Electricity Over Glass 187
guddan writes "Running a live wire into a passenger jet's fuel tank seems like a bad idea on the face of it. Still, sensors that monitor the fuel tank have to run on electricity, so aircraft makers previously had little choice. But what if power could be delivered over optical fiber instead of copper wire, without fear of short circuits and sparks? In late May, the big laser and optics company JDS Uniphase Corp., in San Jose, Calif., bought a small Silicon Valley firm with the technology to do just that."
Is this needed? (Score:4, Insightful)
What, no one ever heard of vacuum lines? Or maybe pressurized lines? I'm not a rocket scientist, or even a plane scientist, and I could figure that out before I was finished reading the frickin' summary, let alone the frickin' article.
People love to make work for themselves...
Setting that aside, the idea sounds awesome!...what with all the planes we lose every year to short-circuiting wires...BUT, I'll wait to see if this materialized before I get all excited about it.
Re:Is this needed? (Score:5, Insightful)
Re:Is this needed? (Score:4, Informative)
Re:Is this needed? (Score:4, Informative)
The wires for your electric fuel pump are inside the tank too.
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Oh course when you run your tank low the pump is above the fuel level.
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Avionics Tech Saves /. (Score:5, Informative)
Speaking as a former USAF Avionics Specialist, who worked on C-5's, C-141's, and C-130's, and who personally saw a parked C-141 burst into flames on the ramp because of a fuel probe maintenance accident, let me explain things simply.
Design considerations:
JP4, the fuel that makes most jets run, is difficult to ignite. It needs a heat source. You could run a bare wire into a full tank and not have a problem. However, heat that wire up, and get the fuel/air mixture just right, and you have a problem. Big Boomba Problem, to quote JJB.
The big problem is the mostly empty tank and exposed heat sources. The C-5 has a nitrogen purging system. Basically, as fuel empties from a tank, it is replaced by nitrogen. The only way that wing is going to explode is if something other than a bare wire acts on it. Then, you've got bigger problems.
The big problem comes when you open the tank for maintenance. So, there are massive safety considerations. The C-141 that exploded in the mid-90's at Travis AFB in California blew because a jackass tech did not follow lockout/tag out procedures. The 141 doesn't have the nitrogen purge, but the tanks were open anyway. Two senior specialists were standing on top of the aircraft when the wing blew. Several others were in the cargo box. Luckily, aside from bumped elbows and bruised body parts, everyone got out o.k. We towed nearby aircraft to safer distances. There was precious little left of the burnt aircraft that identified it as such.
Most amatuers could make a good guess at a practical design for fuel sensors, but most of the solutions developed as such will end up being to costly, too heavy, will introduce other problems such as high maint., or simply won't work in 3-d, or extreme temperatures.
Most jets do NOT burn JP-4 (Score:5, Informative)
JP-4 was also phased out of use by the USAF over ten years ago. JP-8 is used now, which is a completely different formulation from JP-4 and has much higher flash point than JP-4. JP-4 was a naptha-based fuel and JP-8 is a kerosene-based fuel. Today's Jet-A and JP-8 have very similar base formulations, but they have very different additive packages blended in. JP-8 has a much higher flash point than Jet-A too, since it is tailored for use in military aircraft that need to handle supersonic operations.
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Re:Is this needed? (Score:4, Funny)
Hand over your geek card!
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Uh Oh ?! (Score:5, Informative)
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Of the cases listed on that Wiki page, 9 were due to pilot error, 1 due to a fuel leak, and 1 resulting from hijacking. None were a result of instrument failures, and in most of the cases of pilot error there were complicating circumstances, such as heavy storms or landing gear failing to retract, increasing fuel consumption and distracting the crew.
just 2 words: (Score:5, Informative)
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Why? it's extremely difficult to ignite liquid gasoline, or jet fuel. An air-fuel mix ignites quite easily, however. So moral of the story: if you're paranoid that wires in your fuel tank are freyed, keep your fuel tank full. Or get your crappy car fixed.
(In fact, nearly every automobile built in the past 20 years has not one, but two powered devices in the fuel tank -- a fuel pump and a level sensor.)
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Why? it's extremely difficult to ignite liquid gasoline, or jet fuel. An air-fuel mix ignites quite easily, however. So moral of the story: if you're paranoid that wires in your fuel tank are freyed, keep your fuel tank full.
One cannot keep the fuel tanks on any operating vehicle continuously full without shape-changing tanks. Even if one allows for a partial drop in fuel level (with the resulting fuel-air mixture being too rich to burn), this will result in reduced range, and hauling a lot of extra fuel around.
Better to remove potential ignition sources from the tank.
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So what replaces gas when it's pumped out (Score:2)
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Re:Is this needed? (Score:5, Funny)
I doubt it is "easy" to ignite steam
Re:Is this needed? (Score:4, Interesting)
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Re:Is this needed? (Score:5, Insightful)
I'm no rocket scientist either, and I'm sure that those rocket scientists has already consider those options you've mentioned. Perhaps because it is on an airplane going over 500mph and you have all sorts of physics and temperature considerations that vaccuum/pressurized lines are just not best suited for.
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1. Airplanes often travel at 30,000ft which may make it more difficult to do this on the wings (where they keep the fuel)
2. Airplanes have a whole problem with weight versus lift ratio. If you can squeeze a few more passengers by using fiber optics instead of the gear required for the pressurized/vacuum lines then the Airline executives would prefer that.
Old, ignorant, and out of touch with ... (Score:5, Funny)
NOT NEW TECHNOLOGY: They are merely piping light using fiber optics, and then using the light with photocells to create small amounts of power for use with measuring devices. The measurements are communicated back through the fiber optics, using a different wavelength.
PATENTS? The article says, "Photonic Power owns key patents..." Can the generation of power using light be patented again? Can sending information using fiber optics be patented again? Maybe the company has patents, considering that the U.S. government has become corrupt, but it is difficult to believe that any patents could be valid.
IGNORANT: See this quote from the article referenced in the Slashdot story: "... the company's fastest growing sector is currently electric power transmission. One important application is eliminating the transformers used to step down high currents and voltages to measurable levels."
The article should have said, "... the company's fastest growing sector is currently powering and connecting the measuring devices used in electric power transmission."
The writer does not understand that the idea does not change the measuring system, only the method of transmitting the data. If step down transformers are part of the method of measurement, they will still be required. The "senior research analyst" who was quoted, Vincent Lui, doesn't understand that, either, apparently.
REALITY RULES: If you play video games too much, your brain will become partly useless for other things, and, if then try to be a Slashdot editor, you won't be able to do a good job. (This is a theory that seems to fit the facts.)
This is a useful idea for computer professionals in some cases where voltage isolation is needed, but the Slashdot story was mishandled, as often happens.
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Aircraft are required to operate at various altitudes (which have various temperatures and pressures) making compensating for differences in pressures and temperatures in a system that requires vacuum lines more difficult (and more difficult to maintain and keep calibrated). Early aircraft had a sight glass on the outside of the tank, but these are only good for reading volume and at a specific aTTitude (i.e on the ground) intrinsic [omega.com]
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I think it happened a few months after 9/11 and happened to a plane leaving JFK airport, so everyone initially assumed it was terrorists. (Just to help jog anyone's memory, not making a point here)
IIRC the power cables that went into the fuel tanks weren't at a high en
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Back in '76 emissions controls were in full force, so the engine performance had to be tweaked in all kinds of subtle ways. Unfortunately, engine computers were still a pretty exotic idea, certainly not something that they'd consider for a cheap pony car at the end of its model lifespan. So the answer was vacuum lines. Lots and lots of vacuum lines. Some of them were big rubber affairs, like the ones going to the EGR. Others were sti
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friggin laser beams (Score:5, Funny)
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Sounds like a bad idea. (Score:5, Insightful)
You're stilling bringing as much power into the fuel tank. High-power beams of light aren't any safer, a laser can cut inch thick steel.
At least electricity is very well understood, we know how to insulate the wire, we know how much voltage will spark in a given medium, and the low voltage for sensors is very safe.
High energy lightbeams are not at all well understood. Will the fiber heat up? What about light leakage, will that cause an explosion? What if the fragile fiber breaks while the beam is on?
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Re:Sounds like a bad idea. (Score:5, Insightful)
Not much, at least compared to what it takes to run a pump motor. And at least jet fuel isn't nearly as volatile as gasoline, which is pumped every day with submersible electric turbine pumps at nearly every gas station in the developed world. It's a PITA to make intrinsically safe electric circuits, but it's well understood and done every day.
The light powered device might be useful in planes if they could achieve the same degree of intrinsic safety at a lower weight.
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The light powered device might be useful in planes if they could achieve the same degree of intrinsic safety at a lower weight.
I think that makes sense, lower weight means higher overall efficiency.
But it's the safety aspect that they seem to be pushing, Quote TFA;
I might be wrong but I think large aircraft fuel tanks are part of the wings so there is no choice but to put wires through the cavity that holds the fuel.
The article links to a picture of the 1996 TWA flight 800 [wikipedia.org] reconstruction to drive the point home.
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Most of the wing is the tank, but not all of it. There is room behind the 'leading edge' and the trailing edge (between the aft of the tank and the front of the flaps/ailerons. ) This is where other services go, such as air ducts for the leading edge De-Icing (heating) systems, and wires that run to those little navigation lights way out there on the
Could run off a watch battery for months (Score:4, Informative)
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Thus, such a system would be extremely c
The issue is power limiting (Score:3, Informative)
It's a lot easier to ensure the power is properly limited. Running a sensor is a low power application (you wouldn't be using a "steel cutting" laser), and the power is limited with the size of the laser diode. There's no other way to get power through the line.
With electric lines, the issue is whether the wire to the sensor is going to short to another wire somewhere
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Re:Sounds like a bad idea. (Score:5, Insightful)
About the only valid sentence in your post starts with "electricity is very well understood". The rest of it just reflects your ignorance.
"High energy lightbeams are not at all well understood" by you. Light leakage causing an explosion? Seriously?
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What about light leakage, will that cause an explosion? What if the fragile fiber breaks while the beam is on?
Ahh, that's it. I always wondered why the gas tank filler neck on my truck has that little flapper at the top. It's to keep the light out!
The people who made my gas cans sure screwed up, though. No light blocking flappers on them. I'm lucky I haven't been torched. From now on, I only open them at night.
Light Sensors in cameras... (Score:2, Informative)
however, there is a problem with what is called dark current. that is when there is no light hitting the transducer, and there is still a current being developed...
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Re:Light Sensors in cameras... (Score:5, Funny)
Don't cross the beams.
Re:Light Sensors in cameras... (Score:4, Informative)
Intrinsic Safety. (Score:5, Interesting)
However the design is what is known as "Intrinsically Safe"... ie, it can't cause an explosion.
Currents, voltages are limited. Components are overrated by a set amount.
I've never heard of any intrinsically safe circuit igniting gasoline.
So what if you use fiber optics to provide the power. It's still electronic circuits in the tank, except now they are a whole lot more complicated and have power generation and regulation circuits, which make it a whole lot more dangerous...
And please don't just say encapsulate the dangerous stuff, because I'm sure that won't explode with a pressure build up if a component dies (as they tend to do in regulated power circuits).
It really scares me how such "great" ideas like this seem sane, when the original technology was probably safer.
GrpA
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Good point. Note that electronic sensors are also used in underground (and above-ground) storage tanks. Electric turbine pumps, too.
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Other than that, I tend to agree. Stick with the reliable, proven method, until the alternative offers enough benefits to make the risks worthwhile.
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I've never heard of any intrinsically safe circuit igniting gasoline.
Ahh, but flight 800...
The problem wasn't the safe circuit, it was that the wires made a path into the fuel tank. Sometimes circuits don't stay the way you built them :) An optical path would off
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Yes, TWA 800.
Well, the biggest problem with Intrisically Safe designs is that they don't tend to be nearly as safe when they get struck by missiles...
I thought it was interesting though. I don't actually know enough about that aircraft to know if it was an intrinsically safe design that went wrong or just bad design.
Of course, Avtur - or Kerosene, doesn't ignite with a spark or even a flame - try it. It takes a LOT more, so I'm not really sure how the middle tank went up. You need heat and pressure too.
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Or of course, it might really have been that the wires became frayed after being struck by a missile :)
Oh, stop :) I think they made a South Park about people like that!
The center fuel tank was actually empty, and thus full of vapor. It is true that jet fuel would not have exploded, but in certain conditions the vapor can be explosive.
Here is a pretty good, if dated, analysis. [wisc.edu] From the link:
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It really scares me how such "great" ideas like this seem sane, when the original technology was probably safer.
It also bugs me, as an engineer, when people want better, faster, cheaper, but then refuse change. I hear numerous stories from my coworkers who used to design parts for the automotive industry. Apparently they had to come up with improvement plans and present them only to have the "what we have works, why change it?" mentality. Follow this with, now do it for less because we are going to buy the same system for less money each year...but remember, don't change or improve anything. Sounds dumb? Obviou
Re:Intrinsic Safety. (Score:5, Informative)
Intrinsically safe circuits can ignite gasoline when they are hit by lightning. The concern in aircraft applications isn't that the fuel ignites in normal operation. Rather, it is suspected that some airplanes have exploded after being hit by lightning.
If enough power hits just the right wire, and the tanks are near empty (with lots of explosive fuel vapors), and enough planes get hit by lightning in flight in a sensitive location, then potentially disaster can happen. The accident data says fuel tank explosions occur, and this might be a possible cause. Safety problems demand a precautionary approach. Hence the desire to eliminate the wire going to the fuel tank.
Further resources:
http://www.epa.gov/fedrgstr/EPA-GENERAL/1997/April/Day-03/g8495.htm [epa.gov]
http://easa.europa.eu/doc/Events/fueltanksafety_24062005/easa_fueltanksafety_24062005_large_transport_ppt.pdf [europa.eu] [pdf]
Note: a widespread consensus exists that many possible ways for fuel tanks to ignite exist. As such, most of the focus is on minimizing the likelihood of ignition, rather than one specific cause, like the fuel tank wires themselves.
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Even fibre optic cable -- or its outer protective sheath -- can potentially become conductive.
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Actually, gasoline can be used to pu
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Intrinsic Safety [wikipedia.org] is better explained on the Wikipedia that I did in the post.
And the insulation doesn't exist in the rheostat - just wires rubbing together in the presence of fuel and air, but as I mentioned, it's extremely rare for car fuel tanks to spontaneously explode, which is probably a good example of why intrinsic safety designs work so well
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If the wires short with something outside the tank (even far away), that power is now going inside the tank where it could cause sparks. With fiber optics it's virtually impossible to cause a spark via light. I'm assuming the fiber would carry very weak light, on the level a solar calculator uses,
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If the diode driver circuit is hit by lighting, the output will be in the order of watts before the diode disappears... Way more than a CD burner. Anyone who's worked with LEDs knows how easily you can overdrive them if you have the duty cycle low enough. Basically, the power limitation in LEDs is based on how quickly they can dissipate the heat. This is the same for many electronic circuits.
But having thought it through, I'm thinking that even with wires inside the tank, I've heard of
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There are a million ways to do this. Some tech firm just came up with an idea to combine laser transponders with solar cells and is trying to find something to do with it.
I saw once on TV that they add agents to the fuel to make it even less flammable and a red dye of some sort but it was years ago an
Fuel Gauges (Score:2)
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There are battery charging monitors that integrate the current over time to get an idea of how many amp-hours are remaining, but even these don't account for the tendency of most battery chemistries to self-discharge.
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The pulse would be short but I wonder if it might be enough to cause damage/ignition at the other end.
Diodes seem really easy to overdrive in my experience.
GrpA
They could go farther (Score:2, Informative)
Having said the above, the product seems like a solution in search of a problem. I can't recall any incidents where a fire or explosion was caused in an airplane because of faulty wiring in the fuel tank. There are lots of places where an electrical spark could cause an explosion. For instance in a mine, or factory, dust explosions are
Ok, so I read the article... (Score:2, Interesting)
Say what?!? Ok...so, yes, I'd much rather have the manufacturer disclaim that they can't be sure that their product won't expl
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Sounds bogus (Score:2)
We already have intrisically safe electrical technology for such things. As long as you limit the power so that there isn't enough to create an ignition source, you're golden.
Personally I'd prefer new sensor technology that allows sensing the desired quantity with either less power or from a safe distance, like ultrasonic level sensors and such.
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Re:Reading and understanding the article.. (Score:2)
There isn't much diffrence between feeding 100 mW opticaly or not.
"where electromagnetic interference is more than just an inconvenience"
Feeding 100 mW sensor and getting a 50 nW signal back with 25 mW of induced ground radar or cell telephone signal on top is the problem. It swamps the signal. In extreme cases such as a close lightning strike, the induced power could be enough to create
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This makes a lot more sense. We already have industrial protocols like SERCOS for closed loop motion control that are based on fiber, specifically for high data rate and noise immunity. H
Galvanic isolation. (Score:3)
How much Power? (Score:3, Interesting)
Current ATEX regs make it awkward to supply anything above about 1Watt at 6V.
Most people resort to pneumatics and/or keeping the computational logic outside the zoned areas.
Disappointingly for IEEE, he article is sparse in terms of technical details, such as the power/size ratio.
So much safer (Score:2)
That could lead to... (Score:3, Funny)
Acoustic impulse pneumatic probes (Score:2)
A small tube is lightly pressurized with a known gas. A mechanical sensor at the far end moves a tiny piston in or out of the tube to measure fuel level or temperature. At the near end, a device emits an acoustic pulse into the gas and measures the return reflection timing. This timing gives the length the piston has moved in the tube. The tube can be made of metal (well grounded to the tank frame at many points) or other reasonably rigid materials.
One tube can even be used for multiple sensors. This
Glass fiber = static electricity? (Score:3, Insightful)
The safety of stuff in a fuel tank depends on a) how well the risks are understood, and b) how well the engineering to mitigate them is performed.
It's a standard rhetorical ploy to assert that because something is different from an older technology, it is automatically free from the problems of the older technology... and, without saying so in so many words, allowing the listener to infer that it does not have equivalently bad new problems of its own.
The first time I heard groove-skipping on a CD, I laughed out loud. With all the promotion of the digital perfection of the CD, the fact that it suffered from exactly the same problem as a vinyl LP was... delightful.
High Transmission Lines? (Score:2, Interesting)
For an idea of the scale of loss versus cost of power: some power companies are currently willing to take the hit in lost power by using aluminium lines instead of copper, because they can engineer the towers holding
Lousy Science (Score:3, Insightful)
Unless those techniques are patented?
Formidably silly article (Score:5, Interesting)
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Exploding gas tanks are very low on the list of problems, sorted by frequency and severity. If we spend money on these less severe problems, we're taking money away from figting more serious and cost-effectively attakcable problems.
Running a cost:benefit analysis on problems is a really stupid way to design something. Especially an airplane.
Engineers spend a disproportionate amount of effort (which means money) working to prevent things that might happen 1% of the time.
Why? Because those 1% events usually end up as huge fucking disasters.
"But it only happens 1% of the time!" say the penny pinchers.
Multiply all the airplanes in service by 1% and they'd start blowing up left and right because you thought it is good to be "figting more
What about capacitance fuel sensors? (Score:4, Interesting)
And for all of the people asking how often sparking inside a fuel tank causes a tank to explode, yes, it *does* happen sometimes. The final NTSB report on the airliner that crashed off New York about a decade ago (you know, the one that the conspiracy theorists said was shot down by a hand-held SAM) was due to sparking inside the fuel tank. I'd link to it, but I can't recall the flight number, and I don't have time to search for it right now...
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Flight 800? [wikipedia.org]
The NTSB investigation ended with the adoption of their final report on August 23, 2000. In it they concluded that the probable cause of the accident was "an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank. The source of ignition energy for the explosion could not be determined with certainty, but, of the sources evaluated by the investigation, the most likely was a short circuit outside of the CWT that allowed excessive vol
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You're right, nothing new here (Score:2)
Venture capitalists (Score:2)
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It solves the problem because you can't have a short circuit with light. An electrical short circuit can end up pulling in far more current than anticipated, causing excessive heat.
The light is converted into electricity inside the tank, so potential