Battery packs - fire danger?

Discussion in 'Electric Propulsion' started by Bille Floyd, Nov 5, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Nov 11, 2019 #21

    Tiger Tim

    Tiger Tim

    Tiger Tim

    Well-Known Member

    Joined:
    Apr 26, 2013
    Messages:
    2,899
    Likes Received:
    1,621
    Location:
    Thunder Bay
    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.
     
  2. Nov 11, 2019 #22

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member HBA Supporter

    Joined:
    Aug 22, 2016
    Messages:
    308
    Likes Received:
    83
    Location:
    Lt
    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.
     
  3. Nov 11, 2019 #23

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member HBA Supporter

    Joined:
    Aug 22, 2016
    Messages:
    308
    Likes Received:
    83
    Location:
    Lt
    Or, one could think about this weirdo style AFTER detaching part of wing with tail boom and motor :

    [​IMG]
     
  4. Nov 11, 2019 #24

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,196
    Likes Received:
    260
    Location:
    YMM
    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.
     
    litespeed likes this.
  5. Nov 11, 2019 #25

    Bille Floyd

    Bille Floyd

    Bille Floyd

    Well-Known Member

    Joined:
    Sep 26, 2019
    Messages:
    64
    Likes Received:
    28
    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
     
  6. Nov 11, 2019 #26

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,196
    Likes Received:
    260
    Location:
    YMM
    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.
     
  7. Nov 12, 2019 #27

    Dan Thomas

    Dan Thomas

    Dan Thomas

    Well-Known Member

    Joined:
    Sep 18, 2008
    Messages:
    4,871
    Likes Received:
    2,083
    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.
     
  8. Nov 12, 2019 #28

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,196
    Likes Received:
    260
    Location:
    YMM
    @Bille Floyd 's idea not mine... I was just pointing out the obvious flaws with his "not dropping it" plan.
     
  9. Nov 12, 2019 #29

    litespeed

    litespeed

    litespeed

    Well-Known Member

    Joined:
    May 21, 2008
    Messages:
    1,493
    Likes Received:
    296
    Location:
    Sydney
    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.
     
    Hephaestus, pictsidhe and stanislavz like this.
  10. Nov 12, 2019 #30

    Bille Floyd

    Bille Floyd

    Bille Floyd

    Well-Known Member

    Joined:
    Sep 26, 2019
    Messages:
    64
    Likes Received:
    28
    BUMMER !
    I was all excited about E-power ; till you guys , woke
    me up to "Reality".

    Bille
     
  11. Nov 13, 2019 #31

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,013
    Likes Received:
    2,008
    Location:
    BDU, BJC
    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.
     
    BoKu likes this.
  12. Nov 13, 2019 #32

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,958
    Likes Received:
    1,915
    Location:
    North Carolina
    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 likes this.
  13. Nov 13, 2019 #33

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,196
    Likes Received:
    260
    Location:
    YMM
    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.
     
  14. Nov 13, 2019 #34

    emir_82

    emir_82

    emir_82

    Active Member

    Joined:
    Jun 25, 2014
    Messages:
    43
    Likes Received:
    9
    Location:
    Rosario
    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.
     
  15. Nov 13, 2019 #35

    Bille Floyd

    Bille Floyd

    Bille Floyd

    Well-Known Member

    Joined:
    Sep 26, 2019
    Messages:
    64
    Likes Received:
    28
    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
     
  16. Nov 13, 2019 #36

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,958
    Likes Received:
    1,915
    Location:
    North Carolina
    Redrives aren't easy to make reliable.
     
  17. Nov 13, 2019 #37

    Hephaestus

    Hephaestus

    Hephaestus

    Well-Known Member

    Joined:
    Jun 25, 2014
    Messages:
    1,196
    Likes Received:
    260
    Location:
    YMM
    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.
     
  18. Nov 14, 2019 #38

    litespeed

    litespeed

    litespeed

    Well-Known Member

    Joined:
    May 21, 2008
    Messages:
    1,493
    Likes Received:
    296
    Location:
    Sydney
    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.:dead:

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

    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.:pilot:

    Safety by design is never more important.
     
  19. Nov 14, 2019 #39

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member HBA Supporter

    Joined:
    Aug 22, 2016
    Messages:
    308
    Likes Received:
    83
    Location:
    Lt
    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....
     
    BoKu and emir_82 like this.
  20. Nov 14, 2019 #40

    litespeed

    litespeed

    litespeed

    Well-Known Member

    Joined:
    May 21, 2008
    Messages:
    1,493
    Likes Received:
    296
    Location:
    Sydney
    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?
     

Share This Page



arrow_white