Incorporation of pitch bias actuator function into an existing afcs

Abstract

An aircraft automatic flight control system (AFCS) includes a pair of fast, limited authority inner loop actuators responsive to signals indicative of aircraft attitude or other flight parameters such as airspeed, the inner loop being recentered by an outer loop actuator responsive to attitude or other aircraft parameter-indicating signals (54,55). Commands applied to the outer loop are applied in a lagged fashion in opposite direction so as to drive the inner loop actuators back toward the center of their authority. The rate of response of the outer loop is adaptive in response to magnitude of inner loop input (101, FIG. 2). A pitch bias command is provided to the inner loop as a function of airspeed multiplied inversely with collective pitch, and as a function of the rate of change of collective stick position, so as to provide a positive static pitch trim gradient and decouple collective pitch from the longitudinal cyclic pitch channel. When the inner loop runs out of authority, the outer loop may assume a high gain mode to keep pace with the demand of the pitch bias function. When the AFCS is operating single-on, the outer loop response is normally delayed for three seconds to allow a pilot time to recover from a hardover. However, when a collective maneuver is being made, the outer loop response is not delayed so as not to interfere with the pitch bias function, especially with regard to collective decoupling.