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Propeller RPM Fluktuation


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Hi.

Wenn I set 2500 RPM on my Hartzell HC-C2YK-1BF Prop (Lycoming O 360 A1D on M20C) I observe that RPM are not constant, but they change  +- 50 RPM.

Those +- RPM are not only on Tachometer, but really on Prop/Motor.

The same I observe at different Prop. Speeds (23500-2700)

You folks, how much is acceptable? Troubleshooting?

Thanks,

milos

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The title reminds me of a joke.  A Korean woman is exchanging currency at the bank, and she gets 10 dollars for 10,000 won.  The next week she goes back, but she only gets 8 dollars.  She asks the teller why she got ten last week and only 8 this week.  He says "fluctuations".

She says "fluk you too"

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I vote your Tach cable needs to be lubed or the tach needs an OH.    Now if you come back and say it is electronic.  Then I am going to say check your grounds.

Try a Tach App on your phone and see what results you get.  It uses sound to determine RPM.

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Congrats Milos,

For clearly defining your challenge...

1) Engine and rpm changes are real, not just an instrument failure...

2) happen over a few seconds

3) +/- 50 rpm over 5-10 seconds...

 

Since the gov is the most likely challenge since they are imperfect and fail as they wear.... they also have the other issues mentioned above...

1) What gov do you have?

2) How many hours on it?

3) The gov has its own gear pump, control valve, and fly-weights, and has methods of leaking oil internally... fly weight systems start to wear and get sticky causing control oscillations...

4) the gov also has been proven to leak air in... through bad seals...

5) I didn’t follow Rich’s air, oil pump, and oil pressure oscillation very well... the oil pressure being delivered to the prop for rpm control doesn’t get measured in flight... but the air possibly entering the system is equally important...

6) If engine oil pressure is oscillating... there is going to be lots of air bubbles in the oil to contend with... check the engine oil level to see when this occurs...

 

See if you can add your location to your avatar area...

PP thoughts only, not a mechanic...

Best regards,

-a-

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