Today's Message Index:
----------------------
1. 05:36 AM - Re: Airframe ground connection (Robert L. Nuckolls, III)
2. 07:27 AM - Re: Airframe ground connection (user9253)
3. 08:23 AM - Re: Re: Airframe ground connection (George, Neal Capt 505 TRS/DOJ)
4. 09:15 AM - Re: Re: Airframe ground connection (Robert L. Nuckolls, III)
5. 10:05 AM - Re: Airframe ground connection (Louie928)
6. 10:19 AM - Lamar MC 10 with internally regulated alternator (josnooze)
7. 11:30 AM - Re: Re: Airframe ground connection (Robert L. Nuckolls, III)
8. 12:20 PM - Re: Airframe ground connection (Louie928)
9. 01:22 PM - l5t06e 1ipfv (Vincent Welch)
10. 01:32 PM - Re: l5t06e 1ipfv (Harley)
11. 01:44 PM - Re: l5t06e 1ipfv (RGent1224@aol.com)
12. 03:22 PM - Re: l5t06e 1ipfv (Vincent Welch)
13. 03:32 PM - Re: l5t06e 1ipfv (Harley)
Message 1
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Subject: | Re: Airframe ground connection |
>
>Or, run a +12V #4, and a ground #4, to the starter and engine
>thereby bypassing the airframe from the large starter current. The
>wire length from battery to engine is about 7 feet.
That's the 'clean' way to do it. #4 welding cable
for battery wires. Take battery (-) to firewall
feed through bolt, battery (+) through battery
contactor and then firewall to starter contactor.
Bob . . .
Message 2
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Subject: | Re: Airframe ground connection |
> Something like 1/8" aluminum 2" or 3" in diameter riveted with, say 8 #4 rivets,
to the underlying thin aluminum or galvanized steel to distribute the current?
Rivets do not make very good electrical connections unless there are many of them
in parallel (electrically). Certain brands of switches are prone to fail because
they use rivets to carry the current.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=347383#347383
Message 3
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Subject: | Re: Airframe ground connection |
The switches that we've seen fail at riveted joints didn't fail because
of the rivets, per se. They failed because rivets were used to join
grossly dissimilar materials - Bakelite/plastic sandwiched between metal
tabs - AND the leads were not supported adequately. In service,
movement of the wire leads relative to the switch body flexed the
terminal tabs, eventually loosening the riveted joint. As the riveted
joint works and loosens, the gas-tight electrical connection is
compromised. The less-than-ideal electrical connection introduces
electrical resistance which manifests as heat. The heat further damages
the loose rivet/plastic/copper interface thru corrosion and differential
thermal expansion rates, and a destructive cycle of rising resistance,
higher heat and accelerated damage results until the Bakelite cooks and
crumbles or the copper bits inside anneal and deform to the point that
the actuator can't move the rocker far enough to make/break the
connection.
Neal
> Rivets do not make very good electrical connections unless there are
many of them in parallel (electrically). Certain brands of switches are
prone to fail because they use rivets to carry the current.
Joe Gores
>> Something like 1/8" aluminum 2" or 3" in diameter riveted with, say 8
#4 rivets, to the underlying thin aluminum or galvanized steel to
distribute the current?
Message 4
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Subject: | Re: Airframe ground connection |
At 10:19 AM 7/22/2011, you wrote:
TRS/DOJ" <Neal.George@hurlburt.af.mil>
The switches that we've seen fail at riveted joints didn't fail because
of the rivets, per se. They failed because rivets were used to join
grossly dissimilar materials - Bakelite/plastic sandwiched between metal
tabs - AND the leads were not supported adequately. In service,
movement of the wire leads relative to the switch body flexed the
terminal tabs, eventually loosening the riveted joint. As the riveted
joint works and loosens, the gas-tight electrical connection is
compromised. The less-than-ideal electrical connection introduces
electrical resistance which manifests as heat. The heat further damages
the loose rivet/plastic/copper interface thru corrosion and differential
thermal expansion rates, and a destructive cycle of rising resistance,
higher heat and accelerated damage results until the Bakelite cooks and
crumbles or the copper bits inside anneal and deform to the point that
the actuator can't move the rocker far enough to make/break the
connection.
An excellent recap of some extensive discussion
shared here on the List some time back.
Emacs!
Rivets have been used to assemble gazillions
of switches for decades. The designers of such
devices strive for rivets not to be the "weakest"
link in the chain of stresses on service life.
Let's look at the inner workings of a Carling toggle
(common to tens of thousands of Cessnas and certainly
thousands of OBAM aircraft). We observe TWO features
in the current carrying path that are more vulnerable
to wear-out or environmental failure. One is the
contacts. Resistance across the contacts is a function
of spring pressure and contact surface condition.
Resistance across the pivot-saddle is also a function
of spring force and surface condition . . . but at least
it gets "scrubbed" each operating cycle. Contacts just
get "hammered". Contacts also benefit from the cleansing
effects of electrical arcing to burn away products of
corrosion.
When installed with some attention to stresses on riveted
terminals, one can expect failure of the low-pressure,
moving-components to precede failure of the rivets by
perhaps an order of magnitude of service life.
Rivets in the switches are used in tension and they
join a stack of materials that includes a plastic.
Rivets in sheet metal are used in sheer. Further, if
properly drilled and set, they swell up in the hole to
form a metal-to-metal, gas tight fit . . . not unlike
the gas-tight fit of wires properly mashed in the
barrel of a terminal.
Riveted doublers to reduce sheet current density
around a high-current ground to airframe is probably
not a 'bad' idea . . . but if there are concerns
for getting a good ground in a thin-metal assembly,
perhaps going around it entirely with a bundle of
copper "cat-hairs" is a 'better' idea.
Bob . . .
Message 5
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Subject: | Re: Airframe ground connection |
Neal.George(at)hurlburt.a wrote:
> The switches that we've seen fail at riveted joints didn't fail because
> of the rivets, per se. They failed because rivets were used to join
> grossly dissimilar materials - Bakelite/plastic sandwiched between metal
> tabs - AND the leads were not supported adequately. In service,
> movement of the wire leads relative to the switch body flexed the
> terminal tabs, eventually loosening the riveted joint. As the riveted
> joint works and loosens, the gas-tight electrical connection is
> compromised. The less-than-ideal electrical connection introduces
> electrical resistance which manifests as heat. The heat further damages
> the loose rivet/plastic/copper interface thru corrosion and differential
> thermal expansion rates, and a destructive cycle of rising resistance,
> higher heat and accelerated damage results until the Bakelite cooks and
> crumbles or the copper bits inside anneal and deform to the point that
> the actuator can't move the rocker far enough to make/break the
> connection.
>
> Neal
>
>
> > Rivets do not make very good electrical connections unless there are
> > many of them in parallel (electrically). Certain brands of switches are
> >
>
> prone to fail because they use rivets to carry the current.
> Joe Gores
>
>
> > > Something like 1/8" aluminum 2" or 3" in diameter riveted with, say 8
> > #4 rivets, to the underlying thin aluminum or galvanized steel to
> >
>
> distribute the current?
You make a valid point regarding the riveted connectors on the switches. I've come
across the exact problem you describe in my work. It can lead to intermittent
problems before identification of the actual trouble spot. I bought all my
switches from B&C and was dismayed to see they have the riveted connection to
the push on spade connector. It takes little effort to move the connector under
the rivet. These have apparently been used in a lot of airplanes over a long
time so maybe no problems have surfaced. I'll need to be sure I have the wires
well supported near the switch with no strain on the riveted connector.
Yes, distribute the current over a wider contact area of the thin aluminum, or
steel. A simple bolted connection to 0.032" aluminum or the 0.018" galvanized
steel firewall has a ridiculously small cross sectional area for the current to
pass through. If it was wire it would be a very small CMA, like a fuse link.
True, it is a short distance and the voltage drop won't be a lot. Heat will be
generated which can contribute to problems down the road. If the bolted connection
can be made through a thicker piece of material of 2 or 3 square inches
area, and that thicker piece electrically connected to the thinner piece, the
current will be distributed out to a much larger area of the thin metal and the
current density won't be so high.
--------
Louis W. Ott
601XL beginner Quick Build
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=347398#347398
Message 6
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Subject: | Lamar MC 10 with internally regulated alternator |
Does anyone know of any problems using a Lamar MC 10 all-in-one electrical control
box with a plane power 60 amp internally regulated alternator? The MC 10
has internal crowbar overvoltage and overcurrent protection.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=347403#347403
Message 7
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Subject: | Re: Airframe ground connection |
It takes little effort to move the connector under the rivet. These
have apparently been used in a lot of airplanes over a long time so
maybe no problems have surfaced. I'll need to be sure I have the
wires well supported near the switch with no strain on the riveted connector.
Good practice . . . whether the terminals are riveted
or not.
Yes, distribute the current over a wider contact area of the thin
aluminum, or steel. A simple bolted connection to 0.032" aluminum or
the 0.018" galvanized steel firewall has a ridiculously small cross
sectional area for the current to pass through.
If you study the three sheets of Figure Z-15 found
at http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/
You will see a directed effort to minimize the use of airframe
for any ground return currents.
If it was wire it would be a very small CMA, like a fuse link. True,
it is a short distance and the voltage drop won't be a lot. Heat will
be generated which can contribute to problems down the road. If the
bolted connection can be made through a thicker piece of material of
2 or 3 square inches area, and that thicker piece electrically
connected to the thinner piece, the current will be distributed out
to a much larger area of the thin metal and the current density won't
be so high.
Assume a firewall ground feed-through stud is the
central, single-point ground. Assume further that only
a limited number of low-current remotely mounted accessories
enjoy local airframe grounds, then current density and bonding
issues go away. The firewall sheet carries a small percentage
of the total system currents and never cranking current.
Bob . . .
Message 8
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Subject: | Re: Airframe ground connection |
Thanks very much for helping clear this up.
--------
Louis W. Ott
601XL beginner Quick Build
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=347416#347416
Message 9
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http://www.telegazeta.com/wp-content/plugins/img/eyog.html
o3jgtyj9m=2C ixozyzgz5c. bua83i0f2l 1e694c6ehk1j 39g0sfdlllc.
Message 10
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Subject: | Re: l5t06e 1ipfv |
Another one got through...don't click on it.
Harley
-----------------------------------------------------------------
> http://www.telegazeta.com/wp-content/plugins/img/eyog.html
> o3jgtyj9m, ixozyzgz5c. bua83i0f2l 1e694c6ehk1j 39g0sfdlllc.
> *
>
> *
Message 11
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Subject: | Re: l5t06e 1ipfv |
YOU BETCHA
In a message dated 7/22/2011 3:33:12 P.M. Central Daylight Time,
harley@AgelessWings.com writes:
Another one got through...don't click on it.
Harley
____________________________________
_http://www.telegazeta.com/wp-content/plugins/img/eyog.html_
(http://www.telegazeta.com/wp-content/plugins/img/eyog.html)
o3jgtyj9m, ixozyzgz5c. bua83i0f2l 1e694c6ehk1j 39g0sfdlllc.
(http://www.matronics.com/Navigator?AeroElectric-List)
(http://www.matronics.com/contribution)
Message 12
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This did not come from me. Something has attacked my hotmail account and i
s sending to everyone on my contact list.
From: harley@agelesswings.com
CC: welchvincent@hotmail.com
Subject: Re: AeroElectric-List: l5t06e 1ipfv
Another one got through...don't click on it.
Harley
http://www.telegazeta.com/wp-content/plugins/img/eyog.html
o3jgtyj9m=2C ixozyzgz5c. bua83i0f2l 1e694c6ehk1j 39g0sfdlllc.
Message 13
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Subject: | Re: l5t06e 1ipfv |
I suspected that your email was probably just spoofed, just
wanted to warn others. It's happened to me a couple of times, and
if you just wait it out, it'll probably go away in a few days.
If you're password still works on your account, then it's
probably not hijacked...someone just "temporarily borrowed" your
address by putting it in their own "From" line.
If that's the case, your account is not in any danger. If you
start getting a bunch of returned emails with "address ubnknown"
on them, that's definitely the case...it'll go away eventually.
Harley
-----------------------------------------------------------------
On 7/22/2011 6:18 PM, Vincent Welch wrote:
> This did not come from me. Something has attacked my hotmail
> account and is sending to everyone on my contact list.
>
> -----------------------------------------------------------------
> Date: Fri, 22 Jul 2011 16:29:54 -0400
> From: harley@agelesswings.com
> To: aeroelectric-list@matronics.com
> CC: welchvincent@hotmail.com
> Subject: Re: AeroElectric-List: l5t06e 1ipfv
>
> Another one got through...don't click on it.
>
> Harley
> -----------------------------------------------------------------
>
> http://www.telegazeta.com/wp-content/plugins/img/eyog.html
> o3jgtyj9m, ixozyzgz5c. bua83i0f2l 1e694c6ehk1j 39g0sfdlllc.
>
> *
>
> *
>
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