Today's Message Index:
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1. 01:12 PM - Re: Re: Review request for RV-9 Electrical System (G3X, GTN, etc) (Robert L. Nuckolls, III)
2. 03:38 PM - Re: Re: Review request for RV-9 Electrical System (G3X, GTN, etc) (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: Review request for RV-9 Electrical System |
(G3X, GTN, etc)
At 02:14 PM 6/14/2016, you wrote:
>
>OK, I think I see your point on not needing breakers and going with
>fuses but I'm not 100% there yet. For my personal sense of comfort
>I'd like to have items on the endurance bus on breakers. Does this
>seem like a reasonable compromise?
Compromise for what? If a breaker ever opens it means
something is broke . . . and that something threatens
to set a wire on fire. You want to give it a second
chance?
What items in your airplane are high priority equipment
for comfortable termination of flight? From that list
of items, how many of them can fail in ways that do not
open a breaker? I can tell you that the vast majority
of equipment failures never open a breaker . . . if that
item is so necessary/useful that you're worried about
being able to reclose a breaker, then you'd better have
a plan-b . . . a back up for when the system decides
to take a vacation.
>It allows me to load-shed even further by pulling breakers if needed
>and uses much fewer breakers and panel space. Thoughts?
Load shed? What's the e-bus for? The LAST thing
you should be doing in flight is running any kind
of mental gymnastics calculated to reduce risks
of dealing with some kind of failure. ALL such
things are done at THIS phase of your design
and fabrication. Should a necessary item go T.U.
then you go to plan-b. If the item is not necessary,
then there is no plan-B.
The idea behind the e-bus is to do a two-switch
load shed that either (1) does not overtax an
SD-8 or (2) produces a KNOWN endurance value
running battery only based on periodic capacity
checks of your battery.
Messing with any breaker or fuse in flight is a
demonstration of poor planning that should have
been managed during THIS phase of your project's
development. Put the fuse blocks out of sight and
out of mind. Deal with system difficulties as a
pilot with a plan . . . not an in-flight diagnostician
and maintenance technician.
Bob . . .
Message 2
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Subject: | Re: Review request for RV-9 Electrical System |
(G3X, GTN, etc)
>Could you elaborate on the e-bus switch vs relay? Up to what
>amperage is it ok for it to be a regular switch?
Sure. Any generic toggle switch of any rating
is unlikely to be overstressed in your airplane.
> I was planning on using the S700 Carling switches sold by b&c and
> they claim 15A VAC but a quick search for them seems to bring up
> more failure posts than details on the switches. Is there a better option?
The Carling switches sold by B&C are direct descendants of
those used by the hundreds of thousands on Cessna and Piper
aircraft for decades. What details are you lacking? Keep
in mind that nobody posts about their working switches . . .
only the ones that have presented some problem . . .
hence, a dozen posts of problems over a period of years
may have the appearance of describing a quality issue.
Switches, like every other device or bit of material
in your project, are subject to failure . . . nothing
lasts forever. Switches on personally owned airplanes
have nearly zero service stress compared to, say the
light switch in your bathroom.
When doing the failure modes analysis for your
project the questions to be asked are:
How can this part fail?
How will I know that it has failed?
Is the failure pre-flight detectable?
The answer to the third question drives your
architecture and checklist decisions.
Does failure present some degree of elevated
risk for uncomfortable termination of flight?
The answer to the fourth question drives your
decisions for having a plan-b assuming that the
part will fail.
The beauty and comfort to be secured by an artfully
crafted FMEA is that you don't care if the part
fails . . . it's not an issue of increased risk.
It's only effect is a cost-of-ownership. You
might upgrade a part because you're tired of
replacing it . . . not because it #@%%@% near
got you killed.
THAT is failure tolerant design . . . stone simple,
cheap, easy to do.
>For the fuse blocks I'm looking at the ones sold by b&c and they
>come in different sizes. Does it make sense to have 2 or 3 to split
>up the load a bit? Where should they feed from? i.e. should I have
>one large wire for the firewall passthrough and then split that up
>somewhere between the fuse blocks?
Generally, each block represents one bus. In figure
Z-13/8 you need three. Battery, Main and E-bus blocks.
Other architectures will call for more or fewer
blocks. Install blocks larger than needed today
to allow for easy, future expansion.
Bob . . .
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