Identification of aeroelastic parameters for helicopter tail rotor limit cycle oscillation monitoring

The aeroelastic parameters of helicopter main rotor and tail rotor are required in the monitoring and evaluation of rotor aeroservoelastic instability incidents such as limit cycle oscillations. However, in situ measurement of these parameters on helicopters is generally difficult due to the need to transfer vibration data across a rotating interface. This article presents a novel center frequency scaling factor relationship of the aeroelastic parameters between the rotating and stationary frames. Together with the stochastic parameter identification technique, this methodology enables real-time estimation and tracking of the critical aeroelastic parameters in the rotating frame during limit cycle oscillation events based on vibration information measured exclusively in the stationary frame. The methodology has been validated using flight vibration data measured from both the rotating and stationary frames of a helicopter tail rotor system during a limit cycle oscillation event. Moreover, this methodology has been applied to the analysis of vibration data measured from the teeter tail rotor system on the Canadian CH-149 Cormorant helicopters to derive the critical aeroelastic parameters during several limit cycle oscillation events.