Fault-tolerant flight control for a fixed-wing unmanned aerial vehicle with partial horizontal and vertical stabiliser losses

Maggott, Ryan Lee (2016-12)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: In the study reported here, a fault-tolerant flight control system for a fixed-wing unmanned aerial vehicle with partial stabiliser loss is designed, analysed, implemented and verified. The partial stabiliser damage changes the natural dynamics of the aircraft and causes asymmetry. The control system must maintain aircraft stability and transition from the healthy to the damaged configuration without depending on in-flight knowledge of the change in dynamics. The control system must also provide satisfactory transient performance for both the healthy and the damaged configuration. Using existing reference frames and conventions, a six-degrees-of-freedom equations of motion model of the aircraft is derived that can model the effects of the partial horizontal and vertical stabiliser loss on the aircraft dynamics. This model considers the changes in the mass, moment of inertia, aerodynamic model, control authority of the aerodynamic control surfaces, as well as the shift in the centre of gravity. The altered aerodynamic coefficients are calculated using vortex lattice techniques for the different damage configurations. In order to determine the trim states and inputs of the aircraft as a function of the partial horizontal and vertical stabiliser loss, a multivariate Newton–Raphson technique is applied to the equations of motion. The required trim actuator deflections are compared to the physical actuator limitations to establish the feasibility of maintaining trim flight for each damage case. Assuming feasible trim states and inputs, the system is linearised and the open-loop dynamics of the aircraft are investigated as a function of partial stabiliser loss. A combination of classical and acceleration-based control architectures are designed and implemented. The stability, performance and robustness of the flight control system are verified in simulation for damage cases up to 70% left horizontal stabiliser loss and 20% vertical stabiliser loss. The fault-tolerant flight control system is verified with flight tests. A release mechanism is designed and manufactured to allow 70% of the left horizontal stabiliser and 20% of the vertical stabiliser to be jettisoned in flight. The flight control system is implemented on a practical unmanned aerial vehicle and successful reference tracking is demonstrated. Practical flight tests showed that the flight control was stable for both the healthy and the damaged aircraft configurations, and able to handle the transition following an in-flight partial stabiliser loss event.

AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwerp, analise, implementasie en verifikasie van ‘n fout-tolerante vlugbeheerstelsel vir ‘n vastevlerk onbemande vliegtuig met gedeeltelike stabiliseerder verlies. Hierdie verlies veroorsaak ‘n verandering in die natuurlike dinamika van die vliegtuig en veroorsaak asimmetrie. Die beheerstelsel moet in staat wees om stabiliteit te handhaaf en die oorgang van die gesonde na die beskadigde konfigurasies te hanteer, en moet nie staatmaak op in-vlug kennis van die verandering in die dinamika nie. Die beheerstelsel moet ook bevredigende oorgangsgedrag vertoon vir beide die gesonde en die beskadigde konfigurasies. Bestaande verwysingsraamwerke en konvensies is gebruik om ‘n ses-grade-van-vryheid bewegingsvergelykingsmodel vir die vliegtuig af te lei wat die effekte van die gedeeltelike horisontale en vertikale stabiliseerder verlies op die vlugdinamika modelleer. Hierdie model neem die veranderinge in die massa, traagheidsmoment, aerodinamiese model, beheergesag van die aerodinamiese oppervlakkeverskuiwing en massamiddelpunt in ag. Die veranderinge in die aerodinamiese koëffisiënte word bereken met draaikolk rooster tegnieke vir die verskillende beskadigde konfigurasies. ‘n Meerveranderlike Newton–Raphson tegniek word gebruik om die bewegingsvergelykings op te los om die ekwilibrium toestande en intrees van die vliegtuig te bereken as ‘n funksie van persentasies gedeeltelike horisontale en vertikale stabiliseerder verlies. Die benodigde aktueerder defleksies vir ekwilibrium vlug word vergelyk met die fisiese aktueerder limiete om te bepaal of dit haalbaar is vir die spesifieke hoeveelheid skade. Gegee haalbare ekwilibrium toestande en intrees, word die stelsel gelineariseer en die ooplusdinamika van die vliegtuig ondersoek as ‘n funksie van gedeeltelike stabiliseerder verlies. ‘n Kombinasie van klassieke en versnellingsgebaseerde beheerargitekture is ontwerp en implementeer. Die stabiliteit, prestasie en robuustheid van die vlugbeheerstelsel word verifieer in simulasie vir skade tot by verlies van 70% van die linkerkantste horisontale stabiliseerder en 20% van die vertikale stabiliseerder. Die fout-tolerante vlugbeheerstelsel is ook verifieer met praktiese vlugtoetse. ‘n Loslaatmeganisme is ontwerp en vervaardig om 70% van die linker horisontale stabiliseerder en 20% van die vertikale stabiliseerder in vlug af te gooi. Die vlugbeheerstelsel is implementeer op ‘n praktiese onbemande vliegtuig en suksesvolle verwysingsvolging is gedemonstreer. Die praktiese vlugtoetsresultate wys dat die vlugbeheer stabiel is vir beide die gesonde en die beskadigde vliegtuig konfigurasies, en dat dit in staat is om die oorgang te hanteer na in-vlug gedeeltelike stabiliseerder verlies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100136
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