Accurate autonomous landing of a fixed-wing unmanned aircraft under crosswind conditions

De Bruin, Andrew (2017-03)

Thesis (MScEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: This thesis presents the design, implementation and verification of an autopilot system with strong disturbance rejection characteristics, capable of landing a fixed-wing unmanned aircraft accurately under crosswind conditions. All aspects of the autopilot design are considered, from first principles to the final practically verified product. A mathematical aircraft model is derived, verified and analysed in detail to ensure the design of a high-fidelity, high-bandwidth flight control system. A synergistic controller architecture is proposed, where the approach is to design a structure capable of executing one of three crosswind landing techniques, or a combination thereof, by strategically sequencing controllers throughout the landing procedure. Various landing techniques, developed for manned aircraft, are investigated and emulated by the flight control system to exploit the advantages of each and to mitigate the risks associated with crosswind landings. A highbandwidth acceleration-based control architecture was augmented with Direct Lift Control to improve gust alleviation performance in the aircraft’s longitudinal axis. A state machine was used to facilitate effective controller sequencing and continuous hierarchical monitoring through strategically planned state transitions. Monte Carlo simulations were used to develop a landing accuracy prediction system that provides statistical information regarding the expected touchdown region given certain atmospheric conditions. Results from sixteen days of flight tests demonstrate the autopilot’s success, and correspond exceptionally well with results obtained from high-fidelity hardware-in-the-loop simulations. Verification of the autopilot through practical flight testing and extensive simulations proved that the system is capable of performing crosswind landings accurate to within 0.5 m of the intended touchdown point.

AFRIKAANSE OPSOMMING: Hierdie tesis stel bekend die ontwerp, implementering en verifikasie van ‘n selfvliegstelsel met sterk versteuringsverwerpingseienskappe, wat ‘n vastevlerk-onbemande vliegtuig in staat stel om akkuraat onder dwarswindtoestande te land. Alle aspekte van die selfvlieg-ontwerp word in ag geneem, vanaf eerste beginsels tot by die finale, prakties geverifieerde produk. ’n Wiskundig ontwikkelde vliegtuigmodel word afgelei, geverifieer en in fyn besonderhede ontleed om die ontwerp van ’n ho¨etrou-, ho¨ebandwydte-vlugbeheerstelsel te verseker. ’n Sinergistiese beheerderargitektuur word voorgestel, waar die benadering is om ‘n struktuur te ontwerp wat in staat is tot die uitvoer van een van drie dwarswind-landingstegnieke, of ‘n kombinasie daarvan, deur opeenvolgende beheerders strategies te gebruik regdeur die landingsproses. Verskeie landingstegnieke wat vir bemande vliegtuie ontwikkel is, word ondersoek en deur die vlugbeheerstelsel nagemaak om die voordele van elkeen te ontgin, en om die risiko’s wat met dwarswindlandings verband hou, te verminder. ’n Ho¨ebandwydte-versnellingsgebaseerde beheerargitektuur is aangevul met direkte stygbeheer om die rukwind-verligtingsprestasie van die vliegtuig se longitudinale-as te verbeter. ’n Toestandsmasjien is gebruik vir effektiewe beheerder-opeenvolging en deurlopende hi¨erargiese monitering deur middel van strategies beplande toestandsoorgange. Monte Carlosimulasies is gebruik om ’n akkurate landingsvoorspellingstelsel te ontwikkel, wat statistiese inligting aangaande die verwagte landingstreek onder sekere gegewe atmosferiese toestande kon bied. Die resultate van vlugtoetse wat oor ‘n periode van sestien dae versamel is, bewys die sukses van die selfvliegstelsel, en stem besonder goed ooreen met die resultate verkry uit ho¨etrouhardeware- in-die-lus-simulasies. Verifikasie van die selfvliegstelsel deur dit aan praktiese vlugtoetse en uitgebreide simulasies te onderwerp, bewys dat die stelsel in staat is om onder dwarswindtoestande akkuraat tot binne 0.5 m van die beplande landingspunt te land.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101195
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