Synchronizer & Synchrophaser
 

Does anyone have a good reference, diagram, link, or explanation for the mechanics behind synchronizer & synchrophaser? I've done extensive research on the internet & FAA approved handbooks, but have not encountered too much system detail.

I understand that there are magnets that rotate with the prop along with stationary magnets on the spinner, which send electric signals to a sync box that then sends signals to the prop governor to regulate RPM.

If I have a misunderstanding of the system so far, please correct me. But I'm looking for specifics about HOW the electrical signals result in the mechanical movement of the prop governor.

Thanks.

Generally how it works, is that you have a "Master" and a "Slave" prop (I've only flown twins, so a P3 guy or Herk guy can chime in on those).

Box reads master prop RPM and blade position from magnet. How many times it sees the magnet in a given time is the speed, and when it sees the magnet is the location.

It then does the same for the slave prop.

Through what was an analog circuit in the T-44 (King Air 90) or a digital program (E-2 with NP2K 8 blade props), it figures out if it should speed up, slow down or not adjust the slave prop based on where the blades are and the speed of the slave vs the master, and the governor setpoint.

In the case of the E-2, the governor is 100% electronic, and it just changes the RPM setpoint slightly to achieve proper phasing.

In the T-44, I THINK (not 100% sure) it adjusted the governor slightly via an actuator.

It's kind of fantastic to think a system swinging around that fast is so simple.

It's pretty simple, as has been described, with the master/slave deal. Typically on a prop plane the master governor has a couple wires coming from it; that is what "talks" to the "box" (The master governor is different from the rest), the box tells the other propeller(s) to conform to that RPM. The remaining propellers, (governors) are then typically adjusted via electro/mechanical means to match the slave governors setting. A couple notes of caution; 1) whether it is prop Sync or fan Sync in the case of a jet, make sure the system is not activated during TO or Ldg. 2) Note the system will only Sync RPM when RPM's are within a certain range to begin with.

My experience is limited to the Fairchild Metro (SA-227) w/ Garret TPE 331 engines and direct drive Dowty-Rotol props. On our models, we actually didn't have the typical Master/Slave system found on most free turbine turboprops.

On the Metro, each governor had a magnetic RPM sensor that fed into the Sync Controller (The"box"). Each prop governor also had a "Biasing Coil" integrated into the speeder spring/fly-weight assembly so that when an electrical current was ran through the coil, it would cause an "artificial under-speed" condition = fly-weights move in condition (I imagine by either adding a little bit of electrical resistance that the flyweights would have to overcome or by magnetically attracting the flyweights inward ever so slightly). When this condition is induced, normal governor operation will respond as usual by increasing prop RPM until a new higher RPM equilibrium is established. Each prop RPM is fed into the sync controller and the sync controller controls which governor's coil is "biased."

With this type of system, a prop's RPM can only be INCREASED so the sync controller will increase the lower RPM prop to match the higher RPM prop. In other words, there is no master/slave prop, which ever is lower gets raised. Since my knowledge of normal sync systems is purely academic, I imagine this system is preferred for direct drive props because if the prop slows down, so does the engine and I imagine engineers didn't want the prop sync to be able to reduce engine speed. (Note: our training material describes this idea by stating that "The Propeller Synchrophaser will never override the RPM selected with the speed levers.")

Like other prop sync systems, the props needed to be within a certain RPM of each other in order to be allowed to work and ours was a max of 1.4% RPM difference between prop/engine speeds.