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a.s.elliott(at)cox.net
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 Posted: Tue Oct 16, 2018 6:35 am Post subject: Total Power Failure? |
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Just a reply to Bob’s question:
But why this extra hardware? How does one
experience a total failure of the DC
power system in an airplane?
My particular airplane has a single alternator, single main battery. And I do fly IFR and at night. While *I* have never had a paired battery/alternator failure, most assuredly I have read accident cases of those who did. Often, this was due to a combination of poor maintenance and poor pilot decisions.
My last electrically-dependent airplane (dual electric fuel pumps, no mechanical pump) had dual batteries and was set up according to the appropriate Z-diagram. The Precision Airmotive Eagle system is clearly designed as a *retrofit* for existing typical single-battery GA installations, and therefore includes its own back-up battery.
My panel also has internal back-up batteries for the EFISes. These would also be redundant for a properly designed dual-battery system. But even out where I live in the mountains, it is hard to imagine not being able to get the plane on the ground within 30 minutes, with the engine running, EFIS alive and tablet working.
Andy
------------------------
Andrew S. Elliott, CFI
Servicios Aéreos, LLC
Dynamic Propeller Balancing, Flight Instruction
PH: 720-460-1823
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nuckolls.bob(at)aeroelect
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| Posted: Tue Oct 16, 2018 1:37 pm Post subject: Total Power Failure? |
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At 09:33 AM 10/16/2018, you wrote:
| Quote: | Just a reply to Bob’s question:
But why this extra hardware? How does one
experience a total failure of the DC
power system in an airplane?
My particular airplane has a single alternator, single main battery. And I do fly IFR and at night. While *I* have never had a paired battery/alternator failure, most assuredly I have read accident cases of those who did. Often, this was due to a combination of poor maintenance and poor pilot decisions. |
Agreed. I would venture to take it a bit further
and replace "often" to "mostly".
I used to analyze what I called "Dark-n-Stormy
Night" stories from the popular journals to see
if there was measurable value for having read
these narratives.
I found them particularly un-informative.
While they all purported to arm the reader
with information that might serve help
them in a similar situation, virtually
all of the stories were devoid of cause/effect/
remedy details and/or critique of poor
design and/or maintenance.
Chapter 17 in the 'Connection features
one such story . . .
http://www.aeroelectric.com/Book/AEC_R12A.pdf
I ended the chapter with this:
[img]cid:.0[/img]
Some years later, I heard from Mr. Gomez. He
allowed as how my analysis of his story was
correct.He said he was considering an OBAM aviation
project!
| Quote: |
My last electrically-dependent airplane (dual electric fuel pumps, no mechanical pump) had dual batteries and was set up according to the appropriate Z-diagram. The Precision Airmotive Eagle system is clearly designed as a *retrofit* for existing typical single-battery GA installations, and therefore includes its own back-up battery. |
If we think about it, our airplanes have been
'electrically dependent' nearly since day-one.
While early gyros for light aircraft
were vacuum driven, we still had rudimentary
radio-navigation aids. An uncle of mine used
to own a Tri-Pacer with a belly mounted, manual
DF loop on his Single Lear LTRA6 transceiver
with an OmniScope.
A heavy, rather robust trio of boxes full
of vacuum tubes.
He was instrument rated. The equipment was
capable of non-precision approaches but if
only one of those vacuum tubes went belly up,
or a power supply shorted . . . he was committed
to depend on iron gyros and reserve fuel to
navigate to nearest predicted conditions for
safe descent to terra firma.
But it was only 10 years later that S.E. aircraft
began to be fitted with dual nav/coms, glide slope,
ADFs, marker beacons and transponders. I used to
work for a company that built electrically driven
stand by vacuum pumps. But even with all that
'redundancy' the airplanes still had one alternator
and one battery . . . BOTH rather fragile components
compared to today's hardware.
YET . . . there must have been tens of thousands
of successful approaches and/or escapes from un-
anticipated turns of event as long as the most
ignored and abused component of the electrical
system was maintained to minimum conditions
for continued airworthiness . . . the battery.
Many dark-n-stormy night stories featured
weak or failed batteries . . . no doubt, similar
stories were never written because the pilot
did not survive to transcribe his/her experience.
| Quote: |
My panel also has internal back-up batteries for the EFISes. These would also be redundant for a properly designed dual-battery system. But even out where I live in the mountains, it is hard to imagine not being able to get the plane on the ground within 30 minutes, with the engine running, EFIS alive and tablet working. |
Yeah, the manufacturers of these products
are kinda stuck between a rock and a hard place.
They KNOW that a prudently maintained electrical
system is about as reliable as prop bolts . . .
but . . . out of the hundreds of thousands of
light aircraft flying around today . . . how many
carry an un-airworthy battery?
So, let's say you're marketing a really snazzy
electro-whizzie with a prominent role
to play in comfortable termination of some
flights. Okay, what control do YOU have over
the design, operation and maintenance policies
for the customer's electrical system? Easy, it's
ZERO. Hmmmm . . . you can see it now. There's
a momma sitting at the plaintiff's table, three
kiddies are sitting in the front row of the
spectator's gallery with grandma. Momma's lawyer
is hammering your engineers, marketing people, indeed
ANYONE and EVERYONE who touched her husband's airplane
perhaps years before it flew into a mountainside.
What's a poor entrepreneur to do? Eureka! An
internal back-up battery! At least YOUR product
will continue to function even if everybody else's
electro-whizzies are off line due to loss of
power. The guy's engine may be dead but
at least he'll hit the ground wings level and
knowing what his heading is to within
a degree or two.
Now, we're a few milestones further down the
technological highway and there are even more
electro-whizzies necessary for comfortable
arrival with the earth. If every supplier of
such products had his way, they'd all get
back-up batteries . . . mostly because they
have no control over how well the primary
energy sources will be designed, fabricated
and maintained.
If all suppliers of electro-whizzies fondest
dreams were realized, there would be a family
of batteries scattered about the airplane,
each one intended to make up for potential
if not realized deficiencies in the ship's
primary energy source.
Problem is, if the primary energy source
is poorly designed or neglected, what's to
say that the back up battery(ies) will
not be similarly compromised?
Further, every battery in the system,
represents one more preventative maintenance
item demanding $resources$ to secure
airworthiness.
If one is inclined to take good care of
the primary system, the last thing the
owner needs is to spend more $resources$
on maintenance of battery(ies) with an
exceedingly low probability of being
pressed into service.
I cringe when I read 'back up battery' knowing
that it is (1) possible to reduce its contribution
to system reliability to near zero and (2)
the very presence of back up batteries can
lull some owners into a false sense of security.
Yeah, total loss of power has happened. The
last one I was aware of happened in a B390
in South Bend on March 17, 2013. A sad but
interesting read can be found here . . .
http://www.aeroelectric.com/Reference_Docs/Accidents/N26DK_Mar2013/20130317-0_PRM1_N26DK.pdf
The guys up front on this airplane managed to
turn lots of things OFF . . . engines . . .
battery . . . oh well . . . some days the
gods of energy management are simply not on
your side.
Concorde received the battery for evaluation
MONTHS after the accident. The battery
had received NO interim maintenance or examination.
Concorde found it to STILL possessed a high
percentage of its specified energy storage. A
dozen back up batteries wouldn't have helped
these guys
All you need to do is properly size the battery
to a KNOWN endurance requirement and then give
it the same attention as you do the tires,
prop and engine oil. It WILL be there when you
need it most.
Bob . . .
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a.s.elliott(at)cox.net
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| Posted: Wed Oct 17, 2018 8:09 am Post subject: Total Power Failure? |
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At least the designers of the now-defunct Precision Airmotive system used a commonly available 12V SLA battery that is easy and inexpensive J to replace every couple of years, and the system has checks for back-up battery voltage built in. Got one in the hangar that I plug into the charger about 1/month.
On the other hand, the AFS 3400 EFIS back-up battery is an unspecified internal lithium-ion device. I guess you have to open it up to find out if is an off-the-shelf battery or a custom. At least when you go on internal, the unit displays a battery capacity indicator, which can be checked every time you shut the plane down.
Andy
------------------------
Andrew S. Elliott, CFI
Servicios Aéreos, LLC
Dynamic Propeller Balancing, Flight Instruction
PH: 720-460-1823
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nuckolls.bob(at)aeroelect
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| Posted: Wed Oct 17, 2018 10:41 am Post subject: Total Power Failure? |
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At 11:09 AM 10/17/2018, you wrote:
| Quote: | At least the designers of the now-defunct Precision Airmotive system used a commonly available 12V SLA battery that is easy and inexpensive J to replace every couple of years, and the system has checks for back-up battery voltage built in. Got one in the hangar that I plug into the charger about 1/month.
On the other hand, the AFS 3400 EFIS back-up battery is an unspecified internal lithium-ion device. I guess you have to open it up to find out if is an off-the-shelf battery or a custom. At least when you go on internal, the unit displays a battery capacity indicator, which can be checked every time you shut the plane down.
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Sounds like thoughtful design . . .
Bob . . .
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jonlaury
Joined: 06 Nov 2006
Posts: 336
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Mauledriver(at)nc.rr.com
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| Posted: Thu Oct 18, 2018 9:49 am Post subject: Total Power Failure? |
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On 10/17/2018 2:41 PM, Robert L. Nuckolls, III wrote:
| Quote: | At 11:09 AM 10/17/2018, you wrote:
| Quote: | At least the designers of the now-defunct Precision Airmotive system used a commonly available 12V SLA battery that is easy and inexpensive J to replace every couple of years, and the system has checks for back-up battery voltage built in. Got one in the hangar that I plug into the charger about 1/month.
On the other hand, the AFS 3400 EFIS back-up battery is an unspecified internal lithium-ion device. I guess you have to open it up to find out if is an off-the-shelf battery or a custom. At least when you go on internal, the unit displays a battery capacity indicator, which can be checked every time you shut the plane down.
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Sounds like thoughtful design . . .
Bob . .
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And a thoughtful discussion as well. I always find these informative and useful in the ongoing management of my OBAM RV-10 with a Z-14 (dual batts, buses, and alts).
I am about to change my panel by swapping out a backup cluster of a round guage ASI, Alt, and ADI (with backup battery) for a small format non-TSO's PFD with internal AHRS (The HORIS from Karnardia). That will make my panel 100% dependent on the Z-14 electrical system since I did not opt for an internal backup battery on any of my instruments (including 3 GRT EFISs).
I'm confident about doing this because of the confidence I have in the Z-14 design and its operation. After much screwing up, I've also built up confidence in maintaining the 2 Odyssey 680 batteries. For the batteries I now simply follow the voltage checks outlined by the manufacturer and replace when a battery falls short.
I should mention that I'm not discarding the round gauge backup cluster for kicks. For one I wasn't completely confident with the ADI as a backup for keeping the wings level. But the main reason was to free up some panel real estate for a larger GRT EFIS/PFD screen. For some reason, the eyes aren't improving with age.
The nagging question is why do I feel I need to backup the GRT EFISs? I have 3 of them on the panel, 2 easily viewed by the pilot and all of them capable of acting as a PFD, moving map or engine monitor, or all 3 at one time. The answer is one I don't fully buy into but lingers out there; what if there is a software 'bug' or 'hack' that causes all 3 units to fail simultaneously? Never heard of that occurring with any brand of EFIS (?) but I will have a backup PFD with different hw/sw to backup the primaries. But again, no backup batteries. Total dependency on the Z-14.
Bill "flying an electrically dependent RV10 fired by dual Slick mags" Watson
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ceengland7(at)gmail.com
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| Posted: Thu Oct 18, 2018 9:53 am Post subject: Total Power Failure? |
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On 10/18/2018 11:13 AM, jonlaury wrote:
| Quote: |
a.s.elliott(at)cox.net wrote:
> ...
>
> On the other hand, the AFS 3400 EFIS back-up battery is an unspecified internal lithium-ion device.� I guess you have to open it up to find out if is an off-the-shelf battery or a custom. �...
>
> Andy
>
> ------------------------
>
Or call AFS (now Dynon) and ask [Wink]
Search for Advanced Flight Systems, http://www.advanced-flight-systems.com/Support/AF-3000support/replacing-clock-battery.pdf
"We have found that the internal clock battery lasts from 6 to 10 year in a display. Finding a BR chemistry battery is important over the CR type due to the performance in high temperature environments and stable voltage over battery life. CR-1225 batteies will need replacement more often."
Big difference between a clock battery and the operational backup
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battery....
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