Today's Message Index:
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1. 04:27 AM - Fw: Re: Garmin 430W - Comm & Nav Power from Separate Busses (Buckley William)
2. 07:32 AM - Re: Fw: Re: Garmin 430W - Comm & Nav Power from Separate Busses (Robert L. Nuckolls, III)
3. 08:16 AM - Re: Ni-Cad? (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: Garmin 430W - Comm & Nav Power from Separate |
Busses
Bob,
To your question: As currently designed, the equipment list in my panel has
the comm side of the 430 as comm#2 and the nav functions of the 430 as the
primary navigation source. With an alternator failure, I want comm#2 to be
among the equipment that gets dropped while keeping the navigation functio
ns. The comm functions will be handled by a different transceiver as comm#1
.
And why not make the 430 the primary comm and nav source? ...Budget. I'd li
ke to have the full compliment of panel equipment on day one but its likely
that the 430 will be added later. Starting out with only VFR capability an
d I'm planning for the full enchilada later.
Thanks,
William B.
--- On Tue, 7/29/14, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com
> wrote:
> From: Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com>
> Subject: Re: AeroElectric-List: Garmin 430W - Comm & Nav Power from Sep
arate Busses
> To: aeroelectric-list@matronics.com
> Date: Tuesday, July 29, 2014, 1:17 PM
>
>
> To: aeroelectric-list@matronics.com
>
> Subject: Re: AeroElectric-List: Garmin 430W - Comm & Nav
> Power from
> Separate Busses
>
> - How did your ENDURANCE load analysis come to suggest
>
> - that Com functions need not be part of an extended
>
> - battery-only ops scenario?
>
> - Bob . . .
>
>
Message 2
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Subject: | Re: Garmin 430W - Comm & Nav Power from |
Separate Busses
At 06:26 AM 7/30/2014, you wrote:
>Bob,
>To your question: As currently designed, the equipment list in my
>panel has the comm side of the 430 as comm#2 and the nav functions
>of the 430 as the primary navigation source. With an alternator
>failure, I want comm#2 to be among the equipment that gets dropped
>while keeping the navigation functions. The comm functions will be
>handled by a different transceiver as comm#1.
But comm#2 doesn't draw any significant power unless
you talk on it . . . so what is the ENDURANCE advantage
for shutting it down and making comm#2 unavailable
except by bringing the main bus back up?
>And why not make the 430 the primary comm and nav source? ...Budget.
>I'd like to have the full compliment of panel equipment on day one
>but its likely that the 430 will be added later. Starting out with
>only VFR capability and I'm planning for the full enchilada later.
Okay, you're planning ahead . . . good show.
Do you have an battery-only endurance target?
Is your engine electrically dependent? Have
you run the numbers on battery-only flight
at end of battery life?
Bob . . .
Message 3
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At 02:10 PM 7/29/2014, you wrote:
>Pengilly <peter@sportingaero.com>
>
>Back in the early 90s the Royal Navy fleet of
>SeaKing helicopters (S-61 derivative) used NiCad
>batteries. We were pretty much banned from using
>them to start and made sure ground power was
>always available. They didn't turn the engine
>over quickly enough to get a reliable start -
>usually too much fuel and not enough rpm
>resulted in a hot start with sheets of flame out
>the exhaust - and potentially an overheated
>turbine. The batteries were a lot of trouble, I
>remember several being float tested after
>aircraft landed back on-board with over heating
>or smoking battery compartments (now not an
>option as nothing is allowed over the side). We
>could also swap out individual cells if a
>battery went down. I guess the technology has
>moved on in 20 years, but I still would not be rushing to fit one.
The hot-start phenomenon would not have root cause
in the chemistry of the batteries, only the sizing-
to-task irrespective of chemistry.
The volumetric and power density numbers for ni-cad
are superior to lead-acid . . . i.e. a PROPERLY
SIZED ni-cad will be smaller and lighter than the
lead-acid capable of the same starting performance.
But as others have noted, ni-cads are not very friendly
to the cost of ownership. Their alkaline electrolyte
is antagonistic to lead-aced which prompts maintenance
operators to have separate shops for dealing with the
two technologies . . . which could probably be
dispensed with today . . . nobody has to 'maintain'
electrolyte in a lead-acid battery any more.
The thermal runaway thing was the byproduct of some
rather un-creative design decisions. The smaller,
lighter cells were very capable of cranking engines but
when those engines started, generators rated at
hundreds of amps would stuff energy back into the
little batteries causing them to warm up. Ni-Cad
temperature coefficient of voltage causing them
to draw more current from a fixed voltage bus as
their temperature rises . . . which causes them
to warm up still faster . . . you get the picture.
Quoting from Wikipedia at:
http://tinyurl.com/7zm7xee
"One of the biggest disadvantages is that the
battery exhibits a very marked negative
temperature coefficient. This means that as the
cell temperature rises, the internal resistance
falls. This can pose considerable charging
problems, particularly with the relatively simple
charging systems employed for
<http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery>lead'acid
type batteries. Whilst lead'acid batteries can be
charged by simply connecting a
<http://en.wikipedia.org/wiki/Dynamo>dynamo to
them, with a simple electromagnetic cut-out
system for when the dynamo is stationary or an
over-current occurs, the Ni'Cd battery under a
similar charging scheme would exhibit thermal
runaway, where the charging current would
continue to rise until the over-current cut-out
operated or the battery destroyed itself."
People who understood batteries published reams of data
on how to get the best performance from Ni-Cads . . . data
which said "constant current charge" . . . but those-
who-know-more-about-airplanes-than-we-do decided that it
would be too much to expect an air-framer to install
ni-cad friendly starter-generator controllers. They decreed
that thermometers be added to ni-cads with displays
on the panel along with warning lights for battery overheat.
Instead of crafting a battery management system totally
transparent to the pilots . . . the pilots were burdened
with rudimentary system management duties to offset
poor regulatory judgement.
Hence, the ni-cad gets this bad rap for being higher
risk . . . risks driven by inelegant design. As a chemical
energy storage system, ni-cads have a lot going for them.
But as we've discussed here on the List . . . there is
no such creature as an alternative chemistry, drop-in
lead-acid replacement. THERE ARE DIFFERENCES that
beg understanding and deference in design, fabrication,
installation, operation and maintenance.
Whether lead-acid, ni-cad or lithium-ion . . . failure
to pay homage to the physics gods is at best just
expensive . . . at worst it sets airplanes on fire.
Every technology comes with its own constellation of
challenges.
http://tinyurl.com/kxu3s6j
Bob . . .
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