Electro Taurus Experiences

[Michael Fadden]

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

[Curt Lewis - 95]

On Thursday, November 3, 2022 at 10:02:53 AM UTC-5, 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

A recent discovery I found is that it can actually be trailered in a Cobra trailer and assembled without much trouble. Big plus I think.

Curt Lewis
CFIG/ASEL
Genesis 2 (95)
SGS 1-26B (216)

[6A]

On 11/3/2022 8:02 AM, Michael Fadden 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

Contact the dealer for names of customers that have used it for training or in a club. Or
just start calling Taurus owners in the FAA register - not that many to go through.

[2G]

Review ALL of the NZ accident reports regarding this glider before pulling the trigger:
https://groups.google.com/g/rec.aviation.soaring/c/hBC6dag98qo/m/JZzil_psBwAJ

Tom

[Michael Fadden]

Thanks, Curt. I don't how much consideration has been given to trailer options but that's good to know. While its not listed as definite cause of the fire/crash, its clear the owner of the NZ Taurus didn't maintain the battery in accordance with the manufacturer's instructions. The whole battery safety issue is part of the discussion we are having. I was hoping that some owners (worldwide, not just U.S.) of the Electro 2.5 were users of this group and might relay their real world experiences. Pipistrel has been very responsive to our inquiries.

Mike

[Mark Mocho]

"A recent discovery I found is that it can actually be trailered in a Cobra trailer and assembled without much trouble. Big plus I think."

You need to know that the Cobra trailer designed for the Taurus is substantially larger than the normal models designed for single seat or tandem seat gliders. The Taurus' side-by-side cockpit means the fuselage is almost twice the width of a conventional glider, and the trailer has to be specially built for it. The wing is also substantially larger. I have built a couple of specialized WingRiggers for the Taurus, and they too have to be specialized, as the wing has a very wide chord and is set low to the ground. The wings are pretty light, so rigging is not particularly difficult with two people and no rigging aid. Using a WingRigger can make it a single person effort, but it will take some practice.

Another concern about using a Taurus for instruction is whether it is registered as "Experimental." There is a debate going on about using Experimental aircraft for training, primarily in the cases where the instruction is for compensation or not. You should check with the FSDO to find out whether a "Letter Of Deviation Authority" (LODA) is required for instructing in an Experimental aircraft, and whether it is legal to charge for it.

[Eric Greenwell]

On 11/3/2022 8:02 AM, Michael Fadden 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

Operating a MG is substantially different from a towed glider, and the PIC needs to know
these differences, and use the MG often enough to remain competent. For your training
purposes, I think this is practical if the pilots (PIC) are limited to instructors who
really learn how to operate the Taurus, and do so routinely. It's not just flying the
launch, but the basic operations of "fueling", preflight, and emergencies.

An electric powered glider is going to have features new to most instructors, even if they
are also airplane or towpilots. A primary difference is the batteries, which must be
handled carefully when out of the glider, and when they are charged and stored. Their
operation in flight also differs considerably from fuel management in combustion engine
powered aircraft.

If the club can maintain competent instructors, I think this would a good addition to the
club fleet, in part because it would prepare pilots the electric gliders they'd likely be
flying in the future.

[Michael Fadden]

Thanks, this is all good information. The plan is to have only instructors be the PIC, at least initially, and use it both in MG mode and aero-towed like a non-MG. We have excellent instructors with experience in all kinds of aircraft. There is no charge for instruction but checking with the FSDO (probably) wouldn't hurt. I'm not on the committee but those who are don't frequent RAS, as far as I know. Personally, I zero power time but would like the challenge of becoming competent in motorglider.

Mike

[2G]

On Friday, November 4, 2022 at 6:41:16 AM UTC-7, mdfa...@gmail.com wrote:
> Thanks, Curt. I don't how much consideration has been given to trailer options but that's good to know. While its not listed as definite cause of the fire/crash, its clear the owner of the NZ Taurus didn't maintain the battery in accordance with the manufacturer's instructions. The whole battery safety issue is part of the discussion we are having. I was hoping that some owners (worldwide, not just U.S.) of the Electro 2.5 were users of this group and might relay their real world experiences. Pipistrel has been very responsive to our inquiries.
>
> Mike

Mike, that is simply not true. The final report on the accident (https://www.aviation.govt.nz/assets/publications/fatal-accident-reports/ZK-GEL-Final-Report-7-December-2020.pdf) stated:

"At some time between 1415 and 1730 hours, the glider, while soaring, experienced an inflight battery thermal event."

A "thermal event" is also called a fire, which is exactly what it was called later:

"1.14 Fire
1.14.1 During the wreckage examination, evidence of an in-flight fire was identified. The
fire appeared to have originated from, and was isolated to, the battery pack located
behind the pilot’s seat (see Figure 3)."

The fire intruded into the cockpit:

"1.14.3 The pilot’s seat and rudder control cables showed evidence of in-flight heat damage
and sooting. These components were separated from the heat source during the
impact sequence."

and

"1.15.1 Evidence of significant smoke within the cockpit prior to the glider impacting the
ground was identified."

Finally, the analysis concludes that there WAS a fire:

"2. Analysis
2.1 While airborne on a local flight the pilot was faced with a difficult in-flight
emergency, in the form of a battery thermal event.
2.2 The thermal event originated in the lithium polymer battery pack located behind
the pilot’s seat, resulting in fumes and smoke filling the cockpit. This would have
likely had the effect of degrading the pilot’s performance and ability to control the
glider while dealing with the in-flight emergency."

Manufacturing defects were found in another electric glider:

"1.16.1 Following an in-flight battery fire incident involving an HPH Glasflugel 304 eS type
glider in West Sussex, England, the Air Accidents Investigation Branch (AAIB)
conducted an investigation. Their subsequent report could not identify the cause of
the battery fire. They conducted independent testing, however, which revealed the
presence of metallic debris in 7 of the 11 lithium polymer cells sampled.
Furthermore, vibration testing identified that metallic debris could cause fretting on
the cell pouch. The metallic fretting was not significant enough during testing to
penetrate the cell pouch which would cause arcing. However, during other testing
where penetration was achieved ‘the electrical arcing was immediately followed by
rapid inflation of the pouch, followed by light grey smoke, followed by flames.’ For
further information refer to AAIB Bulletin: 9/2018 G-GSGS EW/C2017/08/01."

The owner did not follow the recommended charging of the batteries:

"1.16.4 During significant absences from New Zealand, the pilot would fully charge the
glider batteries and leave them charged while the glider was stored in its trailer. The
pilot was also known to leave the batteries charging for substantial periods of time
between flights. This is contrary to the manufacturer’s Flight manual and
Maintenance manual."

and the report concluded this:

"1.16.5 Research shows that, if the manufacturer’s instructions for charging are not
followed, lithium polymer batteries are prone to hydrogen and dendrite build-up,
that may lead to a battery short circuit, failure, smoking and/or fire"

This, to me, renders this technology unsuitable for aircraft. You will want to fully charge the battery prior to flight, which contributes to hydrogen and dendrite build-up and, ultimately, battery failure. It is just a question of time. I can fill up the fuel tank of my ASH 31 Mi, on the other hand, and leave it that way for months without risk of fire.

Tom

[AS]

>> ... the electrical arcing was immediately followed by rapid inflation of the pouch, followed by light grey smoke, followed by flames. <<

If you want to see the above in action, watch a few episodes of 'Battle Bots', where the contestants build robots with the expressed purpose of beating the crap out of their opponents. These robots are all powered by LiPo-type batteries. Some of them sustain incredible blows, which compromises their batteries. The 'light grey smoke' is heavier than air and creeps out of the stricken bot along the floor, which then - much to the delight of the spectators - is typically followed by fire. The clean-up crew only enters the venue with full-face respirators.
Battery technology will advance and improve with the advent of EVs, so I will wait a little more before placing my order for an electric motor glider.

Uli
'AS'

[Eric Greenwell]

On 11/5/2022 12:35 PM, AS wrote:
> Battery technology will advance and improve with the advent of EVs, so I will wait a little more before placing my order for an electric motor glider.

How long did you want to wait? Place an order now, and you'll likely wait 2, 3, or more
years due to order backlogs. But, if you are waiting for batteries that can survive
sledgehammer attacks and multiple 10 foot drops onto a steel floor (as Battlebots endure),
you'll have to wait much longer.

Eric

[2G]

These batteries can't even survive the bouncing and jarring that typical trailering causes. The Taurus Electro had a gear-up landing that may have contributed, and probably did, to its battery failure. Gear-up landings are not the same as a 10-foot drop.

The gray or white smoke is the electrolyte on fire. This produces toxic smoke, so using full respirators is not just a good idea, but is mandatory. The cargo ship fire, Felicity Ace, with all of the EVs on board put out a tremendous amount of white smoke.

We will be getting a lot more answers to these battery issues with all of the EVs that are now out on the road. One issue, dendrite growth, occurs over a period of time regardless of whether the battery is or is not being used. This phenomenon is not understood, which is very troubling when your life depends upon it (https://www.nature.com/articles/s41524-022-00788-6):

"Some such issues are uncontrolled dendrite formation, large volume changes, and irreversible electrolyte degradation reactions inherent in lithium-metal-based batteries, resulting in severe safety concerns and low Coulombic efficiency."

"However, only a few studies have focused on the aggressive formation or growth of dendrites in organic electrolytes. Even these few previously reported approaches have failed to successfully reproduce and access the experimentally observed lithium electrodeposition behavior during the cyclic charging/discharging process. This is because existing modeling studies involve simplifying assumptions that cannot capture some atomic-scale details."

Dendrites, if you haven't followed the previous discussions, cause internal shorts in lithium batteries which lead to thermal runaway and fires. I would be a lot more comfortable driving an EV than flying an electric glider. If the EV catches fire you can pull over to the side of the road and get out - this is much more problematic if you are airborne.

Tom

[Eric Greenwell]

On 11/5/2022 9:19 PM, 2G wrote:
>> How long did you want to wait? Place an order now, and you'll likely wait 2, 3, or more
>> years due to order backlogs. But, if you are waiting for batteries that can survive
>> sledgehammer attacks and multiple 10 foot drops onto a steel floor (as Battlebots endure),
>> you'll have to wait much longer.
>>
>> Eric
> These batteries can't even survive the bouncing and jarring that typical trailering causes. The Taurus Electro had a gear-up landing that may have contributed, and probably did, to its battery failure. Gear-up landings are not the same as a 10-foot drop.

Is there more evidence for these concerns than this Taurus, particularly for the later
generation batteries from FES?

Of course, Uli can choose to wait for an electric glider using cylindrical lithium
batteries, which are inherently more rugged than the pouch style.

[Arne Martin Güettler]

On Sunday, 6 November 2022 at 13:53:01 UTC+1, Eric Greenwell wrote:
> On 11/5/2022 9:19 PM, 2G wrote:
> > These batteries can't even survive the bouncing and jarring that typical trailering causes. The Taurus Electro had a gear-up landing that may have contributed, and probably did, to its battery failure. Gear-up landings are not the same as a 10-foot drop.
> Is there more evidence for these concerns than this Taurus, particularly for the later
> generation batteries from FES?

The Taurus Electro is not a FES system. In fact it's one of the first electrical gliders (after Antares), and predates the first FES equipped glider by a couple of years. And being built to ultra light rules, it both predates and is not required to follow the certification requirements as current sailplane certified batteries do. That said, I don't know the exact battery type it does use.

[Eric Greenwell]

I agree, and did not mean to imply it was an FES system; however, it did have batteries of
similar design, and the design was revised after the accident, as were important details
in the Taurus airframe. The FES system also has had important revisions in the design and
manufacture of it's batteries, and EASA regulations are more comprehensive now.

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

[2G]

Yes, this is an of intense interest. Here is one surprising scientific review that surveyed all studies in this area (https://journals.sagepub.com/doi/full/10.1177/14613484211008112):

"The authors concluded that the pouch cells showed no degradation or failure in any of the tests; however, the cylindrical cells shaken in the y-direction experienced mandrel loosening during the shock and long-term vibration tests. In addition, it was found that the cylindrical cells stressed in the z-direction also experienced degradation and failures."

and

"The reliability analysis and optimization of internal and external complex structures are urgently needed in the development of battery pack to eliminate all kinds of potential safety hazards in the design stage especially under the shock and vibration environment."

These results are in direct contradiction to your claim that pouch cells are more dangerous than cylindrical cells. The construction of cylindrical cells involves the rolling of four layers simultaneously; apparently this rolling action introduces stresses into the material, especially the separation layers.

Tom

[Eric Greenwell]

"More rugged" was too vague a claim, I think; regardless, the study only used automotive
vibration patterns to test the cells for the equivalent of 100,000 miles, and did not
consider things like damage propagation from a failed cell to adjacent cells, tolerance of
debris while constructing the battery pack, etc. I do think both types of cells can be
used for battery packs suitable for electric glider use.

The study's vibration pattern may not a good representation of glider vibration, and the
tests lasted for the equivalent of 100,000 road miles. That's about 2000 hours of
vibration. Glider vibrations with the intensity of ground vehicles might occur during the
takeoff and landing roll, and perhaps also under power (unlikely, given the smooth
operation of electric motors). My ASH26E, with 4300 flight hours, has only 215 engine
hours, so I don't think flight related vibration is going to be a problem for electric
gliders.

There is also vibration during trailering, but I don't know how that compares to the
vibration they used in the study. Frame mounted batteries in car may be subjected to far
more vibration than a glider carried in a trailer.

[Hank Nixon]

Pouch cells are much more prone to damage that could lead to a fire as has happened a few times with FES ships and the referenced Taurus.
Lion cylinder type cells may fail from vibration but the just die due to open circuits.
That said my battery comes out of the glider for trailering.
UH

[kinsell]

Perhaps in your experience they only fail with open circuits, but there
have been quite a few cases where cylindrical cells have combusted.

Sure glad these things are getting so much safer:

https://gothamist.com/news/e-bike-fire-injures-38-in-midtown-east-apartment-building

[2G]

The clear attitude of eglider enthusiasts here is that we skeptics must prove that lithium batteries are unsafe (which I think I have done, BTW). My attitude is that the proponents, especially the manufacturers, MUST prove that they are safe. This HAS NOT happened to date. Conclusion: fly at your OWN RISK!

Tom

[Eric Greenwell]

On 11/6/2022 7:01 PM, kinsell wrote:
> On 11/6/22 4:22 PM, Hank Nixon wrote:

...

>>>
>>> Tom
>> Pouch cells are much more prone to damage that could lead to a fire as has happened a
>> few times with FES ships and the referenced Taurus.
>> Lion cylinder type cells may fail from vibration but the just die due to open circuits.
>> That said my battery comes out of the glider for trailering.
>> UH
>
> Perhaps in your experience they only fail with open circuits, but there have been quite a
> few cases where cylindrical cells have combusted.
>
> Sure glad these things are getting so much safer:
>
> https://gothamist.com/news/e-bike-fire-injures-38-in-midtown-east-apartment-building

The article says the fire started in an apartment where a guy was repairing e-bikes, with
over 5 found in his room. Seems likely it was case of improper repair and storage in an
unsuitable location, rather than batteries failing from normal use.

[Eric Greenwell]

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.

[2G]

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

[Eric Greenwell]

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.

[Dave Nadler]

On 11/6/2022 11:40 PM, 2G wrote:
> The clear attitude of eglider enthusiasts here is that
> we skeptics must prove that lithium batteries are unsafe
> (which I think I have done, BTW).
> My attitude is that the proponents, especially the manufacturers,
> MUST prove that they are safe.
> This HAS NOT happened to date. Conclusion: fly at your OWN RISK!

I recently returned from the OSTIV SDP and WEP meetings in Stuttgart.
The WEP (working group on electric propulsion) spent most of the day
discussing certification requirements and means of compliance for
battery safety (manufacturers and certification authorities attended).
This is not being taken lightly!
However:
- Light gliders aren't certified and those manufacturers may or
may not actually do the hard testing. VERY hard testing.
- older gliders and battery packs had 'less rigorous' testing
- cell availability is driving pack redesign with associated
retest and re-certify efforts.

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.

[2G]

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

[Eric Greenwell]

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.

[2G]

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

[Eric Greenwell]

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

[2G]

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

[Charlie M. (UH & 002 owner/pilot)]

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.

[Eric Greenwell]

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.

[2G]

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

[Eric Greenwell]

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.

[Hank Nixon]

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

[kinsell]

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

[Eric Greenwell]

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.

[2G]

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

[2G]

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

[Hank Nixon]

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

[Eric Greenwell]

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.

[2G]

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