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FAA Grounds 787s

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FAA Grounds 787s

Old 27th Feb 2013, 15:50
  #1041 (permalink)  
 
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You can talk about the differing batteries until you are blue in the face but most pilots just know that when they do a certain thing, a certain thing happens.
They are not technicians who are versed in all the ins and outs of the various systems.
They want something that does what it says on the box and doesn't introduce too many wobblies into it.
Being of the old school I'd find it hard to adapt to a cockpit that didn't have opening windows! Have I missed something or has this aircraft not got those?
If not then a large part of design philosophy seems to have gone wildly astray.
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Old 27th Feb 2013, 17:33
  #1042 (permalink)  
 
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gcal

No open window.
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Old 27th Feb 2013, 17:36
  #1043 (permalink)  
 
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Cockpit windows on the B787.

gcal,

The cockpit of the B787 does not have any opening windows, but an escape hatch in the roof.

Exactly the same arrangement can be found on the B747 and on other aircraft types, for example ATR42/72 and Bombardier Q400.

In other words, this arrangement is not a new design philosophy.

Last edited by grebllaw123d; 27th Feb 2013 at 17:47.
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Old 27th Feb 2013, 17:55
  #1044 (permalink)  
 
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Thales 2005 hoot about selecting the greatest battery in the history of aviation

http://www.s399157097.onlinehome.us/...06_12_2005.pdf
Note from this 2005 document that Thales says they selected the battery - of course they might have had guidance from their customer.

In 2005 LiCo may well have been the best "proven" technology, and having made that choice, the aerospace industry does not lightly change its path. There is so much "process" involved - drawings, procedures, manuals, ICDs (Interface Control Documents) - that even after two fires and an OAG fleet the best way forward is still to leave everything as unchanged as possible, and put a steel box around it.

In the 80's and 90's we joked about paperwork, saying we couldn't launch until the weight of the paperwork equaled the weight of the vehicle. Those were the good old days. (We also joked that a camel was a horse developed by a committee. Today meeting-rooms full of brain-deadened team players are busily turning out camel after camel.)
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Old 27th Feb 2013, 18:45
  #1045 (permalink)  
 
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poorjohn said:
(We also joked that a camel was a horse developed by a committee. Today meeting-rooms full of brain-deadened team players are busily turning out camel after camel.)
We also would describe an egregiously bad piece of engineering as developed by a committee of camels.
I don't think that the battery system has risen to that level yet, but I think a good attempt is being made.

Last edited by inetdog; 27th Feb 2013 at 18:46.
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Old 27th Feb 2013, 19:59
  #1046 (permalink)  
 
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In echo to the post from Hi_Tech :

Flightglobal - Leahy questions 787’s heavy reliance on electrical power
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Old 27th Feb 2013, 21:42
  #1047 (permalink)  
 
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Bold Pilot?

lomapaseo Quote:-"I'm willing to do it with engines every day, so I'm willing to do it with their safety boxes"

Off you go then, Chuck.

I think that you will find that those engines under your wings are a little more tried, tested and protected than the latest electrickery product from Boeing.

That's what's wrong with aviation nowadays - not enough of the Right Stuff!
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Old 27th Feb 2013, 21:51
  #1048 (permalink)  
 
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I think that's the main issue, from a pilot perspective.

Engines: Outside the pressure hull, multiple fire (heat) detection systems, multiple extinguishing systems (that work on the materials present), fuel, electrical, air and hydraulic isolation with one switch plus hot bits contained within a tested and certified armoured cylinder.

787 batteries: None of the above.
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Old 27th Feb 2013, 22:40
  #1049 (permalink)  
 
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Hi Tec
So they have these two large electrically driven compressors that require 270V DC power.
Make that four. Two per air con system.

After an aircraft lands from a flight, as engine bleed is still available, it is used to start APU as in B777.
B777 is the only type I can think of with a pneumatic starter (in addition to electric).
Are there others? A380 perhaps?


Let me give an emergency situations where there is a total power failure on B777 and B787 at cruise altitude of 40,000 ft.
On a Boeing 777 the bleed air from the engines is still available, (Bleed valves stay open when power is removed), and this is used to automatically start the APU through a pneumatic starter. This source is unlimited unlike a battery with a fixed charge. Bleed air is also available for pressurization of aircraft, so the crew, if they are 40,000 ft, need not worry about pressurization, and when APU starts, power is also restored. Crew have to deal with only the electrical failure during this critical period.
Have there been many (any?) total electrical power failures that haven't been caused by loss of the engines too? I can't think of any.

Point being, the 787 has the same redundancy in regard to engine failure but increased redundancy with regard to electrical power-by a long way.
Four main generators instead of two.
Two auxiliary generators instead of one.

These power conversions generate heat and these panels that are located in the middle of the aircraft (Approximately below the first row of economy seats on ANA), are cooled using 2 large refrigeration units.
Not quite. There are two independent liquid cooling systems. Not refridgeration units. The power conversion units, ATRUs and CSMUs use this cooling fluid in a closed circuit.


Otherwise you're spot on.
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Old 27th Feb 2013, 23:11
  #1050 (permalink)  
 
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RAT

Main bat is needed for brakes after touchdown.

@Golf-Sierra
4 actuators x 8 wheels = 32 actuators. 150A /32 = that's just 4.68A per actuator.
Sounds reasonable.

For inflight needs, the RAT will suffice.

B787 with RAT deployed - Canon Digital Photography Forums
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Old 28th Feb 2013, 00:01
  #1051 (permalink)  
 
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OT...wait until the wake vortex that this bird creates gets out....

(upswept bottom wing and outboard flaps)

virtually ALL of the images of the 787 show the RAT deployed on ARR...WTF?!?!

I would really like to see the fuel econ numbers with the 2 gen/engine....

edit:

So if you go EO on the 787...where does the power to op everything come from?

Last edited by FlightPathOBN; 28th Feb 2013 at 00:05.
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Old 28th Feb 2013, 00:22
  #1052 (permalink)  
 
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So if you go EO on the 787...where does the power to op everything come from?
By design, from the APU and the RAT, with the batteries as a backup for essential systems if it comes to that.
The batteries should not be switched onto the main DC bus until after non-essential loads have been switched off. This is an active (solid state) relay and not just a diode isolator.

Last edited by inetdog; 28th Feb 2013 at 00:24.
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Old 28th Feb 2013, 01:05
  #1053 (permalink)  
 
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poorjohn
The table would have you believe that LiCobalt is a very poor performer compared to later Li technology. It would be interesting to know Boeing's supplier's reason for that choice.
Back in 2004/2005, it was the mainstream cathode chemistry. Many of these newer cathode chemistries either were developed or matured after the 787 program was in full development.

Momoe
Boeing are taking a beating partly because the planes aren't flying for a damn good reason, the other issue is Boeing's perceived lack of clear oversight across the design/implementation.
Designing aircraft batteries of any kind is not a core competency of Boeing Commercial Aviation. Yes, they are ultimately responsible for the decision to go Li-Ion instead of NiCad, but they chose Yuasa because of their expertise in aviation batteries and Li-Ion batteries for industrial uses.
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Old 28th Feb 2013, 07:42
  #1054 (permalink)  
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TURIN :
Have there been many (any?) total electrical power failures that haven't been caused by loss of the engines too? I can't think of any.
Total , can't recall either, but partial ones with severe consequences, yes.
This one for instance :

Martinair -- Further Information from AWST and FI
The last lines of the text are interesting as to the consequences of even partilal E failures.
And this was on a good old cables /hudraulics airplane.
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Old 28th Feb 2013, 07:45
  #1055 (permalink)  
 
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Update on FAA position

787 faces extensive tests to return to air, FAA chief says | Business & Technology | The Seattle Times

For the time being they seem to stay on the safe side ...
let's see how it flies under the Boeing's lobbying barrage ...
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Old 28th Feb 2013, 08:33
  #1056 (permalink)  
 
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Geeze do you think some of guys could let up....just a little? The deployment of the RAT is a function of the flight test program on every airplane prior to delivery. They deploy it to see if it works. What a novel idea.

Last edited by Spooky 2; 28th Feb 2013 at 08:34.
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Old 28th Feb 2013, 08:42
  #1057 (permalink)  
 
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Recharging is not the problem...

Two posters have suggested that the solution would be to remove the battery chargers and fly the batteries as "primary" cells that would be recharged only on the ground. That won't solve the problem.

The problem is "thermal runaway". As the battery gets hot, the internals expand, getting closer to each other, and thus increasing the likelihood of a short-circuit. The more often they are cycled, the greater the likelihood of a short-circuit.

The batteries get hot because of the current passing through them. While this happens to a certain extent during charge (at 2C which is about 130 amps for these cells) it is much worse during discharge (when the APU battery flows more than 1,000 amps for up to 30 seconds while winding up the APU). If it's going to catch fire, the problem is most likely to begin just after you "use" it. Removing the charger doesn't solve that.

The onset of thermal runaway happens at about twice the boiling point of water: this research shows these batteries are well into "coffin corner" by 200 degrees Celcius: Modeling Thermal Runaway for Safer Lithium Ion Batteries

As Lomapaseo points out, hot fires are successfully contained by metal cans every day: in things called "engines". I suggest that Lithium Ion batteries, with a known propensity to spontaneously combust, should be contained in a fire-proof box whenever they fly, whether they are "in use" or not. We know these things are going to burn occasionally: we should ensure the tail (or the cockpit!) doesn't fall off the aircraft when they do. Either would cause the flight crew to think unkindly of the designer/manufacturer.

My greater concern is not that these batteries catch fire, but that they fail! On a fly-by-wire aircraft, that gives a whole new meaning to the term "dead stick". Yes, I know almost everything else has to fail before this matters. But consider Sully's celebrated ditching:

He lost both engines. His APU was not running. If his batteries had failed, and his aircraft had been a 787, he would have had no flight controls. At all.

I think the pilots on this forum would be more than anxious to have this possibility designed out. Before they have to fly a 787 again...

It is easy to see why Boeing chose the Lithium Ion battery. Consider the following article (especially the table it contains):
Rechargeable battery - Wikipedia, the free encyclopedia

Here, I have sorted the data by "Watt/Hours per Kilo":

Type Energy density
(Wh/kg)
Lithium-air (organic)[7] 2000
Lithium sulfur[10] 400
Lithium-ion 200
Molten salt 180
Lithium-ion polymer 165
Sodium-sulfur 150
Silver-oxide 130
Lithium iron phosphate 100
Lithium–titanate 90
Alkaline 85
Zinc bromide 80
Nickel–hydrogen 75
Nickel–zinc 60
Nickel–metal hydride 55
Nickel–iron 50
Nickel–cadmium 50
Lead–acid 35
Vanadium redox 30
Sodium-ion[13] 0
Thin film lithium 0

Sorry, the PPRuNe website doesn't like tables, but you can get the idea. Leaving aside the two outliers at the top that are not on-sale yet, Lithium Ion comes in third. Molten salt is a little aviation-unfriendly.

But Lithium iron phosphate would be my pick. Twice the energy density of NiCad, and already approved for aviation service in an application I know about. OK, they are electrically "fragile", which means you have to pay very close attention to the design of the charger: one spike and they are trash. But that's probably what happened to the 787 batteries.

The benefit of the LiFePo battery is that it does not catch fire when it fails. Another benefit is that it has a very low internal resistance, which enables it to withstand truly prodigious discharge rates (APU starting...) without suffering. And they have around 5 times the in-service life.

Just my thoughts
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Old 28th Feb 2013, 08:46
  #1058 (permalink)  
 
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Hi Tech, I agree with your analysis. but as a commercial pilot of 36yrs & 20K hrs I thought I would look more deeply at what is still a fine a/c.
Multiple failures of systems are a pilots worst nightmare & the Hudson river incident would not have been successful if the Capt had not pre-empted the cck list & started the Apu.
I see the flying controls have 3 hydraulic systems, with the centre electrically powered, so with a double engine failure it is essential to start the APU, (from the battery)? I appreciate the windmilling engines should provide some output of both electrical & hydraulics but again the pilot is faced with pressurisation problems (High Techs) and how to restart engines at 40000ft without electrical power.
I note that the a/c needs 2 GPUs to provide engine starting, I have been to numerous outstations where you are lucky to get even one doubtful unit.
Boeing have said this a/c is a game changer, I agree, but it is very complex, and as such I can see lots of down line problems.
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Old 28th Feb 2013, 08:54
  #1059 (permalink)  
 
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poorjohn

even after two fires and an OAG (sic) fleet the best way forward is still to leave everything as unchanged as possible, and put a steel box around it.
I think there's a lot more involved in the proposed modification than just putting a box around it. There is talk of cell re-design and battery modification to isolate cells thermally.

Walnut

so with a double engine failure it is essential to start the APU, (from the battery)? I appreciate the windmilling engines should provide some output of both electrical & hydraulics but again the pilot is faced with pressurisation problems
The 787 starts the APU automatically in the case of a double engine failure, yes from the battery, but it would be assisted by windmilling engines and the RAT.

The pressurisation problems are no worse than any other twin when faced with a double engine failure. You're going down anyway, so the most important action for loss of pressurisation is already initiated!
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Old 28th Feb 2013, 09:13
  #1060 (permalink)  
 
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You can do some WYSIWIG formatting of tables by wrapping the table text inside CODE tags (The # format button in the toolbar).

Code:
Type	              Energy density
                             (Wh/kg)
 Lithium-air (organic)[7] 2000
 Lithium sulfur[10]	      400
 Lithium-ion	              200
 Molten salt	              180
 Lithium-ion polymer	      165
 Sodium-sulfur	              150
 Silver-oxide	              130
 Lithium iron phosphate	      100
 Lithium–titanate	       90
 Alkaline	               85
 Zinc bromide	               80
 Nickel–hydrogen	       75
 Nickel–zinc	               60
 Nickel–metal hydride	       55
 Nickel–iron	               50
 Nickel–cadmium	               50
 Lead–acid	               35
 Vanadium redox	               30
 Sodium-ion[13]	                0
 Thin film lithium	        0
This will work best if you have formatted the table in a straight text editor and not a word processor and have used a monospace font such as Courier. Try to avoid using TABs if possible.

Last edited by inetdog; 28th Feb 2013 at 09:18.
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