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Rudder control cable wear - 200hrs

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  • #16
    At the other end of aviation, this is how you mitigate risk:

    Identify the problem. What caused it? You want to keep the airplanes flying, so you don't ground the fleet. You come up with a temporary fix? Just a guess. Put a control lock that positions the control cables slightly differently.

    While you do that, you come up with a material solution that brings you back to what the original design intentions commanded.

    You set a timetable for all affected aircraft to comply with the new requirement.

    Maybe easier, ask your local A&P or EAA rep, and buy him a beer.


    • #17
      Battson's plane was only a couple years old when he replaced the cables and is stored indoors.

      My SWAG is tension from both feet on the pedals and vibration durning straight and level flight.

      If I recall correctly another BH had this same issue at about the same number of hours and has put 800hrs on galvanized cables without issue.
      I'm a Tapatalk user so I can't see your "comment"


      • #18
        Originally posted by svyolo View Post
        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.
        No need for guesses....

        This wear was caused by the steel cable rubbing against the plastic. Put simply, the plastic is polishing the steel smooth.

        We can say for sure that creep and corrosion have nothing to do with it. Creep is just the metal changing shape, almost always requiring very high temperatures. The plane has been parked in a hangar when not in use, and external control locks are applied when it sits outside. Nothing to do with weather.

        This damage was almost certainly caused by the tight cable vibrating against the fairlead while the controls are centred, combined with the rubbing action of the controls moving. When I found it, the cable was a lot more oily and covered with powdered metal from the wear, not as pictured. The cable is resting against the fairlead with moderate pressure, and vibrating rapidly, causing the two surfaces to rub together rapidly. Either microcutting or friction, I can't say which. This high cycle wear is causing the plastic to very gradually erode the steel, because of the difference in hardness.

        There was more wear further along the cable too, over a larger area, the photo only represents the worst of the damage.

        I've seen the same wear pattern on stainless cable at the fairleads in the wing root. Albeit slower wear, that has taken 500 hours to start wearing out.
        Last edited by Battson; 11-09-2017, 04:34 PM.


        • #19
          Hi all. Interesting read.

          I have seen this wear on cables so many times on other aircraft I have worked on. In particular big propeller driven aircraft. Galvanised cables are superior and currently are still lasting longer than stainless steel installations.

          The majority of this forum has identified the cause of this accelerated wear however, my inspections of cables such as battsons show high frequency wear caused by the propeller. The prop is a massive frequency generator and that sets up a harmonic hum with tension control cables which act like a guitar sting vibrating. When the aircraft is in cruise and flight controls trimmed straight and level, cables that are close to propeller or within the dynamic range of the blade tips will vibrate like crazy, especially around fairleads causing undue wear. My company had enough evidence to force the aircraft O. E. M to raise a service bulletin to reduce the life limitation on the aileron control system we where working on. To support this we also changed the Entire fleet to modified galvanise cables. This also forced the O. E. M to change there design of cable material. On average we saw cables lasting 200 - 300 hours reaching over 1000 hours. Very big change.

          Another fix for the issue is to install cable support pullies that reduce cable vibration. However this sets up another place for friction wear.

          All the best
          Plane Torque Ltd


          • Mark Goldberg
            Mark Goldberg commented
            Editing a comment
            Welcome to the forum Nic. Nic is putting together a Bearhawk LSA on the North Island of New Zealand. Mark

        • #20
          Those vibrations are also tensile events that are cyclically loading whatever they are attached to. Sort of like flutter, but the control surface isn't causing the flutter, it is being "fluttered" by the vibrations in the wires. Have you seen any adverse effects in the control surfaces whose wires were affected by rapid wear?


          • #21
            I think both points of frequency vibration and a continued static resting point under tension sound very probable. And it sounds like Plane Torque has a bunch of experience leaning towards the frequency vibration issue, and I'd place my bet there. I would think an easy way to prove the biggest culprit would be to see which of 3 positions have the most wear. I'm thinking 1.) The resting position. As mentioned, probably sits on the ground the same way most times?? 2.) Control surface position in straight and level (which would be the most used position under frequency) and 3.) The position at the highest amount of pressure applied to the cable (i.e. climb out adverse yaw via rudder or up elevator in climb.) I believe Jared said that his wear was on the elevator cables. I'm saying all this because I'd really like to know if anyone who has or will have this problem can report on what control surface position the wear is in. If frequency is the culprit, I'd have to think that the middle of any run allows for the most flex and that is where the movement is occurring most. And if that is the case, would dampening at that point be the answer? And I guess we can throw in tension? If the continual resting place is the issue, then heavy tension would aggravate it. If frequency is the issue, then would a lighter tension be the culprit? I'm sorry to beat on this horse, but I have a brand new set of pre-made SS control cables installed in the 4 place project I bought and am working on now and I'm not wanting to change "just in case", but will certainly watch them like a hawk. There has to be something else in this equation considering Mark reported many many more hours on a set of SS cables. My first guess would be prop or engine? Any smoother 3 blade prop planes getting less wear than a 2 blade maybe?? Someone please help me rationalize not buying and remaking all those cables.


            • #22
              Hi Brad

              I recommend you don’t make/purchase another set of cables just yet. All cables will wear, some more than others. My experience has shown me Stainless cables have a harder surface which seems to wear at a faster rate than galvanised. Which is odd when plastic fairleads are softer than stainless.

              All aircraft seem to have their little details and maintenance issues however, make a special inspection note during routine servicing to monitor your cables wear. Anything inspected outside of serviceable limits should be rectified.

              All the best Plane Torque.