Evaluation of the Influence of Upper Extremity Bracing Techniques on Human Response during Vertical Impact

Abstract : A test program was conducted to evaluate the effectiveness of upper extremity bracing techniques during +G sub z impact acceleration. Fifty human impact tests were performed on the Vertical Deceleration Tower up to an impact level of 10.5 G mean (std dev = 0.23), 26 ft/sec velocity change. Subjects were restrained in the operational F-FB-111 crew seat and restraint system and were exposed to comparable impacts in different bracing conditions (including the currently recommended crossed-arms position and a proposed, alternate hands-on-knees position) to allow parametric analysis of the test results. Measured data included seat acceleration and velocity, head and chest translational acceleration components, triaxial forces acting on the seat and footrest, forces acting at the restraint harness attachments, and displacements of various body segments. Six of eighteen subjects physically could not perform the crossed-arms brace and thus could not be tested in that position. For the subjects tested in both conditions, seat pan loads were significantly less in the hands-on-knees position than in the crossed-arms position. There was no significant difference in maximum head displacement in the two conditions. On the basis of these findings, it is recommended that the hands-on-knees position be used by F/FB-111 ejectees preparing for landing impact of the crew module. It appears that this technique may be utilized by all crewmembers and may afford them greater impact protection than the currently recommended procedure.