Identification of Time Periodic Helicopter Rotor Dynamics in LPV State Space Form

Despite extensive research on system identification for helicopters in the past, studies characterizing time-periodic dynamics of helicopter rotors using system identification techniques are limited. In this paper, a study is conducted to explore applicability of linear parameter-varying (LPV) system identification techniques in this domain, and the scope is to obtain low-order state-space models for time-periodic helicopter rotor dynamics. The identified models can then be used for LPV controller applications on active rotor control design or envelope cueing. For this work, the LPV subspace identification scheme is employed for the system identification process, together with an optimization step to enhance the fit performance. The method is demonstrated for blade flapping dynamics using a building-block approach progressing from simulations of a rigid blade model to a higher fidelity elastic blade rotor model and, finally, flight-test data. Findings from simulation and flight-test data in this work support that the employed LPV identification scheme is a viable method to capture periodic characteristics of the rotor system.