Flight control of a small helicopter in unknown wind conditions

This paper presents a novel application of a two-time scale controller, using a disturbance observer, for the hover flight control of a Rotary wing Unmanned Aerial Vehicle (RUAV). Flapping and servo dynamics, important from a practical point of view, are included in the RUAV model. The two-time scale controller takes advantage of the `decoupling' of the translational and rotation dynamics of the rigid body, resulting in a two-level hierarchical control scheme. The inner loop controller (attitude control) tracks the attitude commands generated by the outer loop controller and sets the main rotor thrust vector, while the outer loop controller (position control) tracks the reference position. The proposed controller uses the disturbance observer to approximate the external disturbances such as wind gusts. Hover flight simulation results are presented in this paper using the proposed backstepping-based controller.