Aircrew helmet protection against potential cerebral concussion in low-magnitude impacts

The response of the Gentex DH-151 (contact type) and Gentex 411 (suspension type) aircrew helmets to low-magnitude impacts, such as those sometimes encountered during cockpit buffeting, in ejection, and in parachute landings, was studied to augment the data base on helmet performance. The helmets, mounted on a Hodgson headform, were dropped on the crown and rear at impact velocities up to 4.97 m/s. Acceleration time histories were tape recorded and digitized and Gadd Severity Indices (GSI), among others, were calculated from the resultant acceleration curve. Both helmets kept the GSI below predicted concussion thresholds at 4.97 m/s and were considered to perform well on initial impacts. On second impacts, the GSI rose considerably because the shell and liner of the DH-151 cracked and the suspension of the "141" stretched during the first blow. Improvement of the multiple impact performance of both helmets appears desirable, although the suspension helmet performed slightly better than the contact helmet with respect to the criterion used.