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nuckolls.bob(at)aeroelect
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 Posted: Thu Jan 07, 2010 6:10 am Post subject: Z-14 variations |
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At 12:13 PM 1/6/2010, you wrote:
| Quote: |
<MauleDriver(at)nc.rr.com>
This fuse versus CB discussion raises this questions with me -
perhaps someone can clear it up.
Are any of the current/modern avionic boxes really depen
depending on the CB or fuse for their internal 'protection' of anything?
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I'm not aware of any supplier to the TC aircraft industry
that ADMITS to such a philosophy in print. I seem to recall
a company that offered some little whiz-bang . . . perhaps
a digital Clock/OAT/Timer? I think they asked that their
supply line be protected by a fuse of 1A max.
Further, I've opened up "smoked" accessories where traces
or internal components were burned as a consequence of
some downstream fault. This kind of failure is often not
repairable. Would the customer have been better served
if the bus feeder were less robust?
| Quote: | I know many units specify a fuse/CB size and sometimes a wire size
but I just size the fuse to protect the wire and try to use a
limited number of adequate wire sizes.
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Greg suggested a one-size-fits-all approach to selection
of feeder sizes in his proposed power distribution and
control described in
http://www.aeroelectric.com/articles/richter/response_1.pdf
I think all his PTC's were 20A devices . . . what do
you mean by "limited number of adequate wire sizes"?
Generally MOST of your electronics will fuse at 5 or 7A
You'll have a handful of larger branches like 10A for 100W
landing and taxi lights. Maybe one 20A for a pitot heater.
But I recommend that you not avoid tailoring the size of
individual feeders to their respective tasks.
| Quote: | My understanding is that various units have various means of
protecting themselves from spikes, etc. And if any kind of failure
starts drawing more amps than the wire/fuse/cb can provide, pop goes
the external protection.
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One generally assumes that feeder protection at the
bus has the highest risk of operating from a faulted
wire someplace between the bus and the appliance. The
next risk is generally limited to motor driven devices
where some kind of failure inside the motor draws a
hard-fault level of current.
Beyond this, your fuses/breakers are going to run the
lifetime of the airplane never being called upon to
do their job.
| Quote: | So I'm thinking that if the radio fails, it fails and I use the backup radio.
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Yup.
| Quote: | If the wire leading to the radio shorts on rough edge or something,
the radio fails and I use the backup radio.
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Yup.
| Quote: | And since fuses are so cheap, I have a separate circuit for
practically every unit on the panel so there is a 1:1 ratio between
units and fuses.
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Good lick . . .
| Quote: | If multiple things fail, then it's an electrical system problem -
haven't worked out the details yet but I hope on my Z-14, I just
crossfeed to use the backup Alt/Batt system or otherwise go to the backups.
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Likelihood of multiple independent failures in
systems during any single tank full of fuel
is exceedingly rare. So yes, the design goal for
electrical system design is to have no single failure
take down so much bus structure that you loose
so much equipment that the mission is at risk.
Z-11 with the e-bus and a well maintained battery
and a dual feed-path endurance bus was our first
crack at that.
This first step in the evolutionary process was
VERY strong. When the vacuum pump pad opened up,
Z-13/8 increased the continuous load one could
support on the e-bus while holding all the battery
in reserve for approach to landing.
| Quote: | And if it smokes, open the windows, make sure it stopped smoking or
hit a master until it does. Land ASAP.
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Certainly, smoke in the cockpit calls for killing
the whole electrical system ASAP. Then bring up
the e-bus (and SD-8 if you have it) and see if
you can drop to the get-home mode. If smoke doesn't
come back you're in business. If smoke comes back,
turn everything off and get out the stuff in your
flight bag . . .
http://www.aeroelectric.com/Pictures/Misc/Vacination_for_Dark_Panel_Syndrom.pdf
You DO plan to carry this kind of capability
in the flight bag . . . right?
With Z-14, smoke still calls for shutting down
everything right now. Then bring up half of the
system at a time. The cross-feed contactor
would probably never be closed after a smoke-
in-the-cockpit event.
| Quote: | What are the holes in this thinking?
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No 'holes'. Continue to think, rethink, and
PLAN how you'll react to any single failure
you can imagine. It's unlikely that you'll
have more than one . . . With Z-14 you have
LOTS of options. Experiments with how those
options best play out should be part of a
plan devised on the ground . . . not in flight.
Bob . . .
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MauleDriver(at)nc.rr.com
Guest
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| Posted: Thu Jan 07, 2010 9:47 am Post subject: Z-14 variations |
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Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 12:13 PM 1/6/2010, you wrote:
> I know many units specify a fuse/CB size and sometimes a wire size
> but I just size the fuse to protect the wire and try to use a limited
> number of adequate wire sizes.
I think all his PTC's were 20A devices . . . what do
you mean by "limited number of adequate wire sizes"?
I meant essentially what you are saying here. Going back to my diagram
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I see that in fact I have 2, 5, 10, and 15 amp circuits and appropriate
wire sizes
| Quote: |
Beyond this, your fuses/breakers are going to run the
lifetime of the airplane never being called upon to
do their job.
Yep, I've never experienced an electrical failure in a powered aircraft
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in 40 years of fun flying (I did smoke a glider's electrical system once).
| Quote: | > If multiple things fail, then it's an electrical system problem -
> haven't worked out the details yet but I hope on my Z-14, I just
> crossfeed to use the backup Alt/Batt system or otherwise go to the
> backups.
I know the Z-14 is overkill. The peace of mind feature I'm after has
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little to do with failure tolerance and everything to do with having a
battery available for running the panel for extended periods (or
charging portable batteries, running lights or whatever) and a separate
battery available for starts. I've found that the peace of mind to stay
on the ground and do whatever I want for as long as I want, valuable in
bad weather flying, especially when FBO facilities aren't available
(e.g. stuck in New Orleans before the terminal was reestablished).
There are many ways to achieve that but the symmetry and robustness of
the Z-14 seduced me.
| Quote: | >
>> What are the holes in this thinking?
> No 'holes'. Continue to think, rethink, and
> PLAN how you'll react to any single failure
> you can imagine. It's unlikely that you'll
> have more than one . . . With Z-14 you have
> LOTS of options. Experiments with how those
> options best play out should be part of a
> plan devised on the ground . . . not in flight.
Good advice, I plan to do that.
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| Quote: |
Bob . . .
Thanks as always.
|
Bill
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