Prop Governor

[Seth]

I may have noticed an issue with my prop governor and would appreciate any input.  My aircraft is '67 M20F with a three bladed prop installed about 100 hours ago.  The engine has about 150 hours on it.  I noticed this issue during my last three flights.  The air temperature at start was between 40 and 50 degrees F.  I have no pre-heating equipment for the aircraft and do not start the engine under 40 degrees. 

During run-up, when I cycle the propeller, it drops, and is slow to respond back up to the 1700 rpm.  The RPMs stop falling as soon as I place the propeller into the full forward position, but it takes quite a few more seconds until the needle creeps back up to 1700 RPM (usually very slow from 1500 to 1700).  It speeds up after a few cycles (once warmer oil has replaced the cooler oil), but still not to the point where I feel it should be.  I asked the shop and instructor about it, and all parties stated it was good to fly, but to have it looked at during the upcoming annual.  I put the plane in for annual this week (I'm keeping my fingers crossed) but wanted to know what may be causing this.  Was it the cold weather, or am I looking at a real potential problem?  I figure its not a seal because there is no oil leak.  The engine barely burns any oil at all.   It’s just slow to respond coming back up to the preset RPM when cycling the propeller.  

I would have given more numbers and exact maintenance history, but the shop currently has all of the logs and records.  Also, there was no mention of this issue during the prebuy inspection and I didn’t even start to notice it until recently. 

Thanks! 

 

[TurboExec]

The oil is thick and the orfice that lets the oil escape out of the prop hub just takes longer to let it out when it is that thick.  I've had the hubs apart and all it is, is a piston that is pushed down by the oil and moves the prop to a greater pitch....Next time you get back from a flight and the oil is nice and warm cycle the prop I bet it works just fine....

[Seth]

I'm hoping you are right.  I'll find out as soon as I get a call from the shop about my annual.  Thanks for the reply.

[Seth]

You were correct, there is no problem with the Prop Governor whatsoever - just cold oil as you suggested.  As for the annual, there are a couple of items that it was time to replace - rubber biscuts in the suspension system (these were from 1984), and a copule of hoses.  Besides that, the plane is in pretty good shape (knock on wood).  I was actually under the plane on creeper with Tommy (If you know Freeway Aviation and the Mooney Service Center there, you should know Tommy) showing me everything they take a look at during the Annual.  This being my first annual, it was pretty neat.  I'm also glad that it won't be too expensive an annual.

[GeorgePerry]

Seth,

Glad to hear your off to a good start with your new bird.  The guys at Freeway MSC are really good.  Your lucky to have them at your home field.

GP

[TurboExec]

That is what I suspected to hear....glad it didn't turn out to be anything worse.  Nice to hear your first annual wasn't painful either.

[meddesign]

I have a question.  I assume my governor should be set to give red line at takeoff climb.  When I level out it then will over speed.  If it is set to red line in level full power cruse it will not get red line at take off climb. Is this normal?

70E IO360A1A two blade Hartzel, set up by Hartzel.

 

[Ned Gravel]

Quote: meddesign

I have a question.  I assume my governor should be set to give red line at takeoff climb.  When I level out it then will over speed.  If it is set to red line in level full power cruse it will not get red line at take off climb. Is this normal?

70E IO360A1A two blade Hartzel, set up by Hartzel.

 

[meddesign]

Quote: edgargravel

It should give you max power (2700 rpm) at any attitude or configuration.  Not just in climb.  Remember that you are level when you first call for it, on the runway.  And not go overspeed in cruise.

IMO

[kallend]

Quote: edgargravel

It should give you max power (2700 rpm) at any attitude or configuration.  Not just in climb.  Remember that you are level when you first call for it, on the runway.  And not go overspeed in cruise.

IMO

[meddesign]

no, Lycoming talks about problems at +10% which is +270 RPM.  Be happy, wish mine was that close.

 

 

[Ned Gravel]

Quote: meddesign

on takeoff on the runway one is not going as fast.  but further .... is this how a governor begins to fail, not holding RPM precisely?  Or is it a simple cleaning that is needed, etc.  How do they fail, what is to look for.  I have heard of sending out for testing any shops one might use?   Have you ever got one back that did not need overhaul, that would be the shop to use.

 

Don B

A&P

[carusoam]

voodoo or science...

Consider this as "shared experience"

The govenor is made up of three basic sub-systems.

[1] fly-weights.  high engine rpm, the fly weights move out, low engine rpm, the fly weights move in.  flyweights and springs that they work against wear and have limits.

[2] two way valve, it's modulated by the motion of the fly weights.  RPM above setpoint, oil sent to hub. Engine below set point, oil is valved to the sump.  (set point is set by RPM knob)

[3] Oil gear pump, just like the oil gear pump that supplies oil to the engine.  It is shaft driven off the accesory case.  All mechanical and could experience wear.

I once had a governor overhauled (65 M20C).  The prop was stuck in high rpm (failed high).  The fly weights were measured and no longer in spec.  I also had the prop overhauled at the same time.  All put back together, it was still stuck in high rpm.

The real problem was the 50 cent shaft seal that was leaking oil pressure back to the case.  That was an expensive lesson.

When finished properly:  It was the smoothest running 4 cylinder lycoming on the planet that day.  (Add smiley face here)

-a-

[meddesign]

To those that think I know about governors because I have an A&P,....No I would not be asking these questions.  This is my first Mooney, and first Governor.  I am now an expert at adjusting the stop screw which is upside down and in a cutout at the firewall.  Other than that I can  start my Mooney hot better after this.   I have adjusted it about 10 times, and there has to be a better way, maybe on the bench, but from comments enen then the Mechanic needs to tweek it seems.  My Governor is an Edo Aire and is vintage, I am not sure from the logs if it ever has been overhauled.  Right now I have 2670 on climb out and it will hit 2700 clean straight and level.  My last adjustment was 1/2 a turn on the stop screw, and I do not know at this time if I will move it another 1/4 turn or not.  It appears that it is very sensitive at the 2700 goal.  I also have though of adjusting the stop on the prop, but Hartzel replaced my hub and set it up so I am reluctant to do that.

 

Don B

[Alan Fox]

Don the prop stop is set up by degrees as stated in the tcds , so adjusting the prop stop is a NO !!   The cable is not a suitable solution either , so you have to go with the cable stop at the governer ... I know it is a pain in the ass , but I also know that you are a retired engineer by trade and if the rpms vary by more than 3 or 4 rpms it will bother you , I set mine up for 2700 RPM and as long as my power changes are subtle I will not overspeed ...  If I slam it forward , it will overspeed by 75 to 100 rpm , I think this is the time it takes the piston to pull back the pitch , if I do it slowly , it goes to 2700 and stops at 2700 .. Good luck