With the new generation of propeller engines, aircrafts become more prone to whirl flutter, an aeroelastic instability possibly causing irreversible structural failures. The prediction of the motion induced aerodynamic force on the propeller is essential to catch such kind of instability. Classical theory uses a quasi-steady aerodynamic model to obtain analytically the dependence of the forces and moments on the movement. This paper proposes to use an unsteady aerodynamic theory and to take into account the inflow disturbance, to obtain a more realistic model. This leads to a complex dependency of the aerodynamic loads on the vibratory frequency, which is bypassed by the use of a rational matrix approximation (RMA) of the aerodynamic transfer function to obtain a linearized stability problem. Aeroelastic stability studies are performed on a classical two degrees of freedom structural model, and on another one including one more degree of freedom to represent the wing bending. Results demonstrate a strong dependence of the stability boundaries on the aerodynamic model used, and highlight the precision and convenience of the method involving a rational matrix approximation of the aerodynamic transfer function. Wing flexibility is of importance, as some unconventional stability boundaries are obtained in comparison to the classical 2-dof model.