FAA Powerplant Written Practice Test

What is a key characteristic of a modern aircraft engine regarding Friction HP?

1. It is negligible and unimportant

2. It may be as high as 10-15% of the indicated HP

3. It is always higher than indicated HP

4. It does not affect engine performance significantly

The correct answer is: It may be as high as 10-15% of the indicated HP

A key characteristic of a modern aircraft engine regarding Friction HP is that it may represent around 10-15% of the indicated horsepower (HP). This percentage is significant because friction within the engine—caused by various moving parts such as bearings, pistons, and gears—creates resistance that affects overall engine efficiency. Understanding that friction HP exists is crucial for evaluating the performance characteristics of an engine. The indicated HP is the theoretical power produced by the engine based on pressure readings in the cylinders, without accounting for losses due to friction. Thus, recognizing that friction HP can constitute a substantial portion of the total indicated HP adds depth to the analysis of engine performance. This is important in engine design and operation, as it helps engineers and mechanics assess how much power is actually available for thrust after accounting for the energy lost to friction. Knowing the proportion that friction HP contributes to indicated HP aids in improving engine designs to reduce these losses, ultimately resulting in better fuel efficiency and performance.