FAA Grounds 787s

[FlightPathOBN]

Walnut,

If you can believe the Boeing spec...the batteries are 32V 150A...


They state you can only get 16A from NiCd...

[TURIN]

Walnut.
You are barking up the wrong tree.
Normal brakes do not need backup battery.
Refuelling is almost always done with full system power.
Lets not build a conspiracy eh? There's enough around already.

[FlightPathOBN]

SEATTLE (Reuters) - The Federal Aviation Administration said it is not close to approving test flights of Boeing's 787 Dreamliner with a proposed fix for the plane's troubled batteries, denying news reports that such tests could start as early as next week.
"Reports that we are close to allowing 787 test flights are completely inaccurate," spokeswoman Laura Brown said on Tuesday in an email to Reuters.

http://finance.yahoo.com/news/report...w_default=true

[EEngr]

LiON Requirement

quoting Mike Sinnet, VP of Engineering and chief project engineer for the 787:

The driving factor in our design was really the ability of the battery to discharge a large amount of energy in a very short period of time. And this was required for two different functions at an airplane level.

One was for starting the auxiliary power unit and the other was for being able to apply braking to the airplane in the event that all other power sources in the airplane were lost. The 787 braking system is an electrical braking system.

Which function (backup braking or APU start) places the greater demand on the battery system? I'll venture a guess and say its the APU start. That has been possible with NiCad technology for quite some time. And given the variable frequency drive motor/generator, I'd guess that the old school DC starters placed more strain on a battery than these LiON batteries will see.

The brakes, while critical, don't appear to have the same demand as APU start. There are a few pics of the system here:

Messier-Bugatti-Dowty

While there are no electrical demand specs, one can size up the electrical components (motors, connectors and wire bundles) and make some guesses about demand.

So falling back to a NiCad system may not be so far fetched as Boeing would like people to think. The main problem will be building up a 32V NiCad battery assembly and certifying it with a 32V charger. This would be prefferable to redesigning and recertifying the 787 with a 24V DC system (to use off the shelf battery systems). But its still possible.

[deptrai]

some more here: http://www.goodrich.com/gr-ext-templ...ct%20Sheet.pdf

and here, Patent US6402259 - Electromechanical braking system with power distribution and redundancy including a description of the emergency mode

[Kerosene Kraut]

If Boeing would finally change the battery type and recertify the modified system. How long would this take?

[Walnut]

Posting 1038 by "deptrai" shows how complex an electro mechanical braking system can be. It is I suspect a heavy power user, so instead of the Hot battery bus providing power to fire extinquishers & P1 standby instruments etc, all of which use little power, this backup source has to be meaty.
It would be interesting to know why the a/c to date has suffered circa 150 battery replacements? Low voltage?? In a way this is a more serious problem than the two fire instances, since no sane pilot would accept an a/c without ultimate back up power.
I can see the potential for a complete redesign of this part of the electrical system.

[Golf-Sierra]

The brakes, while critical, don't appear to have the same demand as APU start.

I wouldn't underestimate that.

4 actuators x 8 wheels = 32 actuators. 150A /32 = that's just 4.68 A per actuator.

[green granite]

Presumably once the APU is running and or ground power is on, then the batteries are no longer needed, except in an emergency, and could be isolated.
So why not treat them as primary cells and do a swap-out before flight and have the charging system disconnected? The batteries could then be recharged under controlled conditions on the ground and inspected before being used.

That is of course presuming the problem is only due to charging.

I'm probably missing something as it seems too simple a solution, albeit a temporary one.

[cockney steve]

@GolfSierra...on the face of it, -yes you'd think so,,,,but there's a gear-train which multiplies the mechanical effort, The amount of pad-travel is extremely small and, as I postulated a while back, the system is electronically controlled to reflect pedal-pressure.

Effectively, each unit is an electrically powered jack--it only needs max. power to press the pads harder,a small burst of current ,then the thing holds itself in position....I'll grant that an instantaneous peak load MIGHT be quite high ,upon initial application,but I think this line is another red-herring.

Multiple APU starts?....cobblers! it has to cool for 30 minutes otherwise the Turbine-shaft apparently distorts(bends)S0, fire it up and the first thing it does is recharge it's own battery....well. that's what sound practice says it SHOULD do,,,,but the demonstrated masters of fudge and kludge may have a different view.

I'm just an oik, I don't get to gamble/fritter billions of shareholders' money on projects that appear to have a large input of hubris without the applied expertise behind it.

A triumph of marketing over reality?

One thing's for certain, Buyers who feel , justifiably, they've been stitched-up with a very expensive ,short -term Hangar-queen, and have to answer for their own misplaced faith, -should be, and probably are, royally p155ed-off. It'll take more than a lavish dinner and floor-show to placate them.

[TURIN]

Presumably once the APU is running and or ground power is on, then the batteries are no longer needed, except in an emergency, and could be isolated.
So why not treat them as primary cells and do a swap-out before flight and have the charging system disconnected? The batteries could then be recharged under controlled conditions on the ground and inspected before being used.

That is of course presuming the problem is only due to charging.

I'm probably missing something as it seems too simple a solution, albeit a temporary one.

Can you imagine the logistics nightmare that would cause.
Servicable batteries required at ALL line stations. Maintenance time to change the battery. These a/c get turned around in less than 90 mins. Disconnecting the power for 30 mins while you change the batteries would kill that. How many function checks would be required after the swap to ensure the system will work as required.
Then there is the problem of transporting hundreds of batteries all over the globe.
Alternatively you have charging workshops on every line station.

I can't see the airlines wanting to carry the cost of any of that.

Multiple APU starts?....cobblers! it has to cool for 30 minutes otherwise the Turbine-shaft apparently distorts(bends)S0, fire it up and the first thing it does is recharge it's own battery....well. that's what sound practice says it SHOULD do,,,,but the demonstrated masters of fudge and kludge may have a different view.

That 30 min cool down period is a temporary arrangement. A work around. It was certainly not the intention from the manufacturer. It became apparent during service. A permenant fix to the rotor bow will appear in good time.

I take the point though. A Nicad battery would suffice. It has for other types so why not this? Commonality of parts is the only reason I can think of.

Oh, and saving weight.

[green granite]

These a/c get turned around in less than 90 mins. Disconnecting the power for 30 mins while you change the batteries would kill that.

1) If the battery is isolated the A/C does not need to be powered down at all.

2)The battery would only need changing if used, capacity indicators are not rocket science.

Then there is the problem of transporting hundreds of batteries all over the globe.
Alternatively you have charging workshops on every line station.
I can't see the airlines wanting to carry the cost of any of that.

Cheaper for Boeing to pay for that than having them as expensive ornaments twiddling their wheels in a hangar and it would take some of the pressure off of providing a fix. That way a proper engineered solution could be devised and tested.

[Ex Cargo Clown]

Well my LiMn mission was interesting tried to short it, just wouldn't go, twice it's rated ampage as well. So set it on fire with diethyl ether, only thing that burnt was the plastic and solvent. Ordered some LiFePO4 ones to give them a go. But LiCo? Why?

[Speed of Sound]

just wouldn't go,

And that is a problem Boeing will have if this ludicrous 'stronger box' solution is even considered by the FAA.

It is quite easy to force a problem by overcharging a battery or to try to charge a seriously depleted one but to force a thermal runaway due to an internal short circuit will be almost impossible to do short of manufacturing a faulty battery or charge/recharge cycling it until dendrite growth becomes a problem.

This all has to be done in flight too so that thermal effects on the rest of the electronics bay can be measured as well as the efficiency of any venting system.

The 'bigger, stronger blue box' solution may be a quick fix but I can't see proper certification of it being particularly quick. An alternative would be a mathematical extrapolation of the worst-case scenario based on the total energy inside the box but I really don't think anything short of a battery on fire on an actual flight will satisfy the FAA this time round.

[toffeez]

Test a battery on fire on an actual flight

I think the test should be: fly around for 180 minutes after a fire and/or explosion is confirmed to have occurred inside the steel "safety box".

Any volunteers?

[Hi_Tech]

The Boeing 787 could be the last all electric design for an aircraft

The following is a bit long, but if you are a pilot or engineer you might appreciate this discussion.
Design decisions are not given out by aircraft manufacturers. But if you know complete engineering details of several aircraft, like in my case, one can see through the tangle and guess what are the problems Boeing is facing. I am not a design engineer, but one who was trained and worked on the last 5 Boeing jets produced and the last 5 airbus including A380.
On all aircraft till B787 design, there are three prime sources of motive power.
1. Electric. 2. Pneumatic. 3. Hydraulic.
To understand Boeing's problem now one has to know how the motive powers are derived on all previous aircraft.
Electric generators are on the engines and APU. With emergency power from batteries and RAT, which has a small generator the size of a pineapple, 10 KVA capacity on B787. B787 has normal generating capacity of 1450 KW.
Pneumatic is sourced from engine bleed or (if running)APU bleed below a certain altitude about 25000 ft.
Bleed air from APU, when on ground, is used to start engines. After an aircraft lands from a flight, as engine bleed is still available, it is used to start APU as in B777.
Hydraulic pumps are driven by engine, or electrically driven, or in the case of Boeing 777 and 747 bleed air driven during high demand.
When Boeing designed B787, which they called is a game changing design, they took a decision to do away with bleed air system and depend on the electrics and hydraulics only for motive power source. They called it one of the features of their game changing design. But one still needs compressed air for air-conditioning and pressurizing the aircraft. So they have these two large electrically driven compressors that require 270V DC power.
Another decision was to have electric brakes instead of hydraulic brakes. A questionable choice even if saves a few kilos. This required a large battery power for emergency brakes if you have total power failure before landing. There are 8 brakes, and each brake with 4 motors driving worm gears. So you are talking about 32 motors and associated electronics to be driven by battery. (This condition is rare, but it has happened on this plane once during a test flight - Laredo, Texas incident).
But doing away with bleed air is at the heart of the current problems with this design where there is very little room left for maneuver. Engines and APU can only be started with electric starters for which they use the same 3 phase generators, that normally supply the power the aircraft. Theyare driven as starter supplying power from available sources.
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.

On B787, when electrical power fails, they have the additional emergency of pressurization stopping as the compressors that supply air would shut down.
So they have to quickly get the APU started to restore the electric power, using of course the battery. This battery can give 2 start attempts. APUs are traditionally difficult to start at high altitude. So if there is a delay crew will face the additional emergency of diving to a lower altitude to avoid a low cabin pressure situation, while you have a pineapple size generator on RAT powering this all electric plane.
As Boeing has done away with DC starter for APU (unlike in all older airplanes), they require a power conversion circuit to convert the 30V DC power from battery to 3 phase 235 V AC power to start the APU. That could explain why you need all the power drawing capacity for the APU battery.
It may not be easy to find a Ni-Cad battery to supply 150 A. They will need 2 batteries in parallel to supply that current.
Another draw back of doing away with bleed air is engine starting. If APU is not available for any reason, they require ground power. This is only available as 3 phase 115V at all airports. This has to be converted to 235V AC 3 phase to start engines using again a power converter on airplane.
Then the air compressors require 270V DC power, which is obtained using another large power conversion. This 270 V DC is also required to drive the high demand electric hydraulic pumps.
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. In the middle of this power center is the suspect APU battery. So if this goes up in smoke one can expect a total power failure on this aircraft.
After seeing these problems, I doubt if we will ever see an all electric design in future. After all, doing away with bleed air has saved only 2% fuel, the figure many in the industry are already questioning. Is it worth the trouble?

[Annex14]

FPO - #1034

To start with: I am not a battery specialist - at itīs best a thoughtful user ! I only have two 36 V 10,5 Ah battery packs - LiFe4Po of course not these potential life fire bombs types.
However if one looks at that post # 1034 picture of the B787 battery and the attached text something springs in my mind.

Yuasu says in itīs data sheet about the LVP 65 battery that it runs at 3,7 V and 65 Ah per cell. The picture shows clearly the repeatedly mentioned number of 8 cells connected in line NOT parallel. If my little mathematics are not completely gone with the years 8 x 3,7 = 29,6 V !! So how can they claim in the data under that picture that the battery delivers 32 V ???

Furthermore usually these LiIon batteries should be discharged only up to - so called 2 C . That would be in the case of the Yuasu cells - having 65 Ah a max of 130 Ah - not 150 Ah !! for a max period of time of 30 min. There is of course the possibility to discharge at higher rates than 2 C but what Iīve read about that indicates, the higher the discharge rate the hotter the pack gets and the bigger the possibility of battery "problem" become !!

Keep that in mind and look at the dense packing of the cells and simply imagine how hot it might become in the core with no obvious cooling installation at work at all !! if there is is really pulled up to 150 Ah.

There is a website under Basic to Advanced Battery Information from Battery University that has some very interesting facts listed about the different types of batteries. One of these facts they cite is - if an LiIon battery was discharged too low in Volts remaining and an attempt is started to charge it with the normal charging installation it might end up with a shunt and short in the cells with all unwanted consequences.

Since all of this is simple traceable knowledge the more one wonders how in heaven such a fine product - as the B 787 obviously is - was set in such a jeopardy ??

[ionagh]

The cells are rated at 65Ah minimum and 75Ah nominal.
The discharge is rated to 5C so 2C would have a nominal value of 150A.

The 4V per cell is the fully charged value without load.
So yes they are 32V / 150Amp nominal batteries.

[lomapaseo]

I think the test should be: fly around for 180 minutes after a fire and/or explosion is confirmed to have occurred inside the steel "safety box".

Any volunteers?

I'm willing to do it with engines every day, so I'm willing to do it with their safety boxes

[bacp]

HiTech, I have no idea if your analysis is totally correct, but it is very well written with a logical conclusion.
I don't think I'll be queuing up for a 787 Rating quite yet!