TQ
2013-02-01 11:45:28
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SV: Fortsatta problem med B787 Dreamliner
It's impossible to know how long the 787 will be grounded, but we know enough now to make a reasonable guess. My guess is 6-9 months.
Here is my reasoning:
From information shared by the NTSB, we know enough about the design of the Lithium battery to see it has multiple issues. Some of these were picked up my Mr Musk.
- It is hard to be certain about the packs from the photos the NTSB has shared, but it looks to me that there are no individual
temperature monitors for the cells.
- Although it has been stated that the battery was not overcharged, a Reuters article on 25th quoted an investigation insider who said that only the overall battery voltage was recorded in the flight data recorder and the battery circuits are too damaged to recover useful information. This means the battery could have been unbalanced and an individual cell may have been overcharged.
- The photo makes it clear that there is no cell charge balancing system, the batteries are simply charged in series, with individual cell voltage monitoring.
- It is obvious that there is very little thermal protection of one cell from another, as Musk pointed out
- There is no cooling system that I can see
- After the battery caught fire the enclosure failed to contain the fire and spilled burning electrolyte into the electronics bay.
- There have been 10 other battery replacements on the ANA fleet of 17 aircraft (New York Times).
It is becoming plainer by the day that this is a very poor battery design with multiple issues. Personally I think it is far too pessimistic to call into question the suitability of Lithium battery technologies themselves. It's true they hold a lot of energy and flammable electrolyte, but the aircraft itself holds vast quantities of flammable jet fuel, which is perfectly safe if it is handled properly. The same is true of Lithium batteries. Lithium battery technology is actually mature enough so that cell failure is a rare event. I believe the battery can be designed to contain a cell failure.
Clearly Boeing will need a completely redesigned battery. The prospect of a software fix or small patch has gone. The cells will have to be much better protected from each other. There needs to be a cooling/heat dissipation system of some kind, and of course a new battery management system that actually works, perhaps with cell balancing. Given the need for testing, certification, installation, I expect the plane will be grounded for 6 months at least. Moving to a different battery technology would make things worse, because it would have knock on effects in the rest of the electrical system design, and would not fit the same slots in the electronics bays.
It's impossible to know how long the 787 will be grounded, but we know enough now to make a reasonable guess. My guess is 6-9 months.
Here is my reasoning:
From information shared by the NTSB, we know enough about the design of the Lithium battery to see it has multiple issues. Some of these were picked up my Mr Musk.
- It is hard to be certain about the packs from the photos the NTSB has shared, but it looks to me that there are no individual
temperature monitors for the cells.
- Although it has been stated that the battery was not overcharged, a Reuters article on 25th quoted an investigation insider who said that only the overall battery voltage was recorded in the flight data recorder and the battery circuits are too damaged to recover useful information. This means the battery could have been unbalanced and an individual cell may have been overcharged.
- The photo makes it clear that there is no cell charge balancing system, the batteries are simply charged in series, with individual cell voltage monitoring.
- It is obvious that there is very little thermal protection of one cell from another, as Musk pointed out
- There is no cooling system that I can see
- After the battery caught fire the enclosure failed to contain the fire and spilled burning electrolyte into the electronics bay.
- There have been 10 other battery replacements on the ANA fleet of 17 aircraft (New York Times).
It is becoming plainer by the day that this is a very poor battery design with multiple issues. Personally I think it is far too pessimistic to call into question the suitability of Lithium battery technologies themselves. It's true they hold a lot of energy and flammable electrolyte, but the aircraft itself holds vast quantities of flammable jet fuel, which is perfectly safe if it is handled properly. The same is true of Lithium batteries. Lithium battery technology is actually mature enough so that cell failure is a rare event. I believe the battery can be designed to contain a cell failure.
Clearly Boeing will need a completely redesigned battery. The prospect of a software fix or small patch has gone. The cells will have to be much better protected from each other. There needs to be a cooling/heat dissipation system of some kind, and of course a new battery management system that actually works, perhaps with cell balancing. Given the need for testing, certification, installation, I expect the plane will be grounded for 6 months at least. Moving to a different battery technology would make things worse, because it would have knock on effects in the rest of the electrical system design, and would not fit the same slots in the electronics bays.
It's impossible to know how long the 787 will be grounded, but we know enough now to make a reasonable guess. My guess is 6-9 months.
Here is my reasoning:
From information shared by the NTSB, we know enough about the design of the Lithium battery to see it has multiple issues. Some of these were picked up my Mr Musk.
- It is hard to be certain about the packs from the photos the NTSB has shared, but it looks to me that there are no individual
temperature monitors for the cells.
- Although it has been stated that the battery was not overcharged, a Reuters article on 25th quoted an investigation insider who said that only the overall battery voltage was recorded in the flight data recorder and the battery circuits are too damaged to recover useful information. This means the battery could have been unbalanced and an individual cell may have been overcharged.
- The photo makes it clear that there is no cell charge balancing system, the batteries are simply charged in series, with individual cell voltage monitoring.
- It is obvious that there is very little thermal protection of one cell from another, as Musk pointed out
- There is no cooling system that I can see
- After the battery caught fire the enclosure failed to contain the fire and spilled burning electrolyte into the electronics bay.
- There have been 10 other battery replacements on the ANA fleet of 17 aircraft (New York Times).
It is becoming plainer by the day that this is a very poor battery design with multiple issues. Personally I think it is far too pessimistic to call into question the suitability of Lithium battery technologies themselves. It's true they hold a lot of energy and flammable electrolyte, but the aircraft itself holds vast quantities of flammable jet fuel, which is perfectly safe if it is handled properly. The same is true of Lithium batteries. Lithium battery technology is actually mature enough so that cell failure is a rare event. I believe the battery can be designed to contain a cell failure.
Clearly Boeing will need a completely redesigned battery. The prospect of a software fix or small patch has gone. The cells will have to be much better protected from each other. There needs to be a cooling/heat dissipation system of some kind, and of course a new battery management system that actually works, perhaps with cell balancing. Given the need for testing, certification, installation, I expect the plane will be grounded for 6 months at least. Moving to a different battery technology would make things worse, because it would have knock on effects in the rest of the electrical system design, and would not fit the same slots in the electronics bays.
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