Since its founding, NASA has been dedicated to the advancement of aeronautics and space
showsthattheX-CGtrimmedaircraftusesslightlylesspowerinthesesegments.Intheclimbanddescentsegments,Segs1,3,and5,wherethepowersettingisprogrammedtoa xedsetting,theX-CGtrimmedaircraftexperiencesslightlymoreacceleration(Fig.11).Bothofthesephenomenaareattributabletothereductionindragcoef cient,,whichistheresultoftrimmingbyvaryingtheX-CGpositionasopposedtousingthestabilator.ThisisshowninFig.12.
StabilityResults
StabilitymarginsforeachtrimmedconditionareshowninFig.13.Althoughtheresults
betweenthetwotrimparadigmsaremixedoverthereferencemissionpro le,theX-CGtrimmedcaseseemstohavemoretendencytogotoanegativestabilitymarginthanthestabilatortrimmedcase.
Thelateraleigenvaluesarewellbehaved,consideratelyseparatingintotheconventional
spiralmode,rollmode,andDutchrollpair.Thespiralmoderemainsstable(Fig.14),asdoestherollmodewhichisshowninFig.15andtheDutchrollpairwhoserealandimaginarypartsareplottedasafunctionof ightconditionnumberinFig.16.Dutchrolldampingalsoseemsadequate.
Thelongitudinaleigenvalueswerenotsoreadilyidenti able.Fig.17showstherealpart
ofthemostunstablelongitudinaleigenvalue.Fig.18givesascatterplotofallthelongitudinaleigenvalueswiththetwotrimparadigmsplottedseparately.Theraweigenvaluedataaretabulatedattheendofthisreport.
Acknowledgement
TheauthorsaregratefultoDr.ChristopherGraceyofNASALangleyResearchCenterfor
hishelpinlocatingdataforthisstudyandinformulatingtheapproach.
References
[1]RajivSinghChowdhryandCareyButtrill,“Reference-HAssessment:BareAirframeStability
andTrimDragReduction,”MemotoGFCITD,September13,1995.[2]“HighSpeedCivilTransportReferenceH–Cycle3SimulationDataBase.”ABoeingreport
forNASAContractNAS1-20220,TaskAssignmentNo.36,WBS4.3.5.1.2.1.[3]“HighSpeedResearchProgramHSRII–Airframetask20;Task2.1–TechnologyIntegration;
Sub-task2.1.1.1Re neTechnologyConceptAirplane:Con gurationDescriptionDocument;DeliverableReport.”ApprovedbyJ.B.Coffey,BCAG;J.K.Wechsler,MDC;P.F.Sweetland,BCAG;H.R.Welge,MDC.PreparedforNASALangleyResearchCenter,NASAContractNAS1-20220.April1,1996.[4]RajivS.Chowdhry,“User’sManualforMATLABReference