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Exhaust springs 912 ULS

in 912 / 914 Technical Questions 9 years ago

  • Re: Exhaust springs 912 ULS

    by » 9 years ago

    Just close your eyes and you'll never notice. :lol:

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Exhaust springs 912 ULS

    by » 9 years ago

    I'm no metallurgist but I don't think stainless steel is the best material for a spring. I was told the stainless springs break more frequently than the steel springs.
    We have 320hrs on our springs and they have surface rust but no breakage yet.
    We also use the new lockwire method as recommended by Rotax (see installation manual). As Roger says, don't use too much silicon as it will prevent movement (turn it into a solid plug, rather than a spring)

    exhaustSprings320hrs.jpg (You do not have access to download this file.)
      
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  • Re: Exhaust springs 912 ULS

    by » 9 years ago

    Flight Design uses stainless on their aircraft. I haven't seen any broken ones yet, but have seen standard metal springs break.

    Rob,

    I would bet your springs (stainless or carbon steel) last a long time because you apply them in the proper manner. Stainless steel springs should last. Either spring if installed improperly can fail prematurely. I think we have both seen this many times.


    I do know that stainless has more nickle and chrome in the metal and plain carbon steel has more carbon. The carbon is more susceptible to high heat which can make plain steel more brittle after exposure to some high heat and cooling periods. Filling he springs solid with silicone can cause this. It is cooler when it is surrounded by air flow. This is one reason not to use header exhaust pipe wrap on carbon steel pipes. Stainless doesn't have the carbon content so that doesn't happen.

    I used to work at a chemical plant with lots of extreme temps and pressures. We used lots of stainless.

    Any metal handled wrong i.e. over stretched springs and or over heated springs can have it's life reduced.
    I have tried to get the Vans folks to stop filling the springs full of silicone on the RV12 and just apply a bead on the outside of the spring surface, but to no avail.


    Rob,

    I have a question on the safety wire in your picture. If a spring hook breaks the spring stays on the pipe. What happens if a coil breaks above or below the safety wire. I have seen this happen quite a few times. That half will fall off? I think the wire down the center keeps the spring on no matter what breaks.


    What do you think?

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Exhaust springs 912 ULS

    by » 9 years ago

    you make good points, and you see more in-service aircraft and have a proven system, so I cant disagree with you.
    But/also, the chief engineer from Rotax insisted this new lockwire method was better. After all the endurance testing they did with the 912iS exhaust system I trust his advise.
      
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  • Re: Exhaust springs 912 ULS

    by » 9 years ago

    I would ask the question, why are you lock wiring the exhaust springs?

    If the answer is to prevent them from going somewhere they shouldn't if they break, then surely lock wiring them through the middle is the best way to prevent this.

    I think I can make up my own mind which way is best, no matter who it is that tries to tell me different.

    Do you really believe this bloke from Rotax Rob? I think they need to look hard at their title of "Chief Engineer".

    The world has gone mad.........Mad.........MMMAAAAAADDDDDD!!!!!!!!!!!!!!!!!!!!!!!!

    :-)
      
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