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  #1  
Old 08-15-2016, 10:42 AM
woxofswa woxofswa is offline
 
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Default MT P860-3 Prop Gov fail.

This is a new thread branch off of my original AOG thread relating to news and questions concerning the MT prop gov issue.

Original thread here. http://www.vansairforce.com/communit...d.php?t=140840
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Last edited by Mike S : 08-15-2016 at 11:54 AM. Reason: add thread link
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  #2  
Old 08-15-2016, 10:50 AM
woxofswa woxofswa is offline
 
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>>If somehow you didn't overspeed your engine/prop you got very lucky. The other recent (identical?) failure wasn't so fortunate:
http://www.vansairforce.com/communit...ight=overspeed

Might be worth a look at engine monitor data, if you have a record.<<

Thanks for that link. I hadn't seen that and the pix look almost exactly like mine. The only difference is that there must be two pressure chambers in the unit to maintain pitch because my failure caused the RPM to drop rather than overspeed. I was about 18-19 on the RPM at full throttle and 800 on idle descent. Aside from everything else, the landing was much different due to lack of drag. First time I ever slipped the airplane to be honest to get the sucker down as a go-around would have been a nightmare. A short field would have been dicey. Good things to think about and practice on a routine basis.
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Last edited by woxofswa : 08-15-2016 at 10:59 AM.
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  #3  
Old 08-15-2016, 11:55 AM
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Myron,

Have you opened the governor to see what came apart inside?
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  #4  
Old 08-15-2016, 12:12 PM
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I'm confused about something, perhaps somebody can clarify.

As I understand it, single engine airplanes with constant speed props are set up to go to fine pitch, not coarse, upon loss or reduction of governor oil pressure - so that you can still make power.

Twin engine airplanes with constant speed props are set up to go to coarse pitch (feather) upon loss of governor oil pressure - so that you minimize drag on the side with the failed engine.

Yet this incident seems to indicate that an RV-10 (single engine) went to coarse pitch, with 500 RPM lower than expected upon governor failure, which seems strange.

This seems to be a different failure mode than the Todd Stovall RV-10 failure from another thread [or at least different symptoms - coarse pitch (lower RPM) instead of fine pitch (potential overspeed)] - that is, unless this is a prop set up for a multi-engine installation, which seems very unlikely.

What am I missing here?
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  #5  
Old 08-15-2016, 12:17 PM
woxofswa woxofswa is offline
 
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Dan,

No,

The temptation is strong, but I don't want to go there until I know what recourse options I can expect. I am getting conflicting advice as to whether to get the FAA involved in this or not. My natural tendency is keep experimental aviation free of Feds, lawyers, etc. However, this is a certified part and three fails in a short period is a GIGANTIC RED FLAG. This is a ticking bomb that when it goes off, you've got about 10 mins to get on the ground or be a glider with a seized engine. I guess I was lucky that the failure caused coarse pitch instead of overspeed, because the latter can trash an engine on top of everything else.
As much as I would like to keep our community "pure", I would feel terrible if a failure of something I could have alerted to caused damage, injury, or death.

Regardless of where this goes, they are going to want to examine the assembly as it is, not after an amateur inspection. It really needs to go to a NTSB level tombstone lab and before the tombstones are required.
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Last edited by woxofswa : 08-15-2016 at 12:28 PM.
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  #6  
Old 08-15-2016, 12:23 PM
woxofswa woxofswa is offline
 
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Quote:
Originally Posted by Noah View Post
I'm confused about something, perhaps somebody can clarify.

As I understand it, single engine airplanes with constant speed props are set up to go to fine pitch, not coarse, upon loss or reduction of governor oil pressure - so that you can still make power.

Twin engine airplanes with constant speed props are set up to go to coarse pitch (feather) upon loss of governor oil pressure - so that you minimize drag on the side with the failed engine.

Yet this incident seems to indicate that an RV-10 (single engine) went to coarse pitch, with 500 RPM lower than expected upon governor failure, which seems strange.

This seems to be a different failure mode than the Todd Stovall RV-10 failure from another thread [or at least different symptoms - coarse pitch (lower RPM) instead of fine pitch (potential overspeed)] - that is, unless this is a prop set up for a multi-engine installation, which seems very unlikely.

What am I missing here?
I don't know myself yet. My semi educated guess at this point is that there are two pressure chambers within the unit to balance and control the prop position. In this type of failure, there is no loss of pressure from the engine to the PG as the pressure loss is by wall breach of the case instead. I imagine that such is something that the engineers think they have eliminated as a possibility. I suspect that my failure was on the side that caused it to go to coarse pitch, which, in a way, I am grateful for as it kept the engine from overspeeding.
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  #7  
Old 08-15-2016, 12:35 PM
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Somewhere from a dark dusty corner of my memory I seem to recall that aerobatic planes use a different setup so that if the oil pressure is momentary lost, the prob does not go crazy.

Any chance you have a governor from an aerobatic application?
MT is big in the aerobatic world.

Or, maybe the cobwebs need sweeping.......??
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  #8  
Old 08-15-2016, 12:48 PM
woxofswa woxofswa is offline
 
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Here I have tried to depict two different failures with like orientation. Obviously the data sticker is oriented differently.
Mine (bottom) appears closer to the lever side and slightly more to the right at punchout point. Still remarkably similar.
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Last edited by woxofswa : 08-15-2016 at 01:04 PM.
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  #9  
Old 08-15-2016, 02:07 PM
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Quote:
Mine (bottom) appears closer to the lever side and slightly more to the right at punchout point. Still remarkably similar.
Same failure. One of the rotating weights has broken loose and the rotor tried it shove it through the case. See Joel's photo here:

http://www.vansairforce.com/communit...9&postcount=20
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  #10  
Old 08-15-2016, 02:16 PM
moosepileit moosepileit is offline
 
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Mike S, I am no expert, but you are on the right track wrt aerobatic CS props- the springs and counterweights that make low total drag, low rpm and high prop pitch with oil pressure loss are in the propellor, not the governor.

Is there a chance this RV-10 has a prop setup like an aerobatic plane?

Is it possible that the same governor failure will overspeed a prop setup to go fine pitch/climb/high rpm and cause an acro/twin setup prop to go low rpm/coarse/high pitch?

Prop should have limit stops with either setup in both directions? (Not an expert).

I have seen nasty overspeeds in acro before accumulators and governors were all shaken down, limit serttings alone didn't stop overspeeds where counterweights were set for climb pitch/fine with oil pressure loss.
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