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Tying knots in aircraft cable.

Discussion in 'Question of the Day' started by Footer, Aug 12, 2010.

  1. 2mojo2

    2mojo2 Member

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    That is not the accepted method of installing suspended ceilings.
    Ceilings are hung on #10 solid steel wire that is passed once through the hole in the ceiling main and then wound tightly with a pair of Kleins.
    The free end is clipped short, not passed back through the bottom of the hitch.
    It is a technique that commercial carpenters must learn.

    While there is little in the photo to give perspective, that looks more like picture hanging wire than substantial wire rope.
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    Here is a website that will give a bit further explenation on how this is tied.

    A few questions have yet to be answered about the circus knot.

    Why should it be used or why should it not be used? What physically is wrong with it that should keep it out of the world of entertainment rigging?

    Is it safer or less safe then crosby clips, swagging sleeves, or a gripple?
  3. MPowers

    MPowers Well-Known Member

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    Now that I can chime in, as several have said, the knot pictured is what is commonly known as a circus knot.

    Now, tying knots in wire rope, good idea or not? A little history here. Back in the stone age when I first learned rigging, one of the common ways to attach a permanent lift line to a batten was with a clove hitch, plus two half hitches and a single cable clip. It was a secure and reliable way to make an attachment, ..... if you only needed 50% of the cable strength as a maximum. Destructive tests showed that the cable clip had very little to do with the strength of the attachment, when it broke, it always broke at the first 90 turn of the clove hitch, and at anywhere from 45% to 60% of the cable breaking strength. Today we have as an industry grown and developed such that the least acceptable attachment method for permanent connections is a properly terminated cable with a thimble then a trim chain or batten clamp or other rated attachment. So if you are a professional rigger, know the loads and forces that will be involved, know the strength of the cable, then it can be good. A young rigger, student, community theatre volunteer, then no, don't use a circus knot or any knots in wire rope, it's just not worth the consequences if you're wrong.

    Now, back to the circus hitch. First, when used by professionals, it was/is never intended as a permanent attachment. It was developed by riggers with touring shows and fit their world of quick set up, no tools, no parts to lose or store, quick strike without tools, back in the kit and "on the road again" (thank you Willie!). In the situation for which it was developed, it can be a good attachment solution.
  4. derekleffew

    derekleffew Senior Team Senior Team Premium Member

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    A quote by Bill Sapsis, (from a long time ago, possibly even before other flying effects companies existed):
    Several important points:
    1. The circus knot starts with a clove hitch, which does all of the work. The rest of the knot is just to keep the clove in place.
    2. The clove hitch IS NOT any longer, the preferred attachment for a cable to a batten.
    3. The circus knot should only be used with wire rope, and even then, only by professionals who know all the factors involved.

    For a real-world, though by no means conclusive or representative, evidentiary testing,
    see Test #1G, on this site by [user]Delbert[/user], which, by the way, is where the original picture came from.
    Last edited: Aug 26, 2010
  5. MPowers

    MPowers Well-Known Member

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    For everyone reading this thread, the following is part of a private disscussion that I thought would shed some light on the why's and wherefore's, good and bad, about using the Circus Hitch,

    Actually, The half hitches were, like the circus knot wraps, merely a way to prevent slipping at the clove hitch should there be momentary "bounces" or slack or shock loading in the rig. They actually took no weight and were tied with the same degree of looseness as the circus hitch loops in the picture at the top of this thread. The double half hitch method, taught as common practice in the '50's and 60's, was an out growth of hemp house or fiber rope rigging, which was an out growth of navel rigging on sailing vessels, when attaching to a wooden or pipe batten with a clove hitch. The reason we used to use clove hitches was to prevent the rope from sliding along the pipe, that is really the way a clove hitch is designed to work, to cinch around a smooth beam, spar, mast, log, etc and not slip even if there is only one line doing the lifting.

    When using a 10 ton test rig for destructive testing, subjecting this, and various other methods of attaching wire rope to a pipe using clove hitches, the knot always, repeat always, failed at the clove hitch where the live end first entered the knot. Usually at about 40% to 50% of the rated breaking strength of the GAC. If you think about it or look at it, a well tied clove hitch bends the line, whether wire rope or hemp rope or cord, etc. at a hard 90 degree bend right there, thus tremendously weakening the line.

    I do not use nor will I allow workers working for me to put any knots in wire rope. As noted above, the clove hitch is the failure point, not half hitches or circus knot wraps.

    For permanent installations, no knot is permissible in current common practice. Today I would NEVER use a clove hitch with wire rope on a permanent installation. The proper way to terminate a line to a batten is with trim chain and rated and properly moused screw pin shackles, or rated and properly moused turnbuckles attached to a batten clamp.

    If for some reason you must attach wire rope directly to a pipe batten, wrap it 1 1/2 times around the pipe and then attach the proper number of clips for the wire size. Attach the first clip at least the diameter of the pipe away from the pipe, (the spacing is to prevent a sharp bend where the GAC enters and leaves the clip, thus weakening the GAC) i.e. if using schedule 40, 1 1/2" pipe, the closest clip should be at least 2" away. This should NOT be done as a permanent batten attachment, but only as a temporary, single event rigging. This will be at least twice as strong any attachment method that uses a clove hitch (or any other knot in the rope.

    The properly used circus hitch now is used for short term installs such as short run aerialists, one or two week road shows and such types of uses. They are designed to be easy and very quick to install and strike without tools of any kind and with no parts or hardware to find, store or lose. They should only be used by knowledgeable, professional (preferably ETCP Certified) riggers and the cable or GAC being used is derated by 50% at least.

    Hope this helps.
  6. mstaylor

    mstaylor Well-Known Member Departed Member

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    A really good explanation of past common usage of wire rope and tying knots. I personally have never tied wire rope but have seen it used by circus arealists.
  7. Radman

    Radman Active Member

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    I learned this knot from one of the guys at ZFX. He called it a circus knot and we used it for the guy lines only, i.e. just to prevent horizontal movement. It was never used to bear a load, and this was a temporary setup. I have also used this occasionally on the road for quickly securing light scenic elements to a truss. As was mentioned, this knot does create a sharp bend in the wire, so for safety's sake I always just cut the wire off the truss and dispose of the knotted end. (The time savings is a nice bonus.)
    AudJ likes this.
  8. Arez

    Arez The Royal Renaissance Man Premium Member

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    Circus knot/circus hitch

    As you can see from the picture it is a, relatively, fast method of using wire rope, as there is no additional tools/parts needed to terminate it. However, it will not have the same strength of a more "normal" method of termination.

    This depends on who you ask.
    Yes, in temporary situations only. But also, only by those that have been trained how to tie it properly, even then, as sparingly as possible.

    No, unless you are a profesional rigger or are under the supervision/teaching of one (or have been taught by one).

    This is a dangerous knot, especially when people forget to tie the clove hitch first (or tie it incorrectly).


    Sent from my iPhone using Tapatalk


    Anyone considering using this not should note that not only should you cut the used portion of the wire, you absolutely must cut it off.

    Leaving a kink or bend in wire rope is another thing that makes this knot so dangerous to use by those who don't understand it.
  9. MNicolai

    MNicolai Well-Known Member Premium Member

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    Metal fatigue happens. Shortly thereafter -- so does gravity.
  10. Delbert

    Delbert New Member

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    This is my photo and people have correctly identified it as a circus hitch. It will hold 60% of the BS of the cable. It is one of several knots that can be tied in small diameter 7x19 GAC. I am tested the efficiency of several other knots in wire rope. Some can hold up to 100% of the BS of the cable. BTW, ALL flying effects companies use this knot regularly for making guy wires.

    -Delbert Hall
    D2 Flying Effects
    ETCP Certified Rigger
  11. Delbert

    Delbert New Member

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    I am working on an article that describes, step-by-step, how to tie several knots and quick splices in cable. I have done destructive testing to verify the holding capacity of each knot/splice.
  12. DuckJordan

    DuckJordan Well-Known Member

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    Doesnt matter

    Just don't post it here, It would be a violation to show a step by step process, even with the relaxed feel now. just enough knowledge to get it done is very dangerous (this coming from someone who has never done any rigging and probably wont for a while.)
  13. Footer

    Footer Senior Team Senior Team Premium Member

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    There is nothing in the TOS that forbids it. Delbert is a trusted member of the theatre community, there is no reason to doubt anything he would post would be more than safe in the right hands. With anything safety related, a lack of knowledge can be more dangerous then the knowledge itself. I would much rather see this information come from a trusted source then nothing at all .

    Sent from my HTC Incredible
  14. bobgaggle

    bobgaggle Member

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    Just found this thread, did this article ever get published?
  15. BillConnerASTC

    BillConnerASTC Well-Known Member Premium Member

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    I'm not advocating anyone use knots to terminate wire rope but can someone point to evidence - even anecdotal - that one has ever failed? That is what I'm asked about my technical objections to grade 30 trim chain. Where in a standard does it say knots are not permitted? I can point to the standard which prohibits grade 30 from overhead lifting applications.
  16. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Delbert Hall load tested a circus hitched piece of GAC, Test 1G here: http://www.d2flying.com/loadlab/USITT.html

    Breaking strength was over 80% of the breaking strength of the cable...
    cmckeeman and MarshallPope like this.
  17. Euphroe

    Euphroe Member

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    Go Delbert! This is the kind of knowledge that should be preserved even if superceded.

    Like the flipline hitch in wire core rope:

    Competent riggers know how to use every gadget in the catalog. Really good riggers can meet a challenge safely without the gadgets if necessary.
  18. MikeJ

    MikeJ Member

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    Yes it May be efficient, but a whole bunch of stupid theater tech kids on the internet, just read that it was safe to use, and will now proceed to tie it incorrectly, because they are now experts at rigging.
  19. Euphroe

    Euphroe Member

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    Thinking back and I am pretty sure I learned the circus hitch from Peter Foy, who shared that and a lot of other dangerous information that MikeJ would throw down the memory hole. He differs in that regard from Foy, Donovan, Paulson, Glerum, Higgs . . . and Hall, who neither feared/fear information, nor viewed the incoming generation with contempt, thank goodness.
    gafftapegreenia likes this.
  20. BillConnerASTC

    BillConnerASTC Well-Known Member Premium Member

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    What method or technique for terminating wire rope mentioned here or anywhere couldn't be done incorrectly?
    robartsd likes this.

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