2018-12-11 12:00 - Maintenance complete.

Automatic upset recovery for small fixed-wing UAVs

Goosen, Gert Jacobus (2018-03)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: This thesis presents the design, implementation and practical demonstration of an automatic attitude and flight vector upset recovery system for a small xed-wing unmanned aerial vehicle. The objective of the recovery system is to recover the aircraft's airspeed, flight path angle and bank angle to straight and level flight, while minimising the altitude lost during the recovery. It is assumed that the aerodynamic envelope of the aircraft has already been recovered by another recovery system, and that the innerand middle-loop controllers are available again to perform attitude and flight vector recovery. The recovery problem was formulated as an optimal control problem, and solved using dynamic programming. Dynamic programming is a decision making tool that uses a dynamic model discretised in state and time, to consider all initial states and all trajectories to the desired terminal states. The solution yielded the optimal state trajectories, and the sequence of control inputs from all initial states for which trajectories could be found that do not exceed the aerodynamic or structural integrity envelopes of the aircraft. The trajectories were pre-generated off line, and implemented on the onboard computer to be accessed as an optimal recovery trajectory planner when needed. A combination of classical and acceleration based control was used to design inner- and middleloop controllers to control the states that must be recovered. These controllers receive references from the optimal recovery trajectory planner. Four trajectory execution architectures were investigated that use the inner-loop and middle-loop controllers in di erent con gurations to control the aircraft to practically execute the planned recovery trajectory. The recovery procedure is governed by a state machine that identi es the upset condition and provides the control systems with the appropriate references. The attitude and flight vector recovery system was veri ed through extensive simulation and practical ight testing. The results show that the trajectory planning generate kinematically feasible recovery trajectories, and that the execution component successfully controls the aircraft to follow the planned trajectories. The project demonstrated that an automatic upset recovery system can be practically implemented on an unmanned aerial vehicle, and is able to successfully recover the vehicle from upset conditions.

AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwerp, implementering en praktiese demonstrasie van 'n outomatiese oriëntasie en vlugvektor herstel stelsel vir 'n klein vastevlerk onbemande vliegtuig. Die doelwit van die herstel stelsel is om die vliegtuig se lugspoed, vlugpadhoek, en rolhoek terug te kry na gelyke en reguit vlug toe, terwyl die hoogteverlies tydens die herstelproses minimeer word. Daar word aanvaar dat die vliegtuig se aërodinamiese-omhullende reeds herstel is deur 'n ander herstel stelsel, en dat die binneen middel-lus beheerders weer beskikbaar is om die vliegtuig se oriëntasie-en-vlugvektor-omhullende te herstel. Die herstelprobleem is geformuleer as 'n optimale beheer probleem wat opgelos is deur gebruik te maak van dinamiese programmering (\dynamic programming"). Dinamiese programmering is 'n besluitnemings algoritme wat gebruik maak van 'n dinamiese model wat diskretiseer word in tyd en toestand, om sodoende alle aanvanklike toestande en moontlike trajekte na die eindtoestande in ag te neem. Die oplossing lewer die optimale toestandtrajekte en die reeks van beheer intrees van alle aanvanklike toestande waarvoor trajekte gevind kon word, wat nie die vliegtuig se aërodinamieseomhullende en strukturele-integriteits-omhullende oorskry nie. Die trajekte word vooraf gegenereer en dan gestoor aanboord die vliegtuig, sodat die aanboord rekenaar toegang daartoe het, en dit kan gebruik as 'n optimale trajekbeplanner wanneer nodig. 'n Kombinasie van klassieke beheer en versnellings-gebaseerde vlugbeheerwette was gebruik om binne- en middel-lus beheerders te ontwerp vir die toestande wat herstel moet word. Hierdie beheerders ontvang verwysings van die optimale trajekbeplanner. Vier trajek uitvoering argitekture is ondersoek wat die binne- en middel-lus beheerders in verskillende konfigurasies gebruik om die vliegtuig te beheer om die beplande trajekte prakties uit te voer. Die herstelprosedure word gefasiliteer deur 'n toestandsmasjien wat die aanvanklike vlugtoestand identifiseer en dan die toepaslike verwysings voorsien aan die binne- en middel-lus beheerders. Die oriëntasie en vlugvektor herstel stelsel is geverifieer deur middel van simulasies en praktiese vlugtoetse. Die resultate toon dat die trajekbeplanning optimale trajekte genereer wat kinematies gangbaar is deur die vliegtuig, en dat die trajek uitvoering suksesvol die vliegtuig beheer om die trajekte te volg. Die projek demonstreer dat 'n outomatiese herstel stelsel prakties geïmplementeer kan word op 'n onbemande vliegtuig, en dat dit suksesvol die vliegtuig kan herstel vanuit ongewonde vlugtoestande.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103668
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