Application of Eigenstructure assignment to the control of powered lift combat aircraft

Smith, Phillip Raymond (1990) Application of Eigenstructure assignment to the control of powered lift combat aircraft. University of Southampton, Doctoral Thesis.

Abstract

This work reports an examination of the Eigenstructure Assignment control law design technique, and its application to both a vectored thrust aircraft, and a helicopter example. In reviewing the design method new insight is shed upon the r^ole of the left eigenvectors, which are shown to determine the nature of the input coupling into a dynamic system. It is concluded that selection of the right eigenvectors alone, as is often shown in the literature, is insufficient to ensure decoupling in the system response. In each of the application studies, a non-linear aircraft methematical model is examined in a number of different parts of the flight envelope. They are linearised to provide a state space representation of the aircraft and fixed gain controllers are designed using the method of Eigenstructure Assignment. These controllers are then implemented in the non-linear models and their behaviour examined. It is seen that some classes of non-linearity cause degradation of the closed-loop performance, whereas others result in instability or limit cycles. Examination of the frequency domain characteristics of a helicopter example are considered, which allow the controlled aircraft handling qualities to be determined. It is shown that simple dynamic elements in the command path can be used to tune the response when problems in obtaining a sufficiently high bandwidth are encountered. It is finally concluded that the method provides a viable approach to aircraft control law design, a chief attraction being the very simple structure of the resulting control laws.

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