Prop Governor problem?

CJones

CJones

Final Approach
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Mar 14, 2005
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uHaveNoIdea
While flying the RV a few weeks ago, I noticed that it wouldn't hold RPM like it normally does. I normally cruise at 2300/2350 RPM and set it at 2400 in the pattern. Recently when flying, during descent the prop would advance itself to 2400. I would readjust the prop to 2350 or so during the descent, but once leveled out in the pattern, it would drop to 2300 or so and I would have to dial it back up to 2350 then 2400.

My dad flew the plane to San Antonio last weekend and he said when he was descending into Muscatine on the return trip the prop was acting basically like a fixed pitch prop. He's been talking to a MT prop guy in California and they can't seem to diagnose the problem. We've replaced the prop cable (just out of curiosity), but that didn't work.

Now, we're thinking it might be the check valve in the prop governor sticking. Anyone else had this type of problem? Any clues what might be causing it? We're to the point that we're ready to pull the prop governor and have it inspected/overhauled.

By the way -- it's a 3-blade MT prop.
 
I have some time in a DA-40 that had the 3 blade MT prop as well. About 3 hours into a 3.5 hour leg, it started having trouble holding the RPM on the prop. We did all the normal troubleshooting things on the engine and everything looked okay. They pulled the prop and it was making metal shavings, from where I can't recall. As I recall, that one was a warranty claim and we got a 2 blade loaner. I think that the problem was pretty serious, but the company I was flying for would not have told me if it was.

It was weird to be flying along and have the engine slow down all by itself.

I never thought that I would have anything useful to say about aircraft maintenance issues. Sometimes we surprise ourselves.

--Matt
 
The only one that always sticks in my mind is a case where the guy had metal shavings in the oil and somehow they got past the governor screen and jammed up the works, sorry to pipe up with a downer idea.
 
OK.. You guys are NOT giving good (happy) advice! ha!

We've thought about something being in the screen in the governor. The engine had a new crankshaft installed last year due to a Lycoming AD, so that's two 'break-ins' within the first 500hrs of engine/prop life. If it IS something/metal in the screen, hopefully it's just a result of the repetitive tear-downs. If not... well..... let's not think about that right now.
 
You might be able to tap into the oil passage to the prop with a (high) pressure gauge which would help the diagnosis a lot. In any case I wouldn't fly the plane as it is quite likely a malfunction of the prop and might lead to blade separation, something you definitely don't want to experience.
 
I thought about this story of mine whilst driving to the airport...it was actually not past the screen but clogging the screen.
Hopefully yours will be something much simpler!
 
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