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Thread: Nicopress fitting failure report

  1. #1
    Chad Jensen's Avatar
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    Nicopress fitting failure report

    This is a report that was submitted to us by an NTSB investigator who needs to remain anonymous as an impartial investigator. Pictures and words are not mine so I can't offer any answers to questions. This is simply a passing of information to anyone using nicopress fittings to use the proper tools.


    Thankfully, this was a known-circumstance, no-injury accident, and we were hoping to share the lessons learned from it with an interested audience. Your members are likely to be involved in the building of flight control systems, or the re-rigging of those systems in antique aircraft, and that’s why we sought you out.

    The NTSB Accident Number is ERA11CA375. You can go to our website and read the Factual Report as well as the Board’s finding of probable cause. The public docket which contains the documents and photographs used to support the investigation can also be found there. I have attached a number of those items for your convenience.

    Because my position requires that I be an impartial investigator, I am reluctant to self-publish on a website or discussion forum. It am not, however, precluded from sharing the facts and circumstances with you and your members. From there, you can draw your own conclusions, or start a discussion or debate as the situation dictates.
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    Chad Jensen
    EAA #755575

  2. #2
    Mike Switzer's Avatar
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    Did the fitting fail or did the cable break? I can't tell from the pictures. We use similar crimp sleeves for fencing & vineyard wire splices, and if you use the wrong tool it will not crimp properly & the wire will pull out under load.

  3. #3
    Chad Jensen's Avatar
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    Fitting failed, cable slid through. That's all I know though...
    Chad Jensen
    EAA #755575

  4. #4

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    Ultralights often use two copper sleeves instead of one.

    But in his ultralight book, Lack Lambie said using two sleeves will weaken the cable slightly.
    I never understood this. Anybody have the facts on using two sleeves?

  5. #5

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    I can't really tell, but it looks like he didn't crimp them properly, and didn't use a go/no go gauge to ensure they were tight enough.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  6. #6
    Neil's Avatar
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    Don't know in this particular case but I see this type of failure from time to time when a builder tries to make up cables with the "Econo Swagers" that get all their clamp force from a couple of bolts. There is no good substitute for the proper lever type swaging tool.

  7. #7
    Dana's Avatar
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    I don't think there is a problem with the clamp bolt swagers if used properly.

    Some years ago Quicksilver had a problem with a lot of improperly swaged wing cables at the factory. Seems 1/8" cables had been swaged with a 5/32" tool; the swage looked OK but wouldn't pass a go/no go check.

  8. #8
    dewi8095's Avatar
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    Quote Originally Posted by Frank Giger View Post
    I can't really tell, but it looks like he didn't crimp them properly, and didn't use a go/no go gauge to ensure they were tight enough.
    What is a go/no go guage and how does it work?

    Don

  9. #9
    Hangar10's Avatar
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    I've built a few of these cables, but by no means am I an expert on the subject. I'd just like to share a few things that I've discovered.

    For the first cables I constructed I borrowed a pair of Nicopress crimpers and cable cutters from a fellow EAA member. Here you can see the materials and tools I used to construct some turnbuckle ends.


    If used properly (as illustrated in Tony Bengelis' books) they do a nice job.


    The Nicopress tool worked great, but I wasn't the only one in line to borrow them, so I looked around for a pair of my own. There are several different types of nicopress tools... the type that are capable of 3/32", 1/8", 5/32", etc. are not cheap. Somewhere in the neighborhood of $300 was not unusual, even for a used set. So I chose to try the $28 type that Home Depot sells. These are typically used for making dog runs and leads, or for fencing, but I know of others that have used these, and if properly adjusted and monitored I don't see how the end result is any different than the more expensive tools. The authentic Nicopress tool was longer (more leverage when crimping) and the finish and operation were a bit smoother, but otherwise either tool is capable of putting the squeeze on copper sleeves.


    Prior to making my test crimps, I referred to some information I found on the Pietenpol forums.

    Size - Range (Chris Bopka posted as found in EAA Aircraft Volume One File Number 6 on Aircraft Homebuilding Tips, page 34)

    1/16" sleeve - .190-.195" go dimension
    3/32" sleeve - .255-.265" go dimension
    1/8" sleeve - .343-.353" go dimension
    5/32" sleeve - .380-.390" go dimension

    Using the Home Depot tool straight off the shelf, my first crimp on a 1/8" cable/sleeve combo was .318" (way too tight). After a minor adjustment, my second crimp was .355" (slightly too big). Another adjustment and I was able to squeeze a .345" crimp. I grabbed another sleeve and proceeded to squeeze 3 more crimps right around .345" (+/- .0005") as measured with my calipers. In other words, plenty good and on par with the more expensive tool.


    Hope this helps!


  10. #10
    rwanttaja's Avatar
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    Quote Originally Posted by dewi8095 View Post
    What is a go/no go guage and how does it work?

    Don
    A go/no-go gauge is a piece of metal with a slot of a particular width cut in it. After you get done crimping your nicopress sleeve, you attempt to slide it into the gauge. If it won't go in, the sleeve has not be compressed sufficiently. You could use a micrometer the same way. Dimensions are at the bottom of this diagram:
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    One problem with some bolt-type swages is the *width* of the swaged area. One unit I owned didn't swage the entire length of a 3/32 sleeve, you had to do multiple impressions like 1/8" and higher.

    The above diagram is from my Shopsheet page:

    http://www.wanttaja.com/shopsheets/index.html

    Ron Wanttaja

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