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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 18th Mar 2013, 04:05
  #1021 (permalink)  
 
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So bench testing is superior to flight testing and associated ground handling..?

Flight Global:

Boeing's certification plan, which was approved two days ago by the US Federal Aviation Administration, calls for hundreds of hours of laboratory testing and a single flight test to validate the systems.

"That will be the extent of flight testing," says Mike Sinnett, Boeing 787 chief project engineer. "It's not an extensive flight testing programme."
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Old 18th Mar 2013, 13:25
  #1022 (permalink)  
 
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Where does the BMU data goes?

Quoting the NTSB report
http://www.ntsb.gov/investigations/2...787_3-7-13.pdf
BMU1 monitors for cell overcharge, overdischarge, overheating, and imbalance; controls the cell balancing function when any cell reaches a predetermined threshold; and is the source of voltage for the BCU. BMU2 provides a redundant monitor for cell overcharge. BMU3 controls the contactor and provides additional monitoring for battery and cell overcharge. BMU4 monitors for cell overdischarge and high current charge. If any of the battery monitoring thresholds were exceeded, the BMU was designed to send a signal to the BCU to discontinue charging. The BMU main circuit card and sub-circuit card do not contain nonvolatile memory (NVM), and none of the BMU data are recorded on the FDR.
So if it is not stored in NVM, nor recorded in the FDR, where does the data about cell overdischarge goes?

Last edited by fgrieu; 18th Mar 2013 at 14:49. Reason: typo
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Old 18th Mar 2013, 13:28
  #1023 (permalink)  
 
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ITman
So bench testing is superior to flight testing and associated ground handling..?
Often it is. In flight tests the testing is constrained to nominal (normal) usage of the systems they can be pushed to the edge of normal but cannot be exception tested.
In ground testing with all the aircraft systems running - Boeing has test bays with all the production level systems connected but in labs on the ground - the test script can include failures of all types in any areas required . A multi-rotation flight series can be accurately emulated for a baseline then failures of various systems added to more repeated runs. Some of these failures may be impossible to trigger in a flying aircraft or 'catastophic' so dangerous to implement in an airborne aircraft. Even pressure and temperature changes cannot be run in a controlled script in a live aircraft.
Overall the more controlled certification level testing is far more efficient and complete in a ground test than in an unpredictable and limited air test.
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Old 18th Mar 2013, 15:47
  #1024 (permalink)  
 
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Ian W:

Overall the more controlled certification level testing is far more efficient and complete in a ground test than in an unpredictable and limited air test.
Exactly. I'm hoping that Boeing/Thales/GS Yuasa/Securaplane will continue lab testing until the nature of these failures and the battery system characteristics are fully understood.

Unfortunately, I suspect that once Boeing gets the fireproof box solution certified, the battery problem will be put on their back burner (figuratively). The knowledge gained could be used to produce a better design for the next derivative or model.
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Old 18th Mar 2013, 17:54
  #1025 (permalink)  
 
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@EEngr
Unfortunately, I suspect that once Boeing gets the fireproof box solution certified, the battery problem will be put on their back burner (figuratively).
I expect Boeing won't be in a position to wipe their brow and sit back and relax.

The failure rate of batteries once returned to service will need to return to the one-in-a-billion chance per flight hour as I believe that is the certification requirement.

Also, as it appears a failure of the APU battery triggers a failure of the APU, if the APU battery keeps failing at what is considered too high a rate, the 787 will not be able to be certified beyond ETOPS-180 and that is going to cripple it with operators like QF, NZ and others who were planning ETOPS-240 or ETOPS-330 missions.

Last edited by Kiskaloo; 18th Mar 2013 at 17:55.
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Old 18th Mar 2013, 19:23
  #1026 (permalink)  
 
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Kiskaloo:

The failure rate of batteries once returned to service will need to return to the one-in-a-billion chance per flight hour as I believe that is the certification requirement.
Perhaps not if the fireproof box reduces the criticality of the failure. If it can be demonstrated that it is safe to continue flight with a smoldering battery, then the 10E-9 per hour requirement can be reduced. Of course, this depends on whether Boeing will demonstrate containment for some period of time vs permanent containment.

As for ETOPS, that's cutting it pretty close with probabilities. Now its not a probability per hour figure, its a probability that the battery will/will not be available during some flight beyond a range from an alternate. Which is probability per hour times that range (in time). The difference between no ETOPS (a 30 minute diversion range?) to ETOPS-330 is 11:1. Cutting probabilities that close is a dangerous game. In other words, if you can't tolerate the APU battery loss with a 330 minute diversion, you can't for a 30 or 60 minute diversion either. Which pretty much means no flying. On the other hand, if the RAT provides a non-time limited critical power source, then the APU is not a factor anyway.

Same thing goes for the main battery. Look at its braking function. That is a non-time dependant requirement. No matter how long the flight, you need the same braking power at the end. If the probability of failure during a 330 minute diversion is intolerable, then a factor of ten isn't going to buy you more safety.
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Old 18th Mar 2013, 21:59
  #1027 (permalink)  
 
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What happens if BOTH batteries start to smoulder?
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Old 18th Mar 2013, 23:56
  #1028 (permalink)  
 
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http://www.boeing.com/787-media-reso...ry-English.jpg

If the schematic of the BMU wiring harness is accurate, then apart from beefing up the design, there is no change in the data sampled i.e. 8 x voltage and 1 x temperature.
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Old 19th Mar 2013, 00:39
  #1029 (permalink)  
 
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EEngr:
Same thing goes for the main battery. Look at its braking function. That is a non-time dependant requirement. No matter how long the flight, you need the same braking power at the end. If the probability of failure during a 330 minute diversion is intolerable, then a factor of ten isn't going to buy you more safety.
I have not seen it in writing, but the discussion in the Webex seemed to imply that for a plane which is landing the brakes can be powered from the RAT or some other short duration battery, and that the ability to brake using the main battery is only needed when the aircraft is being towed on the ground with neither engines nor APU running.
The APU battery is more significant, since it appears that, regardless of other power sources, loss of the APU battery will render the APU inoperable. I would imagine that taking off with the APU battery inop would not be allowed.

Last edited by inetdog; 19th Mar 2013 at 00:40.
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Old 19th Mar 2013, 06:14
  #1030 (permalink)  
 
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@fgrieu,

So if it is not stored in NVM, nor recorded in the FDR, where does the data about cell overdischarge goes?
Presumably notable events are input to the aircraft's on board diagnostics system and maintenance logger (there's probably correct words for that kind of thing that I don't know).

As an electronics engineer I find it astonishing that the battery management systems don't retain a running log of the battery's operating conditions and status. It's trivial to do that sort of thing, and that sort of data is invaluable when you have problems like this. You'd have to be spectacularly unimaginative or tight fisted not to design that in, especially as it would cost $1.50 in parts to do it.

@ITman

So bench testing is superior to flight testing and associated ground handling..?
It can be, but it depends on knowing what the full range of possible operating conditions are, including severe extremes caused by other problems (eg loss of bay heating). I suspect that Boeing and partners have a rough idea on what those are, but it smells like they've not got many measurements or logs of what they actually go through. What's the bet Boeing lost some ancient battery specialist from the payroll and didn't replace him/her?

That in turn suggests that the spec for the battery was drawn up incorrectly, which is going to be down to a lack of experience on someone's part. That is an assumption backed up by everyone being mystified as to what's going on. The batteries are passing their existing bench test, but that's clearly not thorough enough. Anyway Boeing seem to want to fly the thing just once. That's hardly likely to fill in any knowledge gaps; only sustained operational use with full logging of everything will reveal what's going on.

Thing is, they've changed things. And worse still commercial pilots are going to be very wary of the battery, so they're going to make as little use of it as possible. It might be that the causal conditions don't arise again, meaning that Boeing may never learn what the problem actually is. And that will always leave a nagging doubt about the whole aircraft.
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Old 19th Mar 2013, 07:58
  #1031 (permalink)  
 
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This was sent to me this morning and I thought it might be of interest. It does not reflect my views (quite the opposite in fact) and I am not endorsing it in any way :

Info. about the Boeing 787 Dreamliner by Boeing engineers

The guy who wrote the following is retired from Boeing.
Thought you might find it interesting...... sorta "insider stuff"......
--------------------------------------------------------------------------------------------------------------------------
For one thing the problem may not be with the batteries themselves,
but with the control system that keeps the charge on them at a given level.
And the 'battery problem" is just one problem in many.
Last week I had my regular monthly lunch with 5 fellow Boeing engineers (all but one retired)
and we talked at length about what we call the "nightmare liner". We all agreed we will not book a flight on one.
The one engineer still working (at age 74!!) says the news from inside is not good,
and that there are no quick fixes for the multitude of problems that the 787 has.
The disaster began with the merger with McDonnell-Douglas in the mid-90s.
The McD people completely took over the Board and installed their own people.
They had no experience with commercial airplanes, having done only "cost-plus" military contracting,
and there are worlds of difference between military and commercial airplane design.
Alan Mulally, a life-long Boeing guy, was against outsourcing as President of Boeing Commercial Division,
but instead of making him CEO after he almost single-handedly saved the company in the early 90s,
the Board brought in Harry Stonecipher from McDonnell-Douglas, who was big on outsourcing.
Stonecipher was later fired for ethics violations, and then the Board brought in Jim McNerney,
a glorified scotch tape salesman from 3M and big proponent of outsourcing, to develop the 787.
(Alan Mulally left to become CEO of Ford and completely rejuvenated that company.)
McNerney and his bean-counting MBAs thought that instead of developing the 787* in-house*
for about $11 billion, they could outsource the design and building of the airplane for about $6 billion.
Right now they are at $23 billion and counting, three years behind in deliveries, with a grounded fleet.
That's typical for military contracting, so McNerney and the Board probably think they are doing just fine
. But it will destroy Boeing's commercial business in the same way McDonnell wrecked Douglas when
they took over that company decades ago.
Boeing had a wonderfully experienced team of designers and builders who had successfully created
the 707, 727, 737, 747, 757, 767, and 777 in-house, always on-time,
and mostly within budget, and with few problems at introduction.
That team is gone, either retired or employed elsewhere.
(I took early retirement after the McD takeover of Boeing because I knew the new upper management team was clueless.)
The 787 was designed in Russia , India , Japan , and Italy .
The majority of the airplane is built outside the US in parts and shipped to Seattle and Charleston for assembly.
*Gee, what could possibly go wrong? * Answer: just about everything.
Because the McD people that now run Boeing don't believe in R&D, the structure of the airplane will be tested *in service*.
Commercial airplanes in their lifetime typically make ten times as many flights and fly ten times as many flight hours as military airplanes,
so the argument that composite structure has been "tested" because of the experience of composite military airplanes is just so much BS.
So structure is a big issue. The airplane is very overweight.*
The all-electric controls have the same lack-of-experience issue that the structure has.*
The only good news for me is that the Boeing pension plan is currently fully funded,
although it may not stay that way as the 787 catastrophe develops.
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Old 19th Mar 2013, 08:24
  #1032 (permalink)  
 
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inetdog

The APU battery is more significant, since it appears that, regardless of other power sources, loss of the APU battery will render the APU inoperable. I would imagine that taking off with the APU battery inop would not be allowed.
Not so, the APU Battery is a Cat C MEL item; without it the machine can fly, as long as the Engine Generators are working normally, but is restricted to 180 mins ETOPS.
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Old 19th Mar 2013, 09:48
  #1033 (permalink)  
 
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Capetonian

I've seen that 'email' pop up a few times across various internet boards now.
I suspect it's a hoax with a few grains of truth attached.

We'll see.

Last edited by TURIN; 20th Mar 2013 at 10:40.
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Old 19th Mar 2013, 10:38
  #1034 (permalink)  
 
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Overall the more controlled certification level testing is far more efficient and complete in a ground test than in an unpredictable and limited air test.
As demonstrated by a new model released to service,which has such major incendiary problems that the entire fleet is grounded?

Sure does inspire confidence.....NOT
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Old 19th Mar 2013, 13:20
  #1035 (permalink)  
 
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CockneySteve
Quote:
Overall the more controlled certification level testing is far more efficient and complete in a ground test than in an unpredictable and limited air test. unquote

As demonstrated by a new model released to service,which has such major incendiary problems that the entire fleet is grounded?

Sure does inspire confidence.....NOT
Steve - a word in your shell-like...

You are conflating the scenarios used in the original testing with the capabilities and limitations of ground testing. The original test scenarios obviously did not cover the failures that have occurred, but included a lot of flight testing. This is a limitation of the scenario writers and approvers not of the ground or air testing. A full set of scenarios and test cases that requires extreme failures of systems can only be run successfully on the ground. The aircraft testing can only be of standard battery performance and this nominal testing is just as easy on the ground.

The one area I would test in a live aircraft is having airline first line maintenance and push crews do repeated 'turn around's and routine towing with one of the 'spare' 787s currently clogging Everett. If the FAA would allow it fly a 787 on multiple short rotations and ground turn arounds. While that was happening I would watch the ground crews and see what they really did as opposed to what they say they do and people expect them to do. I suspect that something in the ground handling is unexpected. Does the ground crew safety man ride the brakes running down the main battery when the aircraft is towed? Do they routinely leave nav lights on running down the battery(ies), do they open the electronics bay door and leave it open which on frosty nights could let batteries get too cold etc.

One thing that you can be sure of is that Boeing is very very aware that if one of these batteries causes even a minor problem in the next 5 years the 787 may go the way of the Comet which would be devastating for the company. So they have nothing to gain and everything to lose if these tests are skimped.

As it is, the 787 will be one of those aircraft that is repeatedly pilloried by 'the trade media' in the same way as the Harrier (until the Falklands) and the Osprey - until it went 'live' in action.

Last edited by Ian W; 19th Mar 2013 at 13:25.
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Old 20th Mar 2013, 03:39
  #1036 (permalink)  
 
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Ian W:

The one area I would test in a live aircraft is having airline first line maintenance and push crews do repeated 'turn around's and routine towing with one of the 'spare' 787s currently clogging Everett. If the FAA would allow it fly a 787 on multiple short rotations and ground turn arounds. While that was happening I would watch the ground crews and see what they really did as opposed to what they say they do and people expect them to do. I suspect that something in the ground handling is unexpected. Does the ground crew safety man ride the brakes running down the main battery when the aircraft is towed? Do they routinely leave nav lights on running down the battery(ies), do they open the electronics bay door and leave it open which on frosty nights could let batteries get too cold etc.
That's all good information to have. But that's not the place to capture it. The ground crews know that they are being watched and will work to the rules.

The best way to capture this sort of thing is to have good relationships between customers operations and Boeing engineering. Good enough so that the customer people can tell Boeing (without the risk of word coming back to bite them) the way things really work out on the flight line.

We learned far more in engineering by walking the factory floor and speaking to the mechanics building the things. Back when we had engineers that were not afraid of getting their MBA suits dirty, that is.
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Old 20th Mar 2013, 10:42
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That's all good information to have. But that's not the place to capture it. The ground crews know that they are being watched and will work to the rules.
Spot on Sir.
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Old 20th Mar 2013, 11:42
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Yes they will know they are being watched and yes they will work -to the rules-. However, that in itself will throw up areas that the writers of the rules did not expect. Where the experts who wrote them always did something because they always did it and didn't think to put it in the procedures. I would like to think that the turn around procedures were fully checked initially and when the aircraft was handed over that the procedures on site were fully checked as part of the training. But 'like to think' is an assumption that is often unsafe. Even showing that when the procedures are followed repeatedly the problem does not occur is a useful result. I emphasize repeatedly because that repetition may not have occurred during normal testing.

I think that rather in the way there are fatigue test rigs that keep ahead of the aircraft in fatigue life to identify weak spots, perhaps battery fatigue rigs are needed that emulate a day in the life of a hard worked battery with all the pressure, temperature, charging and discharging cycles running at worst case.
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Old 20th Mar 2013, 16:33
  #1039 (permalink)  
 
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I think that rather in the way there are fatigue test rigs that keep ahead of the aircraft in fatigue life to identify weak spots,
It is however quite usual to find cracks on the in-service aircraft which have not yet occured (or even will not occur during the whole test), simply because the test conditions do perfectly match the design requirements, but unfortunately not the real operational life... There have always been surprises, there will allways be surprises. That´s why we design and test with safety margins and second lines of defense.
So unless we find a production quality issue to be the cause of the failure(s), clearly the tests were not simulating real life. This can happen for new technology. So analogue to the fatigue test: add temperature cycling, environmental exposure etc. to the test, and you may obtain better results. Experience however shows that we can ignore these effects. Unfortunately for batteries we still do not know what we have to simulate (Temperature, Pressure, Vibrations...) to have an effective test. If we test the wrong conditions, it does not help if we are far ahead of the real fleet with respect to simulated flight hours. It is easy to add costs to a test by adding new aspects. It is hard to add relevance to a test...
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Old 20th Mar 2013, 21:13
  #1040 (permalink)  
 
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You are correct that fatigue tests do not always show up what fails in real life but that does not mean that they are not useful to highlight areas of weakness that will show up. It would be a good thing to do anyway with an over-insturmented set of batteries to increase knowledge of the effects of continual cycling.
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