The Effects of Variable Helmet Weight and Subject Bracing on Neck Loading during Frontal -gx Impact

Helmet-mounted systems (HMS), such as night vision goggles and helmet-mounted displays, are designed to enhance pilot performance. Using HMS, however, may also affect pilot safety by increasing the potential for neck injury during ejection due to the increase in dynamic forces generated in the cervical spine as a result of the change in helmet inertial properties. Pilot bracing techniques may also have an effect on ejection injury risk by allowing some of the neck forces to be off-loaded during the acceleration impact phases. A series of tests were conducted on the AFRL/HEPA Horizontal Impulse Accelerator (HIA) using human subjects to investigate the effects of helmet inertial properties and bracing techniques on human response to short-duration frontal impacts of variable magnitude. Head accelerations were measured and neck loads and moments were calculated to compare the head and neck responses using helmets of varying weight. Headrest loads were recorded to monitor and evaluate subject bracing. The neck loads and helmet weights were also extrapolated to higher levels in order to estimate injury thresholds for pilots wearing even heavier helmets at maximum seat accelerations. The results of this study will be used to establish head/neck injury criteria for helmet-mounted systems and to improve bracing techniques to minimize pilot injury during ejections. BACKGROUND Tests by Perry at the Air Force Research Lab’s Biomechanics Branch (AFRL/HEPA) from 1991 through 1997 have evaluated the effects of variable helmet inertial properties on the biodynamic response of male and female human volunteers exposed to vertical (+Gz) accelerations using the Vertical Deceleration Tower (VDT). 4-6, 8 A recent study by Perry and Buhrman investigated the effects of varied helmet weight on human response during lateral +Gy Impact on the Horizontal Impulse Accelerator. Another recent study by Pint explored the effects of varied helmet weight on human neck response during retraction using the Body Positioning and Restraint Device (BPRD). The objective of this study was to provide additional human dynamic response data from a frontal (-Gx) impact environment with a variable weight helmet. This is required to complete the development of multi-axial cervical injury criteria for the three coordinate axes, and to continue the development of head/neck biodynamic models. In particular, the results of this program will contribute to the development of design guidelines for the safe use of helmet-weighted systems and provide information on optimal pilot bracing techniques. METHODS A series of short-duration frontal impact tests were completed at Wright Patterson AFB using the Horizontal Impulse Accelerator (HIA). Report Documentation Page Form Approved