Head and helmet biodynamics and tracking performance in vibration environments.

INTRODUCTION There are potential effects of vibration on aircrew performance and safety when using helmet-mounted equipment. The objective of this study was to quantify the effects of head orientation and helmet center-of-gravity (CG) on head and helmet biodynamics and tracking performance during exposures to aircraft buffeting and quasi-random vibration. METHODS Three head orientations, including two off-axis or off-boresight configurations [Side (40 degree elevation, 70 degree azimuth) and Up (40 degree elevation, 0 degree azimuth)], and three helmet CGs were tested. The overall head, helmet, and helmet slippage displacement rotations, and rms tracking error and percent time-on-target were evaluated. RESULTS For both exposures, the two off-axis orientations produced significantly higher head, helmet, and slippage displacements; a relationship was observed between the orientation and the rotation that was affected (roll, pitch, or yaw). The highest slippage observed was in pitch in the forward (For) and Up orientations. Significantly higher performance degradation occurred with the Side orientation for two of the three CGs during aircraft buffeting, with minimal degradation observed with the quasi-random exposure. Higher head pitch and lower pitch slippage were associated with the CG estimated to produce loading behind the human head CG. CONCLUSIONS The high off-boresight head movements may influence visual performance in operational vibration environments. Helmet instability appeared to be the greatest in pitch, which could have a significant effect on the design size of the exit pupil. The weight distribution or moments-of-inertia of the helmet system may also have a significant influence on both head/helmet biodynamics and tracking performance and should be investigated.