Abstract
The driving-point impedance and transmissibility techniques were used to evaluate the effects of military helicopter seat cushions on human body vibration response. Small females (5th percentile or less for body weight) and large males (95th percentile or greater) were exposed to vibration in the frequency range of 3 to 21 Hz at 0.59 m/s2 rms. Transmissibilities were calculated between the acceleration measured at selected anatomical sites, including the chest, head, spine (C7), and thigh, and the input at the seat. Seating configurations included the rigid seat, a current inventory seat cushion, and a prototype cushion with an inflatable thigh support in both the deflated and inflated positions. Rigid mass tests showed that the single resonance frequency and associated magnitude peaks were significantly lower for the two prototypes. The most dramatic effects in the humans were observed in the magnitudes of the peak head and spine transmissibilities located between 4 and 6 Hz with the use of the prototype cushions. Both the deflated and inflated cushions significantly increased the peak head and spine transmissibilities in the females, while decreasing or attenuating the transmissibilities in the males as compared to the rigid seat and the current inventory cushion.
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