Constant speed prop flattening above 4000 feet

[ItsACardinalRG]

I have a McCauley three blade prop on my Cessna Cardinal. I just had the engine replaced and now I'm having issues with the prop. At elevations below around 4000 feet, the propeller responds correctly to the blue propeller control--full in flattens the blade to full power with higher RPM, and rotating out feathers to cruise angles. However, when I get above 4000 feet, the propeller begins to flatten and the RPMs increase. The prop will flatten out to full power and I have to pull the throttle to prevent redlining the prop. The prop knob has no impact on the blade at that point. It remains in full power. If I drop back down in altitude with the prop knob pulled out for, say 2400 RPMs, at some point around 4000 feet, the blade will suddenly feather for 2400 and the knob begins to function again. This happens every time. The prop adjustment cable is secured and functioning correctly. There aren't any obvious blockages in the oil line to the governor. Manifold pressure is good and is fully responsive to throttle changes. Any ideas?

 

[KRyan]

There are three possible “culprits” here: the engine, the governor, and the prop. Only one has “changed” recently, and that’s the engine, although I assume that the governor was removed from the old engine and installed on the new. Which engine are you running? Look like the Cardinal RG can have an O-360-A1B6, O-360-A1B6D, an IO-360-A1B6, or an IO-360-A1B6D.

Also, was it a “like for like” replacement? In other words, was the new engine EXACTLY the same as the old (including the “alphabet soup” in the engine model)?

 

[luvflyin]

There are three possible “culprits” here: the engine, the governor, and the prop. Only one has “changed” recently, and that’s the engine, although I assume that the governor was removed from the old engine and installed on the new. Which engine are you running? Look like the Cardinal RG can have an O-360-A1B6, O-360-A1B6D, an IO-360-A1B6, or an IO-360-A1B6D.

Also, was it a “like for like” replacement? In other words, was the new engine EXACTLY the same as the old (including the “alphabet soup” in the engine model)?

It was probably an IO-390. They got an STC for that a few years ago. I flew one a few months ago and everything was fine. @ItsACardinalRG , did you get the 390?

 

[ItsACardinalRG]

The engine is an IO-360-A1B6. I was hoping to get the 390 but couldn't find one at a feasible price. The engine was the exact model as the old one. The "stuff" on it was a bit different so most of my old stuff was swapped over to the new engine including governor and prop. They suspected the governor so it was sent to a shop. The shop confirmed the governor was not putting out sufficient pressure and we overhauled it. Unfortunately that didn't fix the problem. I now have excellent manifold pressure and the prop still flattens when I get up to altitude. Yesterday I flew and it did this at around 7500 feet. A bit higher altitude than before but the exact behavior. As soon as I leveled out from my climb and the back pressure on the blades dropped, the RPMs started to climb. At that point, the blue knob becomes ineffective. My only option is to pull the throttle to keep the prop from over-spinning. When I dropped below around 7000 feet, the prop began to respond to RPM adjustments once again.

 

[Salty]

This is a very interesting problem to me. I don’t even have a reasonable theory

 

[Tantalum]

What about oil pressure, are you noticing changes in that? The propeller control is actually pretty simple using just flywheels and a spring and oil pressure.. since you seem to experience this in response to changes in altitude that implies some pressure change somewhere.. even if engine oil pressure is okay there may be some leak somewhere else that is responding to ambient air pressure messing with the governor. If the prop increases the flywheels are flung out, so it's trying to get the prop to go coarse, but for some reason it can't

this post isn't even worth $0.02

 

[KRyan]

OK, here's what I think is happening:
You prop is a dumb animal. It only does what the governor tells it to do. Your governor was tested, and is functional, so what is going on?
On your prop (I'm assuming is a C202, C206 or C208) the pitch is controlled by oil into the prop for high pitch (low rpm), and oil out of the prop for low pitch (high RPM). Remember this.
When you are climbing, your prop is in fairly low pitch. If your RPM starts to creep up, the governor ports oil to the prop, coarsening the pitch to slow the engine down.
In your case, this isn't happening, and the governor is OK.
So, I suspect you have an oil supply problem. I COULD be your oil pump, as Tantalum suggested, but I suspect something else is the issue.
Your governor is supposedly pumping oil to the prop to coarsen the pitch, but the pitch isn't changing. I suspect your new engine has a leaking transfer bearing. Oils is being pumped to the prop, but the governor can't keep up with the leakage rate. There's a Lycoming Service Instruction (SI 1462) that provides a test.
I know you are thinking "It's a new engine" but this is when it's seen - either on new/newly overhauled, or conversely, very high time engines.

 

[Tantalum]

pitch is controlled by oil into the prop

That's basically what I was trying to say, you just stated it more eloquently so!

I know you are thinking "It's a new engine" but this is when it's seen

And this is why I our GA engine tech is so disappointing.. when flying on a "new" engine is scarier than flying on one with 800 hrs on it

But I digress, too early in the day yet here on the left coast for a rant

Cheers all

 

[mondtster]

OK, here's what I think is happening:
You prop is a dumb animal. It only does what the governor tells it to do. Your governor was tested, and is functional, so what is going on?
On your prop (I'm assuming is a C202, C206 or C208) the pitch is controlled by oil into the prop for high pitch (low rpm), and oil out of the prop for low pitch (high RPM). Remember this.
When you are climbing, your prop is in fairly low pitch. If your RPM starts to creep up, the governor ports oil to the prop, coarsening the pitch to slow the engine down.
In your case, this isn't happening, and the governor is OK.
So, I suspect you have an oil supply problem. I COULD be your oil pump, as Tantalum suggested, but I suspect something else is the issue.
Your governor is supposedly pumping oil to the prop to coarsen the pitch, but the pitch isn't changing. I suspect your new engine has a leaking transfer bearing. Oils is being pumped to the prop, but the governor can't keep up with the leakage rate. There's a Lycoming Service Instruction (SI 1462) that provides a test.
I know you are thinking "It's a new engine" but this is when it's seen - either on new/newly overhauled, or conversely, very high time engines.

I agree. I withheld comment earlier because there wasn’t enough information to be certain but it sounded like leakage problems from the start. I’m rebuilding an engine with the same problem only it’s on a twin, so the prop went the other way after the oil warmed up. At least the twin had two of everything so troubleshooting was easier.

And this is why I our GA engine tech is so disappointing.. when flying on a "new" engine is scarier than flying on one with 800 hrs on it

This really has nothing to do with “engine technology” or lack thereof in my opinion. It could potentially be a lack of the use of manufacturing technology however. Those same errors could be present on boat or car motors or anything else really.

 

[bnt83]

https://www.lycoming.com/sites/default/files/Propeller Oil Control Leak Test Procedure.pdf

 

[ItsACardinalRG]

So, I suspect you have an oil supply problem. I COULD be your oil pump, as Tantalum suggested, but I suspect something else is the issue.
Your governor is supposedly pumping oil to the prop to coarsen the pitch, but the pitch isn't changing. I suspect your new engine has a leaking transfer bearing. Oils is being pumped to the prop, but the governor can't keep up with the leakage rate. There's a Lycoming Service Instruction (SI 1462) that provides a test.

https://www.lycoming.com/sites/default/files/Propeller Oil Control Leak Test Procedure.pdf

Thanks for the information. This makes a lot of sense to me and I'll look into it and let everybody know the outcome.

 

[Doggtyred]

Any chance there is an air pocket in the oil plumbing involving the governing system... something pushing on a diaphragm somewhere?

 

[BigBadLou]

As soon as I leveled out from my climb and the back pressure on the blades dropped, the RPMs started to climb.

Very interesting problem you are having. Curious about what y'all find.
Question: when you mentioned 4,000' in your first post, was that in a continuous climb or did you also level off there?

 

[ItsACardinalRG]

I agree. I withheld comment earlier because there wasn’t enough information to be certain but it sounded like leakage problems from the start. I’m rebuilding an engine with the same problem only it’s on a twin, so the prop went the other way after the oil warmed up. At least the twin had two of everything so troubleshooting was easier.



This really has nothing to do with “engine technology” or lack thereof in my opinion. It could potentially be a lack of the use of manufacturing technology however. Those same errors could be present on boat or car motors or anything else really.

I'm curious what the problem turned out to be with your engine. What was leaking?

 

[mondtster]

I'm curious what the problem turned out to be with your engine. What was leaking?

The bearings. Bearings always leak but when you get an engine with excessive wear/clearance they will leak extra and oil pressure can no longer be maintained. This engine had been apart two or three times since the last overhaul and the bearings were reused at least a couple of times. Overall, it all accumulated to being a collection of junk parts that loosely resembled an engine.

 

[KRyan]

The bearings. Bearings always leak but when you get an engine with excessive wear/clearance they will leak extra and oil pressure can no longer be maintained. This engine had been apart two or three times since the last overhaul and the bearings were reused at least a couple of times. Overall, it all accumulated to being a collection of junk parts that loosely resembled an engine.

I hear this all the time on twins used for training. The planes/engines are high time, and flown often, sometimes with one student flying right after another student, so the oil temps are high. The props on the twins will feather, rather than go to low pitch, as you mentioned in your earlier post.

 

[A1Topgun]

Thanks for the closure.

 

[KRyan]

Thanks for the closure.

It's not closed yet, we still don't know what happened to the OP.

 

[hindsight2020]

Hope it's not shoddy bearing re/assembly work. That's gonna be an interesting and awkward conversation with the engine overhauler when it comes out that the bearings are leaking like the Titanic after the iceberg, 6-9 hours after an overhaul. Hope that warranty policy (if any) is worth the ink it was written with.

Infant mortality and re-assembly buffoonery is such a frustrating part of this hobby, for the ridiculous dollars they charge for these engines and labor (essentially, revenue aircraft pricing). For the sake of the OP, here's to hoping it's just more benign and merely a plumbing line boo boo or something that doesn't require cracking open that engine.