Crash Energy Management of Rotorcraft Seat Based on Limit Load Curves and Corresponding Occupant Pelvic Load

In military aircraft and helicopter seat design, the seat system must be provided with an energy absorber (EA) to attenuate the acceleration level sustained by the occupants. Because of the limited stroke available for the seat structure, the design of the energy absorber becomes a trade-off problem between the seat stroke and the impact energy absorption. The available stroke must be used to prevent bottoming out of the seat, and also to absorb as much impact energy as possible to protect the occupant. In this study, the energy absorbing systems in civil and military aircraft seat design are evaluated and improved using a mathematical model of the occupant/seat system. Three load-limit design curves, namely, simple EA, two-stage EA, and two-stage EA with initial spike, are modeled, examined, and compared. A model of the load limiter is recommended to minimize the load sustained by the occupant by limiting the relative velocity between the seat pan and the occupant pelvis. Experimental responses of seat system and occupant from literature are utilized to validate the results from this study for civil and military helicopters. A modified energy-absorber/load-limiter is then implemented for the seat structure so that it absorbs the impact energy in an effective manner below the tolerable limit for the occupant and within a minimum stroke. Results from this study indicate that for a designed stroke, the occupant pelvic/lumbar spine injury level is significantly attenuated using the modified energy-absorber system.Copyright © 2012 by ASME