Ugh... Random Engine arythmia (rocket)

[Austintatious]

Well, this sucks but I am hoping it may be something simple.

TSIO520 Engine w/500 hours SMOH.... 120 Hrs ago it came out of Continental after a repair in which they put in a new cam, new crank and 2 new cylinders.

Starts great, Runs great, runs cool. Oil looks great, not burning much.  I think around 1 quart per 10-15 hours but I just have not had her long enough to really know.

Recently out of D-max PPI/ annual... he never noticed this and neither did I until the last few flights.

However I have noticed I get periodic "surging" of the power plant, perhaps every 5-10 min.  The RPM will increase by 100 rpm or so, the aircraft feels like it is accelerating in association with the RPM increase.  When I first felt it I had assumed that the RPM was dropping and the acceleration was due to the prop going towards  feather and the energy in the prop was jerking the plane forward.  However when I watched the RPM gauge I see RPM jumping UP.   I had suspected an issue with the prop Governor so I did a bunch of cycles on the CS prop to try to move fresh oil in and any possible air bubbles out.  No change.   FYI, prop has 120 hours since NEW.

This was happening at about 27" MP and 2300 RPM .... I Never noticed it at TO power or climb power settings.

It happens VERY quickly... so fast that Not once was I able to look over in time to see what the gauges were doing.  I basically stared at the damned RPM gauge for 10 straight min waiting for it to happen.  Its a 1/4 to 1/2 second event.

 

Any Ideas?

 

 

Edited September 4, 2019 by Austintatious

[jaylw314]

7 minutes ago, Austintatious said:

Well, this sucks but I am hoping it may be something simple.

TSIO520 Engine w/500 hours SMOH.... 120 Hrs ago it came out of Continental after a repair in which they put in a new cam, new crank and 2 new cylinders.

Starts great, Runs great, runs cool. Oil looks great, not burning much.  I think around 1 quart per 10-15 hours but I just have not had her long enough to really know.

Recently out of D-max PPI/ annual... he never noticed this and neither did I until the last few flights.

However I have noticed I get periodic "surging" of the power plant, perhaps every 5-10 min.  The RPM will increase by 100 rpm or so, the aircraft feels like it is accelerating in association with the RPM increase.  When I first felt it I had assumed that the RPM was dropping and the acceleration was due to the prop going towards  feather and the energy in the prop was jerking the plane forward.  However when I watched the RPM gauge I see RPM jumping UP.   I had suspected an issue with the prop Governor so I did a bunch of cycles on the CS prop to try to move fresh oil in and any possible air bubbles out.  No change.   FYI, prop has 120 hours since NEW.

This was happening at about 27" MP and 2300 RPM .... I Never noticed it at TO power or climb power settings.

 

Any Ideas?

 

 

First, you need to buy a lottery ticket. 

No answer here, but I'd expect the plane to accelerate if the prop moves to fine pitch, right?  The RPM would increase and the motor would produce more power.

I don't think there is enough rotational energy in the prop blade to pull the plane forward if the blades suddenly increase in pitch.  That'd only happen with something big like helicopter rotors.

[Austintatious]

6 minutes ago, jaylw314 said:

First, you need to buy a lottery ticket. 

No answer here, but I'd expect the plane to accelerate if the prop moves to fine pitch, right?  The RPM would increase and the motor would produce more power.

I don't think there is enough rotational energy in the prop blade to pull the plane forward if the blades suddenly increase in pitch.  That'd only happen with something big like helicopter rotors.

Heh,  you would be surprised.  Ever flown a King air?  their reverse is basically the props dumping their rotational energy... Then they slow down and do almost nothing until the turbine spools back up.   If you have a CS prop, you can even get a taste of how much energy is in your rotating prop...  Taxi at 1200 RPM and very briefly pull the prop to feather and push it back in ... a 200 RPM dump will shoot you forward pretty good even at that low speed...

Nonetheless...  I am certainly going to try to figure out what is happening here.  I wasn't very clear (will go edit) but this happens so damned fast you cant even get your eyes on the gauges until it is over... it is a 1/4 second event.  The first time I wasn't even convinced it had really happened, I thought it might have been my imagination.

[kortopates]

Do you have data? if so, post a link.

I looked but couldn't find any. But would suspect a prop governor issue if confirmed in data. 

[takair]

Any idea what oil pressure was doing when this happened?  I know it was fast, but the oil pressure may provide some insight.  

[Austintatious]

19 minutes ago, kortopates said:

Do you have data? if so, post a link.

I looked but couldn't find any. But would suspect a prop governor issue if confirmed in data. 

Sadly no... the information I posted is all I have to go on... a EDM900 is on my Christmas list but I don't have it yet.

 

I found a similar, albeit more exacerbated instance of this symptom on another board.  It turned out to be an intake leak.  I will probably go pull my cowl tomorrow and look around very closely for signs of a leak... see if I can find something coming loose or leaking.

[kortopates]

11 minutes ago, Austintatious said:

Sadly no... the information I posted is all I have to go on... a EDM900 is on my Christmas list but I don't have it yet.

 

I found a similar, albeit more exacerbated instance of this symptom on another board.  It turned out to be an intake leak.  I will probably go pull my cowl tomorrow and look around very closely for signs of a leak... see if I can find something coming loose or leaking.

That's odd, but if a leak we should see MAP fluctuations in your engine data but the RPM should be held stable by your governor even with the MAP fluctuations. You really need that engine monitor soonest! A simple test though for an induction leak is to run at slow idle, a higher than normal MAP at idle and rough idle are good signs of leakage. Some leaks can be problematic to find though - may only vent air as opposed to suck air.  

[Austintatious]

2 minutes ago, kortopates said:

That's odd, but if a leak we should see MAP fluctuations in your engine data but the RPM should be held stable by your governor even with the MAP fluctuations. You really need that engine monitor soonest! A simple test though for an induction leak is to run at slow idle, a higher than normal MAP at idle and rough idle are good signs of leakage. Some leaks can be problematic to find though - may only vent air as opposed to suck air.  

that is a good idea.  I will see what sort of MP I get at low idle.

IF the power level changes too quickly, it can indeed overwhelm the prop Governor.  As I said this change happens really fast.  You are right, I need the engine monitor BAD!

About suck vs blow leaks... I had MY 1983 BMW in a shop to get the AC charged... they pulled a vacuum on the system and it sat for 30 min with NO leakdown... However as soon as they put any pressure, PSHHHHHHH!!  out came the refrigerant. A leak like a 1 way valve!

Edited September 5, 2019 by Austintatious

[gsxrpilot]

3 hours ago, kortopates said:

You really need that engine monitor soonest!

You can't afford NOT to have one. I bought both of my Mooneys with money in the budget before purchase set aside for the engine monitor. Engines are seriously expensive and so I'd like to get the full TBO out of it. Just my $0.02.

[Yetti]

I vote Prop governor.   @Cody Stallings  might provide insight.

[thinwing]

Prop governor 

[Austintatious]

Thanks guys.  Is there anything I can look for on the prop governor or will it be an internal issue?  Is it a matter of rebuilding or replacing? 

[kortopates]

19 minutes ago, Austintatious said:

Thanks guys.  Is there anything I can look for on the prop governor or will it be an internal issue?  Is it a matter of rebuilding or replacing? 

A prop shop can bench test and probably polishing/cleaning the pilot valve will remedy it - that's usually the cause of such fluctuations.

[Cody Stallings]

Sounds like a Gov or the Gov linkage.

[Austintatious]

UPDATE!

Took off the prop governor and took it to a prop shop with my fingers crossed that it would be something simple.  Unfortunately The whole thing was basically seized up and could only be turned with a wrench!   Prop Guy told me if it has siezed and sheared I would have lost all oil pressure to the hub and ended up with a feathered propeller! 

So, this particular Prop gov was overhauled 125 tach hours ago in Dec 2017.   I called the shop who did the overhaul ( I wont name them for now) and they were not very helpful and I did not get the feeling they were going to jump to attention and stand behind their work. 

The Prop guy I am working with remembered a service bulletin where McCauley prop governors that were overhauld during a certain timeframe had been done so with bad bearings... Well, I am smack dead in the middle of that time frame. 

My Next call is to McCauley.... I am pissed... I love flying a glider,  but not when I am in a mooney. 

[kortopates]

Glad you got it resolved soonest! Yep, I never understood why Rocket went with a twin pop/governor on a single, but it is what it is. Thankfully governor failures are rare, but engine oil pressure losses are not in turbo's so good to be aware and to use that soon to be installed engine monitor to help prevent you from being caught up at altitude with low oil pressure. 

[Austintatious]

I wouldn't say this is resolved yet... It is pretty definitive where the problem is  and that it's NOT THE ENGINE (good news!).  However it is not resolved until the aircraft is back into the air.

The McCauley tech rep I spoke with has told me I need to check VERY carefully for any evidence that metal from the prop Governor got into the engine...  So We are talking an oil change, oil filter inspection, oil analysis and scrutiny of the Governor by a McCauley ASF.   If there is metal found, then the shit really hits the fan.  I Will have to try to get McCauley to pay for an inspection/repair as necessary which will result in even more down time....

At this point I have owned the airplane nearly 3 months and it has only been flyable for about a broken up week !   OK, 5 weeks of that was new paint but STILL!

 

Guess I need to pull out the glider to get some air time ( My job doesn't count!   That's just work!)

[kortopates]

31 minutes ago, Austintatious said:

I wouldn't say this is resolved yet...

That was meant as kudos to you for getting to the bottom of this before further flight and finding the issue. We don't always see that. Now its just a matter of time. But in my limited experience, its usually the other way around in that metal contaminants from the engine get into the governor. I thought I recall a metal screen on the gasket for the governor as well that would offer some protection - but that's just my recollection - but odds should be very much in your favor that its clean. But of course wise to verify carefully to be sure. 

[Austintatious]

1 hour ago, kortopates said:

That was meant as kudos to you for getting to the bottom of this before further flight and finding the issue. We don't always see that. Now its just a matter of time. But in my limited experience, its usually the other way around in that metal contaminants from the engine get into the governor. I thought I recall a metal screen on the gasket for the governor as well that would offer some protection - but that's just my recollection - but odds should be very much in your favor that its clean. But of course wise to verify carefully to be sure. 

Well, As I said before, I have been in one accident and I don't want any part of another.  The trouble is I still love to fly!

I don't plan to use this aircraft to risk my life.  If things are not right, I'll be fixing them... If I cant afford to do it right, I will sell the aircraft.  Simple as that.

 

The good news is that the screen you spoke of was clean when it came off the motor... also there is no evidence of metal elsewhere so far.  Still have to chop into the oil filter.

Edited September 6, 2019 by Austintatious

[Yetti]

I think the conventional wisdom is to replace.   Just a bit more than repair, but you might have a warranty claim.  and some emotional issues to work out in the most appropriate way.

[aviatoreb]

6 hours ago, Austintatious said:

UPDATE!

Took off the prop governor and took it to a prop shop with my fingers crossed that it would be something simple.  Unfortunately The whole thing was basically seized up and could only be turned with a wrench!   Prop Guy told me if it has siezed and sheared I would have lost all oil pressure to the hub and ended up with a feathered propeller! 

So, this particular Prop gov was overhauled 125 tach hours ago in Dec 2017.   I called the shop who did the overhaul ( I wont name them for now) and they were not very helpful and I did not get the feeling they were going to jump to attention and stand behind their work. 

The Prop guy I am working with remembered a service bulletin where McCauley prop governors that were overhauld during a certain timeframe had been done so with bad bearings... Well, I am smack dead in the middle of that time frame. 

My Next call is to McCauley.... I am pissed... I love flying a glider,  but not when I am in a mooney. 

When I replaced my McCauley with the MT I have now, I had the option to go with a full feathering prop, but the MT flight engineer strongly recommend I not go with such a prop because he was speaking of just this failure mode where the prop governor could fail on an otherwise perfectly good running engine leading to zero thrust despite the engine running.

I am very glad you found your problem in the shop rather than in the air.

E

[Austintatious]

49 minutes ago, aviatoreb said:

When I replaced my McCauley with the MT I have now, I had the option to go with a full feathering prop, but the MT flight engineer strongly recommend I not go with such a prop because he was speaking of just this failure mode where the prop governor could fail on an otherwise perfectly good running engine leading to zero thrust despite the engine running.

I am very glad you found your problem in the shop rather than in the air.

E

it is a double edged sword.   You might be more safe in the event of oil pressure loss during TO, or a gov failure... however if the engine fails in flight, you wont be able to feather and your glide will be greatly diminished.    18:1 is a hell of a glide ratio.  You can do a lot with that if you are on speed.  I fly gliders, a self launching motor glider to be specific, so I am used to going from a powered Aircraft to glider mode. Coincidentally, my motor glider with the engine deployed and windmilling has a worse glide ratio than the mooney with a feathered prop!

I have also experienced an engine failure with a flattened (un-feathered)  prop dragging me out of the sky.    This is NO FUN AT ALL, believe me.

 

For me, thinking through all the scenarios, I have no issues with the full feathering prop.  At least if the prop gov fails or oil pressure drops, I have a lot of glide capability to either get down to a runway or to pick my crash off field.  It would be interesting to see what is more likely during takeoff phase... An engine failure or a Prop governor failure.

[Austintatious]

1 hour ago, Yetti said:

I think the conventional wisdom is to replace.   Just a bit more than repair, but you might have a warranty claim.  and some emotional issues to work out in the most appropriate way.

ohh, there is no way I will allow that prop governor to be put back in my aircraft. 

[aviatoreb]

8 minutes ago, Austintatious said:

it is a double edged sword.   You might be more safe in the event of oil pressure loss during TO, or a gov failure... however if the engine fails in flight, you wont be able to feather and your glide will be greatly diminished.    18:1 is a hell of a glide ratio.  You can do a lot with that if you are on speed.  I fly gliders, a self launching motor glider to be specific, so I am used to going from a powered Aircraft to glider mode. Coincidentally, my motor glider with the engine deployed and windmilling has a worse glide ratio than the mooney with a feathered prop!

I have also experienced an engine failure with a flattened (un-feathered)  prop dragging me out of the sky.    This is NO FUN AT ALL, believe me.

 

For me, thinking through all the scenarios, I have no issues with the full feathering prop.  At least if the prop gov fails or oil pressure drops, I have a lot of glide capability to either get down to a runway or to pick my crash off field.  It would be interesting to see what is more likely during takeoff phase... An engine failure or a Prop governor failure.

I quite  agree - double edge sword.

I thought long and hard when I made the decision to take that advice.

I decided for me anyway, that the loss of thrust on to, so loss of thrust, would possibly be more serious than loss of power and a shortened more standard glide in cruise, since one is often more immediately vulnerable on take off at low altitude.  But that said, knock on wood, you and I both never need to prove who was right here.

[Austintatious]

3 minutes ago, aviatoreb said:

I quite  agree - double edge sword.

I thought long and hard when I made the decision to take that advice.

I decided for me anyway, that the loss of thrust on to, so loss of thrust, would possibly be more serious than loss of power and a shortened more standard glide in cruise, since one is often more immediately vulnerable on take off at low altitude.  But that said, knock on wood, you and I both never need to prove who was right here.

yea, there isnt a right or wrong.. unfortunately we cant know what sort of failure may be ahead of us... Obviously in some failure modes the full feathering is preferable... In some it is not.

All we can do is know how our machines operate and fly accordingly in a way to mitigate our risk.

Cheers!