RPM Starting to Wander

[slowflyin]

I've noticed my RPM starting to wander in cruise.  After getting a digital tach I noticed a need to "fine tune" every fifteen minutes or so.  2500 might go to 2470 or 2510.  Today's flight produced variations from 2430 to 2540 when set at 2500.  Is this a function of an old gov. and a new tach or is it a sign the gov. is beginning to fail?   Thanks in advance,

 

joe

 

PS- M20F, IO360A1A, 500 hours on a no AD prop.  

[EDNR-Cruiser]

My prop/governor with a Hartzell prop is doing the same... - more or less... - and I believe it's normal...
I found that the fluctuations are minimal and mostly because of changes in environment... - OAT fluctuating, turbulences, turns from headwinds to tailwinds and vice versa, minor changes in power setting, etc.,...
There is only so much that our fully analogue prop governor can manage and that is good!!

[Guest]

How is the friction on the prop control cable? It is possible that it turning slowly with vibration.

Clarence

[carusoam]

You can get an additional rpm reading using your smart phone.

How old is your govenor?

Know that the govenor has a tendency to wear. It is a simple set of fly weights connected to a control valve that adjusts oil pressed into the prop.

I don't have digital read out of my rpm, so I have little idea of how much it moves while flying.

Overhauling the gov is not that expensive. Remove and send out. New ones are not that expensive. Somebody was selling one around here recently. PSU2000?

Best regards,

-a-

[Seth]

Set power and RPM when level, then:

Pitch up for a climb and see if the RPM drops or stays consistent.

Then level off - check RPM

Pitch down for a decent and see if the RPM increases or stays consistent.

With our aircraft/a constant speed prop RPM should stay consistent. If the prop governor is heading toward an overhaul or replacement, it will not hold the set RPM in a climb nor decent. There is a range that is considered acceptable before overall or replacement is necessary.

-Seth

[slowflyin]

I guess I'm curious what is the acceptable "range"? 

[HRM]

I've noticed my RPM starting to wander in cruise.  After getting a digital tach I noticed a need to "fine tune" every fifteen minutes or so.  2500 might go to 2470 or 2510.  Today's flight produced variations from 2430 to 2540 when set at 2500.  Is this a function of an old gov. and a new tach or is it a sign the gov. is beginning to fail?   Thanks in advance,

 

joe

 

PS- M20F, IO360A1A, 500 hours on a no AD prop.  

 

I had a "wandering prop" that progressively got worse.

 

I had a UBG-16 and when I upgraded to an MVP-50 it became unbearable.

 

Investigation revealed that it had never had an OH. That cured the problem and now it is back to being solid with a little bit of ±10.

[Seth]

I guess I'm curious what is the acceptable "range"? 

It depends on the prop governor.  I am unsure off the top of my head.  Your A&P or the manufacturer should know.  Regardless of what the acceptable range is (which may be 100 RPM difference, 150, I'm not sure) when you climb and descend, if the prop slows down during ascent and increases during decent, the governor is having issues, and usually this is the beginning of what leads to the overhaul/replacement.

 

This is a good test to do for your aircraft from time to time.

 

-Seth

[slowflyin]

Thanks for all the advice.