課件-1教案第5章

Stabilityand5.1Balanceand1,balanceinstraightandlevel woodenbean木梁 suspendedbean懸吊梁fulcrum control rudder 方向舵腳align,alignmentBalanceconsistsoftwoelements-thetotalforcesactingtheaircraftandthealignmentoftheseforces.Whentheforcesarebalancedandalignedtheaircraftissaidtobeinequilibrium.Therearetwotypesofforces-staticforces,dynamicWeightisastaticforceitcanbeconsideredconstantatanyThrustvarieswithenginepower,propellerrpmandairspeedbutcanbesetataconstantvaluebythepilot.Liftisaerodynamicforcewhichchangeswithairspeedandflapextensionbutwhichcanbecontrolleddirectlybythepilotchangingtheangleofattack.Dragchangeswithangleofattack,configurationandInstraightandlevelflight,liftopposesweightL=WthrustopposesdragT=D.Theliftandweightwillonlydecreasegraduallyastheweightdecreaseswithfuelburn-off.Thethrustanddragwillvaryconsiderablydependingonangleofattackandthereforeairspeed.2,pitchingUndermostconditionsofflighttheCPandCGarenoti.e.arenotattheonepoint,causingnose-downpitchingmomentoranose-uppitchingmoment.Thedifferentlinesofactionofthethrustforceanddragproduceanothercouple,causinganose-downpitchingmomentoranose-uppitchingmoment.Ideallythepitchingmomentfromthetwocouplesshouldneutralizeeachotherinlevelflightsothatthereisnoresultantmomenttendingtorotatetheaircraft3,thehorizontalstabilizer counteract平衡,中和 Thefunctionoftailplane（orhorizontalstabilizer）istocounteracttheseresidualpitchingmomentsfromthetwomaincouplesanddampedanyoscillationinpitch,i.e.ithasastabilizingThetailplaneusuallyhasasymmetricaloranegativelycamberedThemomentproducedbythetailplanecanbevariedbyeitherbymovingtheelevatororbymovingtheentiretailplane.Themomentarmoftailplaneisquitelong,andtheforceprovidedbythetailplaneneedsonlytobesmalltohasasignificantpitchingeffect.Theareaofthetailplaneissmallcomparedwiththe（mainTherearetwoelementsofstability,staticanddynamic,andforanaircraft,itisusualtoseparatethemodesintothethreeaxesofThereislongitudinalstability,lateralstabilityanddirectionalThereisaninseparablerelationshipbetweenlateralanddirectionalstability.Staticstabilityanddynamic1,StaticThestaticstabilityoftheaeroplanedescribesitstendencytoreturnitsoriginalcondition（angleofattack）afterbeingandwithoutanyactionbeingtakenbythepilot.Thestrengthofthetendencyisthemeasureofitsstability.2,Dynamic 取消,去除dead 非周期的,無振蕩 y無限 發(fā)shortperiod短周期,longperiod,phugoid長周Dynamicstabilityisconcernedwiththemotionofthebodyafterthedisturbingforcehasbeenremoved.Itisanoscillationwhichmaystop y（well-dampedbeatcontinue（ightlydamped，continueindefini （undampedorwors（dynamcallyordivergentoscillation）.Imaginetheaircraftistrimmedinstraightandlevelflight,theaircraftwillrespondtotheverticalgustbypitchingdowntomaintainitstrimmedangleofattack.Thisoscillationisgenerallywell-dampedandreducestozeroin1or2oscillation.Thedamisprovidedbytheaironthehorizontalareaoftheaircraft.ThepitchingoscillationisknownastheperiodpitchingTheairspeedoftheaircraftmayalsochangeandthiscancauseslower（longperiod）oscillationwheretheaircraftleisurely（慢慢地）followsapathwheretheairspeedandaltitudeareexchanged.Theslowmotioniscalledthephugoid.3,thethreereferenceWerefer（歸類）themotionoftheaircrafttomotionabouteachofthreeaxes-eachpassingthroughthecentreofgravityandeachmutuallyperpendicular（at90otoeachotherThesearecalledbodyStabilityaroundthelongitudinalaxisisknownaslateralstability.Stabilityaroundthelateralaxisisknownaslongitudinalstability.Stabilityaroundthenormalaxisisknownasdirectionalstability.Rotationaroundapointoraxisiscalledangularmotion;thenumberofdegreesofrotationiscalledangulardisplacement,andthespeedwithwhichitoccurs,angularvelocity.Themotionofanaircraftisbestconsideredineachoftheseparay,althoughtheactualmotionoftheaircraftisalittlemorecomplex.Forexample,rollingintoalevelturntheaircraftwillnotonlyrollbutalsopitchandyaw.Wewillconsiderlongitudinalstabilityfirst,thendirectionalstabilityandlateralstability.Rollandyawarecloselyconnected.Longitudinalinbuilt固有的,內(nèi)在的,dart飛鏢,arrowTobelongitudinalstable,anaircraftmusthaveanaturalorinbuilttendencytoreturntothesameangleofattackafteranydisturbancewithoutanycontrolinputbythepilot.Iftheangleofattackissuddenlyincreasedbyadisturbance,thenforcewillbeproducedthatwilllowerthenoseanddecreasetheangleofattack.1，thetailplaneandlongitudinalIfadisturbance,suchasagust,changestheattitudeoftheaircraftbypitchingitnoseup,thetailplanewillbepresentedtotherelativeairflowatagreaterangleofattack.Thiswillcausethetailplanetoproduceupward,ordecreased,aerodynamicforce,whichisdifferenttothatbeforethedisturbance.Thealteredaerodynamicforcegivesanose-downpitchingmoment,tendingtoreturntheaeroplanetoitsoriginaltrimmedcondition.Example：thetailfinofadartoran2，theCGandlongitudinalThefurtherforwardtheCGoftheaircraft,thegreaterthemomentarmforthetailplane,andthereforethegreatertheturningeffectofthetailplaneliftforce.AforwardCGleadstoincreasedlongitudinalstabilityandaftmovementoftheCGleadstoreducedlongitudinalstability.Themorestabletheairplane,thegreaterthecontrolforcethatyoumustexerttocontrolormovetheairplaneinmanoeuvers,whicheThetailplaneprovidesstaticlongitudinal3，designTailplanedesignfeaturesalsocontributegreatlytolongitudinalstability-tailplanearea,distancefromthecentreofgravity,aspectratio,angleofincidenceandlongitudinaldihedralareconsideredbythedesigner.Athighangleofattackthemainplanemayshieldthetailplaneorcausetheairflowoverittobeturbulent.Thiswilldecreaselongitudinalstability.DirectionalDirectionalstabilityofanaeroplaneisitsnaturalorinbuiltabilitytorecoverfromadisturbanceinyawingplanewithoutanycontrolinputbythepilotIftheaircraftisdisturbedfromitsstraightpathbythenoseorbeingpushedtooneside（i.e.Theverticalfin（ortailorverticalstabilizer）issimplyasymmetricalaerofoil.Asitisnowexperiencinganangleofattack,willgenerateasidewaysaerodynamicforcewhichtendstotakethefinbacktoitsoriginalposition.momenteffectoflargeareaandthelengthofitsmomentarmbetweenitandcentreofgravity,iswhatrestoresthenosetoitsoriginalposition.ThegreaterthefinareaandkeelsurfaceareabehindtheCG,thegreaterthemomentarm,thegreaterthedirectionalstabilityoftheaeroplane.ThefinprovidesdirectionalstaticAstheyawcausesrollingmomentsothatbehavioroftheaircraftwithyawandsideslipinvolvesbothitsdirectionalstabilityanditslateralstability.LateralLateralstabilityisthenaturalorinbuiltabilityoftheaeroplanetorecoverfromadisturbanceinthelateralplane,i.e.rollingaboutthelongitudinalaxiswithoutanycontrolinputbythepilot.Adisturbanceinrollwillcauseonewingtodropandtheothertorise.Whentheaeroplaneisbanked,theliftvectorisinclinedandproducesasideslipintotheturn.Asaresultofthissideslip,theaeroplaneissubjectedtoasidewayscomponentofrelativeairflow.Thisgeneratesforcesthatproducesarollingmomenttorestoretheaeroplanetoitswings-levelposition.1，wingdihedralEachwingisinclinedupwardsfromthefuselagetothewingtip,andaddstothelateralstabilitycharacteristicsoftheaeroplane.PositivewingdihedralincreaseslateralAstheaircraftsideslips,thelowerwing,duetoitsdihedral,willmeetthe ingrelativeairflowatagreaterangleofattackandwillproduceincreasedlift.Theupperwingwillmeettherelativeairflowatalowerangleofattackandwillthereforeproducelesslift.Itmaybeshieldedsomewhatbythefuselage,causinganevenlowerlifttobeTherollingmomentsoproducedwilltendtoreturntheaircrafttoitsoriginalwings-levelposition.Negativedihedral,oranhedralhasadestabilizingeffect.Insomeaircraftwithahigh-mountedsweepwing,anhedralisusedtocompensateforexcessivelateralstability.2，wingThewingcanaddtolateralstabilityifithassweepback.Astheaircraftsideslipsfollowingadisturbanceinroll,thelowersweepbackwinggeneratesmoreliftthantheupperwing.Thisisbecauseinthesideslipthelowerwingpresentsmoreofitsspantotheairflowandhighervelocitythantheupperwingandthereforethelowerwinggeneratesmoreliftandtendstorestoretheaeroplanetoawing-levelposition.3，highkeelsurfacesandlowInthesideslipthatfollowsadisturbanceinroll,ahighdraglinecausedbyhighkeelsurfaces（highfin,aT-tailhighonthefin,highwings,etc.）andalowCGwillgivearestoringtendingtoraisethelowerwingandreturntheaircrafttotheoriginalwings-levelposition.4，high-wingIfagustcausesawingtodrop,theliftforceistilted.Theresultantforceswillcausetheaircrafttosideslip.Theairflowstrikingtheupperkeelsurfaceswilltendtoreturntheaircrafttothewings-levelAhigh-wingaroplaneincreaseslateralstability,ithaslesscomparedtoamid-or–lowwing5，lateralanddirectionalstabilityrollfollowedby Forlateralstability,itisessentialtohavethesideslipthatthedisturbanceinrollcauses.Thesideslipexertsaforceonthesideorkeelsurfacesofaircraft,which,iftheaircraftisdirectionallystable,willcauseittoyawitsnoseintotherelativeairflow.Therollhascausedayawinthedirectionofthesideslipandtheaeroplanewillturnfurtheroffitsoriginalheadinginthedirectionofthelowerwing.Thelateralstabilitycharacteristicsoftheaeroplane,suchasdihedral,causethelowerwingtoproduceincreasedliftandtoreturntheaircrafttothewings-levelposition.Therearetwoeffects Thedirectionallystablecharacteristics（largefin）wanttosteepentheturnanddropthenosefurther.Thelaterallystablecharacteristics（dihedral）wanttolevelthespiralmode螺旋模態(tài),Dutchrollright矯正,best極力,wallowIfthefirsteffectwinsout,i.e.strongdirectionalstabilityandweakstabilit（largedihedral,tobankfurtherintothesideslip,towardsthelowerwingwithnosecontinuingtodrop,untiltheaeroplaneisinaspiraldive.Thisiscalledspiralinstability,orthespiralmode.Ifthelateralstability（dihedral）isstronger,theaircraftwillitselftowings-level,andifthedirectionalstabilityisweak（smallfin）theaircraftmayshownotendencytoturninthedirectionsideslip,andcausingthewallowingeffect,Dutchroll,whichisbestyawfollowedby Iftheaircraftisdisplacedinyaw,itiscancausesideslip.Thissideslipwillcausethelateralstabilitycharacteristicsoftheaircraft’swing,suchasdihedral,sweepbackorhigh-wing.Thiscausesarollingmomentthatwilltendtoraisetheforwardwing,resultingintheaircraftrollingtowardsthetrailingwingandawayfromthetoweathercockoryawtheaircraftinthedirectionofstabilitycharacteristicsandaeroplaneIfthedirectionalstabilityispoor（smallfin）andthelateralstabilityisgood（dihedral）itcancauseDutchroll（rolling/yawingoscillation）.Oftentheaircraftisfittedwithayawand/orrolldamper（asmallcontrolsurfacedrivenbyarategyro）tostoptheoscillation.Itis fortableforthepilotandpassengers.Ifthedirectionalspiralisdominant（largefin）andthelateralstabilitynotsostrong,itcancausespiralinstabilityorspiralmode.rategyro阻尼陀螺,dominant6,Stabilityonthetipover groundloop地轉(zhuǎn) 空轉(zhuǎn), brake Thecentreofgravity（CG）mustliesomewhereinthebetweenthewheelsatalltimesontheground,otherwiseaeroplnewilltipover-forwardsorThecontrolsurfacesarethemeansbywhichthepilot thestaticstabilityoftheaircraftandcausesachangeinflightpathorachangeintrimmedconditions.Usuallytherearethreesetsofprimarycontrolsystemandthreesetsofcontrolsurfaces：theelevatorforlongitudinalcontrolandbalanceinpitch,operatedbyforeandaftmovementofthecontrolwheelorcolumn; theaileronsforlateralcontrolandbalanceinroll,operatedbyrotationofthecontrolwheelorsidewaysmovementofthecontroltherudderfordirectionalcontrolandbalanceinyaw，operatedtherudderIdeallyeachsetofcontrolsurfacesshouldproduceamomentaboutonlyoneaxisbut,inpractice,momentsaboutotheraxesareoftenproducedaswell,e.g.ailerondeflectiontostartarollmayalsocauseadverseyaw.Thedeflectionofthecontrolsurfaceschangestheairflowandthepressuredistributionoverthewholeaerofoilandnotjustoverthecontrolsurfaceitself.Theeffectistochangetheliftproducedbythetotalaerofoil-controlsurfacecombination.Anaeroplanewithtoomuchstabilitydesignedintoithaslimitedcontrollability.Thedesignermustachieveareasonablebalancebetweenstabilityandcontrollability.Forinstance,apassengeraircraftwouldrequiremorewhereasafighterwouldbenefitfromgreatercontrollabilityandPitchTheprimarycontrolofangleofattackistheThepilotmovestheelevatorbyfore-and-aftmovementofthecontrolcolumn.Whenthecontrolcolumnismovedforward,theelevatorsmovedownwards,changingtheoverallshapeofthetailplane-elevatoraerofoilsectionsothatitprovidesanalteredaerodynamicforce.TheeffectistocreateapitchingmomentabouttheCGoftheaircraftthatmovesthenosedown.Whenthecontrolcolumnispulledback,theelevatormovesupandanalteredforceisproducedbytailplane-elevatoraerofoil,causingthenoseoftheaircrafttopitchup.ThestrengthofthetailmomentdependsontheforceitandthelengthofthearmbetweenitandtheCG.Theforcegeneratedbythetailplane-elevatorcombinationdependsontheirrelativesizeandshape,thetailplanebasicallycontributingtostabilityandtheelevatortocontrol.Thelargertherelativesizeoftheelevator,themoretheToretainsatisfactoryhandlingcharacteristicsandelevatoreffectivenessthroughoutthedesiredspeedrange,thepositionoftheCGmustbekeptwithintheprescribedrange.TheforwardallowablelimitoftheCGisdeterminedbytheamountofpitchcontrolavailablefromtheelevator.TheaftlimitoftheCGisdeterminedbytherequirementofadequatelongitudinalstability.Steadyflightatalowspeedandahighangleofattackwillrequiresignificantup-elevator,andbackwardpressureonthecontrolcolumn,tokeepthenoseup.Atahighcruisespeedtherewillneedtobeasteadydowndeflectionoftheelevatortokeepthenosedownandmaintainalowangleofattack,henceasteadyforwardpressureonthecontrol2，Thestabilatororall-flyingSomedesignerschoosetocombinethetailplaneandelevatorintotheonesurfaceandhavethewholetail-planemovable-knownastheallmovingtail,theflyingtailortheslabtail.Whenthecontrolcolumnismovedtheentire‘slab’RollTheprimarycontrolinrollistheailerons.Theaileronsareusuallypositionedontheoutboardtrailingedgeofthemainplanes.Theaileronsactinopposingsenses,onegoesupastheothergoesdown,sothattheliftgeneratedbyonewingincreasesandtheliftgeneratedbytheotherwingdecreases.AresultantrollingmomentisexertedontheThemagnitudeofthisrollingmomentdependsonthemomentarmandthemagnitudeofthedifferingliftforces.ThedowngoingaileronisontheupgoingTheupgoingaileronisonthedowngoingwing.2，AdverseaileronyawDeflectinganailerondowncausesaneffectiveincreaseincamberofthatwingandanincreaseintheeffectiveangleofattack.Theliftfromthatwingincreases,butunfortunaysodoesthedrag.Astheotheraileronrises,theeffectivecamberofthatwingisdecreasedanditsangleofattackisless,thereforeliftfromthatwingdecreases,asdoesthedrag.Thedifferingliftforcecausetheaircrafttobankoneway,butthedifferentialailerondragcausesittoyawtheotherway.Adverseaileronyawcanbereducedbygooddesigndifferentialailerons,Friseailerons,orcouplingtheruddertothe Differentialailerons（差動）aredesignedtominimizeadverseaileronyawbyincreasingthedragonthedowngoingwingoninsideoftheturn.Thisisachievedbydeflectingtheupwardaileronthroughagreateranglethanthedownwardaileron.Friseaileronsincreasethedragofthedescendingwingontheinsideoftheturn.Astheailerongoesup,itsnoseprotrudesintotheairstreambeneaththewingcausingincreaseddragonthedowngoingOntheotherway,thewingisrising,thenoseofthedowngoingailerondoesnotprotrudeintotheairstream,socausenoextradrag.Frise-typeaileronsmayalsobedesignedtooperatedifferentially,toincorporatethebenefitofdifferentialailerons.Coupledaileronsandruddercausetheruddertomoveautomaticallyandyawtheaeroplaneintobank,opposingtheadverseyawfromtheailerons.Theprimaryeffectofrudderistoyawtheaeroplane,andthesecondaryeffectistorollit.Theprimaryeffectofaileronsistorolltheaeroplane,andthesecondaryeffectistoyawit.3，RollisfollowedbyyawThesecondaryeffectofaileronsistocauseWhentheaeroplaneisbankedusingtheailerons,theaeroplanewillslip.Asaresultofthesideslip,theairflowwillstrikethesidetheaeroplaneandthelargekeelsurface（rearfuselageandwhicharemainlybehindtheCG,causethenoseoftheaeroplanetoyawinthedirectionofbank.Theprimarycontrolintheyawingistherudder.Therudderhingedtotherearofthefin（orverticalstabilizer).Itiscontrolledfromthecockpitbytherudderpedalstotherudderbar.Bypushingtheleftpedal,therudderwillmoveleft.Thisaltersthefin-rudderaerofoilsection,andsidewaysliftiscreatedthatsendsthetailtotherightandyawstheaeroplanetotheleftaboutnormalaxis.Withleftrudderapplied,theaeroplaneyaws 鉸接 座2，Yawisfollowedby Thesecondaryeffectofrudderisroll.Theprimaryeffectofrudderistoyawtheaeroplane.Havingyawedtheaeroplane,thefurthereffectofrudderistocausearoll.3，SlipstreamAstheslipstreamcorkscrews（螺旋形前進）aroundthefuselage,itstrikesonesideofthefin/rudderatadifferentangletotheother.Iftheslipstreamoverthefinandrudderchanges,thenthedeflectionmustbechangedtobalance4，Rudderincrosswindtake-offandlanding帶側(cè)風起飛、著陸中 起飛 著陸 進近 偏航 crab-wise偏航方向 接地,觸 Ingroundoperation,anycrosswindwillhitthesideoffinandtendtoweathercocktheaircraftintowind.Theruddermustbeusedtostoptheaircraftyawingintowindandkeepittrackingstraightalongtherunway.Onapproachtoland,themostcommontechniqueistocrabaircraftintowindsothatitisflyinginbalance（i.e.directlyintotherelativewindandwiththerudderballcentered）andtrackingsomewhat‘crab-wise’alongextendedcenterlineoftherunway.Justpriortotouchdowntheaircraftisyawedwiththerudder,sothatwhenthewheelstouch,theyarealignedinthedirectionoftheAnothertechniqueinacrosswindlandingisthesideslipNeartheground,youwouldyawtheaeroplanestraight（withrudder）sothatitis thecenterline.Unlessthewheelstouchalmostimmediay,thewindwillcausethetodrifttowardsthesideoftherunway.Toavoidthis,youlower（usingtheailerons）theinto-windwingsufficientlytostoptheaircraftdriftingoffthecenterlinepriortotouchdown.Theaeroplaneisnowsideslipandflyalitterbitoutof5，RudderWhiletheruddermustbesufficientlypowerfultohandletheaboverequirementssatisfactorily,itmustnotbetoopowerful.GivenumdeflectionbythepilotitshouldnotcausestructuralOthercontrolOtherscontroldevicesmodifiedaileron leadingedge speed vortex 1，ModifiedailerondesignandToreduceadverseaileronyaw,thereareseveral differentialFrisespoilers,whichareplate-likesurfacethatareraisedfromtheuppersurfaceofthewingtoincreasedragontheside.Theymaybeusedinconjunctionwiththeraisedaileronorinsteadofit.Thustheailerongoesdownononesideandthespoilerisraisedontheother.aileron/ruddermanualrudderinputTheyareusuallyincorporatedwithinthewingleadingedgeoftheailerontoretainaileroneffectivenessevenathepointofstallMostarefixedandexposedtotheairflowathighangleofSomearecreatedbyamovableplatewhichpopsout（突出）atangleofattackduetothereducedstatepressure.3，Leadingedgestrips/slatsStripsandothershapes,includingrope（鋼索）,areaddtotheleadingedgeofthewingtoencourageatta entoftheairflowathighangleofattack.Inthisway,theaileronsremaineffective.4，SpeedbrakesSpeedbrakesareflatplatesurfacewhichslideoutorhingeupwardfromtheuppersurfaceofthewing.SomeaircraftshavecombinedspoilersandspeedVortexgenerators（VGs）arefinger-likeprotrusionsontheuppersurfaceofthewing.Theyaresmallplatessetatanangletothewhichgenerateasmallvortex.TheymayevenbeaerofoilTheintentistousethevortextostirtheboundarylayerandpromoteanearliertransitiontoturbulentmixedflow.Turbulentflowremainsattachedforagreaterdistanceovertheaerofoil,andturbulentattachedflowisbetterthanturbulentseparatedflow.TheVGsstirtheboundarylayerandeffectivelyreducethehighdragofseparatedflow.Quitecommononaircraftareextensionstolowerleadingedgefintoincreasethechordandstrengthofthefin（dorsalfin）,underthefuselage（ventralfin）.Allofthesedesignadjustmentsaremadetoimprovethecontrolandstabilityatvariouspartsoftheflightenvelope. dorsalfin背鰭 ventralfin腹7，Wingtipsha,fences,endplatesandwinglets翼梢形狀，翼Thesedevicesimproveliftandreduceinduceddragbyreducingthespanwiseflowoftheair.fixed Afixedtabisasmallmetaltabthatcanbendtoasetpositiononthegroundonly.Itisfixedinflight.Itisusualontheaileronsandruddersofsmalltrim Anaircraftisintriminpitch,rolloryaw,whenitmaintainsasteadyattitudewithoutthepilothavingtoexertanypressureonthecontrolcolumn.Thefunctionofthetrimtabistoreducethecontrolsurfaceforcetozeroforthatconditionofflight,sothattheaeroplanewillmaintainit‘hands-off’.Inmostlightaircrafttrimsystemaremechanicallyoperatedbyatrimwheel.balance Onconventionaltailplaneitisquitecommontohaveabalancetabincorporatedaspartoftheelevator.Ifthepilotexertsbackpressureonthecontrolcolumn,theelevatorisraisedandthebalancetabgoesdown.Theelevatorbalancetabunitgeneratesasmallupwardaerodynamicforcethatactstoholdtheelevatorup,therebyreducingthecontrolloadrequiredofthepilot.ThebalancetabactsautomaticallyastheelevatorantibalancetabTheanti-balancetabmovesinthesamedirectionasthetailplanebutmovesfurther.Thedeflectionatthetrailingedgeofthesurfaceincreasesthestickforce.Theincreasedload,thatthepilothastoapply,tomanoeurvetheaircraft,preventsoverstressingthestructure.servo Aservotabisvariationofthebalancetabwherethepilotcontrolisconnected,nottothemaincontrolsurface,buttothetab.Asthecontrolinputmovestheservotabintotheairflow,theaerodynamicforcesgenerateddrivethemaincontrolsurfaceintheoppositedirection,causingthedesiredmanoeurve.Servotabswereusedonlargetransportaircraftastheforcerequiredtomovethesurfacewasbeyondthereasonablestrengthofthepilot.Stabilityversusversus［拉丁語］…對trade-off折衷,權(quán)衡hand-off松手,動手,1，StabilityversusDonotconfusestabilitywithStabilityisthetendencyoftheaeroplanetoreturnitsoriginalconditionafterbeingdisturbedandwithoutanyactionbeingtakenbythepilot.Controllabilityreferstotheeasewithwhichthepilotcanmanoeuvretheaircraftandhence ethestability.Thereisasignificanttrade-offbetweenstabilityandcontrollability.Ahighdegreeofstabilitymakestheaircraftresistanttochangeandtherebytendstoreducethecontrollabilityi.e.goodstabilitymakesitharderforthepilottocontrolandmanoeuvretheAnaeroplaneisinastateofequilibriumwhenthesumofalltheforcesonitiszeroandthesumofalltheturningmomentson