Today's Message Index:
----------------------
1. 06:47 AM - Re: GRT EIS-Fuel Sender (Robert L. Nuckolls, III)
2. 10:54 AM - Re: GRT EIS-Fuel Sender (Dan Morrow)
3. 12:25 PM - Re: testing of backup alternator ()
4. 01:22 PM - Re: testing of backup alternator (Dj Merrill)
5. 05:16 PM - Re: testing of backup alternator (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: GRT EIS-Fuel Sender |
At 09:13 AM 8/25/2010, you wrote:
>"MHerder" <michaelherder@beckgroup.com>
>
>Ive installed my senders (resistance type) and
>routed the 4.7v excitation and the required resistor to the sender
>
>Heres my question:
>
>How is it safe to route 4.7 volts to a fuel tank
>with current traveling through the tank? Spark kaboom?
>
>Is there something I'm missing?
Cars have been running "current" into the fuel
tanks for monitoring liquid level for a lot of
years. See:
http://www.aeroelectric.com/Reference_Docs/Patents/Circa_1923_Fuel_Gage.pdf
While the stuff in the tank is indeed
combustible, the range of conditions over which
it becomes hazardous in storage does have
boundaries.
As long as there is any liquid fuel
in a tank, the vapor above the liquid
is close to saturated. I.e., a long
ways away from the ideal stoichiometric
ratio where ignition is easiest and the
burning most violent.
Further, even in ideal ratios of fuel
and oxygen, the ignition source has to present
a minimum packet of energy in order to trigger
the chain reaction that is burning or even
an explosion. Devices incapable of delivering
these energy levels (adjusted for headroom) are
called "intrinsically safe" . . . meaning
that there are no combinations where the total
system becomes hazardous.
For example, the energy that flows in components
of a capacity fuel sensor falls in the intrinsically
safe category. Variable resistors adjusted by floats
and paired with the right gages are also intrinsically
safe.
But assuming you put a real "sparker" in the
tank, you're still not going to get a hazardous
mixture until after all the liquid has evaporated
and the remaining vapors are sufficiently diluted
so as to approach the "oh s#$t" ratio. This just
doesn't happen accidently in small airplanes.
Doesn't happen in big airplanes either. This is
why a "spark in the tank" hypothesis for any
explosion aboard airplanes is unsupported
by the physics or any demonstrable experiment.
That "unusable fuel" has two important functions.
(1) provide a low-spot for moisture collection
and (2) keep the vapor in the tank saturated.
So the short answer to your question is, don't
worry about it.
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
Message 2
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Subject: | Re: GRT EIS-Fuel Sender |
Bob's answer with respect to explosive dangers with 100LL in the fuel
tank is correct of course. If there is anyone out there thinking of
diesel power, be aware that the situation with respect to jet fuel is
different. Jet fuel vapor can easily reach explosive concentrations in a
fuel tank and special venting requirements are usually recommended. See
www.deltahawkengines.com/questi00.shtml#fuel for a discussion.
On 08/26/2010 06:45 AM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 09:13 AM 8/25/2010, you wrote:
>> <michaelherder@beckgroup.com>
>>
>> Ive installed my senders (resistance type) and routed the 4.7v
>> excitation and the required resistor to the sender
>>
>> Heres my question:
>>
>> How is it safe to route 4.7 volts to a fuel tank with current
>> traveling through the tank? Spark kaboom?
>>
>> Is there something I'm missing?
>
> Cars have been running "current" into the fuel
> tanks for monitoring liquid level for a lot of
> years. See:
>
> http://www.aeroelectric.com/Reference_Docs/Patents/Circa_1923_Fuel_Gage.pdf
>
>
> While the stuff in the tank is indeed
> combustible, the range of conditions over which
> it becomes hazardous in storage does have
> boundaries.
>
> As long as there is any liquid fuel
> in a tank, the vapor above the liquid
> is close to saturated. I.e., a long
> ways away from the ideal stoichiometric
> ratio where ignition is easiest and the
> burning most violent.
>
> Further, even in ideal ratios of fuel
> and oxygen, the ignition source has to present
> a minimum packet of energy in order to trigger
> the chain reaction that is burning or even
> an explosion. Devices incapable of delivering
> these energy levels (adjusted for headroom) are
> called "intrinsically safe" . . . meaning
> that there are no combinations where the total
> system becomes hazardous.
>
> For example, the energy that flows in components
> of a capacity fuel sensor falls in the intrinsically
> safe category. Variable resistors adjusted by floats
> and paired with the right gages are also intrinsically
> safe.
>
> But assuming you put a real "sparker" in the
> tank, you're still not going to get a hazardous
> mixture until after all the liquid has evaporated
> and the remaining vapors are sufficiently diluted
> so as to approach the "oh s#$t" ratio. This just
> doesn't happen accidently in small airplanes.
>
> Doesn't happen in big airplanes either. This is
> why a "spark in the tank" hypothesis for any
> explosion aboard airplanes is unsupported
> by the physics or any demonstrable experiment.
>
> That "unusable fuel" has two important functions.
> (1) provide a low-spot for moisture collection
> and (2) keep the vapor in the tank saturated.
>
> So the short answer to your question is, don't
> worry about it.
>
>
> Bob . . .
> ////
> (o o)
Message 3
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Subject: | testing of backup alternator |
Erich,
I didn't catch how many replies you had on this one. On my system I have
a Dynon which monitors voltage internally and externally. Since I have
the internal battery option, I can sit there with the SD-8 running (no
interruption to the Dynon) and monitor the voltage activity on the
master/essential bus via the Dynon. The key here is having something to
monitor your system voltage that is not tied to switches and other
things you've just lost when the alternator blows. That can come in many
forms. I've seen some inexpensive LED panel voltage monitors that would
do nicely.
They're a nice feature to have when your world changes from inside the
cockpit. A continued downward trend is warning enough to get down
immediately. On the other hand you may feel you have enough output from
the SD-8 to continue on to the next best/safest alternator shop (Pep
Boys).
Hopefully if you've reached that mode you've begun shutting off the
air-conditioning, portable fridge, DVD etc. and are just running the
minimums.
On my ship the minimums take about 3-4 amps, Dynon, 1-radio, portable
gps.
Yes, the SD-8 seems to takes about a 1000 rpm to produce any sort of
useable output. That may vary on your installation. If it's a sunny day
I also have a solar charger to setup on the panel. That will at least
power the GPS. And we're fly'n.
Maybe the real question is whether it is worth real world testing - in
my mind, absolutely. It's a great idea to test it in the air (better
than on the ramp while your CHT's go through the roof) to see how much
endurance you ultimately have. I would like to do the full test one day
soon. Perhaps on a closed course over friendly terrain.
I think most folks will wait for an emergency to perform the real test.
In most cases that will be too late. It takes a bit of stomach to shut
things down and really stretch the limit. I'm ok with that. You will
want to land and re-start the main alternator after the test. From what
I understand it's not recommended to re-start some of these alternators
in flight. It may blow off the cowling and your firewall may melt.
Best,
Glenn E. Long
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Erich_Weaver@urscorp.com
Sent: Monday, August 23, 2010 2:47 PM
Subject: AeroElectric-List: testing of backup alternator
Bob, your recently responded to a couple of posts from Jared Yates, who
was asking (in part) about testing of the backup alternator in a Z-13/8
system.
Cant speak for Jared, but Im not sure his real question was effectively
answered and I am interested in this as well,, so thought I would follow
up. How do I go about assuring myself that my SD-8 will work as
advertised when called upon? Can I just turn off the master, flip on
the switches for the SD-8 and the e-bus alternate feed, and wait to see
if I get a low voltage warning light on my engine monitor? Can I do
this on the ground at idle, or do I need to have the RPM elevated?
Feeling a bit boneheaded about this, but would be more boneheaded to not
ask, and find out later my
SD-8 was providing no backup at all.
thanks for your service
Erich Weaver
Message 4
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Subject: | Re: testing of backup alternator |
On 08/26/2010 03:17 PM, longg@pjm.com wrote:
> From what
> I understand it's not recommended to re-start some of these alternators
> in flight. It may blow off the cowling and your firewall may melt.
Would absolutely love to see some real data to back up this claim...
Can you point us to any references?
Thanks,
-Dj
--
Dj Merrill - N1JOV
Glastar Sportsman 2+2 Builder #7118 N421DJ - http://deej.net/sportsman/
Grumman Yankee Driver N9870L - http://deej.net/yankee/
Join us on the New England Aviation Forums - http://forum.deej.net/
Message 5
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Subject: | Re: testing of backup alternator |
At 03:15 PM 8/26/2010, you wrote:
>
>On 08/26/2010 03:17 PM, longg@pjm.com wrote:
> > From what
> > I understand it's not recommended to re-start some of these alternators
> > in flight. It may blow off the cowling and your firewall may melt.
>
>
> Would absolutely love to see some real data to back up this claim...
>Can you point us to any references?
I've been testing alternators and generators on airplanes,
laboratory test stands and an odd assortment of vehicles
for 40+ years. We turn them on, off, no-load, full-load,
you name it. Whether or not there's a battery on line.
See chapter on engine driven power sources in:
http://www.aeroelectric.com/Book/AEC12A_PDF.zip
Having said that, there MAY be regulator characteristics
(whether internal in or external) that present poor transient
response without a battery on line. Indeed, this is one
of the situations described by "load dump" in automotive
parlance and "battery dump" in aviation parlance. Depending
on how wildly the system behaves without a battery, SOME
devices may be at risk if they're tied to the bus. This
INCLUDES poorly designed regulators. This was the problem
reported but not understood a few years back when some
folks experienced alternator/regulator damage when switching
a Z-24 system off with the alternator loaded. However,
this is the exception.
Bottom line is, as long as the battery stays tied to the
alternator's b-lead, there's nothing you can do with
switches on the panel that will hurt anything . . .
In other words, transients generated by such activities
do not exceed NORMAL operating transients as described
in Mil-STD-704 and DO-160. Even with Z-24 configuration,
an internally regulated alternator worth your hard-earned
dollars is not at-risk for inadvertent switch positioning.
Bob . . .
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