With growing use of UAVs also for civil applications and their intended inclusion in non-segmented airspace, emergency procedures gain importance. In case of total engine failure, rotorcraft UAVs can, provided they are still controllable, perform a safe flight to a landing site using autorotation, which is the topic of this contribution. It is based on extensive modeling, simulation and control design performed at the Department of Flight Dynamics, RWTH Aachen University, Germany in context of research for helicopter UAVs, emergency procedures and autonomous planning capabilities. An autonomous emergency procedure commanding the Flight Control and Guidance System was developed comprising bringing the helicopter into autorotation, planning and commanding trajectories to known landing sites based on the state of the helicopter and its environment and landing the UAV safely. Furthermore, the Flight Control and Guidance System (FCGS) had to be adapted to cope with the changed flight mechanical characteristics of the helicopter during autorotation, mainly due to the change in blade inflow and rotor rotational speed, and to provide the base for following a trajectory safely.
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