飞机设计导论(第六章)

IntroductiontoAircraftDesignChapter6What’sundertheskin?Airframesystems2020年6月26日星期五IntroductiontoAircraftDesign第2页6.1SecondaryPowerSystemsSecondarypowerisusuallyprovidedbyanaircraft’smainengineswhentheyareoperatingbutcanbesuppliedbyothersourcessuchasanauxiliarypowerunit(APU)intheaircraftoranexternalsourceontheground.Almostallpresenta/cSPSareofthreetypes:electricpower,bleedair/pneumaticpower,andhydraulicpower,seeFig.6.1.theengine’shpshaftdrivesanaccessorygearboxonwhicharemountedgeneratorandhydraulicpumpsaswellastheengine’sownaccessories.2020年6月26日星期五IntroductiontoAircraftDesign第3页6.1.1Air-conditioningandpressurizationBleedairistappedfromoneormorepointsalongtheenginecompressortosupplytheaircraft’sair-conditioningandpressurizationsystem.Itisusualtomaintainana/ccabinatapressureequivalenttothatat8000ft(2400m)orlessandthisrequiresaconstantsupplyofpressurizedair.Oxygenusedbytheoccupantsmustbereplacedandthetemperatureandcontaminantlevelscontrolled,requiringasignificantair.2020年6月26日星期五IntroductiontoAircraftDesign第4页6.1.1Air-conditioningandpressurizationFig.6.2showsthemajorelementsofanair-conditioningsystem.Thecombinationofair-conditioning,pressurizationandoxygensystemsareusuallytermedtheenvironmentalcontrolsystem(ECS).Inadditiontocoolingthecrewandpassengercompartmentsonhigh-speeda/citmaybenecessarytoremoveheatfromtheundercarriagebays,electricalequipmentandflyingcontrolareas.2020年6月26日星期五IntroductiontoAircraftDesign第5页6.1.1Air-conditioningandpressurizationMilitarya/cuseECSsystemsworkingonthesameprinciplesasthoseforcivila/c,butThepressurizedcabinhasamuchsmallervolumeandworksatalowerpressuredifferential.Oxygensystemsareusedinnormaloperationsathigheraltitudes.Militaryavionicsaremorecomplexandproducecomparativelymoreheatandthusrequiremorecooling.HawkTrainerisshowninFig.6.3.2020年6月26日星期五IntroductiontoAircraftDesign第6页6.1.2IceprotectionsystemsDangerousicingconditionsarerarelyencounteredbymoderna/cbutitisnormallynecessarytoprovideprotection.Engineintakeicingismorecommonduetothespecialflowconditionspresentandmosta/catleasthaveaprovisionforde-icinginthisregionoftheairframe.Protectionagainsticingcanbeobtainedinvariousways.De-icingallowsicetofromtoacertainextentandthemperiodicallyremovesit.Anti-icingisasystemwhichisactivatedwhenicingconditionsarelikelyandpreventsiceformation.2020年6月26日星期五IntroductiontoAircraftDesign第7页6.1.2IceprotectionsystemsBleedairisnotonlyathighpressurebutalsohightemperature,soitthemainformoficeprotectionfortheairframeandengines.Onlargetransports,onlytheouterportionofthewingleadingedgesorslatsandtheenginecowllipsrequireprotection.Smallera/calsorequireprotectionofthetailsurfaceleadingedges,andwhenoperatingiceprotectioncantake3timestheflowforair-conditioning,fortheshorttimethattheiceprotectionisrequired.2020年6月26日星期五IntroductiontoAircraftDesign第8页6.1.2IceprotectionsystemsTurbo-proppowereda/chaveinsufficientbleedforthermalanti-icing,soalternativeformsofprotectionarerequired.Someleadingedgesareprotectedusingapneumaticpoweredsystem,butthisusesonlysmallamountsofairtoperiodicallyinflateflexible“boots”thusde-icingthearea.Thesebootsarenottotallyeffectiveinallconditionsandarepronetoerosionduetotheirrelativesoftnature(Fig.6.4).2020年6月26日星期五IntroductiontoAircraftDesign第9页6.1.2IceprotectionsystemsAnotherpossibilityistosprayafluidovertheaffectedsurfacetoreducethemeltingpointofthemixtureformedtobelowtheambienttemperature.Localizedanti-icingmaybeprovidedbytheuseofembeddedelectricalheatingelements.Amorerecentdevelopmenthasbeenelectro-inductionde-icing.Wheniceisdetected,thesystemuseselectro-magneticmeanstovibratethewingleading-edgetoshakeiceoff.2020年6月26日星期五IntroductiontoAircraftDesign第10页6.1.3ElectricpowersystemsEngine-drivengeneratorsprovide3-phase400Hz115VlinetoneutralACPower,someofthispowerwillbeconvertedto28VDC.Mosta/chavebothdirectandalternatingcurrentsupplieswiththeformerusedprimarilyforsuchitemsaselectricallydriveninstrumentsandlights.ACpowerforhighenergydevicessuchaselectricalanti-icing.TheusualsourcesofpowersupplyareenginedrivenalternatorswhichsupplyACwhichcanalsobeconvertedtoDCbytransformer/rectifier.2020年6月26日星期五IntroductiontoAircraftDesign第11页6.1.3ElectricpowersystemsLargea/cusesmallturbinesasAPUsforenginestartingandairconditioningwhilstthea/cisontheground.BatteriesareusedtosupplyDCdirectlyandcanbeusedtostartenginesonsmallaircraft.Powersuppliesmustbeduplicatedortriplicatedsothatpowercanbesuppliedevenintheeventoffailuresofindividualcomponents.Fig6.5showsaschematicairlinersystemandFig.6.6describestheBAeHawk’ssystem.2020年6月26日星期五IntroductiontoAircraftDesign第12页6.1.4HydraulicsystemsThemajoruseofhydraulicsona/cistoprovidefortheactuationofdevicessuchasflyingcontrols.Almostallmediumandlargeciviltransportshaveasystemoperatingatapressureof3000psi(210kg/cm2)Undercarriageorlandinggearsareretractedandextendedhydraulically,aswellasbraking.Largedoorsareactuatedbyhydraulicsystems.Highreliabilityisanimportantconsiderationandthisleadstotheduplicationortriplication.2020年6月26日星期五IntroductiontoAircr