newbie question re prop overspeed with constant speed prop

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pantdino

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I'm curious... how does a non pilot choose to buy a demanding experimental airplane like this?
The idea was to hire a pilot to take off and land and teach me to fly as time went on. Seems that's not going to be an option.

EDIT- I am told the T-51 is not difficult to fly, and looking at it reveals a very thick wing, much like a Hawker Hurricane. It was originally designed to fly like a Cub, and while subsequent weight increases have increased speeds, they still land at 70mph on final and have benign stall characteristics. The insurance company requires 250 hrs tail wheel time for the "open pilot" option.
 
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wsimpso1

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I'm thinking it would be best to install the new gearbox without the governor connected and ground run it until the initial fines are cleared. Then install the governor. Otherwise the governor and associated plumbing are going to get contaminated by the initial fines.

Does that make sense?
Given the nastiness you have gone through with your airplane in ground runs, I would be inclined to mount a boneyard Chevy V8 on a simple stand with a big water tub for cooling, then run the new box and a club for break in. A horse trough of water ought to allow a few minutes at a time and a decent cycle time for cool down.

The thing that is bothering me about all of this, is that in the automotive world, we long ago figured out how to keep the amount of fines down and then capture them on initial run. Gear teeth are ground with a subtle crown to them, all parts are washed before assembly, and the amount of solids generated is small. The engine oil filter is designed to be big enough and with a fine enough mesh to capture troublesome fines from first engine run. And automatic trannies now have four, and five planetaries plus transfer gears and a differential, and they are filled once when built, then final filled at the assembly plant, and we expect them, with the pump, all those gears and shafts and bearings and clutches and control valves to run from zero to over 150,000 miles without the oil ever being touched. None of these are supposed to make much crud, and they do not. And yet you have somehow been made to think that dangerous levels of fines are "normal". In my mind, not if the box has been designed and manufactured to live... Are other folks silting the prop and governor when they use gearboxes from this maker?

Looking the other way, there are bunches of big Allison and Rolls-Royce/Packard engines out there with the same gear sets in them that they were built with in the 1940's. Story is the one part set they just keep on reusing is prop drive gear set - they look over the gears and put them back in. 80 year old engines and the gearsets just soldier on. Now I do not know how they do in the monstrously boosted race engines, but at four times they power, they might be expected to live fast and die young.

With either a partial flow filter or an external pump and filter at maybe 25 micron, what debris is generated ought to have very short residence inside. Yet you are concerned that the box will make enough crud to silt up that great big piston in the prop hub and/or the governor...

Billski
 

TFF

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I know it’s pretty hard to get quality gears at such a low volume. I know of a helicopter company that had issues for about four years. Getting the shape is one thing, getting a company to really have the metallurgy and harness down is quite hard at small volumes. Add to it Aviation lawsuits. The company use to have many auto subcontractors that would work with them, and as they died out when stuff went overseas it got harder and harder to get their stuff in the queue. They had one company that made miracle gears that would last three overhauls. When they disappeared, back to ones that last only one. Easy when you need 100,000. Very hard when you need 50 with guarantees of perfection.
 

Voidhawk9

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My understanding is that it is an Autoflight PSRU, and that the company has a long history of reliable boxes, mostly on Subarus attached to gyroplanes.
I also understand that the unit is modified for use on the T-51s by Titan, and that this is where the problems all start?
 

pantdino

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My understanding is that it is an Autoflight PSRU, and that the company has a long history of reliable boxes, mostly on Subarus attached to gyroplanes.
I also understand that the unit is modified for use on the T-51s by Titan, and that this is where the problems all start?
What the owner of Titan told me is that his parts guy felt he could save a few bucks by buying Chinese bearings rather than the SKF they had been using, and that bearing disintegrated in a dramatic fashion in this gearbox. The back story is that the gearbox was designed for use with a 150hp Subaru engine, and to keep weight down needle bearings were used on the idler gear shaft. When they went to the 245hp Honda engine these bearings began to fail, so they replaced them with roller bearings. This gearbox was manufactured in New Zealand with needle bearings and Titan upgraded it with the ball bearing. Unfortunately, they used a Chinese bearing. The newer gearboxes come from NZ (Autoflight) with roller bearings from the factory, so it is not an issue.
 
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pantdino

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Given the nastiness you have gone through with your airplane in ground runs, I would be inclined to mount a boneyard Chevy V8 on a simple stand with a big water tub for cooling, then run the new box and a club for break in. A horse trough of water ought to allow a few minutes at a time and a decent cycle time for cool down.

The thing that is bothering me about all of this, is that in the automotive world, we long ago figured out how to keep the amount of fines down and then capture them on initial run. Gear teeth are ground with a subtle crown to them, all parts are washed before assembly, and the amount of solids generated is small. The engine oil filter is designed to be big enough and with a fine enough mesh to capture troublesome fines from first engine run. And automatic trannies now have four, and five planetaries plus transfer gears and a differential, and they are filled once when built, then final filled at the assembly plant, and we expect them, with the pump, all those gears and shafts and bearings and clutches and control valves to run from zero to over 150,000 miles without the oil ever being touched. None of these are supposed to make much crud, and they do not. And yet you have somehow been made to think that dangerous levels of fines are "normal". In my mind, not if the box has been designed and manufactured to live... Are other folks silting the prop and governor when they use gearboxes from this maker?

Looking the other way, there are bunches of big Allison and Rolls-Royce/Packard engines out there with the same gear sets in them that they were built with in the 1940's. Story is the one part set they just keep on reusing is prop drive gear set - they look over the gears and put them back in. 80 year old engines and the gearsets just soldier on. Now I do not know how they do in the monstrously boosted race engines, but at four times they power, they might be expected to live fast and die young.

With either a partial flow filter or an external pump and filter at maybe 25 micron, what debris is generated ought to have very short residence inside. Yet you are concerned that the box will make enough crud to silt up that great big piston in the prop hub and/or the governor...

Billski
Autoflight recommends oil changes after 5 hours for a couple of times then stretching them out after that. The huge silting in this case was because of the cheap bearing.

One other owner has trouble with prop overspeeds for unknown reasons. I suspect it is the same problem, but no one knows.

I think this will not be a safe drive unit until an external pump and filter have been designed and added to the system. Without that you're just hoping nothing starts making fines between oil changes.
 
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pantdino

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I know it’s pretty hard to get quality gears at such a low volume. I know of a helicopter company that had issues for about four years. Getting the shape is one thing, getting a company to really have the metallurgy and harness down is quite hard at small volumes. Add to it Aviation lawsuits. The company use to have many auto subcontractors that would work with them, and as they died out when stuff went overseas it got harder and harder to get their stuff in the queue. They had one company that made miracle gears that would last three overhauls. When they disappeared, back to ones that last only one. Easy when you need 100,000. Very hard when you need 50 with guarantees of perfection.
The gearboxes are made by Neil Hintz in New Zealand, and I spoke with him. He requires the gears to be made on German machines and is told by the gear engineer they should be good for, IIRC, 70,000 hrs or something like that at 300 hp and 6000 rpm.
 

pantdino

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Do remember that a lot of pitch even at idle will pull the plane. Landing speed will probably be up due to the plane not able to slow down. Be ready for that. Long takeoffs are possible too with a good bit of pitch; just harder to accelerate form a stop with a lot of pitch. No short runways. Actual numbers are only going to make sense to another T51 owner as there is too many variables.

You can plumb a pump that circulates the oil through a filter and have the discharge oil a gear. I know of a certified helicopter that does that in the higher end version. Essentially an electric fuel pump pushing through a car oil filter.
Do you mean literally that a fuel pump and car oil filter would work, or are you saying it is only similar in concept?
 

TFF

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Electric airplane fuel pump and a filter that cross reference to a MR 2 were on the helicopter. Certified that way. You can probably come up with a different pump as long as it can handle oil. You can also put a cooler in line.
 

wsimpso1

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Autoflight recommends oil changes after 5 hours for a couple of times then stretching them out after that. The huge silting in this case was because of the cheap bearing.

One other owner has trouble with prop overspeeds for unknown reasons. I suspect it is the same problem, but no one knows.

I think this will not be a safe drive unit until an external pump and filter have been designed and added to the system. Without that you're just hoping nothing starts making fines between oil changes.
In most airplane engines, the oil filter is full flow, so only clean oil gets sent to the crank, then the governor and prop. Not so here. So the first hope is the governor pump has excess pressure available so you can divert the flow from the pump through a spin-on oil filter before letting the oil go to the prop hub. This is particularly appropriate if the prop hub is a high gain centrifugal filter. I have no idea if it is really good at that or not, and I have no idea if the governor has excess pressure available. Smells like a pretty big bit of instrumentation to figure out if you have excess pump or not.

Next way is rock simple but a partial flow filter. If the governor has a pressure tap or plug on the high pressure side, you can install a line to a filter and back to sump. It does need an orifice to keep this line from taking all the flow from the prop. If it only sees 10% of the flow at any moment, that means every 10 trips the oil makes through the prop, everything filter size and above gets trapped either in the filter or in the prop hub. Ok, maybe the regulator valves wills till trap some crud too. I do not know what the steady state oil flow while the prop governor is regulating is, but I bet it turns over the sump oil pretty regularly. If this filter removes more debris than the valves and prop hub and debris generation is slow, you may have a winner. .

The last way is to install an electric pump that draws from the sump, pushes oil through a filter, and returns at the nominal oil level. This too is a partial flow system, but even small scavenge pumps will flow a lot of oil through your filter, giving it a decreased opportunity to imbed, pit, or scrape surfaces and make more crud.

The filter should be a cleanable one with a screen of 25 micron or so. If you really want to get thorough, use two in series, one at 50 micron, and then another at 5 or 10 micron. The race car supply houses have a bunch of different sized ones that are low loss, sturdy and work great. Unscrew the caps, examine for fines, clean, reassemble.

With the separate pump, yes, you could add an oil cooler. Do you need one? If your PSRU sump is less than 200 F, it is a waste of money and effort plus more leak paths and failure modes. Above 200 F, and yes, a cooler might be in order. The higher the sump temp, the bigger the cooler needs to be, but with a goodly flow, any crud gets much less chance to imbed or pit or scrape surfaces...

Billski
 

pantdino

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My first thought was to keep the governor and gearbox oils separate by providing a quart-sized reservoir for the governor attached to its input and output sides. But I was told there is no seal between the governor and gearbox, so the leakage past the piston from one to the other would be so great that the quart reservoir would be empty in a very short time and you'd end up with a runaway prop.

The pump at the base of the governor is quite small and I doubt it would generate enough volume to maintain pressure if some were bled off.

My current plan is to keep the "damaged" gearbox as a "ground operation only" unit on which I can experiment with an electric pump and filter and keep the new one intact for possible future use once I get a system designed.
 

Dan Thomas

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The governor's pump raises the pressure to around 300 psi. Spin-on filters aren't designed for that. The oil should be filtered before it gets anywhere near the governor.
 

wsimpso1

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My first thought was to keep the governor and gearbox oils separate by providing a quart-sized reservoir for the governor attached to its input and output sides. But I was told there is no seal between the governor and gearbox, so the leakage past the piston from one to the other would be so great that the quart reservoir would be empty in a very short time and you'd end up with a runaway prop.

The pump at the base of the governor is quite small and I doubt it would generate enough volume to maintain pressure if some were bled off.

My current plan is to keep the "damaged" gearbox as a "ground operation only" unit on which I can experiment with an electric pump and filter and keep the new one intact for possible future use once I get a system designed.
Another way is to use an electric scavenge pump sized for more flow than the governor pump, pick up oil from the sump, push it through the filter, cooler if you need it, a pressure relief valve that dumps to the sump, then feeds the governor clean cooled oil.

A failsafe would be to have a check valve in the line between the governor pickup and the sump - when the scavenge pump is running, the check valve is seated. When the electric scavenge pump shuts down, the governor pump will pull a vacuum on oil in the line, pop the check valve, and draw direct from the sump.

If you still have any reason to believe that the PSRU is going to make metal, you would also need an alarm for scavenge pump failure, and treat it as a "diversion mandatory" event. If the PSRU proves reliable and does not make metal at any real rate, you might be ok returning home on the standby system instead of taking an "any port in a storm" approach and then having to repair it away from home.

Billski
 
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pantdino

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How about a pump that draws oil from the bottom of the sump, pushes it thru a filter, and dumps it back into the sump? If it were high enough capacity, it would keep all the oil clean. If it stops working you lose the cleaning action but it wouldn't affect governor function
 

wsimpso1

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How about a pump that draws oil from the bottom of the sump, pushes it thru a filter, and dumps it back into the sump? If it were high enough capacity, it would keep all the oil clean. If it stops working you lose the cleaning action but it wouldn't affect governor function
I mentioned that in post 71. The issue with it is that it is a partial flow filter, dirty oil keeps going to parts to be captured by the governor and/or the prop, you still contaminate the bearings, gears, etc and you still silt up the governor and prop hub, just slower...

If instead oil goes from the pump through the filter, then is the feed to the governor, if anything makes debris, it comes out before it goes to the governor... the sensitive stuff is protected, and scavenge pumps are designed to pass everything.

Billski
 

Toobuilder

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Fortunately, for some men of a certain age the fact that this plane looks and sounds great provides plenty of motivation to keep working on the project.
There is NO aviation experience thats worth dying for, however.

I own a well proven, easy to fly military jet. Its sitting 50 feet from me as I type this and full of gas and ready to fly. I have a 99.9% expectation that I could takeoff, fly and land the airplane today, right now, without injury, damage or drama.

But that .1% just isn't worth it to me.
 

pantdino

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There is NO aviation experience thats worth dying for, however.

I own a well proven, easy to fly military jet. Its sitting 50 feet from me as I type this and full of gas and ready to fly. I have a 99.9% expectation that I could takeoff, fly and land the airplane today, right now, without injury, damage or drama.

But that .1% just isn't worth it to me.
I agree. I think the plane needs a filtering system and a new gearbox which hasn't been messed up by Titan. Not flying until then.
 

pantdino

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What about this oil pump? The only problem I see is their requirement that the gear oil be brought up to at least 104F before the pump is turned on, which would not be ideal in this application. You'd have to remember to turn it on at some point, depending on air temp.

 

TFF

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Turning pump on just becomes part of the pilot checklist. Easily added to run up tasks. In flight, you are scanning gauges and hopefully actually reading them so when a gauge says time, flip the switch. The pilot being the thermostat is not that hard.
 

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