民用飞机设计1415

AircraftSchoolofAeronauticsandAstronauticsShanghaiJiaoTongUniversityOverviewof RefinedweightThrust/WeightratioandwingLandinggearandAircraftPowerStabilityandLoads,materialsandstructures14\15Performance(a,b)AviationMilitaryaircraftdesign–DesignAdvanceddesigntopics(flighttests,retrofit,RoleofperformanceBasicconceptsandPerformanceanalysisfordifferentsegmentsinatypicalflightmission,includingTakeoffSteadylevelSteadyclimbinganddescendingLevelturningGlidingLandingAircraftperformanceanalysistreataircraftasapointmass,notarigidbodyasisdoneinaircraftstabilityAircraftperformancecalculationformsanimportantpartofconceptualdesign,whichlinksdesignparameterswithperformancerequirementsAerodynamicAerodynamicEngineRoleofPerformanceThroughouttheaircraftlifecyclefrommanufacture,flighttesttoProjectdesignstage→requirementanalysis,enginedata(thrust,SFC),etcDetaileddesign→windtunneldata,CFD,CADdrawings,certificationdata,operationalmanual,flighttestplanManufacture→validationofdesign,fullsetoftechnicalmanualsFlighttests→Crossvalidationwithwindtunneldata,certificatedocuments,faultanalysisInputs/OutputsforPerformanceCalculationsAerodynamicforcesfromengineeringestimationmethods/CFD/wingtunneldataEnginedatafromengineWeightestimationincludingC.G.locationsfrominitialsizingTakeoffandinitialClimbtooperatingApproachandPayloadrangeBasicBasicConcepts–𝑉𝐺:Groundspeed,theaircraftspeedrelativetotheground.ItcalculatedfromTASandwindspeedFortakeoffandlanding,headwindtakeForclimb,cruise,anddescend,headwindtake----Groundspeed,trueairspeedand AirspeedasafunctionofBasicConcepts– In±±𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡𝐶𝐴𝑆= ±𝑖𝑛𝑠𝑡𝑎𝑙𝑙𝑎𝑡𝑖𝑜𝑛±𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛𝑉𝑉𝐸≡𝐶𝐴𝑆−𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑏𝑖𝑙𝑖𝑡𝑦𝑇𝐴𝑆BasicConcepts–(Geometry)altitude(𝐻)–theabsolutealtitudeaboveseaPressurealtitude(𝐻𝑃),theISA(geometry)altitudewiththesamepressurelevelForahotday,lowerthangeometryForcoldday,higherthangeometry𝑯=𝐻=𝐻𝑃−𝐻=𝐻𝑃−𝑯=

1−2.25577× 𝑚1−6.87559× 𝐻𝐻

11

𝐻𝑃−𝐻𝑃BasicEquationsofXd,Yd, yrxzBasicEquationsofMotionEquationsofmotioninflightpathcoordinateBody γDHorizontal TypicalFlightProfileofaCivilJet

10000

15001500

M= 20000

爬 爬 巡

进场与滑降

轮档时间Take-offTakeoffVs:stallspeed(intake-offV1:criticalpowerfailureVR:rotationspeed,thiscanequalVmu:minimumunstickspeed,VRmaynotbesufficienttoliftoffduetolimitonrotationangleVLOF:lift-offspeed,theaircraftbecomesV2:take-offclimbspeed,achievedat35ftscreenTake-off Availabletake-offTake-offOptionswithEngineTake-off-allenginesoperatingTDMdVdt RMgTD(MgTake-off-allenginesoperatingGroundrolldistancecanbecomputedbyApproximationcanbeassumedT

5 5VWstatic40.020.01cL,max,t

DW

𝜆isBPRoftheturbofanTake-offallenginesoperatingTransitionflightTake-off-allenginesoperating TransitiontoAircraftacceleratefromVLOFtoSimpleestimationcanbemadebyassumingFlyingalonganLMgcosMV rV

/[g(n ScreenheightTake-offDistance-allenginesoperating(IV)Take-offdistance-allenginesoperating(V)ClimbaftertransitiontoscreenClimbdistance:thegrounddistancefromtheendoftransitiontothescreenheightwhere,htistheheightattheendoftransition,γcisthebestclimbangleTotaldistancefortake-offisthesumofgroundroll,transition,andclimbdistanceTake-offdistance–withoneenginefailedBalancedfieldDefinition:thefieldlengthwhen“accelerate-go”distanceisequaltothe“accelerate-stop”SteadyClimb&DescendTypicalClimbProfileandZ0

constantMachnumberairspeedclimbairspeedclimb ClimbcarriedoutmainlyatconstantequivalentairspeedInitialClimbto1500ftafterTakeoffInitialclimbistypicallydividedintofourAirworthinessdemandscertainclimbgradientwithoneenginefailurefortwinengineorfourengineaircraft–refertocertificationcodeTake-offclimbperformanceisusuallydefinedbysecondsegmentperformancerequirementwhichisthemostcriticalInitialClimbto1500ftafterTakeoffClimbrate(verticalvelocity)canbeobtainedbyanalyzing WTherefore,theclimbrateisrelatedtothrust,drag,andweightoftheaircraftThrustis85%ofthestaticDragofthebasicTheasymmetricdragduetoafailedwindmilldrag,Additionaltrimdrag,5%ofthebasicprofileClimbPerformance:furtherGivenaclimb

=𝑐𝑜𝑠𝜃+𝑠𝑖𝑛𝜃≅1+

𝑉 BestrateofclimbandBestangleofBestrateofclimbprovidesthemaxclimbBestangleofclimbprovidesthemaxclimbTimetoclimbandfueltoTimetoclimeacertaindistanceandcorrespondingfuelusedcanbecalculatedas𝑑𝑡

𝑑𝑊𝑓=Integrationorapproximationcanbeusedtocalculatefrom𝑡1toSteadyLevelEquationsforLevelLαLαVDHorizontal TW RateofchangeofaircraftT=D+Wsinγ=DL=Wcosγ=W

dW

SteadyLevelCruiseAnalysisforunacceleratinglevel

𝑇=𝐷= 𝐿=𝑊= 𝑉 and

=

=

TheseequationscanbeusedinfurtherMinimumcruisethrustrequirementforjetMinimumcruisepowerrequirementforpropellerThrustrequiredforlevelflightjetMinimumthrustforgivenaircraftweightcanbefoundfrom

𝜕 =𝜌𝑉𝐶𝐷0− = 𝑆12𝑉min𝑡ℎ𝑟𝑢𝑠𝑡 and𝐶𝐿𝑚𝑖𝑛𝑡ℎ𝑟𝑢𝑠𝑡AtAtanygivenweight,theaircraftcanbeflownattheoptimalliftcoefficientforminimumdragbyvaryingvelocityorairdensityQuestionQuestionone:WhatisformulafortotalThrustrequiredforlevelflightpropellerMinimumpowerrequiredforpropelleraircraftcanbederivedbyfirstcalculatethepower𝑃=𝐷𝑉= 𝜌𝑉3𝑆𝐶𝐷0+

𝑉 2 2Similartothederivationonprevious

22 𝜌𝑉2𝑆𝐶𝐷0− =22

𝜌𝑉2= and=Questionone:WhatisformulafortotalQuestionQuestiontwo:Willthetotaldragbehigherthanflyingatminthrust?CalculationsonprevioustwoslidesareCalculationsonprevioustwoslidesarebasedontwoassumptions𝐶𝐷0and𝐾areconstantwith𝑉BreguetRangeRateofweight dW

SFCTSFCDWsin

SFC

SFC

L dW

R L aML R dx0

SFC1

<<1,becauseBreguetEquations-DuringSFCremainsroughlyconstant(0.5ConstantL/DalsoroughlyCruisingintropopause,a= W2aMLD WR dx

RaMLD 1

2PayloadRange Rangeisrelatedtofuel/weightaML

W aML

WFR

logW2

log1W 1

1MaximumMaximumMaximumfuel MaximumtakeoffRangeMoreAnalysison Minimumthrustlevel= and=𝐷=𝑞𝑆 + =𝑞𝑆 +Minimumpowerlevel= and=𝐷=𝑞𝑆 + =𝑞𝑆 +Thevelocityforminimumpoweris~0.76timesthevelocityforminimumthrustcruise,whileliftcoefficientis~73%higherThevelocityforminimumpoweris~0.76timesthevelocityforminimumthrustcruise,whileliftcoefficientis~73%higherforminimumpowerflight.Buttotaldragforminpowerisnottwicethatformindrag!LevelTurningAnalysisofLevel Turningrateorrateofturning(ROT)DefinedasradialaccelerationdividedbythevelocityAngularForceVerticalliftcomponentequalsLoadfactorisThereforeturning= =𝜓 𝑔 AnalysisofLevelTurningTurning𝑅

–SmallerVandhighergivessmallerTwotypesofturning,dependsontimeperiodInstantaneous,forshortperiodoftimeSustainedturning,foranextendedperiodoftimeInstantaneousInstantaneousturn–aircraftisallowedtoslowdownduringtheturnTheloadfactor𝑛willonlybelimitedbythemaximumliftcoefficient(stall)orstructuralstrengthCornerspeedisimportantfordogfightDragisgreaterthanthrusthigherthanInsustainedturning,theaircraftisnotallowedtoslowdownorlosealtitude,whichimpliesthat𝑇=𝐷and𝐿=𝑇=𝐷=

with𝐶𝐿

tosolvethisasKandnarebothfunctionsoftheCLtosolvethisasKandnarebothfunctionsoftheCL−−ThisgivestheloadfactorSustainedTurningInasustainedturninggivenflightconditions(speed,altitude,payload),nMaximumnMaximumncanbeachievedwithminFromminimumdraglevelflightanalysis,there𝑉min and𝐶𝐿𝑚𝑖𝑛 Themaximumsustained-turnloadfactorcanbesolved𝐿=𝑛𝑊=

𝜓

𝑛=

GlidingStraightGliding ConditionsforstraightglidingThethrustissettoThedirectionoftheglidingangleis𝐷= 𝐿= =ctan𝛾 HorizontalαGlideGlideratioisdefinedastheratiobetweenhorizontaldistancetravelledandaltitudelostGlideratioisequaltothelift-to-dragMaxglideratiogivesthemaximumrangeforglidingflight,thereforerequiresflyingatmaxL/D–minCD𝑉min and𝐶𝐿𝑚𝑖𝑛 SinkAnotherparametersofinterestforglidingDeterminethetimethataglidermayremaininthe𝑊2cos3𝑊2cos3𝑣=Vsinγ=sin 𝑆𝑆Minimumsinkratecanbeobtainedbyminimizing whichleadsinin=3=00SinkRateandGlide DifferencebetweensinkrateandglideLandingApproachandLandingThelandingphaseissplitintoseveralGroundLandingdistanceisthesumofdistancesrequired Theapproachpathistypicallymadeat3°totheFARcertificationspecifiestheapproachstartsatascreenheightof50ftandendsattheflareheighthFApproachspeedisSAobstacleheighthF/tanhFrAA/Flare–AirAsimplifiedapproachassumesthattheangularaccelerationmaybeignoredTT–D+Wγ=mVdV/dx=(W/2g)dV2/dxL–W=0SaSa=[(W/S)l/(4gρslбCL,lmax)]/[–(D/L)eff+RotationtoTouchGroundRunlOnthesimplestlevel,assumingconstantdeceleration(-a),thedistancecoveredfromVl2to0is V2/2alOnthenextddV/dt=(1/2g)dV2/dx=(T/W)l–(D/W)l–((D/W)l((Fbrake/W)l=mbrake(1-L/W)=mbrake[1–GrounddistancecanbecomputedfromOtherAircraftPerformanceCommonsetofperformanceTurnrate,cornerspeed,loadfactorOtherperformancemeasuresofControlspeedandaltitudePoststallbehavior,60-degreeAOAoperations,forexamplearetypicalfor4thgenerationfightersPerformancewithThrustStoreDynamicMostImportantAircraftPerformanceCharacteristicsCapabilitiesofaircraftcanbemostlyrepresentedMaximumStallingBestingclimbingBestglideRateofMa