飞机设计导论(第七章)

IntroductiontoAircraftDesignChapter7What’sundertheskin?Avionics,flightcontrolandweaponsystems2020年3月7日星期六IntroductiontoAircraftDesign第2页7.1AvionicsSystemsAvionicsisoneofthemostrapidlydevelopingfieldsofaircraftdesign.Itsimportanceandrangehasincreasedoverrecentyearsandasmuchas40%ofthecostofnewaircraftcanbeattributedtoavionics.Thereisabewilderingrangeofavionicssystems,eachofwhichusuallyrequirestheuseofmanyacronyms.Fig.7.1showsanavionicsfitforasmallexecutiveaircraft.2020年3月7日星期六IntroductiontoAircraftDesign第3页7.1AvionicsSystemsModernefficient,reliableavionicshavedramaticallysimplifiedtheflightoperationandhaveeliminatedtoneedofcrewmemberssuchasnavigator,wirelessoperatorandflightengineer.Thegrowthinthecapabilitiesofmilitaryavionicshasbeenevenmoredramaticandmakeitpossibleforpilotofsingle-seataircrafttonavigate,communicate,detectandattacktargetsatheightsof30mandspeedsapproachingthespeedofsound.Fig.7.2and7.3.2020年3月7日星期六IntroductiontoAircraftDesign第4页7.1.1CommunicationAirbornecommunicationssystemsvaryconsiderablyinsize,weight,range,powerrequirements,qualityofoperation,andcost,dependinguponthedesiredoperation.ThemostcommoncommunicationsysteminusetodayisVHF,largea/careusuallyequippedwithHF,somearefittedwithUHFsystems.VHF(100~150MHz)radiowavesfollowapproximatelystraightlines.Therangeofcontactisdeterminedbytheheightsofthetransmittingandreceivingantennas.2020年3月7日星期六IntroductiontoAircraftDesign第5页7.1.1CommunicationTypicalrangesare200miles(320km)at20000ft(6000m).UHFsystemsaresimilartoVHFbutoperateinthe200~400MHzband.HF(2~30MHz)communicationsystemisusedforlongrangecommunication,whichoperatesessentiallyinthesamewayasVHFsystems.CommunicationsoverlongdistancesarepossiblewithHFradiobecauseofionosphericreflection.2020年3月7日星期六IntroductiontoAircraftDesign第6页7.1.1CommunicationAirtrafficcontrollersneedtoknowthepositionofalla/cwithintheircontrolareas.Ground-basedradarsystemsdetectalla/cbutsomesystemisrequiredtoidentifythem.Civila/ccarryequipmentscalledATCtransponderswhichreceivepulsesfromthegroundradarsets.Thetransponderthetransmitsasequenceofpulseswhichidentifiesthea/candgivesitsheighttothecontroller.IFF(identificationfriendorfoe)formilitarya/crespondstosignalsfromeitherground-basedorairborneradars.2020年3月7日星期六IntroductiontoAircraftDesign第7页7.1.2NavigationsystemsTheknowledgeofaircraftpositionhasalwaysbeenimportantinflyingandinitiallyinvolvedvisual‘fixes’madeingoodvisibility,withtheaidofacompass.Thismethodisstillusedbysomelightaircraftpilots,butincreasingsophisticatednavigationsystemshavebeendeveloped.2020年3月7日星期六IntroductiontoAircraftDesign第8页7.1.2.1Automaticdirectionfinding(ADF)Theaerialisdirectionalandthesignalbecomesweakerorstrongerastheradioisrotatedaboutaverticalaxis.Ona/c,loopaerialsarerotatedinthedirectionofaground-basednon-directionalbeacons(NDBs).TheradiomagneticindicatorgivesthemagneticbearingoftheNDBswhichwillgiveinformationtolocatethea/conamap.Max.rangeis10-150nmilewithatypicalaccuracyof±4°.2020年3月7日星期六IntroductiontoAircraftDesign第9页7.1.2.2VHFomnidirectionalrange(VOR)systemTheVORisanelectronicnavigationsystem.Theall-directionalrangestationprovidesthepilotwithcoursesfromanypointwithinitsservicerange.Itproduces360usableradialsorcourses,anyoneofwhichisaradiopathconnectedtothestation.Theradialscanbeconsideredaslinesthatextendfromthetransmitterantenna.ItoperatesinVHFbandandtherangeisupto130nmileat12000ftwithanaccuracyof±1°.2020年3月7日星期六IntroductiontoAircraftDesign第10页7.1.2.3Distancemeasuringequipment(DME)Thisisainterrogationandresponsesystem,wherethea/cequipmentsendsaVHFsignaltoagroundstationwhichthenrespondstothea/c.TheDMEreceivercomputesthetimedelayandcalculatesthedistancefromthebeacon.ItsdistanceissimilartothatofVOR,withanaccuracyof±0.5nmile.TACAN(tacticalairnavigation)isusedformilitarya/c,whichcombinesfeaturesofbothVORandDMEandgivesrangeandbearing.2020年3月7日星期六IntroductiontoAircraftDesign第11页7.1.2.4DopplernavigationThisisamediumtolong-rangeself-containedsystem.Atypicalsystemaccuracymightbe1%indistanceandheading,whichwouldbeseriousatlongrangesunlesscorrectedbyothersystems.TheDopplerradaremitsnarrowbeamsofenergyatonfrequency,andthesewavesofenergystriketheEarth’ssurfaceandarereflected.Theearth-returnedenergyisinterceptedbythereceiverandcomparedwiththeoutgoingtransmitterenergy.Thedifference,duetoDopplereffect,isusedtodevelopgroundspeedandwinddriftangleinformation.2020年3月7日星期六IntroductiontoAircraftDesign第12页7.1.2.5Longrangenavigation(LORAN)andOmegaLORANhasbeenamajornavigationsystemwhichutilizesthehyperbolicprinciple.Positionisfixedbyusingseveralgroundstationstoproduceintersectinghyperbolicsystemswhoseintersectionsdescribeuniquepoints.Fig.7.4Therangesisupto2500nmilewherethesignalreflectedfromtheionosphere.AmoremodernsystemisOmega,whichuseseightgroundstationsworld-wideandusesVLFtransmitters.2020年3月7日星期六IntroductiontoAircraftDesign第13页7.1.2.6Globalpositioningbysatellite(GPS)ThisIisarelativelyrecentsystemwhichisbeingincreasinglyusedbycivilandmilitarya/c.Ittakespositionfixesfromsignalsfromaglobal