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Rudder control cable wear - 200hrs

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  • Rudder control cable wear - 200hrs

    Hi everyone,

    Just a note to encourage you to inspect your rudder cables closely. Mine have failed on condition after 200hrs.

    I have seen considerable wear on all the fairleads in the cabin, and at the aft bulkhead. The plastic fairlead has worn away the steel cable - similar to the wear shown in this picture:


    The wear [as pictured above] is clearly bad enough to fail the cables on condition inspection alone. I will be cutting them out and installing new ones ASAP.

    I did not see similar wear on any other cables at the fairleads.

    My fairleads are the stock-standard aircraft spruce variety. My Bearhawk is the variety which has fairleads at each station inside the cabin (i.e. the fairleads at the back of the back seat are not omitted).

  • #2
    Perhaps some sort of guid pulley arrangement might be worth consideration for those of us in build mode?
    Dave Bottita The Desert Bearhawk
    Project Plans #1299
    N1208 reserved www.facebook.com/desertbearhawk/

    Comment


    • Battson
      Battson commented
      Editing a comment
      My thoughts are that would be over-engineering it. First step is to see if anyone else had the problem, then look for causes.

  • #3
    Over engineering is right in my wheelhouse!
    Dave Bottita The Desert Bearhawk
    Project Plans #1299
    N1208 reserved www.facebook.com/desertbearhawk/

    Comment


    • #4
      How worn is the corresponding fairlead?

      Comment


      • Battson
        Battson commented
        Editing a comment
        The fairlead shows no noticeable wear whatsoever. There is a lot of black oxidised metal on the carpet on either side of the fairlead though.

        As with all things, it is always the softer material which wears away at the harder material.

        I have no idea why this happens on a microscopic level, but leather cable patches on Cubs wearing away at the control cable is a common example.
        Like water wearing away at rock I suppose.
        Last edited by Battson; 08-10-2014, 09:58 PM. Reason: fix typo

    • #5
      You might consider galvanized cable for the replacement. It is supposed to be a bit more durable. How tight and strong are your springs?

      Comment


      • #6
        I have ordered galvinised cable - I hope to see some improvement.
        My rudder springs are quite weak. Of course my feet are always putting the most force on the pedals.

        The wear is quite localised, I wonder if A) my continual rudder adjustments to counteract yaw during turbulence are causing excessively fast wear; or B) the tight cables are vibrating causing. wear.

        Comment


        • #7
          I wonder if you find yourself often pressing on both rudder pedals. The wear certainly seems related to high cable tension.

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          • #8
            I know of one other builder who replaced most of his stainless control cables with galvanized due to undue wear at about the same airframe age.

            Comment


            • #9
              I replaced mine at 500 hrs with the exact wear pattern posted here. I'll be watching them closely.

              Comment


              • Brad Ripp
                Brad Ripp commented
                Editing a comment
                Hi, were the cables replaced at 500 hours stainless or galvanized? Do you know how the looked at the 200 or 300 hour mark? My kit has pre-made stainless cables and I'm trying to decide whether to change them now or later?? I think if I could get a couple hundred hours out of them I'd wait until later. I have plenty enough things to build now. Did you get 500 hours out of stainless?

            • #10
              Battsons original post is 3 years old, but the picture is good. Interesting, I will have to think about it. 304 SS wire loses about 30% of its strength pretty quickly due to internal corrosion. There is also very fast corrosion called "oxygen concentration cell" that corrodes faster than just about anything else. Battsons corrosion looks very localized, like it was not from rubbing on the fairlead, but from "sitting on the fairlead" in the same position for a long time.

              Oxygen concentration cell happens at panel joints, fastners, steel beams entering the water. The different amounts of oxygen over a short distance cause a large potential difference, and corrosion. When you leave the airplane, do you always lock the controls in one position? Centered, aft left, aft right, etc? If that is the case, you cable is touching the fairlead and pulleys at exactly the same place, for most of their life, for years.

              I have looked at the picture a bunch. It looks to me like it is just in one place, from sitting in the same place for too long.

              Comment


              • #11
                Would a drop of oil on the control cable at the pulley/fairlead points be prudent then? Does the use of Galvanized control cable eliminate the oxygen concentration corrosion issue?
                Brooks Cone
                Southeast Michigan
                Patrol #303, Kit build

                Comment


                • #12
                  I get a lot of dust, sand in the carpet. I find that the lubricants on the cable attract grit and lead to increased wear and tear. I try to keep the outside of the cable dry.
                  Float operations would dictate a different approach.

                  By the way. The carpet is pretty good at catching the grit to keep it away from the rest of the aircraft until I can vacuum it up.

                  Comment


                  • #13
                    Originally posted by Bcone1381 View Post
                    Would a drop of oil on the control cable at the pulley/fairlead points be prudent then? Does the use of Galvanized control cable eliminate the oxygen concentration corrosion issue?
                    I am not sure. It might have some other negative benefits.

                    I would say that putting the controls in a slightly different position every time you park it would help. Having the exact same spot on the fairlead or pulley for 7 years might be much more adverse for the cable than 300 hours of flying. Can you remove the cables, and swap them, end to end? You could move the contact point on the cables that way as well.

                    Stainless vs galvanized I don't know. In the marine world you have the option of 304 or 316 SS. The 304 loses a lot of strength in a year or two, I think it was 30% if I remember right. Then the curve flattens out. 316 is 10-15% less strong, but loses little strength over time. It has far less internal corrosion. It is also twice the price.

                    I know synthetic rope is used in some aviation applications. Dyneema, Spectra etc. Is it "legal" for use as control cables? Some have unbelievably low stretch under load (creep). Some high tech sailboats are using them for standing rigging. They have been using them for running rigging (ropes) for decades.

                    Comment


                    • #14
                      Galvanized cable has been shown to last longer. And that has been confirmed by mechanics in the field. Personally - with an item as important as control cables staying "on the reservation" would seem a prudent way to build. Not going beyond FAA approved cables would seem wise. We can do what we want on these experimentals. But sticking with the tried and proven in important areas is good. Mark

                      Comment


                      • #15
                        Mark:
                        Sailboats went away from galvanized probably for cosmetic reasons. The people that own sailboats have more disposable income and would pay extra for "pretty".. They at first went for 304. When they found out 304 sucked, they went to 316. Is 316 SS better than galvanized for 30 lb tension controls cables. I don't have a clue.

                        Staying "on the reservation" I completely agree with. But in todays world, I don't trust my knowledge or ability to do so. Where was the wire made, and by whom? In the last 15 years, we are in a brave new world of "who made this". Galvanized vs stainless was an easy argument 30 years ago, now, there are more variables.


                        Battsons wires to me don't look like they were worn from operating the controls. They look like they were damaged by sitting in one place, under tension, for a long time. Corrosion, creep, a combo of both? Sitting outside, controls in the same position, wind moving the controls a tiny amount, a million times? To my eyes, it is not wear from being operated.

                        My experience overlaps the light plane world, but only maybe 30% My biggest limitation is no experience in this field. But I do have a lot that overlaps in other fields. Battsons' rudder control cable pics don't show friction wear over a pulley or fairlead. They show wear over a very limited area.

                        Probably in the past others have had the same problems. Maybe Bearhawk community just hasn't absorbed that yet. And I don't have a definitive answer. The answer is not that the cables are not big enough.

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