Optimal Autostabilizer for a Supersonic Fighter Aircraft

AMODERN approach to supersonic fighter aircraft design is the control configured fighter (CCF).1 In this approach, an unstable airframe is purposely designed with a view to obtaining superior handling qualities, and an autostabilizer is incorporated as an integral part of the design to obtain stability. Autostabilizers have hitherto been designed using classical control system design techniques based on Bode plots, root locus plots, etc. In this investigation, the modern optimal control theory has been employed to design an autostabilize r for a supersonic fighter aircraft. A novel method based on Krotov's method of approaching the solution of Bellman's equation of dynamic programming has been developed to solve the optimal control problem. The resulting suboptimal bang-bang control law is remarkable inasmuch as 1) it contains only a linear combination of the state variables and, consequently, is easy to implement and 2) the results obtained with it are excellent.2 Contents Application of optimal control theory to autostabilize r design involves four steps as described in the following. Derivation of State Equations for the Aircraft Linearized equations describing the longitudinal shortperiod mode of the aircraft in question have been derived using the standard procedure.3 These equations may be expressed in the standard form