Today's Message Index:
----------------------
1. 10:38 AM - Wiring Best Practices? (Allen Maris)
2. 11:01 AM - Re: Wiring Best Practices? (Charlie England)
3. 11:30 AM - Re: Wiring Best Practices? (allenmaris)
4. 11:59 AM - Re: Wiring Best Practices? (Robert L. Nuckolls, III)
5. 12:03 PM - Re: Re: Wiring Best Practices? (Charlie England)
6. 12:23 PM - Re: Wiring Best Practices? (user9253)
7. 01:45 PM - Re: Wiring Best Practices? (An anecdotal follow-up) (Robert L. Nuckolls, III)
Message 1
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| Subject: | Wiring Best Practices? |
Im designing the wiring for my RV-7A. Ive been reading and looking at manufactures
recommendations, Bobs best practices, etc. Seems there are just not enough
routes in the plane to keep so many wires separated as recommended by best practices.
With 2 conduit routs down from the sub-panel to the floor of the plane,
things are going to have to go into route 1 or route 2. Im using shielded wire
as recommended by manufacturers and keeping the UAT and the Com antenna runs
apart from either other. But I still have to run the power wires for strobes,
landing light, flaps, fuel pump, trim, etc. Where do I draw the line of good
enough??
Message 2
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| Subject: | Re: Wiring Best Practices? |
On 1/30/2022 12:37 PM, Allen Maris wrote:
>
> Im designing the wiring for my RV-7A. Ive been reading and looking at manufactures
recommendations, Bobs best practices, etc. Seems there are just not enough
routes in the plane to keep so many wires separated as recommended by best
practices. With 2 conduit routs down from the sub-panel to the floor of the plane,
things are going to have to go into route 1 or route 2. Im using shielded
wire as recommended by manufacturers and keeping the UAT and the Com antenna
runs apart from either other. But I still have to run the power wires for strobes,
landing light, flaps, fuel pump, trim, etc. Where do I draw the line of good
enough??
My understanding is that with few exceptions, grounding practices are
far more critical than adjacent wires. The UAT & comm *antennas* might
need some separation, but properly terminated shields on quality coax
should prevent any issues with the wires themselves.
Which combinations are most concerning to you?
Charlie
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Message 3
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| Subject: | Re: Wiring Best Practices? |
Ceengland wrote:
> On 1/30/2022 12:37 PM, Allen Maris wrote:
>
> >
> >
>
> My understanding is that with few exceptions, grounding practices are
> far more critical than adjacent wires. The UAT & comm *antennas* might
> need some separation, but properly terminated shields on quality coax
> should prevent any issues with the wires themselves.
>
> Which combinations are most concerning to you?
>
> Charlie
>
Hi Charlie, the biggest ones I've written down from various sources:
Keep some separation between strobe lines and any audio wires, coax or headset
jacks. I HAVE to run this next to some coax, and the UAT seems like a better option
just to avoid any possible audio feedback on the Comm frequency which I
might hear.
Separate UAT and Comm coax (I can do that)
Avionics/Audio wiring shouldn't share bundles with power distro lines (assuming
this means the big battery/Alternator connections and not just standard device
power)
Keep Can Bus wires away from power/ground lines, especially pertaining to loads
for motors.
I know some of this is ideal/best-case scenario, I just don't have enough experience
to know where that line is. All I remember is the days of installing car
stereos in my cars when I was younger and hearing the telltale hum of a poor
install!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=505848#505848
Message 4
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| Subject: | Re: Wiring Best Practices? |
At 01:06 PM 1/30/2022, you wrote:
On 1/30/2022 12:37 PM, Allen Maris wrote:
I'm designing the wiring for my RV-7A. I've been reading and looking
at manufactures recommendations, Bob's best practices, etc. Seems
there are just not enough routes in the plane to keep so many wires
separated as recommended by best practices. With 2 conduit routs down
from the sub-panel to the floor of the plane, things are going to
have to go into route 1 or route 2. I'm using shielded wire as
recommended by manufacturers and keeping the UAT and the Com antenna
runs apart from either other. But I still have to run the power wires
for strobes, landing light, flaps, fuel pump, trim, etc. Where do I
draw the line of good enough??
My understanding is that with few exceptions,
grounding practices are far more critical than
adjacent wires. The UAT & comm *antennas* might
need some separation, but properly terminated
shields on quality coax should prevent any issues
with the wires themselves.
Which combinations are most concerning to you?
Charlie
Exactly!
It's my suspicion that authors for 'best practices' in wire
routing have not spent much time working with the heavy iron
birds . . . I worked for every airframe manufacturer in Wichita
at least once . . . one of them three times. In 40+ years
I can recall but a couple of times that stimulus coupled
between a 'victim' and 'antagonist' was initially attributed
to 'poor separation of wiring'.
A couple of stand-out incidences included a recovery parachute
system that spontaneously launched from the tail of an airplane.
The event was first blamed on lack of shielding and/or separation
of critical wires from potential antagonists.
The second was at Beech on a Hawker 800 where a host of warning
annunciators were triggered by the energizing of a 400Hz, AC
blower motor in aft cabin.
In BOTH cases I discovered effects of poor grounding practice.
The blower took a SINGLE power wire through the ship's wire
bundle tunnels and GROUNDED the motor at the tail of the airplane.
This turned that wire into the primary winding of a TRANSFORMER
that was relatively tightly coupled to lots of other wires. In
the first case, the designers routed SINGLE conductor firing signals
from the control panel to explosive devices in the parachute system
and grounded those initiators in the tail. To complete the
design guaranteed to fail, they grounded the source end of those
same wires in the control panel . . . ostensibly to reduce the
possibility of introducing hazardous stray signals into the
firing lines. This guaranteed that those feeders combined with
voltages induced in the fuselage to set up a low impedance
source of extraneous energy that simultaneously lit up every
initiator in the system. It was later deduced that the airplane
had flown past a active thunderstorm and while there was
separation of sufficient miles for safe flight, it was probably
a lightning strike that provided the PRIMARY energy source
for initiating the event.
This was one of a couple reasons that yours truly was assigned
the task of designing and constructing the last four recovery
parachute systems installed in Beech flight test aircraft before
my retirement. The other reason was that our original contracted
supplier of a control system for the parachute on the Premier I
blew off a couple hundred thousand dollars and two years of
development time before delivering a system that launched the 'chute
in the hangar.
A long time friend and colleague Dean Matson and I along with
the capable hammer-n-tongs guys in the Beech Targets Division
designed, built and qualified a system from scratch in about
30 days for a budget of well under $20K.
There were no doubt others but I'd have to stir the memory
pot for awhile to dig them up. Bottom line is that ROUTING
of wires in community of systems where proper attention is
given to GROUND LOOPS is not an issue. In fact, there are rigorous
qualification tests for all appliances designed for TC aircraft
that makes sure that appliances will be peaceful and
harmonious citizens of the aircraft.
While at Lear working on the GP180 program, I witnessed first
hand the battles between hydraulics, controls, fuel, wire
slingers and HVAC guys for space in the aircraft. Anyone
who complained about proximity of his hardware with any
other might well find his car covered ten or so rolls
of soggy toilet paper when he got of work that day.
Don't worry about HOW wires are routed and bundled. If you've
paid attention to good GROUNDING practices and particularly
good assembly practices for coax connectors, you stand a much
better chance of being brought down by a meteor strike than by
an altercation between electro-whizzies in the airplane.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 5
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| Subject: | Re: Wiring Best Practices? |
On Sun, Jan 30, 2022 at 1:35 PM allenmaris <allenmaris@gmail.com> wrote:
> allenmaris@gmail.com>
>
>
> Ceengland wrote:
> > On 1/30/2022 12:37 PM, Allen Maris wrote:
> >
> > >
> > >
> >
> > My understanding is that with few exceptions, grounding practices are
> > far more critical than adjacent wires. The UAT & comm *antennas* might
> > need some separation, but properly terminated shields on quality coax
> > should prevent any issues with the wires themselves.
> >
> > Which combinations are most concerning to you?
> >
> > Charlie
> >
>
>
> Hi Charlie, the biggest ones I've written down from various sources:
>
> =A2Keep some separation between strobe lines and any audio wires, c
oax or
> headset jacks. I HAVE to run this next to some coax, and the UAT seems li
ke
> a better option just to avoid any possible audio feedback on the Comm
> frequency which I might hear.
>
> =A2Separate UAT and Comm coax (I can do that)
>
> =A2Avionics/Audio wiring shouldn't share bundles with power distro
lines
> (assuming this means the big battery/Alternator connections and not just
> standard device power)
>
> =A2Keep Can Bus wires away from power/ground lines, especially pert
aining to
> loads for motors.
>
> I know some of this is ideal/best-case scenario, I just don't have enough
> experience to know where that line is. All I remember is the days of
> installing car stereos in my cars when I was younger and hearing the
> telltale hum of a poor install!
>
>
> I'll defer to Bob for 'final answers', but...
Strobes *can* be problematic, but don't have to be. Traditional strobe
issues can be minimized a bit with 'home run' grounds and proper
shields/terminations per mfgr specs. I had an RV with the 'whoop whoop' of
its strobe in the intercom, and it was about 99% related to the ground
location (locally grounded) of the strobe power pack. The charge/discharge
power variations were riding on the ground path of the audio system. (I
didn't wire the a/c.) LED strobe noise can be minimized by using properly
filtered LED drivers (and good grounding practices).
My UAT experience is limited to the uAvionix, and all its components are in
the wingtip as recommended by one of their engineers. The power supply to
the assembly runs in bundles with everything else in the plane. This one is
an RV6 (again, I didn't do the initial wiring), and all the wires
(including xpndr & comm coax) leaving the panel go down the center support
in two fat bundles, and then through the spar and fan out to their
destinations throughout the airframe. No noise in this installation.
Avionics/audio: Again, grounding practices predominate. If it's convenient
to keep the mic lines at least a few inches away from the 'fat' power
wires, why not? But for most installs, you'd have to try to get them close,
anyway. Keeping audio grounds isolated from airframe grounds and tying them
directly to the audio panel/intercom as shown by the mfgr will almost
always have more effect than any 'adjacency'. What risk there is of
electromagnetic noise introduction can be minimized by using twisted pairs
for the audio, and minimizing to the degree that's practical, the length of
the adjacency. Crossing at close to 90 degrees doesn't hurt anything at all
.
CAN bus stuff I haven't dealt with (yet), but if it works in cars, consider
the automotive environment. Again, if mfgr's recommendations are followed
as to wire type and shielding....
The simple fact that you're paying attention, and following the AEC book,
should give you a big leg up on having a noise free install. Remember,
there are a lot of the same model flying successfully with the same routing
restrictions.
Charlie
Message 6
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| Subject: | Re: Wiring Best Practices? |
Mount headset jacks with insulating washers to be sure that they are not grounded
locally. (They will be grounded at the instrument panel end)
-
Run power and ground wires as a twisted pair for electrically noisy devices.
-
A very knowledgeable person once wrote: If cables are modern coax (RG400 or RG142),
you can run them right together with any wires in any system.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=505851#505851
Message 7
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| Subject: | Re: Wiring Best Practices? (An anecdotal follow-up) |
>The second was at Beech on a Hawker 800 where a host of warning
>annunciators were triggered by the energizing of a 400Hz, AC
>blower motor in aft cabin.
This problem was a combination of TWO cases where
the designers stubbed their toe . . .
The motor power wiring was poorly laid out and installed
but the real ace-kicker was that sense wires from various
monitored systems in the aircraft were NEVER qualified
to modern (post 1975) EMC compatibility practices.
Those sense wires had ZERO protection from fast-rise-
time, low energy events. I.e. they were literal
'antennas' connected to dozens of 'receivers' in the annunciator
system just waiting around for an insulting event to
happen. That annunciator system was the recipient of
dozens of band-aid hacks to work around false warnings.
I only had occasion to wrestle with one such event.
The second incident was a real hand wringer, again Hawker 800,
where the HF transceiver would cause all three generators
to shut down during transmission . . . this was discovered
about Dec 15 on a group of airplanes that were slated for delivery
on or before Dec 31 to meet certain financial expectations.
That turned out to be a combination of two issues. (1)
the generator controllers were all solid state designs with
rather old pedigrees. Again, NEVER qualified to
contemporary EMC compatibility requirements . . . and
(2) somebody decided that an airplane like the Hawker
really looked shabby with that open wire HF antenna strung
from vertical fin to the top of cabin. So Collins came
to the rescue and offered an antenna tuner that would
make a wad of bailing wire and a 55-gallon drum 'look'
like an efficient antenna.
Hawker engineering insulated the leading edge cap
on the vertical fin from the rest of the skin and
structure. The antenna tuner would excite that strip
of metal to the satisfaction of the HF transceiver
but . . .
The ground return system for that 'antenna' was never
designed for such service. A result was that the interior
of the hell-hole behind the pressure bulkhead became
RF 'hot' like you wouldn't believe. Combine this with
the out of date generator controllers and guess what?
Nuckolls and crew spend some panic driven days down in
Little Rock trying to figure out how to deliver these
airplanes.
I posted a photo array of the bubble-gum-n-baling-wire
solution at https://tinyurl.com/ybsl2zsq
I didn't know which of the signal wires to the GCU
were vulnerable . . . no time to go to the lab
and measure anything. Sooo . . . put capacitors on
EVERY possible wire. So after a trip to the warehouse
and an overnight from Digikey, we built a number of
'filtered harnesses' to insert between ship's wiring
and the vulnerable GCU's. They built up 3 or 4 ship-sets
of these things and got them bought off.
We were modifying a harness which was a Beech
fabrication, NOT a GCU which was a 'qualified' supplier
product, so it seems I could stuff a wad of bubble gum into
a connector and nobody cared . . . just don't
mess with a PMA/TSO device . . . you need god's permission
to do that.
I never did like that 'fix' but my boss was happy.
Just a few Tales from the Crypt to emphasize the need
for skepticism when you read about practical
imperatives for doing things to your airplane.
The question that is always good to ask, "Has
anyone conducted repeatable experiments and documented
the recommended practice deduced with data from those
experiments?"
Folks who pass along various and sundry admonitions
for 'avoiding problems' are offering the ideas
in good faith. But it can be difficult to separate ol'
hangar tales and legends from good physics. There
are plenty of talented engineers and technicians
who are victims of poor advice propagated in the
name of safety and good performance.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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