Due to the growing applications involving Unmanned Aerial Vehicles (UAVs), Flight Controllers for rotary wing UAVs are playing an important role in guaranteeing proper flight performances and high stability. Many companies are investing to improve drones’ reliability and extend their use to several applications ten years from now. Flight performance of drones needs to be improved to meet this increasing demand, and researches about best-performing control strategies have been carrying on. To increase flight performance and control strategies efficiency, an "open" platform is needed, so that the Flight Controller software can be fully accessible and easily modifiable. In the following thesis, an Open-Source Flight Controller for rotary wing UAVs is developed and tested in a real environment, while a Linear Quadratic Regulator (LQR) controller is implemented to perform the auto-stabilizing function and maneuvres.