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Old Oct 06, 2014, 01:07 AM
Diesel Danny
danny mz's Avatar
Australia, VIC, Bellbridge
Joined Nov 2013
319 Posts
Discussion
Terminating Lead-Outs & Control Lines

G'day.

Last weekend I saw a fine C/L model destroyed when the lead-out broke at the wing tip.

The modeller is very experienced but I could not help thinking that the method that he used to terminate his lead-outs at the wingtip contributed to the accident.

The lead-outs were stranded, doubled over, bound with fine wire and soldered. The break was at the junction of the flexible cable and the rigid solder joint.

A stress point was created at the junction (in my opinion).

My own practice, learned as a young bloke from Ron Moulton's 'Control Line Manual' has been to double the wire ends, bind them with a few layers of fine wire (or linen thread), with extra layers at the loop. Thus creating a tapered profile.

Next I simply cover the join with 24 hour 'Araldite' (strong epoxy). I also do this for line terminations as well. Before making the loops I slip a piece of heat shrink tubing over the line, and when the epoxy is almost set, I slide this over the joint and use a heat-shrink gun to tidy things up a bit.

I think that this creates a flexible join with less chance of the type of fracture that my friends model suffered. Because it was a racing event, the model did pass the mandatory 'pull-test' before being flown.

Also I bush the holes in bellcranks and have never had a failure.

Anyway C/L flyers, if this helps save somebody's model it's been worthwhile.

Any other ideas on this?

* Danny M *
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Old Oct 06, 2014, 03:29 AM
Size doesn't matter!!!
Belgium
Joined Sep 2005
108 Posts
Danny, you are 100% right on your method of terminating the lines and lead outs. Never (NEVER!) use solder on lines! Solder makes the lines go brittle after a while and the joint is too rigid. I still use sets of lines I made in 1974 with araldite epoxy. I have seen brand new soldered lines break on their first flight, just because they were stressed at scrutineering...
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Old Oct 06, 2014, 07:06 AM
Greggles47
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Sydney OZ
Joined May 2007
415 Posts
Hi Danny,

You do make a good point, but I'm sure the advocates of soldering will be able to point to many years of operation without failure.

I have recently started doing my leadouts in this fashion, without failure (but my experience is only a few years.
I have been doing my line terminations in the same manner as you describe for very many years (possibly near 2oyears) without failure.

It is possible that the model in question had not had whatever flux removed from the joint and possibly set up a failure point that way.

As you say the modeller in question is greatly experienced, with successes at local, state, national & international level.

Greg
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Old Oct 06, 2014, 07:40 AM
Bagpipes spoken here
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United States, MN, St Paul
Joined Aug 2007
115 Posts
Never solder flex cable leadouts. Never...

Use the method shown in the AMA rule book, control line section.

http://www.modelaircraft.org/files/2...LGeneral-1.pdf
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Old Oct 06, 2014, 12:25 PM
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United States, OK, Norman
Joined Jul 2014
21 Posts
Quote:
Originally Posted by Pipemajor View Post
Never solder flex cable leadouts. Never...

Use the method shown in the AMA rule book, control line section.

http://www.modelaircraft.org/files/2...LGeneral-1.pdf

If you read the fine print.. it says "coat wrapping with epoxy or solder to secure''.

I have C/L aircraft that are 37 years old and the lead-outs are still fine.. they are all soldered.. the catch is you HAVE TO KNOW HOW TO SOLDER.. and MANY people don't.. soldering does NOT cause a break.. weaken the line by overheating .. or making a poor (cold) solder joint will cause a failure.. Corrosion is the next concern.. If you create a stress point even using epoxy you have built a failure point..
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Old Oct 07, 2014, 07:55 PM
Registered User
United States, MN, Eagan
Joined Jul 2013
179 Posts
is it possible that the solder now day's is cheap that contains more tin.
I would think that silver solder would be a better choice
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Old Oct 07, 2014, 11:51 PM
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United States, OK, Norman
Joined Jul 2014
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Quote:
Originally Posted by jbonice View Post
is it possible that the solder now day's is cheap that contains more tin.
I would think that silver solder would be a better choice
Yes it would.. but then there are even fewer people that are comfortable doing that... besides its overkill..

A properly wrapped, soldered and cleaned lead out is plenty strong..
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Old Oct 08, 2014, 02:21 AM
Diesel Danny
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Australia, VIC, Bellbridge
Joined Nov 2013
319 Posts
Soldering Lead-Outs

G'day.

I am not querying the strength of the join and also agree that silver solder is overkill. SS is better put to use for joining horns to wire links imho.

What I am concerned about is that the junction of a rigid soldered joint with a flexible cable creates a potential fracture point. (Just like if one puts a piece of wire in a vice and keeps flexing it - the wire will break, and rapidly too!).

Soldering flux residues are a whole new problem, the most aggressive (killed spirits, 'Baker's Fluid' for example) give great results but as beercamel said proper cleaning is vital.

Rosin cored flux may be a bit more gentle (especially if it is RMA) but I prefer to use that for it's original purpose of soldering electronic components. More info regarding soldering flux may be found at http://store.curiousinventor.com/gui...kind_of_solder if one is curious.

Anyway, horses for courses. I am sure that many of us have used a soldered joint for C/L lead-outs for years without a problem, but the demise of my friend's model did make me think about the matter.

Regards * Danny M *
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Old Oct 08, 2014, 03:04 AM
KE your cub.
Curare's Avatar
in the gutter, again....
Joined Jun 2005
4,205 Posts
I'm another one for the 'no solder' camp.

Bind and coat in epoxy. Hell if you're cool, you can even tint the epoxy so you know which is 'up' and 'down'

Flexible and reliable.
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