CHAPTER AIRCRAFT BASIC CONSTRUCTION INTRODUCTION Naval aircraft are built to me - PDF document

AIRCRAFT BASIC CONSTRUCTIONINTRODUCTIONNavalaircraftarebuilttomeetcertainspecifiedrequirements.Theserequirementsmustbeselectedsotheycanbebuiltintooneaircraft.Itisnotpossibleforoneaircrafttopossessallcharacteristics;justasitisn'tpossibleforanaircrafttohavethecomfortofa Cuttingapieceofpaperwithscissorsisanexampleofashearingaction.Inanaircraftstructure,shear(fig.4-1,viewD)isastressexertedwhentwopiecesoffastenedmaterialtendtoseparate.Shearstressistheoutcomeofslidingonepartovertheotherinoppositedirections.TherivetsandboltsofanaircraftexperienceBending(fig.4-1,viewE)isacombinationoftensionandcompression.Forexample,whenbendingapieceoftubing,theupperportionstretches(tension)andthelowerportioncrushestogether(compression).ThewingsparsofanaircraftinflightaresubjecttoTORSIONTorsional(fig.4-1,viewC)stressesresultfromatwistingforce.Whenyouwringoutachamoisskin,youareputtingitundertorsion.Torsionisproducedinanenginecrankshaftwhiletheengineisrunning.ForcesVARYING STRESSAllstructuralmembersofanaircraftaresubjecttooneormorestresses.Sometimesastructuralmemberhasalternatestresses;forexample,itisundercompressiononeinstantandundertensionthenext.Thestrengthofaircraftmaterialsmustbegreatenoughto withstand maximum force of varying stresses.SPECIFIC ACTION OF STRESSESYouneedtounderstandthestressesencounteredonthemainpartsofanaircraft.Aknowledgeofthebasicstressesonaircraftstructureswillhelpyouunderstandwhyaircraftarebuiltthewaytheyare.Thefuselageofanaircraftissubjectthefivestypesofstress—torsion,bending, tension, shear, and compression.Torsionalstressinafuselageiscreatedinseveralways.Forexample,torsionalstressisencounteredinenginetorqueonturbopropaircraft.Enginetorquetendstorotatetheaircraftinthedirectionoppositetothedirectionthepropelleristurning.Thisforcecreatesatorsionalstressinthefuselage.Figure4-2showstheeffectoftherotatingpropellers.Also,torsionalstressonthefuselageiscreatedbytheactionoftheaileronswhen the aircraft is maneuvered.Whenanaircraftisontheground,thereisabendingforceonthefuselage.Thisforceoccursbecauseoftheweightoftheaircraft.Bendingincreaseswhentheaircraftmakesacarrierlanding.Thisbendingactioncreatesatensionstressonthelowerskinofthefuselageandacompressionstressonthetopskin.Bendingactionisshowninfigure4-3.Thesestressesaretransmittedtothefuselagewhentheaircraftisinflight.Bendingoccursbecauseofthereactionoftheairflowagainstthewingsandempennage.WhentheFigure 4-1.—Five stresses acting on an aircraft. aircraftisinflight,liftforcesactupwardagainstthewings,tendingtobendthemupward.Thewingsarepreventedfromfoldingoverthefuselagebytheresistingstrengthofthewingstructure.Thebendingactioncreatesatensionstressonthebottomofthewingsandacompressionstressonthetopofthewings.Q4-1.Theresistancetopullingapartorstretchingproducedbytwoforcespullinginoppositedirectionsalongthesamestraightlinesisdefined by what term?Q4-2.Theresistancetocrushingproducedbytwoforcespushingtowardeachotherinthesamestraight line is defined by what term?Q4-3.Definethetermshearasitrelatestoanaircraft structure.Q4-4.Define the term bending.Q4-5.Define the term torsion.CONSTRUCTION MATERIALSLEARNINGOBJECTIVE:IdentifythevarioustypesofmetallicandnonmetallicAnaircraftmustbeconstructedofmaterialsthatarebothlightandstrong.Earlyaircraftweremadeofwood.Lightweightmetalalloyswithastrengthgreaterthanwoodweredevelopedandusedonlateraircraft.MaterialscurrentlyusedinaircraftconstructionareclassifiedaseithermetallicmaterialsornonmetallicTORSIONALROTATIONFigure 4-2.—Engine torque creates torsion stress in aircraft fuselages.Figure 4-3.—Bending action occurring during carrier landing. METALLIC MATERIALSThemostcommonmetalsusedinaircraftconstructionarealuminum,magnesium,titanium,steel, and their alloys.Analloyiscomposedoftwoormoremetals.Themetalpresentinthealloyinthelargestamountiscalledbasemetal.Allothermetalsaddedtothebasemetalarecalledalloyingelements.Addingthealloyingelementsmayresultinachangeinthepropertiesofthebasemetal.Forexample,purealuminumisrelativelysoftandweak.However,addingsmallamountsorcopper,manganese,andmagnesiumwillincreasealuminum'sstrengthmanytimes.Heattreatmentcanincreaseordecreaseanalloy'sstrengthandhardness.Alloysareimportanttotheaircraftindustry.TheyprovidematerialswithpropertiesthatpuremetalsdoAluminumalloysarewidelyusedinmodernaircraftconstruction.Aluminumalloysarevaluablebecausetheyhaveahighstrength-to-weightratio.Aluminumalloysarecorrosionresistantandcomparativelyeasytofabricate.TheoutstandingMagnesiumistheworld'slighteststructuralmetal.Itisasilvery-whitematerialthatweighstwo-thirdsasmuchasaluminum.Magnesiumisusedtomakehelicopters.Magnesium'slowresistancetocorrosionhas limited its use in conventional aircraft.TitaniumTitaniumisalightweight,strong,corrosion-resistantmetal.Recentdevelopmentsmaketitaniumidealforapplicationswherealuminumalloysaretooweakandstainlesssteelistooheavy.Additionally,titaniumisunaffectedbylongexposuretoseawaterandAlloysteelsusedinaircraftconstructionhavegreatstrength,moresothanotherfieldsofengineeringwouldrequire.Thesematerialsmustwithstandtheforcesthatoccurontoday'smodernaircraft.Thesesteelscontainsmallpercentagesofcarbon,nickel,chromium,vanadium,andmolybdenum.High-tensilesteelswillstandstressof50to150tonspersquareinchwithoutfailing.Suchsteelsaremadeintotubes,rods,Anothertypeofsteelusedextensivelyisstainlesssteel.Stainlesssteelresistscorrosionandisparticularlyvaluable for use in or near water.NONMETALLIC MATERIALSInadditiontometals,varioustypesofplasticmaterialsarefoundinaircraftconstruction.Someoftheseplasticsincludetransparentplastic,reinforcedplastic, composite, and carbon-fiber materials.Transparent PlasticTransparentplasticisusedincanopies,windshields,andothertransparentenclosures.Youneedtohandletransparentplasticsurfacescarefullybecausetheyarerelativelysoftandscratcheasily.Atapproximately225°F,transparentplasticbecomessoftReinforced PlasticReinforcedplasticisusedintheconstructionofradomes,wingtips,stabilizertips,antennacovers,andflightcontrols.Reinforcedplastichasahighstrength-to-weightratioandisresistanttomildewandrot.Becauseitiseasytofabricate,itisequallysuitableReinforcedplasticisasandwich-typematerial(fig.4-4).Itismadeupoftwoouterfacingsandacenterlayer.Thefacingsaremadeupofseverallayersofglasscloth,bondedtogetherwithaliquidresin.Thecorematerial(centerlayer)consistsofahoneycombFACINGS(MULTIPLELAYERSOFGLASSCLOTH)Figure 4-4.—Reinforced plastic. structuremadeofglasscloth.Reinforcedplasticisfabricated into a variety of cell sizes.High-performanceaircraftrequireanextrahighstrength-to-weightratiomaterial.Fabricationofcompositematerialssatisfiesthisspecialrequirement.Compositematerialsareconstructedbyusingseverallayersofbondingmaterials(graphiteepoxyorboronepoxy).Thesematerialsaremechanicallyfastenedtoconventionalsubstructures.Anothertypeofcompositeconstructionconsistsofthingraphiteepoxyskinsbondedtoanaluminumhoneycombcore.Carbonfiberisextremelystrong,thinfibermadebyheatingsyntheticfibers,suchasrayon,untilcharred,andthenQ4-6.Materialscurrentlyusedinaircraftconstruc-tion are classified as what type of materials?Q4-7.Whatarethemostcommonmetallicmaterialsused in aircraft construction?Q4-8.Whatarethenonmetallicmaterialsusedinaircraft construction?LEARNINGOBJECTIVE:Identifytheconstructionfeaturesofthefixed-wingaircraftandidentifytheprimary,secondary,andauxiliary flight control surfaces.Theprincipalstructuralunitsofafixed-wingaircraftarethefuselage,wings,stabilizers,flightcontrolsurfaces,andlandinggear.Figure4-5showsthese units of a naval aircraft.NOTE:ThetermsusedinrelationtoanyofthestructuralunitsrefertotherightorlefthandFUSELAGEThefuselageisthemainstructure,orbody,oftheaircraft.Itprovidesspaceforpersonnel,cargo,controls,andmostoftheaccessories.Thepowerplant,HORIZONTALSTABILIZEROFWINGVERTICALSTABILIZERAIRINLETFAIRINGELEVATORFigure 4-5.—Principal structural units on an F-14 aircraft. Therearetwogeneraltypesoffuselageconstruction—weldedsteeltrussandmonocoquedesigns.TheweldedsteeltrusswasusedinsmallerNavyaircraft,anditisstillbeingusedinsomeThemonocoquedesignrelieslargelyonthestrengthoftheskin,orcovering,tocarryvariousloads.Themonocoquedesignmaybedividedintothreeclasses—monocoque,semimonocoque,andreinforcedThetruemonocoqueconstructionusesformers,frameassemblies,andbulkheadstogiveshapetothefuselage.However,theskincarriestheprimarystresses.Sincenobracingmembersarepresent,theskinmustbestrongenoughtokeepthefuselagerigid.ThebiggestprobleminmonocoqueconstructionismaintainingenoughstrengthwhilekeepingtheSemimonocoquedesignovercomesthestrength-to-weightproblemofmonocoqueconstruction.Seefigure4-6.Inadditiontohavingformers,frameassemblies,andbulkheads,thesemimonocoqueconstructionhastheskinreinforcedbylongitudinalThereinforcedshellhastheskinreinforcedbyacompleteframeworkofstructuralmembers.Differentportionsofthesamefuselagemaybelongtoanyoneofthethreeclasses.Mostareconsideredtobeofsemimonocoque-typeThesemimonocoquefuselageisconstructedprimarilyofaluminumalloy,althoughsteelandtitaniumarefoundinhigh-temperatureareas.Primarybendingloadsaretakenbythelongerons,whichusuallyextendacrossseveralpointsofsupport.Thelongeronsaresupplementedbyotherlongitudinalmembersknownasstringers.StringersaremoreTheverticalstructuralmembersarereferredtoasbulkheadsframes,andformers.Theheavierverticalmembersarelocatedatintervalstoallowforconcentratedloads.Thesemembersarealsofoundatpointswherefittingsareusedtoattachotherunits,suchThestringersaresmallerandlighterthanlongeronsandserveasfill-ins.Theyhavesomerigiditybutarechieflyusedforgivingshapeandforattachmentofskin.Thestrong,heavylongeronsholdthebulkheadsandformers.Thebulkheadsandformersholdthestringers.Allofthesejointogethertoformarigidfuselageframework.StringersandlongeronspreventtensionandcompressionstressesfrombendingtheTheskinisattachedtothelongerons,bulkheads,andotherstructuralmembersandcarriespartoftheload.Thefuselageskinthicknessvarieswiththeloadcarriedandthestressessustainedatparticularloca-Figure 4-6.—Semimonocoque fuselage construction. ThereareanumberofadvantagesinusingtheThebulkhead,frames,stringers,andlongeronsaidinthedesignandconstructionofastreamlinedfuselage.TheyaddtothestrengthThemainadvantageofthesemimonocoqueconstructionisthatitdependsonmanystructuralmembersforstrengthandrigidity.Becauseofitsstressedskinconstruction,asemimonocoquefuselagecanwithstanddamageandstillbestrongenoughtoholdtogether.Pointsonthefuselagearelocatedbystationnumbers.Station0isusuallylocatedatornearthenoseoftheaircraft.Theotherstationsarelocatedatmeasureddistances(ininches)aftofstation0.Atypicalstationdiagramisshowninfigure4-7.Onthisparticularaircraft,fuselagestation(FS)0islocated93.0 inches forward of the nose.050100150200250300350400450500550600650700750800850ARRESTINGHOOKFULLYEXTENDEDSTATICFS-FUSELAGESTATIONWS-WINGSTATIONAIRCRAFTSTATIONS20WING75WINGFigure 4-7.—Fuselage station diagram of an F-14 aircraft. Wingsdevelopthemajorportionoftheliftofaheavier-than-airaircraft.Wingstructurescarrysomeoftheheavierloadsfoundintheaircraftstructure.Theparticulardesignofawingdependsonmanyfactors,suchasthesize,weight,speed,rateofclimb,anduseoftheaircraft.Thewingmustbeconstructedsothatitholdsitsaerodynamicsshapeundertheextremestresses of combat maneuvers or wing loading.Wingconstructionissimilarinmostmodernaircraft.Initssimplestform,thewingisaframeworkmadeupofsparsandribsandcoveredwithmetal.Theconstructionofanaircraftwingisshowninfigure4-8.Sparsarethemainstructuralmembersofthewing.Theyextendfromthefuselagetothetipofthewing.Alltheloadcarriedbythewingistakenupbythespars.Thesparsaredesignedtohavegreatbendingstrength.Ribsgivethewingsectionitsshape,andtheytransmittheairloadfromthewingcoveringtothespars.RibsextendfromtheleadingedgetothetrailingedgeoftheInadditiontothemainspars,somewingshaveafalsespartosupporttheaileronsandflaps.Mostaircraftwingshavearemovabletip,whichstreamlinesMostNavyaircraftaredesignedwithawingreferredtoasawetwing.Thistermdescribesthewingthatisconstructedsoitcanbeusedasafuelcell.Thewetwingissealedwithafuel-resistantcompoundasitisbuilt.ThewingholdsfuelwithouttheusualrubberThewingsofmostnavalaircraftareofallmetal,fullcantileverconstruction.Often,theymaybefoldedforcarrieruse.Afullcantileverwingstructureisverystrong.Thewingcanbefastenedtothefuselagewithouttheuseofexternalbracing,suchaswiresorAcompletewingassemblyconsistsofthesurfaceprovidingliftforthesupportoftheaircraft.Italsoprovides the necessary flight control surfaces.NOTE:Theflightcontrolsurfacesonasimplewingmayincludeonlyaileronsandtrailingedgeflaps.Themorecomplexaircraftmayhaveavarietyofdevices,suchasleadingedgeflaps,slats,spoilers,andspeed brakes.Variouspointsonthewingarelocatedbywingstationnumbers(fig.4-7).Wingstation(WS)0islocatedatthecenterlineofthefuselage,andallwingstationsaremeasured(rightorleft)fromthispoint(inSTABILIZERSThestabilizingsurfacesofanaircraftconsistofverticalandhorizontalairfoils.TheyarecalledtheTRAILINGEDGESPARSLEADINGEDGEFigure 4-8.—Two-spar wing construction. verticalstabilizerfin)andhorizontalstabilizerThesetwoairfoils,alongwiththerudderandelevators,formthetailsection.Forinspectionandmaintenancepurposes,theentiretailsectionisconsideredasingleempennageThemainpurposeofstabilizersistokeeptheaircraftinstraight-and-levelflight.Theverticalstabilizermaintainsthestabilityofheaircraftaboutitsverticalaxis(fig.4-9).Thisisknownasdirectional.Theverticalstabilizerusuallyservesasthebasetowhichtherudderisattached.Thehorizontalstabilizerprovidesstabilityoftheaircraftaboutitslateralaxis.Thisisknownaslongitudinalstability.Thehorizontalstabilizerusuallyservesasthebasetowhichtheelevatorsareattached.Onmanynewer,high-performanceaircraft,theentireverticaland/orhorizontalstabilizerisamovableairfoil.Withoutthemovableairfoil,theflightcontrolsurfaceswouldlosetheir effectiveness at extremely high altitudes.Stabilizerconstructionissimilartowingconstruction.Forgreaterstrength,especiallyinthethinnerairfoilsectionstypicaloftrailingedges,ahoneycomb-typeconstructionisused.Somelargercarrier-typeaircrafthaveverticalstabilizersthatarefoldedhydraulicallytoaidaircraftmovementaboardFLIGHT CONTROL SURFACESFlightcontrolsurfacesarehinged(movable)airfoilsdesignedtochangetheattitudeoftheaircraftduringflight.Thesesurfacesaredividedintothreegroups—primary, secondary, and auxiliary.Primary GroupTheprimarygroupofflightcontrolsurfacesincludesailerons,elevators,andrudders.Theaileronsattachtothetrailingedgeofthewings.Theycontroltherolling(orbanking)motionoftheaircraft.Thisactionis known aslongitudinal controlTheelevatorsareattachedtothehorizontalstabilizerandcontroltheclimbordescent(pitchingmotion)oftheaircraft.ThisactionisknownaslateralcontrolTherudderisattachedtotheverticalstabilizer.Itdeterminesthehorizontalflight(turningoryawingmotion)oftheaircraft.Thisactionisknownasdirectional controlTheaileronsandelevatorsareoperatedfromthecockpitbyacontrolstickonsingle-engineaircraft.Ayokeandwheelassemblyoperatestheaileronsandelevatorsonmultiengineaircraft,suchastransportandYAWVERTICALAXISLATERALAXISLONGITUDINALAXISFigure 4-9.—Axes and fundamental movements of the aircraft. patrolaircraft.TherudderisoperatedbyfootpedalsonSecondary GroupThesecondarygroupincludesthetrimtabsandspringtabs.Trimtabsaresmallairfoilsrecessedintothetrailingedgesoftheprimarycontrolsurface.Eachtrimtabhingestoitsparentprimarycontrolsurface,butoperatesbyanindependentcontrol.TrimtabsletthepilottrimoutanunbalancedconditionwithoutexertingSpringtabsaresimilarinappearancetotrimtabsbutserveanentirelydifferentpurpose.Springtabsareusedforthesamepurposeashydraulicactuators.Theyaidthepilotinmovingalargercontrolsurface,suchasthe ailerons and elevators.Auxiliary GroupTheauxiliarygroupincludesthewingflaps,spoilers, speed brakes, and slats.WINGFLAPS.—Wingflapsgivetheaircraftextralift.Theirpurposeistoreducethelandingspeed.Reducingthelandingspeedshortensthelengthofthelandingrollout.Flapshelpthepilotlandinsmallorobstructedareasbyincreasingtheglideanglewithoutgreatlyincreasingtheapproachspeed.TheuseofflapsduringtakeoffservestoreducethelengthofthetakeoffSomeflapshingetothelowertrailingedgesofthewingsinboardoftheailerons.LeadingedgeflapsareusedontheF-14TomcatandF/A-18.Fourtypesofflapsareshowninfigure4-10.Theplainflapformsthetrailingedgeoftheairfoilwhentheflapisintheupposition.Inthesplitflap,thetrailingedgeoftheairfoilissplit,andthelowerhalfishingedandlowerstoformtheflap.Thefowlerflapoperatesonrollersandtracks,causingthelowersurfaceofthewingtorolloutandthenextenddownward.Theleadingedgeflapoperatesliketheplainflap.Itishingedonthebottomside.Whenactuated,theleadingedgeofthewingactuallyextendsinadownwarddirectiontoincreasethecamberofthewing.LandingflapsareusedinSpoilersareusedtodecreasewinglift.Thespecificdesign,function,andusevarywithdifferentaircraft.Onsomeaircraft,thespoilersarelongnarrowsurfaces,hingedattheirleadingedgetotheuppersurfacesofthewings.Intheretractedposition,theyareflushwiththewingskin.Intheraisedposition,theygreatlyreducewingliftbydestroyingthesmoothflow of air over the wing surface.SPEEDBRAKES.—Speedbrakesaremovablecontrolsurfacesusedforreducingthespeedoftheaircraft.Somemanufacturersrefertothemasbrakes;othersrefertothemasdiveflaps.Onsomeaircraft,they'rehingedtothesidesorbottomofthefuselage.Regardlessoftheirlocation,speedbrakesservethesamepurpose—tokeeptheairspeedfrombuildingtoohighwhentheaircraftdives.Speedbrakesslow the aircraft's speed before it lands.SLATS.—Slatsaremovablecontrolsurfacesthatattachtotheleadingedgeofthewing.Whentheslatisretracted,itformstheleadingedgeofthewing.Whentheslatisopen(extendedforward),aslotiscreatedbetweentheslatandthewingleadingedge.High-energyairisintroducedintotheboundarylayeroverthetopofthewing.Atlowairspeeds,thisactionimprovesthelateralcontrolhandlingcharacteristics.Thisallowstheaircrafttobecontrolledatairspeedsbelownormallandingspeed.Thehigh-energyairthatflowsoverthetopofthewingisknownaslayercontrolair.Boundarylayercontrolisintendedprimarilyforuseduringoperationsfromcarriers.Boundarylayercontrolairaidsincatapulttakeoffsandarrestedlandings.Boundarycontrolaircanalsobeaccomplishedbydirectinghigh-pressureenginebleedair across the top of the wing or flap surface.SPLITFLAPLEADINGEDGEFLAPPLAINFLAPFOWLERFLAPFigure 4-10.—Types of flaps. FLIGHT CONTROL MECHANISMSThetermflightcontrolreferstothelinkagethatconnectsthecontrol(s)inthecockpitwiththeflightcontrolsurfaces.Thereareseveraltypesofflightcontrolsinnavalaircraft;somearemanuallyoperatedwhile others are power operated.Manuallyoperatedflightcontrolmechanismsarefurtherdividedintothreegroups—cableoperated,push-pulltubeoperated,andtorquetubeoperated.Somesystemsmaycombinetwoormoreofthesetypes.Inthemanuallyoperatedcablesystem,cablesareconnectedfromthecontrolinthecockpittoabellcrankorsector.Thebellcrankisconnectedtothecontrolsurface.Movementofthecockpitcontrolstransfersforcethroughthecabletothebellcrank,whichmovesthe control surface.Inapush-pulltubesystem,metalpush-pulltubes(orrods)areusedasasubstituteforthecables(fig.4-11).Push-pulltubesgettheirnamefromthewaytheyInthetorquetubesystem,metaltubes(rods)withgearsattheendsofthetubesareused.MotionisOnallhigh-performanceaircraft,thecontrolsurfaceshavegreatpressureexertedonthem.Athighairspeed,itisphysicallyimpossibleforthepilottomovethecontrolsmanually.Asaresult,power-operatedcontrolmechanismsareused.Inapower-operatedsystem,ahydraulicactuator(cylinder)islocatedwithinthelinkagetoassistthepilotinmoving the control surface.Atypicalflightcontrolmechanismisshowninfigure4-12.Thisistheelevatorcontrolofalightweighttrainer-typeaircraft.ItconsistsofacombinationofThecontrolsticksinthesystemshowninfigure4-12areconnectedtotheforwardsectorbypush-pulltubes.Theforwardsectorisconnectedtotheaft(rear)sectorbymeansofcableassemblies.Theaftsectorisconnectedtotheflightcontrolbyanotherpush-pulltube assembly.BeforeWorldWarII,aircraftweremadewiththeirmainlandinggearlocatedbehindthecenterofgravity.Anauxiliarygearunderthefuselagenosewasadded.Thisarrangementbecameknownasthetricycletypeoflandinggear.Nearlyallpresent-dayNavyaircraftareequippedwithtricyclelandinggear.Thetricyclegearhas the following advantages over older landing gear:Maintains the fuselage in a level positionMakeslandingeasier,especiallyincrosswindsANf0411Figure 4-11.—Push-pull tube assembly.Figure 4-12.—Typical flight control mechanism. Thelandinggearsystem(fig.4-13)consistsofthreeretractablelandinggearassemblies.Eachmainlandinggearhasaconventionalair-oilshockstrut,awheelbrakeassembly,andawheelandtireassembly.Thenoselandinggearhasaconventionalair-oilshockstrut,ashimmydamper,andawheelandtireassembly.Theshockstrutisdesignedtoabsorbtheshockthatwouldotherwisebetransmittedtotheairframeduringlanding,taxiing,andtakeoff.Theair-oilstrutisusedonallnavalaircraft.Thistypeofstruthastwotelescopingcylindersfilledwithhydraulicfluidandcompressedairornitrogen.Figure4-14showstheinternalconstructionof one type of air-oil shock strut.ThemainlandinggearisequippedwithbrakesforstoppingtheaircraftandassistingthepilotinsteeringThenosegearofmostaircraftcanbesteeredfromthecockpit.ThisprovidesgreatereaseandsafetyontherunwaywhenlandingandtakingoffandonthetaxiwayAcarrier-typeaircraftisequippedwithanarrestinghookforstoppingtheaircraftwhenitlandsonthecarrier.Thearrestinggearhasanextendiblehookandthemechanical,hydraulic,andpneumaticequipmentnecessaryforhookoperation.Seefigure4-15.Thearrestinghookonmostaircraftreleasesmechanically,lowers pneumatically, and raises hydraulically.Thehookhingesfromthestructureundertherearoftheaircraft.Asnubbermetershydraulicfluidandworksinconjunctionwithnitrogenpressure.TheACTUATINGSELECTORVALVEDOORANDDOORLATCHMAINGEARTOLEFTMAINGEARNOSEGEARTIMERVALVESAREUSEDINMAINGEARSYSTEMTOCONTROLPROPERSEQUENCE.Anf0413Figure 4-13.—Typical landing gear system.TOWINGEYETORQUEMETERINGPIN(PISTON)AIRVALVEWHEELAXLEORIFICEPLATEFigure 4-14.—Internal construction of a shock strut. snubberholdsthehookdownandpreventsitfrombouncing when it strikes the carrier deck.CATAPULT EQUIPMENTCarrieraircrafthavebuilt-inequipmentforcatapultingofftheaircraftcarrier.Olderaircrafthadhooksontheairframethatattachedtothecablebridle.Thebridlehookstheaircrafttotheship'scatapult.Neweraircrafthavealaunchbarbuiltintothenoselandinggearassembly.Seefigure4-16.Theholdbackassemblyallowstheaircrafttobesecuredtothecarrierdeckforfull-powerturnupoftheenginepriortotakeoff.Fornosegearequipment,atrackattachestothedecktoguidethenosewheelintoposition.ThetrackhasprovisionsforattachingthenosegeartothecatapultNOTE:Theholdbacktensionbarseparateswhenthecatapultisfired,allowingtheaircrafttobelaunchedwith the engine at full power.Q4-9.Infuselageconstruction,whatarethethreeQ4-10.PointsonthefuselagearelocatedbywhatQ4-11.Inanaircraft,whatarethemainstructuralmembers of the wing?Q4-12.What does the term “wet wing” mean?Q4-13.ThestabilizingsurfacesofanaircraftconsistQ4-14.WhatarethethreegroupsofflightcontrolQ4-15.Whatisthepurposeofspeedbrakesonanaircraft?Q4-16.Mostpresent-dayNavyaircraftareequippedwith what type of landing gear?ROTARY-WING AIRCRAFTLEARNINGOBJECTIVE:Identifytheconstructionfeaturesoftherotary-wingaircraftandrecognizethefundamentaldifferencesbetweenrotary-wingandfixed-wing aircraft.Withinthepast20years,helicoptershavebecomeareality,andarefoundthroughouttheworld.TheyperformcountlesstaskssuitedtotheiruniqueAhelicopterhasoneormorepower-drivenhorizontalairscrews(rotors)todevelopliftandpropulsion.Ifasinglemainrotorisused,itisnecessarytoemployameanstocounteracttorque.Ifmorethanonemainrotor(ortandem)isused,torqueiseliminatedThefundamentaladvantagethehelicopterhasoverfixed-wingaircraftisthatliftandcontrolareindependentofforwardspeed.Ahelicoptercanflyforward,backward,orsideways,oritcanremaininstationaryflight(hover)abovetheground.Norunwayisrequiredforahelicoptertotakeofforland.Forexample,theroofofanofficebuildingisanadequatelandingarea.Thehelicopterisconsideredasafeaircraftbecausethetakeoffandlandingspeediszero,andithasautorotationalcapabilities.ThisallowsacontrolleddescentwithrotorsturningincaseofenginefailureinFUSELAGELikethefuselageofafixed-wingaircraft,thehelicopterfuselagemaybeweldedtrussorsomeformofmonocoqueconstruction.ManyNavyhelicoptersareFigure 4-15.—Arresting gear installation. CATAPULTCATAPULTAIRCRAFTCATAPULTBRIDLEHOOKSBRIDLEARRESTERLANYARDSLIDELANYARDCATAPULTCATAPULTCATAPULTLANYARDCATAPULTCATAPULTLANYARDCLEATDECKCLEATCATAPULTHOLDBACKAIRCRAFTCATAPULTHOLDBACKFITTINGFigure 4-16.—Aircraft catapult equipment. AtypicalNavyhelicopter,theH-60,isshowninfigure4-17.Someofitsfeaturesincludeasinglemainrotor,twinengine,tractor-typecantedtailrotor,controllablestabilizer,fixedlandinggear,rescuehoist,externalcargohook,andweaponspylons.Thefuselageconsistsoftheentireairframe,sometimesknownasthebody groupThebodygroupisanall-metalsemimonocoqueconstruction.Itconsistsofanaluminumandtitaniumskin over a reinforced aluminum frame.LANDING GEAR GROUPThelandinggeargroupincludesalltheequipmentnecessarytosupportthehelicopterwhenitisnotinflight.Thereareseveraltypesoflandinggearonhelicopters—conventionalfixed(skidtype),TheH-60'snonretractingmainlandinggearconsistsoftwosingleaxle,air/oiltypeofshock-strutassembliesthatmounttothefuselage.Eachisequippedwithtubelesstires,hydraulicdiscbrakes,tie-downrings,dragbraces,andsafetyswitches.Theyarepartofthe lower end of the shock strut piston.Tail Landing GearTheH-60'staillandinggearisanonretracting,dualwheel,360-degreeswivelingtype.Itisequippedwithtubelesstires,tie-downring,shimmydamper,tail-wheellock,andanair/oilshock-strut,whichservesasanafttouchdownpointforthepilotstocushiontheMAIN ROTOR ASSEMBLYThemainrotor(rotorwing)androtorhead(hubassembly)areidenticalintheoryofflightbutdifferinengineeringordesign.Theyarecoveredherebecausetheirfunctionsarecloselyrelated.Thepowerplant,transmission,drive-train,hydraulicflightcontrol,androtorsystemsallworktogether.Neitherhasafunctionwithout the other.Rotary WingThemainrotorontheH-60(fig.4-17)hasfouridenticalwingblades.OthertypesofhelicoptersmayAnf0417Figure 4-17.—H-60 helicopter. havetwo,four,five,six,orsevenblades.Figure4-18shows some typical rotor blades.Rotary-wingbladesaremadeoftitanium,aluminumalloys,fiberglass,graphite,honeycombcore,nickel,andsteel.Eachhasanitrogen-filled,pressurized,hollowinternalspar,whichrunsthelengthoftheblade.Thecuffprovidestheattachmentofthebladetotherotorhub.Atitaniumabrasionstripcoverstheentireleadingedgeofthesparfromthecuffendtotheremovablebladetipfaring.ThisextendsthelifeofTheexamplesshowninfigure4-18showotherfeatures—trimtabs,deicingprotection,balanceTherotorheadisfullyarticulatingandisrotatedbytorquefromtheenginesthroughthedrivetrainandmaingearboxortransmission.Theflightcontrolsandhydraulicservostransmitmovementstotherotorblades.Theprincipalcomponentsoftherotorheadarethehubandswashplateassemblies(fig.4-19).Theisonepiece,madeoftitaniumandsitsontopoftherotormast.Attachingcomponentsarethesleeveandspindles,bladefoldcomponents,vibrationabsorber,bearings,bladedampers,pitchchangehorns,adjustablepitchcontrolrods,bladefoldhinges,balanceweights, antiflapping and droop stops, and faring.consistsofarotatingdisc(upper),stationary(lower)portionwithascissorsandsleeveassemblyseparatedbyabearing.Theswashplateispermittedtoslideonthemainrotorverticaldriveshaftandmountsontopthemaintransmission.TheentireassemblycantiltinanydirectionfollowingthemotionThehydraulicservocylinders,swashplate,andadjustablepitchcontrolrodspermitmovementoftheABRASIONSTRIPBALANCESTRIPTRIMTABSTIPCAPBLADECUFFBLADEINSPECTIONINDICATORROOTPOCKETICEGUARDSPARSPARABRASIONTIPCAPPOCKETIDENTIFICATIONFigure 4-18.—Types of main rotor blades. flightcontrolstobetransmittedtotherotary-wingblades.Thesleeveandspindleandbladedampersallowlimitedmovementofthebladesinrelationtothehub.These movements are known aslagLeadoccursduringslowingofthedrivemechanismwhenthebladeshaveatendencytoLagistheoppositeofleadandoccursduringaccelerationwhenthebladehasbeenatrestFlapisthetendencyofthebladetorisewithhigh-liftdemandsasittriestoscrewitselfupward into the air.Antiflappingstopsanddroopstopsrestrictflappingandconningmotionoftherotary-wingheadandbladesat low rotor rpm when slowing or stopping.TAIL ROTOR GROUPThedirectionalcontrolandantitorqueactionofthehelicopterisprovidedbythetailrotorgroup.SeeBLADEFOLDACTUATORFAIRINGPITCHLOCKACTUATORROTORHUBASSEMBLYROTATINGSCISSORSLOWERPRESSUREPLATESWASHPLATEPITCHCONTROLPITCHCHANGEANf0119ROTORHEADFigure 4-19.—Main rotor head/hub assembly. figure4-20.Thesecomponentsaresimilarinfunctionto the main rotor.Thepylon,showninfigure4-20,attachesontheaircrafttothemainfuselagebyhingefittings.Thesehingefittingsserveasthepivotpointforthepylontofoldalongthefuselage.Foldingthepylonreducestheoveralllengthofthehelicopter,whichhelpsforconfined shipboard handling.Thepylonhousestheintermediateandtailrotorgearboxes,tailrotordriveshaft,cover,tailbumper,position/anticollisionlights,hydraulicservos,flightcontrolpush-pulltubes/cables/bellcranks,stabilizer/elevatorflightcontrolsurface,someantennas,androtary rudder assembly.Therudderheadcanbelocatedoneithersideofthepylon,dependingonthetypeofaircraft,andincludessuchitemsasthehub,spindle,pitchcontrolbeam,pitchChangeinbladepitchisaccomplishedthroughthepitchchangeshaftthatmovesthroughthehorizontalshaftofthetailgearbox,whichdrivestherotaryrudderassembly.Astheshaftmovesinwardtowardthetailgearbox,pitchofthebladeisdecreased.Astheshaftmovesoutwardfromthetailgearbox,pitchofthebladeisincreased.Thepitchcontrolbeamisconnectedbylinks to the forked brackets on the blade sleeves.Likethebladesonamainrotorhead,thebladesfoundonarotaryrudderheadmaydiffer,dependingonthetypeofaircraft.Tailrotorbladesmayconsistofthefollowing components:Aluminumalloy,graphitecomposite,orAluminumpocketandskinwithhoneycombcore or cross-ply fiber glass exteriorPITCHCHANGELINKROTARYRUDDERBLADEROTARYRUDDERHUBPITCHCONTROLBEAMTAILROTORGEARBOXFigure 4-20.—Tail rotor group. AluminumorpolyurethaneandnickelabrasionAdditionally,rotaryrudderbladesmayhavedeicingprovisions,suchaselectrothermalblanketsthatarebondedintotheblade'sleadingedge.oraneopreneanti-icingguardembeddedwithelectricalheatingQ4-17.Whatisthemainadvantageofrotary-wingaircraft over fixed-wing aircraft?Q4-18.Whatarethethreetypesoflandinggearusedon helicopters?Q4-19.Thedirectionalcontrolandantitorqueactionof the helicopter is provided by what group?AIRCRAFT HYDRAULIC SYSTEMSLEARNINGOBJECTIVE:IdentifythecomponentsofaircrafthydraulicsystemsandTheaircrafthydraulicsystemsfoundonmostnavalaircraftperformmanyfunctions.Somesystemsoperatedbyhydraulicsareflightcontrols,landinggear,speedbrakes,fixed-wingandrotary-wingfoldingmechanisms, auxiliary systems, and wheel brakes.HydraulicshasmanyadvantagesasapowersourceHydraulicscombinetheadvantagesoflightweight,easeofinstallation,simplificationofinspection,andminimummaintenanceHydraulicsoperationisalmost100-percentefficient,withonlyanegligiblelossduetoHowever,therearesomedisadvantagestousinghydraulics.Thepossibilityofleakage,bothinternalandexternal,maycausethecompletesystemtobecome inoperative.Contaminationbyforeignmatterinthesystemcancausemalfunctionofanyunit.Cleanlinessin hydraulics cannot be overemphasized.COMPONENTS OF A BASIC HYDRAULICBasically,anyhydraulicsystemcontainsthefollowing units:reservoirtoholdasupplyofhydraulicfluidto provide a flow of fluidTubingselector valveto direct the flow of fluidactuatingunittoconvertthefluidpressureinto useful workAsimplesystemusingtheseessentialunitsisshown in figure 4-21.Youcantracetheflowoffluidfromthereservoirthroughthepumptotheselectorvalve.Infigure4-21,theflowoffluidcreatedbythepumpflowsthroughthevalvetotherightendoftheactuatingcylinder.Fluidpressureforcesthepistontotheleft.Atthesametime,thefluidthatisontheleftofthepistonisforcedout.Itgoesupthroughtheselectorvalveandbacktothereservoir through the return line.Whentheselectorvalveismovedtothepositionindicatedbythedottedlines,thefluidfromthepumpflowstotheleftsideoftheactuatingcylinder.Movementofthepistoncanbestoppedatanytimesimplybymovingtheselectorvalvetoneutral.Whentheselectorvalveisinthisposition,allfourportsareclosed, and pressure is trapped in both working lines.ANF0421PRESSURELINESELECTORVALVEIN"DOWN"SELECTORVALVEIN"UP"ACTUATINGRESERVOIRFigure 4-21.—Basic hydraulic system, hand pump operated. Figure4-22showsabasicsystemwiththeadditionofapower-drivenpumpandotheressentialcomponents.Thesecomponentsarethefilter,pressureregulator,accumulator,pressuregauge,reliefvalve,andtwocheckvalves.Thefunctionofthesecomponents is described below.filter(fig.4-22)removesforeignparticlesfromthefluid,preventingmoisture,dust,grit,andotherpressureregulator(fig.4-22)unloadsorrelievesthepower-drivenpumpwhenthedesiredpressureinthesystemisreached.Therefore,itisoftenreferredtoasanunloadingvalve.Withnoneoftheactuatingunitsoperating,thepressureinthelinebetweenthepumpandselectorvalvebuildsuptothedesiredpoint.Avalveinthepressureregulatorautomaticallyopensandfluidisbypassedbacktothereservoir.(Thebypasslineisshowninfigure4-22,leading from the pressure regulator to the return line.)NOTE:Manyaircrafthydraulicsystemsdonotuseapressureregulator.Thesesystemsuseapumpthatautomaticallyadjuststosupplythepropervolumeofserves a twofold purpose.1.Itservesasacushionorshockabsorberbymaintaining an even pressure in the system.2.ItstoresenoughfluidunderpressuretoprovideforemergencyoperationofcertainactuatingTheaccumulatorisdesignedwithacompressed-airchamberseparatedfromthefluidbyaflexiblediaphragm, or a removable piston.pressuregaugeindicatestheamountofreliefvalveisasafetyvalveinstalledinthesystem.Whenfluidisbypassedthroughthevalvetothereturnline,itreturnstothereservoir.Thisactionprevents excessive pressure in the system.Checkvalvesallowtheflowoffluidinonedirectiononly.Therearenumerouscheckvalvesinstalledatvariouspointsinthelinesofallaircrafthydraulicsystems.Acarefulstudyoffigure4-22showswhythetwocheckvalvesarenecessaryinthissystem.Onecheckvalvepreventspowerpumppressurefromenteringthehand-pumpline.Theothervalvepreventshand-pumppressurefrombeingdirectedtotheaccumulator.HYDRAULIC CONTAMINATIONHydrauliccontaminationisdefinedasforeignmaterialinthehydraulicsystemofanaircraft.Foreignmaterialmightbegrit,sand,dirt,dust,rust,water,oranyothersubstancethatisnotsolubleinthehydraulicTherearetwobasicwaystocontaminateahydraulicsystem.Oneistoinjectparticles,andtheother is to intermix fluids, including water.Particlecontaminationinasystemmaybeself-generatedthroughnormalwearofsystemcomponents.Itistheinjectionofcontaminantsfromoutsidethatusuallycausesthemosttrouble.Regardlessofitsorigin,anyformofcontaminationinthehydraulicsystemwillslowperformance.Inextremecases,itseriously affects safety.Asinglegrainofsandorgritcancauseinternalfailureofahydrauliccomponent.Usually,thistypeofcontaminationcomesfrompoorservicingandfluid-handlingprocedures.Forthisreason,thehighest1. Reservoir2. Power pump4. Pressure regulator6. Check valves8. Pressure gauge9. Relief valve10. Selector valveFigure 4-22.—Basic hydraulic system with addition of power levelofcleanlinessmustbemaintainedwhenworkingon hydraulic components.Onlyapprovedfillstandunitsareusedtoservicenavalaircrafthydraulicsystems.Byfollowingafewbasicrules,youcanservicehydraulicsystemssafelyand keep contamination to a minimum.Neverusefluidthathasbeenleftopenforanundeterminedperiodoftime.Hydraulicfluidthat is exposed to air will absorb dust and dirt.Neverpourfluidfromonecontainerintoanother.Useonlyapprovedservicingunitsforthespecific aircraft.Maintainhydraulicfluid-handlingequipmentAlwaysmakesureyouusethecorrecthydraulic fluid.Contaminationofthehydraulicsystemmaybecausedbywearorfailureofhydrauliccomponentsandseals.Thistypeofcontaminationisusuallyfoundthroughfilterinspectionandfluidanalysis.ContinuedoperationofacontaminatedsystemmaycausemalfunctioningorearlyfailureofhydraulicQ4-20.WhataretwodisadvantagesofahydraulicQ4-21.Onabasichydraulicsystem,whatistheQ4-22.Onabasichydraulicsystem,whatistheQ4-23.Define hydraulic contamination.PNEUMATIC SYSTEMSLEARNINGOBJECTIVE:IdentifythecomponentsofaircraftpneumaticsystemsandTherearetwotypesofpneumaticsystemscurrentlyusedinnavalaircraft.Onetypeusesstoragebottlesforanairsource,andtheotherhasitsownaircompressor.Generally,thestoragebottlesystemisusedonlyforemergencyoperation.Seefigure4-23.Thissystemhasanairbottle,acontrolvalveinthecockpitforreleasingthecontentsofthecylinders,andagroundcharge(filler)valve.Thestoragebottlemustbefilledwithcompressedairornitrogenpriortoflight.Airstoragecylinderpneumaticsystemsareinuseforemergencybrakes,emergencylandinggearextension,emergencyflap extension, and for canopy release mechanisms.Whenthecontrolvalveisproperlypositioned,thecompressedairinthestoragebottleisroutedthroughthe shuttle valve to the actuating cylinder.NOTE:Theshuttlevalveisapressure-operatedvalvethatseparatesthenormalhydraulicsystemfromtheemergencypneumaticsystem.Whenthecontrolhandleisreturnedtothenormalposition,theairpressureinthelinesisventedoverboardthroughthevent port of the control valve.Theothertypeofpneumaticsysteminusehasitsownaircompressor.Italsohasotherequipmentnecessarytomaintainanadequatesupplyofcompressedairduringflight.Mostsystemsofthistypemustbeservicedonthegroundpriortoflight.TheairFigure 4-23.—Emergency pneumatic system. compressorusedinmostaircraftisdrivenbyahydraulicmotor.AircraftthathaveanaircompressorusethecompressedairfornormalandemergencyQ4-24.Whatarethetwotypesofpneumaticsystemscurrently used in naval aircraft?SUMMARYInthischapter,youhavelearnedaboutaircraftconstructionandthematerialsusedinconstruction.Youhavealsolearnedaboutthefeaturesandmaterialsusedtoabsorbstressonbothfixed-wingand