Control System Design Risk Assessment Using Fuzzy Logic

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Introduction

This manual describes a technique that can be used to assess the impact of the flight control system on aircraft configuration geometry. The primary purpose is to perform trade-off studies between different aircraft configurations in the preliminary design phases of development. It can also be easily automated and adapted for use in aircraft configuration optimization problems.
The underlying approach is to determine the control system structure that is needed to correct deficiencies in the dynamics of the aircraft. The complexity of the control system is assumed to measure the amount of risk associated with that aircraft (if it were built). Configurations that require a very simple control system architecture would incur only a small risk. Configurations with a very complicated control system would be assigned a higher risk.
The required control system architecture is determined using a set of fuzzy logic rules. These rules are developed using experience and knowledge about how control systems are designed. Using this approach, a control system is not actually designed for a given configuration under study. Only the required control system structure is determined. The final design of the control system would come after the final configuration has been selected and detailed aerodynamic and structural models are developed.
This report describes a procedure and rule base to determine the flight control design risk for the longitudinal axis of aircraft motion. Only one specification regarding aircraft flying qualities is considered. However, the rules and methods described in this report could also be expanded to include other design requirements and specifications.