飞机设计导论(第八章)

IntroductiontoAircraftDesignChapter8Whydoaircraftcostsomuch?2020年3月7日星期六IntroductiontoAircraftDesign第2页8.1GeneralThischapterdiscussesthecostsofbuyingandoperatingcivilandmilitaryaircraft.Theformercostsaretermedacquisitioncostsforbothclassesofaircraft,whilstthelatteraretermedoperatingcostforcivila/candlife-cyclecostsformilitarya/c.ThecostsassociatedwithaircraftreliabilityandmaintenancearesignificantcontributorstooperatingandLCCs.2020年3月7日星期六IntroductiontoAircraftDesign第3页8.2AcquisitioncostsThereasonsforhighaircraftacquisitioncosts:highperformancerequirements,safetyconsideration,qualitycontrol,toolingrequirements,labor-intensiveproduction(Fig.8.1),highoverheads,largefinancialinvestment,interestcost(Fig8.2),shortproductionruns.Theadventofintegratedcomputeraideddesignandmanufacturesystemshasgonesomewaytoreducingtheaboveproblems,particularlyinreducingdevelopmenttimesandimprovinginitialbuildquality.2020年3月7日星期六IntroductiontoAircraftDesign第4页8.2.2AcquisitioncostpredictionmethodsThetwomainapproachestocostpredictionaretermed‘top-down’and‘bottom-up’.Theformerisusedduringtheconceptualorpreliminarydesignstages,whilstthelatterisutilizedduringthedetaileddesignanddevelopmentphases.Thereislittlepublishedinformationaboutthe‘bottom-up’approach.2020年3月7日星期六IntroductiontoAircraftDesign第5页8.2.2AcquisitioncostpredictionmethodsThereareseveraltop-downapproaches,butallusestatisticaldatafromaswidearangeaspossibleofexistingaircraft.Someusedataforcompleteaircraft,asshowninFig.8.3.MuchofthepublishedworkhasitsoriginsinworkbytheRandCorporation.Statisticaldataaregatheredandanalyzedtopredictcostsofbothdevelopmentandproductioncosts.2020年3月7日星期六IntroductiontoAircraftDesign第6页8.2.3TypicalacquisitioncostsFig.8.4showscivilaircraftcosts,basedonpublisheddata.Fig.8.5showscalculatedandquotedpricesofcombataircraft,basedonworkperformedbyaCrandfieldstudent,SpencerWoodford,whichistobepublishedinhisPhDthesis.2020年3月7日星期六IntroductiontoAircraftDesign第7页8.3CivilaircraftoperatingcostsTransportaircraftcostsaresub-dividedintowhataretermedindirectanddirectcosts.Theindirectoperatingcosts(IOC)arethoseassociatedwithrunninganairline,ratherthanthosedirectlyconcernedwithoperatingaircraft.Suchcoatscoversuchthingsascentraladministration,salesandpublicity,airportcostsandpassengerservice.Theaccommodationforpassengersdelayedbyanaircraftfailurewouldbetakenasindirectly.2020年3月7日星期六IntroductiontoAircraftDesign第8页8.3.2DirectoperatingcostsDirectoperatingcosts(DOC)dovarywithaircrafttypeandtriplength.Fig.8.6showsapie-chartwithrecentdataofDOCelementsforBoeing747-400.Ownershipcostscoverthecostofdepreciatingtheaircraftacquisitioncostsoverareasonableaircraftlife.Airframeandenginesparesmayalsobeincludedinthisfigure.2020年3月7日星期六IntroductiontoAircraftDesign第9页8.3.2DirectoperatingcostsSomewaysinwhichitwashopedthatadvancesinaircraftdesigncouldimproveDOCfornewaircraftinthesameperformancecategoryasthe747-400areprovidedinareferencebook.TheprojectedsavingsareshowninTable8.1.Theseareverychallengingtargetsanditremainstobeseeniftheyareachievedbythetargetdateof2015.2020年3月7日星期六IntroductiontoAircraftDesign第10页8.4Militaryaircraftlife-cyclecostsThelife-cyclecostsofamilitaryaircraftareanalogoustothesumofbothindirectanddirectoperatingcostsofciviltransports.Thereisasurprisingnumberofself-explanatorycostelementsasshowninFig.8.7.Table8.2showsasummaryofthevariouselementsofRoyalAirForceExpenditureduringthemid-1980s.Table8.3givesabreakdownofthetotallife-cyclecostsforamilitaryaircraft.2020年3月7日星期六IntroductiontoAircraftDesign第11页8.5ThecostsofreliabilityandmaintainabilityThemostdramaticformofunreliabilityisanaircraftcrashwithlossoflife.Itisimpossibletoquantifythevalueofahumanlifealthoughsomeattemptshavebeenmadetoputcashvaluesonlives.Thenextitemofunreliabilitycostisthatofdelaysandcancellations.Fig.8.8showstheproportionsofcausesofdelay.Fig8.9showsatypicalbreakdownofthesystemcausingtechnicaldelays.The3rdmajorcostofunreliabilityisfaultdiagnosis,removalandrepairorreplacementoffaultycomponents.2020年3月7日星期六IntroductiontoAircraftDesign第12页8.5.2MilitaryaircraftunreliabilitycostsAircraftcrashesareagaincostlyintermsoflifeandmaterialcosts.Fig.8.10showsthepossiblemaintenancecostsavingsthatwerepredictedfor385TornadoaircraftrelativetotheF-4Phantom,overa10yearperiod.Fig.8.11shows1987figuresforfailureratesagainstaircraftemptyweight.Thelatterisameasureofthecomplexityoftheaircraft.2020年3月7日星期六IntroductiontoAircraftDesign第13页8.5.2MilitaryaircraftunreliabilitycostsFigure8.12showstrendsinspecificreliabilityovera25-yearperiod.Specificreliabilityisdefinedasthenumberoffailureperflyinghourperunitofaircraftmass.F-22AaretodoublethesortierateoftheF-15,anddosowithhalfthemaintenancepersonnelrequiredandtwicethemeantimebetweenfailures(MTBF).2020年3月7日星期六IntroductiontoAircraftDesign第14页8.5.3FactorsaffectingmaintenancecostsThemagnitudeofmaintenancecostshasalreadybeenmentioned,andiscloselylinkedtotheunreliabilityoftheaircraft.Anaircraftwithlowoperationcostswillneedtohavehighreliability.Fig.8.16showsanoverallp