Momentary constant speed prop overspeed

KRyan

KRyan

Pre-takeoff checklist
Joined
Jun 29, 2011
Messages
438
Location
Piqua, Ohio
Display Name
Display name:
KRyan
OK, so here is my question for the day.
I was contacted by a Cessna 182 pilot. He says he was flying during “a stable unmolested cruise” and twice had the governor on the prop "let go" for just a second.
The tach surged from 2300 to 2500+ for just a second, literally, and then returned to normal as if nothing had happened. The two episodes were about an hour apart.
I asked him about any recent maintenance, but he said there hadn’t been any. I was thinking he either had
1) A governor problem
2) An oil supply problem
3) A propeller problem
He’s asking what I think about him flying some more to see if it happens again. If it’s a governor or prop problem, he’ll just end up with a flat pitch prop, and he’ll have to reduce throttle and limp it home. If it’s an oil supply problem, he could lunch the engine.
What do you think about his “fly some more & see if it happens again” idea?
 
I wouldn't fly it until I eliminated oil from the suspect list, and it's at the very top of it in my mind.

Do we know how much oil is in the thing? Hell what kind of tach does he have, are we sure it really is overspending? When my tach died recently it read fast at differing amounts before wrapping around to zero.
 
My guess, in order is.

1- Governor issues

2- Prop issues

3- Oil Pressure issues.

The first two are basically minor to repair.

The last one could get REAL expensive.:yesnod:
 
He said he could "feel the plane "drop" from the lack of prop pull" (when the blade flattened out). I woud imagine he could hear it as well. This doesn't seem like a tach problem.
 
KRyan said:
He said he could "feel the plane "drop" from the lack of prop pull" (when the blade flattened out). I woud imagine he could hear it as well. This doesn't seem like a tach problem.
Click to expand...
Agreed. That plane should be grounded until the problem is isolated and fixed.
 
KRyan said:
He said he could "feel the plane "drop" from the lack of prop pull" (when the blade flattened out). I woud imagine he could hear it as well. This doesn't seem like a tach problem.
Click to expand...

That answers that question:wink2:
 
Ron Levy said:
Agreed. That plane should be grounded until the problem is isolated and fixed.
Click to expand...

Next question, What happens when the mechanic runs it up, cycles the prop and no discrepancy is found?

IOWs it never does it again.?

How much money would you spend trying to get it to do it again?
 
No great answers here either but...

No likey. :(

The mechanism inside a McCauley hub (assuming factory prop) just isn't that complex.

That said, is he darn sure the Manifold Pressure didn't change? I ask 'cause McCauley's also aren't super fast to respond to big quick power changes.

I wouldn't rule out the engine on this one. A big cough at altitude could be ignition problems or even just carb ice if it's an O-470.

It's also time to change the oil and look for debris in the filter...
 
I would vote for the engine issue.

The engine momentarily looses power the prop goes to flat pitch, this is why he feels it slow down. The engine catches by which time he looks down at the tach and sees that it is high, due to the high power and flat pitch from the momentary power loss.

If it was just the prop going to higher RPM I don't think he would feel it slow down, if any thing I think it would accelerate a bit when it does it.

Just my .02 cents worth, and that is probably overpriced.

Brian
 
Im leaning away from the prop, all it does is react to oil pressure and this plane is seeing a sudden momentar drop in oil pressure in the propeller, short of a big leak I'm not seeing how it could depart from steady state operation then return if the prop is faulty.

So why did the oil pressure go away from the prop?
 
There's another weird one to mention if it was cold. But since it's not that cold out, this probably isn't it.

If he has the non-cold-weather style oil cooler and there was a "slug" of cold oil trapped in it, those can come loose as a glob.

Usually associated with problems in the thermostat at the oil cooler itself too. Or a badly clogged up cooler.

But that's usually reserved for really really cold weather flying, non heavy duty oil cooler with small galleys and not large galleys to warm the cooler up, no winterization cover plate over the cooler face, and happens around takeoff when it'll supposedly scare the bejesus out of you.

Quite rare. I'm still going with an engine cough. ;)
 
It is a three blade Hartzell Top Prop. I'm going to get back to him with these comments. I thank you all.
 
I imagine he's speculating why a guy from Piqua, Ohio might be writing in with propeller questions. :D
 
KRyan said:
OK, so here is my question for the day.
I was contacted by a Cessna 182 pilot. He says he was flying during “a stable unmolested cruise” and twice had the governor on the prop "let go" for just a second.
The tach surged from 2300 to 2500+ for just a second, literally, and then returned to normal as if nothing had happened. The two episodes were about an hour apart.
I asked him about any recent maintenance, but he said there hadn’t been any. I was thinking he either had
1) A governor problem
2) An oil supply problem
3) A propeller problem
He’s asking what I think about him flying some more to see if it happens again. If it’s a governor or prop problem, he’ll just end up with a flat pitch prop, and he’ll have to reduce throttle and limp it home. If it’s an oil supply problem, he could lunch the engine.
What do you think about his “fly some more & see if it happens again” idea?
Click to expand...

You have the possibilities in the correct order. One other is the plug at the rear of the cavity at the front of the crank has come loose dumping governor pressure oil back into the crankcase. My bet goes on the governor. Charlie Melot Zephyr Engines
 
On the next flight try a higher or lower RPM setting and check if the problem goes away or get worse. If it does most likely the cause is the governor or the control linkage/cable to it. Some governors may surge at different RPMs.

Another possible cause of surge is mixture setting. If the engine was running too lean on LOP a minor change on the fuel or air flow can cause a sudden power drop that can cause a momentary RPM change.

José
 
Last edited:
Let'sgoflying! said:
Would metal in the gov. screen result in a constant overspeed?
Click to expand...

That will deprive the prop of oil, depending upon which prop you have will determine what the results will be.
 
Piloto said:
On the next flight try a higher or lower RPM setting and check if the problem goes away or get worse. If it does most likely the cause is the governor or the control linkage/cable to it. Some governors may surge at different RPMs.

Another possible cause of surge is mixture setting. If the engine was running too lean on LOP a minor change on the fuel or air flow can cause a sudden power drop that can cause a momentary RPM change.

José
Click to expand...

That cause will not come and go, RPM will decay until you do some thing about it.
 
You must log in or register to reply here.
Back
Top