Digital aircraft flight controls design using output feedback

An approach that uses linear quadratic output feedback techniques is given for designing digital control systems of specified structure for shaping the closed-loop step response. This approach results in digital controllers that take advantage of the wealth of experience in aircraft controls design. The correct initial conditions for determining the output-feedback gains are not uniformly distributed as is traditionally assumed, but are shown to be explicitly given in terms of the step command magnitude. Arbitrary systems are treated, not only those with integrators in the forward paths, by adding a term to the performance index that weights the steady-state error. Necessary conditions are derived that may be used in a gradient-based routine to determine the optimal digital control gains. The approach does not rely on redesign of a continuous control system using techniques like the bilinear transformation, but uses direct discrete-time design