Design of the flare control law for longitudinal autopilot using H∞ synthesis

The authors present the results of a design exercise in which H_∞ synthesis theory was applied to the problem of designing a flare mode for automatic landing for the longitudinal autopilot for a typical transport airplane. The controller must provide good touchdown performance in the presence of ground effects. The bulk of the engineering effort was in the formulation of an appropriate synthesis model. The linear design was suitably modified to satisfy some of the performance constraints. Results of linear analysis and simulation of the controller are presented. Its robustness characteristics are discussed