Hole in muffler

[tennesseect]

My 07 CTsw slowly got noisier over the past few months and then got real loud.  When I opened the cowling I found a chunk of metal - about 2" X 6" - missing from the front right of the muffler.  My wife and I flew it 40 miles home.  There were no abnormal instrument readings other than a somewhat lower than normal left cylinder head temp.

Is this normal wear and tear?  Do I just replace the muffler or is there something else I should check?

[Anticept]

You need to fix that as soon as possible, it is a fire hazard. The muffler also drives a certain back pressure into the exhaust of the engine; without it you lose fuel economy and increase wear on the valves. *

 

Also, have someone look at the muffler to make sure there's nothing else wrong with it. I don't know if CTs have internal baffles to help with the back pressure tuning; if they do, it can block the exhaust and exacerbate the problems.

 

* Explaination: Engines are tuned to have a certain amount of "valve overlap," which is the time between the exhaust and intake strokes that both valves are open. The reason is as follows: the exhaust valve is open throughout the exhaust stroke, the intake valve opens right at the end of said stroke. This means there is inertia of the exhaust gasses leaving the exhaust port, and high pressure at the intake. Exhaust ports are also smaller than the intake port, and Bernoulli's principle takes effect. The intake port air is at a higher pressure, and the exhaust port air is at a higher velocity. Coupled with the fact there is already inertia carrying the exhaust gases out, this allows some of the intake air to further purge the combustion chamber of exhaust gasses, and help with cooling. With no back pressure, the cooling effect is amplified, and you lose a lot more intake air (which means more fuel goes out the exhaust too in carb engines). This is where the efficiency part comes from.

 

Valves, without back pressure, can slam into their seat, increasing wear. That's why it's bad for valves to have no back pressure.

[FastEddieB]

I agree with Anticept - that plane should have been grounded.

 

Not only a fire hazard, but carbon monoxide poisoning hazard as well.

 

Must be fixed before further flight, via repair or replacement.

[Tom Baker]

Roger, I know there is a part number in the CTSW parts manual for the muffler and piping, but  do you know if it is a Flight Design only part or a standard Rotax part? I have ask Ted to send me pictures to figure out what is going on.

[Jacques]

the muffler alone  [ # 973674 ] is MORE expensive than the 'kit' [ # 973676 ] which includ the muffler

 

kit 973676 is ~$300 less

[mocfly]

It would be nice if the pictures could be posted so we can see the failure, Seems very odd. 

[FastEddieB]

Agreed.

 

If we're talking a chunk out of the muffler shroud, that's completely different.

[Anticept]

It makes no sense if it's the shroud. tennesseect said it was getting louder and louder, missing a piece of the shroud doesn't do that.

[FastEddieB]

True. I forgot that part.

 

A hole in a muffler would ground me in a heartbeat.

[Tom Baker]

He sent me a picture in a text. The hole is in the muffler. It looks to originate at the tail pipe and go forward towards the heat shroud.

[tennesseect]

I have attempted to attach a picture I took today of my muffler.  I hope it is visible.

[FastEddieB]

Again, this is important.

 

You should not have flown the plane in that condition.

 

Glad it worked out for you, but exhaust problems like this can and have killed lots of pilots.

[Anticept]

You might have baked your cowling. Have a mechanic look at it too. Can you take a few pictures of the inside of the bottom half?

[mocfly]

WOW!

I'm off to the hangar in the am to check that area.

[sandpiper]

The welds in the muffler need to be looked at every time the cowl is off and for sure at annual. I posted here a couple of years ago that I had a weld go bad. I had it welded immediately not wanting the crack to get worse.