AeroElectric-List Digest Archive

Thu 08/26/10


Total Messages Posted: 5



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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    Time: 06:47:59 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    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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    Time: 10:54:22 AM PST US
    From: Dan Morrow <danfm01@butter.toast.net>
    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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    Time: 12:25:40 PM PST US
    Subject: testing of backup alternator
    From: <longg@pjm.com>
    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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    Time: 01:22:13 PM PST US
    Subject: Re: testing of backup alternator
    From: Dj Merrill <deej@deej.net>
    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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    Time: 05:16:35 PM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
    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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