PREDICTION OF ROTORCRAFT-PILOT COUPLING PHENOMENA THROUGH REDUCED-ORDER AERODYNAMIC MODEL

Rotorcraft-pilot couplings are adverse interactions between pilot and helicopter. They are usually divided into two main classes of phenomena. The first one considers Pilot Induced Oscillations (PIO) and basically concerns flight dynamics and behavioural processes; the second one, which will be investigated in this study, is conventionally named Pilot Assisted Oscillations (PAO) and is caused by unintentional actions on the controls, caused by the reaction of the pilot body to the vibrations on his seat. PAO are strictly related to the aeroelasticity of the main rotor, the structural dynamics of the fuselage and involve also aspects related to the servoelasticity. This paper presents a model for rotorcraft-pilot coupling predictions that includes a reduced-order model for the unsteady aerodynamics of the main rotor. The introduction of an unsteady aerodynamic model is suggested by the important role that rotor aeroelasticity plays in PAO phenomena, while its reduced-order modelling is convenient in stability and response analysis, and for control applications. The numerical investigation concerns both the stability analysis of vertical bouncing (a type of instability which might be caused by the coupling, through the pilot, of vertical acceleration of pilot seat with collective control stick), for different helicopter aeroelastic models. and gust response in hovering (which is an interesting problem for many applications and missions, such as rescue, patrolling and positioning of loads).