Message-ID: <000e01bf1d74$1e67e380$da818ed1@pavilion>
From: "J. N. Cameron" <CIC@centurytel.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: Wire types for experimentals;   LNCE & others
Date: Sat, 23 Oct 1999 11:27:17 -0500
Mime-Version: 1.0

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>
Seems like there was some misinterpretation of my earlier post regarding the
merits of tefzel-insulated, milspec wire vs. more ordinary types like PVC-
and teflon-insulated wire.  I was not advocating using PVC wire, rather
thinking aloud about whether there might be an easier, more decipherable way
to wire our beasts.  Whenever I see an inch-thick bundle of all white wires,
the electronic repairman in me cringes at the thought of trying to track
anything down without color-coding or wire labelling.

That said, I do appreciate the responses, and they've made me realize there
was a lot I didn't know about aircraft wiring.  I therefore have tried to do
a bit of research, which I'll pass along in case anyone's interested.

Tefzel:  This is a DuPont trademark, first registered about 1969, for
ethylenetetrafluoroethylene, or ETFE.  It's a chemical cousin of Teflon
(also a DuPont mark), but mechanically tougher and less subject to cold
flow.  It's supplied by DuPont in pellets or powder for various sorts of
molding and extrusion processes.  Depending on how it's used in fabrication
and whether or not it's crosslinked, its mechanical properties can vary
somewhat in the finished product.

MIL-W-22759/xxx   The actual text of the milspecs can be accessed at
www.dscc.dla.mil/Downloads/MilSpec/Docs, and it turns out there are quite a
number of variants, revisions, etc., to this one.  The latest seem to be
/32C and /46A, but some leftover wire I have from my ES is marked /16, which
is similar, but a superseded revision, I think.  Anyway, this is the
applicable milspec for most of the unshielded hookup wire we use.  Aircraft
Spruce carry it only white, whereas my normal electronics suppy houses
(Allied, Newark, Digi-Key) don't list it as either a Belden or Alpha Wire
product (these are the two largest wire mfr's in the U.S., I think).  Newark
has a listing for Dearborn Wire & Cable, but only in black and white.
Thanks to Brent Reagan for posting the EDMO number -- I'll be calling them.
I also found a website for Milspec Wire & Cable Co. (www.milspecwire.com);
I've e-mailed them to see if I can get a catalog, whether they sell direct,
and what their minimum orders are.

Coaxial & Triaxial Cable:  This seems to be more problematical.  The book
titled "Avionics" by John Ferrara refers to RG58 as the most common type
used in aircraft.  Correct me if I've missed something, but all the RG58
I've found has PVC insulation.  Jim McMillan suggests RG142, then further on
in his post and in one or two of the others, the point is made that teflon,
due to its cold-flow property, is not acceptable for use in aircraft.  Well,
Belden's RG-142B/U, which meets milspec MIL-C-17D, has teflon insulation
(and costs about $4 per foot).  Aircraft Spruce list RG-400 but gives no
spec's;  Newark's catalog lists Dearborn #6400 as RG-400, also with teflon
(TFE) insulation ($4.18/ft).   In searching for triaxial cable (to try to
get really low RF loss on COM antenna wires) I've had even less luck.  There
is a part of MIL-C-17 that deals with triax, but the only commercially
available stuff I've found is Belden's yellow-jacketed, PVC-insulated stuff.

Conduit:  The Lancair construction manuals say little about providing
conduit, except for the wing leading edge PVC pipe.   Does anyone have a
good suggestion for alternate materials?  Inside the fuselage, standard
aluminum electrical conduit could be used, but it would add some weight.  If
no conduit is used, then extra precautions have to be taken to avoid chafing
at each place where wire bundles go through bulkheads.

Further rooting in the leftovers box came up with these items:   Wire left
over from Whelen strobe installation, supplied by Whelen, is marked MW13860.
Anyone know what that means?  Cabling supplied by S-Tec for the autopilot
installation is unmarked, and in my informal flame test it appeared to be
PVC insulated.

A further note, or question, really:  I looked at FAR 23.1365, which is
under the airworthiness standards for certificated aircraft, electric cables
and equipment.  All its says is:  "Each cable ... that would overheat in the
event of circuit overload or fault must be at least flame resistant and may
not emit dangerous quantities of toxic fumes."  Not very informative, but
probably eliminates PVC, even the "Flamarrest" treated stuff.  Part 21 has
to do with certification of parts, etc., but is not on-line.  Does anyone
know if there is more detailed info in there?

Finally, I heartily agree with the comments made by several of you that the
cost of wiring is not really a consideration, given the potential risk of
using the wrong stuff.  It is not always an easy task, however, to find out
exactly what to use in a given situation, and having found out, it's not
easy to locate a source.

Jim Cameron,   LNCE (once and future)

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html