Effect of seat cushions on human response to +Gz impact

Human response to vertical (+Gz) impact acceleration was evaluated as a function of various seat cushions, including current operational cushions used in such aircraft as the A-10, F-15, and F-111 and proposed alternative cushions comprised of rate-dependent, slow-recovery polyurethane foams. There were 133 tests conducted of volunteer subjects in seven different experimental conditions, using a vertical deceleration tower facility. The mean peak acceleration of the impact carriage for these tests was 9.85 G (S.D. = 0.07) and the mean carriage velocity change was 8.01 m X s-1 (S.D. = 0.05). Resultant seat loads and head and chest accelerations were significantly higher for the F-111 cushion than for the rate-dependent foam cushions, which included cushions comprised of Confor foam or Temper foam. Resultant head and chest accelerations were also significantly higher for the ACES II cushion than for the rate-dependent foam cushions. Therefore, from an impact protection standpoint, the operational cushions were inferior to the proposed alternative cushions. Operational use of rate-dependent foam cushions is recommended to improve the impact protection performance of escape systems. Flight tests conducted by the USAF Strategic Air Command have shown that these cushions enhance crewmember sitting comfort during long-duration missions.