1 Roll Control of a Tail-Sitter VTOL UAV Helmi Abrougui Samir Nejim Habib Dallagi helmiabrougui@yahoo.fr samir.nejim@centraliens.net habib.dallagi@ept.rnu.tn Automatic Control & Marine Robotics Research Unit Naval Academy, Tunisia Abstract :—This paper deals with the development of a flight controller in order to stabilize the roll motion of a vertical take- off and landing unmanned air vehicle (VTOL-UAV) during hover flight. Using Newton Euler approach, a dynamic model is firstly described then a Proportional-Integral and Derivative regulator for the stabilization of the VTOL aircraft in the vertical plan is synthesized. Next, simulations are carried out in order to test the regulator performances. Finally, the proposed control law is executed in real time by an AtMega2560 micro- controller which is built in an Arduino module in order to stabilize the roll motion of a balance platform. Keywords—VTOL aircraft; roll control; digital PID techniques. 1-Introduction: The use of planes onboard a naval vessel is very important for the projection of the naval forces and the increase of the action range. Hence, the necessity of deploying big ships equipped with long runways that could exceeds the ship’s length in order to be able to embark fixed wings planes. A remedy for this issue, is the use of vertical take-off and landing aircrafts. Due to the transition mechanism and airframe VITOL aircrafts can be generally classified into two main types [9]: Convertiplanes and Tail-Sitters. A convertiplane is an aerial vehicle that takes off, cruises, hovers and lands with remaining horizontal, it means that the main body configuration does not change during flight as Tilt-Rotors [10] and Tilt-Wings [11]. A Tail-sitter is an aircraft that takes off and lands vertically and the aircraft main body tilts forward using differential thrust or control surfaces to flight horizontally; as Control Surface Transitioning Tail-sitters (CSTT) [12] and Differential Thrust Transitioning Tail-sitters (DTTT) [13]. In addition to the operability onboard small platforms, VTOL aircraft offers several advantages such as high energy autonomy in comparison with multirotor aircraft. The development of unmanned aerial vehicles (UAVs) has increased during the last few years, due to their wide range applications in both military and civilian. One of the latest trends in the UAV’s technology is the development of mini aerial vehicles with vertical take-off and landing capabilities that are deployable even when no landing runway is available. Also, many autopilot systems are designed based on classical control techniques. These control methods can be found in many flight controls studies such as [4,5]. Modern control techniques are also used in UAVs autopilot applications [6]. Fuzzy logic control was used too in order to control aircraft in [7]. Besides, in his project, Octavio Garcia [8] has presented a nonlinear control strategy based on Saturated- Proportional-Integral and Derivative technique. The tail-sitter VTOL aircraft shows a natural unstable behavior in vertical flight according to previous projects so, the manual control is a difficult task. Therefore, this paper aims to design a regulator in order to stabilize the roll position of the tail-sitter VTOL aircraft during hover flight. The paper is organized as follows. Section 2 presents the dynamic model obtained using the Newton-Euler approach. The roll control strategy is developed in section 3. The simulation results of the proposed roll control strategy applied to the system are given in section 4. Finally, the experimental platform and the embedded system were described and the real-time experimental results of an autonomous stabilized flight of the two-rotor mini UAV were discussed. Figure 1: VTOL mini aircraft 2- Dynamic model of the tail-sitter VTOL aircraft: In this section, a modeling approach of a VTOL aircraft will be presented. The VTOL aircraft is considered to be a solid plane moving in aerospace, it is submitted to torques