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seat55a
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Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 2:57 am

Quote:
The European planemaker said late Thursday that it has decided to revert to nickel-cadmium batteries for the A350.
http://www.nytimes.com/aponline/2013.../14/us/ap-us-airbus-batteries.html
 
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zeke
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 4:01 am

Yet another lesson learned.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
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n797mx
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 4:04 am

Saw this coming. Maybe the should ask Musk for help if they ever change their minds to go back? 
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rotating14
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 5:14 am

Hhmnmm, so with this change of battery type, does this change any design that was frozen prior to this? Weight changes also??
 
panampaul
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 5:28 am

Quoting n797mx (Reply 2):
Saw this coming. Maybe the should ask Musk for help if they ever change their minds to go back?

Musk might be stuck on the side of the road...

Stalled Out on Tesla’s Electric Highway
 
dougbr2006
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 10:46 am

I think this is a wise move by Airbus especially as there is still no clearly defined source of failure on the 787 batteries.
Doing in now means probably no delays on implementing it on production aircraft though they state that the first test flight aircraft will have the original lithium-ion install so as not to delay / preserve the flight-test and entry-into-service schedule though for sure they will probably get the Ni-Cad's onto the rest of the flight test aircraft ASAP for final certification reasons.

You can probably be sure that Airbus have been do a work around on the lithium-ion system architecture and how to revert back to Ni-Cad since the 787 incidents caused the grounding and can implement the changes relatively easily. I would guess the changes may involve the monitoring and charging circuits which may only be box changes with obviously the main change probably being a larger and heavier battery and associated structure, cooling and venting system. How much extra weight will probably not effect things too much. Theses guys know what to do with respect of weight changes.

What this does in way of effecting the FAA on the 787 is probably very little unless the FAA panics due to the public nature of the proposed withdrawal by Airbus in using the lithium-ion technology on the primary electrical systems of the A350. There is use of these batteries on the A380, but mainly on a secondary role and as yet with no issues. Airbus are probably checking those batteries and in service failure etc. If they see a problem you can be sure they will remove them from their flagship aircraft.

Looks like Airbus are gaining free assistance and less of a personal learning curve through the problems on the 787 both during production and now with the batteries.

Boeing has a great product which eventually is going to prove to be a reliable money maker for the airlines, but the financial punishment that Boeing has taken due to all the issues in its development will make them take more time and care in their next big program that's for sure.
 
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anfromme
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 10:51 am

I'm slightly surprised at this step, I have to say.

In any case, according to a Reuters report, Airbus intends to perform the first few test flights with Li-Ion batteries (which are presumably already installed on MSN001) and then switch its test fleet to NiCd before EIS.
They state that they still have an intention to mature Li-Ion technology for airplane use in the future but are making the switch to avoid any risk to the A350 schedule due to uncertain certification requirements.

The NiCd batteries are expected to be supplied by SAFT, the same contractor that would have provided the Li-Ion batteries for the A350.

Makes me wonder - I am sure Airbus is in constant contact with aviation authorities; given that they are now reverting back to NiCd to effectively save time and be able to stick to their intended A350 EIS date - what conclusions does this allow regarding how long the 787 is still going to be grounded? Seems to me like there is still huge uncertainty about any permanent fix and how to implement it.
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71Zulu
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 11:01 am

Quoting PanAmPaul (Reply 4):
Musk might be stuck on the side of the road...

Maybe you should read this....

http://www.teslamotors.com/blog/most-peculiar-test-drive
Clickable links only please!
 
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Pellegrine
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 11:07 am

Not surprised at all. I have not commented on the Boeing threads, but I do think their Li-Ion chemistry was poorly mistaken. They should have used a metallic chemistry like LIP or LNMC and not a more chemically unstable lithium cobalt oxide.

Airbus will most likely switch back to Lithium-Ion/Polymer technology in the future.
oh boy, here we go!!!
 
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RayChuang
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 11:29 am

Given that the A350XWB is NOT a "bleedless" engine airliner, this is more a symbolic gesture. I believe most electrical accessories on the A350XWB will be powered off bleed-air systems.
 
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anfromme
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 11:39 am

Quoting RayChuang (Reply 9):
Given that the A350XWB is NOT a "bleedless" engine airliner, this is more a symbolic gesture. I believe most electrical accessories on the A350XWB will be powered off bleed-air systems.

Not just that, but the whole airplane architecture relies less heavily on electrical systems; Boeing replaced large parts of what in, say, the 777 would be the hydraulic and pneumatic systems with electrical ones in the 787. Airbus didn't take electrification that far on the A350.
This will surely make the task of replacing NiCd for Li-Ion in the A350 much easier, as the loads and voltages involved are much lower than they are on the 787, i.e. it's less costly to come up with a NiCd alternative that can still support the electrical systems on board the A350.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 11:53 am

Quoting 71Zulu (Reply 7):
Maybe you should read this....

http://www.teslamotors.com/blog/most...drive

Not aviation-related, but still very interesting reading; thanks for that!
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nomadd22
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 12:17 pm

I'm a little surprised they didn't wait a little longer. Certification changes might not just be for lithium, but for all battery types.
Anon
 
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Pellegrine
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 12:23 pm

Quoting nomadd22 (Reply 12):
Certification changes might not just be for lithium, but for all battery types.

It will be for Lithium-Ion/Polymer.
oh boy, here we go!!!
 
dougbr2006
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 12:34 pm

Quoting nomadd22 (Reply 12):

I'm a little surprised they didn't wait a little longer. Certification changes might not just be for lithium, but for all battery types.

Nicad batteries are flying in almost all new aircraft from Boeing's / Airbus to Citations / Gulfstreams to Helicopters / other GA twins an singles. It's a proven technology and in all my time working with Ni Cad batteries on Eurocopter helicopters we never experience a thermal runaway or other technical issue. A well maintained Ni Cad is reliable and safe.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 12:37 pm

Quoting nomadd22 (Reply 2):
I'm a little surprised they didn't wait a little longer. Certification changes might not just be for lithium, but for all battery types.

NiCad batteries are proven technology. The A350 test program is very tight with no room for error and certification changes could require extra work and might delay the EIS. Airbus don't want to gamble.

[Edited 2013-02-15 04:38:42]
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spokemd
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 1:40 pm

How much weight will this add to the each plane?
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rfields5421
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 1:53 pm

Quoting rotating14 (Reply 3):
Hhmnmm, so with this change of battery type, does this change any design that was frozen prior to this? Weight changes also??
Quoting spokemd (Reply 16):
How much weight will this add to the each plane?

The physical size of the battery compartments will have to be approx 3x larger than the design for the LI battery.

For the B787 the weight change would be from a man portable battery approx 50 lbs to a battery requiring mechanical assistance to move and change weighing near 200 lbs.

The A350 will have to change the battery storage enclosure, and spacing, but the biggest change will be to enable some type of mechanical lift device to enable a battery change to occur - IF the A350 is designed like most other aircraft for where the battery packs are located.

The loss of payload capacity will be minor - under 300 lbs. Maintenance is the bigger issue.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 1:54 pm

I believe that by staying with a bleed-air system, the A350XWB only needs a relatively small NiCad battery to start the systems that power up the APU and the Rolls-Royce Trent XWB engines. Given the size of the A350XWB, battery size is not so much an issue.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 2:10 pm

Quoting rfields5421 (Reply 18):
The loss of payload capacity will be minor - under 300 lbs. Maintenance is the bigger issue.

You're comparing it to the 787 which requires far more battery power. I suspect the A350 batteries will be a lot smaller. Yes still bigger relative to the LI batteries but smaller than the equivalent 787 batteries.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 3:14 pm

Quoting 71Zulu (Reply 7):
Maybe you should read this....

http://www.teslamotors.com/blog/most...drive

Most of Tesla's post has been successfully rebutted by disinterested third parties: http://www.theatlanticwire.com/techn...laims-new-york-times-fakery/62149/

According to Jalopnik, the only actual witness to the test drive - a tow truck driver - also supports the NY Times review.

The takeaway is that Broder may not have driven the car the way Musk wanted him to, but that's kind of the point - consumers aren't always going to use your products in the exact way you intend. And that has parallels in the airline industry as well.

I like Elon Musk and what he's had to say about 787 batteries, but it seems to me that he's capable of playing both sides of the battery issue (probably because he can't accept that he's not the one guy with all the answers).

[Edited 2013-02-15 07:15:15]
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 3:26 pm

Quoting spacecadet (Reply 20):
Most of Tesla's post has been successfully rebutted by disinterested third parties: http://www.theatlanticwire.com/techn...laims-new-york-times-fakery/62149/

According to Jalopnik, the only actual witness to the test drive - a tow truck driver - also supports the NY Times review.

The takeaway is that Broder may not have driven the car the way Musk wanted him to, but that's kind of the point - consumers aren't always going to use your products in the exact way you intend. And that has parallels in the airline industry as well.

I like Elon Musk and what he's had to say about 787 batteries, but it seems to me that he's capable of playing both sides of the battery issue (probably because he can't accept that he's not the one guy with all the answers).

And this all has nothing to do with the topic at hand.
oh boy, here we go!!!
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 3:36 pm

Quoting KarelXWB (Reply 15):
NiCad batteries are proven technology. The A350 test program is very tight with no room for error and certification changes could require extra work and might delay the EIS. Airbus don't want to gamble.

Which is very wise in my opinion. If clarity and possible design changes on the Lithium-Ion batteries have become clear, it will not be a bog change to install the Lithium-Ion in later produces A350's. But the current situation leaves no room for error or a further delay. So again I think this is a smart move to make in this stage of the program.

Quoting RayChuang (Reply 18):

I believe that by staying with a bleed-air system, the A350XWB only needs a relatively small NiCad battery to start the systems that power up the APU and the Rolls-Royce Trent XWB engines. Given the size of the A350XWB, battery size is not so much an issue.

Not as big an issue as on the B787, but still something to carefully consider.

Quoting zeke (Reply 1):

Yet another lesson learned.

Indeed.  .
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 3:48 pm

Quoting Pellegrine (Reply 8):
I have not commented on the Boeing threads, but I do think their Li-Ion chemistry was poorly mistaken. They should have used a metallic chemistry like LIP or LNMC and not a more chemically unstable lithium cobalt oxide.

At the time Boeing started development of the 787, most of the newer Li-Ion chemistries did not exist yet.

If Boeing makes a change (be it forced or by choice), I could see them go from the current lithium cobalt oxide with manganese to lithium nickel manganese cobalt (which was not developed until 2008) as it is closest to the current chemistry and is less volatile. They could also go with lithium iron phosphate, which is evidently the most thermally stable, though it would require an additional cell to provide the 75 Amp Hours of capacity.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 3:54 pm

Would Boeing be able to change the 787 to Ni-Cad batteries? Either way you look at it this does not make the 787 program look good. I am certain that Boeing will work out the changes needed and make the 787 a success but still, if I were a 787 customer I would not be happy.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 5:03 pm

Quoting JoePatroni707 (Reply 24):
Would Boeing be able to change the 787 to Ni-Cad batteries?

They could, but evidently it would require significant modifications to the electrical system. While I haven't seen any details, I have read that the 787's electrical system was designed specifically for use with lithium-ion batteries so Boeing appears to have chosen the technology for reasons other than smaller size and lighter weight.

As such, Boeing appears to be committed to Li-Ion on the 787 and will therefore have to sufficiently prove that they can contain thermal runaways / battery fires with the existing formulation and then develop a new Li-Ion battery using safer chemistries (such as lithium nickel manganese cobalt or lithium iron phosphate) that are far less likely to enter thermal runaway.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 5:36 pm

Quoting anfromme (Reply 10):
Not just that, but the whole airplane architecture relies less heavily on electrical systems; Boeing replaced large parts of what in, say, the 777 would be the hydraulic and pneumatic systems with electrical ones in the 787.
Quoting RayChuang (Reply 18):
I believe that by staying with a bleed-air system, the A350XWB only needs a relatively small NiCad

As has been reported multiple times in these threads - the size of the 787 battery is largely driven by the computer/avionics systems, not the electrical architecture. The electric architecture requires much more generating capability (offset by the deletion of bleed air system), but the battery would be effectively the same.
rcair1
 
airtechy
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 6:01 pm

There is no reason that the replacement nicad battery has to be one battery. It could be several batteries connected in series/parallel to yield 24 volts with the required amperage. As such, each individual battery could be designed to be removed/installed by one person.

Despite their claims to the contrary, I still haven't seen anyone explain why changing to a more electrified airplane requires a battery with more amperage. The electrical components that replaced the bleed air ones don't necessarily run off the batteries even in situations where an engine or the apu has died reducing available generator power.

Jim
 
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Pellegrine
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 6:07 pm

Quoting Stitch (Reply 23):
At the time Boeing started development of the 787, most of the newer Li-Ion chemistries did not exist yet.

? At the start of any development program there are many technologies which are not yet mature. The problems with lithium cobalt oxide were very well known. Furthermore LIP has been around since the mid-90s, and it is one of the safest lithium battery chemistries.

In any case, Airbus is smart to do this, as switching to Li-Ion/Poly technology later on will only achieve further efficiencies.
oh boy, here we go!!!
 
servantleader
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 6:52 pm

Smart move by Airbus from a strategic / PR standpoint alone -- it will likely force Boeing's hand to do the same as it builds on the public perception that LI-ion batteries are unsafe, which will in turn extend the period of time that the 787 stays grounded.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 7:11 pm

Reinforces my belief that the A380 and any other LiIon aircraft should also be grounded until their containment and battery designs can be "decertified" or replaced. Airbus claims A380 system is smaller, for emergency lighting only, and is not charged and discharged as often, still can't see how that matters at all when compared with the stated reasons for grounding the 787.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 7:17 pm

Quoting ikramerica (Reply 30):
Reinforces my belief that the A380 and any other LiIon aircraft should also be grounded until their containment and battery designs can be "decertified" or replaced. Airbus claims A380 system is smaller, for emergency lighting only, and is not charged and discharged as often, still can't see how that matters at all when compared with the stated reasons for grounding the 787.

And where are the A380 diversions which are traced back to the battery? Do not be bitter and show your colors so obviously.
oh boy, here we go!!!
 
Kaiarahi
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 7:21 pm

Quoting ikramerica (Reply 30):
Reinforces my belief that the A380 and any other LiIon aircraft should also be grounded until their containment and battery designs can be "decertified" or replaced. Airbus claims A380 system is smaller, for emergency lighting only

It's a fact, not a claim.
The batteries are smaller than those in a laptop. So to be consistent, all consumer electronics should be banned from the cabin / checked baggage - not to mention the flightdeck. Pilots should go back to paper and pencil and pocket calculators with alkaline batteries.

[Edited 2013-02-15 11:28:24]
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Pacific
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Fri Feb 15, 2013 8:32 pm

As reliable as the non-aviation press is, this is what I found.

Quote:
The European planemaker said it would use traditional nickel-cadmium batteries instead, as already used in the A380 and other models.

http://www.bbc.co.uk/news/business-2...77126
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sat Feb 16, 2013 5:56 pm

Quoting RayChuang (Reply 18):
I believe that by staying with a bleed-air system, the A350XWB only needs a relatively small NiCad battery to start the systems that power up the APU and the Rolls-Royce Trent XWB engines.

Huh? Both aircraft use the batteries to start the APU which then is used to start the main engines in normal use.

I imagine these APUs have similar demands for starting current. It is known that the 787 APU drives generators that produce more current, but that shouldn't mean that the starting current is much different.

In emergency use the batteries are used in conjunction with the RAT to power crucial avionics and control systems.

I also can't imagine these systems have very different current demands on the two aircraft.
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anfromme
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 12:32 pm

Quoting Revelation (Reply 34):
Huh? Both aircraft use the batteries to start the APU which then is used to start the main engines in normal use.

Not quite. Both aircraft also have a second electrical bay which houses the battery/ies to power the plane's main systems.

Quoting Revelation (Reply 34):
I imagine these APUs have similar demands for starting current. It is known that the 787 APU drives generators that produce more current, but that shouldn't mean that the starting current is much different.

One difference is that the A350 uses two batteries to start the APU, not one, like the 787 does. The A350 was supposed to get a total of four smaller Li-Ion batteries (apparently with a lower voltage rating than the 787's batteries), not two, i.e. the load would be spread across more batteries, and as far as I know the APU generator rating on the A350 is also going to be lower than on the 787.
Which in turn should also make it a bit easier to exchange Li-Ion for Ni-Cd on the A350, particularly as Airbus still hasn't completed certification, i.e. they won't have to re-certify any change they make at this point.
Also, if the APU power requirements were a) the only driving factor behind determining the 787's aft battery specs and b) identical on the 787 as on previous types, why would a higher voltage Li-Ion battery be required to begin with, given that APUs on other airplanes start just fine with a lower voltage?

Boeing themselves state that, instead of using a single 120kVA APU generator, the 787 has two 225kVA APU generators. I would imagine that battery requirements in both cases are quite different.

Quoting Revelation (Reply 34):
In emergency use the batteries are used in conjunction with the RAT to power crucial avionics and control systems.
I also can't imagine these systems have very different current demands on the two aircraft.

This article from Boeing would suggest otherwise:
http://www.boeing.com/commercial/aer...rticles/qtr_4_07/article_02_3.html
Particularly check the diagram at the bottom.
Currents, voltages and the whole electrical system design are vastly different from Boeing's previous airplanes. While we don't have quite the same detail on the A350's system from Airbus, the bits we do know would indicate that the A350's electrical systems are much closer to a traditional design than to the 787's.
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rwessel
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 1:06 pm

Quoting anfromme (Reply 35):
Also, if the APU power requirements were a) the only driving factor behind determining the 787's aft battery specs and b) identical on the 787 as on previous types, why would a higher voltage Li-Ion battery be required to begin with, given that APUs on other airplanes start just fine with a lower voltage?

Boeing themselves state that, instead of using a single 120kVA APU generator, the 787 has two 225kVA APU generators. I would imagine that battery requirements in both cases are quite different.

Don't confuse voltage and current. Both are 28V systems, but Boeing's requires at least somewhat more current. It's been reported that the main driver on battery capacity has been the load on the main ship's battery, and not the APU starting load, but having the same battery in both spots has a number of logistical advantages.

And you cannot compare the generator output of at A350s APU to the 787s in this context. The A350 APU may generate less electricity, but it also has to "generate" a large quantity of compressed air (which the 787's APU does not). That certainly counts when you're sizing the APU's turbine, and the size of the turbine is the main driver of how big your APU battery needs to be.
 
rcair1
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 1:53 pm

Quoting anfromme (Reply 35):
s, and as far as I know the APU generator rating on the A350 is also going to be lower than on the 787.

This is not relevant. Yes - the generator capacity on (alternators really) on the 787 APU are higher, but the APU does not generate compressed air for the bleed system. The starting load for the APU is not the factor.

The batteries on the 787 are sized primarily by aviation/computer load - not APU load and not 'all electric architecture'
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EPA001
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 2:07 pm

Quoting rcair1 (Reply 37):
The batteries on the 787 are sized primarily by aviation/computer load - not APU load and not 'all electric architecture'

Would that load be similar to those on the A350-XWB? Or are there significant differences between the B787 and the A350-XWB in this area?
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 4:28 pm

Quoting Revelation (Reply 34):
I imagine these APUs have similar demands for starting current. It is known that the 787 APU drives generators that produce more current, but that shouldn't mean that the starting current is much different.

I had done the research and found out the A350 APU is actually quite more powerful than the 787 APU. It's a 1700shp unit whereas the 787 APU is only a 1100shp one.
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Stitch
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 4:48 pm

Quoting anfromme (Reply 35):
Also, if the APU power requirements were a) the only driving factor behind determining the 787's aft battery specs and b) identical on the 787 as on previous types, why would a higher voltage Li-Ion battery be required to begin with, given that APUs on other airplanes start just fine with a lower voltage?

Boeing could have used different batteries for the Ship's and APU, however they chose to use the same one because you can MEL with an inoperative APU battery, but not an inoperative Ship's battery. By having the same unit, you can pull the APU battery to replace an inoperative Ship's battery and dispatch the plane.



Quoting Aesma (Reply 39):
I had done the research and found out the A350 APU is actually quite more powerful than the 787 APU. It's a 1700shp unit whereas the 787 APU is only a 1100shp one.

I'm guessing this is due to the need to drive the A350's pneumatic systems?
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 6:21 pm

Quoting anfromme (Reply 35):
One difference is that the A350 uses two batteries to start the APU, not one, like the 787 does.

The 787 does use two batterys--the Main battery assists the APU battery during APU start.

Quoting rcair1 (Reply 37):
The batteries on the 787 are sized primarily by aviation/computer load - not APU load and not 'all electric architecture'

The Main battery provides power to the Capt's instruments "momentarily" until the RAT deploys, it's not sized to do that for an extended length of time. If you lose all four engine generators, the APU won't start and the RAT doesn't deploy you better be VFR with a very long runway right in front of you - the battery won't last long.

I believe the main reason for the Main battery to be sized the way it is, is for backup power for the electric brakes during normal operation and normal brake power during towing operations.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 6:24 pm

Quoting rwessel (Reply 36):
And you cannot compare the generator output of at A350s APU to the 787s in this context. The A350 APU may generate less electricity, but it also has to "generate" a large quantity of compressed air (which the 787's APU does not). That certainly counts when you're sizing the APU's turbine, and the size of the turbine is the main driver of how big your APU battery needs to be.

Question being if the amount of power to start a 1,100 shp (820kW) APU is that much lower than the power required to start a 1,700 shp (1,300kW) unit. In any case I have to admit that I expected the 787's APU to be larger than the A350's, while it's actually the other way round.

Quoting rcair1 (Reply 37):
The batteries on the 787 are sized primarily by aviation/computer load - not APU load and not 'all electric architecture'

Regarding the sizing based on avionics/computer load being a bigger factor than APU start load: I know - which is why I mentioned the following:

Quoting anfromme (Reply 35):
Not quite. Both aircraft also have a second electrical bay which houses the battery/ies to power the plane's main systems.

Sorry if I wasn't clear about that - I focused on the APU because I was responding to a post that was primarily concerned with the battery-APU interaction.
I'm not sure if the 787 battery size was not partly driven by its "all electric architecture", though. I may miss something here, but I would expect that if you replace pneumatic and hydraulic systems with electrical ones the emergency battery would need to be able to cover those systems as well.

Quoting rwessel (Reply 36):
Don't confuse voltage and current. Both are 28V systems, but Boeing's requires at least somewhat more current.

As far as I could find, the batteries on the 787 are rated at 32V, not 28V?
Sorry if I wasn't clearly stating that I meant battery requirements in terms of currency, not voltage. As I understand, voltage is comparatively easy as a battery design requirement - connect two 1.5V batteries in series and you get 3V - while being able to get the required amperes (current) and storing a sufficient amount of Wh (ideally in a sufficiently small form factor) are much bigger challenges.
Having said that, I do think that the 787's use of four instead of two voltage types in its systems fed into the battery design specs and added complexity to the overall system, as there's more transforming to be done between the four voltages.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 6:34 pm

Quoting 7BOEING7 (Reply 41):
Quoting anfromme (Reply 35):
One difference is that the A350 uses two batteries to start the APU, not one, like the 787 does.

The 787 does use two batterys--the Main battery assists the APU battery during APU start.

Thanks for the clarification.
My main point was the total number of batteries that the load gets distributed among. AFAIK, Airbus was going to give the A350 four identically-sized batteries, vs. two on the 787. It's possible that the two main A350 batteries were also going to help the two APU batteries in the same manner as you state is the case for the 787's APU and main batteries. However, the principle remains that on the A350, the load was to be distributed among a higher number of batteries which in turn were smaller in size and capacity than their counterparts on the 787.

Quoting 7BOEING7 (Reply 41):
The Main battery provides power to the Capt's instruments "momentarily" until the RAT deploys, it's not sized to do that for an extended length of time. If you lose all four engine generators, the APU won't start and the RAT doesn't deploy you better be VFR with a very long runway right in front of you - the battery won't last long.

Again, thanks for the details!

Quoting 7BOEING7 (Reply 41):
I believe the main reason for the Main battery to be sized the way it is, is for backup power for the electric brakes during normal operation and normal brake power during towing operations.

Hmm - would make sense given that the 787's brakes are no longer hydraulically actuated, but electric.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 7:02 pm

Quoting anfromme (Reply 43):
AFAIK, Airbus was going to give the A350 four identically-sized batteries, vs. two on the 787.

And all 4 batteries are in the forward EE bay. Probably another reason to rethink Li-Ion, at least short term.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 7:38 pm

Quoting anfromme (Reply 35):
Boeing themselves state that, instead of using a single 120kVA APU generator, the 787 has two 225kVA APU generators. I would imagine that battery requirements in both cases are quite different.

I think the nominal case of starting the APU would require similar amounts of power. I'd imagine that one would not be putting load on the generators during starting, rather one would start the APU and let it stabilize before putting any loads onto the generator. As above, the A530 APU has the requirement to drive pneumatic systems as well, which may or may not be easy to unload during starting.

Quoting rcair1 (Reply 37):
The batteries on the 787 are sized primarily by aviation/computer load - not APU load and not 'all electric architecture'

I thought I read on the other thread that the determining factor was that the in the two engine out / RAT deployed scenario, the 787 needed battery power to drive the brakes upon landing. Both A/C should have pretty similar demands up to that point, but it's the electric brakes that make the difference.

Quoting Aesma (Reply 39):
I had done the research and found out the A350 APU is actually quite more powerful than the 787 APU. It's a 1700shp unit whereas the 787 APU is only a 1100shp one.

Thanks!
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 8:24 pm

In other threads, some knowledgeable people have said the 787 uses the main computers to monitor activities like fuelling, unlike other aircraft.

This was one suggestion for the higher than expected number of batteries being drained to the "lock out" level.

Anyone have reliable info of how the A350 will behave for similar operations - does it have a similar computer wake-up for basic maintenance?
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 8:49 pm

Quoting seat55a (Reply 46):
This was one suggestion for the higher than expected number of batteries being drained to the "lock out" level.

The incidents would also suggest that the 787 batteries are not too "powerful" but rather not enough.
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 8:55 pm

Quoting Aesma (Reply 47):
The incidents would also suggest that the 787 batteries are not too "powerful" but rather not enough.

Power delivery isn't the issue - capacity is. And if you run it longer than it's rated capacity, it doesn't matter how large the battery is.
 
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RE: Airbus Reverts To Nicad For 350 (AP Report)

Sun Feb 17, 2013 9:02 pm

Quoting seat55a (Reply 46):
Anyone have reliable info of how the A350 will behave for similar operations - does it have a similar computer wake-up for basic maintenance?

On most systems the A350 is a moderately modernized version of an A380 so find out how the A380 does it and you have a good guess of how the A350 does it. This has been the strategy for Airbus to lower the risks budget in the A350 program, they had a recent donor project they could take technologies from. The 787 program did not have this luxury, the 777 program was to old and they decided they had to take big jumps on several fronts. This bites them today but the frame architecture is there for 40 years so lets see what the Airliners verdict is around 2030 to see who laughs last  .

There is not saying that the A350 program has also gained with the 787 program plowing the track  Wow! , the batteries being just one example.

[Edited 2013-02-17 13:03:58]
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