I. Introduction
Unmanned aerial vehicles (UAVs) are of great interest for intelligence, surveillance and reconnaissance applications, and also for rescue operations. They reduce risk to life, and have a relatively low operational cost. In recent years, the work on UAV autonomy has added a new dimension to the utility of these vehicles. Autonomy is the ability to perform a task (mission) without being directly or remotely controlled by a human operator [1]. Autonomous vehicles must have sufficiently advanced path planning algorithms, combined with effective and robust guidance and automatic control systems. Successful control system design for high-performance UAVs requires efficient and effective techniques for the design of guidance and control algorithms that ensure satisfactory operation in the face of system uncertainties and environmental disturbances. A key performance criterion for the guidance and control system is to have the ability of precise ground track control in the presence of disturbing forces. A criterion for assessing the lateral performance and handling qualities for such vehicles is presented in [2].