Prop governor behavior - acceptable or not?

[DXB]

I've had my M20C about 6 months and had never flown behind a constant speed prop prior to this, so I don't know what's normal.  After I level off for cruise, I usually set power at 23 MP, 2300 rpm. Then I futz around with trim and mixture for a bit.  When I'm done with this, rpm usually reads about 2350, and then I pull it back again to 2300.  It might drift up again to 2350 one more time, and then generally it stays put after pulling it back again.  But yesterday I was surprised to notice it had come up to 2400 about an hour into the cruise during  my scan- I may have neglected checking for a while, but it had never drifted so far off before.

 

So to test the governor, I pitched up firmly and slowed to 120mph IAS.  Then I pitched down and came up to 170mph IAS - 20 mph above my cruise IAS.  The governor did its job and held 2300 rpm like a rock the whole time.  

 

My question is - is the amount of drift I am seeing in cruise concerning or in the range of normal?   It has a Top Prop which was installed in 2011 but the last governor overhaul that I can find in the books was in '97.

[eman1200]

I am BY NO MEANS a cs prop expert but could it be as simple as tightening the throttle lock a bit more? Dunno.

[Guitarmaster]

Sounds like the prop control is slowly working it's was back in.  I agree, check your prop control tension.

[N201MKTurbo]

I have to agree. It could also be where the cable attaches to the governor. If the outside of the cable moves in its mounting it will do this.

 

Take the top cowl off, grab the outside of the cable and try to move it back and forth where it is fastened to the aluminum angle. It should not move at all.

 

A problem I had with my F was when my flying buddy would use the plane he would always push the prop control in as hard as he could when going to full RPM. If there is any over travel in the cable, it will push the cable out of its mount. I always told him to just gently push it in until it stops, but he would always seem to push it in to the firewall. Then I would have to re-rig it.

[Hank]

The easy check is the friction lock on the throttle lever. Mine is on the right side of the quadrant, where I can feel it but not see it. After annual this year, I had the same problem, the friction lock was very loose, maybe 1-1/2 turns.

Another thing is to check after setting power and leaning. When I set power down lo to 23/2300, I lower MP to 22" then set 2300 and verify MP. Touching either one after that will affect the other.

[yvesg]

Check if the pitch control is slowly rotating. Mine does that because someone did lubricate it too much. if this is your problem, the solution is to prevent it from turning with something like an elastic.

Yves

[tony]

When you put the prop full forward, does it go over 2700?

[DXB]

Diagnosis made!  The knob rotates clockwise slowly during flight- GF's hair elastic hooking it to flap release lever fixed the problem (I know, hardly an optimal solution and will look funny on printed checklists).  The control has very little friction to hold it in place for part of its travel.  I think may be wear-related in the part, as it happens in range of travel where it is most often used (2300-2500rpm)- it holds well in other parts of the range.  Is there a safe, clever solution that costs much less than a >$500 replacement? I guess I can live with it for a while as it's not about to make me fall out of the sky...

[yvesg]

The safe, clever solution that does not cost much is the rubber band (elastic) trick...

Yves

[Guest]

The safe, clever solution that does not cost much is the rubber band (elastic) trick...

Yves

Or you could just fix it!

Clarence

[yvesg]

On my way to Oshkosh, was able to snap this picture of the rubber band trick.

Yves

[Guest]

On my way to Oshkosh, was able to snap this picture of the rubber band trick.

Yves

Why not just reset the friction on the control cable, it should be adjustable.

Clarence

[DXB]

Why not just reset the friction on the control cable, it should be adjustable.

Clarence

Thanks, wasn't aware- just added to my list for annual...

[yvesg]

Why not just reset the friction on the control cable, it should be adjustable.

Clarence

OK, will do it at annual.

Yves