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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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 Posted: Wed Mar 04, 2015 10:55 am Post subject: Shorted battery caused crash |
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There is an article on page 50 of the April 2015 issue of Kitplanes Magazine about aircraft design risks. The article mentions a 2012 crash of a P-51 replica that made a forced landing after one of the two batteries shorted, resulting in the stoppage of the electrically dependent engine.
NTSB Report: http://tinyurl.com/nbso2eg
Quote from Kitplanes, ". . .the design must allow the pilot to disconnect the batteries from each other to prevent dual-battery depletion. This FEW Mustang's battery connections didn't include a disconnect feature."
Does anyone know what type of batteries these were, flooded or AGM? If an electrically dependent aircraft with dual batteries experienced an electrical failure due to a short circuit, either internal to a battery or external, and the engine and electronics quit, would there be any other symptoms like battery contactors chattering? Would the pilot know what action to take? Shutting off one or both battery contactors might seem counter-intuitive if the pilot had not previously thought about this scenario.
Joe
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nuckolls.bob(at)aeroelect
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| Posted: Wed Mar 04, 2015 12:36 pm Post subject: Shorted battery caused crash |
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At 12:55 2015-03-04, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
There is an article on page 50 of the April 2015 issue of Kitplanes Magazine about aircraft design risks. The article mentions a 2012 crash of a P-51 replica that made a forced landing after one of the two batteries shorted, resulting in the stoppage of the electrically dependent engine.
NTSB Report: http://tinyurl.com/nbso2eg |
Yeah, read that. Not enough information. The
NTSB assertions MIGHT be correct but even if
so, there is little to be gained from this
event-narrative other than "Be careful out there,
what you don't know might prevent you from
ever knowing further . . ."
I've read perhaps 100 of what I call, "dark-n-stormy
night stories" over the years. I don't recall reading
a single narrative that offered an analysis of
root cause and potential remedy for a design
deficiency. The author's assertions could not
go beyond, "Be attentive and ask around . . .
particularly from informed sources."
From the NTSB probable cause statement:
The pilot reported that there was an electrical system failure during the cruise portion of the test flight, which resulted in insufficient voltage to maintain engine operation using either the primary or secondary battery circuits. Following the total loss of engine power, the pilot elected to perform a wheels-up landing on a gravel road. The non-certificated automobile engine that was installed in the airplane was equipped with a computer-controlled electronic ignition system and high-pressure fuel pumps. According to the pilot/builder, the airplane incorporated two 12-volt batteries wired in parallel to supply voltage to the main power bus to power the engine systems. Post accident examination revealed that the primary battery had an internal short and would not take a charge. The secondary battery was found below normal service voltage, but could be recharged. Postaccident testing revealed that the two batteries were not isolated from each other; as a result, an internal short of one of the two batteries could drain the other battery’s charge. No anomalies were found with the remaining electrical system components or wiring paths.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows: - An internal failure of one of the electrical system’s two batteries combined with the inadequate electrical system design, which resulted in a total loss of engine power.
Clearly, this system did not benefit from
an artfully conducted FMEA. This had
nothing to do with selection of batteries
but upon how the batteries were implemented.
Just between you and me, I'm skeptical of
the shorted battery thingy . . . if one cell
shorts, it becomes a 10v battery. The alternator
goes into full-bore output in an attempt to
bring it's terminal voltage back to 14+
volts but in any case, system voltage does
not drop below 11 volts.
What was the alternator doing all this time?
Was there any provisions for annunciation
of low voltage?
If his system was not designed to function
at 11+ volts (well short of battery
depletion) then there were probably additional
design features/limits that stacked on top of
each other to ruin his day.
Without seeing the architecture, reading
a narrative of design goals capped off
with tests conducted to verify that the goals were
achieved . . . the article is of little value
beyond that "Be careful" thingy.
Bob . . . [quote][b]
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Mar 14, 2015 5:45 am Post subject: Re: Shorted battery caused crash |
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The pilot of the the accident airplane emailed to me the following: | Quote: | | The magazine article is not correct, I did have a disconnect system in place. However the failure occurred so fast (I could literally see my volt meter dropping), that I could not trouble shoot the problem quickly enough. The primary battery rapidly depleted the secondary battery and even overwhelmed the alternator output. If I recall correctly, the fuel injectors quit operating at around 10.5 volts and that happened in a couple of minutes. |
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ceengland7(at)gmail.com
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| Posted: Sat Mar 14, 2015 7:26 am Post subject: Shorted battery caused crash |
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On 3/14/2015 8:45 AM, user9253 wrote:
| Quote: |
The pilot of the the accident airplane emailed to me the following:
> The magazine article is not correct, I did have a disconnect system in place. However the failure occurred so fast (I could literally see my volt meter dropping), that I could not trouble shoot the problem quickly enough. The primary battery rapidly depleted the secondary battery and even overwhelmed the alternator output. If I recall correctly, the fuel injectors quit operating at around 10.5 volts and that happened in a couple of minutes.
--------
Joe Gores
Still doesn't make any sense if only one cell was shorted. If he had a
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catastrophic dead short across multiple cells, then maybe so.
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Mar 14, 2015 2:16 pm Post subject: Re: Shorted battery caused crash |
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Has anyone ever measured the current draw of a battery with a shorted cell (with a second battery and alternator connected)?
Joe
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nuckolls.bob(at)aeroelect
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| Posted: Sat Mar 14, 2015 6:44 pm Post subject: Shorted battery caused crash |
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At 08:45 2015-03-14, you wrote:
| Quote: |
The pilot of the the accident airplane emailed to me the following:
> The magazine article is not correct, I did have a disconnect
system in place. However the failure occurred so fast (I could
literally see my volt meter dropping), that I could not trouble
shoot the problem quickly enough. The primary battery rapidly
depleted the secondary battery and even overwhelmed the alternator
output. If I recall correctly, the fuel injectors quit operating at
around 10.5 volts and that happened in a couple of minutes.
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I'd sure like to duplicate that on the bench.
The fact that a battery shorted in the first
place is mystifying . . . what kind of battery
was this. Had it been cap and load checked
recently? Alternators don't get "overwhelmed"
and quit. They will attempt to raise the foreshortened
10v battery up to the normal 14v bus voltage.
They'll run current limited during this time and
may get pretty warm but they don't smoke, roll
over and die.
What was the condition of the alternator after
the event?
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Mar 14, 2015 6:54 pm Post subject: Shorted battery caused crash |
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At 17:16 2015-03-14, you wrote:
| Quote: |
Has anyone ever measured the current draw of a battery with a
shorted cell (with a second battery and alternator connected)?
Joe
--------
Joe Gores
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No way to predict. The fact that a cell shorted
offers questions about the condition of the battery
in the first place. An SVLA battery that's less
than airworthy will suffer swelling plates due to
sulfation. This wouldn't be expected to occur unless
the battery was left in service long after it failed
a load/cap check.
This mechanical stress on plate separators can raise
the risk of shorting. If the battery is sulphated
badly, it wouldn't deliver much current, nor would
it draw spectacular amounts of current in the shorted
cell scenario. The ability of the 'good' battery
to deliver energy into the shorted-cell battery
is similarly influenced by age and service related
degradation.
If these were identical batteries with similar
histories, perhaps neither one would have tested
airworthy.
It would be very interesting to know the pedigree
of the batteries involved and to see a schematic
of the system architecture.
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Mar 14, 2015 6:59 pm Post subject: Re: Shorted battery caused crash |
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I also asked what type of battery, flooded or AGM, but did not get a reply. Other than the single email quoted in my previous post, I have not received any more info from the pilot-builder.
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Joe Gores |
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Sat Mar 14, 2015 7:06 pm Post subject: Re: Shorted battery caused crash |
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Judging from the limited information available, I speculate that the aircraft was wired similar to Z-19. It is hard to come to any conclusions about the cause of the electrical failure without knowing all of the facts and details about the type of batteries and their condition and age.
Joe
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