Simulator of a Light and UltraLight Sport Aircraft.docx
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Simulator of a Light and UltraLight Sport Aircraft.docx
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SimulatorofaLightandUltraLightSportAircraft
SimulatorofaLightandUltra-LightSportAircraft
Ing.EvženThöndel,Ph.D.(thoendel.jr@pragolet.cz)
Thispaperprovidesaninsightintothedevelopmentandimplementationofaflightsimulatorintendedforthetrainingofpilotsoflightandultra-lightsportsaircraft.Therearemanysimulatorsoflargeairlinersandmilitaryaircraftinservicetoday;however,simulatorsofsportsairplanesareextremelyrare.Thiscanbeattributedmainlytohighdevelopmentandproductioncostsofsuchsimulators.Theprimaryaimofthisprojectisthedevelopmentofareasonably-pricedflightsimulatorforpotentialcustomers(sportsflightschools)whilemaximizingsimulationauthenticityandaccuracy.Inadditiontoaudiovisualandcontrolsystems,thesimulatorisequippedwithmodulesenablingthesimulationofmotioneffects,whichcanhave,particularlyinthistypeofaircraft,asignificantimpactonthepilot’sreactionsanddecisions.Amajorpartofthispaperprovidesadescriptionofaparallelmanipulator(Stewartplatform)andtheoptionsofemployingitformotionsimulationpurposes.
Introduction
Thispaperdescribesthedevelopmentofaflightsimulatoroflightandultra-lightsportsaircraft.
Simulatorsaredevicesreproducing,asaccuratelyaspossible,thecharacteristicsandbehaviourofrealdevicessuchasaerospaceandlandvehicles.Flightsimulatorsaretypicallyusedforpilottrainingandforresearchanddevelopmentpurposes.
Involvingasimulatorinthetrainingprocesshastwomainbenefits:
First,anymistakesthepilotmakesintrainingdonotjeopardizehishealth.Thesecondbenefitisaneconomicone–itismuchcheapertooperateasimulatorthanarealdevice.
Therearemanysimulatorsoflargeairlinersandmilitaryaircraftinservicetoday;however,simulatorsofsportsairplanesareextremelyrare.Thiscanbeattributedmainlytohighdevelopmentandproductioncostsofsuchsimulators.However,rapiddevelopmentofinformationtechnologyandasignificantpricedropinrecentyearshasmadeflightsimulatorssuitableforthetrainingofpilotsoflightandultra-lightaircraftaswell.Flightsimulatorswouldallowfuturepilotstopracticeinsafetyandlearnhowtocopewithdifficultanddangeroussituations–whichtheycouldneverdoinarealplane.Inaddition,simulatorscandecreasetrainingcostssignificantly.
Inthefirstplace,anysimulatorintendedforthispurposehastoaffordableforpotentialcustomers,inparticularflightschools.Atthesametime,however,ithastobeuseful,i.e.provideaccurateandauthenticexperience.
Therestofthispaperdescribesthecurrentstatusandfuturedevelopmentofaflightsimulatorofalightorultra-lightaircraftdesignedbyPragolet,s.r.o.
SimulatorStructure
Figure1 showsthegeneralblockstructureoftheflightsimulator.Thecentrepieceofthesimulatorisamathematicalmodelofthedynamicbehaviouroftheplane.Themathematicalmodelisconnectedtoothercomponentsviadifferentcommunicationinterfaces.Thefollowingsectionsprovideadescriptionofthemostimportantcomponents,explainingtheirroleinthedesignofthesimulatoroflightandultra-lightaircraft.
Fig.1:
Flightsimulatorstructure.
MathematicalModel
Thecentrepieceofthesimulatorisamathematicalmodelofanairplane.Theaccuracyofthemathematicalmodeldeterminestheoverallqualityandauthenticityofsimulation.Themodelreadstheoutputsofindividualcontrolelementsandcalculatesthevaluesofforcesandmomentsactingonthesimulator,thusdetermining,takingintoconsiderationtheeffectsoftheoutsideenvironment,thecurrentstateoftheairplane(suchasitsposition,speed,etc.).
Therearetwobasicapproachestodesigningmathematicalmodelsforaircraftsimulators.Thefirst,morecomplexapproachmakesuseofactualairplanegeometry,whereasthesecond,morestraightforwardapproach(atleastinmathematicalterms)isbasedonaerodynamiccoefficients.Aerodynamiccoefficientsarefigureswhich,aftermultipliedbyanothervalue(suchaswingareaanddynamicpressure),providetheforcesandmomentsactingupontheaircraft.
Asitsmainbenefit,thefirstapproachmakesitpossibletostudyaircraftbehaviourundernon-standardoperatingconditionsaswell.However,thereisaflipsidetooasthemodelisverydifficulttoderiveandinvolvesdifficultcalculations,thusbeingmoresuitableinparticularforexperimentalpurposes.
Theotherapproachismuchmorestraightforwardbutrequiresaerodynamiccoefficientsoftheairplaneinquestion;thesecaneitherbeobtainedfromtheaircraftmanufacturerormeasured.Inaddition,theaccuracyofamathematicalmodelusingaerodynamiccoefficientsislimitedtothescopeofmeasureddata.
Themathematicalmodelfortheflightsimulatordescribedinthispapermakesuseofthesecondapproach,i.e.aerodynamiccoefficients,andhasbeenimplementedinJSBSim.
JSBSimFlightDynamicsModel
JSBSimisacross-platformopen-sourcegenericflightdynamicsmodelwritteninC++[4] andhasbeenincorporatedintomanylargeflightsimulationapplicationsandframeworks(suchasFlightGearandOpenEaagles).Aircraftdata,includingaerodynamiccoefficientsandotherparameters,arestoredinoneormoreXMLfiles.JSBSimrunsasastandaloneapplication,communicatingwithitsenvironmentviastandardinterfaces(forinstancesockets).Moredetailsofthemodelanditsbehaviouraswellastheequationsusedfornumericalcalculationscanbefoundinthedocumentation [4].Atheoreticalanalysisoftheseequationsisprovidedforexamplein [2] orin [1].
ThefirstreleaseofthesimulatorsoftwaremadeuseofanalreadyexistingmodeloftheCessna172Skyhawk.Infutureversionsofthesimulator,itisenvisagedtointroducemoreaerospacevehicles,specificallyotherlightandultra-lightaircraftfrequentlyusedinflightschools.
Na Figure2 showsanextractfromtheflightdynamicsmodelcodeoftheCessna172Skyhawk.
Fig.2:
ExtractfromtheflightdynamicsmodelcodeofCessna172.
VisualisationSystem
Visualisationsystemsformanintegralpartofmodernsimulators.Thesystemgeneratesimageryoftheoutsideworldbasedonthecurrentpositionoftheaircraftandusingdatafromtheterraindatabase,sendingthisdatatothedisplaydevice.Othervisualisationelementsareoftenusedinadditiontothecentralunitdisplayingthevicinityoftheaircraft,suchassystemsrepresentingtheplane’scontrolpaneland/orotherpartsofthecockpit.Ingeneral,visualisationsystemelementsusedinflightsimulatorscanbedividedintothefollowingcategoriesbasedontheirrole:
∙imagegeneratorand
∙displayingsystem.
ImageGenerator
Therearemanycommercialandnon-commercialimagegeneratorsavailabletoday,someofthemdesignedexclusivelyforflightsimulators.ThesimulatordescribedhereinmakesuseoftheFlightGearimagegenerator(Figure3),thereasonsforthisdecisionbeinglistedbelow:
∙FlightGearisdistributedasopen-sourceundertheGNUGeneralPublicLicenseandthuscanbemodifiedinfutureifrequired.
∙FlightGearisamulti-platformdevelopmentproject;currently,therearebuildsforMicrosoftWindows,Linux,MacOSandotheroperatingsystems.
∙FlightGearmakesuseoftheJSBSimflightdynamicsmodeldescribedintheprevioussection.
∙FlightGearsupportstheMATLAB-SIMULINKdevelopmentenvironment.
Fig.3:
FlightGearimagegenerator.
FlightGearmakesuseofOpenGL,themostpopularprogramminginterfaceforapplicationsrendering2Dand3Dgraphics.Hardwarerequirementsarecomparabletostandarddesktopcomputers.Itisrecommendedtouseavideocardwithadedicatedhardwareaccelerator(GPU)supportingtheOpenGLstandard.
AsFlightGearisopensource,itscorefunctionalitycanbeextendedwithmanyadditionalplug-insandprogrammesavailableontheInternet,suchasvariouseditorsofterraindatabasesandobjects(buildings,bridges,etc.).
FlightGearisusedforR&Dpurposesbymanyuniversitiesworldwide(TechnischeHochschuleAachen,UniversityofIllinoisandmanyothers) [10].
DisplayingSystem
Whiletheimagegeneratorcreatesobjects,texturesandothersceneryelements,thedisplayingsystempresentsthisdatatothepilot.Generallyspeaking,oneofthreemaindisplayingsystemtypescanbeusedinflightsimulators:
simpleprojection,directviewdisplayordirectviewdisplaywithacollimator(collimateddirectdisplay).(Dualprojectionsystemsarenotusedveryofteninflightsimulators.)Eachdisplayingsystemtypehasitsprosandconsandtheirpricesaredifferenttoo.Thelistbelowgivesanoverviewofthecriteriawhichneedstobetakenintoconsiderationwhendeterminingthemostsuitabledisplayingsystemtypefortheflightsimulatordescribedherein:
∙Price:
Assetforthinthebeginning,thepriceofthesimulatorhastoberelativelylowwithregardtoaffordabilityforpotentialcustomers.
∙Lowweightandcompactdesign:
Giventhatitisintendedtosimulatemotioneffectsaswellandasthedisplayingsystemhastobeplacedinthecockpitofthesimulator,ithastoberelativelylightandcompact.
∙Viewaccuracy:
Forpilotsoflightorultra-lightaircraft,spatialorientationismuchmoreimportantthan,forexample,forpilotsofalargeairlinerscruisingathighaltitudes.
Giventhatsimpleprojectionhasconsiderablespatialrequirements,itcannotbedeemedsuitableforthesimulatordescribedinthispaper.Thesecondmethod,directviewdisplay,istypicallyimplementedusingLCDorplasmascreenstoday,whichalsoguaranteehigherluminancethansimpleprojection.Recommendedluminancelevelsforsimulatorsamountto300cd/m2 [3].Themaindisadvantageofdirec
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