In this study, a fuel system controller for a gas turbine engine was examined. Controller design in this application is challenging due to nonlinearities in the closed loop system, as well as uncertainties associated with hardware components from part variation or degradation. Current closed loop design methodologies are discussed, as are the limitations or challenges facing these systems. Details on fuzzy logic control and its benefits in this type of application are explored.Information on genetic algorithms is presented, along with a study on how this optimization approach can be utilized to enhance the fuzzy logic controller process. A fuzzy logic controller structure was developed for providing closed loop fuel control in the gas turbine application, using a genetic algorithm to tune the system to provide an accurate and fast response to changing input demands. With a genetic fuzzy controller in place, closed loop analysis was performed, along with a stochastic robustness analysis to assess controller performance in an uncertain environment. Results show that the genetic fuzzy system performed well in this application, resulting in a system with fast rise and settling times to stepping inputs, while also minimizing overshoot and steady state error. Robustness characteristics of the fuzzy controller were also demonstrated, as the stochastic robustness analysis yielded acceptable performance in each simulation of the closed loop system with uncertainties included.ii iii

We develop a PID based fuzzy logic pitch attitude hold system for a typical fighter jet under a variety of performance conditions that include approach, subsonic cruise and supersonic cruise. In this approach, the gains found in a classic PID controller are replaced with fuzzy systems, still contributing the overall effects of a proportional, integral, and derivative controller. The response is compared to conventional PID control. In addition, the design is tested for an F-4 in the approach condition, then with a 50% reduction in both longitudinal stability and pitch damping, and finally subsonic and supersonic cruise conditions. The different cases allow analysis of the off-design performance characteristics, or fault-tolerant capabilities, for the fuzzy logic and proportional gain controllers. Results show that for all flight conditions, the fuzzy PID controller was able to perform comparably to the conventional controller, while exhibiting faster rise times.