FAA Powerplant Written Practice Test

What is the main function of the automatic propeller synchronizing system on multi-engine aircraft?

1. To adjust pitch angle

2. To increase engine output

3. To control engine rpm and reduce vibration

4. To feather the propellers

The correct answer is: To control engine rpm and reduce vibration

The primary function of the automatic propeller synchronizing system on multi-engine aircraft is to control engine RPM and reduce vibration. This system works by adjusting the pitch of the propellers to maintain a synchronized speed between them, which minimizes the differential in RPMs. When the engines are running at different RPMs, it can create uneven thrust, leading to vibrations and potential handling issues. By synchronizing the propeller speeds, the system ensures smoother operation, improved efficiency, and a better overall flying experience. This balancing act is crucial for multi-engine aircraft, where engine performance is closely tied to balanced propeller output. The reduction in vibration not only contributes to passenger comfort but also helps in prolonging the life of the engine and the aircraft's components. The other options do not fully encapsulate the broad and critical impact of synchronizing propellers on performance and passenger experience.