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SYNCHROPHASER


munirabbasi
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We are facing  prop synchrophaser problem,  after one hour of flight either master selected(2 or 3) auto disengaged( slaves engines not following) Resyncing held procedure got normal but again master selected disengage its own after 30 to one hour of flight. we have replaced valve housing all, electronic control unit, wiring checked got no effect. the problem does not duplicate on ground as well as short mission   

 

Munir abbasi

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Lkuest  RPM different,

The first thing to do that is absolutely critical is to not fully trust the indicators. You must have a digital tachometer plugged in that can give you RPM to within 0.1% RPM. Next, tune all 4 propellers so that they are all within 0.2% of 100%. The purpose is to put minimum stress through the valve housing clutch assembly to prevent slippage and "bias". Also know that, whatever your digital tachometer reads, your aircraft RPM indicator must read accurate to within 1% rpm.

Now, when the synchrophaser system is not malfunctioning, what do all four RPM indicators read?

During the malfunction, what do all four RPM indicators read with #2 as a master? #3 as a master? No master selected?

Hypothetically, if there was a defect in #2 pulse generator circuit, the synchrophaser would think #2 is slowing down, and would cause #1,3,4 to reduce to 98% suddenly, even though #2 is at 100%. In this same case, if you select #3 as a master, #1 and #4 would both remain at 100% while #2 would increase to 102%. While this case would possibly indicate a defective pulse generator, it is more likely bad wiring with the defective master propeller within the pulse generator electrical circuit. It is difficult to trace an intermittent problem, but we've had issues with the pulse generator electrical circuit short to ground within the 6-pin conduit itself, and the only way we could see it was to disconnect it from the propeller, check the pulse generator pins to ground while we move and yank on the conduit to allow it to hit that sweet spot where it just barely shorts out. You could also check for recessed or broken pins in the conduit. Of course, as PJVR recommends, a sync test set would help out immensely, but if one is not available, you can still make do with just a wiring schematic.

It may prove difficult or impossible to guess further on a cause of the malfunction without knowing exactly what the RPMs of all 4 propellers are doing during the malfunction, with both #2 and #3 selected as a master, when no master is selected, and assurances that all 4 governors are set to 100% within 0.2% RPM. Not correctly setting mechanical RPM usually causes gradual malfunctions instead of sudden ones, but if the mechanical settings are off by a lot, you may just have a power issue to the synchrophaser, and propellers would return to the mechanical setting without the syncrophaser receiving power.

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