Abstracts Engineering

An investigation of oscillations in an adaptive aircraft control system under large input commands.

by Larry Smith Wilser

An adaptive control scheme for aircraft was studied to find the cause of limit cycles which occurred under large input commands and to find a method for eliminating the oscillations. The complexity of the system equations dictated that all analytical studies be performed on simplified versions of the adaptive control scheme. After exhaustive analysis of the cause of limit cycles in the simplified systems and an investigation of possible fixes for this problem, it was decided that the oscillations were an inherent feature of the control scheme resulting from the servo and actuator lags. A second adaptive control scheme was thus developed which obtained more feedback information downstream of the aircraft actuator and series servo. A comparison of the two adaptive systems was made under similar flight conditions for the F-4 aircraft and the modified adaptive controller was shown to be practical and free of limit cycle oscillations by analog simulation.