In this paper, first, system identification experiments for a large-scale unmanned helicopter are carried out to obtain a numerical model of aircraft dynamics. The attitude error of the helicopter is compensated by a stability augmentation system that permits the experiments during the flight. System identification results are shown on the dynamics using the measured input and output data. Next, the position control systems based on the H-infinity control theory is constructed by using the identified model. Finally, the position control experiments suggest that the proposed modeling and design approach is effective enough for practical applications.