Attitude and trajectory control system design for the emergency maneuver of a unmanned helicopter

The constant growth in the Unmanned Aerial Systems industrial sector, and the perspective of new applications in various, operational scenarios pose a challenge in the development of more performing and safe systems. In this context, crucial importance will be the development of systems with higher emergency management capabilities and enhanced control performance. The main objectives of this thesis are 1) the development of the automatic autorotation maneuver for a small-scale helicopter, and 2) the implementation of a nonlinear dynamic controller, allowing precise reference attitude and velocity trackiing. The design of a suitable maneuver has been conducted by dividing the maneuver into its two fundamental phases and analyzing the key variables to be considered and controlled. In particular, all the possible steady descent conditions were calculated with a trim algorithm, and a suitable flare profile was adopted and optimized. A PID-based control architecture has been adopted to follow the nominal autorotation maneuver in a closed loop. Several simulations have been considered to test the maneuver for a wide range of different initial conditions. Also, a nonlinear dynamic inversion controller made of an inner loop for attitude stabilization and an outer loop for velocity control has been designed. The attitude control systems has been derived by inverting a medium-order helicopter rotational dynamics model, while for the velocity controller, a simpler translational dynamics system has been developed. To ensure adequate control performance, an extended Kalman filter allowing the estimation of the inflow ratio, has been developed and implemented. An extensive simulation campaign has been conducted in order to validate the controller in different flight maneuvers, including the autorotation.