Unmanned aerial vehicles suffer from inherent instabilities in the pitch axis due to their small size and the lack of pilot feedback. Therefore a flight control system is needed whose primary function consists of artificial stabilization of the aircraft. This system is known as pitch axis stability augmentation system. Control augmentation system is a common part of modern airplane control and is best characterized as a form of tracking control. In this paper, a flight control system is to be designed that augments both stability and control for an unmanned aerial vehicle called Aerosonde. This control system is designed using Linear Quadratic Gaussian technique. The performance of the control system is compared with the performance of a classical PID controller in terms of input tracking and disturbance rejection properties.