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Thread: Safety cables

  1. #41

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    Thanks all for replies.
    Thought there would be more hardware (bolt) failures, guess not.
    Upper cabane cables appear to be pretty effective when ears on fuselage fail. Safety cable plate on lower cabane looks to serve as an effective load distributing “doubler” protecting that area.

    Re shock struts, I’m kind of with Bill on this, seems most failures are a result of older, abused parts, but safety cables provide extra insurance for sure.

    Looking into synthetic rope - Obvious advantage is weight (though minimal) not as bulky, provides some give when loaded (about 5%). Most importantly, get rid of those damn prickly wires that poke your fingers when wiping them down.
    Re splicing, only way to achieve a loop over thimble while preserving rated line integrity is via backsplice. This requires backsplicing a recommended min 14” (for 3/8” line)
    Relatively short lengths of cabane safety cables makes this a challenge as the splices will overlap.
    Shock strut cables may be doable though.
    im going to mock up a set and do a simulated shock load.
    Not sure how to measure load generated without ruining my load scale.
    Thinking to anchor one end to a fixed point, other end to backhoe bucket, slack the rope to half (gradually increasing) its length and swing the shovel over hard and see what results. Should be plenty of inertia generated with all that moving mass (and 500lb shovel) even for relatively short swing.
    Last edited by Oliver; 10-30-2018 at 10:27 AM.

  2. #42

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    Made up a cable with 1/4” Dyneema (Amstel Blue), rated breaking strength 7,000 lbs.
    Ill pull on it a bit at work tomorrow. If it looks promising I’ll make up another out of 1/4” stainless and compare the two.

    Click image for larger version. 

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  3. #43

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    Oliver, I love the excavator idea... If only I had one! Thanks.
    Here's a thought... to save the weight and extra "pieces".. How about a thimble through that gusset at the bottom of the gear leg on the inside (axle) there is usually a gap there. I think you could fit 7/16 synthetic without modification. (#19,000 test?)
    Then a loop around the top of the forward gear leg (nice and round no thimble needed).
    Set the length up to come tight when straight at max gear extension (or 1/2" less) and secure it behind the tubes (hockey tape whatever).
    It's a little less leverage than going to the cabane and then to the bottom axle (the cabane is not a straight line) but only one piece and hooks the two things you want to keep together,.. together. That center plate is a lot of weight just to serve as a doubler.. especially when redundant..
    For practical puposes when going on wheel gear.. you could splice the end which goes at the bottom end around the thimble (inside the bottom axle gusset) and just simply slide the top loop (at top forward hear leg) over the gear leg when installing the gear. That way unless you see frays or fear UV you could do it every year without making new ones.
    I too have a hard time having faith in synthetics over metal but I've seen plenty of steel cables fail, (not Cub gear but elsewhere for rust and wear) and also think it's good to see if some of the new stuff might be worth exploring.
    Thank you very much for taking the time to rig a test sample, and for being willing to use your equipment to test it.
    Please forward your results! But be nice to your excavator.. because I have a feeling it's as strong as they say it is..

  4. #44

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    What if you hook 1/4" steel and 1/4" synthetic thimble-to-thimble and then saw what broke first? Then bump up size on the loser until you found a match?
    I'll buy the materials!
    Thanks for exploring it.
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  5. #45

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    Gave the hardware a good tug today.


    First attempt: connected cable and synthetic cord together as 46 suggested.
    Cable crimped sleeve failed, I think, due to suspicious crimp job.
    did manage to jerk a 7000 lb trailer with tandems and locked air brakes about a foot forward as it failed.

    Second attempt: with only remaining Dyneema cord (already severely shock loaded from first attempt)
    Parted mounting plate at the hole, elongated all the other holes,
    Re steel plates: same thickness and dimension as atlee hardware. Made from mild steel flat bar vs stainless (alloy unknown) as provided with atlee hardware.

    This was not a pull test, it was truly a shock load test, I’ll try to post a video, meantime photos show results.



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    Last edited by Oliver; 10-31-2018 at 07:51 PM.
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  6. #46

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    How does one post a video here from an I phone?

  7. #47
    www.SkupTech.com mike mcs repair's Avatar
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    those are the sizes of the OLD VERSION of Atlee's hardware, and they WOULD fail..... new version is much thicker & SS

  8. #48
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by 46 Cub View Post
    Oliver, I love the excavator idea... If only I had one! Thanks.
    Here's a thought... to save the weight and extra "pieces".. How about a thimble through that gusset at the bottom of the gear leg on the inside (axle) there is usually a gap there. I think you could fit 7/16 synthetic without modification. (#19,000 test?)
    Then a loop around the top of the forward gear leg (nice and round no thimble needed).
    Set the length up to come tight when straight at max gear extension (or 1/2" less) and secure it behind the tubes (hockey tape whatever).
    It's a little less leverage than going to the cabane and then to the bottom axle (the cabane is not a straight line) but only one piece and hooks the two things you want to keep together,.. together. That center plate is a lot of weight just to serve as a doubler.. especially when redundant..
    For practical puposes when going on wheel gear.. you could splice the end which goes at the bottom end around the thimble (inside the bottom axle gusset) and just simply slide the top loop (at top forward hear leg) over the gear leg when installing the gear. That way unless you see frays or fear UV you could do it every year without making new ones.
    I too have a hard time having faith in synthetics over metal but I've seen plenty of steel cables fail, (not Cub gear but elsewhere for rust and wear) and also think it's good to see if some of the new stuff might be worth exploring.
    Thank you very much for taking the time to rig a test sample, and for being willing to use your equipment to test it.
    Please forward your results! But be nice to your excavator.. because I have a feeling it's as strong as they say it is..
    interesting, I like the installation idea, but that wouldn't help keeping wingtip off ground with a cabane ear pull failure... I don't think....(when the cabane breaks, even with the upper relatively close fitting safety cable the wing tip is almost on the ground by the time the thimbles elongate... its weird geometry when the cabane goes sideways with one side still attached to fuselage & with the shocks still attached...)..... hmmmm... someone will have to mock that up and measure.....

    I should probably clarify the incident I'm thinking of he was on strait landes skis.... regular length cub gear...

  9. #49
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    Speaking of pull testing using heavy equipment, I've pull tested aircraft cable with my 30 ton boom truck, using it's winch that is. It's load moniter is accurate once the tare is properly setup, to within 50-100 lbs or so as near as I can tell. Using 1/8" 7x7, I made a splice using one nico, an inline splice no thimbles or anything, an improper way to do it of course, but I have such faith in a proper swedge being strong as hell I was not surprised when the cable broke before the single swedge/nico sleeve, right at 1800lbs, it's stated breaking strength. This was a gradual pull, no shock loading. That Dyneema cord looks like some pretty good stuff, I wonder how a few years of UV would effect it? Synthetic rope is being used more and more in light cranes for the hoist lines instead of wire rope, the much lesser weight means a bit more capacity, when you're talking several hundred feet of it.

    WE all know better, but the other day I had to comment (on an e bike forum I'm on) on a guy who didn't know any better then to buy some coated cable at the ACE hardware or maybe his nearest farm supply outlet, who then tried different sizes of swedges until he found the size that slipped over the still plastic coated cable, and then beat it down with a hammer! His use was not aircraft, but still such a non proper way to do it.....he ended up with a 1/8" nico over the 3/32 coated cable, that kind of thinking killed a few people back in my ultralight days, and put one company (rightfully) out of business.
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  10. #50

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    Mike,
    i copied hardware from a fairly new set of safety cables.
    Yes, new ones are 3/16” stainless flat bar (I assume 304)
    i used 3/16” mild steel which is, to my knowledge, stronger than 304 but I may be mistaken.
    I also bent a couple 3/8” shackles beyond use during the pull, something’s gotta give.
    i was very surprised at the strength of the cord.
    Not trying to bash time tested cables, just trying to think outside the box a bit.
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  11. #51
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Oliver View Post
    Mike,
    i copied hardware from a fairly new set of safety cables.
    Yes, new ones are 3/16” stainless flat bar (I assume 304)
    i used 3/16” mild steel which is, to my knowledge, stronger than 304 but I may be mistaken.
    I also bent a couple 3/8” shackles beyond use during the pull, something’s gotta give.
    i was very surprised at the strength of the cord.
    Not trying to bash time tested cables, just trying to think outside the box a bit.
    hmmm i was thinking it was 1/4".... but don't have any around to measure... good test!!

  12. #52

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  13. #53
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  14. #54

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    Quote Originally Posted by mike mcs repair View Post
    interesting, I like the installation idea, but that wouldn't help keeping wingtip off ground with a cabane ear pull failure... I don't think....(when the cabane breaks, even with the upper relatively close fitting safety cable the wing tip is almost on the ground by the time the thimbles elongate... its weird geometry when the cabane goes sideways with one side still attached to fuselage & with the shocks still attached...)..... hmmmm... someone will have to mock that up and measure.....

    I should probably clarify the incident I'm thinking of he was on strait landes skis.... regular length cub gear...
    Ya I think the only way to be sure would be to mock-up and measure.
    I would never put it on my own airplane (at least if I were the first one to try it) without hoisting it, pulling the cabane bolt at the top, and letting it down (slowly) to find out.. same for removing a shock strut to see what I had for margin.
    By your statement it did make me realize that to follow the tubes (for streamline and not catch brush) with the ropes then there would have to be extra length plus the shock travel extra, to make it work... Thought about bungee cord wrap to hold it to the tube for stretch when you get close to the gear travel and have used up the "slack loop" around the shock strut.
    Then I measured the difference in length from the top front gear leg to the bolt hole on the inner axle extention, both straight line and following the cabane, shock strut, etc..
    It looks like the difference is only about 1/4". I imagine anyone who remembers their basic high school geometry could have figured it out, but I just used a steel tape..
    That would seem to come under the tolerance left by that extra elongating thimble eye..
    I don't know how close the wing tip is to the ground at full travel on one side but I'd bet 1/4" of distance between upper front gear leg and opposing axle would not be the deciding factor.
    My friend has already substituted synthetic rope for his cable.. it's just that he kept the other hardware, which minimized his gain. It seems one could gain even more by re-thinking it a bit.
    I really like seeing the results of Oliver's tests, and really appreciate his trying it out. It gives me a bit more faith in the new material. Now I wonder if plastic thimbles would really compromise it that much over a sharp surface like that tab? Oliver?
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  15. #55

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    I've been trying to picture the weird geometry and why it would make a difference..
    So Mike, when the upper cabane breaks on one side, does it pull the center pivot (bottom of cabane where the shock struts attach) down on the remaining good leg? That would draw the opposing gear farther in and exacerbate the lean and close-to-the-ground tip? Wondering if a straight connection might actually help avoid that?
    These are purely questions and thoughts out of interest.. I have no agenda.. but this may help me figure out what to do when sometime in the far-off future I put my own Cub back together. I'ts a J3 and I'd like to have some back-up for the gear with minimal weight and drag gain.

  16. #56
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    Any more developments in the area of Kevlar safety cables. I’m trying to workout if there is some sort of crimp that can be used.?
    Back Country O-375 wide body extended wing cub

  17. #57
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  18. #58

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    Quote Originally Posted by cgoldy View Post
    Any more developments in the area of Kevlar safety cables. I’m trying to workout if there is some sort of crimp that can be used.?
    I don’t think synthetic ropes can be crimped in the manor that cable is crimped. Synthetic rope is reduced in diameter when under tension.
    Using a back splice is the preferred method to preserve rated strength.

    just checked out Atlee’s new product (thanks for the link Steve)
    looks like they omitted thimbles, defiantly make things easier during assembly, Also shave a bit of weight.
    id be curious is they have a recommended TBO. rope fiber is prone to collecting oil, grit and exhaust byproduct in that location wich will degrade fiber over time. Simple enough to replace cord in place as needed (If needed). I’ve got about 400 hrs on mine, they are a little grimy but appear to be holding up well. I may take one off and pull on it back to back with a fresh one soon and see what happens.

    btw: my pull tests technique has improved dramatically, now incorporating a hydraulic log splitter with system pressure gauge. Line tests are performed using the down stroke of cylinder while monitoring system pressure up to point of failure
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  19. #59
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    Quote Originally Posted by Oliver View Post
    I don’t think synthetic ropes can be crimped in the manor that cable is crimped. Synthetic rope is reduced in diameter when under tension.
    Using a back splice is the preferred method to preserve rated strength.

    just checked out Atlee’s new product (thanks for the link Steve)
    That's correct, the rope has to be woven back through itself to create a closed end. And it's Airframes not Atlee

  20. #60
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    Hey Oli, did you back splice yours? I want to make some but have been thinking that the back splice will be difficult with the upper cables as they are so short. Not enough length to get the required splices. Maybe that a continuous loop might work? . Also it will be difficult to get the length accurate on such a short splice. Looking to make carbon fibre tabs. Might be able to form a radius into the tab to eliminate the need for thimbles. Did you replace 3/8 cable with 3/8 Kevlar or did you upspec the rope?
    Back Country O-375 wide body extended wing cub
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  21. #61

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    Goldy,
    I went with 1/4” synthetic rope, same diameter as cables that were replaced.
    upper cables are too short to get the recommended tail length when backsplicing.
    you can cheat a little by “step” tapering the tails and overlapping them on backsplice.
    Be sure to lock the splices with a couple of stitches.
    Looks like Airframes covered their cords with heat shrink, good idea to prevent debris from entering and a abrading fiber, The ends where they attach to hardware are still exposed to the elements which leads me to think it would be wise to replace the cord every couple of years.
    I’m not sure about omitting thimbles, I assume it would compromise strength.
    Also, theres a product called G-10, epoxy infused laminate sheet that may work well in place of carbon fiber (or metal) for mounting tabs.
    maybe more testing is in order...

    edit: just checked re sharp bends, Amsteel recommends min 3:1 circumference to preserve rated strength:
    Min circumference of bend = 3x diameter of cord
    Last edited by Oliver; 07-30-2020 at 09:07 PM.

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