Hybrid propulsion benefit in optimal power-off landings of light multi-role helicopters

Abstract

The present paper focuses on the simulation of helicopter Power-Off maneuvers. These complex dynamic flight conditions are here formulated as trajectory optimization problems. Our numerical procedures can be conceptually used with any blackbox flight mechanics simulators, with minimal assumptions on the functionalities of such third-party software components, and can cater to a wide range of vehicle models of varying complexity. The Maneuver Optimal Control Problem is solved through a direct approach, by means of Direct Transcription techniques or Multiple Shooting methods depending on the model complexity and problem characteristics. By considering a model similar to the Kopter AW09 single-engine helicopter, three main applications are here addressed, i.e. the Autorotation Entry, the Flare, and the full Power-Off Landing. A specific effort of this work is focusing on the effects of an extra electrical power supply following the failure of the thermal engine to enhance safety in critical conditions (”1.5 engine” concept). The delicate trade-off between the additional weight of the electrical power kit and the energy booster available in case of an emergency is addressed for typical Power-Off Landing procedures in proximity of the ground.