Optimal trajectory and tracking control system for a helicopter safe landing in autorotation

Abstract

In case of engine failure autorotation represent a safe maneuver for helicopter emergency landing. In autorotation, the rotor is no longer engine-powered but keeps rotating thanks to the impinging flow. During the descent, rotor angular velocity is constant for a given setting of collective pitch and the power dissipated by its rotation is compensated by a loss of potential energy during the descent. A steady descent is then possible down to a fixed altitude where, exploiting rotor residual energy, it is possible to perform a flare bringing the helicopter to minimum touch down velocity. For small scale helicopters an autonomous control system for autorotation can reduce damages and economic losses, saving the rotorcraft and its payload in case of an engine failure. In this paper, a preliminary investigation on steady descent conditions in autorotation, and the design of a possible flare maneuver has been made through a model-based design approach. Also, a closed loop control system has been developed, to perform the two main phases of autorotation maneuver. Simulations results show the suitability of the proposed approach for a wide range of initial conditions (altitude and advancing velocity).