2H4
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Control Cables

Wed Apr 05, 2006 2:27 pm



Here's a question for the maintenance folks:

When installing new control cables, what procedures do you follow to pre-stretch them before installation?

I've heard about a procedure in which technicians hang weights on the end of the cable for a certain amount of time. Is this a fairly standard practice? If so, how much weight is typically used, and for long is the weight hung?

Thanks in advance for any info!




2H4


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KevinL1011
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RE: Control Cables

Wed Apr 05, 2006 2:50 pm

Quoting 2H4 (Thread starter):
what procedures do you follow to pre-stretch them before installation?

.....and can this technique be applied on smaller gauge cable?.......like , maybe the shift cables on a Trek ZR 9000?  biggrin 
474218, Carl, You will be missed.
 
viv
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RE: Control Cables

Wed Apr 05, 2006 6:22 pm

Quoting Kevinl1011 (Reply 1):
and can this technique be applied on smaller gauge cable?.......like , maybe the shift cables on a Trek ZR 9000?

Yes. I have a Trek 8500, and I do it for shift cables. I would do it for brake cables, but my Trek has hydraulic disc brakes..

I also do it for guitar strings.
Nikon D700, Nikkor 80-400, Fuji X Pro 1, Fujinon 35 f/1.4, Fujinon 18 f/2
 
EMBQA
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RE: Control Cables

Wed Apr 05, 2006 7:29 pm

Quoting 2H4 (Thread starter):
When installing new control cables, what procedures do you follow to pre-stretch them before installation?

You don't pre-stretch them...
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
Matt72033
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RE: Control Cables

Wed Apr 05, 2006 7:40 pm

dont they come "ready to fit"
 
2H4
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RE: Control Cables

Wed Apr 05, 2006 9:53 pm




Quoting Kevinl1011 (Reply 1):
.....and can this technique be applied on smaller gauge cable?.......like , maybe the shift cables on a Trek ZR 9000?

Boy, you saw right through that question...  Smile




Quoting EMBQA (Reply 3):
You don't pre-stretch them...

At least one of Duncan Aviation's locations does.




2H4


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474218
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RE: Control Cables

Wed Apr 05, 2006 10:49 pm

Raw cable where you would swage on you own fittings comes pre-streached. However, most maintenance organizations buy cable assemblies that are completely built and tested. Then all that's required is to install the cables and bring them up to the correct tension.
 
Lemmy
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RE: Control Cables

Wed Apr 05, 2006 10:53 pm

I once had a SRAM engineer lecture me for 20 minutes on the "myth of cable stretch." He was on a crusade or something.

How are aircraft cables tensioned and adjusted once on the plane? Turnbuckes?
I am a patient boy ...
 
2H4
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RE: Control Cables

Wed Apr 05, 2006 11:14 pm




Quoting Lemmy (Reply 7):
I once had a SRAM engineer lecture me for 20 minutes on the "myth of cable stretch."

I assume he was focusing on housing compression, then?




Quoting Lemmy (Reply 7):
How are aircraft cables tensioned and adjusted once on the plane? Turnbuckes?

I know turnbuckles are used on light GA aircraft...




2H4


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FDXmech
Posts: 3219
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RE: Control Cables

Wed Apr 05, 2006 11:39 pm

Quoting 2H4 (Reply 8):
I know turnbuckles are used on light GA aircraft...

Also on large commercial jets.



Quoting Lemmy (Reply 7):
How are aircraft cables tensioned and adjusted once on the plane? Turnbuckes?

The cables are tensioned using turnbuckles.
But it goes much further than that. The cables must also be be rigged so that the components that drive the cable and and that are driven by the cable are positioned correctly. This is mainly accomplished using rig pins.

Its been of my limited cable experience (don't work heavy maintenance) that new cables are tensioned to twice the normal tension, the cable cycled ten or so times then the cable is properly tensioned and rigged.

Interestingly, cable tension is based on outside temperature.
You're only as good as your last departure.
 
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HAWK21M
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RE: Control Cables

Wed Apr 05, 2006 11:44 pm

Are they prestreched for Commercial Aircraft.

Quoting Lemmy (Reply 7):
How are aircraft cables tensioned and adjusted once on the plane? Turnbuckes?

Turnbuckles.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Lemmy
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RE: Control Cables

Wed Apr 05, 2006 11:45 pm

Quoting 2H4 (Reply 8):
I assume he was focusing on housing compression, then?

I guess. The whole thing was surreal. He was convinced that the notion of cable stretch was some sort of industry conspiracy. I just smiled and nodded.

Quoting FDXMECH (Reply 9):
Also on large commercial jets.

This is an incredibly vague question, but it would seem to me that very long cable runs on big aircraft are trouble waiting to happen. How are these designed to minimize the chances of cables coming off of pulleys, cables getting pinched, cables loosening over time, etc.?
I am a patient boy ...
 
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HAWK21M
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RE: Control Cables

Wed Apr 05, 2006 11:56 pm

Quoting Lemmy (Reply 11):
How are these designed to minimize the chances of cables coming off of pulleys, cables getting pinched, cables loosening over time

Safeting,Inspections.....
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
777wt
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RE: Control Cables

Thu Apr 06, 2006 12:18 am

Quoting Lemmy (Reply 11):
This is an incredibly vague question, but it would seem to me that very long cable runs on big aircraft are trouble waiting to happen. How are these designed to minimize the chances of cables coming off of pulleys, cables getting pinched, cables loosening over time, etc.?

Self compenstating cable tenisors which keeps the tension at the correct setting as the OAT changes.
 
FDXmech
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RE: Control Cables

Thu Apr 06, 2006 12:29 am

Quoting Lemmy (Reply 11):
This is an incredibly vague question, but it would seem to me that very long cable runs on big aircraft are trouble waiting to happen. How are these designed to minimize the chances of cables coming off of pulleys, cables getting pinched, cables loosening over time, etc.?

Vague question? Not at all.

Though some cable runs are extremely long, surprisingly they cause few problems. Occasionally, cables do cause problems.

The cable system has pulleys to allow the cable to change its direction.

Oftentimes a cable pulley has seized causing higher than normal control input forces.

Or sometimes a cable "birdcages" which means the cable untwists in a localized area.

There is a bolt that prevents the cable from coming off the pulley. The bolt is positioned to let the pulley rotate but not enough clearance to allow the cable to get by.

The cables are prevented from loosening mechanically by putting locking clips in each turnbuckle. Though the cable could lose some tension by stretching.
You're only as good as your last departure.
 
474218
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RE: Control Cables

Thu Apr 06, 2006 1:37 am

quote=Lemmy,reply=11]but it would seem to me that very long cable runs on big aircraft are trouble waiting to happen.[/quote]
On long straight cable runs Lockheed aircraft use Lockclad cables. Basically a Lockclad cable is a cable (1/8, 5/35 or 3/16 inch diameter) with an aluminum tube swaged over the entire length of the cable an then the end fittings swaged on the entire assembly. This allow for much smoother operation and wears longer than standard cable. The Lockclad cable act like a push rod, but are much lighter. When a pulley is required to change directions a bare section of cable is used.

Cables do tend to lose tension over time, mainly due to cable or pulley wear, not from cable stretch.
 
A/c train
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RE: Control Cables

Thu Apr 06, 2006 1:56 am

Cables are tensioned by turnbuckles, you check the tension by using a T5 cable tensiometer, this figure when compared to ambient air temperature as has been stated will read off a graph and compare to the AMM to make sure it is correct, cables are not regularly changed more rigged using turnbuckles and rig pins as has been sated, never seen many problems with cables except when they require rigging.
regds a/c
 
2H4
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RE: Control Cables

Thu Apr 06, 2006 2:00 am



Can one of you knowledgeable techs describe how the cables are anchored at each end? Is there some kind of cable stop welded on to create an end-stop? Is the other end simply clamped into a fitting?




2H4


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EMBQA
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RE: Control Cables

Thu Apr 06, 2006 5:28 am

Quoting 2H4 (Reply 5):
At least one of Duncan Aviation's locations does.

Dosn't mean it's right. Unless it's in the AMM you don't do it.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
2H4
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RE: Control Cables

Thu Apr 06, 2006 6:17 am




Quoting EMBQA (Reply 18):

Dosn't mean it's right.

Are you suggesting that Duncan....an award-winning, renowned Falcon/Challenger/Gulfstream/Learjet MRO center is using unapproved maintenance procedures?

I think it's a little more likely there's an AMM or two out there that you aren't 100% familiar with...

 Wink




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SFOMB67
Posts: 371
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RE: Control Cables

Thu Apr 06, 2006 7:58 am

Quoting EMBQA (Reply 3):
You don't pre-stretch them...

98% of all control cables come pre-stretched (ready to use), but I have heard of cable that needs to be pre-stretched, although I've never used it.

Quoting Matt72033 (Reply 4):
dont they come "ready to fit"

Some cables come cut to length with all the fittings installed. Others may come with one end left off to allow you to attach it to the cable being replaced. You would cut the end off that cable and join them together with shrink tubing or other suitable means and pull the old cable out from the other end, while pulling the new one in behind it. Being VERY careful not to pull them apart or you will have problems if they come apart in an inaccessable area. You then cut off a predetermined length of the new cable and swege a turnbuckle terminal or ball on it.

Quoting Lemmy (Reply 11):
How are these designed to minimize the chances of cables coming off of pulleys

There are cable keepers (pins or bolts accross the pulley groove) or some pulleys have a metal shroud around the pulley, to keep the cable in the pulley groove, should it become slack.

Quoting Lemmy (Reply 11):
cables loosening over time

Cables do loose tension over time (several years), but generally we're talking of tension dropping from 80# to maybe 50-60#.

Quoting 2H4 (Reply 17):
Can one of you knowledgeable techs describe how the cables are anchored at each end?

Usually one end of the cable has a ball that fits into a slot on a bellcrank (this may be attached to the rudder actuator mechanism in the vert. stab) and the other end has a threaded terminal (may be located in cabin ceiling or cargo pit ceiling). It is joined to another cable, with a turnbuckle (note, one cable has a LH thrded terminal and the other a RH thrded terminal), which would go forward and attach under the cockpit floor to the rudder pedal with a ball, also. Hope this isn't too confusing.

In the years of the 707 & DC-8, cables would wear quite often and require replacement during C-Cks, but most newer airliners have very little maintenance on cable systems, and now we're moving to FBW.
Not as easy as originally perceived
 
FDXmech
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RE: Control Cables

Thu Apr 06, 2006 8:47 am

sfomb67

It's rare we get a cable change on the line. Yet it often turns into a can of worms. You get the tension right but the holes are off. You get the rig on but the tension is off. Everything comes together then a turnbuckle bottoms.
You guys doing heavy maintenance obviously have it down to a science. Hats off to you.
You're only as good as your last departure.
 
SFOMB67
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RE: Control Cables

Thu Apr 06, 2006 9:12 am

FDXMEC

You get pretty comfortable after about 15 years of rigging flight controls at heavy maint visits.
Not as easy as originally perceived
 
pilotpip
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RE: Control Cables

Thu Apr 06, 2006 9:32 am

Quoting Lemmy (Reply 7):
I once had a SRAM engineer lecture me for 20 minutes on the "myth of cable stretch." He was on a crusade or something.

They'll also tell you that their 1:1 system works better than shimano. The only reason it works "better" is the heavier spring in the parallelogram and the spring loading in the twist shifters throwing the cable back to lower tension settings.

Not ragging on SRAM, after all, I have X.O on my Kona.
DMI
 
2H4
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RE: Control Cables

Thu Apr 06, 2006 9:51 am




Quoting Pilotpip (Reply 23):

Looking forward to trying the Force group this summer....




2H4


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EMBQA
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RE: Control Cables

Thu Apr 06, 2006 11:35 am

Quoting 2H4 (Reply 19):
Are you suggesting that Duncan....an award-winning, renowned Falcon/Challenger/Gulfstream/Learjet MRO center is using unapproved maintenance procedures?

I think it's a little more likely there's an AMM or two out there that you aren't 100% familiar with...



Quoting EMBQA (Reply 18):
Unless it's in the AMM you don't do it.

......and that, as you can see, is what I said...!! Unless it is in the AMM you don't do it. I've installed LOTS of control cables in my career and never once did the AMM have me pre-strech a cable.

[Edited 2006-04-06 04:38:52]
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
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HAWK21M
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RE: Control Cables

Thu Apr 06, 2006 6:45 pm




Quoting FDXMECH (Reply 14):
Or sometimes a cable "birdcages" which means the cable untwists in a localized area

Any history on that term.

Quoting 2H4 (Reply 24):
Looking forward to trying the Force group this summer....

Whats this.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
2H4
Topic Author
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RE: Control Cables

Thu Apr 06, 2006 10:33 pm




Quoting HAWK21M (Reply 26):
Whats this.

It's a new bicycle component group.  Smile




2H4


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474218
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RE: Control Cables

Thu Apr 06, 2006 11:13 pm

Hawk21M,

Could you please tell me the type of aircraft the picture of the cable run, Reply 26.

Also you seem to have no trouble posting pictures, please tell me how you do it.

Carl
 
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HAWK21M
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RE: Control Cables

Thu Apr 06, 2006 11:46 pm

Quoting 474218 (Reply 28):
Could you please tell me the type of aircraft the picture of the cable run, Reply 26.

B-17.

Quoting 474218 (Reply 28):
posting pictures, please tell me how you do it.

To add a graphic within your message, just encase the URL of the graphic image as shown in the following example

In the example above, the UBB Code automatically makes the graphic visible in your message. Note: the "http://" part of the URL is REQUIRED for the [img] code.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
474218
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RE: Control Cables

Thu Apr 06, 2006 11:53 pm

Quoting HAWK21M (Reply 29):
B-17.

Thanks Mel,

I was confused about the lack of any corrosion protection. I guess B-17's were not expected to last long enough to corrode.

Carl
 
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HAWK21M
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RE: Control Cables

Fri Apr 07, 2006 1:07 am

Quoting 474218 (Reply 30):
guess B-17's were not expected to last long enough to corrode.

A Nice LINK to the Aircraft.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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