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LandingGearArrangement• TailWheel/TailDragger/Conventional• Tricycle• Tandem
v GlidersorMilitary
• Floatsv Amphibious
• Skisv Retractable
• Amphibiousseaplane/flyingboat• Fixedorretractable
ShockAbsorbing• Leaf-TypeSpring
v Gearflexes• Steel,aluminumorcomposites
• Rigidv Usuallyhelicopters
• Bungeecordsv Oldertube/fabrictypeaircraft
• Solid,donut-typerubber• Shockstruts
v Calledoleostrutsv Combinationofhydraulicandgasshockabsorbers
ServicingShockStrut• Checknormaloperation
v Checkheightv Checkreboundaction
• Lookforleaks• Jack-upaircraft• Inspectforphysicaldamageandleaks• Releasepressure
v Ifpossible,removevalvecoreafterreleasingpressure
v Valvesmarkedwitha“H”arehighpressurevalves,becareful
ServicingShockStrut• Ifthestrutmustberebuilt,takecarenotscratch• Fill/replacehydraulicfluidperinstructions• Installnewvalvecore(theyareinexpensive)andslowlypressurizev Nitrogenispreferablev PressurizationlevelmaybedefinedbyPSIorextensionofstrut
Alignment• Toe-in/Toe-outisameasurementalongthelongitudinalaxis(centerline)v Toe-in–frontoftirepointstowardfuselagev Toe-out–frontoftirepointsawayfromfuselagev Correctedbyinserting,removing,orchangingthelocationofwashersorspacersatthecenterpivotalpointofthescissortorquelinks.
• Camberisthealignmentalongtheverticalaxis(upanddown)
RetractionSystems• Smallaircraft
v Mechanicalv Allelectricv Combinedelectricandhydraulic
v Powerpackcombinationofelectricmotorandhydraulicpump
• Largeaircraftv Usuallyhydraulic
• Usuallyenginedrivenv Sequencevalvetocontrolorderofopeningandclosing
v Orificecheckvalvewillhelpslowdownloweringoflandinggear
EmergencyExtension• Iftheretractionfailsorlossespower,thesystemshouldfailintheextendedposition
• Gravity/freefallv Unlockthegearanditfalls/locksintoplace
• Handcrankorpump• Backuphydraulicsystem
v Redundantpumpv Backupelectricpumpv Ramairdrivenpump
• Compressedair
LandingGearComponents• Positionselectorswitch–upisupanddownisdown
• Landinggearindicatorlightsv Greenis“down&locked”v Controlledbypositionswitches
• Warnsystemwillalertthepilotwhenthethrottleisretartedandthegearisstillup
• Squatswitchdetectswhenpressureisongearv Usedtopreventretractiononthegroundv Controlsautomaticbrakeapplicationandenginereversers
v Controlsairframetimers
LandingGearMaintenance• Gearshouldbeinspectedandtestedateachannual(100hourinspection)v Cleanv Checkforwearandsmoothactionv Checklightandindicatorsv Lubricatev Checkdoors,latchesandbracesv Checklocksv Performretracttestsv Checkemergencyextension
NoseGearSteering• SmallAircraft
v Nosewheeldrivenbytherudderpedals• Pushrods• Springoftenusedtoprovidegive
v Tailwheeldrivenbytherudderpedals• Cableconnectedtotailwheel• Tailwheelconnectedtorudder• Springsoftenusedtoprovidegive
v Freeswivelingnosewheel• Differentialbrakingusedtosteeraircraft
ShimmyDampers• Reducenosewheelvibration(shimmy)• Beforerebuildingshimmydampercheckforothercausesofshimmyv Tire/wheelbalancev Tirewearv Wheelbearingsv Linkages
• Steering• Dampers
Wheels• Twopiece• Relievepressurebeforesplittingwheels
v Precautionincasewheelboltshavebeendamaged
• Oftentubeless• Aluminumormagnesium
v Inspectfordamagesuchascracksandcorrosion• Canberefinished/painted
v HighstressedwheelhaveregularscheduledNDT• NDT–NondestructiveTesting
Wheels• Highstresswheelsusethermalplug
v “Melts”whenwheelgetstohot• Preventswheelfromexploding
v Preventoverheatingwithshortgroundrolls,slowtaxispeeds,minimumbraking,andpropertireinflation.
v Wheelmustbecompletinginspectedafterathermalplugfailure
• Tireshouldbereplaced
• Wheelhavewhitemarksappliedtoboththewheelandtirev Themarksareusedtodetecttireslippagev Servicewheel/tireifslippageisdetected
Bearing• Consistofthebearingandbearingcup
v Bearingcupisalsocalledthebearingrace
• Bearingandcuparematchedv Don’tmix
• Bearingandcuphavehardenedmetalsurfacesv Anydamage,replacev Replacebothbearingandcupv Cupusesaninterferencefit
• Heatwheeltoremove• Heatwheelandrefrigeratecuptoinsert
Bearing• Bearingare“packed”withgreaseorpacking
v Lubricatesbearingandkeepswater/dirtoutv Followmanufacturesrecommendationforgreaseused
v Cleanbearingandcupbeforepacking• Usemineralspiritsandsoftbrush• Drybeforepacking• Don’tspinbearingwhendry
• Inspectregularly–RTFMv Manufactureroftenrecommendsatimeinterval
• Alsoconsidercalendartime
v Everyannualisrecommended
Bearing• Wheelheldonbyaxlenut
v Followtorquerecommendationv Someprocedurescallfortwosteptorquingv Insureaxlenutislockedv Insurewheelturnsfreely
Brakes• Floatingsingledisc
v “Goodyear”v Discfloatsinwheel/caliperisfixed
• Fixedsinglediscv “Cleveland”v Discisfixedtowheel/caliperfloats
• Multiplediscv Largeaircraft
• Expandertube–obsoletev Mustbehydraulic/can’tbemechanical
BrakesActuatingSystem• Allmodernbrakesystemsarehydraulic• Independentsystem–allhumanpowered• Boostersystem–usetheaircraft’shydraulicsystemintermittently
• Powersystem–completelypoweredbytheaircraft’shydraulicsystem
IndependentMasterCylinder• Pilotpushesonthetopoftherudderpedal,whichpushesonthemastercylinderv Leftandrightwheelsareindependent
• Mastercylindercreatespressurethatissenttothecaliberswhichsqueezesthebrakepadsagainstthebrakedisc
• Reservoirsv Storesextrahydraulicfluidv Built-in–partofthemastercylinderv Remote–Containerseparatefromthemastercylinder
IndependentMasterCylinder• Compensatingportpermitsthefluidtoflowtowardorawayfromthereservoirastemperaturechangesv Fluidcomesfrom/goestoreservoirv Helpscompensateforfluidleaks
LargeAircraftBrakes• Boostedbrakes–Partofthebrakingforcecomesfromthepilot,partoftheforcecomesfromthehydraulicsystem
LargeAircraftBrakes• PowerBrakes
v Allthebrakingpowercomesfromthehydraulicsystem
v Usedbecausetheaircraftistoolarge,toofastorthesystemrequirestoomuchhydraulicfluidforhumanpowertosupply
v Abrakecontrolvalveisusedtoconvertthepilot’sinputtohydraulicpressure
• Aspecialhydraulicvalvethatgraduallycontrolspressure• Alsocalledabrakemeteringvalve
LargeAircraftBrakes• PowerBrakes
v Brakedeboostervalves/systemsreducethehydraulicpressuretoalevelmoresuitedtobrakingsystems
• Likeagearsystem,tradespressureforvolumev Reducespressure,increasesvolume
• Lowerpressurehelpsincreasereleasebrakesmorerapidly• Lockoutdeboosterspreventmainhydraulicandbrakehydraulicfluidsfrommixing
BrakeSystems• Emergencybrakesystems–backupsystemtohelpintheeventofafailureintheprimarysystemv Shuttlevalvesareusedtoisolateemergencysystemfrommainsystem
• Parkingbrakeareusedtoholdtheaircraftinastationarypositionv Physicallockbrakepedaloruseavalvetolockpressureinbrakes
v Don’tapplywhenbrakesarehot–warpsdisksv Don’tleaveonforlongperiodsoftime
BrakeSystems• Anti-skidsystem–preventsthetirefromskiddingwhilebrakingv Onceatirestartstoskid,itlosestractionv Skidscanalsodamagethetiresandcauseblowoutsv Iftheonsetofaskidisdetected,thebrakepressurewillbereleased
• Pressurereleasemaybeaccomplishbypulsing
v Wheelspeedsensorsareusedtodetectwheelspeed
v Acontrolunitdeterminesifthewheelisslowingdowntoofastandreleasesbrakes
BrakeSystems• Touchdownprotection–willpreventtheapplicationofbrakesatthemomentoftouchdownv Wheelsshouldberollingbeforeapplyingbrakesv Landinggearsquatswitchesareusedtodetectthattheaircraftsweightisonthetires
• Autobrakes–somelargeaircraftswillautomaticallyapplybrakestoreducerollingdistancev Thelevelofbrakingcanbeselectedbythepilot
BrakeSystemMaintenance• Lining–measureminimumthickness
v Rivetnewliningstobackplate
• Calipermaintenancev Checkforcracks,corrosion,andleaksv Canberebuilt
• Insurepistonsandcylinderssurfacesarecleanandnotscratched
BrakeSystemMaintenance• Mastercylindermaintenance
v Checkforcracks,corrosion,andleaksv Canberebuilt
• Insurepistonsandcylinderssurfacesarecleanandnotscratched
v Brokenspringcancausedraggingofbrakes
• Diskmustbecheckedforphysicaldamageandminimumthicknessv Somediskscanbe“turned”torepairdamagev Warpeddiskscancausechatteringorsquealing
BrakeSystemMaintenance• Fluidmaintenance
v Followreplacementschedulev Replaceifcontaminatedv Bleedingthebrakesmustfollowanyopeningofthehydraulicsystem
• Removeairfromsystem• Systemwillfeelspongyifairisinsystem
v Firmbrakesareanindicationtheairhasbeenremoved
v Followproceduresexactlyforanti-skidsystems
• Checkconditionofbrakelinesv Oldbrakelinescanflexandcausespongybrakes
CurrentTireTypes• TypeIII–typesmallaircraft
v Designation–A-B• A-Tirewidth• B–Rimdiameter• e.g.9.00-6is9”widthwitha6”rimdiameter
v Lowpressure
• TypeVII–highperformanceforjetsv Designation–AXB
• A–Totaldiameter• B–Tirewidth• e.g.26X6.6is26”talland6.6”wide
v Highpressure
CurrentTireTypes• TypeVIII–highperformanceforjets
v Designation–AXB-C• A–Totaldiameter• B–Tirewidth• “-”–“-”meansbiasply,Rmeansradial• C–Rimdiameter• e.g.30X8.8R15is30”tall,8.8”wide,radial,15”rim
v Prefixes• B–thetirehasa60to70percentwheelrimtosectionwidthratiowithabeadtaperof15degrees.
• H–thetirehasa60to70percentwheelrimtosectionwidthratiowithabeadtaperof5degrees.
v Highpressure
Tires• PlyRating–pliesarereinforcinglayers
v Plyratingusedtoindicatethenumberoflayersv Nowadays,plyratingisnotanindicationoftirelayers
• Tube-typeortubeless–bothtypesarestillused• Biasplyorradial–classificationonhowtheconstructionpliesarewrappedv Biaspliesare30°to60°inrelationtorotationv Radialsare90°v Bothtypesareused
• Radialareusuallyusedonhighspeedaircraft
TireConstruction• Bead–anchorstiretowheel• Carcassplies–formsthetirecarcassandprovidesthetire’sstrength
• Tread–crowntothetire,comesincontactwiththeground
• Sidewalls–outsiderubberdesignedtoprotectcarcassv Greenorwhitedotsmarkseepagereleaseventsontubelesstires
• Mustbekeptclean
TireInflation• Properinflationhelpsmaintaintirelifeandoperation
• Checkinflationwithacalibratedgauge• Checka“cold”tire
v Shouldbeatambienttemperaturev Afterlanding,thetireshouldbeallowedtocooldownfor3hoursbeforecheckinginflation
• Pressurechanges1%forevery5°Fv Ifgoingfromhotairporttocold,inflatetomaximumv Ifgoingfromcoldairporttohot,inflatetominimum
TireInflation• Inflationshouldbecheckeveryweek• Inflationinformationcomesfromtheaircraftmaintenancemanualnotthetiremanual
• Ifamulti-tiregearhasmorethan5poundsinflationdifference,thedifferenceshouldbecorrectedandrecordedinthelogbookv Thelogbookentrieswillhelptrackifthereisaproblem
• Overinflationcandamagethewheelflange
TireCondition• TreadDepth–Replacement
v Worntothebottomofatreadgroovealongmorethan1/8ofcircumference
v Ifthefirstlayerofplyisexposedformorethan1/8ofthecircumference
• UnevenWearv Determinecauseandfix
• Flatspotsmayinvolvepilottraining
v Switchingtiresfromsidetosidemayhelpwithwear
• Fordamagelimits,consultmanufacturer
Tires• Tirerepairshouldbehandledbyacertifiedtireshop
• Tirescanberetreadedanunlimitednumberoftimeifthecarcassisnotdamaged
• Tirestoragev Stackverticallyv Keepawayfromozonesources–electricequipmentv Wrapindarkplasticorpaperv KeepawayfromUVlight(sun),fuel,oil,hydraulicfluidsandsolvents
v Keepawayfromextremeheatandcold
TireMounting• Assemblewheelintire
v Lightsideofwheelhalvesshouldbeoppositeeachother
• Lightsideismarkedwithan“L”,S/Norreddot
v Lubricatewheelhalf“O”ring• Useproperlubricate
v Tirebeadmayrequirelubricationv Alignheavypartofwheelwithlightpartoftire
• Lightpartoftirehasredmark• Defaultheavypartofwheelisvalvestem
v Followtorquerequirementsv Video
TireMounting• Inflateinasafetycage• Nitrogenisusedforinflationtominimizecorrosionfrommoisture
• Afterinflation,leaveunloadedfor12hoursv 5-10%pressurelossisnormalduetotirestretching
TubeTireMounting• Lightlyinflatetubetogiveitshapebeforeinstallingtirev Insuretubeiswrinklefree
• Matchheavyspotontubewithlightspotontirev Valvestemisdefaultheavyspot
• Usetiretalcinsidetireandoutsideoftube• Completelyinflatetire,completelydeflateandtheninflateagainv Helpstubeseatproperly
TireBalancing• Preventsheavyspots(landonthesamespot)andvibrations
• Mosttirebalancingisdonestaticallyv Thetireshouldnotstopatthesameplaceeverytimeitisrotated