Wiring a Sailplane

On Dec 12, 3:44 pm, Todd wrote:
I would suggest you take a look inside your car. You wont find
anything but crimped connectors EVERYWHERE.

High quality connectors applied with the correct tool gives a very
reliable and repeatable connector. Look inside your next B787, you
wont find any soldered connectors there either.

But if you look inside all the things that are connected together by
the crimped pin wiring harnesses you will find all the complex
electronics modules use surface mount soldered components!

The avionics of the 787 or any other modern transport aircraft would
not be possible without thousands, if not millions, of soldered
connections.


Andy

Thank you, Darryl and Todd, for your replies. Thanks also to John for
his off-line message.

Darryl, my experience has been with coaxial cables having BNC, UHF,
microdot and LEMO connectors. It's interesting that one of the URLs
you provided, http://www.aeroelectric.com/articles/bnccrimp.pdf, shows
the exact BNC crimp connector that has proven most troublesome in the
field. I've seen many of these connectors be electrically noisy
straight from the factory. But also, there's no true strain relief on
this connector, so the ground braid tends to break in a completely
invisible manner. A soldered BNC connector (the type with the
compression nut on the bottom) doesn't seem to have this problem, and
especially so if it's been fitted with a strain relief boot.

I thank you for this URL, http://www.aeroelectric.com/articles.html. I
was aware of Mr. Nuckolls' site, but somehow I had missed this page.
He appears to be a no nonsense, practical man, and as far as I can
tell he doesn't have a preference for either solder or crimp - as long
as they are done properly, that is!

One thing he points out is not to tin a wire you'll use a crimp
connector on, nor should you solder a crimped connector. You shouldn't
do the second because it destroys the strain relief, and you shouldn't
do the first because the connection loosens over time. Very, very
interesting, because Tefzel wire is pre-tinned...

I'm not a member of IEEE, so references to their journal won't do me
any good. But I take the point that there are indeed unbiased studies
favorably comparing crimp to solder in a production environment.
Manufacturers of course care a lot about unskilled labor being able to
make quick connections, as it maximizes their profit. And I don't
doubt that connector manufacturers take considerable design care so
that their connectors can approach the reliability of a good solder
joint. But speed and skill isn't generally an issue when it comes to
you yourself wiring your own glider. Personally, I'll take the time to
make a good solder joint having proper strain relief. YMMV, but I've
seen too many bad crimp connections to rest easy with having them in
my own plane.

Todd, the fact that car and aircraft manufacturers use crimp
connectors doesn't really sway me. Look at Consumer Reports and you'll
see that the major source of complaints for reliability in cars is
electrical systems. And don't overlook the fact that the Space Shuttle
flight has just been scrubbed because of intermittent connections. As
I said above, I think manufacturers' prime motivation is assembly
speed using unskilled labor. Reliability is also important, don't get
me wrong, but I think they're more interested in minimizing their cost/
benefit ratio. And as Jerry Pournelle of Chaos Manor fame likes to
say, "better is the enemy of good enough".

-John

On Dec 12, 4:44 pm, "
wrote:
On Dec 12, 11:04 am, jcarlyle wrote:



On Dec 12, 11:51 am, ContestID67 wrote:

- Solder - Is to be avoided in liu of crimp connectors. However,
sometimes you just can't avoid it.

Why do you make this statement, John? I've dealt with tens of
thousands of cables professionally for over 35 years, and during that
experience I've found that if a connection is crimped, it's crap. By
that I mean it's highly likely to be either electrically noisy or
mechanically weak.

I did a Google search, and basically discovered that crimping vs
soldering discussions are, in some quarters, a quasi-religious war. I
don't want to add fuel to that fire, but are there authoritative,
unbiased studies (eg, not from connector manufacturers) that bear out
your assertion?

-John

I'm not sure what sort of cable you are talking about. Some cables
e.g. professional audio cables are probably going to fail regardless
of how they are done just form the handling they get. Similarly I've
spent many hours repairing RF and microwave coax cables in research
labs and I'm sure most failere are from gross abuse (peopel pulling on
the cables etc.) and these have had all times of connections,
soldered, crimped, spot welded, exotic super conducting connections,
etc. For my money in my glider I'll take properly done crimp
connections.

There are quite a few research papers that demonstrate superiority of
crimp connectors in production environments - ie. where both solder
joints and crimp connections are performed properly. Even with good
control and technique solder suffers from dry joints and surface
contaminatation issues amongst others and in general take a lot more
skill to do properly than an equivalent crimp joint. Most of the
papers I recall are in IEEE publications not from vendors, if you are
an IEEE member or have access to their publications I'll try to find
them for you. Crimping may be faster and lower cost in production
environments but automotive and aerospace company also do not want to
pay for the cost of failed connections in the field - if soldering was
superior you would see it being used more in these applications.

It seems many people's experience with crimp connectors is using some
no brand PVC jacketed connector from the local hardware or auto parts
store with a cheap single action crimp tool. All bets are off if that
is the case.

Getting back to the original request, there are some interesting
articles on general aviation wiring etc. athttp://www.aeroelectric.com/articles.html
I've not looked through them all but some seem to have a good
perspective from a professional A&P who does this stuff for a living.
He seems to have lots of practical examples of good tools and
workmanship, eg. -

http://www.aeroelectric.com/articles...s/bnccrimp.pdf

Cheers

Darryl Ramm



On Dec 12, 5:44 pm, Todd wrote:
I would suggest you take a look inside your car. You wont find
anything but crimped connectors EVERYWHERE. And the continue to
function even when corroded by the road salt the local highway
departments love to spread around here.

High quality connectors applied with the correct tool gives a very
reliable and repeatable connector. Look inside your next B787, you
wont find any soldered connectors there either. The technology is
quite well proven.

On Dec 13, 6:53 am, jcarlyle wrote:
[snip]
One thing he points out is not to tin a wire you'll use a crimp
connector on, nor should you solder a crimped connector. You shouldn't
do the second because it destroys the strain relief, and you shouldn't
do the first because the connection loosens over time. Very, very
interesting, because Tefzel wire is pre-tinned...

Apples and oranges. Tefzel and many other wires are pre-tinned,
covered with a thin hard coat of tin or similar metals. You are
confusing this with the completely different process of "tinning" with
solder. Different chemicals, different processes, different thickness,
etc. etc.

Darryl

On Thu, 13 Dec 2007 06:53:03 -0800 (PST), jcarlyle
wrote:

One thing he points out is not to tin a wire you'll use a crimp
connector on, nor should you solder a crimped connector. You shouldn't
do the second because it destroys the strain relief, and you shouldn't
do the first because the connection loosens over time. Very, very
interesting, because Tefzel wire is pre-tinned...

Pretinned and "bunch tinned" as we used to call it are different; the
pretinned has each strand tinned. Bunch tinned has the group of
strands "glued" together with tinning or solder. Which is Tefzel
aircraft wire?

Aside ... back in the 1970's, the best wiring for boats was considered
to be the bunch tinned; a combination of good vibration resistance and
corrosion protection according to the wire salesmen calling on us
trying to get our chief engineer to use it on mobile radios. It was
said to be formable to a path but resistant to fatigue failure.

I AM NOT STATING THAT AS FACT, rather as what we were told.

George, I don't know. Until I read Darryl's message, I didn't know
that wire was sometimes tin plated. To me, the word "tinned" meant
that it had solder applied to it.

-John

GeorgeB wrote:
On Thu, 13 Dec 2007 06:53:03 -0800 (PST), jcarlyle
wrote:

One thing he points out is not to tin a wire you'll use a crimp
connector on, nor should you solder a crimped connector. You shouldn't
do the second because it destroys the strain relief, and you shouldn't
do the first because the connection loosens over time. Very, very
interesting, because Tefzel wire is pre-tinned...

Pretinned and "bunch tinned" as we used to call it are different; the
pretinned has each strand tinned. Bunch tinned has the group of
strands "glued" together with tinning or solder. Which is Tefzel
aircraft wire?

Aside ... back in the 1970's, the best wiring for boats was considered
to be the bunch tinned; a combination of good vibration resistance and
corrosion protection according to the wire salesmen calling on us
trying to get our chief engineer to use it on mobile radios. It was
said to be formable to a path but resistant to fatigue failure.

I AM NOT STATING THAT AS FACT, rather as what we were told.

Pretinned and "bunch tinned" as we used to call it are different; the
pretinned has each strand tinned. Bunch tinned has the group of
strands "glued" together with tinning or solder. Which is Tefzel
aircraft wire?

Good question to which I cannot find a definative answer on the web.
However, the Tefzel wire which I have worked with, definately would be
called "bunch tinned" (just this side of solid wire). I have always
felt that the importance of this is so that if the wire covering
becomes abrated that individual strands of wire are less likely to
fray and become a [short/spark/fire] hazard.

As was mentioned, "bunch" tinning causes the wire to become stiffer
than untinned. It hadn't occured to me until just now that this is
another safety attribute as the stiffness mitigates vibration of the
wire and thus reduces the possibility of abrasion.

Note that Tefzel refers to the cover of the wire (not the metal wire
itself) so I suspect that some "Tefzel Wire" may not be aviation
worthy. Look for the MIL specification to be sure. MIL-W-5086A for
non-shielded and MIL-C-27500 & replaces MIL-C-7078/3 for shielded.

The important of Tefzel is that 1) is very smooth and slick and
doesn't abrate easily and 2) when burned doesn't emit toxic gasses as
PVC (the typical wire covering) can.

Finally, I understand everyone's comments about "What is the big deal
about the type of wire we use?". We don't have fuels, we don't have a
lot of vibration, we don't typically have lots of sharp aluminum
edges, etc, etc. However we can get (and I have seen) gliders with
shorts and smoke in the cockpit. The amount of cost difference
between "crap" wire and Tefzel wire is just too small to be a reason
to avoid it. The real reasons are; that many people don't know know
any better and that it is just easier to buy the cheap stuff.
Hopefully, I have blown holes in both arguments.

Bite the bullet and do the right thing!

I've never seen an aircraft Tefzel hookup wire that was "bunch
tinned". For most stuff here we are talking about a multi-strand
unshielded hookup wire i.e. look for MIL-W-22759/16. You'll see that
code printed on the jacket. I am aware of variants with different
strand materials and plating materials (tin, nickel, silver etc. on
the individual strands) none of which involve bulk tinning of the
entire set of strands. A bulk tinned type wire is going to be much
more awkward to bend, and I don't like the potential stress on
individual strands at any bend site or the idea of crimping to these
sorts of wires. I believe the apparent higher rigidity of multi-strand
Tefzel wire compared to garden variety PVC junk crap comes from the
twist geometry (higher pitch than usual wires) and the rigidity/bond
of the Tefzel jacket on the wire core.

BTW rigidity itself in wiring is not necessarily a good thing and
could lead to more vibration/fatigue related failure particularly if
the wiring is not well secured.

Yep, do it right or stay home. Tefzel wire is the way to go.

Darryl

On Dec 13, 7:49 pm, ContestID67 wrote:
Pretinned and "bunch tinned" as we used to call it are different; the
pretinned has each strand tinned. Bunch tinned has the group of
strands "glued" together with tinning or solder. Which is Tefzel
aircraft wire?

Good question to which I cannot find a definative answer on the web.
However, the Tefzel wire which I have worked with, definately would be
called "bunch tinned" (just this side of solid wire). I have always
felt that the importance of this is so that if the wire covering
becomes abrated that individual strands of wire are less likely to
fray and become a [short/spark/fire] hazard.

As was mentioned, "bunch" tinning causes the wire to become stiffer
than untinned. It hadn't occured to me until just now that this is
another safety attribute as the stiffness mitigates vibration of the
wire and thus reduces the possibility of abrasion.

Note that Tefzel refers to the cover of the wire (not the metal wire
itself) so I suspect that some "Tefzel Wire" may not be aviation
worthy. Look for the MIL specification to be sure. MIL-W-5086A for
non-shielded and MIL-C-27500 & replaces MIL-C-7078/3 for shielded.

The important of Tefzel is that 1) is very smooth and slick and
doesn't abrate easily and 2) when burned doesn't emit toxic gasses as
PVC (the typical wire covering) can.

Finally, I understand everyone's comments about "What is the big deal
about the type of wire we use?". We don't have fuels, we don't have a
lot of vibration, we don't typically have lots of sharp aluminum
edges, etc, etc. However we can get (and I have seen) gliders with
shorts and smoke in the cockpit. The amount of cost difference
between "crap" wire and Tefzel wire is just too small to be a reason
to avoid it. The real reasons are; that many people don't know know
any better and that it is just easier to buy the cheap stuff.
Hopefully, I have blown holes in both arguments.

Bite the bullet and do the right thing!

On Dec 13, 9:54 pm, "
wrote:
Yep, do it right or stay home. Tefzel wire is the way to go.

I disagree. I think there's shades of gray to it. Given a good day in
the offing, I'd rather wire a new vario with zip cord and get into the
air than stay on the ground waiting for the UPS guy to bring me a reel
of Tefzel.

Sure, Tefzel is good stuff, and crimping is most easily done well
using the expensive tools. And the greatest expense is the time you
commit to it, so wherever practical you should use the very best
materials available, and do it right rather than doing it twice. No
question about that.

However, I'm still convinced that a careful and conscientious amateur
can do a perfectly reasonable job using more pedestrian materials and
processes. We're not going to the moon here, and a lot of what you
wire this season will just get re-wired in two years hence when the
SN15 or whatever comes out.

One of my first jobs in the Silicon Valley was making wiring harnesses
for computer subsystems. We used relatively standard 16ga and 18ga
wire, standard AMP ring and fork terminals, and a mix of expensive
ratchet-action crimpers and inexpensive crimpers. We saw very few
returns with wiring harness problems, and few of those were attributed
to poor crimping.

Of course, safety is paramount, regardless of the tools and materials
you use should do things so that when (not if) they fail they will do
so gracefully. But, that's what fuses are for, and that's why I have a
separate 9V battery on the gear warning and a 9V battery backup on the
main electric vario. And even so, I have not had an in-flight wiring
or power failure in all the time I have been operating my own
sailplanes.

I think that how you wire stuff is as important, if not more so, than
what you wire it with. Wires should be well-supported and have
frequent anchorages. They should be protected by grommets (OK) or snap
bushings (better) where they penetrate bulkheads. They should be well-
organized and each wire should be labeled at both ends. Power and
signal wires and terminals should be physically protected from contact
with stray conductors. I could go on, but AC43.13 chapter 11 pretty
much says it all for me. And of course, AC43.13 chapter 11.178 says
you're supposed to use the ratchet-type crimp. But AC43.13 is not
necessarily binding for aircraft with Experimental airworthiness
certificates, so I'll take my chances on the cheap crimpers plus tug-
testing.

And the thing about Tefzel being better than PVC insulation in a fire?
My glider, though only partially composite, is like most composite
ships in that it contains about five pounds of PVC and many many other
compounds known to liberate noxious gasses under combustion. The few
grams of PVC wire insulation doesn't add much to it. You could say
that the wire is an especial worry because it could get hot enough to
burn under a short circuit. But that's what the fuses are for. I build
a fuse into every main battery pack, and also have fuses for every
major draw.

I've used all of the so-called "bad stuff" in gliders, including
speaker wire, zip cord, Radio Shack switches, Ace Hardware terminals,
glass fuses, and automotive-grade wire. Some of that stuff, I sure
wouldn't use as a regular practice, but it got me into the air and
worked perfectly for as long as I needed it to work.

Thanks, Bob K.

On Dec 14, 6:44 pm, Bob Kuykendall wrote:

I disagree. I think there's shades of gray to it.
SNIP
I've used all of the so-called "bad stuff" in gliders, including
speaker wire, zip cord, Radio Shack switches, Ace Hardware terminals,
glass fuses, and automotive-grade wire. Some of that stuff, I sure
wouldn't use as a regular practice, but it got me into the air and
worked perfectly for as long as I needed it to work.

Thanks, Bob K.

Bob,

You're right. This is much more entertaining than the annual PW-5
bashing or the periodic outraged name calling and reputation impugning
over 12 volts vs. 14! In my 40+ years of soaring, the failures I've
seen have been almost exclusively the result of poor workmanship, not
the wrong materials, although these do seem to go hand in hand.

But just in case your posting calms things down on the wiring front, I
assume you'd probably fly on Sunday even if your parachute repack
interval expired on Saturday?

Chip Bearden

You're right. This is much more entertaining than the annual PW-5
bashing or the periodic outraged name calling and reputation impugning
over 12 volts vs. 14! In my 40+ years of soaring, the failures I've
seen have been almost exclusively the result of poor workmanship, not
the wrong materials, although these do seem to go hand in hand.

But just in case your posting calms things down on the wiring front, I
assume you'd probably fly on Sunday even if your parachute repack
interval expired on Saturday?

Chip Bearden

Yikes!

Hey, how about replacing a broken variometer with a new audio vario
and actually going flying with it - instead of waiting for the
appropriate FAA - endorsed Real Smart Guy to install it and sign it
off as "legal"? I've seen a brand new working audio TE vario
(installed by overenthusiastic club members) yanked out of a club ship
because the paperwork wasn't complete and the installation didn't meet
the A&Ps standards (it was too close to the mag compass), leaving the
ship with only a dodgy mechanical vario. Absolutely correct action by
the A&P, of course. But safer? Hmmm.

No way - It 's better to be legal than safe, always. Yessir!

(Diving for cover, after unplugging the modem....)

Seriously, Safe is essential, Legal is a requirement, most often the
two are in agreement, but sometimes Safe trumps Legal. I'd rather
argue with the FAA than have them praise me posthumously.

Of course, your definition of Safe may vary....

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