Nonlinear Non-cascaded Reference Model Architecture for Flight Control Design

Abstract

A nonlinear reference model architecture motivated by dynamic inversion based flight control is introduced. As a novel feature, only one integrated reference model is used to provide reference commands, for longitudinal axis: the flight path angle, vertical load factor (or angle of attack), and pitch rate, while admitting flight path rate command as input; for lateral axis, bank angle and roll rate; for directional axis, lateral load factor and yaw rate. Flight dynamics, actuator dynamics with rate and position limits, and envelope protections can also be incorporated in a straight forward way in the reference model. One advantage of this non-cascaded reference model is that at least the attitude of the reference response can be restored and flown at an early stage of the flight control system design cycle. The second feature is that the reference model is parameterized, allowing the opportunity of updating the knowledge of aircraft dynamics (e.g. damaged) and flying qualities design. With these two aspects, the physical consistency in terms of the reference commands among different channels and reference commands reasonable with respect to true aircraft dynamics can be assured. Although designed for General Aviation aircraft, the framework can be generalized for other aircraft considering only rigid body dynamics.