Lumbar load attenuation for rotorcraft occupants using a design methodology for the seat impact energy-absorbing system

Abstract

Aircraft occupant crash-safety considerations require a minimum cushion thickness to limit the relative vertical motion of the seat-pelvis during high vertical impact loadings in crash landings or accidents. In military aircraft and helicopter seat design, due to the potential for high vertical accelerations in crash scenarios, the seat system must be provided with an energy absorber 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 minimizing the stroke and maximizing the energy absorption. The available stroke must be used to prevent bottoming out of the seat as well as to absorb maximum impact energy to protect the occupant. In this study, the energy-absorbing system in a rotorcraft seat design is investigated using a mathematical model of the occupant/seat system. Impact theories between interconnected bodies in multibody mechanical systems are utilized to study the impact between the seat pan and the occupant. Experimental responses of the seat system and the occupant are utilized to validate the results from this study for civil and military helicopters according to FAR 23 and 25 and MIL-S-58095 requirements. A model for the load limiter is proposed to minimize the lumbar load for the occupant by minimizing the relative velocity between the seat pan and the occupant's pelvis. The modified energy absorber/load limiter is then implemented for the seat structure so that it absorbs the energy of impact in an effective manner and below the tolerable limit for the occupant in a minimum stroke. Results show that for a designed stroke, the level of occupant lumbar spine injury would be significantly attenuated using this modified energy-absorber system.

A Numerical Investigation of Risk Factors Affecting Lumbar Spine Injuries Using a Detailed Lumbar Model

“…For the cushion angle, the highest injury risk occurred when the lumbar spine orientation was perpendicular to the cushion. These trends are widely consistent to the findings from other studies on lumbar spine injuries [ 22 ] and cervical spine injuries [ 23 ].…”

A comparative study of the viscoelastic constitutive models for frictionless contact interfaces in solids

“…Finally, a "plastic" contact leaves an involved part permanently deformed. The deformation of a body in this case is independent of the indentation rate [79][80][81]. In the present study, only the two first mechanisms are considered, and the issue of plastic deformation is considered out of the scope of this work.…”

Impact Loads on the Occupant under the Protection of an Inversion Tube Energy Absorber during a Helicopter Crash

“…Chandcer and Shanahan developed a lumbar load criterion that the maximum spine load should be no more than 6675N, which is now integrated into the Federal Aviation Regulation(FAR) [6].…”