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Thread: Control cable?

  1. #11
    Senior Member efwd's Avatar
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    Default Re: Control cable?

    I used heat shrink only on the end of the nicopress with the free cable end to protect me from being snagged by the cut ends of the cable.
    Eddie Forward
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  2. #12
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    Default Re: Control cable?

    Speaking of rudder cables. I was installing mine yesterday and when I picked up the coiled mass that represents the four cables I couldn't help but notice how heavy they are.

    I have to ask what will probably seem like an insane question, but why has no one used Spectra or Kevlar? I did a google search because I thought there would be examples. The marine industry uses Spectra in shrouds, which see WAY more abuse than a pair of rudder cables will ever see. Kevlar is used in the marine industry all the way through space applications (Kevlar "cables" were used extensively in getting rovers on the surface of Mars). Both materials are very stable thermally, don't suffer from the same corrosion issues that plague steel cables and damn are they light.

    I looked up 1/8" 7x19 Stainless (which is weaker than galvanized) and it has a breaking strength of 1150 lbs (the one source I found). I found some 1/8" kevlar with a coating that protects it from abrasion and it has a breaking strength of 825 lbs (again, single example with no in depth research).

    I don't know what kind of quad muscles you folks have but I can't squat 825 lbs, and certainly not with one leg.

    Am I crazy?
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  3. #13
    Senior Member PapuaPilot's Avatar
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    Default Re: Control cable?

    Quote Originally Posted by alexM View Post
    I looked up 1/8" 7x19 Stainless (which is weaker than galvanized) and it has a breaking strength of 1150 lbs (the one source I found). I found some 1/8" kevlar with a coating that protects it from abrasion and it has a breaking strength of 825 lbs (again, single example with no in depth research).?
    FYI AC 43.13-1B, Chp. 7 gives the specs for aircraft cable and 1/8" 7x19 has a min. breaking strength of 2000# for steel and 1300 or 1760# for CRES/SS. It would best to at least match the lowest spec if you want to substitute types. All aircraft cables have to meet a certain MIL spec.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  4. #14
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    Default Re: Control cable?

    Thanks Phil. Another quick search shows that 1/8" Spectra has a breaking strength of 1800 lbs. And a 600' spool of it weighs 3.2 pounds, which my swag says is 1/10th the weight of steel. All academic but worth asking about (I think).
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  5. #15
    Senior Member Eric Page's Avatar
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    Default Re: Control cable?

    Alex, is there an accepted and reliable means to terminate Spectra or Kevlar cable, in place of the Nicopress sleeves we use with steel? What does this stuff cost?
    Eric Page
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  6. #16
    Senior Member 109JB's Avatar
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    Default Re: Control cable?

    Dyneema ropes are terminated using splicing methods specific to that type rope. In other words, knots. I use dyneema lines on my little sailboat and while they are fantastic for that application and have low stretch when compared to other ropes, I think they would have more stretch that wire cable. It is also easier to cut than wire cable. A sharp knife and a cutting board and you can cut dyneema, but SS or galvanized cable you can't cut that way. My model 4 doesn't have much cable so il be sticking with it for the rudder.
    John Brannen
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  7. #17
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    Default Re: Control cable?

    Quote Originally Posted by Eric Page View Post
    Alex, is there an accepted and reliable means to terminate Spectra or Kevlar cable, in place of the Nicopress sleeves we use with steel? What does this stuff cost?
    As John says, it is spliced in an "eye" loop. It appears splicing is also how one would join the right and left cables in the aft fuselage.

    That would take me back to my days earning a sailing merit badge in Boy Scouts. I'm seeing it for $0.64/foot in 1/8" diameter, 2500 lb breaking strength. They call it low stretch but I'm currently searching for data to compare it to 7x19 1/8" SS cable for apples:apples.

    I weighed a set of bare stainless cables last night and they were just over 1 pound per pair, so not quite as hideous as I thought.

    Still just an academic exercise at this point. I ran my SS cables last night, but so far only the front ends are crimped.
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  8. #18
    Senior Member Eric Page's Avatar
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    Default Re: Control cable?

    Wow, barely more than 1/3 the cost of 1/8" 7x19 SS cable, and a complete installation would weigh a few ounces. Might be worth buying 20' of the stuff just to see how difficult the splicing work would be, and how much it stretches. Very interesting...
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
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  9. #19
    Senior Member PapuaPilot's Avatar
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    Default Re: Control cable?

    Quote Originally Posted by 109JB View Post
    Dyneema ropes are terminated using splicing methods specific to that type rope. In other words, knots. I use dyneema lines on my little sailboat and while they are fantastic for that application and have low stretch when compared to other ropes, I think they would have more stretch that wire cable. It is also easier to cut than wire cable. A sharp knife and a cutting board and you can cut dyneema, but SS or galvanized cable you can't cut that way. My model 4 doesn't have much cable so il be sticking with it for the rudder.
    That's exactly what I was thinking. What happens when a sharp rock hits this type cable by the rudder?

    I can think of dozens of other safe ways to save weight.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  10. #20

    Default Re: Control cable?

    Coming from the climbing/ascending and parachuting world with dyneema, there is a working load and friction point load you need to consider with rope. Rope used for ascending and climbing with specific equipment such as carabiners, ascending slides, tie-offs, etc all reduce the life of the rope; these factors are the same on pulley's, come-alongs, snatch-blocks, etc in aircraft, boats, and winches just as it is with any other functionality of the rope. Specific knots and tie-offs even change the working load of a rope; the factors are almost endless.

    Working loads under these specific environments are significantly reduced which leads to fraying, glazing (friction burn), and shearing of the rope; think of this as the same portion of the rope is contacting the pulley and the exposure to climate outside and inside the aircraft. Additionally, rope of any type is significantly impacted with moisture, heat, cold, or any factor of the various environmental concerns aircraft are exposed to. Any dyneema rope that is exposed to moisture should be thoroughly dried out in a controlled environment (not heat or sunlight, etc) before used again. The wet to dry and back to wet and dry again significantly reduces the life of dyneema; hence why any ropes that are used professionally in any environment have cycle and life limits.

    What those limits would be on your Kitfox or any aircraft remains to be seen I guess. Add this to your research because there are far more factors than shear load when ropes are involved; that's a straight pull shear load is calculated in perfect conditions and to be honest SS cables have the same testing and factor requirements.

    Please do not take this as anything other than offering and trying to look out for safety for all of us!

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