毕业设计论文方案论证报告提要.doc

毕业设计论文方案论证报告提要.doc

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Toascertaintheperformancecapabilitiesoftheprototypedevelopmenthardwareunderthenewtwo-fail/operaterequirements,theBA609FlightControlsIPTinitiatedaprogramofpilot-in-the-looptestingofactuatorfailuremodes.ThesetestscomprisedpilotevaluationsofBA609flightcontrolsystemhandlingqualitiesfollowingtheoccurrences:

•Dualelectricalsystemfailures.

•Dualelectricalcomponentfailures.

•Dualhydraulicsystemfailures.

•Dualhydrauliccomponentfailures.

•Singleelectricalsystemcombinedwithsinglehydraulicsystemfailures.

•Singleelectricalcomponentcombinedwithsinglehydraulicsystemfailures.

•Singleelectricalsystemcombinedwithsinglehydrauliccomponentfailures.

•Singleelectricalcomponentcombinedwithsinglehydrauliccomponentfailures.

Foreachtestcondition,theworstcasesystemorcomponentfailuremodewaseitherinitiatedorsimulated.ForEHSVfailures,secondstagespoolswerefailedhard-overinbothdirections,aswellasatnullposition,causingthecylindertohydraulicallylock.Solenoidswerefailedbothopenandclosed.LVDTswereshortedandcoresweresimulatedtostructurallyfail.Bypass,pressurerelief,anddeltapressuresensorhydraulicspoolsweresimulatedtobestuckinanyposition,andtheirspringsweresimulatedasfailed.Foranycomponentwhoseproperfunctioningcouldnotvalidatedeitherinflightorduringpreflightbuilt-intesting（PFBIT）,thecomponentwasconsideredtobeanexistingdormantfailure.BecausetheBA609isatiltrotoraircraft,ithasthreedifferentmodesofflight:

airplane,conversion,andhelicopter.Asaresult,testingofeachrelevantfailuremodeconditionineachofthethreeflightmodeswasrequired.

OneareainwhichtheVMSILtestingwasnotrepresentativeoftheactualaircraftwasthestructuralstrengthofthesimulatedflaperonandelevatorsurfaces.Althoughtheflaperonandelevatoractuatortestrigshadbeenmodifiedtorepresenttheaircraftstructuralstiffness,itwasimpracticaltosimulateactualaircraftstructuralstrengthwiththetestrigs.Therefore,actuatorloadsweremonitoredduringtestingtodetermineifacceptablestructuralloadswereexceeded.

BasedonVMSILpilot-in-the-loopevaluations,testdatafromthefailuremodetesting,andarevisedfailuremodeanalysis,itwasconcludedthatallactuatorinstallations（collective,longitudinal,flaperon,andelevator）oftheprototypedevelopmentactuatordesignprovidedunacceptableperformancefortheproductionBA609aircraft.Dualfailuremodetestingrevealedacriticalfailuremodecombinationthatimpactedallprototypedevelopmentactuatorinstallations.TheBA609hydraulicsystemarchitecture,utilizingthreehydrauliccylinderstoactuateeachflightcontrol,placesauniqueimportanceontheproperfunctioningoftheprototypemanifoldbidirectionalpressurereliefvalve（PRV）.ProperoperationofthePRVbecomescriticalforfailuremodesthatresultinblockageofthecylinderports（evenmomentarily）,suchasanEHSVand/orbypassvalvefailure.FunctionalintegrityoftheprototypePRV,however,couldnotbeverifiedontheaircraft,leadingtoapotentialdormantfailure.Figure15comparesthepotentialactuatorinternalpressuresgeneratedbyablockedcylinderportfortheconventionaltwo-cylinderarchitectureandtheBA609threecylinderarchitecture.Botharchitecturesillustratedrepresentfly-by-wiresystemsusing3,000psisystempressure,equalextend-and-retractcylinderpistonareas,andanexternalairloadequivalentto50%ofstallofonecylinder.

Withaconventionaltwo-cylinderhydraulicarchitecture,ablockedcylinderportcangenerate4,500psiinternalhydraulicpressure.Thehydrauliccomponentproofpressure（asdefinedinbothARP-5440andinFARPart27）requireshydrauliccylinderstowithstand150%ofoperatingpressure（4,500psi）withnoevidencematerialyielding.Therefore,theeffectofablockedcylinderporthasminimalimpactonstructuralsizing.

WiththeBA609three-cylinderarchitecture,ablockedcylinderportcangenerate7,500psiinternalhydraulicpressure.Thisdual-failure-modegeneratedpressurenotonlyexceedsthe150%ofoperatingpressurestandard,butitalsoreachesthelimitoftherecommendedcylinderburstpressure（250%ofoperatingpressure）.Theeffectofablockedcylinderportforthisconditionismoredetrimentalintheflaperonandelevatoractuatorscylinders,duetotheirunequalextendend-retractpistonareas,whichamplifyinternalpressureto8,955psiand9,676psi,respectively.Therefore,topreventdamagefromoccurringeithertoanactuatorortheaircraftstructurefromablockedcylinderport,eithertheactuatorsortheaircraftstructureneedstobesizedtowithstandthehigherresultingpressuresandloads,orareliablePRVmustbeincorporatedintoeachactuatormanifold.

Pilot-in-the-loopVMSILtestingalsorevealedthatalthoughalltheactuatorssharedacommonprototypemanifolddesign,theimpacttotheaircrafthandlingqualitieswasverydifferentwhenthesamefailuremodecombinationswereappliedtodifferentactuators.Degradationofaircrafthandlingqualitiesresultingfromfailuremodesinducedinthelongitudinalorcollectiverotorcontrolactuatorswereofgreaterseveritythanfortheelevatorandflapperonfixed-wingcontrolactuators.Thiswasinpartduetothecapabilityoftheleftflaperon,rightflaperon,andelevatorcontrolsurfacestoaerodynamicallycompensateforthelossinperformanceofanyoneofthethreesurfaces.Inairplaneandconversionflightmodes,undesiredrollfromasloworjammedflaperonsurfacecanbecompensatedbytheoppositeflapperon.Uncommondedpitchfromasloworjammedelevatorcanbecompensatedbythepilot’smanualoperationoftheflapperonsurfaceflappositioncontrol.

Othermajorfactorsinfluencingtheactuatorsfailuremodeperformancedegradationwerethemarginofactuatorstallloadoverflightloadsandactuatorcylinderconfiguration（triplexversussimplex）.Theimpactofthesefactorsbecameespeciallyapparentwhenevaluatingtheprototypemanifold’sperformancewithdualfailuresthatincludedfailureofthesolenoid-controlledbypassvalve.Combinedwithotherprobablefailures（FCC,wiring,EHSV）,somebypassvalvefailurecasesrequirethetwounaffectedcylindersontheflightcontroltofightagainstthefailedcylinder.ThemagnitudeofthisforcefightconditionwasdependentonthefailedpositionoftheEHSVsecondstagespool.Loadsrangedfrom100%ofcylinderstallload,iftheEHSVfailedoffitsnullposition,to150%ofstallload（PRVopeningsetting）,iftheEHSVfailedatnull,blockingthecylinderports.

Underthesefailuremodecombinations,thesimplexactuatorflaperonandelevatorsurfacessufferareductioninflightcontrolloadcapacityequaltotheforcefightloadimpartedbythefailedcylinder.Frompilot-in-the-loopsimulationitwasconcludedthat,fortheflaperonandelevatorsurfaces,thesefailuremodeswererecoverable.Withtherigidlyjoinedthree-cylindertriplexcollectiveandlongitudinalflightcontrolactuators,however,thesefailuremodesareconsiderablyworse.Forcefightloadsbetweenthecylindersbentthepistonrods,inducinglargefrictionforcesthatreducedflightcontrolloadcapacityevenfurther.Inthecaseofthecollectivecontrolthathasasmallmarginofactuatorstallloadoverflightloads（15%）,thisfailuremoderenderedtheactuatorinoperable.Forthelongitudinalcontrolthathasalargemarginofactuatorstallloadoverflightloads（400%）,thisfailuremodewasrecoverablebutwithextremedifficultybythepilot.

Thehighsusceptibilityofthecollectiveactuatortoperformancedegradationfromforcefightloadswasevenapparentduringteststhatsimulateddualfailuremodesthatincludedthedeltapressuresensor.Intestssimulatingworst-casedeltapressuresensorfalsereadings,frictionresultingfromforcefightloadsseverelyreducedthecollectiveactuatorfrequencyresponseandpositioncontrolaccuracy.Bothfrequencyresponseandpositioncontrolarecriticaltothecollectiveactuators’capabilitytofunctionproperlyasarudderinairplanemodeandminimizeloadsinthedrivetrainconnectingtheproprotorgearboxes.ComplicatingthisfailuremodefurtherwastheinabilitytopositivelyverifytheintegrityofthedeltapressuretransducerduringPFBIT.IthadbeenplannedtousetheprototypedevelopmentmanifoldPFBITconcepttoverifycollectivedeltapressuretransduceraccuracybyinitiatingacontrolledforcefightbetweenthetriplexcylinders,inordertoprovideacrossreferencewithrotorsturning（noAPU）.However,frictionalloadsgeneratedfromcollectivecylinderforcefightsmadetheconceptimpractical.Theramificationsofasinglecollectivedeltapressuretransducerfailureweredeterminedtobeunacceptableformeetingbothhandlingqualitiesandfatigueloadsrequirements.