newbie question re prop overspeed with constant speed prop

[rv6ejguy]

I've used these for turbocharger oil scavenging (engine oil). They work well but being a gear pump, won't tolerate much in the way of metal bits going through them. For that, the diaphragm pumps like the Tilton/ Flo-Jet ones are better but heavy, vibrate a lot and draw a lot of current. I've used these too.

 

[wsimpso1]

To be able to evaluate these things, I would want to know what the oil flow rate and feed pressure the governor needs at its inlet, plus pressure drop through your filter and any cooler. I suspect that ambient pressure at the governor feed is adequate as the governor is currently drawing from the sump, correct? If governor specs do not help you with flow rate, measuring the piston bore, stroke, number of cylinders, and spin rate relative to the engine can produce an estimate of flow. Pressure drop through filter and HX might require a test.

The idea of having to wait until oil is warmed up before turning the pump on is wrong on couple levels:

• You want clean oil to the governor and prop all the time;
• You most likely want the pump to be run automatically when the engine is running;
• A check valve feed to the governor is supposed to be a back up, not a primary. If it becomes primary during warm up, you will require a much higher degree of reliability of actuation than if it only has to open when something else breaks.

Billski

 

[pantdino]

Yes, the pump in the governor can lift oil a distance to it, so even slight negative pressure at the input is OK. As it is installed the governor is about 2 feet above the sump.

I wonder what happens if the pressure supplied to the input is 50psi or so. Would that lead to overpressurization in the governor? Probably not, as I understand governors work in the 300 psi range, so it is not significant.

I think one concern would be if the pump is not able to push enough volume thru the filter to keep the governor supplied, which would starve it.

 

[TFF]

Without seeing inside, the filtered oil discharge may be directed at the pickup for the prop governor, but feeding directly the governor, is probably not possible without some major modifications, and verifications on operation. The volume has to be there. What does the gov oil pickup look like? To me it’s more like an in pool sweep. Trying to move contaminants away to be easily picked up. The contaminates are in the oil and hopefully cleaned before sucked up by the gov pickup.

 

[Dan Thomas]

I'd be trying to avoid an electric pump altogether. An electrical failure means a dead pump, and what does that do for governor operation? If it cavitates your prop overspeeds. Governors are designed to feed off the engine's oil system, which can be 80 PSI.

An electric pump also surrounds itself with magnetism, which could attract iron or steel debris from the oil and encourage it to pile up in the pump, failing it. Now you need more than a simple filter; you need a magnetic debris trap too, before the electric pump.

I'd be looking at creating a small oil pump, belt-driven off a pulley behind the prop or maybe even installed at the other end of the engine and running off the accessory stuff. Located low enough that it's always full of oil so it doesn't need priming if it sits for weeks.

 

[wsimpso1]

Yes, the pump in the governor can lift oil a distance to it, so even slight negative pressure at the input is OK. As it is installed the governor is about 2 feet above the sump.

I wonder what happens if the pressure supplied to the input is 50psi or so. Would that lead to overpressurization in the governor? Probably not, as I understand governors work in the 300 psi range, so it is not significant.

I think one concern would be if the pump is not able to push enough volume thru the filter to keep the governor supplied, which would starve it.

Since the governor does work with a significant lift, I agree that any pressure left the governor is likely to be OK.

The feed pump has to have more flow than the governor - less will slow the prop response. Once you have more flow to th governor than it can accept, you could over pressure the governor. A blowoff valve after the feed pump, filter, and cooler and before the governor adjusted to some modest pressure would make sure the governor is fed but not not over pressured. This blowoff pressure regulator could either feed the pump inlet (called supercharging the pump) or simply vent to the sump.

I had also mentioned a check valve between sump and this part of the circuit. This is a device to make sure the governor keeps getting oil to run the prop, even if the feed pump is blocked or stopped. The governor pump would then draw a modest vacuum on the check valve, unseating it and allowing draw of unfiltered oil from the sump. As a contingency for feed pump failure, this will keep the prop running. Oil in the sump that has been filtered up until the feed pump fails should not be awful, and allow a safe diversion or maybe even return to base. Depending upon how clean the new PSRU filter runs.

 

[pantdino]

At the risk of asking a stupid question, why not just tap into the filtered engine oil? There's already an external line going to the filter and cooler.

You'd have to make sure the engine oil pump was putting out enough pressure and volume to keep the engine lubricated with the added outflow to the governor.

If the engine stopped turning you'd also lose control of the prop, but isn't that how most CS props work?

 

[wsimpso1]

The PSRU is already plumbed from sump to governor to prop and then back to sump. To us engine oil for the prop, you would have to work both a line from engine oil to the governor inlet and a return from the prop to the engine sump. We are already talking about the feed line to the governor. I do not know the details, but I bet you will have to cap off the inlet, drill and tap for AN hardware for the new feed.

Once the oil goes to the prop hub, there is most likely either leakage back to the gearbox sump or a deliberate return path to the gearbox sump or both. That is all fine if you are pumping gearbox oil in a circle.

If you want to use engine oil to run the prop, the return path will have to be made to send oil back to the engine sump. That could be dicey indeed if the gearbox was designed to just sort of splash return oil to the sump, like the insides of most Machines that pressure feed their bearings...

One way that could work is if the gearbox and engine share one oil supply. The gearbox could be rigged to maintain an oil level with a simple overflow at the desired level that flows back to engine sump. This will only be acceptable if they use the same spec oil. If the engine uses one specific engine oil and the gearbox uses a different specific gear oil, then oil sharing will not work.

Billski

 

[AdrianS]

There's also the problem that engine oil sees more contamination from eg blowby than gear oil.

 

[wsimpso1]

There's also the problem that engine oil sees more contamination from eg blowby than gear oil.

Engines have the same sorts of elements that the PSRU and prop have: Bearings, gears, hydraulic actuators, pump, high pressure valves, check valves, regulator valves... The unique item in the Rotax gearbox is the overload clutch - it is sensitive to lead from 100LL, and is fine with unleaded fuels in its specified oils.

For the AutoFlight PSRU, they specified their gear oil for a reason. Yes, there might be an issue with the acids that build up in oil due to blowby in a mingled engine and PSRU oil system - engine oils and all those internal systems work fine with blowby gas conamination just fine - but it could be an issue in the PSRU. I suspect that the big issue is that the engine oil is lower viscosity than the PSRU bearings and gears were intended for...

I would keep the specified gear oil in the gear box, and the specified engine oil in the engine for ALL of the mentioned reasons. Then I would investigate running the governor with filtered and cooled oil from a feed pump with both a pressure limiting return valve and with a low loss check valve for feed pump failure contingencies.

Billski

 

[TXFlyGuy]

We are now running AMSOIL, 75W-110 Severe Gear Oil.
The Titan supplied oil is Valvoline 75W-90.

Because of no filter, we will do changes every 4 hours, after 25 hours the oil changes will be made at 10 hour intervals until 50 hours TT. Then changes every 25 hours.

There is a new history of reports dealing with prop governors failing due to ingestion of gearbox debris.

 

[pantdino]

UPDATE: I have installed a new PSRU and NOT installed the governor or any associated plumbing (which were fully cleaned of debris.) My plan is to ground run it for maybe an hour to get the initial fines out before installing the governor and plumbing. Should I run it for 30 minutes, change the oil, run it another 30 minutes, and then inspect the second fill for fines? If I don't see any fines, does that mean the governor can be installed? If I send it for analysis, how many PPM of iron is "OK"?

I think the development of an electric pump and filter is beyond my abilities.

Would changing the oil every 2 hours be a reasonable alternative?

Thoughts?

Jim

 

[TXFlyGuy]

UPDATE: I have installed a new PSRU and NOT installed the governor or any associated plumbing (which were fully cleaned of debris.) My plan is to ground run it for maybe an hour to get the initial fines out before installing the governor and plumbing. Should I run it for 30 minutes, change the oil, run it another 30 minutes, and then inspect the second fill for fines? If I don't see any fines, does that mean the governor can be installed? If I send it for analysis, how many PPM of iron is "OK"?

I think the development of an electric pump and filter is beyond my abilities.

Would changing the oil every 2 hours be a reasonable alternative?

Thoughts?

Jim

Autoflight New Zealand does not clean their gears, or housings. There will be lots of dust left inside from the machining, as you know.

However, until you run the PSRU with a full load on it (propeller installed), and at high rpm, you will not accomplish much in the way of break-in of the gears. Thus you will not hasten the clean out of the fines and other metal that is inside. Realize that you will continue to "make metal" for a number of hours. How many? I do not know.

When I did my first oil change, the oil was a mild gray color. After letting the oil sit in the drain bucket a couple days, it all settled out to the bottom. It was shocking to my eyes, but it was explained that this is completely normal for a new PSRU.

Yes, I would change the oil at two hour intervals, 3 hours at the most for the first 20 or 25 hours. Oil is relatively inexpensive, especially with an airplane that is costing 200K and up. And send it to Blackstone Labs for analysis.

 

[pantdino]

It seems to me the only rational approach would be to adjust the prop to give enough thrust to fly slowly for a few hours with frequent oil changes to clean out the fines, then install the governor and plumbing. If you install the governor and plumbing initially they will clog with fines and we'll get a runaway prop and I'll have the joy (NOT!) of cleaning out the governor and plumbing again.

 

[TFF]

How are you able to lock the propeller in position?

 

[pantdino]

Autoflight New Zealand does not clean their gears, or housings. There will be lots of dust left inside from the machining, as you know.

However, until you run the PSRU with a full load on it (propeller installed), and at high rpm, you will not accomplish much in the way of break-in of the gears. Thus you will not hasten the clean out of the fines and other metal that is inside. Realize that you will continue to "make metal" for a number of hours. How many? I do not know.

When I did my first oil change, the oil was a mild gray color. After letting the oil sit in the drain bucket a couple days, it all settled out to the bottom. It was shocking to my eyes, but it was explained that this is completely normal for a new PSRU.

Yes, I would change the oil at two hour intervals, 3 hours at the most for the first 20 or 25 hours. Oil is relatively inexpensive, especially with an airplane that is costing 200K and up. And send it to Blackstone Labs for analysis.

But what is the magic number for ppm iron on the Blackstone analysis? How low is "low enough," since you know its not going to be super low like an engine would be.

Was what settled out in the drain bucket, dark fuzz or shiny, visible pieces?

 

[TXFlyGuy]

The metal at the bottom of the bucket was wispy, medium gray (gun barrel gray), not shiny.

Report sent to you via text / email, could not load it here.

 

[pantdino]

The metal at the bottom of the bucket was wispy, medium gray (gun barrel gray), not shiny.

Report sent to you via text / email, could not load it here.

That's very reassuring, even though that's the kind of fine "dark dust" that caused my governor to stick. The metal I see from the old PSRU is thousands of pieces of maybe few thous of an inch, as the photo I sent you.

 

[Toobuilder]

It seems to me the only rational approach would be to adjust the prop to give enough thrust to fly slowly for a few hours with frequent oil changes to clean out the fines, then install the governor and plumbing...

Imagine your "future self" reading this post again - several weeks from now, post crash, from the burn ward of the hospital.

Would this still seem like a "rational approach"?

Considering what is on the line here, I think a "more" rational approach is spending a few hundred bucks on a used 5.3 from a junkyard, an engine test stand from Summit, and run the PSRU on the ground with a test club until you are satisfied it's going to survive for more than a flight or two.

 

[TXFlyGuy]

Imagine your "future self" reading this post again - several weeks from now, post crash, from the burn ward of the hospital.

Would this still seem like a "rational approach"?

Considering what is on the line here, I think a "more" rational approach is spending a few hundred bucks on a used 5.3 from a junkyard, an engine test stand from Summit, and run the PSRU on the ground with a test club until you are satisfied it's going to survive for more than a flight or two.

Or...simply ground run Lady Elaine, with everything installed, until you are satisfied. No need to buy an engine and a test stand when you already have one in house!

Yes, ensure that you have adequate cooling for the engine. Maybe a fan in front of the belly scoop to keep things cool.