What type of lubrication system is used in an APU?

The correct choice is the positive-displacement, dry sump system, which is commonly used in Auxiliary Power Units (APUs). This type of lubrication system is designed to ensure that the oil is circulated to the engine components more effectively than other systems.

In a positive-displacement, dry sump lubrication system, the oil is stored in a separate reservoir rather than in a sump beneath the engine. This design is beneficial for APUs because it allows for more efficient lubrication under varying operating conditions and orientations. The positive-displacement aspect means that as the engine operates, a pump generates a consistent flow of oil to critical engine parts, ensuring that all moving components receive an adequate supply of lubrication. This is particularly important in an aircraft, where operational conditions can change dramatically during flight.

The dry sump design also reduces the overall weight of the system and allows for lower oil temperatures, which can enhance the performance and reliability of the APU. Additionally, this system helps in preventing oil foaming, which can occur in wet sump systems when subjected to high G-forces or rapid maneuvers.

Understanding the rationale behind the choice of a positive-displacement, dry sump system is crucial for those in mechanical roles, as it directly influences the maintenance and operational performance of APUs in