The Principles of Aircraft Lubrication

In aircraft systems such as the engine, lubrication serves to protect moving assemblies through the reduction of friction and heat. No matter how thorough or precise the manufacturing process is, there will always be microscopic imperfections on assembly surfaces that can break or seize when coming into contact with other irregularities. Beyond damaging the surface of a particular component, broken off pieces may continue to flow through a system, resulting in more wear and tear to various structural parts. To prevent these hazards from affecting the service life of a particular assembly, it is important to properly implement and manage lubrication on regular intervals.

The friction that results between two moving metal parts will vary based on a number of factors, those including temperature, surface finish, load, movement speed, movement type, and present lubricants. While components such as bushings and bearings may serve for friction reduction in a number of aircraft assemblies, lubrication is a simplistic way to mitigate friction through the adjustment of viscosity. Additionally, cooler lubrication may also serve for heat reduction as the lubricant absorbs heat from the surface of parts for reducing extreme temperatures. When lubricating a sliding or rolling surface, the primary lubrication regimes are boundary lubrication, hydrodynamic lubrication, and elastohydrodynamic lubrication.

Boundary lubrication is used when rolling or sliding surfaces come into contact under low speed or high load conditions. As boundary lubrication is the regime that accounts for most engine wear, it is paramount that proper lubrication is implemented. Generally, a lubricant that has anti-wear or extreme pressure additives is the most beneficial as it will have the means of creating a sacrificial chemical film on moving surfaces. Boundary friction may also be combated through the increase of viscosity, though care should be given when making such adjustments so that too much heat does not build up in the assembly during standard operating conditions.

Hydrodynamic lubrication is used for separating the engine shaft from its support, and the breaking of contact may be achieved through a full film of oil. Due to the viscosity of such lubrication, the only friction that occurs between the moving parts is within the lubrication itself. To properly take advantage of hydrodynamic lubrication, the surfaces of the assembly must feature high geometric conformity and must operate under low pressure. Benefiting camshaft, crankshaft, and bushing lubrication, the hydrodynamic regime is the most beneficial operating condition for an engine at standard temperatures and speeds.

Elastohydrodynamic lubrication is best for assemblies that feature low conformity and high contact pressures. This occurs in assemblies such as gear drives and rolling bearing elements, and lubrication viscosity is increased under high-pressure to create a semi-solid film that separates surfaces. Such lubricants are long-lasting when operating conditions remain the same, and the metallic surfaces may even begin to deform before the breakdown of the lubrication.

As proper lubrication ensures the mitigation of friction and heat between moving parts, pilots should know how to properly refer to oil system gauges for monitoring oil system operation in regard to the engine. With the oil pressure gauge, operators can oversee the oil system to ensure that the lubricating oils supplied to the engine are within a normal operating range. The oil temperature gauge is also crucial, as it will allow crew members to know when lubricating oils are either too hot or cool to be effective. High oil temperatures often decrease viscosity, resulting in higher friction. Low oil temperatures can increase viscosity, preventing the system from properly protecting assemblies.

With the proper implementation, replacement, and management of lubrication, many moving assemblies of an aircraft can be protected to guarantee long and reliable service lives. At Aviation Sphere, we operate as an online distributor of aircraft parts with countless new, used, obsolete, and hard-to-find items readily available for purchase on our website. Take the time to explore our vast part and manufacturer catalogs at your leisure, or you may conduct a lookup for specific items quickly and easily with our included search engine and filters. Once you have found the items that you would like to purchase, we invite you to begin with a personalized quote for your comparisons which you can receive through the submission of a completed RFQ form as provided on our website. Experience how Aviation Sphere can serve you for all your operational needs when you get started with us today.

1. sofia jonas
2. Posted on May 11, 2021
aviation

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