Is My Prop Governor Headed South?

[MBDiagMan]

I keep my F hangared and have a small heater that blows into the engine cowl.  I shoot it with an IR gun for a temperature reading and I usually have 60 or 70 F when I get it out and start it.  Saturday morning early and this morning early I rolled it out and started it in about 35 F ambient temperature.  I kept the Rpm very little above idle and slowly taxied to the run up area and waited for min oil temp before doing a run up.  Both days when I made my first takeoff with everything to the firewall, I only got about 2,560 RPM on take off.  Both days I flew about an hour before coming in, then did another takeoff.  Both days on the second takeoff I got a normal 2700 RPM.

In Winters past, regardless of oil temp I always had max RPM on take off.  Is this pointing toward a prop governor that is asking to be serviced?

Thanks in advance for sharing your experiences.

BTW, it has a JPI 930, not a mechanical tach.

[EricJ]

Do you cycle the prop during runup?   Does it behave "normally"?   My governor went TU last summer and that was the indicator, it was behaving differently during runup.   Still flew fine, but was continually moving away from "normal" behavior during runup.

Even my brand-new one I cycle it twice now, as the first one will be a little slow, then the second one will be livelier.   That's the new "normal" behavior for me.

 

[MBDiagMan]

Thanks Eric!  Both mornings I cycled the prop at least three times and it appeared normal.  I will pay more attention tomorrow morning.

Did yours ever do anything alarming in flight?  What led you to have it attended to?

[EricJ]

11 minutes ago, MBDiagMan said:

Thanks Eric!  Both mornings I cycled the prop at least three times and it appeared normal.  I will pay more attention tomorrow morning.

Did yours ever do anything alarming in flight?  What led you to have it attended to?

Mine was always fine in flight, it just started getting really slow to respond during cycling during run-up.    Over only two flights it went from "that's unusual" to "that's way, way beyond normal".   i.e., pull the prop and it sits there and does nothing for a long time and then slowly starts pulling the rpm down.   It was very responsive prior to that.

The local prop shop said it had eaten itself pretty well and most parts were well outside of rebuild spec and some were chewed up pretty good.   I opted to buy a new one, which they advised was going to only cost me about $60 more than rebuilding mine since it needed so many parts, and I got the old one back in a bag with all of the chewed-up parts.   I'm saving it as a potential overhaul turn-in with my motor when it need rebuilding, if I ever get to that point.

The other good news was that my engine had started making metal in the oil filter about a year prior, way less than Lycoming says to be worried about, but definitely enough to notice and start tracking.   Every oil change there was a significant bunch of metal on the magnet after running it over the filter media.    That stopped entirely with the new governor, so right now it looks like that's where it all came from.

That's how it went for me, anyway.   I think it's different for everybody.

[MBDiagMan]

Thanks very much for taking the time for this explanation Eric!

When you pulled the prop control on run up how long did it take for the RPM to fall?  One second?  10 seconds?

Thanks again.

[Hank]

6 minutes ago, MBDiagMan said:

Thanks very much for taking the time for this explanation Eric!

When you pulled the prop control on run up how long did it take for the RPM to fall?  One second?  10 seconds?

Thanks again.

Last Saturday morning, it was 37° out and I had not flown in far too long. Going to my EAA meeting, running behind, so no time to plug in the oil oan heater for an hour. Pulled her out, cranked up on the third try, taxied away. First prop cycle took maybe 3 seconds for anything to change, but it felt like forever. Second pull, the response was almost immediate; third pull was quick to respond.

This is how my C has done in cold weather since I bought her in 2007.

What is your normal?

[carusoam]

Starting to sound like it’s not normal...

+1 For exercising it a lot to see if anything improves...

My M20C lived outside and didn’t get much pre-heat until below 20°F...

The govenor is mostly a gear pump, a valve, and the actuator out at the prop...

Cold weather may cause oil to flow slower, but gear pumps won’t be affected by it...

The valve in the gov directing oil may not be moving very freely...(?)

Lets see if @Cody Stallings has any insight...

Best regards,

-a-

[EricJ]

2 hours ago, MBDiagMan said:

Thanks very much for taking the time for this explanation Eric!

When you pulled the prop control on run up how long did it take for the RPM to fall?  One second?  10 seconds?

Thanks again.

A very rough guess might be around four or five seconds, maybe more.   One of the concerns was that it wasn't consistent, too.   It was just behaving strangely enough, and differently enough from "normal",  that I wasn't comfortable flying it until it got looked at.  

[chriscalandro]

When mine died I was starting to roll the control back when it suddenly acted like I had pulled the control all the way out, probably did this passing through 2550. Going back to 2550 got me back to normal. Going 10 rpm below 2550 acted again like I’d pulled the control all the way out. 
 

that was a fun flight, and now I have the PCU5000

[MBDiagMan]

Great feedback guys!  Competing mine I don’t think there’s anything alarming about the way mine cycles on run up.  I am anxious now to cycle it with all this in mind. There was nothing alarming about the way it cycled, but I wasn’t aware that this was something that should be observed.

In the mean time, please keep the thoughts and experiences coming,

Thanks a bunch!

[PT20J]

The governor shouldn't be governing during static runup or early in the takeoff roll as the prop should be sitting on the low pitch stop. As airspeed increases, the prop will want to speed up and then the governor kicks in to increase the pitch and hold it at redline. Since you can make 2700 rpm in flight and subsequent takeoffs and the the governor is not hunting or otherwise behaving abnormally it might not be the culprit. 

On my airplane, the prop cable is really stiff when very cold. Is it possible that you didn't get it all the way back to high rpm after the prop check? Also, there should be about an eighth inch or so gap between the prop control and the panel nut when the control is fully pushed in to ensure that the prop control goes all the way to the stop screw on the governor.

Another possibility is that something was keeping the engine from making full power. It would be worth noting the fuel flow if it happens again as compared to takeoff fuel flow when warm.

You should be able to test all this with full power runups so you are not trying to fly and troubleshoot at the same time 

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[MBDiagMan]

Thanks for the great responses!

This morning with my heater blowing through the cowl all night temp in several areas of the engine compartment was about 70F.  I turned up the thermostat on my heater a little.  I rolled the plane out, started it and slowly taxied to the run up area.once it made 100F oil temp I ran up and cycled the prop four times during run up.  The delay between pulling the control and RPM drop was probably less than a second every time.

I made sure everything was forward and hit 2700 RPM before rotation speed.

Although I will be monitoring this closely for a while, I believe the comments about cables being stiff when cold is the explanation.  I will report any changes.

Again, thanks for the experience sharing.

[Hank]

5 hours ago, MBDiagMan said:

Although I will be monitoring this closely for a while, I believe the comments about cables being stiff when cold is the explanation.

It also has to do with the engine oil being cold, which increases its viscosity and therefore reduces flow rate. Flushing the cold oil out of the governor and prop makes it respond faster.

[Cody Stallings]

The prop gov isn’t online until 300ft or so in the takeoff roll.

Dont think the Gov is going to be your issue.

Your Mooney maybe a lot like a women, wants to be really heated up before it’s time to get busy. I Flew a 180hp CS Cessna 177 that acted the same way. If you took your time on the grd on the cold days an let everything under the hood get well into the green arc’s there was no problems, if it was hurried in anyway, she didn’t like that at all.

bout 2600 all it would make.

[tmo]

On a tangent - is it OK to have cowl flaps closed on the ground, when things are getting warmed up? So perhaps between startup and runup?

[Shiny moose]

My heater keeps my oil at 75. I use a oil temp target of 125 or above before my take off roll. Slow taxi, dont get in a hurry in the winter. 

[Yetti]

4 hours ago, tmo said:

On a tangent - is it OK to have cowl flaps closed on the ground, when things are getting warmed up? So perhaps between startup and runup?

Yes.  Manage the heat as needed.   In the what we have as winter here in Humidston.  I just leave them closed.

[PT20J]

14 hours ago, Yetti said:

Yes.  Manage the heat as needed.   In the what we have as winter here in Humidston.  I just leave them closed.

In the round engine days, the admonition was to not try to hasten warm up by operating with the cowl flaps closed because of the risk heat damage to the ignition harness. I've always just followed this practice in all airplanes.

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