Attitude and velocity high-gain control of a tilt-trirotor UAV

The tilting trirotor presented in this paper is able to perform levelled flight at almost null attitude which is an important requirement for fixed wing tilt rotors in view of the lift control during transition from hovering to forward flight. The nonlinear dynamics, the large effect of wind due to the small scale, and the absence of aerodynamic data at low speed and Reynolds numbers, are crucial factors when designing controllers. A two nested loops, high-gain controller scheme is proposed to control attitude and both longitudinal and vertical speed. Controller design is based on the selection of high-gain PI control actions together with suitable sliding surfaces where the closed loop system state variables are forced to evolve. This approach guarantees robustness and fast tuning. To demonstrate the effectiveness of the proposed controller, also in the presence of actuator dynamics and saturations, numerical simulations have been conducted on a detailed simulator of the tri-rotor.