Present and future trends in rotorcraft pilot couplings (RPCs) - A retrospective survey of recent research activities within the European project ARISTOTEL

Fixed and rotary wing pilots alike are familiar with potential instabilities or with annoying limit cycle oscillations that arise from the effort of controlling aircraft with high response actuation systems. Understanding, predicting and supressing these inadvertent and sustained aircraft oscillations, known as Aircraft (Rotorcraft)-Pilot Couplings (A/RPCs) is a challenging problem for the designers. Recent experiences show that especially modern designs are being confronted with an increasing degree of dangerous A/RPCs. The reason for this is that modern aircraft feature a significant level of automation in their Flight-Control-Systems (FCS). FCS is generally intended to relieve pilot workload and allow operations in degraded weather and visibility conditions. Especially in the modern rotorcraft, there seem to be embedded tendencies predisposing the FCS system towards dangerous RPCs. As the level of automation is likely to increase in future designs, extending to smaller aircraft and to different kinds of operation, the consequences of the pilot 'fighting' the FCS system and inducing A/RPCs needs to be eradicated. In Europe, the ARISTOTEL project (2010-2013) has been launched with the aim of understanding and predicting modern aircraft's susceptibility to A/RPC. The present paper gives an overview of the current status in RPCs and what can be expected in future designs.