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Marks on Flying Wires


Teckair
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Over the years I have noticed dark brown marks on the structural wires of air craft like the Drifter and Lightwing. There has been some debate about this as to whether it is safety issue or not, some say it is corrosion and some say it is some sort of lubricant used in the manufacture of the cable. I have contacted some people about this with no result so far. I would like to find out one way or another about this, hopefully someone out there has some answers.

 

 

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I know what you mean and it was of some concern to me too at one stage. Some cables do have lubrication but I thought it was mainly for control cables which work around sheeves, certainly Aircraft Spruce catalog states that their cable is lubricated during manufacture for this purpose and that it makes it superior for control cables compared with 'standard' cables.

 

On my Drifter the marks showed up in completely irregular patterns, and they were predominantly on the forward facing side of the cables so I concluded that they were bug stains. They did seem to be quite hard to clean off but I used Brasso on one occasion and the cables came up nice and shiny again but you could still see where the stains were by the discolouration between the strands. I had a careful look at the areas through a jeweler's loupe and I couldn't see any signs of surface corrosion. I couldn't find any record of a Drifter's wires having broken - even the early ones with thin wires - so I stopped worrying about it. I took extra comfort in the knowledge that stainless rigging wires on yachts (which are 1x19 construction and therefore much more affected by work hardening and cracking of the outer strands) don't fail suddenly and catastrophically but instead they start to break outer strands which unravel and show that it's time to replace them.

 

Yacht shrouds are generally recommended to be replaced after 10 years if they are on performance vessels or are light rigs on cruising vessels and most insurers will insist on a Master Riggers inspection and non-destructive testing annually after that time with a maximum life and therefore compulsory replacement, if you want to stay insured, after twenty years in service.

 

 

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You may be able to disconnect the cable and gently twist it in a direction that opens in up slightly to be sure it is not internal corrosion. It is more common to have the swages flaking off, which really isn't good. AN-8-2004 on the RAA website, goes into some detail.

 

 

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I took extra comfort in the knowledge that stainless rigging wires on yachts (which are 1x19 construction and therefore much more affected by work hardening and cracking of the outer strands) don't fail suddenly and catastrophically but instead they start to break outer strands which unravel and show that it's time to replace them.

I don't think that is correct. My understanding is that the older non-stainless stays tended to "whisker", before they should be replaced, but stainless just breaks without whiskering.

 

I have experienced this in a 14' catamaran, and it is sudden, complete, and entertaining. The effect is pretty much what you would expect: a loud crack, and then a pile of mast, rigging and sail in a heap next to you.

 

If we translate that experience to effects in an aircraft, I would replace stainless wires at any time you have any suspicion they are not OK, for example: on purchase of a second hand aircraft (unless you intimately know who has flown it, and how they flew it), at a certain number of hours or years, and if anything looks odd or wrong.

 

dodo

 

PS - that experience is using using 7 x 7 wires - 1 * 19 is only good for applications where the wire stays in place and is not flexed or bent too much.

 

 

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Guest Maj Millard

There were some past warnings about cable with a single strand that would rust. Probabily an AD or service instruction issued ,but I don't have details to hand.

 

I had a similar problem on my Drifter also, and made a point of lubricating all cables at least every six months with a reputable penetrating lubricant. Cables can rust from the inside- out, so you do need to get a lubricant that penetrates and dries to a protecting film ideally.

 

I personally used ACF50 which is a specialised aviation lubricant and corrosion protectorant. LPS 3 would also work. Apply liberally with a small rag soaked in whatever you choose to use...........................Maj.....014_spot_on.gif.1f3bdf64e5eb969e67a583c9d350cd1f.gif

 

 

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There were some past warnings about cable with a single strand that would rust. Probabily an AD or service instruction issued ,but I don't have details to hand.I had a similar problem on my Drifter also, and made a point of lubricating all cables at least every six months with a reputable penetrating lubricant. Cables can rust from the inside- out, so you do need to get a lubricant that penetrates and dries to a protecting film ideally.

I personally used ACF50 which is a specialised aviation lubricant and corrosion protectorant. LPS 3 would also work. Apply liberally with a small rag soaked in whatever you choose to use...........................Maj.....014_spot_on.gif.1f3bdf64e5eb969e67a583c9d350cd1f.gif

Where can we get LPS 3?

 

 

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Guest Maj Millard
Where can we get LPS 3?[/A good mechanical or tractor supply shop should carry it. Have also seen it listed on aviation supply catalogs.....Some auto. Supply shop may carry it also...There are three types of LPS 1,2, and 3................Maj........014_spot_on.gif.1f3bdf64e5eb969e67a583c9d350cd1f.gif

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Perhaps of interest, Teckair, I replaced some cables on the 95.10 that I bought from Wolfgang. There was some minor corrosion , out of interest, I put them on the cable test rig, they showed no sign of failing, even when the eye ends with the thimbles started to flatten out.

 

 

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Ther are plenty of places to buy cable and swages. Then make them to length . I have a cable pull testing rig as well.

I'm not certain of all the ins and outs of it but I suspect the problem here is whether it is permissible to make your own, and I'm fairly sure that in many cases it isn't.

 

Drifters that were made by Austflight after about 1986 were built and certified to comply with ANO/CAO 95.25 and can be used for training but may not be modified from standard at all without an Engineering Order (or similar) so you can't make your own new cables, or fit them come to that, unless signed out by an L2. And I think that applies whether or not the aircraft is actually used for training.

 

19 registered Drifters (Maxairs, Fishers etc) can have the cables made up and replaced by the original builder but not by a subsequent owner, if I understand the process correctly. An L2 may or may not be permitted to make up new cables, it would be worth getting a determination on that I would think. It needs to be borne in mind that the cables are very much Primary Structure and getting it wrong would be catastrophic. It needs to be thought of in the same way as who may or may not be permitted to make up a new strut, for example.

 

Don't get me wrong, I'm not being a wowser and I'm all for having all the reasonable freedoms to work on our aircraft that we can but these days we have to be so vigilant in regard of potential liability issues. I've met M61A1 and know he would be eminently capable of making and testing new cables, I'd fly under them without any hesitation, but I wouldn't suggest folks make up cables without very careful consideration, and knowledge of how the maintenance and modification rules apply to the different categories of recreational aircraft.

 

In answer to f_t's question I think that possibly the only way you can now get new cables for a former 95.25 (now 95.55) Drifter, legally, would be from the holders of the Type Certificate which is the factory at Dalby, they do still make some parts to order I understand. Otherwise you might need to employ a Reg35 and have a special Engineering Order written. Co-incidentally, I don't think that has changed as a result of the closure of Spectrum at Lismore, unless Wayne had some specific agreement to manufacture certified Drifter parts under licence that I am not aware of.

 

As for how you'd get legal new cables for a Gemini, for example, I expect an engineering order might be the only way.

 

If Dafydd reads this he would know the details better than I and might be able to clarify the issues for us?

 

 

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Good point, I'm assuming the person doing it is at least an L2 if it's on a certified drifter. You need to be very sure of the type and size cable you purchase? That said, I bought some rudder cables from Jim Fenton at Boonah some years ago, he handed me a plastic bag with enough cable and a handful of swages, then asked "do you need to borrow the swaging tool?"

 

The AC 43 would be the document I used as a reference.

 

 

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Otherwise you might need to employ a Reg35 and have a special Engineering Order written.

CAR 35... which is now CASR21M I believe... but that relates to modification/repair design approvals. Is 'replacing' something on a plane a modification or repair. I don't think so. Or else you would need a CASR21M approval for changing a tyre.

 

 

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Perhaps of interest, Teckair, I replaced some cables on the 95.10 that I bought from Wolfgang. There was some minor corrosion , out of interest, I put them on the cable test rig, they showed no sign of failing, even when the eye ends with the thimbles started to flatten out.

Point taken, but the problem is once the rust appears how do you know when they are no longer safe? My guess is the only sure way is to replace the cables once rust appears, For a certified aircraft, I do not believe it would be legal to make them your self not even if you are a L2.

 

 

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If your have any doubts about your cables, you should change them, I tested the ones I removed as an exercise, and they weren't badly corroded. As for making your own, if an approved maintainer is using approved cable, approved swages and iaw the correct procedure, no problem. To my knowledge, Austflight didn't sell you a complete assembly, they sold the cable and swages, because between aircraft the lengths vary slightly, or you took your aircraft there and they made new cables to fit.

 

 

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Contact some one like Bullivants etc They do all the swaging for the crane lifting industry and can make up and test it to destruction. Usually the cable fails before the swage.

 

Most wire rope slings have a safety factor of about 5 x WLL

 

 

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Lubricating cables can lead to unwanted contamination adhering to the cable,thus increasing the rate of wear between the strands and around pulleys.SS cables are best left alone as the surface requires O2 to be in contact to maintain a thin chromium oxide film for protection.[ you can Google under Tea Staining of SS for further info]

 

 

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