Battery packs - fire danger?

[Tiger Tim]

NO--- i will not be placing that battery pack, under my butt

It would be good for fire detection there...

I only say that partly in jest (like everything else I say) but I too am on team Put the battery pack on the C.G. and have a means of ditching it in a hurry.. Maybe even have two packs in parallel side-by-side so you could keep half your power in an emergency. Off the top of my head I’d have a long orange streamer that unfurls behind the battery as it falls, both as a signal to those on the ground and to slow the descent a little bit.

I also believe pretty strongly in prevention which is why I’m comfortable with a solution as extreme as dropping a burning thing on people and their stuff. I’m not convinced that battery fires are a weird lottery, the LiPo troubles I’m familiar with (in radio controlled models, mind you) are the result of battery abuse whether it’s excessive charge or discharge rate and/or the pack has already been compromised from a previous impact, and those are probably the cheapest and least quality controlled batteries available. I would think if you take proper care of and monitor your batteries (and have the discipline to replace them if they go outside of limits) they ought to be extremely reliable. At least that’s the way I see it, thoughI admit I don’t have a horse in this race.

 

[stanislavz]

Putting all the weight of the batteries, a big mass fraction at each tip may sound good in theory but does create a lot of problems handling and strength wise.

The spar would have to be many times stronger than normal. The leverage effect would be huge.

Nope, vice versa. Any weight which you take out from fuselage, and put it onto a wing tip, will make life of spare easier. On the flight of course. On ground - yes, it will be more load.

Differently, if you could distribute weight off all load across the whole wing - spar would minimum at all.

 

[stanislavz]

Or, one could think about this weirdo style AFTER detaching part of wing with tail boom and motor :

 

[Hephaestus]

team Put the battery pack on the C.G. and have a means of ditching it in a hurry..

Have a look at pack construction in the leaf and tesla and you'll understand what the difference is... 18650s bundled tight together then foamed in place. RC batteries they're running usually minimal strips of fiberboard/strapping to reduce the risk of cells rubbing through their wrapper and shorting. And the space is open to allow heat to dissipate.

Starting to think rc guys know better than tesla

Anyway in a previous thread i proposed how i would do it. LongEZ style luggage pods to mount batteries on cg. Use fire protection style fusible links and a drop mechanism, so theres an automatic @ this temp = let er rip tater chip.

 

[Bille Floyd]

My search perimeters, before posting a new Thread , will
need to get a bit better in the future. --------sorry

Dumping a burning battery pack on the public , is
not really an option , (for me) ; and no way do i want
the mass of my packs much over a few feet from the
CG, because it definitely will affect the handling for
pitch and roll. Also the further the mass is from the CG
in pitch ; the more difficult it will be to Stop a tumble
without a tail.

I have flown both HG and PG with a 1000ft of broken tow-line
under me ; it wasn't especially difficult, so i did figure-8's
over the dry-lake , slowly drifting down-wind ,till i was about
100-ft AGL, and then released it, (made recovering the line easy).
SO
Why the concern for flying with a 10-ft SS tether, to the
burnt-out pack ? I could easily, adjust the pilot weight
to compensate for the battery weight; and dump it just before
landing !


Bille

 

[Hephaestus]

Your cable isn't going to last for one. Either the frame or the cable itself (remember what happens when you fan a fire) is going to melt.

Keeping it tethered and swinging will be worse as you'll be explosively jettisoning burning batteries along your flight path... And you'll be throwing lots of oxygen in there to really get her going.

The risk of an object falling and hitting a person or structure is minimal - insurance would put odds near 0. Unless of course you're intentionally flying over heavily populated areas - which seems like poor idea for a first gen electric aircraft.

 

[Dan Thomas]

Keeping it tethered and swinging will be worse as you'll be explosively jettisoning burning batteries along your flight path... And you'll be throwing lots of oxygen in there to really get her going.

A burning battery soon doesn't weigh much, so the cable idea to maintain CG is a waste of time.

Batteries out at the wingtips is a deadly idea. They would weigh much more than wingtip fuel tanks, and few airplanes have those. Weight at the tips is one way to make a spin almost impossible to stop, and slows the roll rate a lot and makes stopping the roll much harder.

And weight far from the CG in a fore/aft direction is no good either. A heavy engine balanced by a bunch of ballast in the tail has the effect of flattening a spin, another deadly problem. Now one has to start making compromises to make the airplane stall-proof, narrowing the performance envelope. A good aircraft design minimizes the number and severity of compromises involved.

 

[Hephaestus]

A burning battery soon doesn't weigh much, so the cable idea to maintain CG is a waste of time.

@Bille Floyd 's idea not mine... I was just pointing out the obvious flaws with his "not dropping it" plan.

 

[litespeed]

Billie,

I know you are concerned about the dump and run- but it is really the only solution in a thermal runaway situation.

As others have stated the pack will act like a moving furnace and drop burning debris along your path. It is normal for them to burn for 30 minutes or more intensely. Unless you are going quite fast- the flames will reach you on a ten foot tether- it is intense and unrelenting. It will also likely erupt in a explosive manner when it gets going.

I know you do not like the idea, but please consider the risks for yourself in a emergency event. If it never happens- sweet no issue. If it does, without dumping- you are really playing russian roulette with all 5/6 chambers loaded.

It is like WW1 pilots- the were refused parachutes because that was strange and considered cowardly. Instead they gave them a gun- no chance of survival from fire, so shoot yourself.

I know that sounds alarmists. But burning to death is a major issue to me.

 

[Bille Floyd]

BUMMER !
I was all excited about E-power ; till you guys , woke
me up to "Reality".

Bille

 

[mcrae0104]

I believe everything the media tells me about incendiary vehicles. We all know they're impartial and they're not just trying to whip up ratings.

 

[pictsidhe]

BUMMER !
I was all excited about E-power ; till you guys , woke
me up to "Reality".

Bille

Just fit the pack in a mildy fireproof part of the plane with fusible mounts so it drops away in the unlikely scenario that goes into thermal runaway. I think the tethered idea is a worse option.

 

[Hephaestus]

What @picsidhe said...

If you've done rc for a while... You'll have seen it. But those get beat around and mistreated a wee bit more than what we would be willing in GA...

That said the systems exist to make you safe. If you spend a modicum of time thinking through the end goal. As far as i know we've only had 1 in flight fire of a light aircraft. I think there were 2 on the ground incidents as well.

We're not talking degrees of safety where you're talking likely and imminent harm. But we are talking about a first generation electric aircraft where you probably want to ensure if unexpected occurs - you have a safe exit strategy.

 

[emir_82]

I would like to remember you that there is 200 sailplanes equipped with the FES(front electric sustainer) that has the battery in the fuselage and they had only a couple of fires. They were because of mistreated battery pack. In total flying hours the two fires are a very good number in probability. In my project I will put the batteries on the wings, so I am pretty comfortable with those figures and because I bought new cells.
I don't want to be repetitive, but with a stainless steel firewall and heat insulator away from critical systems will be more effective that the hanging torch option.

 

[Bille Floyd]

I will NOT drop a burning battery ; if a fire-fighter dies,
fighting a fire i started ; I will be Really bummed !

For now --- I'm looking at twin apposed 2-strokes , that
put out 27 to 30-Hp ; and weigh in the 15 to 18-Lb range. I
then need to build my own reduction gears to spin a
larger prop. I'll go electric , when the battery chemistry
gets a bit more user friendly.

Bin flying LIPO batterys in RC helicopters, for near a few decades
now ; had one heli burn up from a bad ESC ,which shorted
out the BEC. Everything came down in flames !!
It's not Just , (battery maintenance) that can cause a fire.

Bille

 

[pictsidhe]

Redrives aren't easy to make reliable.

 

[Hephaestus]

I will NOT drop a burning battery ; if a fire-fighter dies,
fighting a fire i started ; I will be Really bummed !

For now --- I'm looking at twin apposed 2-strokes , that
put out 27 to 30-Hp ; and weigh in the 15 to 18-Lb range. I
then need to build my own reduction gears to spin a
larger prop. I'll go electric , when the battery chemistry
gets a bit more user friendly.

Bin flying LIPO batterys in RC helicopters, for near a few decades
now ; had one heli burn up from a bad ESC ,which shorted
out the BEC. Everything came down in flames !!
It's not Just , (battery maintenance) that can cause a fire.

Bille

A firefighter would be at greater risk fighting a full aircraft crash and fire seeking survivors over a battery pack burning. Talk to your firefighters we all seem to know one or two.

In the electric conversion world its the systems as a whole... Battery is highest risk, but there's a thousand points of failure along the way. How many rc planes have burnt up because of those crappy tamiya connectors we used to run... There's going to be esc failures, connector failures, overheats, motor shorts, and how many others - we have a very long learning curve ahead.

 

[litespeed]

Comparing the risk to a firefighter is the wrong way to think if it.

It is a almost given that unless the pack is very small and low energy- a failure and thermal runaway will kill the pilot before you can get to the ground. It is seconds before a thermal event goes volatile and burns. The time to survive is very limited.

No amount of firewall protection can save you, the fire will be substantially bigger than a fuel line break (assuming you cut fuel flow) or oil fire. The pack will burn and produce immense toxic smoke into the cabin, you wont be able to see, breath or control the aircraft. That assumes a firewall fwd pack.

Two fires in a SES sailplane of 200 flying is 1% failure rate on small packs. A normal aircraft will have a much bigger pack and greater risk profile. Most of those are also professionally developed systems and go in very expensive aircraft.

If you place them in the wings or under them, it still needs to be done so no heat soak can effect the wing structure or controls/surfaces. That in practice can be difficult and heavy.

There are relatively very few electric aircraft flying, it is a new field and much is needed to improve safety.

As I have stated and others have also.......................if a thermal runaway happens and you or the pack don't immediately depart the aircraft...........You are toast.

The Siemens aircraft burn says it all, millions in R and D. A runaway meant death well before they could get near the ground.

Dump it and live must be the electric safety motto until massive improvements are made to batteries.

The risk to a firefighter would be millions to one of death. Staying with the pack is much more likely one to one risk of death.

I like electric and would consider one- so am not a anti person. I just want pilots to survive if it all goes wrong.

Safety by design is never more important.

 

[stanislavz]

I am still a fan of "controlled burning" I do have made an kiln for aluminum melting - And it was insulated using 35 mm thick plate, to the level - that you can place bare hand on other side to molten aluminium.

And a box or tube, made from stainless + isolation between it and construction - will do the trick. With funnel for gas escape....

 

[litespeed]

Stanislav,

What thickness of insulation and of what type do you have in mind?
I would think you would need a lot plus a inner and outer wall.

It could work if well designed and a downdraft ejection tube that extends beyond the wing structure.

So maybe as a pod that hangs on the wing, one each side.

What would each weigh, do you think?