Message-ID: <19981005231512.24689.qmail@www08.netaddress.usa.net>
Date: Mon, 05 Oct 1998 23:15:12
From: Dan Schaefer <dfschaefer@usa.net>
To: lancair.list@olsusa.com
Subject: Nav Aids, crimp vs solder, cables
Mime-Version: 1.0

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Stu Seffern asked about anyone using a Nav Aids autopilot in a 360.

Both Jim Gates and I have them installed in our 235's. My plane runs
a Lyc 235 and and Jim is running a 320. These a/p's are working fine
in both of our aircraft for several years. I find it a necessity, at
least to have it in the wing-leveler mode when I'm solo and need to look at a chart or airport book. Both of us have installed a switch
and wiring to allow coupling to either the VOR or GPS. We both are 
using a KLX 135A GPS/Com, though we have different types of VOR 
receivers. The Nav Aid seems to track both VOR brands reasonably well
(mine's a King KX 155 and Jim's is a Narco unit).

I rode to and from the Redmond bash in Jim's plane and he had the Nav
Aids coupled to the GPS almost all the way and it sure seemed to 
track just fine. There is a noticeable difference if the way the a/p
reacts in tracking the VOR vs GPS course signal, due to the way the 
output is developed (variable vs constant course-width) but the a/p
tracks either with the main difference seeming to be in how far off
the course center-line it settles down. To me, it's not an issue.

To the best of my recollection, both of our units worked right out of
the box. The only difficulty either of us had was deciding how to 
install the servo unit - but that shouldn't affect whether the unit
works or not. Unfortunately, the original owner of the company was 
killed in an airplane crash soon after I bought my unit but I have
the name and contact information I think is current for the folks 
who are taking care of Nav Aid units. It is:

Navaid Devices, Inc. 
  Richard Ray, President 
  641 North Market Street 
  Chattanooga, TN 37405 
  Phone: (423) 267-3311 
  FAX: (423) 756-6154 
  email: rdray@mindspring.com 

If you're having problems, try Mr. Ray.

On the soldered vs crimped wires discussion and the pro's 'n con's. 
Whether you solder or crimp, remember that either way, there is always
a point of transition from rigidity to flexibility (the end of the 
terminal barrel or the end of the solder) where vibration-created
bending can be concentrated. In either case, one must do something 
to eliminate that flexure, or spread it over some length of wire, in
order to stop the stresses from being concentrated. Shrink tube is 
one good way to do this as long as it extends some way on either side
of the transition point, and as long as it sized so that it firmly 
grips the material on both sides. (Polyolefin shrink-tube is pretty
good for this, in my opinion - if things behind your panel get hot
enough to soften it up significantly, you've got bigger problems than
eventual failure of some of your wiring!) The follow-on to this, then,
is what else in the terminating process can cause failure? I tend to
agree with the comments about the possibility of soldering creating
possible corrosion - so as long as you eliminate the cause of 
vibration induced failure, why not crimp?

I also agree (once again) with John Cooper regarding the fields 
surrounding the battery cables. Keeping them together if you can is
really the best but twisting a couple of #4 (or worse, #2) cables
is kind of impractical. And the magnetic fields created during engine
start are, of course, only present during....all together now.....
starting! It's still best to keep them as far from the stuff like
compasses though, since at least the ground cable is most likely 
going to be carrying the full load alternator output return current.
Depending on your airplane, and it's nominal electrical load, not 
counting battery recharge current, that could be anything up to the 
full capacity of your alternator flowing back as far as the point 
where the panel loads are taken off - like the distribution bus-bar
if you're using that method. So the there will be a magnetic 
steady-state field associated with at least the front half of the 
ground cable all the time.

In all this talk about wire failure, here's a tip taken directly from
the Air Force imposed requirements for wiring critical systems (at 
least on the airpoanes I've been associated with. Use redundant 
wiring. For instance, where you might normally run a #10 wire 
(for instance) from your alternator output, use two parallel wires of
about half the size, each with it's own terminal lugs, and etc. I did
this for my alternator output and I found it gave me a bonus of being
easier to install. (Wire cross-sectional area doubles (or halves) for 
a change of three wire sizes, i.e., #10 has about 10,400 circular 
mil (cm) area while #13 has half that, at about 5,200 cm.)

Cheers,

Dan Schaefer


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