[ARC5] Tuning Cable Question

[Mike Hanz]

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