[ARC5] Tuning Cable Question

[Robert Eleazer]

Didn't we discuss this before?   And wasn't the answer we came up with that 
the bends and loops tend to use up more of the outer cable than they do the 
inner one?  Unlike coax, the two parts of the cable can move independently. 
I think I have observed something similar with tachometer cables; I had to 
change one on my airplane.

That tends to lead to the question of how they measured the cables.  Or did 
they just hook up one end and then pull the cable through and put the outer 
securing cap on when they got to the end?

There are published standards for bending metal, in terms of how much set 
back or shortening you get from a bend.  Anyone ever find any similar 
standards for the tuning cables, how much bends and loops add to the outer 
and inner lengths?

Wayne
----- Original Message ----- 
From: "Mike Everette" <radiocompass at yahoo.com>
To: "Robert Eleazer" <releazer at earthlink.net>; "Mike Hanz" 
<aaf-radio-1 at aafradio.org>
Cc: <arc5 at mailman.qth.net>
Sent: Tuesday, June 03, 2014 12:46 PM
Subject: Re: [ARC5] Tuning Cable Question


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?

73

Mike
WA4DLF

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

 Subject: Re: [ARC5] Tuning Cable Question
 To: "Robert Eleazer" <releazer at earthlink.net>
 Cc: arc5 at mailman.qth.net
 Date: Sunday, June 1, 2014, 12:54 PM

 On 5/31/2014 8:51 AM,
 Robert Eleazer wrote:
 > Note that with
 the 274-N receivers, there was a huge increase in the
 > number of tuning cables - from one to
 three compared to an RU
 >
 installation. That may have been a driver, too.

 Sounds reasonable. Every
 pound counts, I guess.

 >
 It's odd, but that tuning cable that is attached to the
 coil box on
 > that RU in the F4F-4
 picture I sent actually seems to run aft from the
 > radio, toward the tail, and then
 presumably makes a U-turn and goes
 >
 back forward to the cockpit. I wonder if the larger cables
 had less
 > flexibility and so they had
 to make big sweeping loops of that sort.

 Going out to the shack and grabbing examples of
 both the MC-124 and
 MC-215 control shafts,
 it appears empirically that a 4" radius is about
 the smallest you can practicably use with
 *either* cable without
 deforming the outer
 sheath. That's consistent with the warning in the
 SCR-**-183/283 manuals not to plan any tighter
 turns than 6"R with the
 MC-124. I
 couldn't find any guidance for the MC-215 in a quick
 scan.
 Of course, the tighter the turn,
 the higher the torque required due to
 friction, and that interferes with the
 "feel" necessary to do fine
 tuning, so that may have something to do with
 the long loop in the F4F-4.

 73,
 Mike

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