Today's Message Index:
----------------------
1. 04:09 AM - Re: UN-FUSED MAIN BUS FEEDER (Robert L. Nuckolls, III)
2. 02:40 PM - OT-AA battery performance at low temp (rayj)
3. 04:06 PM - Re: UN-FUSED MAIN BUS FEEDER (user9253)
4. 06:12 PM - Re: Re: UN-FUSED MAIN BUS FEEDER (Robert L. Nuckolls, III)
5. 07:15 PM - Re: UN-FUSED MAIN BUS FEEDER (user9253)
6. 07:28 PM - Re: OT-AA battery performance at low temp (Bob McCallum)
7. 08:42 PM - Re: OT-AA battery performance at low temp (Henry Hallam)
Message 1
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| Subject: | Re: UN-FUSED MAIN BUS FEEDER |
At 23:45 2015-01-12, you wrote:
>Joe,
>
>Thanks for bringing this to our attention. Very scary and very
>interesting. A poster on the VansAirforce forum states that the
>RV-12 is "certified" under an ASTM standard.
>
>I found this:
>ASTM F2245 - 14. Standard Specification for Design and Performance
>of a Light Sport Airplane.
><http://www.astm.org/Standards/F2245.htm>http://www.astm.org/Standards/F2245.htm
>
>The abstract for that document suggests that it discusses electrical
>systems. I would like to get a look at that document but I'm
>hesitant to spend $60 just for a look-see.
>
>Does anyone have a copy of that document that I could look at? Has
>anyone on this forum seen/read that document and would care to comment on it.
>
>
>Back to the VansAirforce post - The original poster did not post any
>pictures of the before & after. That's a shame because it might be
>very instructive if we could see how that feeder was routed.
>
>-Jeff
>
>PS - As long-time members of this forum may recall, I have been a
>proponent of protecting all feeders and my designs incorporate such
>protection. This current (no pun intended) issue is a good example
>of why. If this fire had occurred while airborne the results could
>have been catastrophic.
Yes, there are a constellation of risks associated
with materials and processes for assembling
airplanes. I recall a couple of instances
of fuel fed fires on Glasairs waaayyy back when
with root cause traced to poorly installed
fire wall fittings on fuel lines. An RV8
went down in flames with the pilot electing
to do a no-parachute egress from the aircraft.
Root cause for this unhappy event will never be
known . . . but a whole lot of history and FMEA
practices can give us some good ideas . . . and
I'll bet none of them are mitigated by ADDING
another feature to a proven system. It's more
likely that some simple failure to observe
good practice is the root cause. Missing safety
wire, o-ring pinched, cracked line, etc. etc.
Hard Reality of Life: No amount of ISO9000
documentation and holy-watered work instructions
will guarantee that one of life's little
"Aw S@#$s" won't jump up an bite you.
Are you working under the assumption that the
triggering event was a hard faulted 12AWG bus
feeder?
In your hypothesis, how does a relatively young,
robust wire get compromised severely over
a short period of time to produce such
a high energy event?
I'm going to sift through the narrative but
there was one poster to the thread that wondered
about engine grounding. Those control cables
(wound jacket Bowden controls?) are steel and
relatively poor conductors. If the airplane's
engine were not properly bonded to a high integrity
ground system, then the current demands of an engine
start circulating in the control cables offers
a plausible explanation for the energy flows
that triggered the event.
Before we chase the rabbit down the bus-feeder-
protection hole, let's assure ourselves that
it was a hard-faulted WIRE that started the unhappy
event and not a couple of heater-coil control
cables being tasked to do things never intended
by the designers. I am skeptical that a burning
12AWG wire bundled with steel engine controls would
do much damage to them. On the other hand, engine
controls masquerading as crankcase grounds would
not only exhibit severe heat stress, they would
compromise the insulation on wires bundled together
the controls.
I looked at the link for the ATSM document . . .
33 pages for $60 ???? I'm pretty sure Textron
has a subscription to such documents, I'll see
if I can put my hands on one. But at best, it's
an index to a bunch of other documents or at
worst, a gathering of lofty words speaking
to design goals dreamed up by individuals with
little or no experience at the craft.
If you look through the z-figures, you'll see
fusible links at the source end of bus feeders
on 'tiny alternator' airplanes. Airplanes with
big alternators are assumed to carry the same
gage wire throughout the cranking circuit and
bus feeders . . . 4AWG or larger. Probability
of hard faulting a fat wire in a manner that
puts the wire at risk is exceedingly low as
demonstrated in hundreds of thousands of examples
over the last century of aviation history.
The fact that the 12AWG wire in question burned
only ahead of the fire wall suggests that it
came to ground at the fire wall penetration
site. How would/did this happen? Just
for grins . . . connect a 12AWG wire to a
battery grounded to a 'fire wall', run the
wire through a hole in that piece of metal
then work the wire against the edge of the hole
until you produce a fault sufficient to
burn the wire. How much time? How much force?
What kind of motion? What was going on from
the time sparks first started to fly (soft
fault) until connection could be made to
cook the wire? Now, how did this happen in
the event airplane?
The discussion I downloaded last night is
long on supposition and conjecture . . . short
on failure analysis. It seems more likely that the
controls got hot first and compromised the
insulation which triggered an electrical
compromise of the wire but without sifting
the aftermath in a logical and ordered manner,
the facts are elusive.
We need to be sure of the simple-ideas in
physics and proven practices before painting
this event as a justification for pasting
a band-aid on a system that was bleeding
profusely somewhere else.
Bob . . .
Message 2
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| Subject: | OT-AA battery performance at low temp |
Greetings,
Does anyone know how the voltages of AA disposable lithium batteries and
AA alkaline compare at temps in the neighborhood of -20F.
I'm trouble shooting a weather station with an intermittent problem and
wondering if AA lithium will give more voltage/current, and possibly
solve my problem.
Thanks,
do not archive
--
Raymond Julian
Kettle River, MN
The things we admire in men, kindness and generosity, openness, honesty,
understanding and feeling are the concomitants of failure in our system.
And those traits we detest, sharpness, greed, acquisitiveness, meanness,
egotism and self-interest are the traits of success. And while men
admire the quality of the first they love the produce of the second.
-John Steinbeck, novelist, Nobel laureate (1902-1968)
Message 3
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| Subject: | Re: UN-FUSED MAIN BUS FEEDER |
> Are you working under the assumption that the
> triggering event was a hard faulted 12AWG bus
> feeder?
Yes, that is what happened, in my opinion, after reading the builder's description in this post: http://www.vansairforce.com/community/showpost.php?p=945235&postcount=17
Posts by others in that thread are only speculation.
> In your hypothesis, how does a relatively young,
> robust wire get compromised severely over
> a short period of time to produce such
> a high energy event?
The #12 awg wire that burned is the main feeder between the contactor and the instrument panel. The wire does NOT run parallel to or with choke or throttle cables through the firewall. Wires in the RV-12 pass through a separate hole in the firewall. The #12 wire runs perpendicular to and under the throttle cables. In my RV-12, there is a half inch space between the #12 wire and throttle cables and both are held apart by cushion clamps. In the accident RV-12, the #12 wire must have been in contact with the underside of a throttle cable. I suspect that the insulation on the wire was abraded by a vibrating throttle cable. The copper wire then welded itself to the steel cable. The builder is adamant that his engine is well grounded and thus had nothing to do with the incident. The Rotax engine starts so quickly, within 1 or 2 seconds, that it seems unlikely that throttle and choke cables would have time to heat up over their entire length to a temperature high enough to melt wire insulation. The Rotax dynamo does not use engine ground for conducting current as would a conventional alternator. The single phase AC output of the dynamo is conducted through two wires to the rectifier/regulator which is mounted on the firewall. After engine start, only engine-instrument-sensor current is dependent on the engine ground. Without having the fire damage to examine, all we have to go by is the post by the pilot-builder. Below is a link to a picture of the wire in question in my airplane, not the accident aircraft. http://tinyurl.com/RV-12-wires
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=436974#436974
Message 4
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| Subject: | Re: UN-FUSED MAIN BUS FEEDER |
The #12 awg wire that burned is the main feeder between the contactor
and the instrument panel. The wire does NOT run parallel to or with
choke or throttle cables through the firewall. Wires in the RV-12
pass through a separate hole in the firewall. The #12 wire runs
perpendicular to and under the throttle cables. In my RV-12, there
is a half inch space between the #12 wire and throttle cables and
both are held apart by cushion clamps. In the accident RV-12, the
#12 wire must have been in contact with the underside of a throttle
cable. I suspect that the insulation on the wire was abraded by a
vibrating throttle cable. The copper wire then welded itself to the
steel cable. The builder is adamant that his engine is well grounded
and thus had nothing to do with the incident. The Rotax engine
starts so quickly, within 1 or 2 seconds, that it seems unlikely that
throttle and choke cables would have time to heat up over their
entire length to a temperature high enough to melt wire
insulation. The Rotax dynamo does not use engine ground for
conducting current as would a conventional alternator. The single
phase AC output of the dynamo is conducted through two wires to the
rectifier/regulator which is mounted on the firewall. After engine
start, only engine-instrument-sensor current is dependent on the
engine ground. Without having the fire damage to examine, all we
have to go by is the post by the pilot-builder. Below is a link to a
picture of the wire in question in my airplane, not the accident
aircraft. http://tinyurl.com/RV-12-wires
Joe
Aha! Good data points. Just got a task mailed off to
a customer and had time to read the thread downloaded
last night.
It seems clear that the wire insulation was compromised
against the control cables . . . failure to observe
common practice for the maintenance of spacing.
Picked this out of the downloaded thread . . .
On the issue of a fusible link, it is not true that it would create a
weak spot electrically. A fusible link will not fail in the event of
a spurious spike in current; only in the event of a major,
uncontrolled power draw....a short circuit. It is true that it is 4
wire sizes smaller ( or 4 numbers larger); 16 awg in the case of the
RV-12 battery power wire. Regarding the philosophy of aircraft
design, to wit; the issue of a system failure versus a fire aloft is
hardly worth discussion. Seriously? In a VFR, daytime-only RV-12,
we'd consider a fire aloft a better deal than a display failure?! I
appreciate all the redundant advice to carefully route & shield the
battery power wire. Great advice. Took care of it. But that is a
separate issue of the wire becoming shorted for whatever unforeseen
reason. And there seems to be much naive comment on this blog that if
there's a problem, a fuse would blow. It needs to be clearly
understood here that if a power wire shorts out in the RV-12, a
fantastically dangerous hot spot will result; in essence, an arc
welder. That's what I had, and the damage was devastating.
Additionally, it needs to be understood that proper
engine-to-fuselage grounding will not protect against such a short
circuit. My engine is properly grounded, In fact, I long ago took the
precaution of an additional ( and very substantial) electrical ground
wire. Unprotected +12v current will find ANY path when it "shorts"
out. In my case, it virtually welded right through both the throttle
& choke cables, as well as destroying the #22 (black) ground wire in
the GPS antenna/receiver cable all the way to the connector on the
Vans AV-5000A control module in the avionics bay (a $600 piece)
As I mentioned last night, as wire sizes drop out
of the relatively invincible 'fat wire' category,
they do become vulnerable a hard-fault burn. The
fusible link is one way to go. It's compact, inexpensive
and effective. Cars have used them for years but
to my knowledge, the TC aircraft industry has never
embraced them. There's a class of circuit protector
with LONG fusing constants commonly referred to as
a current limiter. The ANL series devices . . .
http://tinyurl.com/k9tmfmh
. . . have been a common ingredient in time-delay,
hard-fault protection for over 70 years. The
automotive industry has used a variety of
heavy-fuses as well. An interesting line
that popped up 30 or so years ago was the
miniature current limiters or MANL series
devices. They're popular with installers
of kilowatt boom boxes in automobiles. They're
readily available from hundreds of sources.
http://tinyurl.com/pcuscp2
I've not seen a MANL holder from the automotive
world that instilled much confidence. Not sure
about the base materials but they're probably
okay. If it were my installation, I'd make base
our of a piece of phenolic or Delrin . . .but
the current limiters are just fine,
Fusible link wire is available in bulk from
a host of automotive supply houses. Here's
one such product
http://tinyurl.com/p3hrq22
The fusible link is mechanically attractive.
Installs with splices, ties right into a wire
bundle with the rest of the wires. If it's in
a bundle, it would e a good thing to add a layer
of silicon impregnated fiberglas sleeving like
that described in my articles and offered in
B&C's fusible link kit.
In any case, protecting light feeders
directly attached to a battery is a good idea.
Bob . . .
Message 5
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| Subject: | Re: UN-FUSED MAIN BUS FEEDER |
Thanks for your insight, Bob.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=436978#436978
Message 6
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| Subject: | OT-AA battery performance at low temp |
I cant give any hard numbers, and dont know about voltage/current
comparison details but I can provide a small bit of anecdotal information.
Im Canadian living in a part of the country where we see temperatures
approaching -40 from time to time. I have a monitoring device on my hydro
meter powered by 2 AA batteries. The instructions which came with that
device said to use only lithium batteries as alkaline wouldnt provide
accurate information in winter cold. They were correct. With lithium the
monitor works at all temperatures, with alkaline it becomes intermittent
near 0 and stops working altogether about -15 or so.
Bob McC
> -----Original Message-----
> From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-
> server@matronics.com] On Behalf Of rayj
> Sent: Tuesday, January 13, 2015 5:39 PM
> To: aeroelectric-list@matronics.com
> Subject: AeroElectric-List: OT-AA battery performance at low temp
>
>
> Greetings,
>
> Does anyone know how the voltages of AA disposable lithium batteries and
> AA alkaline compare at temps in the neighborhood of -20F.
>
> I'm trouble shooting a weather station with an intermittent problem and
> wondering if AA lithium will give more voltage/current, and possibly
> solve my problem.
>
> Thanks,
>
> do not archive
>
> --
> Raymond Julian
> Kettle River, MN
>
> The things we admire in men, kindness and generosity, openness, honesty,
> understanding and feeling are the concomitants of failure in our system.
> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
> egotism and self-interest are the traits of success. And while men
> admire the quality of the first they love the produce of the second.
> -John Steinbeck, novelist, Nobel laureate (1902-1968)
>
> _-
> =====================================================
> =====
> _-
> =====================================================
> =====
> _-
> =====================================================
> =====
> _-
> =====================================================
> =====
>
>
Message 7
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| Subject: | Re: OT-AA battery performance at low temp |
Compared to alkalines, lithium primary cells have a slightly higher
nominal voltage than alkalines, lower internal resistance, a greater
total capacity, and hold up much better at low temperatures. At -20 F
there will still be some capacity degradation compared to room
temperature, but I think you should have much better luck than with
alkalines.
Henry
On Tue, Jan 13, 2015 at 7:27 PM, Bob McCallum
<robert.mccallum2@sympatico.ca> wrote:
>
> I cant give any hard numbers, and dont know about voltage/current
> comparison details but I can provide a small bit of anecdotal information.
> Im Canadian living in a part of the country where we see temperatures
> approaching -40 from time to time. I have a monitoring device on my hydro
> meter powered by 2 AA batteries. The instructions which came with that
> device said to use only lithium batteries as alkaline wouldnt provide
> accurate information in winter cold. They were correct. With lithium the
> monitor works at all temperatures, with alkaline it becomes intermittent
> near 0 and stops working altogether about -15 or so.
>
> Bob McC
>
>> -----Original Message-----
>> From: owner-aeroelectric-list-server@matronics.com
> [mailto:owner-aeroelectric-list-
>> server@matronics.com] On Behalf Of rayj
>> Sent: Tuesday, January 13, 2015 5:39 PM
>> To: aeroelectric-list@matronics.com
>> Subject: AeroElectric-List: OT-AA battery performance at low temp
>>
>>
>> Greetings,
>>
>> Does anyone know how the voltages of AA disposable lithium batteries and
>> AA alkaline compare at temps in the neighborhood of -20F.
>>
>> I'm trouble shooting a weather station with an intermittent problem and
>> wondering if AA lithium will give more voltage/current, and possibly
>> solve my problem.
>>
>> Thanks,
>>
>> do not archive
>>
>> --
>> Raymond Julian
>> Kettle River, MN
>>
>> The things we admire in men, kindness and generosity, openness, honesty,
>> understanding and feeling are the concomitants of failure in our system.
>> And those traits we detest, sharpness, greed, acquisitiveness, meanness,
>> egotism and self-interest are the traits of success. And while men
>> admire the quality of the first they love the produce of the second.
>> -John Steinbeck, novelist, Nobel laureate (1902-1968)
>>
>> _-
>> =====================================================
>> =====
>> _-
>> =====================================================
>> =====
>> _-
>> =====================================================
>> =====
>> _-
>> =====================================================
>> =====
>>
>>
>
>
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