Robust Aircraft Longitudinal Control Using Model-Error Control Synthesis

In this paper a robust control for aircraft longitudinal motion is presented. The ModelError Control Synthesis (MECS) is developed for this application, which consists of a nominal controller with a model-error predictive filter. The control input is updated directly using the estimated model-error from a predictive filter to cancel the unmodeled dynamics or disturbance inputs. The predictive filter is used only to estimate the model error, whereas an extended Kalman filter is used to provide state estimates from noisy measurements. The nominal control is chosen to be an LQR/dynamic inversion outer/inner loop controller for the longitudinal direction. The control law robustness to unmodeled dynamics and external disturbances is verified when MECS is active and not active. From various simulation results, MECS is shown to have better performance characteristics over the stand-alone nominal control.