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This paper summarizes the results and findings of a program to design, develop, and evaluate actuator rod seals for use in advanced aircraft high-temperature hydraulic systems. The rod seals are intended to function efficiently and reliably for 3000 hr in the temperature range of -40-500 F. Preliminary studies of various material and design combinations showed that a polyimide low-pressure second-stage V-seal in a two-stage configuration had the greatest potential in long-term duty cycle testing in a simulated actuator test system. Modifications of this seal that provided for improved fatigue life and more efficient loading met the test objectives of 20 X 106 short-stroke cycles of operation at 500 F. Severity of this testing was equivalent to 3000 hr of duty cycle operation. The validity of design techniques used to achieve performance goals was shown.

The feasibility of using presently available liquid lubricants in advanced, high speed aircraft engines has been investigated with a recirculating inerted lubrication system. Three fluids performed satisfactorily for short durations of 3-10 hr in a full-scale simulated aircraft bearing and seal assembly at an outer race bearing temperature of 700 F and with a bulk fluid temperature of 500 F. The principal problem has been with excessive leakage of the oil side bellows face seals which has accounted for a majority of the test terminations. With only one lubricant (a MIL-L-7808E oil) could bearing failure be blamed on a lack of lubricating ability. An inerted oil mist once-through system was also tested, but with less promising results with only one lubricant running successfully at 600 F bearing temperature. The mist system appears to be limited by its inability to maintain stable bearing temperatures and requires further development.