What do you think about "e-soaring"?

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John.Roo

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looking at middle video the takeoff elevator position is much more level than all the 3rd video ......were there CG issues in the configuration of the 3rd video?
Very good observation đź‘Ť
Reason is simple - in the "middle" video was inside other pilot - much lighter than me.
In third video (from different day) I had light tail wind and due to my weight I had CG position far in the front.
So after we added more weight in the tail ;)
 

John.Roo

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Thanks to very interesting post from addaon would be good to open one more question about batteries...
It is better to use less bigger cells or more small cells?
Some time ago I had very interesting discussion with engineers from Skoda automotive and they told me that they prefere large cells to reduce parallel connections.
True is that every solded connection can be in amateur conditions possible source of problem so if would be possible to use large prismatic cells it could help to reduce hot spots.
From other point of view.... work with small 18650 (21700) cells is known and cells are succesfully used in many applications (EV bikes etc).
Any opinion? 🤔
 
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John.Roo

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By the way...
This looks like interesting offer.... I fount it on one Czech web with second hand parts.
1660199205204.png
New pack from Hyunday Ionic - 2.41 kWh for 250 USD.
Here are details about used cells...
1660199455860.png
1660199470208.png
 
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John.Roo

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Battery modules from BESTGO.... also interesting.
Weight of battery 88,8 V nominal, 74 Ah (set from 4x 22,2 V packages) is 34,4 kg.
1660210713787.png
 

addaon

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Bigger cells are easier to work with, and way cheaper for your BMS (especially if you’re doing a PCB per cell, but even if not — you have a lot of per-cell components). Smaller cells are easier to cool, easier to get for higher C ratings (some of which is the cooling, but some of which is different chemistry), and you lose less capability when one or a few cells are failed and bypassed. Of course with smaller cells you’re more likely to have one fail (explosively or not) on any given flight.

It’s also worth considering that prismatic, cylindrical, and pouch cells are manufactured differently, regardless of size or chemistry. The auto industry has been focusing on cylindrical cells and they’ve gotten quite good and very consistent and reliable. Meanwhile pouch cells often look best on paper but still seem to have a much higher tendency to go “boom” just due to extra edges and manufacturing challenges.
 

addaon

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Also be aware that when you’re working with an existing pack with an integrated BMS… you’re stuck with that BMS behavior. If it has a 1C limit, does it have an eFuse to enforce that because the car should never exceed that limit? If so is it a slow eFuse so it kicks in just as you get past takeoff speed? Similarly does the battery disconnect to protect itself at over temp assuming the car it’s in can just pull over, instead of damaging the battery but providing power to the end? Very different trade offs for an auto BMS and an airplane one, so unless you get something with great documentation, expect a lot of testing. Honestly probably less work to build your own BMS than test someone else’s undocumented one enough to trust it.
 

peter hudson

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proppastie

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If so is it a slow eFuse so it kicks in just as you get past takeoff speed?
I believe there was a Self Launch E-Glider here crashed into a house because of a failure just like that.......battery banks going open to protect from fire is an issue in ones battery selection.....as is fire if there is no protection

 

addaon

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Yeah. A good BMS is your best friend. A bad one is your worst enemy. It doesn’t need to be particularly expensive or complex, especially if you don’t need cell bypass, but it needs to be designed for aviation requirements and well understood.
 

addaon

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Also, you can design to minimize the chance of cell thermal runaway, but you can’t eliminate it. Sometimes a cell just gunna go boom — at higher probability than would be acceptable for either Catastrophic or Hazardous. You really really have to design to prevent propagating cell failures, and unless you’re a pure self-launcher that doesn’t have go-around requirements, think about how you’re going to maintain capabilities when a cell is burning.
 

proppastie

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What I do not understand......with all the noise about fire how come there is not more fires what with the millions of Laptop, Tablet, Phone, Drills, etc out there.
 

addaon

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(a) There have been issues — remember when you couldn’t take a Samsung phone on commercial flights? (b) Laptops and similar are strictly limited to < 100 Wh batteries so that when they do go, they won’t take out an airplane with them. (c) A huge amount of engineering and testing has gone into those BMS systems to make them as safe as physics allows. And they still fail, often.
 

John.Roo

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Yeah. A good BMS is your best friend. A bad one is your worst enemy. It doesn’t need to be particularly expensive or complex, especially if you don’t need cell bypass, but it needs to be designed for aviation requirements and well understood.
Good BMS is definitelly important - I agree.
So far I have been using active BMS only during charging. During flight has been BMS monitoring temp of cells (not each cell, just paralelly solded packs).
And in first prototype we had BMS in charger and separated temp sensors in battery case.
Again... that was over 10 years ago and it was really difficult to get any info.

Since beginning we have been using common sense.
Therefore I don´t believe info from cells producers about "super high charge and discharge C rate". 3C discharge rate is for me maximum for takeoff, horizontal flight max. 1C or below.
It is really scary that many designers are calculating with very high C rate even for horizontal flight.
charging is anyway limited by electric net on airfields so max. I ever used way 0,3-0,5 C.

Of course we can find out many examples of fire.... and not only related to electric propulsion.
My diesel car has been burned on HWY few years ago and I still use diesel car.
On our arfield has been burned agricultural airplane - fault of fuel installation - and they are still in use.

We managed to use highly flamable fuel in aviation and automotive. Now you can see even highly compressed hydrogen in cars where risk of crash is higher than in airplanes.

I definitelly agree that we have to be very carefull and try to precede any known (an try to imagine even unknown) danger. Therefore we are discussing here not only about aerodynamic solutions, but also about actual cells chemistry and other parts of electric propulsion.

Idea of e-soaring is based on self launch gliders able to use electric propulsion also for "L/D sponsoring". Gliders are very efficient so energy we need is relativelly small (in compare with LSA or GA airplanes). So in aviation could be e-glider someting like electric bicycle in ground transportation world ;)

Quotefancy-2039515-3840x2160.jpg
 

John.Roo

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Also be aware that when you’re working with an existing pack with an integrated BMS… you’re stuck with that BMS behavior. If it has a 1C limit, does it have an eFuse to enforce that because the car should never exceed that limit? If so is it a slow eFuse so it kicks in just as you get past takeoff speed? Similarly does the battery disconnect to protect itself at over temp assuming the car it’s in can just pull over, instead of damaging the battery but providing power to the end? Very different trade offs for an auto BMS and an airplane one, so unless you get something with great documentation, expect a lot of testing. Honestly probably less work to build your own BMS than test someone else’s undocumented one enough to trust it.
Thanks for detailed info đź‘Ť
Seems that best way is to follow your recommendation ;)
"Honestly probably less work to build your own BMS than test someone else’s undocumented one enough to trust it."
 

Carpetman

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353D37CD-E646-42E5-966B-41001DEBC409.jpeg I have a e glider I am interested in selling complete, less battery pack
 

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