Lube Oils, Hydraulic Fluids Meet More Challenging Environments

OEMs of modern engine and hydraulic components increasingly mandate “high performance capable” (HPC) fluids for their systems, as opposed to “standard performance capable” (SPC) products. The major difference between the two types is thermal stability, according to Andrew Markson, aviation fluids technology director of Eastman Aviation Solutions, a division “With HPC engine oils, there is less degradation, of which the most common, under high temperature conditions is oil coke formation,” Markson explains. “If oil coke blocks a supply pipe, oil cannot lubricate and cool critical bearings. Engines can fail, experience an un-ommanded inflight shutdown, and damage can be significant.” To handle the requirements of hotter running, more fuel efficient engines, Eastman designed Eastman Turbo Oil 2197, a 5 cSt (centistokes) oil for engines and accessories, and capable of meeting AS5780 HPC standards. To date, it has achieved nearly 350 million flight hours of proven performance. Markson notes that Eastman’s HPC lubricants are compatible with legacy engines, thus maximizing engine performance over mixed fleets. “Research and development activity is focusing on engine lubrication requirements anticipated over the next 20-30 years, when engines will burn at core temperatures of as much as 100 to 200F above what they are today,” he notes. Eastman also is a major supplier of fire-resistant hydraulic fluid products under its Skydrol brand—specifically Skydrol 500B-4, Skydrol LD-4, Skydrol 5 and Skydrol PE-5. Terry Wolfe, Eastman Aviation Solution’s global technical service fellow, reports that Skydrol 5 and Skydrol PE-5, known as Type 5 hydraulic fluids, were developed with improved thermal stability compared to the other Skydrol products, which are classified as Type 4 fluids. For example, Wolfe says that Skydrol PE-5, approved in 2009 to meet AS 1241 specs, was developed to remain on the aircraft longer, while exposed to the higher temperatures of new technology engines which drive the hydraulic system pumps. “As the engines burn hotter, pump temperatures increase, and that raises the temperature to which the fluid is exposed,” he explains. “The fluid stays on the aircraft longer, because the components driven by the hydraulic fluid stay on-wing longer.” Eastman’s Skydrol 500B-4, says Wolfe, is a “standard density,” fluid, especially favored by some component OEMs for general aviation aircraft application. “However, most airline customers use the lower density Skydrol PE-5 or LD-4,” he remarks. Wolfe adds that, currently, hydraulic fluids used on commercial airliners “are subjected to a pressure of about 3,000 pounds per square inch (psi),” but in the future, it will increase to 5,000 psi, which will mandate more durable fluids. On the solvent product side, Eastman’s SkyKleen products are finding expanded uses beyond that of hydraulic fluid removers. As examples, it is now used for polysulfide sealant removal, pre-painting surface preparation, and even brake dust cleaning from wheel wells. A low volatile organic solvent, it is easier, and less hazardous to use than Freon, chlorinated and hydrocarbon solvents, which present greater flammability and health risks. “Freon solvents are all but gone, and chlorinated solvents are getting harder to find. Hydrocarbon solvents are still being used, but they have a high flammability risk,” Wolfe says. “What SkyKleen does is to address safer ways of cleaning.”