Unmanned aerial vehicles (UAVs) have become a hot research topic in the worldwide due to their great potential in numerous military and civil implementations. This motivated everincreasing attraction of designing UAV flight control systems to achieve robust stability and acceptable performance across specified flight envelopes. Therefore, this paper is devoted to design an adequate flight control system for stabilizing a fixed wing (Aerosonde) UAV. To achieve this objective, successive activities are considered including the derivation of aircraft nonlinear equations of motion and tailoring them for use on the underlying aircraft. The dynamics of both sensors and actuators are integrated to the nonlinear model in a modular Simulink model. Trimming the nonlinear model for steady-state flight and extracting the linearized models for the UAV are then considered. Two different design techniques are used for designing the UAV flight
controller; the classical PID and the fuzzy controllers. A comparative synthesis between these controllers is performed for specific altitude and speed commands. Simulation results showed acceptable responses except that the fuzzy approach yields better time responses and disturbance rejection than the classical one.