An LQR-LMI Longitudinal Stability Augmentation System for a Subscale Fighter Aircraft with Variable Center of Gravity Position

Abstract

© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The development of microelectronics combined with the cheapness of manufacturing processes has allowed the construction of subscale models equipped with sensors and control systems equivalent to a real aircraft. This work analyses the Generic Future Fighter (GFF) subscale concept developed by Linköping University under the Future Aircraft Design and Demonstration (FADEMO) project. The GFF subscale is a radio-controlled aircraft with 14% of the size of the full-scale concept aircraft. A Stability Augmentation System (SAS) will be designed to stabilize the longitudinal dynamics for different positions of the c.g., artificially modified for three different positions. Despite the several control techniques currently available, methods such as the Linear Quadratic Regulator (LQR) are still adopted for the stability control of aircraft in flight. However the LQR method present in their classic form, limitations to incorporate performance parameters and operational restrictions in the design phase. A promising alternative to circumvent this problem is the use of Linear Matrix Inequalities (LMIs) as a tool to convert stability and control problems into optimization problems. This work presented an LQR-LMI formulation augmented by D-stability criterion to simplify the determination of a single feedback gain matrix that guarantees the stability and keeps the flight characteristics by varying the c.g. position.