Aviation lubricants

Abstract

Aviation lubricants must be extremely reliable, withstand high specific loadings and extreme environmental conditions within short times. Requirements are critical. Piston engines increasingly use multi-grade oils, single grades are still used extensively, with anti-wear and anti-corrosion additives for some classes of engines. The main gas turbine lubricant problem is transient heat exposure, the main base oils used are synthetic polyol esters which minimise thermal degradation. Aminic anti-oxidants are used together with anti-wear/load-carrying, corrosion inhibitor and anti-foam additives. The majority of formulation viscosities are 5 cSt at 100°C. Other considerations are seal compatibility and coking tendency. Aviation hydraulic fluids are divided into military, mainly PAO based, and civil aircraft which are mainly phosphate ester based. The first contains anti-oxidant, anti-wear and seal compatibility additives, the second prefers trialkyl over triaryl phosphates and contains anti-hydrolysis additives. Aviation greases are subject to extreme operating conditions, such as high-temperature conditions up to 550°C in wheel bearings and resisting water ingress. Airframe and wheel bearing greases are of two types, either lithium soap/complex or clay based. Helicopter transmission lubricants serve the most critical gears in aviation, carrying power for both thrust and lift. Ester-based lubricants are either the same grade as the engine, or a different engine lubricant grade, or a grade intended specifically for helicopter transmissions. © 2010 Springer Science+Business Media B.V.