Bioaeroservoelastic Analysis of Involuntary Rotorcraft-Pilot Interaction

Abstract

This work presents the integration of a detailed biomechanical model of the arm of a helicopter pilot and an equivalently detailed aeroservoelastic model of a helicopter, resulting in what has been called a ‘bioaeroservoelastic’ analysis. The purpose of this analysis is to investigate potential adverse interactions, called rotorcraft-pilot couplings, between the aeroservoelastic system and the controls involuntarily introduced by the pilot into the control system in response to rotorcraft vibrations transmitted to the pilot through the cockpit: the so-called biodynamic feedthrough. The force exerted by the pilot on the controls results from the activation of the muscles of the arms according to specific patterns. The reference muscular activation value as a function of the prescribed action on the controls is computed using an inverse kinetostatics/inverse dynamics approach. A first-order quasi-steady correction is adopted to mimic the reflexive contribution to muscle activation. Muscular activation is further augmented by activation patterns that produce elementary actions on the control inceptors. These muscular activation patterns, inferred using perturbation analysis, are applied to control the aircraft through the pilot's limbs. The resulting biomechanical pilot model is applied to the aeroservoelastic analysis of a helicopter model expressly developed within the same multibody modeling environment to investigate adverse rotorcraft pilot couplings. The model consists of the detailed aeroelastic model of the main rotor, using nonlinear beams and blade element/momentum theory aerodynamics, a component mode synthesis model of the airframe structural dynamics, and servoactuator dynamics. Results in terms of the stability analysis of the coupled system are presented in comparison with analogous results obtained using biodynamic feedthrough transfer functions identified from experimental data.