broken rotax muffler spring

[Gfeldman]

Hi all,

Preflight inspection of my Phoenix revealed a broken muffler spring (see below). I have ordered replacements from California Power Systems.

George Feldman N33GF

 

 

 

[No longer active on TMGA]

Hi George,

A few questions:

• Do you have any idea of why it broke?
• Where did it break?
• Do the other springs show any sign of distress?
• How many hours on the engine?
• How did you discover it?
• Are you going to replace all the springs, just in case?

Maybe each of us should carry a few springs as spares. What was the part number you used to order it?

[Gfeldman]

17 minutes ago, Eric Greenwell said:

Hi George,

A few questions:

• Do you have any idea of why it broke?
• Where did it break?
• Do the other springs show any sign of distress?
• How many hours on the engine?
• How did you discover it?
• Are you going to replace all the springs, just in case?

Maybe each of us should carry a few springs as spares. What was the part number you used to order it?

Hi Eric

Great questions.

1) Not sure why it broke. The classic answer is too much vibration or too much tension. Other springs look fine so it could have been an accumulation of stress at one point along the length of the wire.

2) 2/3-3/4 from one end

3) other springs look fine

4) about 130 hours

5) I was doing a preflight of the engine with the muffler caused fire in the Sinus motorglider that was on the cover of this months Soaring magazine on my mind.

6) I have ordered extra springs just in case but I have no plans to replace the others. Just go to the CPS website and look for rotax 912 muffler.

Hope this helps

George

[No longer active on TMGA]

That sounds like it was a defective spring to last only 130 hours. I have 650 hours, springs look fine; nonetheless, I'll order some springs and carry them - an easy fix, even while traveling somewhere.

[Jim Lee]

Broken muffler springs are very common on the Rotax engines.  In pusher configurations, the springs are safety wired to keep a broken spring out of the prop.  I'm surprised that this is the only one on a Phoenix, to my knowledge.  Might be because of a good exhaust system design, the composite structure and/or the lightweight Woodcomp prop.  In any case, the vibration in the Phoenix is less than other LSA's, maybe that is the difference.

[tim wilson]

On 12/1/2019 at 10:46 PM, Jim Lee said:

Broken muffler springs are very common on the Rotax engines.  In pusher configurations, the springs are safety wired to keep a broken spring out of the prop.  I'm surprised that this is the only one on a Phoenix, to my knowledge.  Might be because of a good exhaust system design, the composite structure and/or the lightweight Woodcomp prop.  In any case, the vibration in the Phoenix is less than other LSA's, maybe that is the difference.

Jim, is there not an SI from Rotax that shows adding a bead of RTV (high temp silicone) longitudinally along the outer portion of the spring (in conjunction with the safety wire)?  The RTV dampens harmonic oscillations at certain engine RPM's that promote brittle fracture of the spring material.  Just a thought this may assist.

[Gfeldman]

I have had all my muffler springs safety wired.

george feldman

[Doug Levy]

I had one of my muffler springs break.  I've now added silicon RTV to the springs after replacing that one.  I carry a couple of them in my tool kit in the Phoenix.  Something to look for while doing each pre- flight. 

If you are doing a five year rubber hose change it might be a good time to replace them as you will be removing the muffler. 

[Gfeldman]

I think it’s also a good idea to safety wire them in place.

George Feldman

[No longer active on TMGA]

32 minutes ago, Gfeldman said:

I think it’s also a good idea to safety wire them in place.

George Feldman

Is that to keep the pieces from falling off? Or is the safety wire intended to hold the pipes together, even if they then leak a bit?

[Gfeldman]

Hi Eric,

Both. A few years ago a Rotax powered Sinus motorglider was destroyed in North Palm Beach County airport because I think of a muffler induced fire due to broken springs.

George