航空专英1教案第5章ForcesinFlight

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1、Ch.5Stabilityandcontrol5.1Balanceandtrim1,balanceinstraightandlevelflightbalance
see-sawᩨᩚbean᫡woodenbeanᩈ᫡suspendedbean᫡fulcrumtrimequilibrium⊝controlcolumn᫃rudderpedalᔣalign,alignmentᡂFigure2.2-1See-saw.Figure2.2-2UnbalancedFigure2.2-3RebalancedFigure2.2-4RebalancedBala

2、nceconsistsoftwoelements-thetotalforcesactingtheaircraftandthealignmentoftheseforces.Whentheforcesarebalancedandalignedtheaircraftissaidtobeinequilibrium.Therearetwotypesofforces-staticforces,dynamicforces.Weightisastaticforceitcanbeconsideredconstantatanytime.Thrustvarieswithenginep

3、ower,propellerrpmandairspeedbutcanbesetataconstantvaluebythepilot.Liftisaerodynamicforcewhichchangeswithairspeedandflapextensionbutwhichcanbecontrolleddirectlybythepilotchangingtheangleofattack.Dragchangeswithangleofattack,configurationandairspeed.♦LLift(2,000units)T:hrust(200units)

4、""brag(200units)WWeight(2,000units)Figure2.2-7Liftbalancesweight.3ndthrustbalancesdrag,instraightandlevelflight.Instraightandlevelflight,liftopposesweightL=WthrustopposesdragT=D.Theliftandweightwillonlydecreasegraduallyastheweightdecreaseswithfuelburn-off.Thethru

5、standdragwillvaryconsiderablydependingonangleofattackandthereforeairspeed.2,pitchingmomentLift-Nose-downCGCPWeightyLiftAkWeightyFigure2.2-8Lift-weightcoupleproducesapitchingmoment.Nose-upThrustWNose-downFigure2.2-9Thrust-dragcoupleproducesapitchingmomentUndermostconditionsofflightthe

6、CPandCGarenotcoincident,i.e.arenotattheonepoint,causingnose-downpitchingmomentoranose-uppitchingmoment.Thedifferentlinesofactionofthethrustforceanddragforceproduceanothercouple,causinganose-downpitchingmomentoranose-uppitchingmoment.Ideallythepitchingmomentfromthetwocouplesshouldneut

7、ralizeeachotherinlevelflightsothatthereisnoresultantmomenttendingtorotatetheaircraftALiftThrust-dragcouplenose-upLift-weightFigure2.2-10coupleLift-weightcoupleandthrinose-downdragcoupleinequilibrium.Weight▼Figure2.2-11VerticallyoffsetthrustlineALiftThrust-dragThrusl-dragcoupleIcouple

8、(Reduced(nose-upnose-upmoment)momen