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nuckolls.bob(at)aeroelect
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 Posted: Mon Feb 02, 2009 10:59 am Post subject: Z-14 with dual Lightspeed III and SD-8 |
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At 09:52 AM 2/2/2009, you wrote:
| Quote: |
<bob.condrey(at)baesystems.com>
Direction to use CBs is in the installation literature, however no
specific or caution against fuses is not. This came up during a
conversation when I mentioned driving the ignitions off the battery
buss fuse blocks.
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No, I was asking about the built in crowbar ov
protection. To include such a feature without
specific explanation of its value, installation
and operation would not be viewed with benevolence
among the designers I work with.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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nuckolls.bob(at)aeroelect
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| Posted: Mon Feb 02, 2009 11:29 am Post subject: Z-14 with dual Lightspeed III and SD-8 |
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| Quote: | This whole thing gives me the willies, but I'm in the same boat and not
jumping off. I'm gonna buy 2 CB's and hog tie them to the battery. Oddly
enough they will be wired through a switch on the panel which is another
point of failure. Perhaps I'll braze the fast tabs on so they don't fly
off over a bump. We could also fly around with a spare battery at our
feet and two alligator clips drooping down from the panel. In an
emergency, just hook them up. I guess it's just a matter of what one is
comfortable with. Different strokes for different paranoia's.
On a similar note, in the recent KitPlanes mag there is an article
about Precision's "near" FADEC system which requires the whole system is
wired to a separate battery. In this they are taking the next step to
completely isolate dependency on the primary battery components.
Perhaps that is a good first step. Just add a battery in series and wire
the 2 CB's to it.
|
"Perhaps it's a good first step" is not a well directed
thought process. While motivations of most builders is
to shrug off the debilitating effects of self-serving
regulation, the history of TC aviation is rich with examples
of successful repeatable experiments. Ever watch an
episode of "House"? There is a thought process demonstrated
in every episode where the characters participate in
a "diagnosis differential." In aviation we all it
a failure modes effects analysis (FMEA). This experiment
is repeated in the operation of ANY successful sifting
of simple-ideas looking for the optimized combination
that meets design goals.
If OBAM aviation suffers from any debilitating if not
dangerous faults, it's the lack of diagnosis differential
discussions amongst successful practitioners of the craft.
The Lists, newsgroups and forums are replete with
discussion noteworthy for their emotional dithering
and stirring the pot of "idea-stew" which almost never
moves toward a cleanly distilled solution.
It's your airplanes guys . . . and your choice of
installed hardware. If it were my airplane and it came
with any built in OV protection that places the airplane
at risk, I would conduct the following study:
(1) What duration and magnitude of over voltage can
the "protected" appliance withstand by design?
Does it even come close to the spirit and intent
of DO-160 power input recommendations?
(2) Can the supplier offer me product with the OV
protection disabled if I accept the system integrator's
responsibility for assuring that the product will not
be stressed beyond those limits quantified in
Mil-Std-704 and DO-160?
Pending assuring answers to those questions, I
would be strongly disposed to seek an alternative
product that meets my design goals. Of course,
I could craft special power sources for the products
that insure they're never presented with an over
voltage. How's that for a parts-count boondoggle?
Put in more parts to offset the undesirable effects
of parts that don't need to be there. In addition
to being surplus to the well crafted system, inclusion
of extra parts WITHOUT NOTIFYING the customer/installer
of their existence and function is inconsistent
with conduct I expect from an honorable supplier.
This isn't rocket science. It's not about customer
loyalty. It's not about performance at any risk.
There are well proven processes by which we can
minimize risk while meeting design goals and keeping
costs bearable. Operations outside those processes
is at best fearful and frustrating and at worst
hazardous.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Tue Feb 03, 2009 2:53 pm Post subject: Z-14 with dual Lightspeed III and SD-8 |
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At 11:26 AM 2/3/2009, you wrote:
| Quote: | | I dont think I am fully understanding this discussion. Bob, perhaps you could provide a simple summary of the issue and concerns here for the less enlightened? There are a lot of folks out here with single or dual lightspeed ignitions. Under what circumstances are they at risk? |
The roots of this discussion go back a lot of years
and is not limited to any particular manufacturer's
design goals. Let me see if I can give you a distilled
down synopsis that moves toward focus on the specifics
of Lightspeed ignition systems.
History: Conventional wisdom for design and
fabrication of electrical systems suggests we
provide ship's accessories with power constrained
within the boundaries cited numerous documents
but they're all about the same. For our purposes,
let's talk about Mil-Std-704. For details, use the
search engine on my website and look for hits on
"mil-std-704". A similar search term on the
Matronics archives search engine will yield another
discussion and data-set. In particular, you can
get your own copy of this document at:
http://www.aeroelectric.com/Reference_Docs/Mil-Specs/Mil-Std-704f.pdf
On the accessory side, there's an equally large
library of documents that speak to design goals for
accessories. The TC aircraft industry is fond of
RTCA DO-160. I can't post a copy of this document
as the folks at RTCA are pretty protective of their
work product. Again, use the search engine on my
website and the Matronics archives to look up
"DO-160". You can access an outline of the spirit
and intent of DO-160 at:
http://www.aeroelectric.com/articles/DO-160.pdf
Irrespective of any words you read where the writer
brushes off the simple-ideas offered in these
documents, they have a long and rich history of
successful product design, development and operation
in both military and civilian certified aviation.
I've made a good living by bench-marking my work-
product and that of my associates against the design
goals suggested therein.
I've been guilty of plenty of screw-ups in 40+ years
that have cost my employer some dollars and some
customers some inconvenience. But mistakes of
attention or understanding were never attributable
to inadequacies of 160/704 used in concert to
craft robust and reliable systems. This is why
I've offered up these two documents as THE
STARTING PLACE for every new design.
OBAM aviation is blessed with the opportunity
to develop and exploit a constellation of new
ideas and products that promise to reduce weight,
cost, complexity with increases in performance
and safety. Best yet, these ideas can come into
the marketplace unburdened by the regulatory,
policy and procedural albatrosses that are dragging
once great companies down into the tar-pits of
economic and intellectual paralysis.
Since my first visit to OSH in '86, I've been aware
of dozens of exciting and useful ideas that
should be explored and perhaps exploited in OBAM aviation.
While listening to some starry-eyed entrepreneur's
excited explanation of an idea, I was acutely aware
of a lack of foundation in system integration basics.
From that very first year, I've offered my services
to any and all takers to help them craft input,
output and power connections that will improve
upon seamless integration with the rest of the airplane's
accessories.
To date, perhaps a half dozen folks have seen
fit to take advantage of this offer. Only
one required enough of my attention to justify billing
them. I made this same offer to Klaus (and his
competition!) on several occasions. I reminded them
all that I'm aware of the intellectual property
secrets of dozens of clients who do not perceive
risks for having used my services. Nonetheless,
for whatever reasons, very few folks have availed
themselves of my offer.
Current Events: Now comes a new revelation to the
community that a popular product is fitted with crowbar
ov protection. This raises a question as to
perceived value for adding such a feature internal
to a system accessory. NORMALLY . . . one designs
an accessory assuming that the prospective customer/
system integrator is aware of and complies with
the spirit and intent of 160/704. Further, given that
engine operations depend on the function of at least
one of two installed systems, what are the design goals
that prevent BOTH systems from responding to the same
OV event and shutting themselves down?
Why would a designer believe that adding this feature
adds value/safety to their product? Could it be a lack
of faith in the customer/integrator's ability to comply
with 160/704? This is a legitimate concern. My seminars
are sprinkled liberally with folks who's professional
skills have not trained them to think about these ideas.
We can only guess at the thoughts and motivation for
the case before us.
The questions to be explored:
(1) If the crowbar OV protection were left out, what
is the product's ability to stand off Mil-Std-704 compliant
transients.
(2) If so, would it not be BETTER to tell the customer
that their airplane's power generation system should
be crafted to stay at or below those limits? If you
buy a radio from King, Garmin, etc., this goes without
asking or answering.
(3) If not so, what if anything should be considered
to make the product more robust? This is usually very
easy. Power conditioning compliance taxes only a tiny
portion of the total design and qualification time
for clean-piece-of-paper designs.
(4) Finally, if the product under discussion is
not accompanied with detailed explanations of all
features that influence in-flight operations, why
not? The customer/system-integrator is severely
limited in crafting a best-we-know-how-to-do
system if there are hidden or inadequately described
features that affect performance. Even worse, overlooked
or hidden features could become root cause in a hazardous
scenario. This is why we do FMEA studies in groups with
a goal of leaving no failure mode unconsidered.
Path Forward: I will suggest that customers of the
Lightspeed systems invite Klaus to join the AeroElectric-
List for the purpose of sharing and sifting the
constellation of simple-ideas from which we can craft
the optimum solution.
| Quote: | Any suggested course of action? A lot of concern seems to have been expressed without much direct input from the manufacturer.
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Exactly. I'll make the List members aware that not all
of my past contacts with Klaus have been without
tension. This is why I'll suggest that any participation
by yours truly be carried out in this open forum. Klaus
may choose not to participate here. It's important that
he believe this is not a Star-Chamber being set up to abuse
him. But if there's any forum that offers the highest
probability of achieving understanding and crafting a
successful solution . . . it's right here.
As a first contribution to the solution I will assert
that crafting a 704-compliant power source is NOT
difficult.
Bob . . . [quote][b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Feb 03, 2009 3:18 pm Post subject: Z-14 with dual Lightspeed III and SD-8 |
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At 03:41 PM 2/3/2009, you wrote:
| Quote: |
Sausen)" <rvbuilder(at)sausen.net>
Like I said, slightly larger fuse.  Normal operation lists an
LSEIII at 7.5AMP requirement with a 10Amp fuse. My reasoning is
that doubling the initial fuse would allow the breaker to go first
under normal circumstances. I do agree that a slo-blo type fuse
would probably decrease the likeliness of the fuse blowing first.
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The fuse would need to be a LOT bigger. Crow-baring
a 5A breaker would open a 20-30A up-stream fuse.
This is because the I(square)*R time constant for
opening a breaker is MUCH larger than for fuses
of the same size. You can easily do this experiment
for your self. Go out to your car's battery and hook
an in-line fuse holder in series with a 5A breaker.
Put about 5 feet of 20AWG wire in the loop too to
limit max current.
Connect this combination across your car battery
and see how large the fuse has to be to stay closed
while the breaker trips. This is why we have fusible
links upstream of crowbar ov protection breakers in
all the Z-figures.
| Quote: | I would just assume deal with this back at the batteries but it's
not practical to have the CB's back there with no easy way to reset
when I'm flying alone troubleshooting an overly quiet engine. I
could feed one LSE from the main bus and the second directly from a
battery which would probably cover most circumstances.
|
The big band-aid is to install a separate high
current relay to the battery through a LARGE
in line fuse . . . probably 30A. Run 14AWG wire
from the relay up to the panel mounted 5A breaker.
Continue on with what-ever wire is called out
to continue on to the ignition system. Now you
need switches to control right and left ignition
system relays at the battery. See:
http://aeroelectric.com/Pictures/Schematics/Battery_Feed_for_Ignition.pdf
This approach could be blessed in a TC aircraft
as providing circuit protection commensurate with
wire sizes AND making the system max-cold when
the switches are OFF.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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msausen
Joined: 25 Oct 2007
Posts: 559
Location: Appleton, WI USA
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| Posted: Tue Feb 03, 2009 4:51 pm Post subject: Z-14 with dual Lightspeed III and SD-8 |
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Hmm, not a big fan of replacing one failure mode with another. I see a relay as being a bit of a step back and probably more likely to fail than to see an OV event. Maybe something as simple as using a 15amp breaker instead of a fuse would be less complex and eliminate the problem of a fuse blowing faster than a breaker, albeit more expensive.
Michael
--
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bcondrey
Joined: 03 Apr 2006
Posts: 580
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| Posted: Tue Feb 03, 2009 5:24 pm Post subject: Re: Z-14 with dual Lightspeed III and SD-8 |
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I actually don't have an issue with this behavior (crowbar design) as long as it's a published design feature. Lacking that, there's nothing providing any clues to somebody installing these units that use of a CB vs a fuse should be considered mandatory.
Text from the LSE Plasma III install instructions section 2.6:
• When connecting the power supply, route the positive lead to a 5A pull-able circuit breaker and then to the battery plus terminal, bypassing any electrical buss or master solenoid. Refer to the Input Connector Diagram.
At this point not having specifics about voltage level, duration, etc. that causes a crowbar event within the ignition is really just academic curiosity to me. Real point is that there is apparently a crowbar circuit internal to the units that is meant to trip a CB if overvoltage is detected (maybe also overtemp?) and using an inaccessible fuse instead of a CB is just flat unacceptable (to me). I haven't grounded the plane simply because I've got redundancy with a 12 volt Z-14 implementation with B&C alternators and regulators. Not sure if the regulators are faster than the Plasma III, but since the Plasma III will accept 28 volt power I suspect the 12 volt regulator would trip an offending alternator offline before the Plasma III crowbarred. Even if something went really wrong with an alternator/regulator and an ignition popped the fuse, I've still got a second, isolated system. I will however be reconfiguring the ignition power supply wiring in the next couple of months.
I hope nobody interprets me being sour on LSE, I actually love the ignitions! Klaus can be a little difficult to deal with and I can also accept that. My purpose was simply to inform of a failure mode. Given that there are a lot of LSE ignitions in the field and a lot of those are being powered through, this can't be that big of a problem - except for the poor soul that has an overvoltage condition which then causes the big fan up front to stop.
Bob
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Wed Feb 04, 2009 6:00 am Post subject: Z-14 with dual Lightspeed III and SD-8 |
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At 07:24 PM 2/3/2009, you wrote:
| Quote: |
<bob.condrey(at)baesystems.com>
I actually don't have an issue with this behavior (crowbar design)
as long as it's a published design feature. Lacking that, there's
nothing providing any clues to somebody installing these units that
use of a CB vs a fuse should be considered mandatory.
|
How about the fact that an OV condition
can cause BOTH ignition systems to become
inoperative in a manner that requires
pilot action to notice, interpret, diagnose
and react to get them back up and running?
<snip>
| Quote: | At this point not having specifics about voltage level, duration,
etc. that causes a crowbar event within the ignition is really just
academic curiosity to me. Real point is that there is apparently a
crowbar circuit internal to the units that is meant to trip a CB if
overvoltage is detected (maybe also overtemp?) and using an
inaccessible fuse instead of a CB is just flat unacceptable (to me).
|
. . . as it should be.
| Quote: | I haven't grounded the plane simply because I've got redundancy
with a 12 volt Z-14 implementation with B&C alternators and
regulators. Not sure if the regulators are faster than the Plasma
III, but since the Plasma III will accept 28 volt power I suspect
the 12 volt regulator would trip an offending alternator offline
before the Plasma III crowbarred.
|
Excellent question.
| Quote: | Even if something went really wrong with an alternator/regulator
and an ignition popped the fuse, I've still got a second, isolated
system. I will however be reconfiguring the ignition power supply
wiring in the next couple of months.
I hope nobody interprets me being sour on LSE, I actually love the
ignitions! Klaus can be a little difficult to deal with and I can
also accept that. My purpose was simply to inform of a failure
mode. Given that there are a lot of LSE ignitions in the field and
a lot of those are being powered through, this can't be that big of
a problem - except for the poor soul that has an overvoltage
condition which then causes the big fan up front to stop.
|
The performance of the product to function
under normal conditions is not germane to this
discussion. There are questions that the prudent
system integrator needs to ask. They go to understanding
why nearly a century of lessons learned and repeatable
experiments in aviation history have at least
gone unexplored or at worst simply cast aside.
Any time I've blazed a new trail in the TC world,
I was obliged to explain the combination of
simple-ideas to everyone who asked and particular
those who had authority over me. Finally, there
was the gauntlet of qualification and certification
to run unscathed. Sometimes you do it several times
on the same new trail. Crowbar OV protection being
but one example. Only had to do it a couple of times
in the certified world. The OBAM aviation world
made me do it a half dozen times!
I am mystified as to the reasoning that supports
this particular combination of simple-ideas. I have
never seen a product offered into aviation or any
other venue that shuts itself off for the purpose
of surviving what is supposed to be a predictable
and non-threatening event BY DESIGN AND QUALIFICATION.
Worse yet, recovery requires pilot notice, interpretation,
and action. This would not be tolerated in the
TC aircraft world for what I believe are obvious
reasons.
Suppose your EFIS had such a feature? How about
a fuel pump? A nav radio? This idea is much larger
than arm-wrestling with one supplier about one
product. It's a core component of how we think
about the electrical systems and accessories
in our airplanes.
Bob . . .
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