Helmet-mounted systems (HMS), such as nightvision goggles and helmet-mounted displays,are designed to enhance pilot performance.Using HMS, however, may also affect pilotsafety by increasing the potential for neck injuryduring ejection due to the increase in dynamicforces generated in the cervical spine as a resultof the change in helmet inertial properties. Pilotbracing techniques may also have an effect onejection injury risk by allowing some of theneck forces to be off-loaded during theacceleration impact phases. A series of testswere conducted on the AFRL/HEPA HorizontalImpulse Accelerator (HIA) using humansubjects to investigate the effects of helmetinertial properties and bracing techniques onhuman response to short-duration frontalimpacts of variable magnitude. Headaccelerations were measured and neck loads andmoments were calculated to compare the headand neck responses using helmets of varyingweight. Headrest loads were recorded tomonitor and evaluate subject bracing. The neckloads and helmet weights were also extrapolatedto higher levels in order to estimate injurythresholds for pilots wearing even heavierhelmets at maximum seat accelerations. Theresults of this study will be used to establishheadeck injury criteria for helmet-mountedsystems and to improve bracing techniques tominimize pilot injury during ejections.
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