Today's Message Index:
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1. 06:59 AM - Re: Re: Dual master solenoids (Sacha)
2. 07:53 AM - Re: Re: Dual master solenoids (Stein Bruch)
3. 11:56 AM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III)
4. 12:35 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III)
5. 01:34 PM - Re: Re: Dual master solenoids (Sacha)
6. 04:11 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III)
7. 06:59 PM - Re: Dual master solenoids (user9253)
8. 07:30 PM - Re: Re: Dual master solenoids (Sacha)
9. 07:42 PM - Re: Re: Dual master solenoids (Robert L. Nuckolls, III)
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Subject: | Re: Dual master solenoids |
It's also a safety issue with some starter configurations. For instance if you
had a momentary push button for the starter instead of a key switch, even with
the master off you would still be able to push the button and turn the prop.
I have this configuration and as an added safety while the aircraft is stopped
and the master needs to be on, I always pull the starter CB.
Sacha
> On 14 Jul 2014, at 14:06, "user9253" <fransew@gmail.com> wrote:
>
> Having two contactors in series makes sure that the circuit can be opened.
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Subject: | Re: Dual master solenoids |
Aside from some anecdotal references that are oft repeated at hangar flying
sessions and on the interwebs, have you or do you know of a specific
instance where a master contactor/solenoid of standard design failed
repeatedly? All mechanical things have "been known to fail", but we build
airplanes around the 99th percentile, not the 1th percentile. If you built
a perfectly safe airplane, it would be one that wouldn't leave the
ground....so to that end you design in for the 99th, but also take into
account the 1th percentiles without doing crazy things like putting in two
master contactors or two tachometers (unless of course you have two
batteries, or two busses, etc..). If you are going to put in two of those,
why not two starter buttons, or two circuit breakers for each circuit, or
two throttle cables, or two rudders, or two elevator pushrods, (after all,
those have also been known to fail)? You still do only have one camshaft
and one propeller and one crankshaft and one carb/fuel injector, one brain,
etc..
My point is that the probability of failure of that specific components is
likely less than the probability of other equally as important mechanical
things in your plane. There is no reason to randomly pick one particular
component and focus on it over another when it has not proven to be a weak
point in the entire aerospace vehicle system design.
Just my 2 cents as usual, but one could come up with all sorts of 1th
percentile "possibilities" that are really not worth expending energy, time,
money, weight or complexity on as the return on all of that in actuality
becomes a negative. Remember, adding things for "redundancy" does not
necessarily and automatically translate into reliability - many times it has
the inverse effect (increased complexity = decreased reliability).
Cheers,
Stein
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of user9253
Sent: Monday, July 14, 2014 7:07 AM
Subject: AeroElectric-List: Re: Dual master solenoids
> are heavy duty continuous service relays any less reliable than mechanical
relays? If about the same reliability, what are the reasons that they aren't
used more often for a master solenoid?
There are several ways that a relay or contactor can fail. The contacts can
develop a high resistance, the coil can burn open, springs or other
mechanical parts can break, and etc. I do not know which type is more
likely to fail. The current carrying capability determines which relay or
contactor to use. Starters can draw a few hundred amps initially to get the
engine rotating. A 30 amp automotive relay would not last very long
carrying that much current.
So why have the starter current go though the master contactor? The
starter contactor could be wired directly to the battery. I think the
reason is that contactors have been known to fail closed. Having two
contactors in series makes sure that the circuit can be opened.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=426626#426626
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Subject: | Re: Dual master solenoids |
At 08:57 AM 7/15/2014, you wrote:
>
>It's also a safety issue with some starter configurations. For
>instance if you had a momentary push button for the starter instead
>of a key switch, even with the master off you would still be able to
>push the button and turn the prop.
Irrespective of the kind of switch that energizes
the starter, I'm aware of no TC aircraft, or any
OBAM aircraft wired per a Z-figure where this is
the cased. The general rule of thumb for all
airplanes is that opening the battery master
contactor removes ALL power from the aircraft
except for those items wired to a battery bus.
Starters should be dead-in-place with the
battery master off.
>I have this configuration and as an added safety while the aircraft
>is stopped and the master needs to be on, I always pull the starter CB.
How was it that you came to wire your airplane
this way?
Bob . . .
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Subject: | Re: Dual master solenoids |
My point is that the probability of failure of that specific components is
likely less than the probability of other equally as important mechanical
things in your plane. There is no reason to randomly pick one particular
component and focus on it over another when it has not proven to be a weak
point in the entire aerospace vehicle system design.
Precisely . . .
When opening the seminar segment on
reliability, I like to put a z-figure
up on the screen, point to a component
and ask, "What do you need to do if THIS
part malfunctions?"
At least one participant will suggest
that it be replaced with a 'better part'.
That's the segment where I pose the notion
that the flight SYSTEM consists of an airframe,
pilot, environment and expendable resources.
From the time the wheels break ground until
you're parked at the destination, the design
goal is not break a sweat . . . irrespective
of any component failure.
The last few ideas offered at the end of
the segment suggests that it doesn't matter
if you buy electrical parts from Autozone, $high$
parts from Honeywell or TC aircraft parts from
the Cessna warehouse . . . it is possible to
ARCHITECTURE the electrical system such that
no single component failure will induce an
in-flight sweat.
In the final analysis, you're more likely
to have a bad day in the cockpit driven by
events and conditions far removed from
things electrical. #1 cause of engine
stoppage is fuel starvation. #1 cause
for unplanned arrivals with the earth
are most often based on human factors for dealing
with environment: weather, mountains,
night ops, etc.) As we have studied many
times here on the List . . . mishaps
that included electrical issues were
FIRST driven by lapses in assembly skills,
failure tolerant design or poor maintenance.
See: http://tinyurl.com/ky7szec
In other words, "two parts" or a "better
part" would not have produced a better
outcome.
Bob . . .
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Subject: | Re: Dual master solenoids |
>It's also a safety issue with some starter configurations. For instance
>if you had a momentary push button for the starter instead of a key
>switch, even with the master off you would still be able to push the
>button and turn the prop.
Irrespective of the kind of switch that energizes
the starter, I'm aware of no TC aircraft, or any
OBAM aircraft wired per a Z-figure where this is
the cased. The general rule of thumb for all
airplanes is that opening the battery master
contactor removes ALL power from the aircraft
except for those items wired to a battery bus.
Starters should be dead-in-place with the
battery master off.
Hi Bob, I was referring to the hypothetical situation that Joe brought up
where the starter contactor would be always hot, i.e. wired to the battery
bus.
>I have this configuration and as an added safety while the aircraft is
>stopped and the master needs to be on, I always pull the starter CB.
How was it that you came to wire your airplane
this way?
My apologies, I wasn't very clear... My electrical setup is essentially
Z-16, but the starter button is a push button. So whenever I am tinkering
around on the ground and the master needs to be on, I pull the starter CB
just to be safe. Another situation is when my three year old wants to sit
next to me in the a/c and see the panel light up and pretend he's flying the
aircraft... :)
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Subject: | Re: Dual master solenoids |
My apologies, I wasn't very clear... My electrical setup is essentially
Z-16, but the starter button is a push button. So whenever I am tinkering
around on the ground and the master needs to be on, I pull the starter CB
just to be safe. Another situation is when my three year old wants to sit
next to me in the a/c and see the panel light up and pretend he's flying the
aircraft... :)
Understand . . . thanks!
Bob . . .
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Subject: | Re: Dual master solenoids |
> I was referring to the hypothetical situation that Joe brought up
> where the starter contactor would be always hot, i.e. wired to the battery
> bus.
I did not bring that up. I was referring to tomhanaway's post where he wrote,
"the always hot side of the starter solenoid (always hot when master solenoid
is hot)".
It is much easier to understand each other when talking face to face compared
to email or forum postings. :-)
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=426748#426748
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Subject: | Re: Dual master solenoids |
Hi Joe
Sorry for the confusion. Indeed it would be easier face to face.
Sacha
Do not archive
> On Jul 16, 2014, at 3:57, "user9253" <fransew@gmail.com> wrote:
>
> I did not bring that up. I was referring to tomhanaway's post where he wrote,
"the always hot side of the starter solenoid (always hot when master solenoid
is hot)".
> It is much easier to understand each other when talking face to face compared
to email or forum postings. :-)
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Subject: | Re: Dual master solenoids |
>
> It is much easier to understand each other when talking face to
> face compared to email or forum postings.
I'm wrestling with a similar phenomenon in
crafting recommendations for crafting requirements
documents. I use as many drawings and pictures as
I can . . . a picture is worth 10,000 words.
The flip side is not true . . . 10,000 words interpreted
by ten different readers will NOT create identical
images in the minds of the readers. My clients
a loath to ask their charges to learn to draw . . .
That's why I use my scanner, cameras and links to
posted illustrations to augment the words . . . you
can't have too many pictures but more words you
have, the fuzzier the ideas become.
Bob . . .
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