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Roger Lee

Header Wrap pictures

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Nice pictures Roger and timely, I have just removed my muffler as part of my 5-yr rubber replacement.  But I don't understand the rational for the RTV on the springs, mine had none when I removed them.  Enlighten me.

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Nice pictures Roger and timely, I have just removed my muffler as part of my 5-yr rubber replacement.  But I don't understand the rational for the RTV on the springs, mine had none when I removed them.  Enlighten me.

 

It serves as a dampener to prevent vibration of the spring. This will help the springs to not wear as fast.

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Wrapping the pipes also means the pipes get very hot. On another aeroplane I used to own that I wrapped the pipes I had an inflight exhaust failure. Lots of noise and easy to work out the problem but I didn't know where the break was, Exhaust flame going some place it may cause a fire so I shut it down and carried out a forced landing. Further metallurgical examination indicated excessive heat induced fatigue caused the breakage at the flange (just after). This diagnosis cannot be confirmed but I removed the wrap anyway. As a side note I noticed pitting where the wrap was. This happened after about 500hrs after I wrapped the pipes. I would be interested to know if others have had a problem with this. I am not criticising wrapping because it helps with noise and under cowl temps. but there may be unintended outcomes after a while. Please add your thoughts.   

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I've wrapped probably 80+ Rotax pipes in my time and know many who have done their own. None have had failures. If the pipes on any aircraft are not a good grade of stainless steel (18 different grades of stainless)  and have too much iron the heat can be a factor called carbonization. Stainless has less iron and more nickel and chromium.  I have seen a few dozen breaks over the years.

The next cause of failure is poor installation technique. Mainly over wrapping. If using 2" wide wrap it should only wrap over each preceding edge by 3/8". If you over wrapped 1" then this does cause heat retention. Most causes of a Rotax pipe failure or any other pipe failure is either poor stress relief during the weld process, poor alignment  during installation and pulling a pipe to make it fit, failing to lube the two end joints, over wrapping. Last, but by no means least is vibration. Things like poor gearbox maint. and lack of or poor carb sync even failure to change rubber engine mounts or poor prop balance increases vibration you have no idea is going on in the cockpit.  Wrapping header pipe goes back decades. racers use it to keep exhaust hot out the exhaust to keep it from cooling and causing back pressure and a small loss in HP. It also keeps close proximity areas from too much radiated and convected heat and is the main reason we use it. Wrap Mfg's claim up to a 70% change in heat. I don't always believe mfg's, but even a 50% is good. Our exhaust pipes can handle well in excess of the Rotax max EGT temp of 1616F. Most of us run anywhere from 1250F-1475F and it is only for about 15" of pipe.

 

Most of the Rotax cracked pipes I have seen over 20 years have all been bare with no wrap.

 

Ask Andy. 

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Most of the Rotax cracked pipes I have seen over 20 years have all been bare with no wrap.

 

Ask Andy.

 

It's true that my pipe did have a complete failure, and it was unwrapped. But it failed right at the weld, and looking at the other pipes the welds are not great. I don't think the lack of wrap caused the failure, but vibration probably did. I think wrap helps longevity of under cowl components like ignition modules and rubber hoses and seals, but I'm not sure it protects the pipes themselves.

 

I think if I had wrapped the pipe would have still failed. But I do plan to wrap at my next annual to keep under cowl heat down.

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Roger I think you are correct on the stainless steel with higher nickel content it will be more temperature tolerant. The pipe that broke on me was mild steel with about 0.35% carbon content, this is not poor quality steel but not suitable for higher temps.

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