FAA Aviation Mechanic Powerplant (AMP)PropellersMedium
A technician is asked to explain the purpose of a synchrophaser system installed on a multi-engine turboprop aircraft. What does this system primarily accomplish?
- AIt matches engine fuel flow between engines to improve fuel economy
- BIt controls the phase angle relationship between propellers of different engines to reduce cabin noise and vibration
- CIt matches propeller RPM between engines only, without controlling blade phase relationship
- DIt automatically feathers all propellers simultaneously in the event of a dual engine failure
Show answer & explanationAnswer & explanation
Correct answer: B. It controls the phase angle relationship between propellers of different engines to reduce cabin noise and vibration
A synchrophaser goes beyond simple RPM synchronizing by controlling the phase relationship (relative blade position) between propellers, in addition to matching RPM. This reduces the beat frequency noise and vibration that occurs when propellers turn at the same speed but with blades passing at different points in their rotation.
Why the other options are wrong
- A. Synchrophasing relates to propeller RPM/phase, not fuel flow scheduling.
- C. This describes a basic synchronizer, not a synchrophaser, which also controls phase.
- D. Feathering is a separate, manually or automatically triggered function unrelated to synchrophasing.
Synchrophaser
A system that controls both propeller RPM matching and the phase angle between propellers on multi-engine aircraft to reduce cabin noise and vibration.
- Goes beyond basic synchronizing (RPM-only matching)
- Reduces beat frequency noise from mismatched blade phase
- Common on turboprop and some piston twin aircraft
Memory trick: Synchronize = same SPEED; Synchrophase = same speed AND same BEAT