Definition
A system installed on multi-engine airplanes that not only matches the rotational speed (RPM) of all propellers but also controls the angular position, or phase relationship, of each propeller's blades relative to the others to minimize cabin noise and vibration.
Plain English
A device that keeps every engine spinning at exactly the same speed and also lines up the blades of each propeller in a set pattern, so the airplane runs more smoothly and quietly.
Context Anchor
You encounter this in multiengine propeller airplane operation, especially when setting propeller controls for cruise and reducing the uneven sound or vibration between engines.
Derivation
From 'synchro' (same, together) and 'phase' (the position of something within a repeating cycle). A synchrophaser does both jobs at once: it synchronizes speed and aligns phase.
Why Pilots Care
Reduces cabin noise and vibration, lowering fatigue on long flights and decreasing wear on airframe components.
Analogy
It is like two people walking not only at the same pace, but with their steps landing in the right pattern together. Same pace is synchronization; matched step timing is phasing.
Intuition Check
Do not confuse a propeller synchrophaser with a basic propeller synchronizer. A synchronizer matches propeller speed; a synchrophaser also controls the timing position of the blades relative to each other.
Example Sentence 1
Once established in cruise, the pilot manually set the propellers to within 25 RPM of each other and then engaged the propeller synchrophaser.
Example Sentence 2
The synchrophaser automatically adjusted blade timing so the left and right propellers stayed perfectly in phase during cruise.