FAA Grounds 787s
More bang for your buck
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Without extra instrumentation I don't see what they are going to learn, unless of course there was no testing of that part of the system in the original flight test programme.
Actually it would be interesting to know how many batteries Boeing had to change during the flight testing up to certification
Actually it would be interesting to know how many batteries Boeing had to change during the flight testing up to certification
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Boeing built an immense indoor temperature controlled replica of the fuel system of the 777 post 038. Full size. The results that were published were inconclusive
Obviously, I am a known sceptic, gg, what they have aboard as to personnel and instrumentation will be doled out to the public through Boeing...Correction through NTSB from BOEING
And it will not be detrimental to Boeing...at worst, "inconclusive". Boeing knew the problem or it would not have developed an expensive, embarrassing, and FAR illegal FRP.
IMO
Obviously, I am a known sceptic, gg, what they have aboard as to personnel and instrumentation will be doled out to the public through Boeing...Correction through NTSB from BOEING
And it will not be detrimental to Boeing...at worst, "inconclusive". Boeing knew the problem or it would not have developed an expensive, embarrassing, and FAR illegal FRP.
IMO
Last edited by Lyman; 8th Feb 2013 at 15:38.
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no hazmat or autonomous breathers?
pax2908...by "previous flights" do you mean prior to the replacement program?
Or, since.
Good Heavens.... "what a surprise". not.
1. Lithium a known problem, that's why they were illegal.
2. Boeing wanted Lithium, designed a criteria to allow it
3. The criteria did not ignore the dangers, but allowed Lithium, if it could be shown "manageable".
4. It proved unmanageable.
5. All of a sudden there is a mystery?
6. It is performing in ways the FARs PREDICTED, eg, catches fire, spills electrolyte, damages collaterals....
7. The whole idea is to present the problem as mysterious...
8. A ""NEW" criterion (#10) will be added, and bob's your uncle.
9. Dusted, and done.
10 if BOEING wanted a nuclear pile on board, the FARS would accomodate.
11. Jeezuz
pax2908...by "previous flights" do you mean prior to the replacement program?
Or, since.
Good Heavens.... "what a surprise". not.
1. Lithium a known problem, that's why they were illegal.
2. Boeing wanted Lithium, designed a criteria to allow it
3. The criteria did not ignore the dangers, but allowed Lithium, if it could be shown "manageable".
4. It proved unmanageable.
5. All of a sudden there is a mystery?
6. It is performing in ways the FARs PREDICTED, eg, catches fire, spills electrolyte, damages collaterals....
7. The whole idea is to present the problem as mysterious...
8. A ""NEW" criterion (#10) will be added, and bob's your uncle.
9. Dusted, and done.
10 if BOEING wanted a nuclear pile on board, the FARS would accomodate.
11. Jeezuz
Last edited by Lyman; 8th Feb 2013 at 15:55.
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Disappointing that engineering at the arguably-best transport-aircraft company on the planet led itself down this path - and got it so wrong. Given that, can we trust the objectivity of the 2007 report "Flammability Properties of Aircraft Carbon-Fiber Structural Composite"? (The report specifically examines the composite spec'ed by Boeing, but the work seems to have been done by University of Maryland for the FAA, so the answer may well be 'yes', but it's a pity to even have to think the question.)
HeadingSouth:
Yes. But this brings up another failure mode/load incompatibility issue. Current balance and thermal runaway are more or less a steady state issue. They are a function of the thermal characteristics of the battery cells. I'm going to give Boeing and its subcontractors the benefit of the doubt and assume that many combinations of load or charge and ambient temperature were tested for the initial certification of this subsystem.
The 'current spike' brings up another issue which I have found to be often overlooked. That is: the electrical loads on these batteries are not steady state DC. Particularly in the case of the APU, the starter/generator is driven by a controller that draws very high levels of ripple currents from the source.
Batteries, in addition to being an electrochemical voltage source have an equivalent AC model that (overly simplified) can be represented as a series LCR circuit at higher frequencies (tens or hundreds of kHz). If one excites such a circuit near its resonance, it is possible to generate extremely high voltages across the various internal points of this equivalent circuit.
There is the possibility that the various combinations of load ripple and battery AC impedance was not properly characterized when the initial certification analysis was done*. I imagine that subsequent flight tests will be instrumented to capture exactly this kind of data.
*Back in my days at Boeing, I was involved with the 767 static inverter and its adaption to the 747-400. Initially, it had been certified to drive linear AC loads. This was because the smaller loads (typically driven by the standby AC bus) were exempt from limits on harmonic current draw. But, as it turns out, being exempt from a spec requirement doesn't meant that it shouldn't be considered. It turned out that an inverter rated at 1kVA was only capable of delivering about 400 VA to the connected loads before the voltage waveform became so flat-topped that it's output fell out of spec. This new 'all electric' airplane may turn out biting some old school engineers in the a
.
They tend to auto balance as long as charge/discharge currents are not too high. If for some reason a sudden current spike occurs,
The 'current spike' brings up another issue which I have found to be often overlooked. That is: the electrical loads on these batteries are not steady state DC. Particularly in the case of the APU, the starter/generator is driven by a controller that draws very high levels of ripple currents from the source.
Batteries, in addition to being an electrochemical voltage source have an equivalent AC model that (overly simplified) can be represented as a series LCR circuit at higher frequencies (tens or hundreds of kHz). If one excites such a circuit near its resonance, it is possible to generate extremely high voltages across the various internal points of this equivalent circuit.
There is the possibility that the various combinations of load ripple and battery AC impedance was not properly characterized when the initial certification analysis was done*. I imagine that subsequent flight tests will be instrumented to capture exactly this kind of data.
*Back in my days at Boeing, I was involved with the 767 static inverter and its adaption to the 747-400. Initially, it had been certified to drive linear AC loads. This was because the smaller loads (typically driven by the standby AC bus) were exempt from limits on harmonic current draw. But, as it turns out, being exempt from a spec requirement doesn't meant that it shouldn't be considered. It turned out that an inverter rated at 1kVA was only capable of delivering about 400 VA to the connected loads before the voltage waveform became so flat-topped that it's output fell out of spec. This new 'all electric' airplane may turn out biting some old school engineers in the a
.
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EEngr
pardon my ignorance. Is the tickle current at the SG modulated? is the generated current "controlled".....what pathway to the BATTERIES? I am wondering why the NTSB claimed the "charging current" never exceeded spec at the Battery?
poorjohn....I think the specs on CFRP are highly pertinent at this point.
CFRP + FIRE = gas.......What is the nature of the products of onboard fire, aloft, and at the GATE?
pardon my ignorance. Is the tickle current at the SG modulated? is the generated current "controlled".....what pathway to the BATTERIES? I am wondering why the NTSB claimed the "charging current" never exceeded spec at the Battery?
poorjohn....I think the specs on CFRP are highly pertinent at this point.
CFRP + FIRE = gas.......What is the nature of the products of onboard fire, aloft, and at the GATE?
Last edited by Lyman; 8th Feb 2013 at 16:57.
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EEngr, fascinating point about the AC characteristics of the battery. Is it well-enough-known in the field so that "everyone" will realize they have to consider it in their design?
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Europe's Airbus is considering whether to drop Lithium-Ion batteries and switch back to traditional ones on its new A350 as investigators probe Boeing 787 battery problems, several people familiar with the matter said.
Airbus studies dropping Li-Ion battery for A350: sources | Reuters
Airbus studies dropping Li-Ion battery for A350: sources | Reuters
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In reply to jcjeant,
I was sufficiently influenced by the DC-10 crashes that I made a point of not flying in the 10, I did fly 747 and Tristar but never the 10.
Granted people continued to fly in the 10 but I wonder how many voted with their feet?
I was sufficiently influenced by the DC-10 crashes that I made a point of not flying in the 10, I did fly 747 and Tristar but never the 10.
Granted people continued to fly in the 10 but I wonder how many voted with their feet?
poorjohn:
It should be at a theoretical level. But LiON batteries are relatively new beasts. So engineers used to dealing with SLA and NiCad and their relatively large plate spacings (and low shunt capacitance) might be dropping this phenomenon out of their analysis. Battery plate configurations look nothing like battery cells of yore.
Its back to first principles, where things like electrical resistance have to consider charge mobility and density rather than just Ohms.
Is it well-enough-known in the field
Its back to first principles, where things like electrical resistance have to consider charge mobility and density rather than just Ohms.
EEngr:
Very good point.
Power density is much higher for LI and the thinner separator material might
be prone to high voltage transients. Separator breaks down enough to negate
self healing, cell shorts, thermal runaway and bang
.
As for instrumentation, there are probably development versions of the charger
and BMS software that provide more debug data, which would normally be
removed for production...
Very good point.
Power density is much higher for LI and the thinner separator material might
be prone to high voltage transients. Separator breaks down enough to negate
self healing, cell shorts, thermal runaway and bang
.As for instrumentation, there are probably development versions of the charger
and BMS software that provide more debug data, which would normally be
removed for production...
syseng68k
Charger and battery testing is one thing. But I'm thinking more of battery/load compatibility. That's not something I'd expect Thales or GSYuasa to be able to do easily. One needs a relatively accurate simulation of variable frequency drives, power supplies and other stuff on the battery busses. The best place to find that is on the airplane.
This brings up some interesting philosophical points in handling development and certification testing. The 777 was developed with an "iron bird". A mockup of all the aircraft systems where compatibility issues could be researched. But that was expensive. It may have cost Mullaly his shot at CEO, but he's doing fine at Ford. As far as I know, nothing to this extent was done for the 787. Flight testing is going to be more expensive than an iron bird test.
Charger and battery testing is one thing. But I'm thinking more of battery/load compatibility. That's not something I'd expect Thales or GSYuasa to be able to do easily. One needs a relatively accurate simulation of variable frequency drives, power supplies and other stuff on the battery busses. The best place to find that is on the airplane.
This brings up some interesting philosophical points in handling development and certification testing. The 777 was developed with an "iron bird". A mockup of all the aircraft systems where compatibility issues could be researched. But that was expensive. It may have cost Mullaly his shot at CEO, but he's doing fine at Ford. As far as I know, nothing to this extent was done for the 787. Flight testing is going to be more expensive than an iron bird test.
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Eengr - as I mentioned in a previous post, some large aerospace companies have replaced expertise with process, so the grey-beard who ran the department, was fanatical about every detail of "his" electrical systems, and had enough clout to insist to Project that they consider the AC aspects is long gone.
And (sadly imo) "his" has become "the team's". Back in the day, we emphasized individual responsibility, tossing "a camel is a horse designed by a committee" at those who needed a poke.
I have no idea if Boeing Commercial is particularly far along that path.
And (sadly imo) "his" has become "the team's". Back in the day, we emphasized individual responsibility, tossing "a camel is a horse designed by a committee" at those who needed a poke.
I have no idea if Boeing Commercial is particularly far along that path.
EEngr:
I would think that they at least had a fully instrumented test rig in house
for the battery subsystem, including expected worst case load profiles such
as apu starting and fast charging. If they didn't, I would see that as a
serious deficiency.
There's no reason why they shouldn't use a production a/c to do this,
much as a/c such as the Concorde prototypes had strain gauges everywhere and
instrumentation racks right down the isle. It probably costs orders
of magnitude more to do design in production, rather than during development,
but with subsystem parts coming from so many suppliers, how do project
management maintain full visibility ?. For software, it's easy to show that
a single module works as expected, but very difficult once hundreds
of modules are linked together for the application. It's the same for any
complex project. Managing complexity probably has dozens of books written
about it, but do management actually read them ?.
Attention to detail and due diligence are everything. Much harder to argue
for in this world of bean counters, cost centres and hr departments, who
are often more interested in whether you ever inhaled, rather than your
passion and ability to get the job done...
This brings up some interesting philosophical points in handling development
and certification testing. The 777 was developed with an "iron bird". A mockup
of all the aircraft systems where compatibility issues could be researched.
But that was expensive.
and certification testing. The 777 was developed with an "iron bird". A mockup
of all the aircraft systems where compatibility issues could be researched.
But that was expensive.
for the battery subsystem, including expected worst case load profiles such
as apu starting and fast charging. If they didn't, I would see that as a
serious deficiency.
There's no reason why they shouldn't use a production a/c to do this,
much as a/c such as the Concorde prototypes had strain gauges everywhere and
instrumentation racks right down the isle. It probably costs orders
of magnitude more to do design in production, rather than during development,
but with subsystem parts coming from so many suppliers, how do project
management maintain full visibility ?. For software, it's easy to show that
a single module works as expected, but very difficult once hundreds
of modules are linked together for the application. It's the same for any
complex project. Managing complexity probably has dozens of books written
about it, but do management actually read them ?.
Attention to detail and due diligence are everything. Much harder to argue
for in this world of bean counters, cost centres and hr departments, who
are often more interested in whether you ever inhaled, rather than your
passion and ability to get the job done...
Eengr - as I mentioned in a previous post, some large aerospace companies have replaced expertise with process, so the grey-beard who ran the department, was fanatical about every detail of "his" electrical systems, and had enough clout to insist to Project that they consider the AC aspects is long gone.
And (sadly imo) "his" has become "the team's". Back in the day, we emphasized individual responsibility, tossing "a camel is a horse designed by a committee" at those who needed a poke.
I have no idea if Boeing Commercial is particularly far along that path
And (sadly imo) "his" has become "the team's". Back in the day, we emphasized individual responsibility, tossing "a camel is a horse designed by a committee" at those who needed a poke.
I have no idea if Boeing Commercial is particularly far along that path
I espect that Boeing's technical Fellows are playing a significant part in reviewing what processes contributed to this. I also expect that any non-propietary weaknesses in this regard will be shared among all the appropriate industry wide technical fellows.
On a similar vein the FAA also has a much smaller cadre of identified technical expertise and leadership.
The crunch in all this is that in problems like the current one, this level of review doesn't get done until there is a fire to put out.
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The 777 was developed with an "iron bird". A mockup of all the aircraft systems where compatibility issues could be researched.
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repariit,
You are describing a structural test rig. The 'iron bird' is a systems test rig that is used to test moving parts such as actuators, hinges, springs, valves, cables, trolleys, etc. Only these parts are as used in the airplane, the 'iron' structure is only representative of the airplane in terms of dimensions and mass properties.
You are describing a structural test rig. The 'iron bird' is a systems test rig that is used to test moving parts such as actuators, hinges, springs, valves, cables, trolleys, etc. Only these parts are as used in the airplane, the 'iron' structure is only representative of the airplane in terms of dimensions and mass properties.
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One potential failure mode occurred to me this morning as I was enjoying the blizzard. Perhaps the battery failures are related to pressure cycling. Since the batteries are normally sealed, each flight cycle will put a pressure differential on the cases of the individual cells. This, combined with vibration and G-forces, could result in very small, but repeated changes in the cell plate spacing/position - especially with a rectangular plate design. This could then lead to internal shorting, especially when coupled with charging errors and/or high current discharge (e.g., starting the APU). I'm sure Boeing validated the battery system for pressure changes, but perhaps it's all about the number of pressure cycles.
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areobat
I think you are on the right page. The CT scan shows bulging battery cases, with intact interior folds. My sense is that the cases are bulging due to thermal expansion of the contents, perhaps including some trapped gaseous electrolyte.
The prismatic shape of the batteries does of course bear on the internal stresses. To the extent that the interior stresses of folding work against a dissipation of "wear", in my opinion, the separator material is subject to abrasive forces. The application of the paste to the poly film creates a stress simply by virtue of the relative physical properties of the two materials.
Any one who has opened a water bottle at cabin altitude after launch knows the pressure differential has an effect on the clear plastic bottle, the bottle will snap and crack, audibly.
Simplistic? Most problems start just that way.
The poly separator in the batteries is twenty five microns in thickness. The standard is a minimum of ten, to a maximum of forty (microns) dependent on application, (from the industry website I posted.
These batteries have a patent failure profile, consistent with the FAA considerations, the research data, and the evidence of failures since 2006.
Including the dramatic failures which caused the Japanese safety board and FAA to ground the fleet.
bill
I don't think the problem is mysterious. The actual temperature range for suitable performance of the poly may be much more narrow than that allowed.
I've had experience with plastics in normal temps. When it gets cold, it disintegrates, when it gets hot, it loses its resilience, and expands/contracts sufficiently to destroy its "shape". Since the perforations in this application are critical, my guess is that the poly deforms, the perforations change dimension, and allow short circuiting, which greatly accelerates the deterioration, and causes the need to "replace" the unit. Feverishly replaced, as Boeing has shown.
I think you are on the right page. The CT scan shows bulging battery cases, with intact interior folds. My sense is that the cases are bulging due to thermal expansion of the contents, perhaps including some trapped gaseous electrolyte.
The prismatic shape of the batteries does of course bear on the internal stresses. To the extent that the interior stresses of folding work against a dissipation of "wear", in my opinion, the separator material is subject to abrasive forces. The application of the paste to the poly film creates a stress simply by virtue of the relative physical properties of the two materials.
Any one who has opened a water bottle at cabin altitude after launch knows the pressure differential has an effect on the clear plastic bottle, the bottle will snap and crack, audibly.
Simplistic? Most problems start just that way.
The poly separator in the batteries is twenty five microns in thickness. The standard is a minimum of ten, to a maximum of forty (microns) dependent on application, (from the industry website I posted.
These batteries have a patent failure profile, consistent with the FAA considerations, the research data, and the evidence of failures since 2006.
Including the dramatic failures which caused the Japanese safety board and FAA to ground the fleet.
bill
I don't think the problem is mysterious. The actual temperature range for suitable performance of the poly may be much more narrow than that allowed.
I've had experience with plastics in normal temps. When it gets cold, it disintegrates, when it gets hot, it loses its resilience, and expands/contracts sufficiently to destroy its "shape". Since the perforations in this application are critical, my guess is that the poly deforms, the perforations change dimension, and allow short circuiting, which greatly accelerates the deterioration, and causes the need to "replace" the unit. Feverishly replaced, as Boeing has shown.
Last edited by Lyman; 9th Feb 2013 at 14:35.