A finite-state aeroelastic model for rotorcraft–pilot coupling analysis

Rotorcraft–pilot coupling (RPC) denotes inter- play between pilot and helicopter (or tiltrotor) that may give rise to adverse phenomena. These are usually divided into two main classes: pilot-induced oscillations driven by flight dynamics and behavioural processes, and pilot- assisted oscillations (PAO) caused by unintentional actions of pilot on controls, owing to involuntary reaction to seat vibrations. The aim of this paper is the development of mathematical helicopter models suited for analysis of RPC phenomena. In addition to rigid-body dynamics, RPCs (especially PAO) are also related to fuselage structural dynamics and servoelasticity; however, a crucial role is played by main rotor aeroelasticity. In this work, the aeroelastic behaviour of the main rotor is simulated through a novel finite-state modeling that may conve- niently be applied for rotorcraft stability and response analyses, as well as for control synthesis applications. Numerical results, first are focused on the validation of the proposed novel main rotor model, and then present appli- cations of the developed comprehensive rotorcraft model for the RPC analysis of a Bo-105-type helicopter. Specif- ically, these deal with the stability of vertical bouncing, which is a PAO phenomenon caused by coupling of ver- tical pilot seat acceleration with collective control stick, driven by inadvertent pilot actions. Further, considering quasi-steady, airfoil theory with wake inflow correction and three-dimensional, potential-flow, boundary element method approaches, the sensitivity of PAO simulations to different aerodynamic load models applied within the main rotor aeroelastic operator is also investigated.