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Syncro fixes oddball problem.


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Fun one. Induction run for Mod aircraft (KC130T) had a problem on #1. Above lights out, with either 2 or 3 selected as Master #1 would flux (increase) about 4000 in lbs. 500 pph, and about 125 degrees. But get this, RPM stable. De-selecting a master, or putting #1 in mechanical would fix the problem. Pitchlocked it a couple of times, but every time I would follow up with a re-index, same thing. Pitchlocks were normal. STABLE rpm was bugging me, but I asked to borrow a sync box for troubleshooting.

Outgoing runs. borrowed sync box on hand, but not installed. #1 ran without problems. Could not duplicate the incoming discrepancy. Had some other stuff pop up...down for maint. changed #2 prop..ect... A couple of runs later the same problem popped up on number #3, No fluxing this time, just a steady Increase +- 4000 in lbs, 500 pph, 150 degrees. WTF? Turn sync off, problem goes away in about 10 sec. Put in mech., prob goes away in about 5 secs. RPM still stable this whole time. Put in the borrowed sync box and the problem goes away and stays away. Full runs without issue.

Now I would like a Fuel Control for the first and second instances at a glance with the RPM;s being stable. But being able to control it with the sync switch and Normal/Mech switch kind of makes it a no brainer.

I know they are touchy boxes, and I have seen problems move around engines, but how can the sync box get this kind of reaction at the engine without any effect on RPM?

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