Ovation power loss

[Little Dipper]

Making a long story short.    My Ovation started using up a lot more runway than normal and flying much slower than it used to on the same power settings.    All engine instruments, cht, egt temps etc. operated normally but could feel a vibration at high rpm.   As it turns out I have some sort of blockage in the muffler.    My  A&P estimates blockage at 70%.   This happened gradually over a period of several months.    I never had this happen before  and thought I would share it with the group.  Pictures attached.

Norm

N995K

[KSMooniac]

Flame tubes fail and block the exit area.  Should be a frequent inspection, and on preflight you might want to tap the exhaust tube with a stick or similar and listen for rattles.

[PeterRus]

Could someone elaborate, please?

[Schllc]

3 hours ago, KSMooniac said:

Flame tubes fail and block the exit area.  Should be a frequent inspection, and on preflight you might want to tap the exhaust tube with a stick or similar and listen for rattles.

Do you mean the actual exhaust tubes have collapsed or is this delamination?

[KSMooniac]

A lot of mufflers have perforated tubes inside, not the tubes running down from the cylinders. I don't remember the reason they're present, but they rust and erode and eventually fail. Big enough pieces can break loose and block the exit opening.

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[Fly Boomer]

23 minutes ago, PeterRus said:

Could someone elaborate, please?

Parts inside your muffler can come loose and partially block the exhaust gasses from escaping the engine, which prevents your engine from developing full power.  Someone should stick a borescope or endoscope up there every year during the annual inspection to be sure the muffler is not beginning to disintegrate.

EDIT:  Dang!  @KSMooniac beat me by seconds.

[A64Pilot]

The inside of almost all aircraft mufflers have a tube that is full of holes welded to the exhaust entry of the muffler, the end of this tube is welded shut with a cap, so that all of the exhaust has to go through the holes, sort of a primitive baffle.

‘Anyway these tubes disintegrate pretty often, usually into smaller pieces that just blow out, but occasionally the pieces are big enough to get caught in the exhaust blocking exhaust and causing excessive back pressure.

It’s something that should be checked frequently, easiest way is a borescope, if the muffler is used without the flame tubes often the shell burns through putting CO into the heater shroud and into the cockpit too of course, it can also cause a fire.

‘Sometimes a muffler can be rebuilt and new flame tubes installed

You would be surprised at how many are flying around with burnt out flame tubes and don’t know it, it’s a common failure

 

Edited January 13 by A64Pilot

[Scottknoll]

This is inside the muffler of our Ovation. As I understand some Mooneys don’t have mufflers. I was bored during my first true owner assisted annual this June so I stuck a borescope up the exhaust. IA had already taken the heat shroud off the muffler and there were no cracks. I don’t think it would have been caught, feel lucky we found it.

We used aerospace welding (now a Hartzell company I think) and it was about 3amu and 5 weeks.

Aerospace Welding Minneapolis, Inc.
3344 Highway 149
Eagan, MN. 55121

800-597-4315

Here is a picture from my borescope. They are supposed to be tubes straight through the muffler that have holes in them to dissipate the flame (hence the term flame tube). As they get old and deteriorate they start to warp and block the flow. These were this bad and we still had strong takeoff performance, glad we found it when we did. No record of replacement in ~ 2500 hours.

Also, an additional thought to consider is that we had no rattle. Even after removing the exhaust and muffler there were no loose pieces, just deformed metal inside the muffler potentially blocking flow.

[Scottknoll]

The inside of almost all aircraft mufflers have a tube that is full of holes welded to the exhaust entry of the muffler, the end of this tube is welded shut with a cap, so that all of the exhaust has to go through the holes, sort of a primitive baffle.
‘Anyway these tubes disintegrate pretty often, usually into smaller pieces that just blow out, but occasionally the pieces are big enough to get caught in the exhaust blocking exhaust and causing excessive back pressure.
It’s something that should be checked frequently, easiest way is a borescope, if the muffler is used without the flame tubes often the shell burns through putting CO into the heater shroud and into the cockpit too of course, it can also cause a fire.
‘Sometimes a muffler can be rebuilt and new flame tubes installed
You would be surprised at how many are flying around with burnt out flame tubes and don’t know it, it’s a common failure
 

The Ovation has a cross flow muffler. Cylinders 1/3/5 enter the right side, go straight through the muffler via a tube with holes. That 1/3/5 exhaust then goes out the left side. Opposite for 2/4/6, left to right and out the right side. Perhaps that makes it easier for broken pieces to exit the exhaust.

[Scottknoll]

Another pic after we removed the muffler.

[A64Pilot]

Grumman, but it’s pretty similar on most all small GA. I only watched the first part but think it shows the issues