Nonlinear aeroelastic stability analysis of hingeless helicopter rotor blades using FRF coupling and condition number

In this paper, aeroelastic stability analysis of hingeless helicopter blades in frequency domain is studied. In this regard, the nonlinear structural beam model of Hodges-Dowell and an unsteady aerodynamic model based on Greenberg theory and using Loewy aerodynamic function are considered to construct the aeroelastic model. Then, the concept of optimum equivalent linear frequency response function (OELF) is implemented to derive the aeroelastic FRF by coupling the aerodynamic and structural FRFs. Finally, for stability analysis, the efficient and simple criterion of condition number (CN) of aeroelastic OELF is applied. The comparison of the obtained results against those in the literature shows the capability of the OELF and condition number criterion for capturing the instability boundaries of a complex, nonlinear, aeroelastic system such as helicopter blades.