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This report was developed under SBIR Topic AF98-196. Modern aircraft engines use recycled fuel loops as coolants to remove excessive heat from engine components. This heated fuel is returned to the bladder, exposing the fuel inlet area to fuel that has not had time to cool. The temperature of the returned fuel was initially expected to be in the range of 135 deg F to 160 deg F. In today's fighter aircraft, fuel used to support engine cooling operations can create temperature spikes in the range of 300 deg F to 400 deg F at the bladder inlet of the return loop, and prolonged exposure to temperatures between 200 deg F and 250 deg F are now quite common. Under this program, METSS clearly demonstrated the technical feasibility of using commercially available material technologies to support the development of high temperature resistant fuel bladders that can be readily integrated into the existing fuel bladder manufacturing processes. Under the Phase II program, METSS identified two specific rubber materials based on hydrogenated nitrile rubber and epichlorohydrin that meet the criteria needed for a fuel cell bladder operating at 225 deg F. Of these, the hydrogenated nitrile rubber compound was particularly adaptable to the manufacture of fuel bladders. This relationship will establish a solid foundation for Phase III product commercialization efforts, providing a viable path for rapid technology transfer and implementation.

Materials used in the construction of aircraft hydraulic and fuel system o-rings and seals must provide long-term performance in aggressive chemical environments over a wide range of temperatures and loads. Current materials, while chemically compatible with existing aircraft fuels and hydraulic fluids, are subject to both low temperature and high temperature performance deficiencies and failure. New o-ring materials are needed that exhibit good low temperature performance characteristics at -40 F (with a preference for -65 F performance) while maintaining durability and service life requirements at operating temperatures up to 225 deg F in fuels systems and 275 deg F in hydraulic fluid systems. Multiple materials representing eight different classes of rubber chemistries were evaluated under this program for high temperature resistance to aircraft hydraulic fluids and jet fuels, and low temperature sealing performance before and after 3- and 28-day high temperature fluid exposure. Performance criteria and program test methods were derived from MIL-P-83461 and MIL-P-53153. In situ compression stress relaxation testing was also performed to evaluate static sealing performance as a function of fluid exposure time at high and low temperatures. The results of the testing performed under this program demonstrate the deficiencies of conventional o-ring materials, and the availability of new classes of o-ring materials that provide exceptional high temperature chemical stability and low temperature performance., The original document contains color images.