An Innovative Experimental Approach to Lateral-Directional Flying Quality Investigation for Tailless Aircraft

Tailless aircraft suffers from limited yaw control power and poor directional stability inherently. To address these issues in the early design process of a tailless configuration with low costs and risks, this paper presents an innovative experimental approach to control law validation and quantitative flying quality evaluation with a dynamically scaled model mounted on a three degree-of-freedom rig in the wind tunnel. The motion equations of the tailless demonstrator on the rig are derived, and then the comparisons of the lateral-directional flight dynamics between the rig constrained model and the free flight model are carried out. Construction of the control augmentation system for yaw and roll motion is accomplished according to the scale modified criteria of flying qualities. Effectiveness of the designed control law is demonstrated with steady pilot-in-the-loop flights at different airspeeds and angles of attack. The achieved closed-loop flying qualities are evaluated by applying multistep maneuvers for low order equivalent system identification. Whereas severe instability is observed in yaw for the open-loop case, the closed-loop flying quality of the Dutch-roll mode can be improved to level 1 at low angle of attack.