Influence of Added Head Mass Properties on Head/neck Loads during Standard Helicopter Impact Conditions

Thirty-degree pitch-down helicopter crash pulses were examined at the Patuxent River Horizontal Accelerator facility. The pulses used were representative of standard seat qualification crash corridors for a variety of rotary wing platforms. The primary objectives of this effort were 1) to quantitatively determine the effect of varying helmet weight and center of gravity (CG) during simulated rotary wing crash scenarios, and 2) to perform data analysis using existing injury criteria to identify maximum requirements for helmet weight and CG for the extremes of the rotary wing aviator population. Quantification of risk was based upon aviator size, helmet mass properties and impact severity. Testing included a Hybrid III 95 percentile male, a 50 percentile male, and a 5 percentile female. In order to achieve the necessary helmet weight and CG values required for the tests, a head-mass fixture was developed and used in place of the manikin’s head that allowed weights to be added both forward and laterally on the head to generate a wide array of weight and CG configurations. Modeling of the system was performed using MADYMO, which was used to refine the test matrix for the weight and CG locations that would most likely define the mass properties envelope from the known criteria force/moment limits. A comprehensive analysis of the data was performed using available injury predictors to determine the likelihood of injury to the upper and lower cervical spine. The Nij cervical injury criterion developed by the National Highway and Traffic Safety Administration (NHTSA) was adapted and used to determine the risk of cervical injury. An analysis of variance (ANOVA) with a post-hoc Tukey-Kramer test to determine the source of the difference was conducted on the principal neck parameters to determine whether any of the factors were statistically significant (defined as p≤0.05). Results indicated that pulse severity was the most dominant variable examined during the study. The effect of gender was more related to the different values for the neck injury limits, which were scaled according to weight. As a result of the study, guidelines based on helmet weight, CG, aviator size and impact severity were generated.