On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
> On 11/6/2022 9:24 PM, 2G wrote:
> > On Sunday, November 6, 2022 at 8:59:48 PM UTC-8, Eric Greenwell wrote:
> >> On 11/6/2022 8:40 PM, 2G wrote:
> >>> Conclusion: fly at your OWN RISK!
> >> It's always been that way, Tom, even before the Wright brothers. Corollary: since it's OUR
> >> risk, we don't have to prove anything to you.
> >>
> >> You are welcome to offer opinions, but understand you do so at your own risk. Corollary:
> >> If you don't want people to question your claims, don't offer them.
> >> --
> >> Eric Greenwell - USA
> >> - "A Guide to Self-launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications
> >
> > Well, that is refreshing - you don't claim that egliders are risk free. I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks of lithium batteries. In my judgment the technology is not ready for CRITICAL life-dependent applications. Remember, it was YOU that asked for this information!
> >
> > Tom
> I don't think anyone here has claimed egliders are risk free, or that any motor/engine
> installation is risk free, but many of us believe the risk can be managed to an acceptable
> level. We've learned to manage the risks of unconnected controls, of leaving spoilers
> unlocked, of kiting during tow, and all the other risks involved in flying gliders, and we
> can learn to manage our propulsion systems, too.
>
> Note that it's an inclusive "we": pilots, soaring organizations, manufacturers, and
> regulators.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.

Tom

On 11/7/2022 6:01 PM, 2G wrote:
> On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
https://sites.google.com/site/motorgliders/publications
....
> There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.
>
> Tom

90 miles north of you, the US LAK dealer has sold electric gliders for years; meanwhile,
EASA certifies egliders, manufacturers build them, pilots buy and fly them. UNQUESTIONED
left the building a long time ago.

"I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks
of lithium batteries", but you are not meeting your own standards: "There is a level of
risk above which the technology SHOULD NOT be used..." is not a scientific fact, but your
judgement. Stick to the data, and your remarks will be better received.

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

On Tuesday, November 8, 2022 at 11:33:02 AM UTC-8, Eric Greenwell wrote:
> On 11/7/2022 6:01 PM, 2G wrote:
> > On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
> https://sites.google.com/site/motorgliders/publications
> ...
> > There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.
> >
> > Tom
> 90 miles north of you, the US LAK dealer has sold electric gliders for years; meanwhile,
> EASA certifies egliders, manufacturers build them, pilots buy and fly them. UNQUESTIONED
> left the building a long time ago.
> "I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks
> of lithium batteries", but you are not meeting your own standards: "There is a level of
> risk above which the technology SHOULD NOT be used..." is not a scientific fact, but your
> judgement. Stick to the data, and your remarks will be better received.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.

Tom

On 11/8/2022 9:06 PM, 2G wrote:
> On Tuesday, November 8, 2022 at 11:33:02 AM UTC-8, Eric Greenwell wrote:
>> On 11/7/2022 6:01 PM, 2G wrote:
>>> On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
>> https://sites.google.com/site/motorgliders/publications
>> ...
>>> There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.
>>>
>>> Tom
>> 90 miles north of you, the US LAK dealer has sold electric gliders for years; meanwhile,
>> EASA certifies egliders, manufacturers build them, pilots buy and fly them. UNQUESTIONED
>> left the building a long time ago.
>> "I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks
>> of lithium batteries", but you are not meeting your own standards: "There is a level of
>> risk above which the technology SHOULD NOT be used..." is not a scientific fact, but your
>> judgement. Stick to the data, and your remarks will be better received.
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications
>
> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
>
> Tom

Would you consider an electric glider powered by LiFe cells safe enough?

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

On Wednesday, November 9, 2022 at 8:12:40 AM UTC-8, Eric Greenwell wrote:
> On 11/8/2022 9:06 PM, 2G wrote:
> > On Tuesday, November 8, 2022 at 11:33:02 AM UTC-8, Eric Greenwell wrote:
> >> On 11/7/2022 6:01 PM, 2G wrote:
> >>> On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
> >> https://sites.google.com/site/motorgliders/publications
> >> ...
> >>> There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.
> >>>
> >>> Tom
> >> 90 miles north of you, the US LAK dealer has sold electric gliders for years; meanwhile,
> >> EASA certifies egliders, manufacturers build them, pilots buy and fly them. UNQUESTIONED
> >> left the building a long time ago.
> >> "I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks
> >> of lithium batteries", but you are not meeting your own standards: "There is a level of
> >> risk above which the technology SHOULD NOT be used..." is not a scientific fact, but your
> >> judgement. Stick to the data, and your remarks will be better received..
> >> --
> >> Eric Greenwell - USA
> >> - "A Guide to Self-launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications
> >
> > Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> >
> > Tom
> Would you consider an electric glider powered by LiFe cells safe enough?
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.

Tom

On Wednesday, November 9, 2022 at 7:51:38 PM UTC-5, 2G wrote:
> On Wednesday, November 9, 2022 at 8:12:40 AM UTC-8, Eric Greenwell wrote:
> > On 11/8/2022 9:06 PM, 2G wrote:
> > > On Tuesday, November 8, 2022 at 11:33:02 AM UTC-8, Eric Greenwell wrote:
> > >> On 11/7/2022 6:01 PM, 2G wrote:
> > >>> On Monday, November 7, 2022 at 5:21:11 AM UTC-8, Eric Greenwell wrote:
> > >> https://sites.google.com/site/motorgliders/publications
> > >> ...
> > >>> There is a level of risk above which the technology SHOULD NOT be used regardless of what its proponents say is acceptable. Given the stringent risk levels imposed by the FAA on aircraft systems I say it is UNQUESTIONED that lithium battery problems not easily, but vastly, exceed those levels. The technology simply is not ready for aircraft use.
> > >>>
> > >>> Tom
> > >> 90 miles north of you, the US LAK dealer has sold electric gliders for years; meanwhile,
> > >> EASA certifies egliders, manufacturers build them, pilots buy and fly them. UNQUESTIONED
> > >> left the building a long time ago.
> > >> "I am only trying to offer OBJECTIVE scientific data (not opinion as you say) on the risks
> > >> of lithium batteries", but you are not meeting your own standards: "There is a level of
> > >> risk above which the technology SHOULD NOT be used..." is not a scientific fact, but your
> > >> judgement. Stick to the data, and your remarks will be better received.
> > >> --
> > >> Eric Greenwell - USA
> > >> - "A Guide to Self-launching Sailplane Operation"
> > >> https://sites.google.com/site/motorgliders/publications
> > >
> > > Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> > >
> > > Tom
> > Would you consider an electric glider powered by LiFe cells safe enough?
> > --
> > Eric Greenwell - USA
> > - "A Guide to Self-launching Sailplane Operation"
> > https://sites.google.com/site/motorgliders/publications
> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
>
> Tom
Solved in mass sale batteries?, no. But a much better understanding on the lab scale (as published spring 2021 from multiple sources) of dendrite formation and prevention.

Big culprit is higher charge rates which is the Holy Grail to overcome. Second is the separator materials used.
Currently small scale is orders better than current "over the counter" batteries. I know of more current research but NDA's prevent me from saying more but should be published early 2022.

One paper... https://www.pnas.org/doi/10.1073/pnas.2109654118
another paper... https://onlinelibrary.wiley.com/doi/full/10.1002/aenm.202100666

Plenty more to look at online. I did an online search for "battery dendrites". Looking forward to next spring.

On 11/9/2022 4:51 PM, 2G wrote:

>>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
>>>
>>> Tom
>> Would you consider an electric glider powered by LiFe cells safe enough?
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications
>
> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
>
> Tom
I haven't looked for a paper that asserts anything about dendrites, because I don't think
it's information I need.

I am still curious about this: Would you consider an electric glider powered by LiFe cells
safe enough? You already use at least one Life battery in your glider, so it occurred to
me they might be acceptable for propelling a glider.

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

On Wednesday, November 9, 2022 at 8:26:03 PM UTC-8, Eric Greenwell wrote:
> On 11/9/2022 4:51 PM, 2G wrote:
>
> >>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> >>>
> >>> Tom
> >> Would you consider an electric glider powered by LiFe cells safe enough?
> >> --
> >> Eric Greenwell - USA
> >> - "A Guide to Self-launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications
> >
> > I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
> >
> > Tom
> I haven't looked for a paper that asserts anything about dendrites, because I don't think
> it's information I need.
>
> I am still curious about this: Would you consider an electric glider powered by LiFe cells
> safe enough? You already use at least one Life battery in your glider, so it occurred to
> me they might be acceptable for propelling a glider.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

I am curious why YOU asked for more scientific information on a subject that you didn't need.

I thought my answer was plain enough, but let me state it this way: at this time I don't consider ANY electric glider to be safe, at least by aviation standards.

Tom

On 11/9/2022 9:27 PM, 2G wrote:
> On Wednesday, November 9, 2022 at 8:26:03 PM UTC-8, Eric Greenwell wrote:
>> On 11/9/2022 4:51 PM, 2G wrote:
>>
>>>>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
>>>>>
>>>>> Tom
>>>> Would you consider an electric glider powered by LiFe cells safe enough?
>>>> --
>>>> Eric Greenwell - USA
>>>> - "A Guide to Self-launching Sailplane Operation"
>>>> https://sites.google.com/site/motorgliders/publications
>>>
>>> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
>>>
>>> Tom
>> I haven't looked for a paper that asserts anything about dendrites, because I don't think
>> it's information I need.
>>
>> I am still curious about this: Would you consider an electric glider powered by LiFe cells
>> safe enough? You already use at least one Life battery in your glider, so it occurred to
>> me they might be acceptable for propelling a glider.
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications
>
> I am curious why YOU asked for more scientific information on a subject that you didn't need.
>
> I thought my answer was plain enough, but let me state it this way: at this time I don't consider ANY electric glider to be safe, at least by aviation standards.
>
> Tom
Your answers were plain, but you didn't answer the question either time: Would you
consider an electric glider powered by LiFe cells to be safe enough?

I asked for more evidence about vibration induced problems the Taurus might have suffered,
not specifically scientific evidence. That knowledge might actually be of value to me and
others, as handling the batteries is up to the pilot. I did not ask for evidence on
dendrites, as there is nothing I can do about them.

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

On Thursday, November 10, 2022 at 10:43:10 AM UTC-5, Eric Greenwell wrote:
> On 11/9/2022 9:27 PM, 2G wrote:
> > On Wednesday, November 9, 2022 at 8:26:03 PM UTC-8, Eric Greenwell wrote:
> >> On 11/9/2022 4:51 PM, 2G wrote:
> >>
> >>>>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> >>>>>
> >>>>> Tom
> >>>> Would you consider an electric glider powered by LiFe cells safe enough?
> >>>> --
> >>>> Eric Greenwell - USA
> >>>> - "A Guide to Self-launching Sailplane Operation"
> >>>> https://sites.google.com/site/motorgliders/publications
> >>>
> >>> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
> >>>
> >>> Tom
> >> I haven't looked for a paper that asserts anything about dendrites, because I don't think
> >> it's information I need.
> >>
> >> I am still curious about this: Would you consider an electric glider powered by LiFe cells
> >> safe enough? You already use at least one Life battery in your glider, so it occurred to
> >> me they might be acceptable for propelling a glider.
> >> --
> >> Eric Greenwell - USA
> >> - "A Guide to Self-launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications
> >
> > I am curious why YOU asked for more scientific information on a subject that you didn't need.
> >
> > I thought my answer was plain enough, but let me state it this way: at this time I don't consider ANY electric glider to be safe, at least by aviation standards.
> >
> > Tom
> Your answers were plain, but you didn't answer the question either time: Would you
> consider an electric glider powered by LiFe cells to be safe enough?
>
> I asked for more evidence about vibration induced problems the Taurus might have suffered,
> not specifically scientific evidence. That knowledge might actually be of value to me and
> others, as handling the batteries is up to the pilot. I did not ask for evidence on
> dendrites, as there is nothing I can do about them.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

Interesting to challenge 2G m knowledge base which seems to be fairly extensive but selective in interpretation.
From my investigation I concluded that LiFe cells are not suitable due to low available max discharge rates. The number of cells needed in parallel would be impractical.
Studying available info shows that cell life varies a lot but it is most strongly affected by 3 parameters.
1- How fast is the charge. Fast charge is associated with heating but also significantly increases the rate of dendrite growth which leads to degraded capacity as well as increased internal resistance that reduces current supplying capability. "Fast" chargers that charge at a high rate, and then cut off at a point normally determined by voltage run the risk of over charging some cells before cut off to low rate which leads to early failure. Increases heat can lead to more damage. The auto people are really pushing this because range(top it up) and charge time are big issues in adopting electric cars.
2- Over charge- forcing maximum charge stresses weaker cells more and adds heat. It also accelerates dendrite growth.
3- High high a discharge rate. Higher rates lead to more heating and also promote faster dendrite growth affecting life expectancy. It also stresses the weaker cells more.
Generally it can be reasonably said that dendrite growth is more about life of cells than safety.
Safety can be enhanced a lot by:
1- Charge at low rate . I charge my glider battery at 3 amps maximum. My BMS will dissipate all of that as end of charge is reached.
2- Don't charge to max possible voltage. This stresses cells less by not over charging. In my case this sacrifices about 15% of theoretical possible capacity.
3- Discharge well below manufacturer's data sheet rate. My cells are rated at 25 amps and my max rate is 14 amps for 2 minutes, then about 9 amps after that. I never see a meaningful rise in battery pack temperature.
4- Don't over discharge. I limit to about 20% remaining.
5 Don't drop the damn things. At least one of the FES battery failures was associated with mechanical damage due to dropping. FES ships all now get special carrying boxes to protect batteries when not in the ship. In my battery the likely damage from dropping would probably be to connections. I highly doubt it would hurt individual cells. I wonder how many phones that have have Lipo batteries and caught fire had been dropped.
6- Choice in battery construction. My opinion here- Lion cylindrical(18650 "laptop" style) can be expected to be much more durable than the Lipo pouch type cells. They are simply more robust. That said they are more energy dense per pound and have a lot fewer connections to fail. With about 250 sailplanes currently using the Lipo batteries, they far outnumber the ones in use that have Lion cells.
7- Isolate the battery from the flight crew and vent it. My 24EL has a full fire wall, barrier surfaces in the motor bay, and operates with the motor bay doors open. Our ASH25 does not have a fire wall because it is physically not possible to do so.
FWIW- ready for incoming.
UH

On 11/7/22 6:42 AM, Dave Nadler wrote:

> The packs are better but still not all glider-pilot proof.
> We also discussed means of tracking abuse and the pack
> disabling itself (drop it on the pavement and it shuts off
> permanently). Not currently in certification requirements!
>
> Some of us enthusiasts are also healthy skeptics and engineers
> and live in the real world. And try to improve it.
>

Some things just can't be solved with technology. I keep remembering
how a large percentage of the FES battery packs were shipped back to the
factory fully charged, even after explicit instructions not to do that
(and after three fires!). Seems like some people just haven't gotten
the word yet that storing lithium batteries fully charged stresses them
and encourages the dendrite formation. The Electro Taurus pilot was
known to store his batteries fully charged, but that appears to be
uncommon practice.

My cell phone is smart enough to not charge the battery fully until just
before I typically get up in the morning. Doing something similar for
electric gliders is a much tougher problem.

-Dave

On 11/10/2022 8:52 AM, kinsell wrote:
> On 11/7/22 6:42 AM, Dave Nadler wrote:
>
>> The packs are better but still not all glider-pilot proof.
>> We also discussed means of tracking abuse and the pack
>> disabling itself (drop it on the pavement and it shuts off
>> permanently). Not currently in certification requirements!
>>
>> Some of us enthusiasts are also healthy skeptics and engineers
>> and live in the real world. And try to improve it.
>>
>
> Some things just can't be solved with technology.  I keep remembering how a large
> percentage of the FES battery packs were shipped back to the factory fully charged, even
> after explicit instructions not to do that (and after three fires!).  Seems like some
> people just haven't gotten the word yet that storing lithium batteries fully charged
> stresses them and encourages the dendrite formation.  The Electro Taurus pilot was known
> to store his batteries fully charged, but that appears to be uncommon practice.

It's hard to retrain some people that are accustomed to lead acid batteries, which prefer
a full charge, or end a long-time habit of charging fully overnight, and even just to get
them to Read the Full Manual. The five FES pilots I know are fully aware of the value of
partial charging for periods longer than a day or two, and have the discharging equipment
required to reduce charge when needed.

> My cell phone is smart enough to not charge the battery fully until just before I
> typically get up in the morning.  Doing something similar for electric gliders is a much
> tougher problem.

Getting a partial charge isn't a problem if the battery is at your home, which would be
the case for most FES batteries. The Antares had it's own cell phone, so the pilot could
remotely check battery status, and command a full charge without going to the airport.
Electric gliders that have power and wifi available could easily do same thing remotely,
similar to the Antares, using a wifi controlled relay box. If WiFi isn't available, but
power is, a cell phone activated relay box could do the same thing as easily and almost as
cheaply.

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

On Thursday, November 10, 2022 at 7:43:10 AM UTC-8, Eric Greenwell wrote:
> On 11/9/2022 9:27 PM, 2G wrote:
> > On Wednesday, November 9, 2022 at 8:26:03 PM UTC-8, Eric Greenwell wrote:
> >> On 11/9/2022 4:51 PM, 2G wrote:
> >>
> >>>>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> >>>>>
> >>>>> Tom
> >>>> Would you consider an electric glider powered by LiFe cells safe enough?
> >>>> --
> >>>> Eric Greenwell - USA
> >>>> - "A Guide to Self-launching Sailplane Operation"
> >>>> https://sites.google.com/site/motorgliders/publications
> >>>
> >>> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
> >>>
> >>> Tom
> >> I haven't looked for a paper that asserts anything about dendrites, because I don't think
> >> it's information I need.
> >>
> >> I am still curious about this: Would you consider an electric glider powered by LiFe cells
> >> safe enough? You already use at least one Life battery in your glider, so it occurred to
> >> me they might be acceptable for propelling a glider.
> >> --
> >> Eric Greenwell - USA
> >> - "A Guide to Self-launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications
> >
> > I am curious why YOU asked for more scientific information on a subject that you didn't need.
> >
> > I thought my answer was plain enough, but let me state it this way: at this time I don't consider ANY electric glider to be safe, at least by aviation standards.
> >
> > Tom
> Your answers were plain, but you didn't answer the question either time: Would you
> consider an electric glider powered by LiFe cells to be safe enough?
>
> I asked for more evidence about vibration induced problems the Taurus might have suffered,
> not specifically scientific evidence. That knowledge might actually be of value to me and
> others, as handling the batteries is up to the pilot. I did not ask for evidence on
> dendrites, as there is nothing I can do about them.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

I answered your question as directly as I can. If that is not adequate, so be it.

ALL of the information I have on the Taurus Electro is in the accident report. If you want anything over and above it you will have to research it for yourself.

Tom

On Thursday, November 10, 2022 at 8:31:16 AM UTC-8, Hank Nixon wrote:
> On Thursday, November 10, 2022 at 10:43:10 AM UTC-5, Eric Greenwell wrote:
> > On 11/9/2022 9:27 PM, 2G wrote:
> > > On Wednesday, November 9, 2022 at 8:26:03 PM UTC-8, Eric Greenwell wrote:
> > >> On 11/9/2022 4:51 PM, 2G wrote:
> > >>
> > >>>>> Eric, then come up with ONE peer-reviewed scientific paper that says the dendrite growth problem in lithium batteries has BEEN SOLVED. Just ONE. Until then, you have just got a bunch of scientist wannabees that are only known for sweeping problems under the rug.
> > >>>>>
> > >>>>> Tom
> > >>>> Would you consider an electric glider powered by LiFe cells safe enough?
> > >>>> --
> > >>>> Eric Greenwell - USA
> > >>>> - "A Guide to Self-launching Sailplane Operation"
> > >>>> https://sites.google.com/site/motorgliders/publications
> > >>>
> > >>> I will take that as you can't even find ONE scientific paper that says the dendrite problem has been solved. LFP cells are just less likely to catch fire than other lithium chemistries - not a ringing endorsement. They are also considerably less energy dense, making them marginal for use as an eglider.
> > >>>
> > >>> Tom
> > >> I haven't looked for a paper that asserts anything about dendrites, because I don't think
> > >> it's information I need.
> > >>
> > >> I am still curious about this: Would you consider an electric glider powered by LiFe cells
> > >> safe enough? You already use at least one Life battery in your glider, so it occurred to
> > >> me they might be acceptable for propelling a glider.
> > >> --
> > >> Eric Greenwell - USA
> > >> - "A Guide to Self-launching Sailplane Operation"
> > >> https://sites.google.com/site/motorgliders/publications
> > >
> > > I am curious why YOU asked for more scientific information on a subject that you didn't need.
> > >
> > > I thought my answer was plain enough, but let me state it this way: at this time I don't consider ANY electric glider to be safe, at least by aviation standards.
> > >
> > > Tom
> > Your answers were plain, but you didn't answer the question either time: Would you
> > consider an electric glider powered by LiFe cells to be safe enough?
> >
> > I asked for more evidence about vibration induced problems the Taurus might have suffered,
> > not specifically scientific evidence. That knowledge might actually be of value to me and
> > others, as handling the batteries is up to the pilot. I did not ask for evidence on
> > dendrites, as there is nothing I can do about them.
> > --
> > Eric Greenwell - USA
> > - "A Guide to Self-launching Sailplane Operation"
> > https://sites.google.com/site/motorgliders/publications
> Interesting to challenge 2G m knowledge base which seems to be fairly extensive but selective in interpretation.
> From my investigation I concluded that LiFe cells are not suitable due to low available max discharge rates. The number of cells needed in parallel would be impractical.
> Studying available info shows that cell life varies a lot but it is most strongly affected by 3 parameters.
> 1- How fast is the charge. Fast charge is associated with heating but also significantly increases the rate of dendrite growth which leads to degraded capacity as well as increased internal resistance that reduces current supplying capability. "Fast" chargers that charge at a high rate, and then cut off at a point normally determined by voltage run the risk of over charging some cells before cut off to low rate which leads to early failure. Increases heat can lead to more damage. The auto people are really pushing this because range(top it up) and charge time are big issues in adopting electric cars.
> 2- Over charge- forcing maximum charge stresses weaker cells more and adds heat. It also accelerates dendrite growth.
> 3- High high a discharge rate. Higher rates lead to more heating and also promote faster dendrite growth affecting life expectancy. It also stresses the weaker cells more.
> Generally it can be reasonably said that dendrite growth is more about life of cells than safety.
> Safety can be enhanced a lot by:
> 1- Charge at low rate . I charge my glider battery at 3 amps maximum. My BMS will dissipate all of that as end of charge is reached.
> 2- Don't charge to max possible voltage. This stresses cells less by not over charging. In my case this sacrifices about 15% of theoretical possible capacity.
> 3- Discharge well below manufacturer's data sheet rate. My cells are rated at 25 amps and my max rate is 14 amps for 2 minutes, then about 9 amps after that. I never see a meaningful rise in battery pack temperature.
> 4- Don't over discharge. I limit to about 20% remaining.
> 5 Don't drop the damn things. At least one of the FES battery failures was associated with mechanical damage due to dropping. FES ships all now get special carrying boxes to protect batteries when not in the ship. In my battery the likely damage from dropping would probably be to connections. I highly doubt it would hurt individual cells. I wonder how many phones that have have Lipo batteries and caught fire had been dropped.
> 6- Choice in battery construction. My opinion here- Lion cylindrical(18650 "laptop" style) can be expected to be much more durable than the Lipo pouch type cells. They are simply more robust. That said they are more energy dense per pound and have a lot fewer connections to fail. With about 250 sailplanes currently using the Lipo batteries, they far outnumber the ones in use that have Lion cells.
> 7- Isolate the battery from the flight crew and vent it. My 24EL has a full fire wall, barrier surfaces in the motor bay, and operates with the motor bay doors open. Our ASH25 does not have a fire wall because it is physically not possible to do so.
> FWIW- ready for incoming.
> UH

The fact that the rate and level of charging of lithium batteries affects their longevity and, more importantly, their safety puts them into a separate class altogether from any other propulsion source. I can fill my gas tank at any rate and to any level and not have to worry about it catching fire. I can also drain it completely, also without any concern. I can also run the engine at idle or at full power without concern that it will catch fire. Lithium propulsion batteries are JUST NOT ready for prime time IMHO.

Tom

On Thursday, November 3, 2022 at 11:02:53 AM UTC-4, mdfa...@gmail.com wrote:
> Our club is kicking around the idea of buying a Pipistrel Electro 2.5 to supplement our current training ships (L23, K21 and Grob Twin), one of which would probably be sold. Preliminary impressions are pretty favorable. I'm looking for any first-hand experience anyone may have with this particular glider. Thanks in advance.
>
> Mike
Returning to the original question.
I don't have experience with the Electro but have some electric and a ton of training experience.
Consider the mission carefully.
1) Will it be for primary training? If so there could be some real benefit in efficiency for early air work(no waiting for a tow to do more exercises) , and learning the pattern(easily 6 or 8 patterns per hour). Use this way would mean battery life between charges would become limiting. It would pay to investigate the practicality of having an additional set of batteries to switch out and understanding how long this would take.
2) Are you prepared to deal with the known issues of living with an electric aircraft? Charging facilities. Staff to make sure batteries are charged (properly) and ready to go. Having to re charge during a flying day takes a good bit of time and high charge rates to get done quickly are known to be hard on batteries and known ton have an adverse affect on safety.
3) Doing some of your training in the electric will reduce the load on your tow plane which has several benefits. Less wait for tows for the regular gliders. Less wear on the tug.
Some of the benefits also obviously apply to ICE powered sailplanes. For this mission the ASK-21MI comes to mind.
It is worth noting that Pipestrel has been with this stuff for a while.
FWIW
UH

On 11/10/2022 8:56 PM, 2G wrote:
....
> The fact that the rate and level of charging of lithium batteries affects their longevity and, more importantly, their safety puts them into a separate class altogether from any other propulsion source. I can fill my gas tank at any rate and to any level and not have to worry about it catching fire. I can also drain it completely, also without any concern. I can also run the engine at idle or at full power without concern that it will catch fire. Lithium propulsion batteries are JUST NOT ready for prime time IMHO.
>
> Tom

Gasoline fueled aircraft can leak fuel, which can be ignited and cause a fire. Fuel stored
in hangars has also caused fires. An ASH26E, the predecessor to your ASH31Mi, caught fire
in flight while under power, due to a faulty muffler (miraculously, no injury). Airplane
pilots have died from carbon monoxide poisoning, something electric power avoids. The
vibration from gasoline engines can cause failures as parts crack or break.

Every propulsion system has potential problems. We work to learn to the correct use of
each one, the manufacturers work to make their system easier and safer, and at some point,
each pilot decides the gliders (gas, jet, electric, towed, winched) offered are safe
enough for them, buys one, and flies it.

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

On Friday, November 11, 2022 at 7:49:27 AM UTC-8, Eric Greenwell wrote:
> On 11/10/2022 8:56 PM, 2G wrote:
> ...
> > The fact that the rate and level of charging of lithium batteries affects their longevity and, more importantly, their safety puts them into a separate class altogether from any other propulsion source. I can fill my gas tank at any rate and to any level and not have to worry about it catching fire. I can also drain it completely, also without any concern. I can also run the engine at idle or at full power without concern that it will catch fire. Lithium propulsion batteries are JUST NOT ready for prime time IMHO.
> >
> > Tom
> Gasoline fueled aircraft can leak fuel, which can be ignited and cause a fire. Fuel stored
> in hangars has also caused fires. An ASH26E, the predecessor to your ASH31Mi, caught fire
> in flight while under power, due to a faulty muffler (miraculously, no injury). Airplane
> pilots have died from carbon monoxide poisoning, something electric power avoids. The
> vibration from gasoline engines can cause failures as parts crack or break.
>
> Every propulsion system has potential problems. We work to learn to the correct use of
> each one, the manufacturers work to make their system easier and safer, and at some point,
> each pilot decides the gliders (gas, jet, electric, towed, winched) offered are safe
> enough for them, buys one, and flies it.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications

No, Eric, there IS NO comparison between gas engines and battery failure mechanisms. You are just equivocating. I have NEVER had a fuel tank leak, nor do I expect it to. We have over 100 years of experience with gas engines and their problems. Lithium batteries, on the other hand, can be EXPECTED to grow dendrites - it is just a matter of when and how much.

The problem is solvable and PNNL has a patent on one such solution:
https://www.pnnl.gov/available-technologies/dendrite-growth-prevention-technology-lithium-metal-batteries
But this hasn't found its way into the mass market and has been proven by user experience AFAIK.

Tom