FAA Powerplant Written Practice Test

The centrifugal twisting force of an operating propeller tends to do what to the pitch angle?

1. Increase the pitch angle

2. Decrease the pitch angle

3. Change the pitch frequency

4. Stabilize the pitch angle

The correct answer is: Decrease the pitch angle

The centrifugal twisting force of an operating propeller acts in such a way as to reduce the angle of attack at the blade tips. As the propeller spins, the blades experience forces that attempt to twist them in response to centrifugal pull. This twisting effect generally results in a decrease in the pitch angle of the blades. In a fixed-pitch propeller, there is no mechanism to adjust the pitch; thus, the centrifugal force’s impact is primarily felt at the tips where the blades need to react to the increasing rotational speed. In contrast, controllable or constant-speed propellers have mechanisms to adjust pitch, but even in those cases, the centrifugal force contributes to altering the angle, potentially leading to a decrease in pitch at the blade tips, allowing for more efficient operation at high speeds. This understanding highlights how the mechanics of propeller operations involve balancing forces that can effectively adjust performance parameters like pitch, which is crucial for maintaining optimal thrust and efficiency during various flight conditions.