THEUSEOFGPSTRACKINGANDGUIDANCESYSTEMSFORTHECHICKEN LITTLEJOINTPROJECT’S“ACOUSTICWEEK”FLIGHTTESTPROGRAM MarkHardesty FlightTestEngineer TheBoeingCompany Mesa,Arizona [email protected] DavidConner AerospaceEngineer JointResearchProgramOffice,AeroflightdynamicsDirectorate U.S.ArmyResearch,Development,andEngineeringCommand LangleyResearchCenter, Hampton,Virginia [email protected] CharlesSmith AerospaceStaffEngineer LockheedMartinEngineeringandSciencesCompany LangleyResearchCenter Hampton,Virginia [email protected] WilliamTerrell Acoustic/SeismicProgramManager EglinAirForceBase,Florida [email protected] ABSTRACT Atwo-weekflighttesteffortwasconductedinSeptember2003ataremotelocationatEglinAirForceBasein Florida.Dubbed“AcousticWeek”,thetestwassponsoredbytheChickenLittleProgramOfficeandtheNational GroundIntelligenceCenter.Thetestwasdesignedtoexaminetheeffectivenessofdatacollectiontechniquesfora varietyofsensors,whilesimultaneouslycollectingsignaturedataforavarietyofaircraft.Eightaircraftweretested includingtworotorcraftfromtheUnitedStatesArmyLeadTheFleetprogram,aNavyfixedwingunmannedair vehicle(UAV),aprototyperotarywingUAV,andfourcivil helicopters.Sensorsincludedacousticandseismic arrays,infra-redmeasurementdevices,andahumansoundjury.Essentialvehiclepositiondatawereacquiredby fivedifferentorganizationsusingfivedifferentsystemsofvaryingaccuracyandquality.Thefocusofthispaperis theGPStrackingsystemusedbyanArmy/NASA/Boeingtestteamtoprovideflightpathguidancecues,aswellas toacquireprecisevehiclepositiondata, fortwoofthetestvehicles.The measurementtechnique usedtoobtain vehicle source noise hemispheres and the use of these noise hemispheres to predict ground noise footprints is discussed and the need for precise vehicle position data and precision flight tracks is investigated. A detailed descriptionofGPStrackingsystems,sourcesofanalysiserrorsanddataaccuracydegradation,andthecriticalityof instrumentationinstallationonsystemperformanceareprovided.Flighttrackresultsdocumenttheimprovementin deviations from the desired flight track when guidance cues are provided by course and glide slope deviation indicatorsratherthanthetypicalgroundreferencecues. Presented at the American Helicopter Society Annual Forum, Baltimore,MD,June7-10,2004.Copyright©2004theAmerican HelicopterSocietyInternational,Inc.Allrightsreserved. 1 NOTATION validation of acoustic detection prediction models. Finally, data were collected for a number of non- The following symbols, used in this paper, are acousticsensorsforsystemvalidationpurposes. identifiedforquickreference: Participantsintheexerciseincluded(inpart): ADAM AcousticDetectionofAircraftModel CDI CourseDeviationIndicator • ArmyAeroflightdynamicsDirectorate CORS ContinuouslyOperatingReference • ArmyAviationAppliedTechnologyDirectorate System • ArmyAviationTechnicalTestCenter DGPS DifferentialGlobalPositioningSystem • ArmyResearchLabs DoD DepartmentofDefense • Bell GDI GlideslopeDeviationIndicator • Boeing GOES Geostationary Operational Environmental • DraperLabs Satellite • L3Communications GPS GlobalPositioningSystem • MILTECHResearchGroup L1 GPScarrierfrequencyat1575.42MHz • L2 GPScarrierfrequencyat1227.60MHz NASALangley • MMW MillimeterWave NAVAIR • NAD NorthAmericanDatum NightVisionLabs NOAA National Oceanic & Atmospheric • SandiaNationalLabs Administration • Sikorsky RNM RotorcraftNoiseModel • SouthwestResearch RTK RealTimeKinematic SAM SurfacetoAirMissile TheU.S.Army’sJointResearchProgramOffice, UAV UnmannedAirVehicle Aeroflightdynamics Directorate (JRPO-AFDD), UTC UniversalCoordinatedTime Aviation Applied Technology Directorate (AATD), WAAS WideAreaAugmentationSystem and the NASA Langley Research Center (LaRC) WGS WorldGeodeticSystem participated in the Acoustics Week Flight Test Program with the primary purpose of obtaining a benchmark rotorcraft acoustic database for (1) INTRODUCTION validation of acoustic detection prediction programs and (2) acquisition of a database of acoustic source The Chicken Little Program Office test noisecharacteristicsforavarietyofrotorcraft.More organization was developed specifically for the specifically, it is planned to use this database to purpose of foreign threat system exploitation to aid validate a new acoustic detection prediction code Department of Defense (DoD) organizations in the called the Acoustic Detection of Aircraft Model developmentofseeker/sensorsystems.Exploitation (ADAM) that is currently under development by a consistsofSurfacetoAirMissile(SAM),Millimeter NASA LaRC/AFDD/AATD/Wyle Laboratories Wave (MMW), infra-red, hyper-spectral, visual, team.AttheheartofADAMistheRotorcraftNoise automotive,andmore. Model (RNM), which is an environmental noise predictionprogramdevelopedbyWyle Laboratories AcousticWeekwasconductedtoprovideDOD, under contract to NASA LaRC (Refs. 1-3). RNM US intelligence organizations and industry the estimatesthenoisefootprintforrotorcraft(oranyair opportunitytocollectvarioussignaturesofnumerous vehicle)operationsandthusprovidesatooltoaidin aircraft.Anopendialogwasalsoprovidedtoallow the development of low noise operations. Source the acoustics community to advance signature noisehemispheresarerequiredasinputtotheRNM. collection capabilities. A primary program This paper will focus on the use of a Differential motivationwastoincreasetherotarywingsignature Global Positioning System (DGPS) based tracking data available through the Defense Intelligence and guidance system for the collection of measured Agency’sNationalSignaturesProgramdatabasefor sourcenoisehemispheres. future seeker/sensor development. During this test program relatively short-range acoustic data were collected for source noise hemisphere development. After collection of the short-range acoustic data, long-range acoustic data and aural detection (sound jury) data were collected simultaneously for 2 ROTORCRAFTNOISEMODEL(RNM) propagated through the atmosphere to the specified receiverlocations.Thepropagationmodelcurrently Tounderstandthecriticality ofaccurateaircraft assumesthattheacousticraypathsarestraightlines positiondataandprecisionflighttracksnecessaryto andthatthereisnowindpresent.Programplansare obtainhighqualitysourcenoise measurements,it is toincorporatethecurrentstate-of-the-artatmospheric helpful to have at least a basic understanding of propagation methodology for wind and temperature RNM. RNM is a computer program that simulates effectsintoRNMinthenearfuture.RNMcurrently sound propagation through the atmosphere. As a accounts for spherical spreading, atmospheric noise source, rotorcraft are far more complex than absorption, ground reflection and attenuation, fixed-wing aircraft, with a high degree of noise Doppler shifts and the difference in phase between directionality that is not present for fixed-wing the direct and reflected rays. The most recent aircraft. While a single engine operating state upgrade to the RNM (version 3.0) allows for the parameter (a generalization not applicable to predictionofnoiseovervaryinggroundterrainusing rotorcraft)istypicallyusedtocharacterizefixedwing an implementation of the Geometrical Theory of noise emissions, rotorcraft sources are three Diffraction,whichincludesextensionsfordiffraction dimensionalinnatureandthedirectivityandspectral asdevelopedbyRasmussen(Ref.4).Priorversions content vary with flight condition, namely flight of RNM (Ref. 5) simulated propagation over flat speed and flight path angle. At its core, RNM terrainonly,andareapplicableonlywherephysical utilizes single or multiple sound hemispheres propertiesofthesurroundingareaarenotsignificant. (broadband and pure tone with phase) for a given RNM performs the acoustical atmospheric flight condition to define the three-dimensional propagation for a given vehicle and creates ground spectralsourcecharacteristicsofaflightvehicle. noise predictions and detailed metric time history. RNM is also capable of providing information that RNMcalculatesthenoiselevels,inavarietyof can be imported into a Geographical Information metrics,atreceiverpositionsonthegroundeitherat System (GIS). The noise contours can then be points of interest or on a uniform grid. Rotorcraft overlaidtoscaleonabackgroundmap,whichisideal operationsaredefinedaseithersingleflighttracksor for performing noise abatement studies, airport and as multiple flight tracks with varying vehicle types vertiport noise impact evaluations and land-use andflightprofiles. Acousticpropertiesofthe noise planning studies. Ground mesh time history data source(s)aredefinedintermsofeitherbroadbandor may be post processed into acoustic simulation pure-tone (with phase information) sound animations, which is useful for understanding hemispheres and may be obtained from theoretical propagationovervaryingterrain. predictions, wind tunnel experimentation, flight test measurementsoracombinationofthethree.RNM has been recently expanded to include atmospheric sound propagation effects over varying terrain, including hills and mountainous regions, as well as regions of varying acoustical impedance such as coastal regions. Modifications are currently under development to include the effects of winds and temperature for a two-dimensional stratified atmosphere. The United States Department of Defense and the North Atlantic Treaty Organization (NATO) have adopted RNM as the standard prediction tool for Environmental Impact Assessmentsofmilitaryrotorcraftoperationsnoise. Themajorcomputationalandphysicalelements of the RNM are the sound propagation module and the input