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munirabbasi

RPM FLUTUATION

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Engine rpm fluctuation both the mode up to 5% when tachometer generator is installed on RGB pads

but no fluctuation when same is installed on SS control reason?

Regards

Munir Abbasi

Home of hercules Pakistan

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Does it only do this in the flight range of power, or all the time? In Mech Gov or Normal Gov? Synchrophasing on or off? When RPM goes up, then down, what do the other indicators do? The same direction, or opposite?

The best possibility is both Tach Gen spline holes are worn excessively. At worst, your reduction gearbox tach generator drive gears might be worn out. Both Tach Gen pads are geared into the same idler gear, so possibly the idler gear bearings are wearing out, or even the Hydraulic Pump gear bearings too, as it drives the idler gear. If you have a vibration signature program, I suggest doing a vibration signature readout of the gearbox to check the bearings for wear.

Another possibility might be wiring near the Reduction Gearbox causing intermittent contact as the engine torques within the QEC at power. I would also swap RPM indicators with another engine, because swapping indicators doesn't cost anything.

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Does it only do this in the flight range of power, or all the time? In Mech Gov or Normal Gov? Synchrophasing on or off? When RPM goes up, then down, what do the other indicators do? The same direction, or opposite?

The best possibility is both Tach Gen spline holes are worn excessively. At worst, your reduction gearbox tach generator drive gears might be worn out. Both Tach Gen pads are geared into the same idler gear, so possibly the idler gear bearings are wearing out, or even the Hydraulic Pump gear bearings too, as it drives the idler gear. If you have a vibration signature program, I suggest doing a vibration signature readout of the gearbox to check the bearings for wear.

Another possibility might be wiring near the Reduction Gearbox causing intermittent contact as the engine torques within the QEC at power. I would also swap RPM indicators with another engine, because swapping indicators doesn't cost anything.

With this little info. there a host of possible things that could be the problem. First putting a tach on the speed sensing control only gives you engine rpm, not prop. It sounds like the engine is doing what it is supposed to do , run at 100%. As stated above is the flux in mech and normal gov. or both. have you changed the valve housing. If it is a true 5% flux you are going to hear it. I think if it is an indicating system you should see it just dropping the throttle over the gate, not just at power. Too many loose ends here.

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5% flux? Any other indicators fluxing or just the RPM?

Mounting on the SSC would require separate wires or jumper to the QEC wiring to flight station indicator... Sounds like both RGB pads are worn out... Or the idler gear as pointed out by Lkuest.

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5% flux? Any other indicators fluxing or just the RPM?

Mounting on the SSC would require separate wires or jumper to the QEC wiring to flight station indicator... Sounds like both RGB pads are worn out... Or the idler gear as pointed out by Lkuest.

Why not run the engine and prop and then pitch lock the prop? Check in normal and mechanical modes. This should isolate a prop/engine problem from the indication problem. If it is stable in pitch lock it may be the valve housing if all other indications are stable. If it still flux's, then the RGB drive pads are suspect. We had a drive pad go/no go gage for the square drive of the Tac. Gen pad.

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Thanks All honourable.we facing the problem on many aircrafts engines.but some aircraft RPM drop to 97% both modes i.e normal & mech. at flight rage >35 Degree throttle setting some A/C RPM increase to 103 %, Torque and other indication normal. all aircrafts RGB new/overhaul,RPM fluctuate about 97 -103% . all engine RPM fluctuation behavior different each other.ON SSC RPM became stable /normal.

Munir Abbasi

Home of hercules pakistan

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Thanks All honourable.we facing the problem on many aircrafts engines.but some aircraft RPM drop to 97% both modes i.e normal & mech. at flight rage >35 Degree throttle setting some A/C RPM increase to 103 %, Torque and other indication normal. all aircrafts RGB new/overhaul,RPM fluctuate about 97 -103% . all engine RPM fluctuation behavior different each other.ON SSC RPM became stable /normal.

Munir Abbasi

Home of hercules pakistan

"Torque and other indication normal." this is not a true RPM flux. It is an indication problem.

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With a 5% RPM flux you should be seeing a good swing of F/F and torque.If you aren't seeing this you have only a RPM indication problem.

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