A modern control approach to longitudinal gust alleviation for transport aircraft: Design of an optimal controller

A digital computer investigation has been undertaken to study the feasibility of utilizing modern control (state-space) methods to reduce aircraft dynamic response sensitivity to longitudinal gusts. The analysis is confined to the three-degree-of-freedom, longitudinal, rigid-body dynamics referenced to the body-centered stability axes. A representative jet transport is subjected to random turbulence modelled using the Dryden spectrum. The turbulence is combined with discrete gusts of varying magnitude whose frequencies are "tuned" to the aircraft phugoid and short-period modes.; A robust optimal controller is designed which provides linear full-state feedback to the plant. A full-order Kalman filter (optimal observer) is used to estimate the states unavailable for direct measurement. Furthermore, a quadratic performance index is selected that emphasizes superior flight-path maintenance without disregarding ride quality. Several analyses are undertaken including opened- and closed-loop frequency response, time histories, and singular-value analysis.