Abstract:
Unmanned Aerial Vehicle (UAV) industry is an emerging area in Pakistan with many applications. The objective of this thesis work is to build a basic framework of autopilot system that can provide basis for, as well as facilitate ongoing work in this area. Flight control system is responsible for tracking inputs from navigation and guidance algorithm by controlling actuators on aircraft. Aircraft is intrinsically a nonlinear system and its aerodynamic characteristics vary widely with altitude, speed and atmospheric conditions. In this thesis a nonlinear autopilot system based on the concept of nonlinear dynamic inversion (NDI) is investigated. Major focus of this work is on the ease of implementation and robustness to uncertainties.
Longitudinal mode and lateral mode of aircraft are handled separately for the ease of design and analysis. The autopilot consists of controllers on each of aircraft axes, an altitude and airspeed controller on x-axis, a roll rate controller on y-axis and yaw rate controller on z-axis. They are result of explicit model following, NDI and nonlinear transformations of state variables. A practical methodology is used to analyze the stability and robustness of the control system in presence of model parameter and sensor uncertainties. In last, implementation strategy of the controllers is discussed and further work is explored.
