Frequency-Domain Identification of BO 105 Derivative Models with Rotor Degrees of Freedom.

In general, helicopter linear state space models are formulated for the 6 degrees of freedom for the rigid body motion. Such models can adequately represent the low and mid frequency helicopter dynamics. However, when high-frequency validity is needed they show larger deficiencies because the main rotor dynamics are neglected. It is investigated if higher order models with rotor degrees of freedom can be determined from BO 105 flight test data by a system identification approach. A frequency-domain method was used to extract two different models of 10th and 14th order. The obtained results show that the extraction of extended helicopter models from measured rotor and rigid body data is feasible and provides a realistic description of the aircraft dynamics. The prediction capability of an identified model is demonstrated in verification results.