Evaluation of rotorcraft aeroelastic stability using robust analysis

This paper discusses the impact of different aerodynamics models on rotorcraft-pilot couplings stability using a robust stability analysis approach. Models based on blade element/momentum theory and boundary element method, coupled to a finite element model of the blade, are used to formulate the aeroelasticity of the main rotor of a helicopter. The main rotor is coupled to a dynamic model of the airframe that also includes the dynamics of the control system. The resulting linearized models are used to determine stability limits according to the generalized Nyquist criterion, associated with the accelerations of the pilot's seat caused by the involuntary motion of the control inceptors. The resulting stability curves are discussed considering examples of involuntary pilot transfer functions from the literature.