Modeling and differential flatness based control for a convertible aircraft

One of the latest challenges in the aeronautical field is the research and development of convertible Unmanned Aerial Vehicles (UAV). This kind of aircrafts offers interesting alternatives to fixed-wing and Vertical Take-Off and Landing (VTOL) UAVs. Fixed-wing UAVs are very efficient in the forward flight and they require runways for take-off and landing, VTOL UAVs, in contrast, have the ability to hover but are not very efficient in forward flight. Especially for missions like observation and inspection of structures, in which, for instance, the vehicle has to inspect a wind turbine and then to fly rapidly towards another one, both fixed-wing and VTOL UAVs are unsuitable. Convertible Unmanned Aerial Vehicles (UAV), instead, guarantee a good performance in these kind of missions, as they provide efficient capabilities in both vertical take-off and landing, hovering and forward flight. This research project is initially focused on the accurate dynamic modeling of a birotor, tilt-body, tail-sitter, delta-wing convertible aircraft. Then, the obtained system is proved to satisfy the differential flatness property, for which two different analyses, for zero/small and high aerodynamic velocities, are considered. Differentially flat systems have the property that all the states and control inputs can be expressed as a function of a set of flat outputs and a finite number of their derivatives. This study allows to compute the inverse dynamic model of the system and it is used for the feedforward control. Finally, the linearized system is decoupled with the Singular Value Decomposition (SVD) method, and PID controllers are designed. It is worth to remark that this research project is simulation based, but considerable effort was made in order to keep this work as close as possible to reality.