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Rudder control cable wear - 200hrs

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  • Battson
    started a topic Rudder control cable wear - 200hrs

    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).

  • Bdflies
    replied
    Good point Battson. I can't speculate about whether the tubing sleeve would cause cable wear. I'm thinking that the tubing would act as a 'protective sleeve', because it would be tightly wrapped around the cable, in intimate contact, thus eliminating the high frequency impacts of the cable in the fairlead. The nylon tube/sleeve might impact the fairlead, though. To inspect the cable, one would snip off the safety wire clamps and slide the sleeve away from the protected area. If all looks good, return the sleeve to it's protective position and wire it back on.

    Would this "prophylactic device" eliminate cable wear? I don't know. Would the nylon tube sleeve experience wear in the fairlead? I don't know.
    Discussion of this phenomenon has me closely watching my cables. Only 55 hrs on the Patrol and I can see "polishing" of the cables through the fairleads. I'm also seeing black residue in the fairleads. Nothing scary at all, but I'm seeing some evidence of the phenomenon. Other than replacing every fairlead with a pulley assembly, I don't have a clue how to eliminate the wear. Don't even know if pulleys would be any better. Something just seems wrong here, but I don't know enough about the intracies of the system to know what. Has anyone experienced accellerated wear at pulleys?

    I think I'm going to sleeve a few fairlead passages. Might even sleeve the left side and leave the right side bare, just to see if it makes a difference. In the meantime, I'm listening closely!

    Bill

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  • Battson
    replied
    Originally posted by Bdflies View Post
    I've been thinking about this subject. I'm not so much interested in the technical cause of the accellerated wear, but rather how to prevent it. It seems that the wear everyone is reporting is in the nylon fairleads. A thought occurred to me; What if I put a nylon sleeve, say a length of 1/4" nylaflow tubing, over the cable where it passes through the fairlead? Might need to bore the fairleads a bit, to allow a loose fit. That's not a big deal. A slit in the tube would allow slipping it over existing cables, then fasten it with a snug tie wire clamp on the ends. The nylon sleeve is fastened to the cable and slides through the fairlead. This way, the cable is protected. If the tubing wears, it would be pretty easy to replace and I don't have concerns about sleeving the cable.
    I haven't done this, but it sounds like a good rainy winter day project. I'd like to hear all of your thoughts!

    Bill
    You would need to be able to move the cover to inspect the cable underneath. Who's to say whether the nylon sleeve wouldn't rub like a fairlead does.

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  • Archer39J
    replied
    Originally posted by Chris In Milwaukee View Post

    That stuff is pretty stiff, though. Especially in the cold. I’d check it’s flexibility around pulleys and stuff before committing. Ive used that kind of cable on my snowblower and it can be really hard to work with. Galvanized, not stainless, though.
    Yeah probably not great to use through a pulley, too stiff as you describe. But through a fairlead it might just work.

    Leave a comment:


  • Chris In Milwaukee
    replied
    Originally posted by Archer39J View Post

    Well, some steel cables come nylon coated so this would make sense. Clear, I would think, so you can inspect.

    Beats re-rigging stainless cables that's for sure.
    That stuff is pretty stiff, though. Especially in the cold. I’d check it’s flexibility around pulleys and stuff before committing. Ive used that kind of cable on my snowblower and it can be really hard to work with. Galvanized, not stainless, though.

    Leave a comment:


  • Chris In Milwaukee
    commented on 's reply
    Maule has an SB for the same reason Mark stated for their rudder cables. In some situations, the rudder cable can rub on a tube. The they wrapped the cable in a sleeve as described above. But not for fairlead wear.

  • svyolo
    replied
    I thought or putting a sleeve on the cable and crimp some lead on the wire. All of it would work, but all of it could fall off or jam something as well. I don't know enough about aircraft standards to know what is allowed. You could probably put a GoPro on a stick and record what is happening.

    Leave a comment:


  • Archer39J
    replied
    Originally posted by Bdflies View Post
    I've been thinking about this subject. I'm not so much interested in the technical cause of the accellerated wear, but rather how to prevent it. It seems that the wear everyone is reporting is in the nylon fairleads. A thought occurred to me; What if I put a nylon sleeve, say a length of 1/4" nylaflow tubing, over the cable where it passes through the fairlead? Might need to bore the fairleads a bit, to allow a loose fit. That's not a big deal. A slit in the tube would allow slipping it over existing cables, then fasten it with a snug tie wire clamp on the ends. The nylon sleeve is fastened to the cable and slides through the fairlead. This way, the cable is protected. If the tubing wears, it would be pretty easy to replace and I don't have concerns about sleeving the cable.
    I haven't done this, but it sounds like a good rainy winter day project. I'd like to hear all of your thoughts!

    Bill
    Well, some steel cables come nylon coated so this would make sense. Clear, I would think, so you can inspect.

    Beats re-rigging stainless cables that's for sure.
    Last edited by Archer39J; 12-04-2017, 11:21 PM.

    Leave a comment:


  • Bdflies
    commented on 's reply
    OK, so I'm not completely off the reservation.. Could be a start!

  • Mark Goldberg
    commented on 's reply
    I have done this with cable before but never to protect it from a fairlead. It was to protect it from chafing on other things. Mark

  • Bdflies
    replied
    I've been thinking about this subject. I'm not so much interested in the technical cause of the accellerated wear, but rather how to prevent it. It seems that the wear everyone is reporting is in the nylon fairleads. A thought occurred to me; What if I put a nylon sleeve, say a length of 1/4" nylaflow tubing, over the cable where it passes through the fairlead? Might need to bore the fairleads a bit, to allow a loose fit. That's not a big deal. A slit in the tube would allow slipping it over existing cables, then fasten it with a snug tie wire clamp on the ends. The nylon sleeve is fastened to the cable and slides through the fairlead. This way, the cable is protected. If the tubing wears, it would be pretty easy to replace and I don't have concerns about sleeving the cable.
    I haven't done this, but it sounds like a good rainy winter day project. I'd like to hear all of your thoughts!

    Bill

    Leave a comment:


  • fairchild
    replied
    Thinking about the cable wear----
    I wonder if the combination of tension and frequencies-- has made a resonance between that particular run between supports (pulleys and fairleads) and the driving force. (prop)
    If that IS the case ----if you could change the resonant frequency of the cable between the nodes--- you could decouple the cable from the prop. One way to do that might be
    to change the cable resonance by crimping on lead weights onto the cables to lower the frequency of the cable.
    Possibly you could use something like an electric guitar pickup in the cable to monitor the cable amplitude and frequency and add weights it you get a minimum. Of coarse
    the driving frequency is not fixed but a range....

    The other way could be to find spots to put extra pulleys and/or fairleads to alter the length between nodes.
    i would think that the longer the distance between nodes the lower the frequency and the closer to the fundamental and the larger the effect.

    Just food for thought----

    Not sure if the manufacturers do vibration surveys of cables..... (?) I bet the helicopter companies do but they probably dont use cables much.

    Tim

    Leave a comment:


  • jaredyates
    replied
    I'd speculate that the wear is not coming from the plastic rubbing on the steel, but rather the tiny abrasive contaminants that sit between the plastic and steel. But then I'm not an engineer...

    I did replace the stainless elevator cables. The stainless rudder cables are still installed for now at almost 300 hours, though it's coming up on time to check them again.

    Leave a comment:


  • DemoDollCate
    replied
    I'm pretty sure the wear on my cables was all due to flying time on the aircraft. Mine are galvanized, my feet are always moving a little bit, thus the cable wear in my case at the fairleads. Changing them out isn't a big project though. Cables were not very expensive and came in a few days from Spruce. Convenient to be in the US for fast shipping.

    Leave a comment:


  • PlaneTorque
    replied
    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.

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