Research Article Designing Stipulated Gains of Aircraft Stability and Control Augmentation Systems for Semiglobal Trajectories Tracking Mohamed Mostafa Y. B. Elshabasy, 1 Yongki Yoon, 2 and Ashraf Omran 3 1 Department of Mechanical Engineering, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt 2 Whirlpool Corporation, Saint Joseph Technology Center, 303 Upton Drive, Saint Joseph, MI 49085, USA 3 CNH Industrial, 6900 Veterans Ave., Burr Ridge, IL 60527, USA Correspondence should be addressed to Mohamed Mostafa Y. B. Elshabasy; mohamed elshabasy@alexu.edu.eg Received 29 August 2013; Accepted 11 December 2013; Published 30 January 2014 Academic Editors: J. Yao and C. Yuan Copyright © 2014 Mohamed Mostafa Y. B. Elshabasy et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te main objective of the current investigation is to provide a simple procedure to select the controller gains for an aircraf with a largely wide complex fight envelope with diferent source of nonlinearities. Te stability and control gains are optimally devised using genetic algorithm. Tus, the gains are tuned based on the information of a single designed mission. Tis mission is assigned to cover a wide range of the aircraf’s fight envelope. For more validation, the resultant controller gains were tested for many of- designed missions and diferent operating conditions such as mass and aerodynamic variations. Te results show the capability of the proposed procedure to design a semiglobal robust stability and control augmentation system for a highly maneuverable aircraf such as F-16. Unlike the gain scheduling and other control design methodologies, the proposed technique provides a semi- global single set of gains for both aircraf stability and control augmentation systems. Tis reduces the implementation eforts. Te proposed methodology is superior to the classical control method which rigorously requires the linearization of the nonlinear aircraf model of the investigated highly maneuverable aircraf and eliminating the sources of nonlinearities mentioned above. 1. Introduction Due to stringent performance and robustness requirements, modern control techniques have been widely used to design the fight control systems (FCS s ). However, researchers have been facing the difculties of the complex nature and the nonlinearity strength embedded in the aircraf’s dynamical model. For example, inertia coupling and attitude representations (Euler angles representation or quaternion representation) of the aircraf rigid body motions require nonlinear mathematical models [1]. Special impact on aircraf model comes from the nonlinear aerodynamic submodel such that aerodynamics coefcients signifcantly change with operating conditions. Tis leads to a signifcant change in the stability and performance of the aircraf dynamics. In addition, many other sources of nonlinearities appear in actuator nonlinear subsystems, sensor nonlinear subsystem, and engine nonlinear subsystems. In order to address the designing FCS, gain scheduling, one of the popular methodologies to design controllers for nonlinear systems has been adopted to design stability aug- mentation system (SAS), and control augmentation system (CAS) [2–4]. In the conventional gain scheduling approach, the nonlinear system is linearized at several equilibrium operation conditions. Local linear controllers are designed at each of these points. Te linear controller gains are then scheduled between the selected equilibrium points to obtain a semiglobal nonlinear controller. Tere is, however, still a difculty as to how to schedule the gain from point to point in the operation regime. Even though the gain scheduling method breaks down the nonlinear model into linear models, operating point might have a signifcant nonlinearity, which cannot be overlooked in the control design. Besides, the selection of the operating points and the design of interpola- tion scheme remain a time-consuming procedure. Tere are several approaches to resolve the issue of highly nonlinear Hindawi Publishing Corporation ISRN Aerospace Engineering Volume 2014, Article ID 409408, 10 pages http://dx.doi.org/10.1155/2014/409408