Digital flight control system design using singular perturbation methods

In this paper a longitudinal output feedback tracker is developed for an aircraft and is shown to produce excellent performance for three different flight conditions without change of the control law matrices. The aircraft utilizes flight propulsion control coupling to provide greater control and responsiveness to command inputs. The singular perturbation method is applied to obtain an output-feedback digital multivariable control. Each flight condition has three command modes: positive pitch pointing, vertical translation, and straight climb. Decoupling of the outputs is demonstrated. A sensitivity study is performed to validate the robustness of the design and to illustrate design parameter influences on system response. The paper contains a summary of the control law design method. Since the CB matrix of the aircraft model does not have full rank, the use of a modified output feedback is used to obtain the required tracking performance.