[ARC5] Tuning Cable Question

[Mike Everette via ARC5]

Hi Mike,

I made a typo when composing the last message.  Meant to say that the sheaths were shorter than the inner cables, not longer than the inner cables.  I think the sheaths ended up more than 3 inches shorter.

When I removed the cables, they had to be worked through holes in several bulkheads and not "yanked" out. The ferrules would have hung up otherwise.  

These cables were in terrible shape.  I ended up salvaging the splines from three ends (driving out the pins), along with the ferrules, and mating the splines with 1/4 inch shafts to make some real nice local tuning knobs.  Would have been great if I could have figured out a way to shorten the cables to something like 12-18 inch length for a display setup tuned from the control box, but that would've required special tools that I didn't have and had no access to.

73

Mike
WA4DLF

  
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On Tue, 6/3/14, Mike Hanz <aaf-radio-1 at aafradio.org> wrote:

 Subject: Re: [ARC5] Tuning Cable Question
 To: "Mike Everette" <radiocompass at yahoo.com>
 Cc: arc5 at mailman.qth.net
 Date: Tuesday, June 3, 2014, 1:26 PM
 
 On 6/3/2014 12:46 PM,
 Mike Everette wrote:
 > I have several
 tuning cables which were pulled from a scrapped Twin Beech
 (SNB-5) wherein the metal sheaths had separated or unraveled
 during bends.  I could tell that the actual spline cable
 was noticeably shorter than the sheath and would have been
 even more so had the sheaths not opened up.  Another SNB-5
 from which I removed an ARC-5 setup had a similar problem --
 really tight tuning cables which were almost impossible to
 get back onto both the receivers and control heads without
 stretching the sheaths out straight and pulling on them like
 mad.  Even then it was not easy.
 >
 > Now, metal doesn't shrink... does
 it?  Hmm.  Why would they have been so darn tight?
 
 I think you gave the
 explanation in your first sentence..."pulled". The
 
 sheaths lengthen when they get removed from
 an aircraft because that's 
 the easiest
 way to do it...pull it out...hard.  Since they are spiral
 
 wound, they lengthen when force is applied
 to them. Since the inner flex 
 cable
 isn't part of that pulling force because it is floating,
 and in 
 any case is more resistant to
 tensional changes in length, it stays the 
 same length, so you end up with an inner cable
 that is shorter than the 
 outer sheath. 
 That's the way it was cut in the first place - 3/8"
 per 
 foot to begin with.  On new sheaths,
 the spirals are lubricated and you 
 can push
 and pull the thing to get it to shorten and lengthen quite a
 
 bit.  After years in an aircraft, most of
 them rust in place and lose 
 that axial
 flexibility, so pulling them just forcefully extends them to
 
 the max and they don't return like a
 new cable will.  You can get them 
 loosened
 up a bit with Kroil or other penetrating lubricant, but
 it's 
 hard to get the original
 compressional length back completely.
 
 Or, at least that's been my experience.
 :-)
 
 73,
 Mike