Definition
A system installed on multi-engine aircraft that automatically matches the rotational speed (RPM) of all propellers to a single chosen engine, called the master engine. The pilot sets the desired RPM on the master engine, and the synchronizer adjusts the governor on each slave engine to hold its propeller at exactly the same speed.
Plain English
A device that keeps all the propellers spinning at the same speed automatically, so the pilot does not have to fine-tune each engine by hand.
Context Anchor
Pilots encounter this during multi-engine operation, especially in cruise after the power and propeller speed settings have been set.
Derivation
Synchronizer comes from the Greek 'synchronos,' meaning 'happening at the same time.' In this case, it keeps the propellers turning at the same time at the same speed.
Why Pilots Care
Reduces cabin noise and vibration, lowers pilot fatigue on long flights, and prevents uneven engine stress that can shorten component life.
Intuition Check
A propeller synchronizer does not make both engines produce exactly the same power. It mainly fine-tunes propeller speed so the propellers turn at the same rate.
Example Sentence 1
Once established in cruise, the pilot set both engines to 2,300 RPM and engaged the propeller synchronizer to smooth out the cabin vibration.
Example Sentence 2
With the propeller synchronizer engaged, both engines remained locked at 2450 RPM even as minor throttle adjustments were made for fuel balancing.