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red wrote:From a technical standpoint, if a cable is rigged straight and tight, deflecting the cable by a handspan can put enormous loads on the cable. A cable rigged slack can be deflected by a handspan and that will put a relatively small load on the cable. It's a function relating to trigonometry.
Yes, if you wanted to know how much tension you're putting on the cable, you'd need to know the deflection angle from a straight line connecting the end points in addition to the force applied. The attached example assumes a perpendicular force at the midpoint of the cable's length. With less of a deflection angle (tight rigged cable), you get a much higher tension for a given force.
cable_side_loading_effect_of_angle.png (25.83 KiB) Viewed 1507 times
User avatar
By brian scharp
Funston Accident
http://www.hanggliding.org/viewtopic.ph ... 066#375066
spork wrote:
flyzguy wrote:Someone could do the trigonometry to figure out the resulting line tensions and how they compare to flight loads...
It depends entirely on how bent the wire is at the load. For sake of argument let's say the 50 lb load is applied in the middle of the wire, and the wire is bent by an angle of theta. We can compute the resulting tension on the wire this way...

sin(theta/2) = 50 / tension


tension = 50 / sin(theta/2)

So if the wire is bent 10 degrees the tension would be 573 lbs
If it was bent 30 degrees the tension would be: 193 lbs
http://www.hanggliding.org/viewtopic.ph ... 072#375072
spork wrote:Doing some rough calculations and using the attached HG pic, I get that you want the cable to withstand 360 lbs for a 200 lb pilot to do a coordinated 60 degree banked turn with a 50% safety margin (with some assumptions as indicated).

This seams reasonably in line with the 50 lb test.


Length of 1 wing: 568 pixels
wire attach point: 298 pixels
200 lb pilot (we don't count the weight of the wing since it's being supported by the air)
1/2 pilot's weight goes to each side wire.
Let's put the center of lift at 1/3 of the wing span (based on an elliptical loading and some guess work).
Assume the load is taken entirely by the cables - not the cross-bar.

Moment reguired to hold wing: (568/3) x 200/2
Same moment must be applied by wire attached at 298: 298 * vert_force = (568/3) x 200/2 = 18933
So vert_force on the wire is: 63 lbs (when flying at 1G).
Based on the image the side wires are at an angle of 31 degrees.
Using the equation from the previous post we see that a 63 lb vertical force
applied by a wire at 31 degrees results in a wire tension of: 122 lbs
In a coordinated 60 degree bank we'd be doing 2G's - so each wire would be at about 240 lbs.
And you'd want at least a 50% safety margin so that suggests we should test it to: 360 lbs.

User avatar
By dbotos
Nikita (raquo) was generous enough to send me one of her old wire ends to do some forensics on. I received it at home today and have made a few observations/measurements so far:

1. The wire is 2.5 mm diameter stainless steel.

2. The base material of the sleeve is copper. I drilled into a spot on the sleeve that was free of corrosion and went deep enough to make sure that I was hitting base material and not just getting through the exterior plating to a potential underplating. I could also make out a few hints of copper on other untouched areas of the sleeve near the flared ends and the vees/valleys on the sides.

3. The corrosion appears to be emanating from the vees/valleys on the sides of the sleeve. This makes sense as those areas probably see the most mechanical distortion / stress during the crimping process, conceivably compromising the plating to the point where base material could be a factor in the makeup of the corrosion product.

Should be able to determine more when I get it to the lab. Primarily what the plating is and the makeup of the corrosion product.
Lab results are in - plating and corrosion were analyzed with energy dispersive (x-ray) spectroscopy. The plating is zinc with a conversion coating over top of it (this agrees with what Mike from Wills Wing said and what I suspected about the conversion coating). The corrosion was due to those two being compromised (most likely during the crimping process) and some environmental factor(s).

I don't know why Wills would choose to use the zinc-plated sleeves on stainless cables. If you look at the Nicopress site and MS51844 rev E, both say to use either tin-plated copper sleeves or stainless sleeves on stainless steel wires. The tin-plated copper sleeves should crimp just as easily as the zinc-plated ones and cost should be nearly the same.

This article has some good info on wire rope sleeves and crimping, including this very applicable sentence:

"Zinc-plated sleeves on stainless cable has been an obsolete recommendation for more than 40 years."

http://www.kitplanes.com/issues/30_12/b ... 888-1.html
I emailed Wills Wing with my findings last week and referenced the Nicopress site and the mil spec calling out tin-plated copper sleeves or stainless sleeves for use on stainless wire. I asked if maybe they had used galvanized wire in the past and the sleeve plating just never got updated when the wire got switched to stainless. The only response I got is that they had never used galvanized wire (based on their recollection).

With the multitude of Wills gliders out there, and probably lots being flown in coastal areas where corrosion occurs more readily, you'd think this would be a bigger issue.

I also corresponded a bit with the engineer I'd previously been in contact with at Nicopress. He said the tin-plated sleeves are made from a slightly higher grade of copper than the zinc-plated ones, so the cost would be slightly higher for those (more on that in a minute). The stainless sleeves require different tooling than the copper ones and take more force to crimp. They also cost more. He's in Engineering, so he couldn't give me pricing, but I looked on the internet to see the price difference between the various sleeves for 3/32" wire and found it easy enough:

from Aircraft Spruce:

plain copper: $0.13 ea.
zinc-plated copper: $0.13 ea.
tin-plated copper: $0.15 ea.

from US Rigging:

plain copper: $0.16 ea. ($80 for 500)
zinc-plated copper: $0.18 ea. ($90 for 500)
tin-plated copper: $0.19 ea. ($95 for 500)
stainless: $0.76 ea. ($76 for 100)

Let's just say a typical glider has 20 of these little crimp sleeves (I know there's 12 sleeves for the 6 lower wires, and then some others for the sweep wire(s) (and top rear wire for a kingposted glider)). So that's less than $1 difference total between the cost of zinc-plated and tin-plated sleeves. Jumping up to stainless would be a bit more ( (0.76-0.18)x20 = $11.60 ), but what's $10 when you're talking about $4k+ for a new glider?
I can't speak for WW, but I can see some reasons why they wouldn't do the switch. Nico corrosion doesn't seem like a widespread issue with the current materials, and they have years of evidence of that current materials don't cause any other issues. And a particular nico is not a permanent part of the glider, since the wire needs to be regularly replaced. It is also possible that different nico materials would trigger the need to re-do a glider's certification which I guess is expensive. And if switching to new materials you might get some surprising behaviour / interactions which might necessitate a costly recall down the line.

So, I don't know, I'm just guessing. Since they didn't give a technical reason I'm inclined to think there are other reasons to stick with current materials, or maybe it's just one of those things that simply didn't come up on their radar before.
Proper eye splices, per MS51844, should hold until the wire breaks, regardless of sleeve material or plating. Minimum breaking strength for MIL-DTL-83420 3/32" wire rope is 920 pounds (for both carbon and stainless steel). Switching to tin-plated copper or stainless sleeves would only make things more resistant to corrosion and help ensure long-term strength of the sleeve, so that it does not become the weak link.

I may have to ping Steve Pearson; I haven't talked to him about this yet. It just strikes me as really odd, since aircraft design is typically not an area where you deviate from recommended practices unless you have some overriding reason to do so and lots of test data before you implement it on flight hardware.
Reducing production costs by WW has been an eye raiser of pilots for years. My first report of a fellow pilot about WW was about "maximum price for minimum product-1976". I've watched the redundant use of two nico sleeves go to just one, and the double stitching of seams pass away too. Some of these practices have passed the test of time, and some may be examples of going too far. We as consumers are the ones who have to stand our ground on quality-we can try and motivate the manufacturers -let us hope they listen. Stainless on stainless-- it aint rocket science --it's electrochemistry.
Ground Slammer wrote:
Thu Jul 06, 2017 11:17 pm
....We as consumers are the ones who have to stand our ground on quality....
We as consumers are the ones who have to be willing to pay a fair price for that quality but historically this has not been generally true. Hang gliders have a richly deserved reputation for being tightfisted. So what do you expect manufacturers to deliver for less than fair value? It pays to buy quality and quality costs money. It's what makes hang gliders go up. Lift has little to do with it.

In the movie The Right Stuff, there's a great scene about this same topic in which one of the characters says to the others, "What makes rockets go up?" "Funding!" :goodidea:
Here's what I got back from Steve today:

"My understanding and experience is that the certification and structural performance of copper and zinc plated sleeves are equivalent. http://www.nicopress.com/products/detail/33883/18-2-g

In our experience, the zinc sleeves are less likely to corrode. Also, I've never seen a properly swedged sleeve fail in service or testing. I'm not concerned with minor surface corrosion on a sleeve but rather on the age and service life of the cable assembly. The safety factors are relatively low for aircraft components and sidewires should be replaced every year. That can be extended to 5 years if the cables are in good condition with no evidence of corrosion or permanent deformation. The other cable assemblies are not as critical but should always be replaced if there is any kink, fray or significant corrosion.

Steven Pearson "

When he says "zinc sleeves are less likely to corrode", I'm assuming he means versus bare copper since that's what he mentioned as a comparison in the first paragraph. From reading the second paragraph it sounds like Wills' stance is that service life recommendations should end a cable assembly's usefulness before corrosion does. Still not quite the answer I was looking for.

I cut and splayed open the corroded sleeve today. Fortunately, no corrosion inside. Unfortunately, such a destructive inspection would not be practical on gliders in the field.
Add description
sleeve_inside.jpg (541.98 KiB) Viewed 1058 times
Also snapped a picture of the external corrosion while I had it under the video microscope:
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sleeve_outside_corrosion.JPG (531.25 KiB) Viewed 1058 times
I wonder how much better the tin-plated sleeves would do. After all, there is a likelihood of the plating being compromised in certain areas due to the crimping process. It'd be interesting to see some salt-spray test results for SS cable samples crimped with zinc-plated copper, tin-plated copper, and stainless sleeves.

Going back to my cost comparison, I decided to look up what it would cost to replace the wires on my Falcon 3. Here's what I dug up out of the manual and Wills' site:

40P-3105 WIRE BTM SIDE SLIPSTRM-LITESTR $54 ea, 2 req'd

40P-3201 WIRE SET BOTTM FRONT BALL SWG $87 ea, 1 req'd

40P-3303 WIRE SET BOTTOM REAR TANG $87 ea, 1 req'd

So $282 to replace all the lower wires. There'd be 12 sleeves total among those wire assemblies, so that'd be a whopping $0.12 increase to use tin-plated sleeves or $6.96 increase to go stainless. That seems like a huge bargain if the more corrosion-resistant sleeves keep you from buy replacement wire assemblies quite so often. Even if they bumped up the price a little to amortize the cost of the different tooling that the stainless sleeves require (which I don't think is that expensive), it'd still probably be a good deal. Example:

Set of wires with SS sleeves lasts 5 years. Cost = $300 ($282 + $7 + tooling amortization).

Set of wires with zinc-plated sleeves replaced every 2.5 years out of caution due to visible corrosion. Cost = $564 ($282 x 2) for an equivalent 5-year period.

I'm going to contact North Wing and ask them about their sleeves.
dbotos is now on track with me, it is a bit of a cost to go to an all electrically neutral wire assemblies ( tang, thimble, wire, and sleeves). The manufacture should not have to run a charity, it could be an option for a fee. I am right now working on a project and this thread has made me rethink my nico selection. A glider with a long life expectancy and low wire stress (8 wing wires) that also is not flown regularly, would benefit from stainless sleeves. A ragollo flown every week would be a waste. I like copper sleeves, copper flows better under my nico tool-copper is softer than the wire so it is less insulting to the strands. This has been a good thread for me :popcorn:
Yeah, that befuddles me too now that you mention it - the tang, thimble, and wire are all stainless and then they use a zinc-plated sleeve. Why do all that and then throw in one piece from the other end of the galvanic series?! I feel like I'm in the engineering twilight zone.

Speaking of which, North Wing emailed me back. Guess what kind of sleeves they use. Yup - zinc plated .

I hear you on the copper. Seems like it would mush around the strands of the wire with less potential to distort or weaken the individual strands. It'd be interesting to test samples done with copper and stainless sleeves to failure and attempt to see if that's a factor. You could also do etched cross sections of crimped samples to check for strand distortion.
In that our cables almost always fail at the edge of a sleeve-my guess is that stainless has a greater potential for weakening the assembly. It may be that it is equal if crimped right and worse when miss crimped-- or just worse! But I bet if done right it is on par with copper-but copper will be more forgiving of technique.

I find it interesting that NMERider quoted " The Right Stuff" In that story the astronauts demanded to meet the man in a jump suit with the grease under his finger nails----the next day my father introduced me and my brothers to Allen Shepard and John Glenn in our living room-said they were " A whole lot more than just test pilots!" He almost never had grease under his finger nails-he'd have to explain what happened to the missing grease-and he hated the paper work. What makes a rocket go up with out going bang? Quality Assurance, QUALITY ASSURANCE, QUALITY ASSURANCE. My father never lost an astronaut.
One day I will share with you all how I started designing gliders at the age of 4 years old-those 7 and that Von Broun were at the bottom of it! :cuss: Ground Slammer
Wire breakage at the end of the sleeve could likely be due to the rather abrupt changes in stress on the wire at that point. Outside of the sleeve, the wire only has relatively pure axial tension loads on the strands. Once it enters the sleeve, you add radial compression loads and since the sleeve is essentially locked to the wire rope, it should carry some of the tension load too. This would make for an interesting Master's thesis involving finite element analysis and some experimental work on real hardware.

Got another tid-bit from North Wing today. Kamron said their lower wires would be $165 to $175 to replace. About 60% of what Wills wants for their lower wires.

I looked at the Nicopress tools. For 3/32" cable, the basic hand tool to do copper (bare or plated) or stainless sleeves runs about $200 (it's the same series of tool - the one for stainless just has a different die head). There is also a $220 bench mounted tool (die head not included like with the hand tool). For either, it looks like you can get other size die heads for $112, which wouldn't be much to amortize.
dbotos wrote:
Mon Jul 10, 2017 1:12 pm
Wire breakage at the end of the sleeve could likely be due to the rather abrupt changes in stress on the wire at that point. Outside of the sleeve, the wire only has relatively pure axial tension loads on the strands. Once it enters the sleeve, you add radial compression loads and since the sleeve is essentially locked to the wire rope, it should carry some of the tension load too. This would make for an interesting Master's thesis involving finite element analysis and some experimental work on real hardware.

Flying wires break at the NICO because the wire only pulls on one side of the NICO sleeve. That force tilts the NICO sleeve, bending the wire and causing most of the strain to be on the wire strands closest to the center of the sleeve. Instead of breaking like a rope, the wire "rips" across, like a bedsheet, from one side. I have done the experimental work. I have examined the results by microscope. Please mail me my Masters Degree. :lol:

Double NICO sleeves are used to hold the NICO sleeves straight (NOT tilted) under load, and not because anybody thinks that a single NICO might slip. With two NICO sleeves properly applied at each end of the cable, the cable will usually break in mid-span, rather than at the NICO sleeve. For a cable with a single NICO at each end, the single NICO is a built-in weak spot. The only question is which end of the cable will break at the NICO first.

That is a good point. Looks like it's roughly a couple degrees on a 3/32" cable eye:
3_32_wire_rope_eye_angling_under_tension.png (40.58 KiB) Viewed 939 times
I don't think double sleeves would get it perfectly straight, but rather reduce that angle and the disparity of load carrying by the strands closer to the center of the sleeve.


P.S. I think you're supposed to bring a nice breakfast spread to thesis defense. I like fresh OJ and those cinnamon crunch bagels from Panera. :wink:
My wing has copper with clear heat-shrink and no double sleeves. That seems the most logical to me.

All wire rope of outside of the sail is un-coated with the exception of the lower rear.

Eventually I think I'm going to buy a hand tool and build a jig to do my own as needed and order the materials from Seedwings.

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