IMPROVEMENT OF MAIN ROTOR MODEL FOR COMMERCIAL FULL FLIGHT HELICOPTER SIMULATOR

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. To solve the instability problem a multi-blade coordinates transformation of the existing model is introduced. Additionally, to improve output stability, the rotor model is transformed to be non-rotating and, therefore, independent from the time discretization. The multiblade coordinates transformation acts as a low pass filter in the time integration without any loss of accuracy and any extra hypothesis, permitting to naturally increase stability in a discrete time model. Stopping the rotation of the blades leads to time independent eigenvalues of the system increasing the output stability. The consequent loss of accuracy is partially reestablished by artificially increasing the number of blades and then mediating the output for the real number of rotor blades. This artifice can be performed only with the multi-blade coordinates transformation. The nonexistence of an off-axis response in many flight situations has imputed to the poor quality of the main rotor model. A higher level rotor model is developed and implemented, maintaining the multi-blade coordinates transformation and the time independency artifice. The new model has individual rigid blades featuring flap and lag blade dynamics around offsetted concentrated hinges, a 3 state dynamic inflow model, a non-linear 2D blade aerodynamic and numerical integrated aerodynamic loads. The equations are evaluated without performing any further simplification with Matlab symbolic tool and the implementation scheme is reorganized to maintain higher level of generality.