FAA Powerplant Written Practice Test

What type of bearings are master rod bearings generally classified as?

1. Ball bearings

2. Roller bearings

3. Plain bearings

4. Magnetic bearings

The correct answer is: Plain bearings

Master rod bearings are typically classified as plain bearings. This classification is based on their design and operational principles. Plain bearings, often referred to as sliding bearings, consist of two surfaces in contact with one another, allowing for relative motion with minimal friction. In engine applications, such as in the master rod, these bearings support the load and reduce wear through a thin lubricant film that forms between the bearing surfaces. Plain bearings are favored in many applications due to their simplicity, durability, and ability to handle high loads while allowing for some degree of misalignment, which can be beneficial in engine assemblies where thermal expansion and movement occur. They can be made of materials like bronze or polymer composites, which helps them maintain performance under varying temperatures and pressures. Other types of bearings, such as ball and roller bearings, utilize rolling elements to reduce friction and are more complex than what is needed for typical master rod applications. Magnetic bearings, although advanced and effective for certain specific uses, are not implemented in traditional aircraft engine designs due to their complexity and the need for active control systems. Therefore, the classification of master rod bearings as plain bearings is accurate for their function and application in aircraft engines.