Design of Stability Augmentation Systems for Flexible Aircraft Using Projective Control

Abstract

There are many challenges related to the design and operation of flexible aircraft. Flight control law design for improving handling qualities is one of them because the major problem in the design of controllers then concerns aeroservoelastic stability. To deal with this difficulty, methodologies for flight control law design considering the aeroelastic dynamics of the aircraft are being pursued. In this paper, a static output-feedback-based stability augmentation system is proposed and designed to improve the handling qualities and the structural dynamics decoupling of a flexible aircraft. The design is based on the projective control technique, which allows preserving in the closed-loop system the eigenstructure of certain modes of interest whose dynamic characteristics stem from an optimal state feedback solution. An experimental prototype of a flexible aircraft that mimics a high-altitude long-endurance airplane, called X-HALE, is considered in the case studies. Robustness analysis based on classical and disk-based stability margins, and nonlinear simulations of gusts and turbulent flight conditions evaluated and confirmed the effectiveness of the proposed controller.