The Role of the Backside Parameter in Height Control

Abstract

Height control in continuous gust fields is formulated as a stochastic regulator problem and the relation between mean square (ms) height error and the backside parameter is examined. The following results are shown. First, when the throttle loop is open, elevator alone ceases to be a reasonable control strategy when the backside parameter l/T y is negative. The minimum achievable ms height error is essentially only a function of l/T y; ms error is zero when l/T y >0, while it is inversely proportional to \l/Ty I when l/Ty <0. For the landing approach, this holds true approximately, regardless of airplane type. Second, when the throttle loop is closed, it is generally difficult to tightly control velocity and height simultaneously in conventional airplanes. This is mainly because the thrust change available in control is quite limited, particularly in deceleration. To realize tight control in height, the accuracy in velocity control must be relaxed and the backside parameter has to be properly large.