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

[摘要] ENGLISH ABSTRACT: In the study reported here, a fault-tolerant flight control system for a fixed-wing unmannedaerial vehicle with partial stabiliser loss is designed, analysed, implemented and verified. Thepartial 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 thedamaged configuration without depending on in-flight knowledge of the change in dynamics.The control system must also provide satisfactory transient performance for both the healthyand the damaged configuration.Using existing reference frames and conventions, a six-degrees-of-freedom equations of motionmodel of the aircraft is derived that can model the effects of the partial horizontal andvertical 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 calculatedusing vortex lattice techniques for the different damage configurations. In order to determinethe trim states and inputs of the aircraft as a function of the partial horizontal and verticalstabiliser 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 toestablish the feasibility of maintaining trim flight for each damage case. Assuming feasibletrim states and inputs, the system is linearised and the open-loop dynamics of the aircraft areinvestigated as a function of partial stabiliser loss.A combination of classical and acceleration-based control architectures are designed andimplemented. The stability, performance and robustness of the flight control system are verifiedin simulation for damage cases up to 70% left horizontal stabiliser loss and 20% vertical stabiliserloss.The fault-tolerant flight control system is verified with flight tests. A release mechanismis designed and manufactured to allow 70% of the left horizontal stabiliser and 20% of thevertical stabiliser to be jettisoned in flight. The flight control system is implemented on apractical unmanned aerial vehicle and successful reference tracking is demonstrated. Practicalflight tests showed that the flight control was stable for both the healthy and the damagedaircraft configurations, and able to handle the transition following an in-flight partial stabiliserloss event.

[发布机构] Stellenbosch University