On 8/10/2021 4:07 PM, Tony wrote:
> On Tuesday, August 10, 2021 at 6:39:35 PM UTC-4, Eric Greenwell wrote:
>> On 8/10/2021 2:34 PM, kinsell wrote:
>>>> There is plenty volume in that area, and it could hold 200+ 18650 cells easily, over 2.2
>>>> kWh. Or use a high temperature composite if the tray needs to be a complex shape. The
>>>> interior of the D tube (or the exterior of the tray) could be painted with intumescent
>>>> paint to protect the wing. A fire suppression system that released gas into the tray
>>>> during a cell fire might keep the composite tube from burning until the cell's energy
>>>> was exhausted.
>>>
>>>
>>> Not sure what gas you would propose to suppress a fire, but it wouldn't be effective. In
>>> the warehouse fire Herb noted, they tried dumping 28 tons of dry concrete powder on the
>>> batteries, they kept right on burning.
>> CO2 maybe, just something to keep the composite tube from burning, to help move the hot
>> gases to the external vent, and is compatible with cell gases, It's not something intended
>> to extinguish the cell fire, but to mitigate the effects of the fire. The situation I
>> described was one cell, not 100 TONS of batteries!
>>
>> I wonder what that mountain of batteries cost, and owner of the batteries (and the
>> building) said he didn't have insurance.
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> Eric - the D-tube area is primary structure...if you can only paint it white I think you can forget about using it for heat containment. Just bail out!
>
The battery tube could be insulated in a number of ways, and perhaps provided with a
sufficient flow of CO2 or similar through the interior to carry heat away. The D tube in
the battery area could be made of high temperature carbon composite (eg, prepreg that
cures at 150C/300F) so it would retain it's strength longer, and made stronger to allow
for high temperatures. The interior of the D tube could be painted with intumescent paint
to provide additional insulation at the hot spot.

All those features can buy time. With a 1500 fpm descent rate (full spoilers), you'd need
7 minutes to descend 10,000'. Is seven minutes enough? Calculations and testing would be
needed to know.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On 8/10/2021 4:28 PM, 2G wrote:
> On Tuesday, August 10, 2021 at 4:07:34 PM UTC-7, sgs...@gmail.com wrote:
>> On Tuesday, August 10, 2021 at 6:39:35 PM UTC-4, Eric Greenwell wrote:
>>> On 8/10/2021 2:34 PM, kinsell wrote:
>>>>> There is plenty volume in that area, and it could hold 200+ 18650 cells easily, over 2.2
>>>>> kWh. Or use a high temperature composite if the tray needs to be a complex shape. The
>>>>> interior of the D tube (or the exterior of the tray) could be painted with intumescent
>>>>> paint to protect the wing. A fire suppression system that released gas into the tray
>>>>> during a cell fire might keep the composite tube from burning until the cell's energy
>>>>> was exhausted.
>>>>
>>>>
>>>> Not sure what gas you would propose to suppress a fire, but it wouldn't be effective. In
>>>> the warehouse fire Herb noted, they tried dumping 28 tons of dry concrete powder on the
>>>> batteries, they kept right on burning.
>>> CO2 maybe, just something to keep the composite tube from burning, to help move the hot
>>> gases to the external vent, and is compatible with cell gases, It's not something intended
>>> to extinguish the cell fire, but to mitigate the effects of the fire. The situation I
>>> described was one cell, not 100 TONS of batteries!
>>>
>>> I wonder what that mountain of batteries cost, and owner of the batteries (and the
>>> building) said he didn't have insurance.
>>> --
>>> Eric Greenwell - USA
>>> - "A Guide to Self-launching Sailplane Operation"
>>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>> Eric - the D-tube area is primary structure...if you can only paint it white I think you can forget about using it for heat containment. Just bail out!
>
> Any fire in that tube is going to generate very high temperatures very quickly that will heat up the rest of the cells in the tube. Obviously, adjacent cells will get the brunt of the heat, but the only way to vent the gases is out the ends of the tube structure. A necessary test during development is setting one cell on fire and measuring the temperatures of the other cells in the tube. The tube would have to be metal because of the temperatures. These battery fires go very quickly as the video shows, so an emergency landing is likely not possible unless you are on short final - bailing out is a better option if you are high enough. A BRS would only make things worse.
>
> To repeat myself, lithium battery fires CANNOT be "put out," only slowed down until all of the fuel is consumed, because they inherently provide their own oxygen. Pouring A LOT of water on a battery fire MAY keep adjacent cells below the critical combustion temperature while the burning cells complete their combustion. This seems unlikely if they are sealed up in a tube inside a wing.
>
> Tom
>
Did you read the OSTIV presentation that Dave Nadler referenced? It indicated keeping the
adjacent cells from thermal runaway was not difficult for 18650 cells with adequate
spacing, given the relatively small energy in each cell. It did not even propose a metal case.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Tuesday, August 10, 2021 at 8:53:05 PM UTC-7, Eric Greenwell wrote:
> On 8/10/2021 4:28 PM, 2G wrote:
> > On Tuesday, August 10, 2021 at 4:07:34 PM UTC-7, sgs...@gmail.com wrote:
> >> On Tuesday, August 10, 2021 at 6:39:35 PM UTC-4, Eric Greenwell wrote:
> >>> On 8/10/2021 2:34 PM, kinsell wrote:
> >>>>> There is plenty volume in that area, and it could hold 200+ 18650 cells easily, over 2.2
> >>>>> kWh. Or use a high temperature composite if the tray needs to be a complex shape. The
> >>>>> interior of the D tube (or the exterior of the tray) could be painted with intumescent
> >>>>> paint to protect the wing. A fire suppression system that released gas into the tray
> >>>>> during a cell fire might keep the composite tube from burning until the cell's energy
> >>>>> was exhausted.
> >>>>
> >>>>
> >>>> Not sure what gas you would propose to suppress a fire, but it wouldn't be effective. In
> >>>> the warehouse fire Herb noted, they tried dumping 28 tons of dry concrete powder on the
> >>>> batteries, they kept right on burning.
> >>> CO2 maybe, just something to keep the composite tube from burning, to help move the hot
> >>> gases to the external vent, and is compatible with cell gases, It's not something intended
> >>> to extinguish the cell fire, but to mitigate the effects of the fire. The situation I
> >>> described was one cell, not 100 TONS of batteries!
> >>>
> >>> I wonder what that mountain of batteries cost, and owner of the batteries (and the
> >>> building) said he didn't have insurance.
> >>> --
> >>> Eric Greenwell - USA
> >>> - "A Guide to Self-launching Sailplane Operation"
> >>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> >> Eric - the D-tube area is primary structure...if you can only paint it white I think you can forget about using it for heat containment. Just bail out!
> >
> > Any fire in that tube is going to generate very high temperatures very quickly that will heat up the rest of the cells in the tube. Obviously, adjacent cells will get the brunt of the heat, but the only way to vent the gases is out the ends of the tube structure. A necessary test during development is setting one cell on fire and measuring the temperatures of the other cells in the tube. The tube would have to be metal because of the temperatures. These battery fires go very quickly as the video shows, so an emergency landing is likely not possible unless you are on short final - bailing out is a better option if you are high enough. A BRS would only make things worse.
> >
> > To repeat myself, lithium battery fires CANNOT be "put out," only slowed down until all of the fuel is consumed, because they inherently provide their own oxygen. Pouring A LOT of water on a battery fire MAY keep adjacent cells below the critical combustion temperature while the burning cells complete their combustion. This seems unlikely if they are sealed up in a tube inside a wing.
> >
> > Tom
> >
> Did you read the OSTIV presentation that Dave Nadler referenced? It indicated keeping the
> adjacent cells from thermal runaway was not difficult for 18650 cells with adequate
> spacing, given the relatively small energy in each cell. It did not even propose a metal case.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Yes, I read it, and no, you HAVE to test it - opinions are best left to the opinion page of the newspaper. Nothing but metal will melt and catch fire itself, and, then, the wrong kind of metal will melt - perhaps you should look at pictures of the aftermath of electric car fires.

Tom

On Tuesday, August 10, 2021 at 9:55:20 PM UTC-7, 2G wrote:
> On Tuesday, August 10, 2021 at 8:53:05 PM UTC-7, Eric Greenwell wrote:
> > On 8/10/2021 4:28 PM, 2G wrote:
> > > On Tuesday, August 10, 2021 at 4:07:34 PM UTC-7, sgs...@gmail.com wrote:
> > >> On Tuesday, August 10, 2021 at 6:39:35 PM UTC-4, Eric Greenwell wrote:
> > >>> On 8/10/2021 2:34 PM, kinsell wrote:
> > >>>>> There is plenty volume in that area, and it could hold 200+ 18650 cells easily, over 2.2
> > >>>>> kWh. Or use a high temperature composite if the tray needs to be a complex shape. The
> > >>>>> interior of the D tube (or the exterior of the tray) could be painted with intumescent
> > >>>>> paint to protect the wing. A fire suppression system that released gas into the tray
> > >>>>> during a cell fire might keep the composite tube from burning until the cell's energy
> > >>>>> was exhausted.
> > >>>>
> > >>>>
> > >>>> Not sure what gas you would propose to suppress a fire, but it wouldn't be effective. In
> > >>>> the warehouse fire Herb noted, they tried dumping 28 tons of dry concrete powder on the
> > >>>> batteries, they kept right on burning.
> > >>> CO2 maybe, just something to keep the composite tube from burning, to help move the hot
> > >>> gases to the external vent, and is compatible with cell gases, It's not something intended
> > >>> to extinguish the cell fire, but to mitigate the effects of the fire. The situation I
> > >>> described was one cell, not 100 TONS of batteries!
> > >>>
> > >>> I wonder what that mountain of batteries cost, and owner of the batteries (and the
> > >>> building) said he didn't have insurance.
> > >>> --
> > >>> Eric Greenwell - USA
> > >>> - "A Guide to Self-launching Sailplane Operation"
> > >>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> > >> Eric - the D-tube area is primary structure...if you can only paint it white I think you can forget about using it for heat containment. Just bail out!
> > >
> > > Any fire in that tube is going to generate very high temperatures very quickly that will heat up the rest of the cells in the tube. Obviously, adjacent cells will get the brunt of the heat, but the only way to vent the gases is out the ends of the tube structure. A necessary test during development is setting one cell on fire and measuring the temperatures of the other cells in the tube. The tube would have to be metal because of the temperatures. These battery fires go very quickly as the video shows, so an emergency landing is likely not possible unless you are on short final - bailing out is a better option if you are high enough. A BRS would only make things worse.
> > >
> > > To repeat myself, lithium battery fires CANNOT be "put out," only slowed down until all of the fuel is consumed, because they inherently provide their own oxygen. Pouring A LOT of water on a battery fire MAY keep adjacent cells below the critical combustion temperature while the burning cells complete their combustion. This seems unlikely if they are sealed up in a tube inside a wing.
> > >
> > > Tom
> > >
> > Did you read the OSTIV presentation that Dave Nadler referenced? It indicated keeping the
> > adjacent cells from thermal runaway was not difficult for 18650 cells with adequate
> > spacing, given the relatively small energy in each cell. It did not even propose a metal case.
> > --
> > Eric Greenwell - USA
> > - "A Guide to Self-launching Sailplane Operation"
> > https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> Yes, I read it, and no, you HAVE to test it - opinions are best left to the opinion page of the newspaper. Nothing but metal will melt and catch fire itself, and, then, the wrong kind of metal will melt - perhaps you should look at pictures of the aftermath of electric car fires.
>
> Tom

Does this answer your question?
"Fire ignition establishes that the cathode of the battery can catch fire. The burning lithium creates a metal fire existing at temperatures of 2,000 degrees Celsius/3632 degrees Fahrenheit. Attempting to douse the fire with water is inadvisable since this could lead to a hydrogen gas explosion!"

https://www.envistaforensics.com/blog/electrical-fires-what-you-need-to-know-about-lithium-ion-batteries/#:~:text=Fire%20ignition%20establishes%20that%20the,degrees%20Celsius%2F3632%20degrees%20Fahrenheit.

On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:

> No, Martin - it is an Opel (GM) model, not a BMW. ;-)
> Take a look at the video at time stamp 12:50.
>
Happy to take your word for that. What battery capacity does that model
have?

--
--
Martin | martin at
Gregorie | gregorie dot org

On Wednesday, August 11, 2021 at 3:23:59 AM UTC-4, Martin Gregorie wrote:
> On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:
>
> > No, Martin - it is an Opel (GM) model, not a BMW. ;-)
> > Take a look at the video at time stamp 12:50.
> >
> Happy to take your word for that. What battery capacity does that model
> have?
> --
> --
> Martin | martin at
> Gregorie | gregorie dot org

Hi Martin - I had to look up the model myself - GM doesn't sell this vehicle over here in the US. The German Opel site shows this as a 'Mokka' and it has a 50kWh battery.
https://www.opel.de/fahrzeuge/mokka-modelle/mokka-e/uebersicht.html
One paragraph talks about '216 high density cells with the most advanced thermal management system for maximum range and longevity'.
Well - I guess that didn't work out well for at least that one car .... ;-)

Uli
'AS'

On Tuesday, August 10, 2021 at 4:16:26 PM UTC-4, Eric Greenwell wrote:
> On 8/9/2021 2:40 PM, Kenn Sebesta wrote:
> > On Monday, August 9, 2021 at 7:26:49 AM UTC-4, wtwisn...@gmail.com wrote:
> >> Fire has never mixed well with airframes and probably never will. The goal is necessarily isolating the fire and its gas products.
> >
> > I think this is about the best comment here. I am unaware of any plan to extinguish fuel tank fires in aircraft, and the tragic tale of TWA 800 shows the consequences. We have learned through many years to manage the risk of gasoline and other flammables.
> >
> > The energy required for self-launching a 500kg plane is on the order of 200mL of gasoline so it's easy to think this is a much more manageable problem than it seems at first glance.
> >
> > (If three days for a massive battery farm sounds like a long time, consider that it took *two years* to extinguish a tire fire in California: https://www.sfgate.com/bayarea/article/After-2-Years-Smoking-Tires-Close-to-3236405.php. And we're still dealing with the fire consequences of Chernobyl and Fukushima. In general, anytime you concentrate energy, the fires last for a long time.)
> >
> > When it comes to managing lithium fires, it must be understood that the lithium fire is not the problem but the problem's source. Think of it like a fire starter cube you'd throw under the charcoal to get the charcoal fire going. You can't really extinguish the firestarter (battery) once it's going, but if you can keep it from igniting the charcoal (airframe), then once it source burns itself out you've dodged a bullet. And it will burn itself out somewhat quickly, as the amount of oxygen generated inside the decomposing battery is not that much.
> >
> > If the battery is fuselage-mounted[*], there are two possible routes which come to mind for doing this. One is to eject the battery, and the other is place it in an airtight and fireproof box with a vent to the outside. Ejecting the battery can be dicey because of its impact on the CG, but venting the battery to the outside sounds plausible.
> >
> > The design we're considering is a large metal tube with a pressure release valve. If a battery starts outgassing, then the pressure rises and the valve pops, allowing the hot gasses to escape to the underside of the aircraft. A variety of strategies for fireproofing the box are things such as intumescent paint or simply wrapping it in ceramic insulation.
> >
> > [*] If the battery is wing-mounted you have as many options as the towplane with its 50gal of gasoline does: none.
> How about a 6 foot long metal tube/tray (doesn't have to be round) that slides into the D
> tube in the wing? Having the tube in the wing, with external venting, would keep battery
> gases out of the cockpit.
>
> There is plenty volume in that area, and it could hold 200+ 18650 cells easily, over 2.2
> kWh. Or use a high temperature composite if the tray needs to be a complex shape. The
> interior of the D tube (or the exterior of the tray) could be painted with intumescent
> paint to protect the wing. A fire suppression system that released gas into the tray
> during a cell fire might keep the composite tube from burning until the cell's energy was
> exhausted.

You make a good point, I will back off my assertion that there are no effective fire mitigation strategies for a wing-mounted battery. What I should say is that any successful strategy for the wing will be the fruit of a lot of R&D. This likely has to be paid for by a grant because there's nothing patentable about testing to destruction in order to figure out the right blend of spacing, isolation, insulation, and fire resistant material.

We could easily imagine compartmentalizing the batteries into many fireproof bays, each with individual venting. Maybe even blow-off caps which fully open the bay preventing preventing gasses from spreading laterally. But this kind of product testing won't be done by individuals upgrading their existing gliders nor by manufacturers already struggling to stay in business.

In the meanwhile, awaiting the grant to do the fundamental research, I think we can work with mitigation of wing-mounted battery fires. If you have a fire at >1000', bail out. If it's at fewer than 1000', the airframe only needs to survive 60 seconds. (I have the same strategy in my gasoline self-launcher, which places a hot engine next to a 2gal gas tank.)

It goes without saying that a plane with stored energy is more flammable than one without. Getting a plane up in the air takes releasing that stored energy at some point in the pipeline, and I like to think we're not so egocentric as to assume that it's okay for the tow-pilot to take this fire risk, but not we.

On 8/11/21 7:26 AM, AS wrote:
> On Wednesday, August 11, 2021 at 3:23:59 AM UTC-4, Martin Gregorie wrote:
>> On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:
>>
>>> No, Martin - it is an Opel (GM) model, not a BMW. ;-)
>>> Take a look at the video at time stamp 12:50.
>>>
>> Happy to take your word for that. What battery capacity does that model
>> have?
>> --
>> --
>> Martin | martin at
>> Gregorie | gregorie dot org
>
> Hi Martin - I had to look up the model myself - GM doesn't sell this vehicle over here in the US. The German Opel site shows this as a 'Mokka' and it has a 50kWh battery.
> https://www.opel.de/fahrzeuge/mokka-modelle/mokka-e/uebersicht.html
> One paragraph talks about '216 high density cells with the most advanced thermal management system for maximum range and longevity'.
> Well - I guess that didn't work out well for at least that one car .... ;-)
>
> Uli
> 'AS'
>

Described as an Opal Ampera-E at this website (European version of the
Chevy Bolt)

https://electrek.co/2021/07/28/everything-we-know-about-the-chevy-bolt-ev-fires/

On Wednesday, August 11, 2021 at 10:01:24 AM UTC-4, kinsell wrote:
> On 8/11/21 7:26 AM, AS wrote:
> > On Wednesday, August 11, 2021 at 3:23:59 AM UTC-4, Martin Gregorie wrote:
> >> On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:
> >>
> >>> No, Martin - it is an Opel (GM) model, not a BMW. ;-)
> >>> Take a look at the video at time stamp 12:50.
> >>>
> >> Happy to take your word for that. What battery capacity does that model
> >> have?
> >> --
> >> --
> >> Martin | martin at
> >> Gregorie | gregorie dot org
> >
> > Hi Martin - I had to look up the model myself - GM doesn't sell this vehicle over here in the US. The German Opel site shows this as a 'Mokka' and it has a 50kWh battery.
> > https://www.opel.de/fahrzeuge/mokka-modelle/mokka-e/uebersicht.html
> > One paragraph talks about '216 high density cells with the most advanced thermal management system for maximum range and longevity'.
> > Well - I guess that didn't work out well for at least that one car .... ;-)
> >
> > Uli
> > 'AS'
> >
> Described as an Opal Ampera-E at this website (European version of the
> Chevy Bolt)
>
> https://electrek.co/2021/07/28/everything-we-know-about-the-chevy-bolt-ev-fires/

Interesting! Thanks for the correction.

Uli
'AS'

Was the point of that video to show how difficult (impossible) it was to
douse the fire?  Because the crash didn't start the fire nor did kicking
the battery.  In fact, they had to shove a tray of burning gasoline
under the car for a while to get the fire to start.

Dan
5J

On 8/11/21 7:26 AM, AS wrote:
> On Wednesday, August 11, 2021 at 3:23:59 AM UTC-4, Martin Gregorie wrote:
>> On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:
>>
>>> No, Martin - it is an Opel (GM) model, not a BMW. ;-)
>>> Take a look at the video at time stamp 12:50.
>>>
>> Happy to take your word for that. What battery capacity does that model
>> have?
>> --
>> --
>> Martin | martin at
>> Gregorie | gregorie dot org
> Hi Martin - I had to look up the model myself - GM doesn't sell this vehicle over here in the US. The German Opel site shows this as a 'Mokka' and it has a 50kWh battery.
> https://www.opel.de/fahrzeuge/mokka-modelle/mokka-e/uebersicht.html
> One paragraph talks about '216 high density cells with the most advanced thermal management system for maximum range and longevity'.
> Well - I guess that didn't work out well for at least that one car .... ;-)
>
> Uli
> 'AS'

On 8/10/2021 9:59 PM, 2G wrote:

>>> Did you read the OSTIV presentation that Dave Nadler referenced? It indicated keeping the
>>> adjacent cells from thermal runaway was not difficult for 18650 cells with adequate
>>> spacing, given the relatively small energy in each cell. It did not even propose a metal case.
>>> --
>>> Eric Greenwell - USA
>>> - "A Guide to Self-launching Sailplane Operation"
>>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>> Yes, I read it, and no, you HAVE to test it - opinions are best left to the opinion page of the newspaper. Nothing but metal will melt and catch fire itself, and, then, the wrong kind of metal will melt - perhaps you should look at pictures of the aftermath of electric car fires.
>>
>> Tom
>
> Does this answer your question?
> "Fire ignition establishes that the cathode of the battery can catch fire. The burning lithium creates a metal fire existing at temperatures of 2,000 degrees Celsius/3632 degrees Fahrenheit. Attempting to douse the fire with water is inadvisable since this could lead to a hydrogen gas explosion!"
>
> https://www.envistaforensics.com/blog/electrical-fires-what-you-need-to-know-about-lithium-ion-batteries/#:~:text=Fire%20ignition%20establishes%20that%20the,degrees%20Celsius%2F3632%20degrees%20Fahrenheit.
>
No, it doesn't, because I haven't even mentioned water. But you have answered my question
about reading the OSTIV article. Their opinion was based on tests they ran, and their
opinion is shared by others: 18650 cells in battery packs can be spaced so that a runaway
cell does not cause runaway in the cells adjacent to it. It is much easier to protect a
pack from one burning cell than several cells, and that's one reason car batteries are not
good comparison to glider use: the cells in car batteries are packed much more densely
than they are in glider packs. More pertinent to gliders is the Antares, which uses
cylindrical cells: 17 years since the first delivery, and no battery fires.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Wednesday, August 11, 2021 at 10:15:04 AM UTC-4, Dan Marotta wrote:
> Was the point of that video to show how difficult (impossible) it was to
> douse the fire? Because the crash didn't start the fire nor did kicking
> the battery. In fact, they had to shove a tray of burning gasoline
> under the car for a while to get the fire to start.
>
> Dan
> 5J

Hi Dan - we must be talking about two different videos here. The vehicle in the 'Red Box' video was parked at a charging station. They showed the signage pointing out that this is a spot reserved for e-vehicles during charging. In the link kinsell provided, you can find the narrative by the owner of the 'Langenfeld Fire'. He confirmed that the vehicle was on charge and that it sent him two text messages when the fire started and during the fire fighting activities, informing him of theft and break-in.
There was no crash or tray of gasoline involved here.

Uli
'AS'

On Wed, 11 Aug 2021 07:31:55 -0700, Eric Greenwell wrote:

> On 8/10/2021 9:59 PM, 2G wrote:
>
>>>> Did you read the OSTIV presentation that Dave Nadler referenced? It
>>>> indicated keeping the adjacent cells from thermal runaway was not
>>>> difficult for 18650 cells with adequate spacing, given the relatively
>>>> small energy in each cell. It did not even propose a metal case.
>>>> --
>>>> Eric Greenwell - USA - "A Guide to Self-launching Sailplane
>>>> Operation"
>>>> https://sites.google.com/site/motorgliders/publications/download-the-
guide-1
>>> Yes, I read it, and no, you HAVE to test it - opinions are best left
>>> to the opinion page of the newspaper. Nothing but metal will melt and
>>> catch fire itself, and, then, the wrong kind of metal will melt -
>>> perhaps you should look at pictures of the aftermath of electric car
>>> fires.
>>>
>>> Tom
>>
>> Does this answer your question?
>> "Fire ignition establishes that the cathode of the battery can catch
>> fire. The burning lithium creates a metal fire existing at temperatures
>> of 2,000 degrees Celsius/3632 degrees Fahrenheit. Attempting to douse
>> the fire with water is inadvisable since this could lead to a hydrogen
>> gas explosion!"
>>
>> https://www.envistaforensics.com/blog/electrical-fires-what-you-need-
to-know-about-lithium-ion-batteries/
#:~:text=Fire%20ignition%20establishes%20that%20the,degrees%20Celsius%2F3632%20degrees%20Fahrenheit.
>>
> No, it doesn't, because I haven't even mentioned water. But you have
> answered my question about reading the OSTIV article. Their opinion was
> based on tests they ran, and their opinion is shared by others: 18650
> cells in battery packs can be spaced so that a runaway cell does not
> cause runaway in the cells adjacent to it. It is much easier to protect
> a pack from one burning cell than several cells, and that's one reason
> car batteries are not good comparison to glider use: the cells in car
> batteries are packed much more densely than they are in glider packs.
> More pertinent to gliders is the Antares, which uses cylindrical cells:
> 17 years since the first delivery, and no battery fires.

So, BTW, were the Lithium battery packs that, a few years ago, were self-
combusting in Boeing 787s. Has anybody seen what Boeing's end solution
was?

IIRC their initial change was to fireproof the area containing the
battery pack and add a conduit that would vent the smoke etc overboard
while the battery burnt itself out. Their original battery was densely
packaged in a steel casing, i.e. a very similar arrangement to the self-
launching glider battery packs that caught fire, but I haven't heard
whether they redesigned it later.

--
--
Martin | martin at
Gregorie | gregorie dot org

On 8/11/2021 6:51 AM, Kenn Sebesta wrote:
> On Tuesday, August 10, 2021 at 4:16:26 PM UTC-4, Eric Greenwell wrote:
....
> You make a good point, I will back off my assertion that there are no effective fire mitigation strategies for a wing-mounted battery. What I should say is that any successful strategy for the wing will be the fruit of a lot of R&D. This likely has to be paid for by a grant because there's nothing patentable about testing to destruction in order to figure out the right blend of spacing, isolation, insulation, and fire resistant material.
>
> We could easily imagine compartmentalizing the batteries into many fireproof bays, each with individual venting. Maybe even blow-off caps which fully open the bay preventing preventing gasses from spreading laterally. But this kind of product testing won't be done by individuals upgrading their existing gliders nor by manufacturers already struggling to stay in business.
>
> In the meanwhile, awaiting the grant to do the fundamental research, I think we can work with mitigation of wing-mounted battery fires. If you have a fire at >1000', bail out. If it's at fewer than 1000', the airframe only needs to survive 60 seconds. (I have the same strategy in my gasoline self-launcher, which places a hot engine next to a 2gal gas tank.)
>
> It goes without saying that a plane with stored energy is more flammable than one without. Getting a plane up in the air takes releasing that stored energy at some point in the pipeline, and I like to think we're not so egocentric as to assume that it's okay for the tow-pilot to take this fire risk, but not we.
>
I don't think it'd be that hard at all: my casual search came across several studies and
articles on just this problem (The OSTIV reference is one of them, Feb 2018 Soaring
article on AS efforts is another), so some those may be enough to get a jump start on the
tray design. Even better, find out what AS is doing for their wing mounted batteries in
the AS33/34. AS or one of owners could send pictures of the battery packs and copies of
useful pages from the manuals. That might be all you need to know.

If you want to invent it all, then ...
- sketch the basic tray you'd use, build a one foot section of it, populate with cells,
trigger thermal runaway in the cell in the most critical location. After a few tests, you
will likely know what the tray materials need to be, if insulation is needed, and if you
have the inter-cell spacing right.
- trigger cells a few times in a volume about the same as the tray to get the pressures
and gas volumes a runaway cell produces. Now you can do the basic design for venting the
tray externally. I'm guessing a 4" x 6" g flap on the bottom of the wing, normally held
closed by a weak spring, would be sufficient.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Wed, 11 Aug 2021 06:26:57 -0700, AS wrote:

> On Wednesday, August 11, 2021 at 3:23:59 AM UTC-4, Martin Gregorie
> wrote:
>> On Tue, 10 Aug 2021 16:34:45 -0700, AS wrote:
>>
>> > No, Martin - it is an Opel (GM) model, not a BMW. ;-)
>> > Take a look at the video at time stamp 12:50.
>> >
>> Happy to take your word for that. What battery capacity does that model
>> have?
>> --
>> --
>> Martin | martin at Gregorie | gregorie dot org
>
> Hi Martin - I had to look up the model myself - GM doesn't sell this
> vehicle over here in the US. The German Opel site shows this as a
> 'Mokka' and it has a 50kWh battery.
> https://www.opel.de/fahrzeuge/mokka-modelle/mokka-e/uebersicht.html One
> paragraph talks about '216 high density cells with the most advanced
> thermal management system for maximum range and longevity'.
> Well - I guess that didn't work out well for at least that one car ....
> ;-)
>

I checked what Wikipedia had to say about Opel cars:
https://en.wikipedia.org/wiki/Opel#Current_model_range

That says that the Mokka is an petrol or diesel SUV, sold in the US as
the Buick Encore.

However, there is an externally similar car, the Opel Ampera/
Ampera-e, which is a rebadged Chevrolet Bolt. The latter is known to be
inflammable: two recalls so far, the second for catching fire while being
charged. - saw that in Ars Technica, 7/23/2021

At one point in the video it looks as though there's a charger on the
sidewalk near the front of the burning Opel, so is it possible it was on
charge when it caught fire? The Bolt's charging socket is just behind the
top of the front left wheel arch.

--
--
Martin | martin at
Gregorie | gregorie dot org

On 8/11/21 10:54 AM, Martin Gregorie wrote:

> So, BTW, were the Lithium battery packs that, a few years ago, were self-
> combusting in Boeing 787s. Has anybody seen what Boeing's end solution
> was?
>
> IIRC their initial change was to fireproof the area containing the
> battery pack and add a conduit that would vent the smoke etc overboard
> while the battery burnt itself out. Their original battery was densely
> packaged in a steel casing, i.e. a very similar arrangement to the self-
> launching glider battery packs that caught fire, but I haven't heard
> whether they redesigned it later.
>
>

They separated the cells a bit, and used a stainless steel containment
box vented to the outside with blowout plugs. That was their final
'solution'.

AFAIK, the FES folks have always used a carbon fiber box for their
batteries. They do recommend stainless steel boxes for transporting the
batteries in cars.

Thanks Uli.  I guess I clicked on the wrong link.

Dan
5J

On 8/11/21 8:35 AM, AS wrote:
> On Wednesday, August 11, 2021 at 10:15:04 AM UTC-4, Dan Marotta wrote:
>> Was the point of that video to show how difficult (impossible) it was to
>> douse the fire? Because the crash didn't start the fire nor did kicking
>> the battery. In fact, they had to shove a tray of burning gasoline
>> under the car for a while to get the fire to start.
>>
>> Dan
>> 5J
> Hi Dan - we must be talking about two different videos here. The vehicle in the 'Red Box' video was parked at a charging station. They showed the signage pointing out that this is a spot reserved for e-vehicles during charging. In the link kinsell provided, you can find the narrative by the owner of the 'Langenfeld Fire'. He confirmed that the vehicle was on charge and that it sent him two text messages when the fire started and during the fire fighting activities, informing him of theft and break-in.
> There was no crash or tray of gasoline involved here.
>
> Uli
> 'AS'

> I don't think it'd be that hard at all: my casual search came across several studies and
> articles on just this problem (The OSTIV reference is one of them, Feb 2018 Soaring
> article on AS efforts is another), so some those may be enough to get a jump start on the
> tray design. Even better, find out what AS is doing for their wing mounted batteries in
> the AS33/34. AS or one of owners could send pictures of the battery packs and copies of
> useful pages from the manuals. That might be all you need to know.
>
> If you want to invent it all, then ...
> - sketch the basic tray you'd use, build a one foot section of it, populate with cells,
> trigger thermal runaway in the cell in the most critical location. After a few tests, you
> will likely know what the tray materials need to be, if insulation is needed, and if you
> have the inter-cell spacing right.
> - trigger cells a few times in a volume about the same as the tray to get the pressures
> and gas volumes a runaway cell produces. Now you can do the basic design for venting the
> tray externally. I'm guessing a 4" x 6" g flap on the bottom of the wing, normally held
> closed by a weak spring, would be sufficient.

I don't disagree with the approach, but proving it out at a variety of cell configurations, altitudes, and environmental conditions inevitably takes a lot of money and time. There's just a lot of question marks and we need a large body of evidence before we can be sure we've fully understood the problem.

Much of it might come from modeling, but at a certain point we've got to intentionally sabotage the batteries in flight and then test the wings to destruction to ensure the models are correct. I don't know how many airframes I would want to see go through this process, but I suspect at least 5 before we can truly be sure we've found the edge cases. That gets pricey.

I'm not saying it won't work if you don't do the testing and just rely on the literature, but there will inevitably be lessons to be learned about our specific use case, and I don't think we want to trust our safety to an untested concept when we can simply bail out.

The reason why venting is straightforward in a fuselage is because we can vent everything through just one tube and we don't (necessarily) need to keep the fire from spreading between cells because we can do a much better job of insulating the batteries. So every test can be a worst-case test and in the event of a fire it's much easier, relative to a wing skin and spar, to inspect and repair the fuselage before reuse.

On Wednesday, August 11, 2021 at 3:43:47 PM UTC-4, kinsell wrote:
> On 8/11/21 10:54 AM, Martin Gregorie wrote:
>
> > So, BTW, were the Lithium battery packs that, a few years ago, were self-
> > combusting in Boeing 787s. Has anybody seen what Boeing's end solution
> > was?
> >
> > IIRC their initial change was to fireproof the area containing the
> > battery pack and add a conduit that would vent the smoke etc overboard
> > while the battery burnt itself out. Their original battery was densely
> > packaged in a steel casing, i.e. a very similar arrangement to the self-
> > launching glider battery packs that caught fire, but I haven't heard
> > whether they redesigned it later.
> >
> >
> They separated the cells a bit, and used a stainless steel containment
> box vented to the outside with blowout plugs. That was their final
> 'solution'.
>
> AFAIK, the FES folks have always used a carbon fiber box for their
> batteries. They do recommend stainless steel boxes for transporting the
> batteries in cars.

It would not seem to be a good idea to use a conductive box to contain pouch type cells that could be prone to abrasion and shorting.
I suspect that the new boxes in the FES gliders are glass. The box in my electric ASW-24E is glass. I'm using 18650 cells.
"Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
such a test.
FWIW
UH

On 8/11/2021 2:22 PM, Hank Nixon wrote:
> On Wednesday, August 11, 2021 at 3:43:47 PM UTC-4, kinsell wrote:
>> On 8/11/21 10:54 AM, Martin Gregorie wrote:
>>
>>> So, BTW, were the Lithium battery packs that, a few years ago, were self-
>>> combusting in Boeing 787s. Has anybody seen what Boeing's end solution
>>> was?
>>>
>>> IIRC their initial change was to fireproof the area containing the
>>> battery pack and add a conduit that would vent the smoke etc overboard
>>> while the battery burnt itself out. Their original battery was densely
>>> packaged in a steel casing, i.e. a very similar arrangement to the self-
>>> launching glider battery packs that caught fire, but I haven't heard
>>> whether they redesigned it later.
>>>
>>>
>> They separated the cells a bit, and used a stainless steel containment
>> box vented to the outside with blowout plugs. That was their final
>> 'solution'.
>>
>> AFAIK, the FES folks have always used a carbon fiber box for their
>> batteries. They do recommend stainless steel boxes for transporting the
>> batteries in cars.
>
> It would not seem to be a good idea to use a conductive box to contain pouch type cells that could be prone to abrasion and shorting.
> I suspect that the new boxes in the FES gliders are glass. The box in my electric ASW-24E is glass. I'm using 18650 cells.
> "Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
> such a test.
> FWIW
> UH

That's the Feb 2018 issue. From the article "Electric Propulsion in Gliders Is More Than
an Alternative to Traditional Combustion Engines"

"The temperature near the nailed cell was measured with a thermocouple, and indicated >
500C. These tests have been made several times. At no time was there a chain reaction
leading to thermal runaway or short-circuit of surrounding cells. The voltage level of the
cell package after the test was nearly the same as before. Figure 15 shows different cell
packages after a nail-test."

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Wednesday, August 11, 2021 at 3:23:38 PM UTC-7, Eric Greenwell wrote:
> On 8/11/2021 2:22 PM, Hank Nixon wrote:
> > On Wednesday, August 11, 2021 at 3:43:47 PM UTC-4, kinsell wrote:
> >> On 8/11/21 10:54 AM, Martin Gregorie wrote:
> >>
> >>> So, BTW, were the Lithium battery packs that, a few years ago, were self-
> >>> combusting in Boeing 787s. Has anybody seen what Boeing's end solution
> >>> was?
> >>>
> >>> IIRC their initial change was to fireproof the area containing the
> >>> battery pack and add a conduit that would vent the smoke etc overboard
> >>> while the battery burnt itself out. Their original battery was densely
> >>> packaged in a steel casing, i.e. a very similar arrangement to the self-
> >>> launching glider battery packs that caught fire, but I haven't heard
> >>> whether they redesigned it later.
> >>>
> >>>
> >> They separated the cells a bit, and used a stainless steel containment
> >> box vented to the outside with blowout plugs. That was their final
> >> 'solution'.
> >>
> >> AFAIK, the FES folks have always used a carbon fiber box for their
> >> batteries. They do recommend stainless steel boxes for transporting the
> >> batteries in cars.
> >
> > It would not seem to be a good idea to use a conductive box to contain pouch type cells that could be prone to abrasion and shorting.
> > I suspect that the new boxes in the FES gliders are glass. The box in my electric ASW-24E is glass. I'm using 18650 cells.
> > "Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
> > such a test.
> > FWIW
> > UH
> That's the Feb 2018 issue. From the article "Electric Propulsion in Gliders Is More Than
> an Alternative to Traditional Combustion Engines"
>
> "The temperature near the nailed cell was measured with a thermocouple, and indicated >
> 500C. These tests have been made several times. At no time was there a chain reaction
> leading to thermal runaway or short-circuit of surrounding cells. The voltage level of the
> cell package after the test was nearly the same as before. Figure 15 shows different cell
> packages after a nail-test."
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Here is the report on the Arizona ESS fire:
https://www.aps.com/-/media/APS/APSCOM-PDFs/About/Our-Company/Newsroom/McMickenFinalTechnicalReport.ashx?la=en&hash=50335FB5098D9858BFD276C40FA54FCE

I draw your attention to section 3.2 How thermal runaway is different from a fire. The point out that a chemical reaction takes place that requires no O2 whatsoever. They continue on and make this point:

"In fact, the potential of a non-flame thermal runaway event creates a scenario where high heat and combustible gases can coexist without igniting."

This happened at the McMicken facility, which ultimately resulted in an explosion that blew the doors off the compartment (fig. 5). The entire event was triggered by the failure of a single cell in one rack. And they had a fire suppression system - that was triggered - which had no effect on the fire whatsoever.

The batteries in the NZ Taurus Electro were in a metal container which was blown open, catapulting the cells in all directions. This points to an explosive event.

This report was referenced in the McMicken report, detailing the generation of toxic gases in a lithium thermal runaway (I am going to stop using the word "fire" to describe this event because it is inaccurate and misleading):
https://www.nature.com/articles/s41598-017-09784-z.pdf
One, or more, of these gases is likely what incapacitated the pilot of the Taurus. I am not sure that wing mounted batteries would be that much better because there are openings between the wing root and the fuselage for control linkages and water ballast controls.

I checked the Schleicher website to see what type of battery chemistry is used in the AS 34 Me, but they only mention battery capacity (probably don't want to divulge design secrets). I sent an email to GP Gliders to see what battery chemistry and cell manufacturer they are using and got no reply. This secretiveness will make it more difficult to independently assess battery safety. They will probably have to be more forthcoming to EASA, however.

Tom

On Wednesday, August 11, 2021 at 6:23:38 PM UTC-4, Eric Greenwell wrote:
> On 8/11/2021 2:22 PM, Hank Nixon wrote:
> > On Wednesday, August 11, 2021 at 3:43:47 PM UTC-4, kinsell wrote:
> >> On 8/11/21 10:54 AM, Martin Gregorie wrote:
> >>
> >>> So, BTW, were the Lithium battery packs that, a few years ago, were self-
> >>> combusting in Boeing 787s. Has anybody seen what Boeing's end solution
> >>> was?
> >>>
> >>> IIRC their initial change was to fireproof the area containing the
> >>> battery pack and add a conduit that would vent the smoke etc overboard
> >>> while the battery burnt itself out. Their original battery was densely
> >>> packaged in a steel casing, i.e. a very similar arrangement to the self-
> >>> launching glider battery packs that caught fire, but I haven't heard
> >>> whether they redesigned it later.
> >>>
> >>>
> >> They separated the cells a bit, and used a stainless steel containment
> >> box vented to the outside with blowout plugs. That was their final
> >> 'solution'.
> >>
> >> AFAIK, the FES folks have always used a carbon fiber box for their
> >> batteries. They do recommend stainless steel boxes for transporting the
> >> batteries in cars.
> >
> > It would not seem to be a good idea to use a conductive box to contain pouch type cells that could be prone to abrasion and shorting.
> > I suspect that the new boxes in the FES gliders are glass. The box in my electric ASW-24E is glass. I'm using 18650 cells.
> > "Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
> > such a test.
> > FWIW
> > UH
> That's the Feb 2018 issue. From the article "Electric Propulsion in Gliders Is More Than
> an Alternative to Traditional Combustion Engines"
>
> "The temperature near the nailed cell was measured with a thermocouple, and indicated >
> 500C. These tests have been made several times. At no time was there a chain reaction
> leading to thermal runaway or short-circuit of surrounding cells. The voltage level of the
> cell package after the test was nearly the same as before. Figure 15 shows different cell
> packages after a nail-test."

That points toward a LiFePo4 cell. Those are notoriously stable, to the point that causing a physical breach hardly affects their internal voltage.

LiFePo4 are popular in busses and other EVs which require frequent power surges. The takeoff and initial climbout of a glider are a natural fit for them, although their power density is 20-40% lower than other lithium batteries so they have their limitations.

I applaud your careful reading and study of the science and experience, as they show the daily truth for the billions of lithium batteries out there. I encourage you to join myself and others in not engaging with those who wear their confirmation bias too proudly. They shout out there was an explosion in NZ, despite the accident report to the contrary: https://www.aviation..govt.nz/assets/publications/fatal-accident-reports/ZK-GEL-Final-Report-7-December-2020.pdf. They would have us believe that every cell is an inevitable catastrophe, despite that in the APS Arizona thermal runaway event four of the five primary contributing factors were insufficient design and insufficient response.

Those who have expressed clearly they have no interest in being part of the future have little role to play in a conversation about how we're going to get there.

On 8/11/2021 5:42 PM, 2G wrote:
> On Wednesday, August 11, 2021 at 3:23:38 PM UTC-7, Eric Greenwell wrote:
....
>>> "Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
>>> such a test.
>>> FWIW
>>> UH
>> That's the Feb 2018 issue. From the article "Electric Propulsion in Gliders Is More Than
>> an Alternative to Traditional Combustion Engines"
>>
>> "The temperature near the nailed cell was measured with a thermocouple, and indicated >
>> 500C. These tests have been made several times. At no time was there a chain reaction
>> leading to thermal runaway or short-circuit of surrounding cells. The voltage level of the
>> cell package after the test was nearly the same as before. Figure 15 shows different cell
>> packages after a nail-test."
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>
> Here is the report on the Arizona ESS fire:
> https://www.aps.com/-/media/APS/APSCOM-PDFs/About/Our-Company/Newsroom/McMickenFinalTechnicalReport.ashx?la=en&hash=50335FB5098D9858BFD276C40FA54FCE
>
> I draw your attention to section 3.2 How thermal runaway is different from a fire. The point out that a chemical reaction takes place that requires no O2 whatsoever. They continue on and make this point:
>
> "In fact, the potential of a non-flame thermal runaway event creates a scenario where high heat and combustible gases can coexist without igniting."
>
> This happened at the McMicken facility, which ultimately resulted in an explosion that blew the doors off the compartment (fig. 5). The entire event was triggered by the failure of a single cell in one rack. And they had a fire suppression system - that was triggered - which had no effect on the fire whatsoever.
>
> The batteries in the NZ Taurus Electro were in a metal container which was blown open, catapulting the cells in all directions. This points to an explosive event.
>
> This report was referenced in the McMicken report, detailing the generation of toxic gases in a lithium thermal runaway (I am going to stop using the word "fire" to describe this event because it is inaccurate and misleading):
> https://www.nature.com/articles/s41598-017-09784-z.pdf
> One, or more, of these gases is likely what incapacitated the pilot of the Taurus. I am not sure that wing mounted batteries would be that much better because there are openings between the wing root and the fuselage for control linkages and water ballast controls.
>
> I checked the Schleicher website to see what type of battery chemistry is used in the AS 34 Me, but they only mention battery capacity (probably don't want to divulge design secrets). I sent an email to GP Gliders to see what battery chemistry and cell manufacturer they are using and got no reply. This secretiveness will make it more difficult to independently assess battery safety. They will probably have to be more forthcoming to EASA, however.
>
> Tom

The Jeta uses VTC6 cells (18650 cells), formerly made by Sony, now made by Murata. It's
not a secret, GP are just poor communicators. I contacted JS about their cells, and didn't
get an answer, but I don't think their chemistry is secret, either. The Taurus had lithium
polymer cells, either pouches or prismatic - very different from the cylindrical 18650
cells Li-ion cells I've been talking about. Same for the BESS - it used pouch cells.

Wing mounted batteries are in the D tube ahead of the spar; the control linkages are
behind the spar. The D tube can be sealed off from the fuselage, and vented out of the wing.

Here's a quote from the McMicken BESS report:

"Another method for mitigating cascading thermal runaway in battery design is to use
smaller cells and compartmentalization of batteries. Put simply, limited mass means
limited fuel, and limited fuel means less energy released over time, which in turn
decreases the overall power of the event."

That's what I'm talking about: 18650 cells have low mass (45g) and can be easily spaced to
prevent a runaway cell from triggering runaway in adjacent cells. There are plenty of
articles on avoiding cascading runaway with 18650 cells that are spread out, as they are
in a battery pack in the wing.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Thursday, 12 August 2021 at 06:37:47 UTC+2, Eric Greenwell wrote:
> The Jeta uses VTC6 cells (18650 cells), formerly made by Sony, now made by Murata. It's
> not a secret, GP are just poor communicators. I contacted JS about their cells, and didn't
> get an answer, but I don't think their chemistry is secret, either.

JS lists in their FAQ what batteries they use for their RES system (https://jonkersailplanes.co.za/faq-3/):
Cell Type/Brand is Sony/Murata US18650VTC6

Also from their design, they have a vent from the batteries to the outside in case of a thermal runaway.

On 8/11/2021 7:50 PM, Kenn Sebesta wrote:
> On Wednesday, August 11, 2021 at 6:23:38 PM UTC-4, Eric Greenwell wrote:
>> On 8/11/2021 2:22 PM, Hank Nixon wrote:
>...
>>> It would not seem to be a good idea to use a conductive box to contain pouch type cells that could be prone to abrasion and shorting.
>>> I suspect that the new boxes in the FES gliders are glass. The box in my electric ASW-24E is glass. I'm using 18650 cells.
>>> "Nail tests" have been done on grouped 18650 cells that did not exhibit runaway when a cell was shorted. Soaring magazine had a photo of
>>> such a test.
>>> FWIW
>>> UH
>> That's the Feb 2018 issue. From the article "Electric Propulsion in Gliders Is More Than
>> an Alternative to Traditional Combustion Engines"
>>
>> "The temperature near the nailed cell was measured with a thermocouple, and indicated >
>> 500C. These tests have been made several times. At no time was there a chain reaction
>> leading to thermal runaway or short-circuit of surrounding cells. The voltage level of the
>> cell package after the test was nearly the same as before. Figure 15 shows different cell
>> packages after a nail-test."
>
> That points toward a LiFePo4 cell. Those are notoriously stable, to the point that causing a physical breach hardly affects their internal voltage.
>
> LiFePo4 are popular in busses and other EVs which require frequent power surges. The takeoff and initial climbout of a glider are a natural fit for them, although their power density is 20-40% lower than other lithium batteries so they have their limitations.
>
> I applaud your careful reading and study of the science and experience, as they show the daily truth for the billions of lithium batteries out there. I encourage you to join myself and others in not engaging with those who wear their confirmation bias too proudly. They shout out there was an explosion in NZ, despite the accident report to the contrary: https://www.aviation.govt.nz/assets/publications/fatal-accident-reports/ZK-GEL-Final-Report-7-December-2020.pdf. They would have us believe that every cell is an inevitable catastrophe, despite that in the APS Arizona thermal runaway event four of the five primary contributing factors were insufficient design and insufficient response.
>
> Those who have expressed clearly they have no interest in being part of the future have little role to play in a conversation about how we're going to get there.
>
I engage with the doubters because their pessimism and bias may dissuade other pilots from
considering electric gliders, and because once in a while, I learn something useful from
them ("even a blind squirrel sometimes finds a nut"). I do wish they would focus on glider
applications instead of utility-scale power banks with their huge energies, and also
ignore cars, which have 10 times the cell quantities in dense, water cooled assemblies.

The cell used in the Soaring article's "nail test" was a Panasonic 18650PD, which is NMC
chemistry like the Murata VTC6.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1