FES&electric system batteries

[krasw]

Snipping from another thread (Per):

"And this is exactly why retrofitting an older glider to FES is impossible. With an max weight of non lifting part typically in the range of 230-250kg is it not enough marginal to put in an extra weight of 40-50kg for motor, electronics and battery in the fuselage unless you are a really light weight pilot.
I have asked the FES guys several times if it would be possible to get batteries suitable for wing installation and the answer is no. "

There might be a lot of practical reasons for that. I quess FES is married with Kokam battery (certification/approval) which has it's own form factor unsuitable for wing installation. FES system also requires weight in the rear fuselage as motor is quite heavy. Cutting old wings open and installing batteries in might not be that easy unless you have nice open root rib and empty wing shell to begin with.

GP has announced that they use Sony battery, it would be interesting to know if that consist of box filled with normal-size cells. Schleicher (ASG 32El) and Binder (EB 29DE) seem to use this kind of approach.

One point that has not been discussed is the lifetime of batteries. So far they cost arm and leg to replace, I wonder what kind of experience people have with FES batteries? Only report I have heard is 70% of capacity left after 4 years use, which is not encouraging. FES manual recommends replacing battery when capacity is 30% of maximum, but range of system is useless at that point.

[Per Carlin]

FES has chosen there system on several aspects. One is that they want to be a competitors to combustion engines in new gliders. Therefor is the extra payload in the fuselage not an issue for them. But for me who wants to retrofit. The Mass and Balance can easily be solved by an extra weight at the fin.

When it comes to lifetime of batteries is my experience that it is severely dependent on the usage and abusage.
Best cast scenarios will they hold up for about 1000 charging cycles, maybe more with good battery monitoring.
What kills them is abuse.
Deep discharging is the main problem, do not discharge your lithiumcells to deep (this also goes for you cellphone or laptop), unless necessary to save your life.
Next is heat, do not let them be hot during charging or discharging.
Third is to discharge them to fast i.e. overload by taking out to much power, this generates heat and is not good. The last is to store the batteries discharged to long time, all batteries have a self discharge and long storage without proper storage charge will put them into deep discharge mode.
I expect the designers of the electrical systems to consider this aspects and therefor put in battery monitoring system that keeps them in charge, in correct temperature and not allow the user to deep discharge them. I would expect them to have a long life time, making 30-50 starts per year give me more than 20 years of usage. This is more than I can foreseen as a glider owner, after 20 year will new batteries be better and the cost be motivated in extra performance compared to just replacing them.

[Dave Walsh]

Whilst not strictly comparable the Li Ion cells in the Lange
Antares 20E were initially expected to last at least 10 years of
normal use. Currently there are plenty of Antares 20E's flying
around with their original batteries. I think the batteries are
now expected to last 20 years? (Maybe wrong about that). Of
the 72 cells in my Antares just 3 are now down to about 87%
of their original performance; the batteries are now 11 years
old.

For FES systems, where the batteries might not be used at all
on many flights, I'd expect a similar, or better, battery life
(assuming they are not abused of course; see earlier post).

[Renny[_2_]]

On Wednesday, December 7, 2016 at 2:52:26 AM UTC-7, krasw wrote:
> Snipping from another thread (Per):
>
> "And this is exactly why retrofitting an older glider to FES is impossible. With an max weight of non lifting part typically in the range of 230-250kg is it not enough marginal to put in an extra weight of 40-50kg for motor, electronics and battery in the fuselage unless you are a really light weight pilot.
> I have asked the FES guys several times if it would be possible to get batteries suitable for wing installation and the answer is no. "
>
> There might be a lot of practical reasons for that. I quess FES is married with Kokam battery (certification/approval) which has it's own form factor unsuitable for wing installation. FES system also requires weight in the rear fuselage as motor is quite heavy. Cutting old wings open and installing batteries in might not be that easy unless you have nice open root rib and empty wing shell to begin with.
>
> GP has announced that they use Sony battery, it would be interesting to know if that consist of box filled with normal-size cells. Schleicher (ASG 32El) and Binder (EB 29DE) seem to use this kind of approach.
>
> One point that has not been discussed is the lifetime of batteries. So far they cost arm and leg to replace, I wonder what kind of experience people have with FES batteries? Only report I have heard is 70% of capacity left after 4 years use, which is not encouraging. FES manual recommends replacing battery when capacity is 30% of maximum, but range of system is useless at that point.

This is an interesting discussion. For the record my LAK-17b FES is 5 years old and when fully charged I still have 100% of the battery power. I do take good care of them per the the various messages and bring them home and keep them in my garage during the cold winters at Moriarty, NM. I do not let them discharge too much and keep them charged because you just never know when you are really going to need them...I am very confident these batteries will easily last perhaps 15 or 20 years or perhaps even longer....Thx - Renny

[Casey[_2_]]

I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

[Dan Marotta]

I expect Renny will chime in but, for now, I think the LAK-17bfes,
though there's a video demonstrating a self launch, is a sustainer only
because the propeller tips are so close to the runway. If you lift the
tail during a takeoff run, you'll likely have a very noisy and expensive
surprise.

On 12/7/2016 4:21 PM, Casey wrote:
> I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

--
Dan, 5J

[Bruce Hoult]

On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
> I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?

Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

[krasw]

I think 20 years of good battery life might be bit optimistic. Antares has very expensive milspec batteries that should have long life, apparently that can be 10 years, but no one knows if that is 20 years. Other systems use cheaper (relatively) off-the-self batteries that might not last so well. Realistically, I would probably budget battery change every 5-10 years.

[Per Carlin]

On Thursday, December 8, 2016 at 7:26:05 AM UTC+1, Bruce Hoult wrote:
> On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
> > I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?
>
> Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

To be certified as SLG according to JAR 22 do you need to meet specific performance in roll-out distans and climb. The 13,5m FES is only SLG in dry condition, if you load it with water is it only SSG. I guess that the LAK17 is to heavy to meet the performance requirements to be a SLG.

[Bruce Hoult]

On Thursday, December 8, 2016 at 10:30:26 AM UTC+3, Per Carlin wrote:
> On Thursday, December 8, 2016 at 7:26:05 AM UTC+1, Bruce Hoult wrote:
> > On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
> > > I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?
> >
> > Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.
>
> To be certified as SLG according to JAR 22 do you need to meet specific performance in roll-out distans and climb. The 13,5m FES is only SLG in dry condition, if you load it with water is it only SSG. I guess that the LAK17 is to heavy to meet the performance requirements to be a SLG.

Yes I know. I wasn't talking about certification :-)

Of course there are lots of places that you'd be foolish to try it, but given an airfield large enough that you can circle within the boundary with less than 30 degrees of bank, the difference between a car tow with an aerotow rope and an aerotow to a release on downwind at 500 ft (which lots of people do) is probably ... about 300 ft by the time the motor starts.

[Tony[_5_]]

Battery temperatures rise during use, it is part of what the pilot monitors during the launch. I've never seen or heard of battery temp being the limiting factor on power output. That is always motor temp in my experience.

What I've heard from Leo B-L is that the oldest highest use FES batteries are still charging to 99%. I'd love to hear more details on this 70% claim.

[krasw]

torstai 8. joulukuuta 2016 16.21.22 UTC+2 Tony kirjoitti:
>
> What I've heard from Leo B-L is that the oldest highest use FES batteries are still charging to 99%. I'd love to hear more details on this 70% claim..

I'm a bit confused here. Are we talking about the voltage they charge to? You measure batter capacity by the amount of amperes you get. Obviously even older battery will have same voltage when charged full, but that does not say anything about capacity. If FES with 100% new battery gives you 60 minutes of level flight time (for example), 70% capacity battery would give you 42 minutes.

[Dan Marotta]

Well, since you mention that, I did once launch in a friend's ASW-24E
out of Kelly Air Park (7,050' MSL, 3,500' paved runway) on July 6,
2000. It took two attempts to get airborne and then a little nap of the
earth flying to gain speed. Not for the faint of heart... The '24 is
labeled an "E" but I think "T" would be more reasonable.

On 12/7/2016 11:26 PM, Bruce Hoult wrote:
> On Thursday, December 8, 2016 at 2:21:34 AM UTC+3, Casey wrote:
>> I've noticed that 13.5m FES are advertised as Front Engine Self Launchers and 15m are advertised as Front Engine Sustainers. I did here of a LAK 17b FES launch off asphalt. I wonder if the batteries heat up more from a 15m launching than a 13.5m? Or if the batteries heat up during prolong usage with either the 13.5m or 15m?
> Any glider with a sustainer can self-launch from a sufficiently long hard surface, with plenty of pressure in the tyre and a push start. Or, better, a tow to 100-120 km/h with a car.

--
Dan, 5J

[Tom (TK)]

Dave Walsh, have you installed the Antares hard/soft upgrade yet for "charge plus". The software revision 6 provides for better charging and balancing of the batteries. There are two of us here in the US that are going to have this done in January. The factory is in the process of writing a new software version 7, which ads a number new functionalities.
One of the more interesting functionalities is internet access, which would allow the factory to access the US aircraft remotely and even perform software fixes and upgrades from Germany. On a side note; due to improved monitoring, version 7 will also make the recurring (normally annual) inspection have 3 years of validity, significantly reducing inspection costs for EASA certified aircraft. Version 7 is expected to be certified in the autumn of next year.

[Tom (TK)]

From the Lange website:
The life expectancy of the battery is decisively influenced by two factor the number of cycles and the natural aging process.

The battery capacity decreases with increasing number of charging and discharging processes. The life expectancy of the battery is based on the latest findings with more than 4500 SAE cycles. One SAE cycle stands for full charging of the battery and a discharge to 20% of the capacity. Partial discharge corresponds only to an equivalent portion of a full cycle. After 4500 of these SAE cycles, the capacity of the battery has decreased to 80% of the initial state. For the pilot, this means that the battery allows a minimum of 10,800,000 risers before it is replaced.

In practice, the natural aging of the batteries is more relevant. It is therefore recommended to change the batteries according to the latest findings at an average storage temperature of 20 ° C after approx. 20 years. Even then the battery capacity has decreased to 80% of the initial capacity.

[Dave Walsh]

At 15:45 08 December 2016, Tom TK wrote:
>Dave Walsh, have you installed the Antares hard/soft upgrade
yet for
>"charg=
>e plus". The software revision 6 provides for better charging
and
>balancing=
> of the batteries. There are two of us here in the US that are
going to
>hav=
>e this done in January. The factory is in the process of writing a
new
>soft=
>ware version 7, which ads a number new functionalities.=20
>One of the more interesting functionalities is internet access,
which
>would=
> allow the factory to access the US aircraft remotely and even
perform
>soft=
>ware fixes and upgrades from Germany. On a side note; due to
improved
>monit=
>oring, version 7 will also make the recurring (normally annual)
inspection
>=
>have 3 years of validity, significantly reducing inspection costs
for EASA
>=
>certified aircraft. Version 7 is expected to be certified in the
autumn of
>=
>next year.=20
>
>This thread seems to be drifting into Antares territory; the
Antares and FES (especially an Ultra-light FES self-launcher, i.e.
the Silent Electro) are very different sailplanes. They are only
similar in that electric power should get you to the nearest
airfield/home. In theory the "electrics" option should be more
reliable than the two stroke option, the downside is the much
reduced range of current "electric" systems. In this regard FES is
a much better "get you home" option than a self-launcher.

To answer the previous post I have software version 6.0
("Charge Plus"); it was already installed when I bought the A/C
two years ago. It allows you to charge the batteries to about
118-120%; I don't actually understand this (I'm a biochemist
not an electrical engineer) but what it means is that I can launch
from Sisteron (French Alps 1700 ft elevation, ~30C), climb to
about 5000ft (about the limit before the engine temperature gets
into the red), stow the engine and have about 60% battery
power remaining. If you don't use the "charge plus" feature the
remaining battery power is about 45-50%. These figures are for
10 year old batteries, with a total of <700 flight hours.
Looking at my considerable file of invoices I see that the upgrade
to software 6.0 was not cheap. I am told that one of the big
advantages of version 6.0 is that it prevents catastrophic total
discharge of the batteries which can happen through operator
error (for instance putting the A/C away, going on holiday, whilst
accidentally leaving the radio switched on). This, I am told, can
be a very, very expensive mistake as it requires replacement of
all 72 battery cells.
Version 6.0 "Charge Plus" has some limitations; the batteries
once charged to 120% have to be used, so the A/C has to be
rigged and the engine to be ground run to reduce power back to
<100%. This can take quite some time! (There may be some
other way to do this buried in the software, but as all my
documentation is in German, I have never tried it).
Also if you use "Charge Plus" immediately before flight some of
the electronics and the batteries will be hot. I have heard various
opinions on whether this is a significant factor. I avoid this by
running Charge Plus overnight.

Here in EASA land I am not sure that the extended inspection
periods you mention are relevant?

On your side of the pond Dave Nadler (an ex Antares owner)
might be a good source of information?
Dave Walsh

[Dave Nadler]

On Thursday, December 8, 2016 at 10:45:29 AM UTC-5, Tom (TK) wrote:
> ...One of the more interesting functionalities is internet access,
> which would allow the factory to access the US aircraft remotely
> and even perform software fixes and upgrades from Germany.

Non-USA Antares have had this facility from beginning.
All USA Antares, including yours, already have this capability.
I wrote and installed the facilities required for USA many years ago ;-)

Unfortunately its not so useful in practice.
Poor internet connectivity at many sites makes it dodgy.
Do you want a remote update over a poor connection killing the machine?
For this and other reasons, you always need a qualified tech on site for
updates, which makes this not so useful.

For diagnostics, better is diagnostic dump to USB.
USA Antares, including yours, have had this for years.
You may guess who wrote and installed it ;-)

See ya, Dave

[krasw]

Interesting that while current Kokam batteries for FES cost 8000 euros (2000eur/kWh), at the same time Tesla is building batteries costing under 200 eur/kWh. Assembling FES battery with new Tesla cells would cost one tenth, even doubling or tripling that would still keep it quite affordable. Why use so expensive battery?

[Surge]

On Thursday, 23 February 2017 13:27:10 UTC+2, krasw wrote:
> Why use so expensive battery?

Because we all know that money makes aircraft fly.
If we don't pay lots of money things won't fly.

[Steve Leonard[_2_]]

On Thursday, February 23, 2017 at 5:27:10 AM UTC-6, krasw wrote:
> Interesting that while current Kokam batteries for FES cost 8000 euros (2000eur/kWh), at the same time Tesla is building batteries costing under 200 eur/kWh. Assembling FES battery with new Tesla cells would cost one tenth, even doubling or tripling that would still keep it quite affordable. Why use so expensive battery?

I think this is where Bob K or Darryl R inserts pictures of Flaming Tesslas....

[Bruce Hoult]

On Thursday, February 23, 2017 at 6:40:38 PM UTC+3, Steve Leonard wrote:
> On Thursday, February 23, 2017 at 5:27:10 AM UTC-6, krasw wrote:
> > Interesting that while current Kokam batteries for FES cost 8000 euros (2000eur/kWh), at the same time Tesla is building batteries costing under 200 eur/kWh. Assembling FES battery with new Tesla cells would cost one tenth, even doubling or tripling that would still keep it quite affordable. Why use so expensive battery?
>
> I think this is where Bob K or Darryl R inserts pictures of Flaming Tesslas...

Pretty sure the percentage of Teslas going up in flames is no higher than for petrol powered cars, and only after crashes not before. We're not talking Note 7's here.

[[email protected]]

Tesla is CLAIMING to be building batteries costing under 200 eur/kWh...

[Dave Walsh]

At 21:59 23 February 2017, wrote:
>Tesla is CLAIMING to be building batteries costing under 200
eur/kWh...
>

Here in EASA land I think there are substantial cost
implications to certifying "new(er)" batteries in an existing
certified FES sailplane (for Ultralights it's different). As current
FES performance looks pretty adequate why would the
manufacturers do it; it's not like there has been any radical
evolution in battery performance.
Dave Walsh

[krasw]

On Thursday, 23 February 2017 23:59:50 UTC+2, wrote:
> Tesla is CLAIMING to be building batteries costing under 200 eur/kWh...

I'm sure the size of their project dictates that they can not be much off that price...

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

I think it's a couple things.

1- as soon as you add "aircraft" to a part description, the price goes up. That little stamp on a part has to be backed up by a mountain of paperwork, thus some of the price increase.

2-economy of scale. How many FES battery packs will be made in a year? How many Tesla battery packs will be made in a year? We should know that the more pieces made in a given time frame drops the per piece price.

With Tesla building their own plant, they should have a better handle on manufacturing costs and quality. Time will tell though.

[[email protected]]

Tesla makes all their profits off carbon credit games. Thus Tesla pricing might not match reality.

[[email protected]]

On Friday, February 24, 2017 at 8:03:41 AM UTC-6, wrote:
> Tesla makes all their profits off carbon credit games. Thus Tesla pricing might not match reality.

Plus, they are selling 'vapor ware', what a concept! You give us $$$'s of your hard earned money for something that doesn't really exist yet (but we promise you a spot in the line, maybe). Call back in a couple of years. Oh, and buy our stock, will you?

[Dan Marotta]

Sounds a bit like the BD-5, doesn't it?

On 2/24/2017 8:26 AM, wrote:
> On Friday, February 24, 2017 at 8:03:41 AM UTC-6, wrote:
>> Tesla makes all their profits off carbon credit games. Thus Tesla pricing might not match reality.
> Plus, they are selling 'vapor ware', what a concept! You give us $$$'s of your hard earned money for something that doesn't really exist yet (but we promise you a spot in the line, maybe). Call back in a couple of years. Oh, and buy our stock, will you?

--
Dan, 5J

[kinsell]

Don't think the BD-5 had massive government subsidies to help rich white
guys buy the things. Picking winners and losers didn't extend down to
the homebuilt GA market. Defense contractors, sure.


On 02/24/2017 09:34 AM, Dan Marotta wrote:
> Sounds a bit like the BD-5, doesn't it?
>
> On 2/24/2017 8:26 AM, wrote:
>> On Friday, February 24, 2017 at 8:03:41 AM UTC-6,
>> wrote:
>>> Tesla makes all their profits off carbon credit games. Thus Tesla
>>> pricing might not match reality.
>> Plus, they are selling 'vapor ware', what a concept! You give us $$$'s
>> of your hard earned money for something that doesn't really exist yet
>> (but we promise you a spot in the line, maybe). Call back in a couple
>> of years. Oh, and buy our stock, will you?
>

[Dan Marotta]

Rich white guys? How about people who simply work for a living as most
home builders are? Since you're a glider pilot you must be a "rich
white guy" too. Or are you a female, or a different color, or does it
really matter? Not to me. Is that you, Dave?

My point was that Jim Bede was always promising more than he could
deliver and asking the hopeful builders to hang in there.

On 2/24/2017 9:53 AM, kinsell wrote:
> Don't think the BD-5 had massive government subsidies to help rich
> white guys buy the things. Picking winners and losers didn't extend
> down to the homebuilt GA market. Defense contractors, sure.
>
>
> On 02/24/2017 09:34 AM, Dan Marotta wrote:
>> Sounds a bit like the BD-5, doesn't it?
>>
>> On 2/24/2017 8:26 AM, wrote:
>>> On Friday, February 24, 2017 at 8:03:41 AM UTC-6,
>>> wrote:
>>>> Tesla makes all their profits off carbon credit games. Thus Tesla
>>>> pricing might not match reality.
>>> Plus, they are selling 'vapor ware', what a concept! You give us $$$'s
>>> of your hard earned money for something that doesn't really exist yet
>>> (but we promise you a spot in the line, maybe). Call back in a couple
>>> of years. Oh, and buy our stock, will you?
>>
>

--
Dan, 5J

[kinsell]

On 02/24/2017 10:16 AM, Dan Marotta wrote:
> Rich white guys? How about people who simply work for a living as most
> home builders are? Since you're a glider pilot you must be a "rich
> white guy" too. Or are you a female, or a different color, or does it
> really matter? Not to me. Is that you, Dave?
>
> My point was that Jim Bede was always promising more than he could
> deliver and asking the hopeful builders to hang in there.

Take a deep breath Dan. Yes Bede overpromised on delivery, so there's
that similarity. But Tesla gets huge government subsidies that reduce
the price to the consumer, but still they're expensive and basically a
luxury item. There's no semblance of the free market at play with
Tesla, so expecting the pricing for FES batteries to be comparable to
Tesla's is never going to happen, unless some government wants to pour
taxpayer money into the things, which is never going to happen.


>
> On 2/24/2017 9:53 AM, kinsell wrote:
>> Don't think the BD-5 had massive government subsidies to help rich
>> white guys buy the things. Picking winners and losers didn't extend
>> down to the homebuilt GA market. Defense contractors, sure.
>>
>>
>> On 02/24/2017 09:34 AM, Dan Marotta wrote:
>>> Sounds a bit like the BD-5, doesn't it?
>>>
>>> On 2/24/2017 8:26 AM, wrote:
>>>> On Friday, February 24, 2017 at 8:03:41 AM UTC-6,
>>>> wrote:
>>>>> Tesla makes all their profits off carbon credit games. Thus Tesla
>>>>> pricing might not match reality.
>>>> Plus, they are selling 'vapor ware', what a concept! You give us $$$'s
>>>> of your hard earned money for something that doesn't really exist yet
>>>> (but we promise you a spot in the line, maybe). Call back in a couple
>>>> of years. Oh, and buy our stock, will you?
>>>
>>
>

[[email protected]]

Tesla uses 18650 sized cylindrical cells, lots of them. This cell size was originally designed for laptops and was driven by the dimensions of the disk drives used at the time. As computers became smaller, so did the form factor for cells. For computers, 14650 cylindrical entered the picture for a while (as drives became flatter) and now flat pouches and prismatic. This left a large overcapacity with 18650 equipment which in turn drove pricing down.

The volumetric and gravimetric energy content of the Kokam cells used in the FES vs. typical 18650 is higher. In a battery configuration, cylindricals waste space. In a rolling platform, the weight/size disadvantage of the 1850 could be tolerated but not so much with an aerial platform.

Additionally with the small 18650 cells, you need a lot of them to get to a desired energy content for a car or airplane battery. That means more BMU (battery management) again increasing weight, size, complexity, and opportunities for failure.

The battery solution (and PC diagnostics) for the FES system is well thought out given the tradeoffs. I am eager to see the final design that the GP guys are going to employ for their gliders. I certainly hope they make their batteries easily removable for charging and storage outside the glider. The volume, mass, and energy content of the proposed GP battery is on par with the FES battery although the dimensions are more long and skinny too fit in the wings.

Danny Brotto

[Giovanna Scardino]

Il giorno mercoledì 7 dicembre 2016 10:52:26 UTC+1, krasw ha scritto:
> Snipping from another thread (Per):
>
> "And this is exactly why retrofitting an older glider to FES is impossible. With an max weight of non lifting part typically in the range of 230-250kg is it not enough marginal to put in an extra weight of 40-50kg for motor, electronics and battery in the fuselage unless you are a really light weight pilot.
> I have asked the FES guys several times if it would be possible to get batteries suitable for wing installation and the answer is no. "
>
> There might be a lot of practical reasons for that. I quess FES is married with Kokam battery (certification/approval) which has it's own form factor unsuitable for wing installation. FES system also requires weight in the rear fuselage as motor is quite heavy. Cutting old wings open and installing batteries in might not be that easy unless you have nice open root rib and empty wing shell to begin with.
>
> GP has announced that they use Sony battery, it would be interesting to know if that consist of box filled with normal-size cells. Schleicher (ASG 32El) and Binder (EB 29DE) seem to use this kind of approach.
>
> One point that has not been discussed is the lifetime of batteries. So far they cost arm and leg to replace, I wonder what kind of experience people have with FES batteries? Only report I have heard is 70% of capacity left after 4 years use, which is not encouraging. FES manual recommends replacing battery when capacity is 30% of maximum, but range of system is useless at that point.

The cost of Kwh for the car batteries actually is 180 Dollars /kwh.
The Industry is claiming that after Tesla plant will work at full the costs of batteries will drop to 100 dollars/kwh.
At that time >I think Feb batteries has to switch to another producer in my opinion.
lak 13.5 GLIDER THAT USE THEW SAME BATTERY PACK OF OTHERS GLIDERS totally(with trailer costs less than 90.000 euro) and I suppose the costs of replacing the battery pack is under 5.000 euro

[krasw]

On Saturday, 25 February 2017 15:22:47 UTC+2, wrote:
> Tesla uses 18650 sized cylindrical cells, lots of them. This cell size was originally designed for laptops and was driven by the dimensions of the disk drives used at the time. As computers became smaller, so did the form factor for cells. For computers, 14650 cylindrical entered the picture for a while (as drives became flatter) and now flat pouches and prismatic. This left a large overcapacity with 18650 equipment which in turn drove pricing down.
>
> The volumetric and gravimetric energy content of the Kokam cells used in the FES vs. typical 18650 is higher. In a battery configuration, cylindricals waste space. In a rolling platform, the weight/size disadvantage of the 1850 could be tolerated but not so much with an aerial platform.
>
> Additionally with the small 18650 cells, you need a lot of them to get to a desired energy content for a car or airplane battery. That means more BMU (battery management) again increasing weight, size, complexity, and opportunities for failure.
>
> The battery solution (and PC diagnostics) for the FES system is well thought out given the tradeoffs. I am eager to see the final design that the GP guys are going to employ for their gliders. I certainly hope they make their batteries easily removable for charging and storage outside the glider. The volume, mass, and energy content of the proposed GP battery is on par with the FES battery although the dimensions are more long and skinny too fit in the wings.
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> Danny Brottoaw

I think glider batterys are not especially critical regarding dimensions. Antares uses large cylindrical cells without problems, as does Schleicher. More importantly, owners would probably be happy replace batteries with, say, one with 80% capacity and 20% of the price of the original.