Double Cable Swaging - Risky technique

[NiqueNaque]

Gentlemen,To bring it to your attention, and I will include this in the 'what not to do' page.I have with all my stainless steel cables double swaged them for redundancy and strength.I have discovered this last Sunday that it is not a good idea to have both the swages butting up to each other when you swage the cable, if you do so it preloads the cable between the two swages due to the fact that they squeeze up against each other. Not only that, but any flexing that happens close to the thimble will take place between the two swages, with them working against each other I had a cable break in my mast stay while climbing up to inspect the rotor assembly, I used the cable to pull myself up and it snapped off, fortunately as there were two such cables I avoided a fall, so redundancy is a great thing. The bungee strap running up beside it helped restrain it so it didn't flick either, top idea.I will amend my swaging practice to space the swages at least 25 mm apart or at least 5 diameters apart.Hope this helps,Nick.

[Brian]

Still reckon if its done properly the first time, then one swage is plenty. Even you Nick wold be hard pressed to be as rough on stuff as me and thanks to Rosco, I have never had a swage propblem !!A good idea Nick is use the mast for a hand hold, if it lets go then you certainly do have a problem !!! Brian

[NiqueNaque]

Brian,I beg to differ, my father in law is a boiler maker, for some reason he keeps calling me 'Errol' - any ideas as to why?Cheers,Nick.

[Brian]

naaahh I just cant think of one reason to call a sweet young fella like you a name like that. Brian

[asra]

If you believe the specs and do the job properly with the correct tool there is no reason to believe that the swage is the "weak point" in a cable termination. If you have doubts about it you should do it again properly.Checking the "tail" at the swage as part of the preflight is a good idea, and while covering the "tail" with shrink tube may be criticised by some, the use of clear shrink allows visual and tactile checking, then you won't snag yourself on it.John EvansThink logically and do things well, think laterally and do things better.

[Tim]

If a single swage is done correctly, the cable will break before the swage will slip.Tim McClure

[asra]

Tims, correct, with all the swaging I have done and seen other people do in my yachting days, I never saw a failure, with the acception of the people who did not use the correct swaging tool, thimble, and importantly the correct wire matching swage, these people we refered to as the "pliers merchants".Pete Barsden

[telf]

While on the subject, what/where, etc for buying the correct gear for swaging.Personal opinions anyone??telfFlying - The knack lies in learning how to throw yourself at the ground and miss. (Douglas Adams-The Hitch-Hiker's Guide to the Galaxy)

[asra]

Start with a Yachting supplier dear Liza, dear Liza.Pete Barsden

[asra]

Merry Christmas Telf, are you settled in in Darwin?Most boat places have the right tool, my local Mitre 10 hardware has one they loan out, but it's because they do sell some boaty bits. Even if they'll only loan it out on a deposit you might as well give the boat people a try.John EvansThink logically and do things well, think laterally and do things better.

[telf]

Thanks Pete, obvious really but with the last 15 years in Alice, I still don't think 'yacht' too quickly.John,All's well on the Darwin front. The Goddess and I bought a house (with beer fridge and large pool).Got a great job as manager of a control systems company at the airport.I'll probably be buying Colin Dawson's gyro. It was advertised a few days ago on the forum for $8000.My 503 is a little too marginal up here so I was looking at fitting my old 532 or a 582 just to have enough power to be safe.Along comes Colin with his beast with 26' blades and an EA81.Should be perfect......will see it and decide tomorrow.All the best for xmas and the new year guys.telfFlying - The knack lies in learning how to throw yourself at the ground and miss. (Douglas Adams-The Hitch-Hiker's Guide to the Galaxy)

[NiqueNaque]

Telf,You could mail order from Bias Boating supplies, I bought some cable and swages, pliers and swaging tool to refit my gyro, I've also found it damn handy for work as well and it isn't until you get one you start to stretch the applications.Cheers,Nick.

[asra]

The ultralight Instructor/TA here insists on double swaging of stays with a gap between them and with a bit of extra slack between the swages for the terminating end causing a slight bow in the cable. The benefit is if there is any give in the primary swage, it will show as the bowed cable will tighten.Pete

[asra]

I believe what Tim and I have said above is correct, particularly as there would often appear to be other much weaker components in the system of which the cable is probably the strongest! That said I know of two cases in which a swage was found to have slipped after impact, in one of these incorrect swages had been used, but the constructor had actually proof loaded the cables prior to installation, with no apparent problems. These were rudder cables, and it's hard to envisage any flight load that could approach their limit. In the second case the pilot denied any problems with the rudder until he found out about the slipped swage, video evidence appeared to contradict his later attempts to blame it.At a recent TA course a machine being used to demonstrate things a TA should check for registration had a swage let go when the rudder pedals were given a pretty hard push. They had been incorrectly swaged.While it may be difficult in some cases to get at the cable for proof loading it's probably better than double swaging, particularly if you check the "tails" as part of your preflight.In my view mast cables are a concern as taxiing on rough ground gives them a pretty good workout, jerking them fairly hard. I understand that some time ago in the US one let go at the front in flight resulting in a fatality when it whipped up and wrapped around the rotor. My machine with a mast cable has strong cord knotted to it at 18" intervals to restrain it.John EvansThink logically and do things well, think laterally and do things better.

[asra]

I built a 25 foot yacht years back and simply used a hand swager for all the stays that hold up the mast and transfer the power of sails into the hull, with no problems. Had a mate in quality control in the army who cut and polished a swage and confirmed a perfect result and we only used single swages as doubles are unsightly. However they don't weigh or cost much and gives me peace of mind to know I have a back-up, as I just do not like to think of a failed wire going through a prop or rotor whilst up there flying.Pete