The experimental trajectory control of a Tri- TiltRotor Unmanned Aerial Vehicle in rotorcraft hovering operation is the subject of this paper. This reconfigurable UAV is designed for autonomous conversion between the Vertical Take- Off and Landing, and the Fixed-Wing flight modes. Via employing the additional control authority gained by rotor-tilting, the full actuation of the UAV longitudinal dynamics is achieved. Based on this novel feature, longitudinal thrust vectoring of the main rotors is performed, and the respective degree-of-freedom is significantly benefited while performing rotorcraft hovering flight. The system custom autopilot is based on a Proportional- Integral-Derivative-double Derivative scheme, exploiting the augmented UAV state vector for control, while the customdeveloped sensor suite and state estimation system provides fully autonomous operation. Extensive experimental studies validate the control scheme's efficiency, while remarking the advantageous effects of the longitudinal thrust vectoring-based control authority.