Engine oil pressure varies with prop setting

KRyan

KRyan

Pre-takeoff checklist
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KRyan
OK, I got another one for you.
Got an e-mail from a customer in Australia. He claims that in cruise he has noticed his ENGINE oil pressure drops to as low as 45PSI indicated. However when he moves the prop lever – as the changes the prop pitch setting, the ENGINE oil pressure gauge shoots up to 75PSI then drops back to 45 again.
While the oil is “common” to both the engine & the prop, the pressure systems are separate – that being the pump that supplies engine oil pressure is not the same pump that supplies pressure to the propeller.
This is an aerobatic prop, flying on a Christen Eagle, so it works like a feathering propeller – oil pressure to low pitch. If he is pulling the prop to a lower RPM, oil is exiting the prop and going back to the sump. All I can think here is perhaps his engine oil level is low, and the pressure increases when the sump gets this “new” influx of oil?
Any of you know what possibly could be going on here?
 
KRyan said:
OK, I got another one for you.
Got an e-mail from a customer in Australia. He claims that in cruise he has noticed his ENGINE oil pressure drops to as low as 45PSI indicated. However when he moves the prop lever – as the changes the prop pitch setting, the ENGINE oil pressure gauge shoots up to 75PSI then drops back to 45 again.
While the oil is “common” to both the engine & the prop, the pressure systems are separate – that being the pump that supplies engine oil pressure is not the same pump that supplies pressure to the propeller.
This is an aerobatic prop, flying on a Christen Eagle, so it works like a feathering propeller – oil pressure to low pitch. If he is pulling the prop to a lower RPM, oil is exiting the prop and going back to the sump. All I can think here is perhaps his engine oil level is low, and the pressure increases when the sump gets this “new” influx of oil?
Any of you know what possibly could be going on here?
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Is the oil pressure sender tapped into the wrong gallery? BTW, in a feathering prop, oil pressure drives to flat pitch, spring/accumulator/counterweights drive to feather.
 
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I doubt it would be tapped into the wrong gallery. he'd be showing much higher pressres than normal. His governor puts out about 200 psi during normal operations.
 
Are we to assume spring is at proper tension, nitrogen all full up, everything working as designed?
 
I think that's safe to assume. There is no nitrogen used in this prop.
 
KRyan said:
I think that's safe to assume. There is no nitrogen used in this prop.
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N00b question: Why is there Nitrogen in a prop? Is this a service performed when a prop is overhauled?
 
Jaybird180 said:
N00b question: Why is there Nitrogen in a prop? Is this a service performed when a prop is overhauled?
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It pushes against a diaphragm. There are several different methods of driving the prop/oil back on the pressure release phase.
 
Has it always worked this way, or has something changed?
 
I can't say with certainty, but even if it's the incorrect prop, how is it's operation affecting the engine oil pressure indications. That's the question.
 
Sounds more like he has possibly a stuck oil pressure relief valve (meaning that any oil pumped into the prop briefly lowers pressure), a leaking governor or governor base gasket that's bypassing oil back to the sump when it's trying to pressurize the prop, or an engine oil pump that's worn so much it can barely keep up.

Dan
 
KRyan said:
I can't say with certainty, but even if it's the incorrect prop, how is it's operation affecting the engine oil pressure indications. That's the question.
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The prop operates from engine oil pressure. the governor is not a pump. it is simply a speed sensing valve that regulates the direction of oil flow to coarsen or lessen the blade angle.

to me it seems that he has blown the governor mounting gasket.
 
The governor contains a pump. It takes engine oil pressure and boosts it to about 200 PSI to operate the prop. It is the oil pressure from the governor pump that the flyweights and spool valve control. The engine oil pressure pump is a totally separate pump, and it is the output pressure from this pump that is displayed in the cockpit.
 
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KRyan said:
The governor contains a pump. It takes engine oil pressure and boosts it to about 200 PSI to operate the prop. It is the oil pressure from the governor pump that the flyweights and spool valve control. The engine oil pressure pump is a totally separate pump, and it is the output pressure from this pump that is displayed in the cockpit.
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When the prop pump takes oil, the bypass valve may momentarily pop shut and allow a small surge of pressure when the prop quits taking???
 
So you're talking about the engine oil pressure pump bypass? That's at least a theory.
 
KRyan said:
So you're talking about the engine oil pressure pump bypass? That's at least a theory.
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Correct, there is a spring loaded bypass valve in the primary engine oiling system. This could be a reaction to a pressure wave caused by the boost pump taking oil from the system and stopping again. A "hydraulic knock"... The pressure pickup would likely be between the boost pump and pressure relief. The primary question though is, "Is this new?" or same old same old, "Don't know, always done it though...".
 
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From:
http://www.enginehistory.org/Propellers/Governors/hydgov.shtml

which has numerous really good diagrams, we get a cutaway of typical governor:

HydPropGov.jpg


Note the booster pump. Note, too, the base gasket, which can fail and let the oil intended for the propeller escape back to the sump.

If the engine's relief valve is sticky the oil pressure will be inconsistent. It will drop off when the oil gets hot, might get high when it's cold, might give erratic readings when the demand varies as when the governor takes more oil to feed to the propeller hub.


The relief valve is nothing more than a ball or plunger with a spring behind it, closing off a hole that leads from an oil gallery. When the system pressure reaches the relief valve's setting, it opens and lets the excess oil either drain back into the sump, or back to the pump inlet. Real high-tech stuff.

Dan
 
WE don't even know what engine/prop/gov/ he is asking about. Not all systems have a boost pump in the gov.
 
Oh wait... the guy's in AUSTRALIA. It's because he's on the bottom of the world about to fall off!
 
Is it true that the prop spins the other way down there?

:cheerswine:
 
For all we know, he is dealing with a AN2. yet we paint them all with the Lycoming brush.
 
Tom-D said:
For all we know, he is dealing with a AN2. yet we paint them all with the Lycoming brush.
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AN-2 basically has a Wright Cyclone... But we're talking an "Aerobatic" engine, and most likely that's going to be a Lycoming, probably an AEIO series.
 
TMetzinger said:
Oh wait... the guy's in AUSTRALIA. It's because he's on the bottom of the world about to fall off!
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There's more truth to that than you may realize... I lived there twice 4 years total. That's enough thanks.

There may be an element of "She be right" involved here....
 
Long and short of it, if it's been this way for a long time, don't sweat it, this could just be a normal hydraulic pulse. If it's a recent development,... well, I'd proceed cautiously and at least do some minimal dis-assembly and inspection. I'd be a bit suspicios of the crank plug seal as well. Possibly a pitted crank... These are the things I want to eliminate first.
 
Henning said:
AN-2 basically has a Wright Cyclone... But we're talking an "Aerobatic" engine, and most likely that's going to be a Lycoming, probably an AEIO series.
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You are guessing again.
 
I asked the customer several of these questions, but haven't gotten anything back from him yet. Its a Christen Eagle, and the customer told me in his original correspondence that he "thinks" his customer has an F-6-59 governor, which is the governor used on an AEIO-540 Lycoming. I'll have some better info when he responds.
 
Tom-D said:
You are guessing again.
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KRyan said:
I asked the customer several of these questions, but haven't gotten anything back from him yet. Its a Christen Eagle, and the customer told me in his original correspondence that he "thinks" his customer has an F-6-59 governor, which is the governor used on an AEIO-540 Lycoming. I'll have some better info when he responds.
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Not a bad guess....
 
Apparently the owner of the Aircraft bought a mod kit to remove the engine driven vacuum pump and increase oil flow / pick up for aerobatics. The mod meant removing the vac pump, drive gear and adapter and fitting a blanking plate over the accessory housing. The owner, to save some bucks did the job himself, removed the vacuum pump and drive gear but re-installed the drive pad / adapter and plated that. This gave him a constant bleed of oil from the oil port that supplied oil to the vac pump drive gear, hence bleeding the engine oil pressure down but seeing a rise when the governor output created some back pressure .

Thanks for all your help. I just thought you'd like to see what the answer was.
 
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KRyan said:
Apparently the owner of the Aircraft bought a mod kit to remove the engine driven vacuum pump and increase oil flow / pick up for aerobatics. The mod meant removing the vac pump, drive gear and adapter and fitting a blanking plate over the accessory housing. The owner, to save some bucks did the job himself, removed the vacuum pump and drive gear but re-installed the drive pad / adapter and plated that. This gave him a constant bleed of oil from the oil port that supplied oil to the vac pump drive gear, hence bleeding the engine oil pressure down but seeing a rise when the governor output created some back pressure .

Thanks for all your help. I just thought you'd like to see what the answer was.
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As I suspected, "She be right" was involved...:nonod: NEVER buy something from Australia....
 
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