Trajectory Design and Control of a Small-Scale Helicopter Automatic Autorotation Maneuver

The paper addresses the study and design of the autorotation maneuver for a remotely operated helicopter model, developing guidance and control algorithms to automatically track the designed maneuver in case of engine failure. The steady descent phase is investigated first, during which the rotor angular rate and helicopter velocity components are kept at constant values. During the final flare, rotor kinetic energy is exploited to decrease helicopter speed and sink rate before touchdown. If simple polynomial functions are adopted for velocity components during the flare as a function of altitude, the whole maneuver is identified on the basis of a reduced number of parameters, namely, the velocity components during the steady descent and the threshold altitude for starting the flare. An optimization algorithm allows for the selection of the set of maneuver design parameters that result in a minimum residual forward speed at touchdown. Guidance and control logic for the two phases are developed and tested in a number of simulations, proving that the controllers adequately track the designed trajectory, bringing the helicopter to the ground with minimum residual velocity. Robustness with respect to model errors and initial conditions is also demonstrated.