Stability augmentation control for a BWB aircraft with large sweepback angle

Abstract

This thesis is focused on the stability augmentation control for UCAV1303, the blended wing body (BWB) aircraft with large sweepback angle. The thesis is divided into three parts: one is a modeling and controller design and verification to stabilize the vehicle even at high angle of attack (AoA) region in both continuous and discrete time domain and the other is several applications using the capability flying at high AoA with significant increase in performance especially for the vehicle in discrete time domain. A BWB aircraft with large sweepback angle has high level of nonlinear longitudinal aerodynamic characteristics, vortex lift and pitch break phenomenon. The pitch break makes the aircraft be unstable in pitching motion. To suppress the pitch break phenomenon with augmented stability even at high AoA region, in this research, L1 adaptive control was implemented with baseline Proportional-Integral (PD) control. With velocity and altitude PD controller, several cases of longitudinal nonlinear simulation in continuous time domain verifies the better stability and performance of the designed controller compared with PD controller. For discrete time domain, several cases of Processor-in-the-Loop Simulation(PILS)s was performed in XPLANE. The better sufficient stability and performance of the designed controller with fast adaptation and consistent transient performance was verified compared with PD controller. The pitch angle control rather than AoA control using L1 adaptive controller gives more margin not touching the peak AoA. Note that to simulate in discrete time domain, PILSs were conducted with 25 Hertz control command generated by embedded flight control computer and in the modeling of UCAV1303, the nonlinear model was obtained by the implementation of nonlinear aerodynamic data to linear model generated by Vortex Lattice Method (VLM) and system identification using exponential chirp signal was used to get a model which is assumed to be known in XPLAN...