Characterization of Seat-to-Head Vibration Transmissibility in Rotorcraft Occupants

Aerospace structures generally have flexible and lightweight components which are prone to large amplitude, lowfrequency vibration. In the case of rotorcrafts, the main and tail rotors generate vibration that substantially contribute to the exposure of the pilot and crew to whole-body vibration (WBV) over a wide frequency range. WBV exposure is generally more severe in rotorcrafts compared with ground vehicles, as the transmitted vibration is dominated by the blade passage frequency and its harmonics which typically lie within the range of frequency to which human is most sensitive. Pilots and crew members of helicopters experience WBV produced by the main and tail rotors across a broad frequency range. The fundamental blade passage frequency of the main rotor of different helicopters generally occurs in the 4 to 8 Hz frequency range which coincides with the whole-body vertical mode resonance of the seated human body. The WBV exposure, together with prolonged sitting in confined spaces during long flight missions, has been associated with various adverse health effects on human biomechanical and physiological responses. Throughthe-body biodynamic response functions, such as seat-to-head (STHT) can describe the flow of vibration through the body and thus can yield a better understanding of the potential adverse effects of WBV. The aim of the presents study is to investigate the effect of different measuring systems (a head-strap, bite-bar and forehead Velcro strap) on the the STHT response due to the whole-body vibration encountered in rotorcraft crew.