A study of the flight dynamics helicopter carrying an external load using bifurcation theory and continuation methods

The paper presents a study of the flight dynamics of a helicopter with an articulated rotor, carrying a suspended load. The aircraft model includes rigid body dynamics, individual flap and lag blade dynamics, and inflow dynamics. The load is a point mass with a single suspension point. Results are obtained for load masses of up to 1500 kg, with load-to-helicopter mass ratios up to 33%, and cable lengths up to 55 m. The presence of the external load modifies the flight dynamics and handling quality characteristics of the helicopter because the dynamic and aerodynamic characteristics of the load may make it unstable in certain fight conditions. Maneuvers of this system in wide flight regimes involves non-linear aerodynamics and inertial coupling. In can be stated that the helicopter with the suspended load is a inherently non-linear and time varying system. Theory of dynamical systems provides a methodology for studying such non-linear systems. Bifurcation theory is a part of that theory. It considers changes in the stability of the system which lead to qualitatively different responses of it. In this paper, results from the theory of dynamical systems are used to predict the nature of instabilities caused by bifurcations and the response of the rotorcraft with the suspended load that follow such bifurcations.