"This study investigated the dynamic characteristics and human perception of higher-frequency multi-axis vibration associated with a military propeller aircraft environment. Triaxial accelerations were measured at the interfaces between the occupant and aircraft seat surface (seat pan and seat back) to evaluate and compare the effects of the aircraft seat fitted with different cushions. While all cushions showed a significant reduction in the X-axis seat pan vibration as compared to the original operational seat cushion at the blade passage frequency (BPFnot, vert, similar73.5 Hz), the associated accelerations remained significantly higher than the floor input accelerations. Transmissibility data confirmed these seat system characteristics at higher frequencies. A body region perception survey suggested that the subjects were most sensitive to the BPF component of the operational exposure. In contrast, the weighted acceleration levels (ISO 2631-1: 1997) suggested that the subjects would perceive the highest vibration in the vertical (Z) direction at the seat pan with substantial contributions in the X direction from the seat back, particularly at the propeller rotation frequency (PRFnot, vert, similar18.5 Hz). The overall Vibration Total Value (ISO 2631-1: 1997) suggested that the operational exposures would be perceived as being “not uncomfortable” to “a little uncomfortable.”"

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