FAA Ground School Practice Test

What precaution should be taken when operating an engine with a constant-speed propeller?

1. Maintain high RPM during all phases of flight

2. Use high manifold pressure settings in all conditions

3. Avoid high manifold pressure settings with low RPM

4. Always operate at maximum thrust settings

The correct answer is: Avoid high manifold pressure settings with low RPM

When operating an engine with a constant-speed propeller, it is essential to avoid high manifold pressure settings while maintaining low RPM. This precaution is crucial for several reasons. First, high manifold pressure combined with low RPM can lead to an inefficient combustion process and increase the risk of engine overheating. The engine's design and operation rely on a balance of RPM and manifold pressure to achieve optimal performance. When the RPM is kept low while the manifold pressure is high, it can stress the engine components, leading to potential mechanical failures or damage over time. Moreover, the propeller system is designed to adjust the blade angle to maintain a certain RPM, ensuring that the engine operates within its efficient range. High manifold pressure at low RPM may not provide the necessary thrust or power, as the engine may not be able to breathe properly, resulting in a loss of performance. Understanding the balance between RPM and manifold pressure is key to effective engine management in aircraft with constant-speed propellers. Thus, selecting an appropriate combination helps ensure the reliability and longevity of the engine.