Ejection seat cushions in current U.S. Air Force aircraft are not suitable for comfort during extended missions. Specific physiological problems such as buttock, leg and back pain, numbness and tingling in the extremities, and overall fatigue have been documented in past laboratory research and operational use [1,2,3,4,5]. Designing a single cushion to address the physiological problems of the entire aircrew population is a significant challenge. Cushion material selection, cockpit space restrictions, and limited ability to reposition during flight contribute to discomfort during extended missions. Ejection seat dimensions and contours are fixed in most cases, causing accommodation problems for large and small occupants and often times the cushion itself is the only item that can be replaced to improve comfort.
A study was performed at the Air Force Research Laboratory at Wright-Patterson Air Force Base to investigate objective test methods for determining cushion comfort. Twenty volunteer subjects (12F, 8M) with a range of anthropometry were tested on a variety of operational and prototype cushions (four cushions total). Tests were conducted over eight-hour durations, during which subjective survey data were gathered along with performance data collected by completion of a cognitive task battery. Peak and average seated pressures and contact areas were measured for each cushion as comparative objective data.
In all, 100 eight-hour tests were completed without an incident of deep vein thrombosis (DVT). Peak seated pressures ranged from 0.97–3.37 psi. The majority of the subjects showed no decrease in cognitive performance at the end of each test period; however, many showed a decrease in performance mid-study. The subjective measurements were found to correlate with objective parameters collected at the beginning of the test. This leads to the conclusion that seat cushion comfort can be objectively measured, but its impact on the performance of the subject is not very high. The four cushion combinations tested were used to develop a design guideline for peak pressure and contact area both to prevent DVT and to promote comfort for long duration use.