsopro musttiltinpreciseunisontoavoid lossofcon typicallythickforthe purposeofensuringsuit
vide advantageous thrust vectoring 'up and trol. This has usuallyrequired an additionaltilt ablestiffnessandaeroelasticstability. Yet, the
away'forenhancedmaneuverability. axis cross shaft orfail-safe electronic control. airframeandrotorsystemmustbelightweight.
With the proprotors placed far outboard of In APLN the proprotors rotated up on the The tiltrotor offers some unique VSTOL
the fuselage, excessive asymmetrical rotor lift inboard side, generating an air swirl opposite advantagesthatsupportitsclaimtobeing rev
or propeller thrust would generate rolling or the wingtip vortices. These vortices, common olutionary. The principal benefit is that the
8 V-22Osprey
enginesandthrust generation devicesforver
tical, STOL, conversion, and cruise flight are D
the same. It combines well understood heli
copterand airplanetechnologies. Thetiltrotor Helicopter Airplane
usuallyhasamoregenerousconversion corri Differentialcollective
~
dor. The high-speed end of the corridor is
defined by prohibitive rotor and nacelle/wing
interface loads. The low-speed boundary is
usuallydetelminedbywingstall.Thetiltrotoris
generallyeasiertostabilizethan otherconfigu
rations, especially during conversion and
reconversionwhereboththehelicopterandair LeftproprotorIncreases
colleclivepitch
planecontrolsareavailabletogreaterorlesser Leftflaperondeflectsdownward
Rightproprotordecreases
degrees as airspeed changes. Turn perfor collectivepitch Rightf1aperondeflectsupward
Proprotordiscstilttoright Aircraftrollstoright
manceacrossitsspeedrangeissuperiortothe
Aircraftrollstoright
helicopter.
Theairplaneconfigurationallowsthetiltrotor
tobeflown to altitudesfarabovethatofaheli
copter,ormorecomparablewithturbopropair upperwingsurfaceunderlyingtherotorsisthe Whenclosetotheground,thegroundwash
craft.Thisallowsflightaboveweatherwhereas oppositeofthatdesiredforlift, robbingtheair iscomparabletothatofaheavy lifthelicopter.
a helicopter would be grounded, forced to craftofpotential payloadcapacity.Theflowon When close to the ground the meeting ofthe
divert, or fly in adverse conditions under the the wing moves inboard, meeting and foun outwash from the opposite rotors under the
weather. The exterior noise during hover and taining up at the center to be recirculated centerlineoftheaircraftfountain uptoimpinge
transition is about that of a heavy helicopter through the rotorsforaloss in rotorlift. These on the fuselage bottom and add to lift force.
and much less noisy than nearly all other effects can be reduced with deployed flaps, Thisflowisalsodirectedforward andaftofthe
VSTOLdesigns. InAPLN thetiltrotorisquieter wing fences, and wing design choices. The aircraft, and can liftdustand other material to
than aturboprop aircraft by virtue of its lower leadingedge-to-trailingedgedirectionsofpro obscure vision, although peripheral vision
proprotortip speed, and onlyathree quarters protorrotation also reduces download. Asthe remains good.Theground plumecan recircu
thelevel ofahelicopter- and withoutthe dis aircraftbeginstomoveforwardtherotordown late and produce some loss of performance,
tinctive'whop'- enhancingmilitarycovertness. washis'blown'aftsuchthataslittleas20ktsis although the high engine inlets on tilted
Vibration levels in APLN, where the aircraft requiredtoSUbstantiallyreducedownload. nacellesmayreducethiseffect.Thejetexhaust
spends most of its time, is SUbstantially less Fuel, hydraulics, and electrical connections directlyimpingingonthegroundraisessurface
thaninVSTOL, reducingcomponentwearand must pass through the rotating nacelle inter andaircraftlowerextremitiesheatingconcerns.
failurerates. face that is an added maintenance burden However, the heating is much less than other
In the conversion to forward flight, flight at potentially impacting overall system reliability. VSTOLconceptsand,combinedwiththecom
intermediate nacelle angles, and approach to The wingtip nacelles increase aircraft roll and paratively low velocity proprotor downwash,
hoverthe tiltrotor's deck angle can be main yaw inertia, requiring more control power for represents an acceptably 'soft footprint'. Fur
tained level or at a nose-low attitude for some maneuvers in all flight modes. Con thermore, extended hovers at greater height
improved visibility. This is accomplished with versely, with the proprotors far removed from than comparable helicopters can helpamelio
thrustvectoringindependentofaircraftattitude the fuselage, considerable control power is ratesuchconcerns.
byusingcyclicoppositetheproprotortiltangle availableinVSTOL. Placingtheenginefarout One of the greatest flight safety concerns
(forexample,aftstickforaforwardtilt).Theheli boardsomewhatreducestherisktooccupants with the tiltrotor has been engine-out landing.
copter must raise its nose dramatically to fromenginefiresandturbinebursts. Forasingleenginefailure in atwin-enginetilt-
rapidlybleed speed in the approachto hover.
This is where the windows at the helicopter
pilot'sfeetbecomemostimportantinmaintain E Helicopler Airplane
Rudder
ingsightofthe landingzone.Thesameistrue Differentiallongitudinalcyclic
forthe acceleration to forward flight. The heli
copter must point its nose down, sometimes
considerably,toaffectarapidacceleration.The
proprotortilt also helps to make upslope and
downslope landings safer. The rotor disk can
be kept level to maximize longitudinal cyclic
authorityto handlegustsand unexpected dis
turbances, while the deck angle is made to
matchtheslope.
The principal penalties of the tiltrotor are
found in the weight and complexity of added
gearboxes, tilt mechanisms, and cross shaft
ing,all contributingto increased unitand sup
portcosts.Theissueoftherotordownwashor
download on the wing and fuselage in heli
copter mode is an endemic tiltrotor concern
and one of the primary hurdles to achieving
• Rightproprotordisctiltsforward • Ruddersdeflecttotheleft
good hover performance. A reduction of just
• Leftproprotordiscliltsaft • Aircraftyawsleft
1%indownloadcanadd500lb(225kg)ofpay • Aircraftyawsleft
load.Theoutflowoftherotorsimpingingonthe
V-22Osprey 9