Study on a modified mode tracking technique in support of aeroelastic stability verification by flight testing

Mass and aerodynamic modifications often lead to significant changes in the aeroelastic behavior of an aircraft, requiring flight test evidence to demonstrate the aeroelastic stability within an intended flight envelope. This is particularly true in those cases where no aeroelastic modeling products are available. In this context, the growing interest in Operational Modal Analysis (OMA) poses new challenges when dealing with aeroelastic modes tracking since modal parameters estimation is done considering the aircraft as a linear time invariant system. This is not the case when dealing with mass changes due to fuel consumption. As result, modal parameters estimates could be significantly biased. Consequently, mode shapes tracking could become difficult through consecutive test points, particularly when using the pole-weighted version of the Modal Assurance Criterion (MAC), called MACXP. The purpose of this paper is to propose an improved tracking technique, based on the MACXP, to be applied with modal estimates obtained with the OMA method. The proposed tracking method is validated on a known multiple mass-spring-damper system. Modal parameters estimate accuracy is also compared with the current state of the art MACXP tracking method. An experimental application is also provided for modes tracking on a modified single seat aircraft to evaluate effectiveness with real data from testing.