The influence of rotor wake and ground effect on aeromechanical instabilities, specifically ground resonance is investigated. The analytical model considered has fuselage pitch, roll and blade flap, lag degrees of freedom. To analyze the system stability at different rotor rotational speeds, modal damping and frequency is computed using Floquet method. The Peter He dynamic inflow model is incorporated into the system equations to analyze the influence of rotor wake on system stability. The effect of collective pitch on the system stability, with uniform inflow as well as dynamic inflow, is considered. It has been observed that rotor wake influences the effect of collective pitch on system stability. The influence of full ground effect as well as partial ground effect on the system stability is investigated. © 2015 by the Asian-Australian Rotorcraft Forum. All rights reserved.