Cbm c omponent t esting at the u niversity of s outh c arolina : ah-64 g earbox g rease s tudies

Several experiments on AH-64 tail rotor drive train components have been performed, and key findings relating to the gearboxes and grease are discussed. In the first case study, an intermediate gearbox experienced three successive thermal events beyond the specified operational limits, all of which were characterized by rapid and unexplained changes in temperature at increasingly lower starting temperatures. A second study was performed to determine the effect of a severe leaking output seal on multiple tail rotor gearboxes, during which, previously unobserved grease flow dynamics showing mixing between theoretically isolated sections of the gearbox occurred. A final and ongoing experiment is attempting identify and characterize the cause of a frequently occurring intermediate gearbox grease ejections through its breather port. The studies conclude that tail rotor gearboxes have unit-level replaceable output seals, that temperature-based condition indicators may prove beneficial for health monitoring, and that poor dissemination of lubricant and gearbox information may result in significant costs in aircraft maintenance.