FAA Powerplant Written Practice Test

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

1. To enhance fuel efficiency

2. To control engine RPM and reduce vibration

3. To adjust blade angles automatically

4. To improve takeoff performance

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

The main 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 propeller speeds of the engines to ensure they are synchronized. When the propellers are synchronized, they turn at the same speed, which minimizes the out-of-phase conditions that can lead to vibrations. This synchronization is particularly important in multi-engine aircraft, as it enhances the overall smoothness of operation and contributes to passenger comfort and structural integrity of the aircraft. When the propellers are not synchronized, differences in rotational speeds can cause a phenomenon known as "dynamic imbalance," resulting in vibrations that can impact the airframe and lead to increased maintenance issues. Thus, maintaining a common RPM among the engines helps ensure that the aircraft operates efficiently and reliably, particularly during critical phases of flight.