In mission-critical applications of unmanned and autonomous aerial systems(UAS), it is of significant importance to develop robust strategies for fault-tolerant systems that can countermeasure system degradation and consequently support the integration into the National Airspace (NAS). This thesis research illustrates the results of systems identification that is performed using DATCOM followed by the flight test data. This data is acquired from conducting an intensive flight testings program of a fixed-wing UAS to determine the state-space model of the aircraft. A discrete state-space system is reconstructed from these models to derive Auto-Regressive Moving-Average (ARMA) models used to design a Discrete Direct and Indirect Model Reference Adaptive Control. Description of the UAS, subsystems , and integration is presented in this thesis along with analysis of results from numerical simulation to support the design, development, and validation of adaptive control laws for fault tolerance.A set of performance metrics are defined to perform the analysis in terms of control effort, tracking performance, and reconfiguration of control laws under commonly occurring failures such as partial control surface damage, pilot-induced oscillations, and uncertain ice accretion. v ACKNOWLEDGMENT Though the following dissertation is an individual effort, I believe that it epitomizes my years of hard work, propensity to move forward and most importantly, people who have assisted me in this journey. Recapitulating my journey, I have nothing but utmost appreciation and gratitude for the valuable support, guidance and efforts of people. My passion for contributing to aerospace unmanned industry has been reinforced by a strong organizational resilience and academic guidance. Therefore, I would like to extend my gratitude to my Research advisor Dr. Hever Moncayo for directing me with his experience and aptitude and for being an exceptional coach in my scholastic life. My sincere appreciation towards my Advisory Committee , Dr.Richard Stansbury and Dr. Yan Tang for giving your valuable time and insights. An exceptional thanks to Michael Potash and Bill Russo for your enormous assistance with hardware and calmly noting every one of my inquiries. I would also like to offer gratitude to Dr. Gordan Leishman and Dr. Zheng Zang for their distinctive contribution in helping me calibrate air-data probe and allowing me to use the Subsonic Wind-Tunnel Facility. I acknowledge assistance from Rob, Austin, Ethan and Jeremy for being ever ready to be the test-pilot and not complaining about early morning flights. I likewise recognise contributions from Jorge Begue for providing helping hand in assembling the UAV. On board of this journey, there was unprecedented team of talented individuals that provided valuable expertise and their benevolent support in the advancement of the unmanned iii aerial vehicle thus I will be everlastingly thankful to my lab colleagues turned friends: An