Effects of non-neutral head-neck posture on seat-to-head vibration transmissibility response characteristics in rotorcraft pilot/crew

The whole-body vibration (WBV) encountered in a rotorcraft dominates near 4-6 Hz, causing resonant oscillations of the seated human pilot/crew. Exposure to such WBV has been associated with many health disorders among the exposed pilot/crew, namely, deformities of the spine and loading of neck muscles, apart from discomfort and deteriorated tracking performance. The use of helmet and mounted devices together with non-neutral head-neck complex (HNC) postures, frequently assumed by pilots, further accentuates the dynamic stresses imposed on the HNC. This study experimentally investigates the transmission of vertical seat vibration to HNC of seated human subjects, assuming non-neutral HNC postures. The data were analyzed to highlight the effects of HNC posture on translational and rotational vibration responses of HNC. The experiments were conducted on 14 adult males subjected to band-limited white-noise vibration in the 0.5 to 25 Hz frequency range. Considering four different HNC postures (neutral, yaw rotation, flexion, and combined flexion and rotation) and two back support conditions (NB- no back support and WB- an inclined back support). The responses were measured in the sagittal plane at four different locations (mouth level, forehead, top of the skull, and C7 vertebrae) under three different levels of seat vibration, expressed in terms of root-mean-squared acceleration values (RMS: 0.25, 0.50, and 0.75 m/s 2 ). The results showed pronounced effects of HNC postures, which were also confirmed through statistical analyses of the measured data. The analyses also indicated significant effects of back support condition and measurement location, irrespective of the HNC posture. • The effect of non-neutral head-neck postures on the vibration transmissibility was investigated experimentally. • The experiment design includes four different head-neck postures, two different sitting conditions, and three excitation levels. • The responses were measured in the sagittal plane at four different locations. • The results revealed the considerable effects of non-neutral head-neck postures on the peak transmissibility magnitudes and frequencies. • The statistical analyses also confirmed the significant effects of head-neck posture on the peak transmissibility magnitude and frequencies.