There have been increasing complaints of annoyance, fatigue, and musculoskeletal pain duringprolonged exposures to propulsion-generated vibration in military propeller aircraft. Theobjective of this study was to evaluate the effects of seat cushions on mitigating the higherfrequency (>10 Hz) multi-axis vibration associated with Navy E-2C Hawkeye operations. An E-2C crew seat was used in the laboratory during exposure to a selected operational signal.Triaxial accelerations were measured at the interface between the human and cushion (seat panand seat back). The most pronounced effects were observed at the blade passage frequency(~73.5 Hz). The highest vibration occurred at the seat pan in the fore-and-aft (X) direction of thesubject (lateral direction of the aircraft). Substantial vibration was observed at the seat back inthe vertical (Z) direction. Significantly lower levels of fore-and-aft (X) vibration occurred at theseat pan with all cushions as compared to the original E-2C cushion (P<0.05). The largestreduction in the X acceleration was about 40% with a mean reduction of approximately 20%among the cushions. The results raised questions regarding psychophysical effects and whetherthe vibration mitigation at the blade passage frequency is sufficient for reducing the reportedsymptoms.
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