AMT – 111 Aircraft Landing Gear Systems -...

AMT–111AircraftLandingGearSystems

Chapter13

Complex

HardWorking

HardCore

LandingGearArrangement•  TailWheel/TailDragger/Conventional•  Tricycle•  Tandem

v  GlidersorMilitary

•  Floatsv  Amphibious

•  Skisv  Retractable

•  Amphibiousseaplane/flyingboat•  Fixedorretractable

TailDragger/Conventional

AmphibiousTailDragger

TricycleGear

Tandem

Floats(Amphibious)

Skids(WrongKind)

LandingGearDiagram

ShockAbsorbing•  Leaf-TypeSpring

v  Gearflexes•  Steel,aluminumorcomposites

•  Rigidv  Usuallyhelicopters

•  Bungeecordsv  Oldertube/fabrictypeaircraft

•  Solid,donut-typerubber•  Shockstruts

v  Calledoleostrutsv  Combinationofhydraulicandgasshockabsorbers

Leaf-TypeSpring

BungeeCord

RubberDonut

ShockStruts

Shock–TrailingArm

ShockStrut

MeteringTubeStrut

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)

Alignment

RetractTesting•  Video1•  Video2•  Video3•  Video4

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

NoseGearSteering•  SmallAircraft

v  Nosewheeldrivenbytherudderpedals•  Pushrods•  Springoftenusedtoprovidegive

v  Tailwheeldrivenbytherudderpedals•  Cableconnectedtotailwheel•  Tailwheelconnectedtorudder•  Springsoftenusedtoprovidegive

v  Freeswivelingnosewheel•  Differentialbrakingusedtosteeraircraft

NoseGearSteering•  LargeAircraft

v  Hydraulicallypoweredv  Drivenbyrudderorseparatewheel/tiller

ShimmyDampers

ShimmyDampers•  Reducenosewheelvibration(shimmy)•  Beforerebuildingshimmydampercheckforothercausesofshimmyv  Tire/wheelbalancev  Tirewearv  Wheelbearingsv  Linkages

•  Steering•  Dampers

Wheels

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

ThermalPlug

WheelBearings

Bearing Cup/Race Bearing

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

FloatingDiskBrake

FixedDisc

FixedDisc

Clevelandwheelshowingthebrakediskthatboltstotheinnerwheelhalf.

FixedDisc

MultipleDisc

ExpanderTubeBrake

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

RemoteReservoir

HydraulicallyLink

IndependentMasterCylinder•  Pilotpushesonthetopoftherudderpedal,whichpushesonthemastercylinderv  Leftandrightwheelsareindependent

•  Mastercylindercreatespressurethatissenttothecaliberswhichsqueezesthebrakepadsagainstthebrakedisc

•  Reservoirsv  Storesextrahydraulicfluidv  Built-in–partofthemastercylinderv  Remote–Containerseparatefromthemastercylinder

IndependentMasterCylinder•  Compensatingportpermitsthefluidtoflowtowardorawayfromthereservoirastemperaturechangesv  Fluidcomesfrom/goestoreservoirv  Helpscompensateforfluidleaks

IndependentMasterCylinder

LargeAircraftBrakes•  Boostedbrakes–Partofthebrakingforcecomesfromthepilot,partoftheforcecomesfromthehydraulicsystem

Boosted

LargeAircraftBrakes•  PowerBrakes

v  Allthebrakingpowercomesfromthehydraulicsystem

v  Usedbecausetheaircraftistoolarge,toofastorthesystemrequirestoomuchhydraulicfluidforhumanpowertosupply

v  Abrakecontrolvalveisusedtoconvertthepilot’sinputtohydraulicpressure

•  Aspecialhydraulicvalvethatgraduallycontrolspressure•  Alsocalledabrakemeteringvalve

LargeAircraftBrakes•  PowerBrakes

v  Brakedeboostervalves/systemsreducethehydraulicpressuretoalevelmoresuitedtobrakingsystems

•  Likeagearsystem,tradespressureforvolumev  Reducespressure,increasesvolume

•  Lowerpressurehelpsincreasereleasebrakesmorerapidly•  Lockoutdeboosterspreventmainhydraulicandbrakehydraulicfluidsfrommixing

PowerBrakeSystem

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

BleedingBrakes

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

TireConstruction•  Bead–anchorstiretowheel•  Carcassplies–formsthetirecarcassandprovidesthetire’sstrength

•  Tread–crowntothetire,comesincontactwiththeground

•  Sidewalls–outsiderubberdesignedtoprotectcarcassv  Greenorwhitedotsmarkseepagereleaseventsontubelesstires

•  Mustbekeptclean

TireChine

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

TireWearvs.Inflation

From AC43.13-1B

TireWearvs.Inflation

TireCondition•  TreadDepth–Replacement

v  Worntothebottomofatreadgroovealongmorethan1/8ofcircumference

v  Ifthefirstlayerofplyisexposedformorethan1/8ofthecircumference

•  UnevenWearv  Determinecauseandfix

•  Flatspotsmayinvolvepilottraining

v  Switchingtiresfromsidetosidemayhelpwithwear

•  Fordamagelimits,consultmanufacturer

TireRemoval

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

FAAQuestion•  Anelectricmotorusedtoraiseandloweralandinggearwouldmostlikelybeav  a.shuntfieldseries-woundmotor.v  b.splitfieldshunt-woundmotor.v  c.splitfieldseries-woundmotor.

•  Answer:C

AMT – 111 Aircraft Landing Gear Systems -...

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