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It took a long time and 80-plus rocket sled runs, but the Martin-Baker US16E ejection seat for the Joint Strike Fighter has been qualified to 550 knots for a full range of pilots, just 50 knots short of the specification. However, Goodrich is still mounting a challenge with the ACES 5 seat, claiming that it will offer lower life-cycle costs. Both seats were on display at the Air Force Association convention, held earlier this week at a remote site in Maryland.The JSF ejection system design is challenging in several ways. The seat has to deliver high performance because a STOVL landing problem could mean ejecting at low altitude from a descending aircraft that is also yawed or pitched out of level flight. The JSF is also the first fighter designed to accommodate 95 percent of the potential US pilot population, with body weights from 103 to 245 pounds. Together, these two requirements mean that the lightest pilots experience most acceleration. The JSF's helmet-mounted display, for all the sophistication of its engineering, is heavier and more forward-weighted than a standard helmet. The result is that the pilot's head tips forward on ejection: the concern is not just the forward tip itself, but the slam-back effect as the seat hits the airstream and a 550-knot windblast forces the pilot's head against the seat. Visible for the first time at AFA was Martin-Baker's solution to the problem: an airbag system stowed in the headrest, which deploys to either side of the pilot's head, preventing lateral movement, and then controls the slam-back by deflating at a fixed rate.The Goodrich approach is different, with an articulating headrest resembling a baseball catcher's mitt. The device follows the head down as the ejection sequence starts, and as the pilot's head starts to blow back, captures the helmet and uses shock absorbers to control the speed of the motion.Also visible to the right of the seat is the passive arm-restraint system developed for the ACES 5, comprising nets extended by a hinged arm that deploys under acceleration. The pilot's arms are forced into the net by the windblast, but restrained by the net to avoid injury, Goodrich is claiming a lower life-cycle cost for the ACES 5, mainly because the pyrotechnics and some other routinely replaceable components are common to the widely used ACES 2 series. Meanwhile, some program insiders are still worried about the other element of the JSF escape mechanism, the Transparency Removal System (TRS). The problem is that the JSF canopy is relatively thick because the transparency is in one piece, for stealth reasons - so the entire canopy has to be at or close to windshield thickness. The F-16 and F-22 have a similar configuration, but the canopy is jettisoned before the seat fires. This is unacceptable for STOVL or CV operations, so the JSF has a combination of explosive cord and mechanical breakers to remove the canopy - again, this is a proven technique, but not on a canopy as thick as JSF's. There is some concern that the canopy can fracture into large, sharp-edged shards, posing an injury hazard.
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