Unmanned Aerial Vehicles (UAVs) represent an ideal platform for testing advanced control techniques. In recent years, many researches based on modern control theories and design of UAV autopilot algorithms have been completed. Most of the modern autopilots incorporate controller algorithms to meet the always more demanding requirements of flight maneuvers and mission accomplishment. However, due to the complexity and the computational need of the control algorithms, most of the commercial autopilots are based on Proportional Derivative Integrative (PID) philosophy, in which trial and error methods are used for the definition of the control gains. In this thesis, a PID controller system is proposed and it is compared with a variable structure method (that is a Sliding Mode Controller (SMC)).