Effects of Seat Stroke Distance on the Allowable Mass of Head Supported Devices.

Abstract : The effects of stroking distance of energy attenuating helicopter seat on head supported device (HSD) masses were investigated in various helicopter crash scenarios. The Articulated Total Body (ATB) model was used to simulate the helicopter pilot's biodynamic response to five different crash pulses. Parameters of the simulations included two allowable seat stroking distances (2.5 and 25 cm) and four HSD masses (0.45, 1.4, 2.7, and 4.1 kg). The simulations were performed with the mid-sized Hybrid III manikin as the occupant model, and the HSD center of mass (CM) coincident with the CM of the Hybrid III head. Moments and forces produced by the ATB simulations at the head/neck interface (occipital condyles) were assessed against injury thresholds to determine the risk of neck injury. Acceptable head supported masses were established then for the given impact conditions. The report concludes that acceptable HSD mass was highly dependant on seat stroke distance and impact conditions, which include crash pulse magnitude, direction and shape. For a Hybrid III dummy, increased available seat strokes resulted in lower loads transmitted to the head/neck interface, thereby allowing larger HSD masses to be worn.