FAA Powerplant Written Practice Test

What is the maximum percentage that Friction HP may represent of the indicated HP on a modern aircraft engine?

1. 5-10%

2. 10-15%

3. 15-20%

4. 20-25%

The correct answer is: 10-15%

The correct answer indicates that Friction Horsepower (HP) may represent 10-15% of the indicated Horsepower in a modern aircraft engine. This percentage reflects the efficiency of modern engines, which are designed with enhanced materials and tolerances that reduce friction losses significantly compared to older designs. In modern engines, improvements in lubrication systems, surface finishes, and precision engineering all contribute to minimizing friction, allowing the maximum frictional losses to remain within this efficient range. This allows more of the engine's output to be converted into useful work, such as generating thrust, rather than being lost as heat or through resistance caused by internal friction. Understanding this concept is essential for assessing engine performance and efficiency, as it directly influences the engine's overall power output and helps in diagnosing potential issues related to excessive friction, which could indicate wear or lubrication problems.