Experimental and numerical helicopter pilot characterization for aeroelastic rotorcraft–pilot coupling analysis

Abstract

Pilot–vehicle interaction represents a critical aspect of aircraft design. Very low-frequency, voluntary although unintentional interaction has been extensively investigated in fixed and rotary wing aeromechanics. Higher frequency, involuntary and thus passive interaction received similar attention in fixed wing aeromechanics, but not as much for rotary wing. The results of an experimental campaign for the characterization of the passive behaviour of rotorcraft pilots' biomechanics are presented. A flight simulator has been used to excite human subjects. The accelerations of their limbs and the motion induced by the vibrations of the limbs in the control inceptors have been recorded. The vertical, longitudinal and lateral directions have been independently excited, while measuring the motion of the arm directly involved in the control inceptor mostly affected by motion in each direction, namely the left and the right arms for the collective and the cyclic sticks, respectively. The frequency domain response has been evaluated; resulting noteworthy behaviour is discussed, addressing its relevance in modelling the passive behaviour of pilots within the bioaeroservoelastic rotorcraft analysis. The measurements of human body impedance, under realistic cockpit motion, are used to identify the direct transfer functions between the motion of the seat and the controls inadvertently fed back into the rotorcraft.

A practical biodynamic feedthrough model for helicopters

“…The values c 1 and c 2 can be used to eliminate drift and account for the pilot's ability to correct for lowfrequency disturbances [12]. When c 1 = 0, the first pole becomes an integrator 1/s, canceling the zero in the origin resulting from H mayo,abs (s) − 1.…”

“…To obtain the relative deflection one needs to subtract the absolute acceleration of seat from the absolute acceleration of the hand, resulting in H mayo,abs (s) − 1. The relative deflection of the control device as a function of the acceleration can be thus written as (also see [12]):…”

“…In order to compare this model with the BDFT results obtained in this study, it needs to be adapted to obtain relative control device deflection, in rad, as a function of the seat's vertical acceleration, in m/s 2 . This can be done, as described in [12], by adding a two pseudo-integrators (1/(s + c)), converting acceleration to position, and by dividing by the length of the inceptor L, in m, approximating deflection in rad. To obtain the relative deflection one needs to subtract the absolute acceleration of seat from the absolute acceleration of the hand, resulting in H mayo,abs (s) − 1.…”

“…According to Ref. [12], the second additional pole should be set to a low frequency. In the current study c 1 = 0 and c 2 = 0.2π (= 0.1 Hz) is used, which is in accordance with Ref.…”

“…Here, the effects of BDFT in the helicopter collective control loop were measured, modeled, and simulated. Other, more recent studies regarding BDFT in helicopters have been conducted in the context of the GARTEUR HC-AG16 project (e.g., [10]) and the ARISTOTEL project (e.g., [11,12,13,14]). In these projects, so-called Rotorcraft-Pilot Couplings (RPCs) were/are investigated.…”