High Angle of Attack Landing of an Unmanned Aerial Vehicle

148 Pages·2015·12.52 MB·English

by  Kristoffer Gryte

High Angle of Attack Landing of an
Unmanned Aerial Vehicle
Kristoffer Gryte
Master of Science in Cybernetics and Robotics
Submission date: July 2015
Supervisor: Thor Inge Fossen, ITK
Norwegian University of Science and Technology
Department of Engineering Cybernetics

NTNU Faculty of Information Technology,
Norwegian University of Mathematics and Electrical Engineering
Science and Technology Department of Engineering Cybernetics

MSC THESIS DESCRIPTION SHEET

Name: Kristoffer Gryte
Department: Engineering Cybernetics
Thesis title (Norwegian): Landing av ubemanneded fly ved bruk av stor angrepsvinkel
Thesis title (English): High Angle-of-Attack Landing of an Unmanned Aerial Vehicle

Thesis Description: The purpose of the thesis is to investigate how a control strategy based on high
angle-of-attack (AOA) can be used to automatically land an unmanned aerial vehicle (UAV) in a net.
This involves mathematical modeling of the X8 fixed-wing UAV and simulation of high AOA
maneuvers. Furthermore, the X8 model should be used to design and test an automatic control system
for landing.

The following items should be considered:

1. Define the scope of the thesis and clarify what your contributions are.
2. Development of a flight simulator the X8 UAV, which is valid for high AOA. The simulator
should also include wind loads on the fuselage.
3. Development of a software-in-the-loop simulator for the X8 using JSBSim interfaced with the
ArduPlane autopilot.
4. Formulate landing as an optimal control problem, that has low terminal velocity as the
objective. Use this to investigate how the terminal velocity is affected by different initial
conditions and constraints.
5. Extend the optimal control problem to a model predictive controller, and use this in landing
simulations.
6. Conclude your results.

Start date: 2015-01-05
Due date: 2015-07-01

Thesis performed at: Department of Engineering Cybernetics, NTNU
Supervisor: Professor Thor I. Fossen, Dept. of Eng. Cybernetics, NTNU

Abstract
Motivatedbythelimitedlandingspaceonboardaship,thisthesisinvestigatesthelanding
oftheSkywalkerX8fixedwingunmannedaerialvehicle(UAV)inanet.Furthermotivated
by the way birds abruptly, and equally elegantly, reduce their velocity when landing on
a perch or the branch of a tree, a perched landing strategy utilizing the increased drag
experiencedforlargeanglesofattackisusedtominimizethevelocityatimpactwiththe
net. This is accomplished by expressing landing as an optimal control problem, taking
advantage of a nonlinear model of the X8 that is valid for high angles of attack. At this
stage,theoptimalcontrolproblemisonlyconcernedwiththethreelongitudinaldegrees-
of-freedom. It is solved in an open source optimization framework, using a nonlinear
interiorpoint method. Further, a nonlinear modelpredictive controller(NMPC)that can
control the X8 throughout the landing is developed. At the heart of the optimal control
problem lies a linear model, blended with a flat plate model to increase its validity for
highanglesofattackinlift,dragandpitchmoment. Thelinearmodelisdevelopedusing
aneasy-to-usecomputationalfluiddynamics(CFD)modelingsoftware. Inadditionasix
degrees-of-freedom software-in-the-loop (SITL) simulator is developed for future use in
testing of hardware-near implementations of the controller, and to allow for validation
ofthemodelthroughpilottesting. Comparisonofsixdifferentlandingscenariosyielda
widerangeoflandingvelocities,dependingontheconstraintsofthescenario.Simulations
withthedevelopedNMPCshowthatthesameperformanceisachievablethroughcontrol
of the X8 under minor environmental disturbances. From this it is concluded that the
perchedlandingstrategywillleadtoaconsiderablereductioninterminalabsolutevelocity,
comparedtoalowangleofattackapproach. Itisfoundtobeadvantageoustostartfrom
alowaltitude,landingintoanelevatednet. However,whetheranequallylargereduction
is possible in practice depends on the capabilities of the real-time implementation and
thevalidityofthemodel,particularlythepropellermodel,thepitchingmomentanddrag
coefficients. Finallyitdependsonhowthelateraldegrees-of-freedomareaffectedbythe
highangleofattackflight.
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Samandrag
(NorwegianTranslationoftheAbstract)
Motivert av den avgrensa landingsplassen ombord pa˚ skip, undersøkjer denne oppga˚va
nettlanding av det ubemanna flyet Skywalker X8. Vidare motivert av den snøgge ned-
bremsingafuglarelegantoppna˚rvedlandingpa˚ greiner,serdenneoppga˚vanærarepa˚ ein
landingsstrategi som utnyttar den drastiske auken i luftmotstand, som finn stad for store
angrepsvinklar, til a˚ minimere hastigheita i landingsaugneblinken. Dette blir gjort ved a˚
formulerelandingasomeitoptimaliseringsproblemsomnyttarsegaveinulineærmodell
avX8somergyldigforstoreangrepsvinklar. Optimaliseringsproblemetharblittforenkla
til dei tre fridomsgradene i longitudinalplanet, og blir løyst ved hjelp av eit optimalis-
eringsrammeverk basert pa˚ open kjeldekode som nyttar ein ulineær indre-punkt løysar.
Vidarehareinulineærmodell-prediktivregulatorblittutviklafora˚ kunnekontrollereX8
gjennomlandinga. Einsentraldelavoptimaliseringsproblemetereineigenutviklalineær
modell, der løft-, luftmotstand- og stampkoeffisientane gradvis ga˚r over i ein flat plate
modell for a˚ auke gyldigheita ved store angrepsvinklar. Den lineære modellen har blitt
utviklavedhjelpaveitenkeltprogramfornumeriskstrøymingsanalyse. Itillegghardet
blitt utvikla ein programvare-i-sløyfa simulator i seks fridomsgrader for a˚ kunne nyttast
i testing av maskinvarenære implementeringar av regulatoren, samt for a˚ legge til rette
formodellvalideringgjennompilottesting. Samanlikningavseksulikelandingsscenario,
med ulike avgrensingar, gav ulike landingshastigheiter. Ei simulering med den modell-
prediktive regulatoren har vist at tilsvarande ytelsar er oppna˚elege ved regulering av X8
under ytre pa˚verknader. Basert pa˚ desse resultata blir det konkludert at ein slik land-
ingsstrategi, med stor angrepsvinkel, vil føre til ein stor reduksjon i absolutthastigheita i
landingsaugneblinken, samanlikna med a˚ lande med ein la˚g angrepsvinkel. Det har synt
seg føremonleg a˚ starte landinga fra˚ ei la˚g høgde, samt a˚ lande i eit heva nett. Men om
einlikestorreduksjonermoglegipraksisavhengjeravsanntidsimplementasjonenavsys-
temet og gyldigheita av modellen, herunder særskildt propellmodellen, stampemoment-
og luftmotstandskoeffisientane. Det vil ogsa˚ vere avhengig av korleis fridomsgradene i
lateralplanetvertpa˚verkaavflygingmedstorangrepsvinkel.
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Preface
ThisthesisissubmittedinpartialfulfillmentoftherequirementsfortheMasterofScience
degreeattheNorwegianUniversityofScienceandTechnology.
The work presented in this thesis has been carried out at the Department of Engineer-
ing Cybernetics, and would not have been possible without the inputs and contributions
frommanyofitsassociates. First,IwouldliketothankProfessorThorIngeFossenforhis
inspiring ideas and guidance into the academic world. The team at the UAV-lab deserve
tobeacknowledged;especiallyArturZolich,whohasbeenanimportantsparringpartner
in my aerodynamic endeavors, and Siri H. Mathisen, whom I have worked closely with
onoptimizationandmodelpredictivecontrol. IwouldalsoliketothankmyfellowMSc.
studentsfromroomG232B.Theyhavegivenmeinvaluablefeedbackinacompetitive,yet
friendlyenvironment. FinallyIwouldliketothankmyparentsandbrotherforbelieving
inmeandencouragingmewhentimesgettough.
KristofferGryte
Trondheim,June2015
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