Singular perturbations and time scales in the design of digital flight control systems

This paper presents the results of applying the methodology of singular perturbations and time scales (SPATS) to the control of digital flight systems. A block-diagonalization method is described that decouples a full-order, two-time-scale (slow and fast) discrete control system into reduced-order, slow and fast subsystems. Basic properties and numerical aspects of the method are discussed. A composite, closed-loop, suboptimal control system is constructed as the sum of the slow and fast, optimal feedback controls. The application of this technique to an aircraft model shows close agreement between the exact solution and the decoupled (composite) solution. The main advantage of the method is the considerable reduction in the overall computational requirements for the evaluation of optimal guidance and control laws. The significance of the result is that it can be used for real-time onboard simulation. This paper also contains a brief survey of digital flight systems.