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String tying of cable looms?

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String tying of cable looms?

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Old 19th Sep 2018, 11:29
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String tying of cable looms?

Always wondered, during my walk-arounds, why electrical cables in aircraft looms are tied with knotted waxed string rather than using plastic ty-wraps. (aka Zip ties)

Is it because ty-wraps were not invented when aircraft were first built and the practice has remained, or does the waxed string have an advantage? (It is much less bulky and less likely to catch than a ty-wrap for example).

I ask because the waxed string would seem to be much more labour intensive and time consuming to apply than ty-wraps.
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Old 19th Sep 2018, 11:50
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It takes a lot of care to remove a ty-wrap without nicking the wiring, and when removed the old one becomes a FOD hazard. The "removeable" kind are prone to uncommended release. But the main reason is simply what is in the certified manufacturing standards of the aircraft manufacturer. I know that our's didn't allow ty-wraps, but the RAF and RN would often use them in SEMS, so if the aeroplane came back into us for a major mod, repair or upgrade the first thing we had to do was remove these ty-werapped SEMs as we couldn't legally fly (let alone release) release the aeroplane wuth them fitted.

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Old 19th Sep 2018, 12:12
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In addition to any certification requirements, a properly waxed string tied loom is not only much neater but retains the shape and integrity of the loom along its entire length, even making the loom stronger than the sum of its individual parts. Cable tied looms tend to bulge where there is no tie and loose their form.

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Old 19th Sep 2018, 12:21
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Originally Posted by Uplinker View Post
Always wondered, during my walk-arounds, why electrical cables in aircraft looms are tied with knotted waxed string rather than using plastic ty-wraps. (aka Zip ties)

It's technically called lacing. It's been around since day one and crossed over from the original telephone days which used lacing to tie phone line runs. It's the same lacing used on fabric aircraft to lace the fabric at the ribs. It's also the preferred method on several levels: FAA guidance, durability, strength, weight, etc.

Originally Posted by Uplinker View Post
I ask because the waxed string would seem to be much more labour intensive and time consuming to apply than ty-wraps.
Keep in mind most original wire harnesses or for major electrical/avionics upgrades are built on a board and not in the aircraft. So it's not as labor intensive as it seems. Tywraps have their place but have specific environmental requirements like engine compartments. Plus in my experience they never last as long as lacing or can cause other issues like chafing, or slicing my f'n knuckles open because someone was too lazy to trim the plastic end flush with the lock.

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Old 20th Sep 2018, 22:45
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In all fairness, lacing is not the only authorised way to assemble a loom. Depending on aircraft origin and age, one can also find solutions like plastic spiral wrap or braided sheathing.
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Old 21st Sep 2018, 06:09
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Originally Posted by Ultranomad View Post
In all fairness, lacing is not the only authorised way to assemble a loom. Depending on aircraft origin and age, one can also find solutions like plastic spiral wrap or braided sheathing.
This might explain why, on some factory fresh heaps known as the ATP, parts of the loom running down the left side and under the cabin floor were thoughtfully secured with bog standard string straight from the local hardware shop
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Old 21st Sep 2018, 20:16
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Originally Posted by Krystal n chips View Post
This might explain why, on some factory fresh heaps known as the ATP, parts of the loom running down the left side and under the cabin floor were thoughtfully secured with bog standard string straight from the local hardware shop
To be fair, that was probably the better quality part of the ATP - Aerospace Taking the Piss
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Old 24th Sep 2018, 09:31
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Originally Posted by wrench1 View Post
It's technically called lacing. It's been around since day one................... It's also the preferred method on several levels: FAA guidance, durability, strength, weight, etc..........Plus in my experience they never last as long as lacing or can cause other issues.........slicing my f'n knuckles open because someone was too lazy to trim the plastic end flush with the lock.

(my bold) Yeah, I hear you, and have the scars on my fingers to prove it !

My background is electronics, and we used ty-wraps, but I seemed to be one of the very few who trimmed the ends flush. Everyone else cut them off leaving a half inch ‘knife blade’ sticking out of each lock. I pointed this out to a junior colleague who had built a rack of equipment leaving all these sharp hazards inside for the next engineer who put their hands in. He just said if you’re that bothered, cut the ends flush yourself. Oh, yeah, thanks mate, don’t bother accepting my experience then. You’ll find out the hard way...........
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Old 24th Sep 2018, 12:11
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The other big reason for using lacing is heat , cold and vibration . Tyraps are prone to loosen or break if exposed to extremes of temperature or vibration .
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Old 24th Sep 2018, 15:40
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Back in the day when i worked (!), I had a couple of people
who had traveled the world doing this kind of wrapping on our groundstations.
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Old 24th Sep 2018, 17:28
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Did part of my apprenticeship in the loom shop at Hurn.
Green string was used on BAC 1-11 wiring, however the Concorde wiring used different colours to identify the systems the wiring related to.
ISTR the spacing of ties was 6 ins on the 1-11 but 18 ins on Concorde to save weight.
When various looms are bundled together on the aircraft the string ties don't cause a rubbing issue whereas tie-wraps do.
When the looms were installed in the trunking in the roof of the baggage bays of the 1-11, plastic coated metal straps were used alternating with plastic tie-wraps.
Hope this helps.
P.S. The green waxed string was very good in the garden for peas and runner beans. (I still have some!)
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Old 26th Sep 2018, 14:43
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Thanks for all the replies.

.
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Old 28th Sep 2018, 16:04
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Originally Posted by Uplinker View Post



(my bold) Yeah, I hear you, and have the scars on my fingers to prove it !

My background is electronics, and we used ty-wraps, but I seemed to be one of the very few who trimmed the ends flush. Everyone else cut them off leaving a half inch ‘knife blade’ sticking out of each lock. I pointed this out to a junior colleague who had built a rack of equipment leaving all these sharp hazards inside for the next engineer who put their hands in. He just said if you’re that bothered, cut the ends flush yourself. Oh, yeah, thanks mate, don’t bother accepting my experience then. You’ll find out the hard way...........
that and not taking the tails off at all...

"When I was at" story...
to cut it short it took about 3 yrs from the off to finally get the French to stop using scalpels to remove lacing when de looming bundles on the A380 lines.
About this time the first graduates from their aerospace academy pitched up.
We came back to a section 13 to find (how unusually) that not only was the floor back down and cones, safety tape etc removed with the power bundles left forelornly sticking out af the boards but that a line of 8, new french pattern steps were in their place surrounded by piles of cut loose lacing tape.
Atop each pair of steps was a nice shiney scalpel...
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Old 9th Oct 2018, 20:24
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Does anyone remember the strapping (tyton?) guns that were bought into use in the RAF somewhere in the late 80's - early 90's? Wonderful bits of kit at first, load the magazine with plastic clips, load a clip into the gun, wind the plastic tape round the loom, stuff the ed of the tape into the clip, tighten it up, squeeze the trigger to shove a pin in the clip into the tape, then cut the tape - all very simple & quick apart from one minor problem. The loaded magazine of clips would discharge its contents all over the place if you got it wrong, FOD hazard of the highest order, as in safe s&x the tool was quickly withdrawn!
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Old 9th Oct 2018, 20:48
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I remember the Tyton gun, but the only place I ever saw or used it was in trade training. That was in ‘84 to ‘85. As to the original question about string v cable ties, a good operator can tie remarkably quickly. In addition if you tie off the roll, i.e cut the string only after the tie is complete, there is very little waste.
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Old 12th Oct 2018, 18:51
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Originally Posted by Avionker View Post
I remember the Tyton gun, but the only place I ever saw or used it was in trade training. That was in ‘84 to ‘85. As to the original question about string v cable ties, a good operator can tie remarkably quickly. In addition if you tie off the roll, i.e cut the string only after the tie is complete, there is very little waste.

Indeed, indeed.
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Old 17th Oct 2018, 09:17
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You have a couple of types of ty wrap as well
plastic lock tang or metal lock Tang. I would never use the plastic lock type for anything aviation related. Maybe tying up the apprentices, Are you still allowed to do such things?
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Old 19th Oct 2018, 19:12
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Originally Posted by Ethel the Aardvark View Post
You have a couple of types of ty wrap as well
plastic lock tang or metal lock Tang. I would never use the plastic lock type for anything aviation related.
Just the opposite actually.

But you probably know that anyway, along with external serrations.....
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