APPLICATION OF STRUCTURED SINGULAR-VALUE SYNTHESIS TO A FIGHTER AIRCRAFT

The results of a design study to examine the control of a fighter airc raft at high angles of attack are presented. The flight condition cons idered represents an extreme point along a demanding, large angle mane uver. The control objective is to attain acceptable flying qualities d espite variations and uncertainty in the aircraft's aerodynamic coeffi cients. Control laws are developed for a linear model of the aircraft using structured singular value synthesis to take the parameter uncert ainty structure into account. Desired flying qualities are embedded in ideal models of the angle of attack, sideslip angle, and stability ax is roll rate responses to pilot inputs. The control objective is met b y minimizing the weighted error between the ideal model outputs and th e plant outputs and including structured parameter uncertainty in the design model. Analysis of the closed-loop system assuming interdepende nt parameter variations is done to evaluate conservativeness. Low-orde r optimal Hankel norm approximations of balanced realizations of the c ontrol laws are found that maintain the performance and robustness cha racteristics of the full-order controllers.