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Constant speed propeller intermittent failure

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Constant speed propeller intermittent failure

Old 3rd Jun 2019, 19:40
  #1 (permalink)  
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Join Date: Jun 2019
Location: California
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Red face Constant speed propeller intermittent failure

Hello there, this is my first post, and I'm writing with a constant speed propeller problem that no one has been able to resolve...Have been trying to fix the issue for one year now, and my mechanic is talking to Lycoming, McCauley, engine overhaul shop, etc...

I own a 1979 Cessna 182 Turbo retractable with a Lycoming O 540 engine and a 3 bladed McCauley propeller, 920 SMOH, 300 hours since Top overhaul, 3900 total hours.
In 2015 (before the top overhaul) , the propeller governor went off line in climb-out and the propeller behaved like a fixed pitched propeller. The symptom stopped 10 minutes later. The governor was removed, sent out for testing, and returned without an issue. Subsequently, the same thing happened a year later, and then it happened more frequently. Now it happens every second or third flight and then the propeller returns to behaving normal eventually. The intermittent nature seems to make it so difficult to diagnose.
The prop cycling on the ground is normal, the propeller does not over-speed ever, and when it acts like a fixed pitch propeller, moving the prop control does nothing.
The following was done, to no avail:
  • used a loaner governor, same problem...than installed new McCauley governor..same problem
  • checked all oil galleries for obstructions: Free and clear
  • Overhauled propeller..
  • Checked if the blades move correctly..they do
  • Checked plug in crankshaft that closes off one side of oil flow for constant speed prop: It is securely in its place
  • Oil pressure is always nicely in the green...however, I have the old gauge that does not give me actual psi readings.
  • Oil temperatures are good
  • CHTs great
  • No metal in oil filter or oil analyses
One of the theories is that I have a moving (not spun) front bearing that moves fore and aft in a type of a groove intermittently, so that the two oil openings do not line up exactly, ... just enough to cut off some of the oil flow which will reduce oil pressure to the point that it cannot activate the governor. It clearly does not cut off oil altogether, as my engine would seize then.
Now I'm facing a tear-down or an engine overhaul. I'm not flying due to the fear that a spun bearing might be imminent...on the other hand, I'm afraid that, once the case is open, we'll find nothing wrong with the bearing...I'm truly at my wit's end...and hoping that someone with a fresh view can provide some great insight.

Thank you much for reading my post.

1greenmachine

Last edited by 1greenmachine; 4th Jun 2019 at 15:16.
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Old 4th Jun 2019, 00:23
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fdr
 
Join Date: Jun 2001
Posts: 576
Hi.

When you have the problem, is the RPM increasing or remaining constant? If the problem was a reduction in oil supply to the pitch change piston, then the propeller will tend to fine off and RPM would rise unless you were already on the fine pitch stops, which is unlikely. If the RPM doesn't rise, and the prop was already coarser than fine pitch stop, then the problem is not related to oil supply, it remains with the governor.

Your process of changing out the governor is sound, but as the fault remained then the problem if not oil supply has to be from a loss of input to the flywheel of the governor )it is a simple mechanical device... not much magic there) If the RPM is not following the RPM control changing for steady speed conditions, then the position of the output arm of the governor has to be fixed, and that probably means that the drive to the governor has a failure such as a fracture that sometimes slips and at other times locks in place. It is conceivable that both governors are defective, but if the replacement or your works correctly on another aircraft, then that would remove the governor component as the cause, and only leaves the input from the engine to the governor as a source of the problem.

Your contacts are the right ones to be talking with, but they probably need to observe the problem first hand to really get their head around the matter.
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Old 4th Jun 2019, 05:08
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Join Date: Jun 2019
Location: California
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constant speed propeller intermittent failure


Dear Fdr

Thank you so much for your thoughtful and detailed response...

The propeller does not fine off when this is happening.

The only time l can tell that the problem occurs is when I change the power setting with my throttle control. The rpm will follow my throttle movement, instead staying constant where I set it: When I increase manifold pressure, the RPM goes up, and when I decrease manifold pressure, rpm goes down... so Iím flying a fixed pitch propeller and am adjusting RPM with my throttle control. When I move the propeller control knob, nothing happens...rpm does not change.
After several minutes, or after I land and take off again, the governor comes back on line.

What I donít understand is the increasing frequency of this occurrence: it was starting to happen more and more frequently with my old governor, which is why I sent it in for testing, and it is increasing in frequency with the new one also.

Why could that happen?

Thank you again
1greenmachine


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Old 4th Jun 2019, 08:10
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Join Date: Dec 2001
Location: FL, USA
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Iím shooting totally off the hip here but is it a hollow crankshaft providing the oil?
Does it have an intermittent obstruction in the crankshaft such as a flake of metal?
it wonít be able to make its way past the 90 degree turns and will settle after shutdown.
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Old 4th Jun 2019, 08:31
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Join Date: Mar 2019
Location: French Alps
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In years past we had a problem with the prop governor on an aerobatic plane.
Never totally fixed it until we sold the aircraft to a mechaninc who zeroed in on an oil feed to the governor issue.
He added an oil pressure accumulator and solved the problem.

Edit : Now I seem to remember the origin of the problem was with the oil pickup in the sump, that was not the exact model it should have been.
Still boils down to an oil pressure issue, though.

Last edited by Fly Aiprt; 4th Jun 2019 at 20:53. Reason: Typo, addition
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Old 4th Jun 2019, 10:14
  #6 (permalink)  
 
Join Date: Nov 1999
Location: UK
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Since two governors exhibit similar responses, the problem has to be either the oil supply to the governor or a mechanical jamming of the blades.

What stands out for me is that the problem disappears after a few moments or landing - when the engine/prop rpm and load has reduced - and seems to reappear after the engine/prop has been constant or at least loaded for a while?

I once had a car auto gearbox that after driving for a while would fail to select gears, but if I stopped and idled the car in neutral for a few minutes, the gearbox worked again.

Is it possible to fix an oil pressure gauge to your governor oil supply? And also an oil temperature gauge?

Then, although you say the blades and pitch mechanism move, do they really move freely or could they be mechanically jamming at certain rpms? Is it possible to remove any springs etc and feel the pitch movement of each blade and the governor - moving them by hand - to feel if they move smoothly throughout their range or have crunching or snatching at any point?

I am leaning towards a problem with the oil supply, (I take it you have double checked the oil level and correct quantity?). Another thing you might check is the balance of the prop.





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Old 4th Jun 2019, 10:41
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Join Date: Mar 2019
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What are the exact make and model of the governor ?
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Old 4th Jun 2019, 17:51
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Join Date: Jun 2002
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Is it possible to `borrow` a similar prop from a prop-shop and test fly that..?
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Old 4th Jun 2019, 20:40
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Join Date: Dec 2017
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For the lat 12 yrs. i owned a Ultimate 10-200 lookalike, with a O-540L3C5 out of a Cessna 182TRG, hopped up to Injection and 10-1 Compression (290hp).

During the 100hr inspection/Annual included in the sale, i had Chips in the Filterscreen. Not to many, i would have operated it further, but the buyer insisted on Repair.

"The front Mainbearing was making metal and subsequently all bearings were gone." Oilpressure was still ok around 90psi.

During one of the Last flights in Winter, i had the same Issue: My Prop in a Vertical Up behaved like a Fixed Pitch and i couldnt Change Rpm afterwards. On the Ground it worked quite normal...
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Old 5th Jun 2019, 10:07
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Join Date: Nov 1999
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Yup, sounds like low oil pressure to the CSU; possibly caused by flow restriction. Lower oil pressure works OK when the prop is not loaded but cannot move the pitch mechanism at higher prop loads?
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