Basic architecture and sizing of commercial aircraft gas turbine oil feed systems

The specific thrust and fuel efficiency of gas turbine engines have improved considerably over the last 20 years primarily due to technology advances in materials science and main gas path thermo-fluid analysis. However, a major influence on the improved engine reliability demonstrated over that same timeframe is the performance of engine mechanical systems which rely on the consistent delivery and recovery of oil. The general architecture of oil systems has changed little over this period. However, detailed attention to how oil system components behave and interact with each other, and with the rest of the engine systems, has helped achieve improved engine mechanical performance. For derivative engines this process is facilitated by a substantial amount of in-service data, reflecting both good and bad experiences, which helps to identify the poor designs, manufacturing anomalies or unusual operational circumstances that are likely to cause problems and the design changes that are needed to solve them. However, new engines being designed and certificated in ever-reducing timescales, do not necessarily have the luxury of such directly relevant, in-service, performance data. Hence it is essential that oil systems are designed with a full appreciation of component and system capabilities and the options available. This knowledge is based fundamentally on a general awareness of how an engine oil system achieves its objectives, why sometimes it doesn't, and how it integrates with the rest of the engine. This paper aims to identify some of the decisions that need to be made regarding system architecture and component sizing when designing a gas turbine oil system. Full attention to these matters during the engine design phase should lead to reduced development and in-service problems, less use of development innovation to solve problems and ultimately improved engine reliability.