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newbie question re prop overspeed with constant speed prop

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pantdino

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The governor on my Titan T-51 seems to be a definite weak point, probably because it shares oil with the gearbox and gets gummed up with metal dust.

Anyway, my tentative solution is to treat it like a ground adjustable prop and set the pitch at a midpoint pitch.
My question is whether my thinking is correct, that being IF I reinstall the governor, the fastest I should fly is the speed at which the prop will not overspeed if it suddenly reverts to fine pitch.

In that situation the governor will just be to allow lower rpm and thus less fuel consumption while it is working. When it fails I'll just have to slow down.

Does this make sense? I'm new to aviation so I'm likely missing something.

Thanks
Jim
 

Twodeaddogs

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first thing to do is sort out the metal dust,ie, deal with the oil filtration. You might need to fit a magnetic chip detector. After that,set the maximum static RPM on the ground.
 

pantdino

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Several people have tried to figure out a way to eliminate the metal dust, and it seems there is no way to.
There is no oil pump except at the base of the governor, so no way to have a proper filter

The fines causing the problem are the very fine dust. The screen was clean despite the governor piston being stuck.

I'm thinking determining the proper fixed pitch setting will involve some documentation of climb rate and max speed to determine the best compromise. The current suggestion is to set the minimum pitch to get 14-16" MAP at 1800-2000 engine rpm at full throttle, which is about 125hp. More power than that and the brakes can't hold the plane. Prop redline would be 4750 engine rpm, but the gearbox can only handle 300 hp, which occurs at 4000 rpm..
 

TFF

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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.
 

wsimpso1

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Scary stuff pantdino.

The airplane has been telling you that the gearbox is going to fail, and you have not been listening. Gearboxes are not supposed to make crud... and if they do make crud, there is supposed to be a filter to take the crud out of circulation so it will run long enough to get on the ground before it fails completely. How do I know? 22 years in automatic transmission design. You are not supposed to see stuff in the oil and you are not supposed to silt up the pump, regulator valves, and pistons.

How do you know the gearbox is making crud? See it on the dipstick? See it in the filter? Does it have a filter? Does it silt up the regulator valve and piston?

If it is making crud, I would ground that bird. If your gearbox is making crud that is sticking your prop governor, I would then get the gearbox torn down and fixed. While the gearbox is getting fixed, I would send the the prop and governor out for teardown, clean, inspect, and put back together clean and proper.

I do not know what kind of governor and prop you have, but the option of flying the airplane with the prop misbehaving is scary. Airplanes get wrecked and people get hurt or killed. All three failure modes make your workload really high and can distract you from other flying duties, which can be deadly. With the stops properly set, it should be flyable even if it goes to a stop. Had you confirmed that during your testing? Make sure it is set up correctly so that it will remain flyable when it comes back on line.

Hopefully somebody who knows more about these props and gearboxes will come on and provide more guidance.

Billski
 

wsimpso1

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Pantdino,

Are you saying other folks have this problem too? How do they handle it? Oil changes?

This all sounds like normalization of deviance to me.

Billski
 

proppastie

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I was in an airplane that the governor failed, the prop went to 3600 rpm in a second, and the pilot did/could not get it below 3000 rpm as we circled to land......somewhere on this site there is a picture of the melted aluminum flywheel. In order to set the mechanical stops of the hub to do what You want to do I think you would have to remove the governor and do lots of test flights as the pitch/rpm static on the ground is much different than in the air..... The stops on the prop hub of my Mooney are set for the ground until the governor starts to work, pressure comes up with rpm.....in the air those stops are way over the redline point....at least that is how I think it works, and how it worked with the failed governor plane I was in.
 
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proppastie

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my Lycoming manual says if you have chips/metal in the screen of the governor the engine needs overhaul because the metal is getting to the bearings of the engine.....in your case it is getting to the bearings of the gear box
 

rv7charlie

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Please forgive the slightly off-topic request, but could you tell me what engine/gearbox we're discussing? Which mfgr (other than an old Lyc) pump oil into the engine without any filtration between the pump and engine?

Thanks,

Charlie
 

pantdino

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This is a continuation of this thread:


I had previously been told the metal debris in the gearbox was generated by the idler shaft bearing being installed 15 thou off center, but it turns out that mechanic was just making that up and in fact had not even opened up the gearbox. (!!!!)

It was taken back to the factory, where they found the metal was from a cheap Chinese bearing they had installed. They cleaned out the gearbox (sort of) and replaced the bearing with an SKK / good quality one. I reinstalled the gearbox and prop and after about 20 minutes of flying around the pattern the engine revved to 4000 rpm and the pilot landed the plane. I drained the oil and it had metal dust in it. My guess is the metal dust wasn't cleaned out very well at the factory, so it became suspended again and stuck the governor. (Upon disassembly there was no visible debris but the piston wouldn't move until I manipulated it a bit.)

My plan is to fill the gearbox, run it for 1-2 minutes, then immediately dump the oil to get any resuspended debris out. Then do that 10 times. Then send the last fill for analysis.

The factory sold me a new gearbox at a reduced price, but I want to see if this one is OK now that the bad bearing has been replaced.

An auxiliary oil pump and filter is probably the only real solution for this, but in the meantime hopefully I can fly a bit with a fixed prop. I'm thinking an airplane with a TOW of 1850 lb and 300 hp doesn't really NEED a constant speed prop to fly. But I'm a newbie, so what do I know.
 

pantdino

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Please forgive the slightly off-topic request, but could you tell me what engine/gearbox we're discussing? Which mfgr (other than an old Lyc) pump oil into the engine without any filtration between the pump and engine?

Thanks,

Charlie
This is a GM LS3 430 hp V8 and an Autoflight gearbox made in New Zealand. The governor shares oil with this and not the engine.
 

pantdino

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I was in an airplane that the governor failed, the prop went to 3600 rpm in a second, and the pilot did/could not get it below 3000 rpm as we circled to land......somewhere on this site there is a picture of the melted aluminum flywheel. In order to set the mechanical stops of the hub to do what You want to do I think you would have to remove the governor and do lots of test flights as the pitch/rpm static on the ground is much different than in the air..... The stops on the prop hub of my Mooney are set for the ground until the governor starts to work, pressure comes up with rpm.....in the air those stops are way over the redline point....at least that is how I think it works, and how it worked with the failed governor plane I was in.
It is my plan to fly with different pitches to see what gives adequate takeoff and climb power and hopefully reasonable cruise speed. The pilot with the prop set as I describe (static 1800-2000 rpm and 14-16"MAP) sees 2500-3000 fpm climb, but I don't know what cruise speed that would give
 

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.
As the plane flew from Ohio to California the fine pitch setting only generated 11" MAP at 1800 rpm. When viewed from the side the spinning prop was very thin indeed.
 

Toobuilder

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Not going to comment on the wisdom of flying a gearbox that's making metal or a governor that's so contaminated that it does not function. But stopping a prop overspeed at cruise airspeed means the mechanical low pitch stop (in the prop hub) has to be adjusted so that the lowest pitch possible is the same one used for normal cruise airspeed. And that is going to be very coarse indeed. TO and climb performance is going to suffer greatly, and the approach and landing behavior will be quite different. In this case, the governor will not be doing any "governing" at all.
 

pantdino

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Not going to comment on the wisdom of flying a gearbox that's making metal or a governor that's so contaminated that it does not function. But stopping a prop overspeed at cruise airspeed means the mechanical low pitch stop (in the prop hub) has to be adjusted so that the lowest pitch possible is the same one used for normal cruise airspeed. And that is going to be very coarse indeed. TO and climb performance is going to suffer greatly, and the approach and landing behavior will be quite different. In this case, the governor will not be doing any "governing" at all.
My working hypothesis is that the gearbox MADE metal because an inferior quality bearing was used. That bearing has now been replaced, so it is no longer MAKING metal. And the governor WAS non-functional, but now has been cleaned up and removed, so it is moot.

I don't really care about cruise speed. My airport is only 6-10 miles from my practice areas, so it really doesn't matter. I just want to be able to fly without prop problems and subsequent months of grounding the airplane.
 

Twodeaddogs

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Im not sure the notion of running an engine and gearbox ten times for very limited periods is a good one. The combination is not getting up to it's normal operating temperature/thermal growth. You'd need to run them for at leats enough time to get the temperatures settled down. So the least you are looking at is 15-20 minutes continuous. If you are continuing to get metal dust, especially visible dust, you need to stop operating that combination. It may not be a bearing that's shedding metal, possibly two surfaces fretting off each other.
 

Dana

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If there are metal particles in the oil, you need to disassemble the gearbox, find out why, thoroughly clean it, and reassemble. Running it and changing the oil multiple times and hoping the problem goes away is not the way to fix it.

Flying a familiar airplane with a known minor mechanical issue that you understand (and understand the ramifications of) is one thing, flying a new airplane with a significant problem that you don't understand is a really bad idea.
 

proppastie

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any competent mechanic aircraft or automotive should be able to remove the cowl, prop, and gearbox , take it apart, inspect and clean....from your other thread, I can not remember weather you have given up on Titan or not, but it does appear you hire out these services rather than doing it yourself. See if there is a decent race car mechanic in your area, around my home there are very few professional aircraft mechanics
 

rv6ejguy

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You need a magnetic drain plug in the gearbox. Look at that after every (short) flight, or better yet, just run it hard on the ground for a couple hours. If you keep seeing a lot of metal fuzz on it after cleaning each time and changing the oil, ground the airplane and find out why the gearbox is making so much metal. A new GB may make some fine fuzz for the first few hours but it should get less and less over time, not more. The magnet will only catch ferrous material of course. If there is a lot of shiny stuff still in the oil, could be aluminum which means something is seriously wrong as this shouldn't be wearing in a proper GB design.

You are asking for a forced landing either through GB failure or prop runaway if you ignore the core problem here.
 
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Toobuilder

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My working hypothesis is that the gearbox MADE metal because an inferior quality bearing was used. That bearing has now been replaced, so it is no longer MAKING metal. And the governor WAS non-functional, but now has been cleaned up and removed, so it is moot.

I don't really care about cruise speed. My airport is only 6-10 miles from my practice areas, so it really doesn't matter. I just want to be able to fly without prop problems and subsequent months of grounding the airplane.

I guess im more confused now than before. You have removed/disabled a major component/function of the powerplant (the CS prop functionality) from a high HP, complex airplane because you are willing to limp over to the practice area at pattern speed? Frankly, thats like leaving the gear down on a Bonanza to fly to a pacake breakfast at a nearby airport.

Is this a troublshooting scheme or your "new normal"? If the gearbox is "fixed", then have the governor inspected and reinstall. If you are NOT SURE if the gearbox is fixed - BE SURE before you fly again. And finally, if you do for some crazy reason want to fly with a hobbled propeller system, then the low pitch stop will have to be set to match the maximum speed you DO intend to fly, and then RPM overspeed control is on you - the throtle and airspeed.
 
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