Reliability Assessment of Actuator Architectures for Unmanned Aircraft A THESIS SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Raghu Venkataraman IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

Regulatory agencies worldwide are working towards safely integrating unmanned aircraft into their respective national airspaces. Reliability assessment of unmanned aircraft is a key step in the certification process. This thesis presents an analysis framework for the reliability assessment of small unmanned aircraft. Specifically, the effect of the placement of actuators and control surfaces on the overall aircraft reliability is investigated. The analysis framework is applied to several candidate actuator architectures of an example small unmanned aircraft. The candidate architectures have different numbers of controllable surfaces and servos. It is assumed that a servo fault detection algorithm is available and affected by known rates of false alarms and missed detections. The flight envelope of the aircraft is analyzed to determine the fault magnitudes for which the aircraft can still be flown around a feasible trim point. For these allowable fault magnitudes, it is assumed that the flight control law can be suitably reconfigured such that a safe landing is possible. Finally, the probability of catastrophic failure of the aircraft is estimated. In applying the framework to assess the reliability of the candidate architectures, several interesting and non-intuitive observations are made. These observations, and their resulting conclusions, have implications for the unmanned aircraft design process. Thus, in addition to being used for analysis, the proposed framework provides some insight into how reliability fits into the traditional aircraft design process.