The main rotor model of an existing commercial Full Flight Simulator of a small twin-engine utility helicopter is improved. The existing rotor model implements individual rigid blades with flap blade dynamic in loose way causing an unstable flight dynamic and uncoupled off-axis response. The work aims to obtain a stable response of the flight model after the trim phase and an improved dynamic response more comparable to the flight tests data to reduce the artificial tuning phase. Furthermore, to maintain high general configurability and to respect the real-time simulation constrain a special attention is given to the practical implementation of the code.