Boeing 787 Li-Ion Meltdown

[SeanB]

RAT is a last resort, we have run out of fuel and have nothing left to keep this hunk o junk in the air device. It just allows you to turn and glide, hopefully to a landing that is a little better than a controlled crash. Remember it stops running as you come in to land, as the airspeed drops. No power just when you need some big control inputs.

Basically if it deploys you are so far up shyte creek without a paddle that you better have made a will. You are just going to dig a hole and leave it for somebody to fill.

[Skimask]

Never ran out of fuel, but I did shear both mags shafts on climbout at 2500ft AGL.  The only thing the engine was good for was keeping the C.G. in limits

[Wytnucls]

Here is the basic electrical configuration on the B787:
Some very unusual voltages in aviation: for instance, +/-270VDC to run some big motors that replaced legacy systems.
230VAC generators, instead of more conventional 115VAC.
No constant speed drives on the generators. The frequency is allowed to fluctuate with engine rotational speed.
The hydraulic system pressure is also unusually high at 5000PSI, instead of 3000PSI, to reduce the size and weight of the components. The A380 also uses a high pressure system.
I just noticed that the Blue Distribution bus should have been marked as 115VAC instead of 115VDC.

[Skimask]

270VDC...I've seen that before...somewhere.  (I used to work B-52's, C-135's, C-130's, and other large aircraft, but never saw a 270VDC bus)

3 phase 400VAC from the generators, rectified, x .7071 = ~282VDC.  Knock off a bit for diode drops, ripple, etc, and 270 doesn't sound too far out there.

[IanB]

Once when I was sitting on the flight deck of a 747 and looking at the flight engineer's panel I seem to recall the total in-flight electrical load was surprisingly large, like 100's of kW or perhaps megawatts. This would have been for hydraulic pumps, HVAC systems, lighting, electronics, galley systems, avionics, fuel pumps and all sorts of things I can't recall. It surprises me that generation at 240 VAC or 400 VAC would be sufficient to handle this. I can't recall what the voltages on the the 747 were, but surely higher voltages would lead to thinner wires and lighter weight, or does that have to be offset with the additional weight of transformers?

[tom66]

I didn't know weight was that crucial (given the thing ways 110,000 kg unloaded, a ~1000 kg saving for lighter batteries and lighter systems doesn't seem like much), but I guess wherever you can reduce weight, fuel use and range can be increased.

A little research says the 747-400 has 4 x 70kVA generators, those probably provide 115VAC. One per engine, and it's supposed to be able to keep level with all criticial systems functioning, on just one engine.

[r90s]

Dreamliner sparks doubt...

http://washingtonexaminer.com/dreamliner-fires-spark-new-doubts-about-a-green-energy-technology/article/2519353#.UP7S3jXCz8C

[tom66]

What a load of bollocks. 

Whilst lithium ion batteries can burn and flame, and are extremely volatile, many things on an aircraft are. For example, 33,500 gallons of jet fuel is quite flammable. A well designed battery pack will not cause a hazardous condition if it fails. It appears this happened, and the battery pack simply destroyed itself internally, with limited external carnage.

An electric vehicle battery can also start a fire, but so can gasoline. There's certainly a risk with lithium ion batteries, but understanding them is important, instead of just ruling them out because of a small hazard.

[r90s]

Like I said earlier, Boeing Aerospace would not let Li Ion on the space shuttle, they were not allowed for safety reasons.  I have been in their lab many times, about one mile away from the Johnson Space Center..
have a nice rant...err...day


P.S. I also said that if anyone can make it work it will be Boeing..

[EEVblog]

Apparently it's not due to over-charging/over-voltage. So what else would cause a LiPo battery to burst into flames? Too much current perhaps?

When you combine advanced technology Lithium Ion cells with huge operating temperature and pressure variations and cycling, some are bound to fail, even if used within design specs.

Dave.

[JoannaK]

I have no idea how many those batteries are at one Jumbo, but I'd expect there to be more than one. But whatever the estimated failure rate of these batteries are, there should be a maintenance protocol and schedule to check/replace those before they do melt down while at fly.

Otoh, I have no idea if the Li-Ion destruction is known in a way that they can measure the degradation and make any good estimate about the likelihood of one battery pack going bad.

[SoftwareSamurai]

Apparently it's not due to over-charging/over-voltage. So what else would cause a LiPo battery to burst into flames? Too much current perhaps?

When you combine advanced technology Lithium Ion cells with huge operating temperature and pressure variations and cycling, some are bound to fail, even if used within design specs.

Apparently so...

"In addition, battery experts have questioned whether enough testing was done on batteries to mimic the temperature and pressure of flight. The battery would essentially seek to burst open in flight if not pressurized or built for different pressure at altitude, according to battery experts."

If those batteries aren't designed & manufactured to tolerate repeated large pressure changes (especially if they aren't in a pressurized compartment), I can imagine how cycle-induced stress fractures within the batteries could easily compromise their integrity and cause them to pop.

[smashedProton]

So the APU is the weird exhaust port on  the tail that looks out of place!  I have always thought that was where the poo came out   
I have never thought about it since I first saw them when I was six.

I guess I was too busy looking at the thrust reversers.  That shit is pornographic.

[chickenHeadKnob]

So the APU is the weird exhaust port on  the tail that looks out of place!  I have always thought that was where the poo came out   
I have never thought about it since I first saw them when I was six.

I guess I was too busy looking at the thrust reversers.  That shit is pornographic.

In case you are concerned about where your poo goes on a flight, it should go to a holding tank. Sometimes the cleanout cap to the tank can leak/come loose/fall off and then you get what aviation maintenance crew call "blue ice" for the dye that is in the water. If you ever hear news stories of mysterious blobs of ice falling from the sky, that be them. On aircraft with aft pylon engines like a DC-9 there have been blue ice ingestion events with the result of the whole engine departing the aircraft.

[NiHaoMike]

In case you are concerned about where your poo goes on a flight, it should go to a holding tank. Sometimes the cleanout cap to the tank can leak/come loose/fall off and then you get what aviation maintenance crew call "blue ice" for the dye that is in the water. If you ever hear news stories of mysterious blobs of ice falling from the sky, that be them. On aircraft with aft pylon engines like a DC-9 there have been blue ice ingestion events with the result of the whole engine departing the aircraft.

Why don't they just discharge it just behind one of the engines, using the hot exhaust gas as an incinerator? It seems like they could save quite a bit of weight that way.

[Eliminateur]

because that would contaminate a lot and be extremely UN-sanitary.
besides the engine output is very high pressure combustion gasses, you'd need to be able to pump the liquid against that pressure needing large solid-capable pumps.... not worth it

[Wytnucls]

Apparently it's not due to over-charging/over-voltage. So what else would cause a LiPo battery to burst into flames? Too much current perhaps?

When you combine advanced technology Lithium Ion cells with huge operating temperature and pressure variations and cycling, some are bound to fail, even if used within design specs.

Dave.

On the B787, the batteries are in 2 pressurized EE compartments, which are always at the same temperature and pressure as the cabin (6-7,000 feet max).
The batteries are seldom used on a modern aircraft, unless there is a drastic failure of the electrical system. The only time they are put under some stress is during APU start, if there is no external power available. Even that, seldom happens.
They are always disconnected from the electrical system, except for the hot busses, which are permanently feeding a few low power vital systems. Every now and then, the batteries connect themselves to the main system to top up their charges.
I  would put my money on a battery flaw, possibly made worse by pressure variations and vibrations.

[qno]

I wonder if this could have anything to do with it.

http://www.teledynereynolds.com/product/1singlepin/other/pdfs/page42.pdf

[G7PSK]

I wonder if the seals of the batteries blew out due to reduced atmospheric pressure, I am not sure if the batteries are at cabin pressure or outside pressure, repeated cycling on the seals might cause them to blow out. As for the toilet contents at one time the tanks were emptied at altitude, some years back a large block of yellow ice landed in the garden of a London resident who lived under the Heathrow flight path.

[SoftwareSamurai]

Update: According to the NTSB, at least one that caught fire was due to an internal short and thermal runaway. So, perhaps a manufacturing/QA failure?
Interestingly, these batteries are lithium cobalt oxide, which are apparently "more reactive and have poorer thermal stability" than other lithium variants.

[IanB]

Lithium cobalt oxide is in fact the standard kind of lithium battery that you would find in your laptop battery pack or cellphone.

[tom66]

And, with this battery charging system, the battery voltage was limited to 4.025V; which is a very low limit. A typical cell has a maximum of 4.22~4.25V.

[ptricks]

I am surprised to hear Boeing having problems with the batteries. I was in the Navy as an aviation electronics tech and the APU section was the least problematic of all the parts on the planes .  The APU seldom use the batteries, it just isn't done in commercial aircraft because every minute the plane sits powered down is lost income so they tend to keep them powered and ready for the next flight right away .  I guess Boeing needs to install a really big crank on the front or install some 3 phase sockets on the runway !

[TerraHertz]

Anyone remember how NiCd batteries turned out to be prone to growing metal whiskers between the plates, and thus self-shorting out? One cure for such dead, unchargable NiCd D-cell batteries was to give them a half second blast of 150A AC from an arc welder. Vaporized the whiskers, and the battery could be charged again.

Anyway, I don't suppose Li-ion battery technology could have some similar as-yet unrecognized problem?
Especially when constantly vibrated and pressure cycled, while maintained at near full charge.

I don't do RC aircraft models, but I recall from chats with someone who does that Li-ion batteries are well known to be highly prone to spontaneously bursting into flames. Not from 'overcharge', but while just sitting around with a full charge. My friend told me that because of this it's best to keep Li-ion stored with only about half charge. And to store them in a fridge when not in use.

The energy density of these batteries is getting pretty high. But at least it isn't yet up there with chemical explosives. Fortunately for those planes.

[PChi]

The pictures of the failure are interesting. The construction of the case and the way they appear to have mounted the PCBs on pillars is crude. Though the containment of the failure looks good.
I wonder if we will find out if it was a failure of the protection circuits or was a problem with the cells?

A couple of years ago one day in the lab were I was working there was a very loud bang then the fire alarms went off. I didn't hang around and we had a visit from the fire brigade. The incident was caused by a cycling fanatic who had used what appeared to be genuine Yuasa cylindrical lithium Ion cells for bike lights. He didn't take much care in charging them and one exploded. The cell didn't appear to have any pressure release mechanism, the metal case just ruptured which didn't impress me.