AeroElectric-List Digest Archive

Wed 04/09/08


Total Messages Posted: 6



Today's Message Index:
----------------------
 
     1. 06:18 AM - Risky Jump Starts? (Dennis Johnson)
     2. 07:09 AM - Re: Risky Jump Starts? (Matt Prather)
     3. 08:10 AM - Re: Risky Jump Starts? (Robert L. Nuckolls, III)
     4. 08:14 AM - Re: Risky Jump Starts? (Robert L. Nuckolls, III)
     5. 04:38 PM - Securing Ends of Wires in Wing for Later Use (messydeer)
     6. 07:00 PM - Re: Securing Ends of Wires in Wing for Later Use (Roger Cole)
 
 
 


Message 1


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    Time: 06:18:26 AM PST US
    From: "Dennis Johnson" <pinetownd@volcano.net>
    Subject: Risky Jump Starts?
    Greetings, Someone posted on the rec.aviation.piloting newsgroup a story about damage caused by jumpstarting the airplane with the alternator switch on. According to the story, the jump start was from an FBO tug capable of "much more juice" than the owner's pickup truck that he had successfully used in the past, and as soon as he turned the key, "every breaker in the plane tripped." Sensors for fuel quantity, oil temp, ammeter, and oil pressure strip "got fried and needed to be rebuilt." I'm having trouble understanding how getting a jump start with the alternator switch turned on could cause this problem. Even if it were a 12 volt system and the FBO tug produced 24 volts, I don't see why it would trip the circuit breakers. Any ideas? Dennis Johnson Legacy, now flying


    Message 2


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    Time: 07:09:21 AM PST US
    Subject: Re: Risky Jump Starts?
    From: "Matt Prather" <mprather@spro.net>
    I'm with you.. I don't see how leaving the alternator turned off would have helped. OWT People love to dramatize events. Hooking 24V to a 12V system can blow breakers on some circuits - like lighting. And can damage some items. Doubling the V, doubles the I - when a circuit isn't regulated to constant P (which is true for many things). Matt- > Greetings, > > Someone posted on the rec.aviation.piloting newsgroup a story about damage > caused by jumpstarting the airplane with the alternator switch on. > According to the story, the jump start was from an FBO tug capable of > "much more juice" than the owner's pickup truck that he had successfully > used in the past, and as soon as he turned the key, "every breaker in the > plane tripped." Sensors for fuel quantity, oil temp, ammeter, and oil > pressure strip "got fried and needed to be rebuilt." > > I'm having trouble understanding how getting a jump start with the > alternator switch turned on could cause this problem. Even if it were a > 12 volt system and the FBO tug produced 24 volts, I don't see why it would > trip the circuit breakers. > > Any ideas? > > Dennis Johnson > Legacy, now flying > >


    Message 3


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    Time: 08:10:41 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@cox.net>
    Subject: Re: Risky Jump Starts?
    At 06:14 AM 4/9/2008 -0700, you wrote: >Greetings, > >Someone posted on the rec.aviation.piloting newsgroup a story about damage >caused by jumpstarting the airplane with the alternator switch >on. According to the story, the jump start was from an FBO tug capable of >"much more juice" than the owner's pickup truck that he had successfully >used in the past, and as soon as he turned the key, "every breaker in the >plane tripped." Sensors for fuel quantity, oil temp, ammeter, and oil >pressure strip "got fried and needed to be rebuilt." > >I'm having trouble understanding how getting a jump start with the >alternator switch turned on could cause this problem. Even if it were a >12 volt system and the FBO tug produced 24 volts, I don't see why it would >trip the circuit breakers. 24 volts of normal polarity would not trip all the breakers . . . however 24 volts of REVERSED polarity might. Ground power carts are typically capable of 1000 to 2000 amp currents. A set of paralleled-series diodes in an alternator would attempt to hold off voltage rise of a reversed polarity . . . but the forward conduction drop on a highly stressed diode is 1 volt or more. So in milliseconds, the bus voltage goes minus to the tune of 2 volts or more . . . at MANY amps. The battery would also attempt to stand of the event . . . but we don't know if the battery was even on line for this scenario. But if the battery were dead, it wouldn't be much help. The alternator breaker or b-lead fuse would open first and probably before the alternator was damaged. As soon as the breaker opens, then the bus voltage goes WAAAaayyyy negative and really sad things start to happen . . . which may well include the opening of a few more breakers. I've had line-folks put 24v of the RIGHT polarity to my 14v airplane and that was scary enough. I've addressed this possibility in the designs for ground power jacks in your OBAM aircraft project. I've always recommended (1) ov protection, (2) reverse polarity protection and (3) giving the pilot absolute control of when power is applied to the ship's systems. See: http://aeroelectric.com/articles/grndpwr.pdf The outcome of this story would not have been altered by leaving the alternator switch OFF. I used to contribute to the discussions on Usenet groups but had to give up after discovering that many folks who hang out there are not interested in (or perhaps capable of) understanding the simple-ideas behind the physics that controls behavior of their electrical systems. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 4


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    Time: 08:14:06 AM PST US
    From: "Robert L. Nuckolls, III" <nuckolls.bob@cox.net>
    Subject: Re: Risky Jump Starts?
    At 06:14 AM 4/9/2008 -0700, you wrote: >Greetings, > >Someone posted on the rec.aviation.piloting newsgroup a story about damage >caused by jumpstarting the airplane with the alternator switch >on. According to the story, the jump start was from an FBO tug capable of >"much more juice" than the owner's pickup truck that he had successfully >used in the past, and as soon as he turned the key, "every breaker in the >plane tripped." Sensors for fuel quantity, oil temp, ammeter, and oil >pressure strip "got fried and needed to be rebuilt." > >I'm having trouble understanding how getting a jump start with the >alternator switch turned on could cause this problem. Even if it were a >12 volt system and the FBO tug produced 24 volts, I don't see why it would >trip the circuit breakers. 24 volts of normal polarity would not trip all the breakers . . . however 24 volts of REVERSED polarity might. Ground power carts are typically capable of 1000 to 2000 amp currents. A set of paralleled-series diodes in an alternator would attempt to hold off voltage rise of a reversed polarity . . . but the forward conduction drop on a highly stressed diode is 1 volt or more. So in milliseconds, the bus voltage goes minus to the tune of 2 volts or more . . . at MANY amps. The battery would also attempt to stand of the event . . . but we don't know if the battery was even on line for this scenario. But if the battery were dead, it wouldn't be much help. (UPON FURTHER REFLECTION, THE SCENARIO DESCRIBED MAY NOT HAVE INCLUDED REVERSED POLARITY . . . THIS IS AN EXCEEDINGLY RARE EVENT THAT IS USUALLY LIMITED TO RECENTLY SERVICED BATTERY CARTS THAT HAVE BEEN IMPROPERLY ASSEMBLED. THIS PROBABLY WAS A SIMPLE OVER VOLTAGE EVENT SUPPORTED BY A 1000+ AMP CURRENT SOURCE. YOU THINK AN OV EVENT FROM A 60A ALTERNATOR IS BAD, TRY A 1000A GROUND POWER CART!) The alternator breaker or b-lead fuse would open first and probably before the alternator was damaged. As soon as the breaker opens, then the bus voltage goes WAAAaayyyy negative and really sad things start to happen . . . which may well include the opening of a few more breakers. I've had line-folks put 24v of the RIGHT polarity to my 14v airplane and that was scary enough. I've addressed this possibility in the designs for ground power jacks in your OBAM aircraft project. I've always recommended (1) ov protection, (2) reverse polarity protection and (3) giving the pilot absolute control of when power is applied to the ship's systems. See: http://aeroelectric.com/articles/grndpwr.pdf The outcome of this story would not have been altered by leaving the alternator switch OFF. I used to contribute to the discussions on Usenet groups but had to give up after discovering that many folks who hang out there are not interested in (or perhaps capable of) understanding the simple-ideas behind the physics that controls behavior of their electrical systems. Bob . . . ----------------------------------------) ( . . . a long habit of not thinking ) ( a thing wrong, gives it a superficial ) ( appearance of being right . . . ) ( ) ( -Thomas Paine 1776- ) ----------------------------------------


    Message 5


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    Time: 04:38:40 PM PST US
    Subject: Securing Ends of Wires in Wing for Later Use
    From: "messydeer" <messydeer@yahoo.com>
    Hello! I have one wing ready to skin and have run a bundle of wires from the root out to the tip through the leading edge. The wire may be used for a heated pitot tube (~3' from the root), landing lights (~1' in from the tip), and a tip nav/pos/strobe combo. I will most likely not install the lights and heated pitot until after hours of flying, if at all. So, what are some good ways to tie off wire that won't be used? The first wire I need to figure out is the one for a heated pitot. My bundle goes through the forward of two lightening hole and the pitot tube is located several inches back near the main spar. If I make a few loops of pitot wire and tie it to the bundle, I wouldn't be able to reach it through the access hole, which is only 2". So I'm thinking it should be real close to the access hole, maybe even on the pitot tube assembly itself? Again, it's not a heated tube but would be available if I switched it over to one in the future. Then there are the rest of the wires that end at or near the tip. For now I've coiled them a few times and cinched down a cable tie or two there for the time being. I'm not in a hurry to get this location figured out, because I'll have access to it after the wing is skinned. But the pitot tube wire needs to be figured out in the next few days. Cheers, Dan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=175812#175812


    Message 6


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    Time: 07:00:15 PM PST US
    From: Roger Cole <rcole927@earthlink.net>
    Subject: Re: Securing Ends of Wires in Wing for Later Use
    Dan, I ran a piece of 3/4-inch OD, 5/8 ID polyethylene tube the length of my wings so I can pull the wires when they are needed. That begs the question of a heated pitot. I figure that if I REALLY need a heated pitot, I can use a soldering iron through an access port to melt a hole in the conduit. Roger Cole Murphy Elite #709 Wings and tail done; starting fuselage On Apr 9, 2008, at 6:32 PM, messydeer wrote: > <messydeer@yahoo.com> > > Hello! > > I have one wing ready to skin and have run a bundle of wires from > the root out to the tip through the leading edge. The wire may be > used for a heated pitot tube (~3' from the root), landing lights > (~1' in from the tip), and a tip nav/pos/strobe combo. I will most > likely not install the lights and heated pitot until after hours of > flying, if at all. So, what are some good ways to tie off wire that > won't be used? > > The first wire I need to figure out is the one for a heated pitot. > My bundle goes through the forward of two lightening hole and the > pitot tube is located several inches back near the main spar. If I > make a few loops of pitot wire and tie it to the bundle, I wouldn't > be able to reach it through the access hole, which is only 2". So > I'm thinking it should be real close to the access hole, maybe even > on the pitot tube assembly itself? Again, it's not a heated tube > but would be available if I switched it over to one in the future. > > Then there are the rest of the wires that end at or near the tip. > For now I've coiled them a few times and cinched down a cable tie > or two there for the time being. I'm not in a hurry to get this > location figured out, because I'll have access to it after the wing > is skinned. But the pitot tube wire needs to be figured out in the > next few days. > > Cheers, > Dan > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=175812#175812 > >




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