Full size glider LiPo fire

[John Lee]

"The FES battery packs are removable for charging remotely from the sailplane. Each FES battery pack is built up from 14 Superior Lithium Polymer Battery (SLPB) cells, connected in series and contained within a carbon fibre battery box with a machined aluminium alloy cover plate/heatsink." from AAIB Special Report

[Denis Watkins]

This is dreadful

Most metals will burn at high temperature reached in fires especially aluminium alloy and the like.

Easy to say now, remove the pack

[John Lee]

The incident happened just after the aircraft had landed, not whilst being charged.

[Simon Chaddock]

That's a lot (28) of very big (41000 mAh) cells!.

With that many cells the chances of a LiPo failure are that much greater than using say 6 and with such a huge capacity the consequences of any failure are bound to be that much greater.

A LiPo is a self contained power source, like a rocket, but unlike a rocket the energy is stored just 'molecules' apart rather than in physically separate tanks.

[Piers Bowlan]

Yikes!! Perhaps they should fit the LiPos in pods under the wings rather like drop tanks!

[PatMc]

Posted by Simon Chaddock on 12/11/2017 13:25:10:

That's a lot (28) of very big (41000 mAh) cells!.

Not really that big.

The motor's 23kWH [about 30hp] so that's around 11 min's of power @ around 17W/lb for the aircraft's full gross weight.

[Martin Harris - Moderator]

There was a tale from a world gliding championship in the 60's in Argentina where a glider was on a long aerotow retrieve over very inhospitable territory. The pilot was indulging in a cigarette and dropped it under the seat where it was unreachable. After a while, there was a whiff of burning and then some smoke. The glider wasn't fitted with radio and the chances of a successful landing were very small if he released from the tow so the pilot tried every way he could think of to reach under the seat and extinguish the burning, with the resulting gyrations severely disturbing the tug pilot who was close to dumping the tow...

Finally, he remembered that he had a bag of plums (possibly gleaned from the field where he'd landed earlier?) and rammed them under the seat, which rather fortunately did the job and extinguished the fire.

Somehow, I don't think that a bag of plums would help much in a LiPo fire!

Edited By Martin Harris on 12/11/2017 15:10:34

[Chris Walby]

From the AAIB report:

Other information

The pilot reported that in January 2017 one of the FES battery packs from G-GSGS fell from his car onto a paved surface through a vertical distance of around 0.2 m. There was no sign of damage to the battery pack following this event. The pilot did not record the serial number of this battery pack and therefore it is not possible to determine whether this pack was the battery that caught fire during the landing at Parh am Airfield.

What is concerning is there is no automatic fire suppression system (that could warn the pilot that its deployed and limit the damage to the aircraft.

Firetrace **LINK**

I wonder if the electric race cars use fire suppression systems like the F1 teams?

[John Privett]

Sounds a good idea Chris, but I can't help wondering if it's possible to carry an extinguishing system capable of extinguishing a LiPo fire in a glider. The AAIB report notes,

"The airfield fire truck arrived promptly and an initial attempt was made to extinguish the fire using a CO2 gaseous extinguisher, but this proved unsuccessful. Aqueous film-forming foam (AFFF) was then sprayed into the FES battery compartment and the fire was extinguished."

The Firetrace system seems to CO2 "powered" which is probably great for extinguishing a cable fire, but it the CO2 extinguisher in the fire truck wasn't capable of putting out the LiPo fire then I'm not sure that something light enough to be carried in the glider would fare any better.

[Chris Walby]

I'll check with the Firetrace guys, but I am sure our equipment at work is protected with foam as trying to put a fume cupboard fire out with 0.5 m/s face velocity would be pointless with CO2 (just like trying to put a lipo fire out with CO2).

My example just showed what was available as part of their wide range of solutions.

PS A K21 two seat gilder has a max take off weight of 600kg and its not possible to put in a few Kg of fire extinguisher in.

PPS Some gliders carry water as ballast, perhaps a dump to battery bay option is better than having to leave it and deploy the parachute! This would not add any additional weight + they don't mind gliding with the dead weight of the battery/motor anyway.

[Simon Chaddock]

Would film forming foam actually extinguish the initial part of a LIPo 'runaway' fire?

I wonder it worked in this case as by the time it was deployed the LiPos internal energy was depleted and the fire was then conventional hydrocarbon fire.

I still think carrying that much 'self contained' energy in relation to the size of the plane is a substantial risk.

[Piers Bowlan]

Posted by Simon Chaddock on 14/11/2017 01:03:57:

Would film forming foam actually extinguish the initial part of a LIPo 'runaway' fire?

I wonder it worked in this case as by the time it was deployed the LiPos internal energy was depleted and the fire was then conventional hydrocarbon fire.

I still think carrying that much 'self contained' energy in relation to the size of the plane is a substantial risk.

Petrol contains a huge amount of self contained energy, the difference is that a simple short or electrical failure in a Li-ion battery can cause a runaway fire and the exclusion of oxygen will not put it out, like a conventional fire. Also, you not only have to extinguish the fire but cool the battery too, as it is so hot it will re-ignite once the extinguishant has dispersed. Using water ballast (if carried) to cool the battery is perhaps not such a daft idea. Placing a large lithium battery within inches of the pilot in the confines of a glider sounds quite terrifying to me. If the CAA suggest bailing out is the best option for the pilot surviving such a fire in the air, perhaps my (semi serious) suggestion of jettisoning the battery as not so laughable after all?

[Tim Flyer]

Yes a jettisonable “battery pod” attached above the fuselage might be sensible . If attached above the fuselage in a small pod it would reduce fire spread risk too.

[ceejay]

Jettisonable "pod" hmmm, not the best of solutions methinks!! I would not relish being under a jettisoned "pod" of burning lithium !!!

[Nigel R]

an underslung pod, temperature sensors linked to an auto jettison setup, a small fire extinguisher onboard to prevent fire spreading after jettisoning the pod, a manual override for jettison, a cockpit temp dial and big red flashing panic indicator, please remember not to experience a lipo fire over anything human or flammable

and don't forget the parachute

...bring back IC!

I admit, the thought of large lipos (cars) in the hands of the general public scares me.

Edited By Nigel R on 14/11/2017 10:58:26

[Denis Watkins]

If you watch Formula 1, take care to watch the garage activities,

You will see very large mechanic, with a long pole with a large hook attached

He watches carefully the mechanics working beneath the racing car

For electric shock ! !

He can then hook their belt and pull them clear !

This is true

Edited By Denis Watkins on 14/11/2017 11:32:39

[KiwiKid]

It still remains a bit of a mystery as to what actually caused the batteries to cook off. The AAIB report is inconclusive and they plan to do a detailed analysis of the batteries to try and determine a cause. The report was dated 25th September so perhaps some more info will be available before Xmas. The only "smoking gun" is a comment from the pilot that he dropped one of the batteries which may have caused fracture damage. The pilot should have had some warning in flight if the batteries were starting to cook off as the Front Electric Sustainer Control Unit is fairly detailed.

 

 

The batteries have built in fan units to help with cooling, so overheating should not have been a problem and even if it was the pilot should have had warning. As the combustion appears to have erupted on landing, perhaps a bump on touchdown triggered the failure.

Dumping a flaming mass of combusting lipo batteries is probably highly illegal and could lead to all sorts of grief. Even bailing out and leaving the glider to crash is going to potentially cause a nasty conflagration on impact.

Edited By KiwiKid on 14/11/2017 12:45:01

[Piers Bowlan]

Posted by ceejay on 14/11/2017 10:17:12:

Jettisonable "pod" hmmm, not the best of solutions methinks!! I would not relish being under a jettisoned "pod" of burning lithium !!!

Neither would I ceejay but the alternative is for the pilot to bail out, according to the report- and leave the burning glider to crash who knows where? I took as it as read that it would be attached to a parachute as free falling batteries can give you an awful headache if they land on you! The ANO allows you alleviations to do most things with the caveat 'for the purpose of saving life' including the restriction on dropping 'persons or property from an aircraft inflight'. I think this would qualify.

What worries me is that for all the monitoring technology and sensors there was no warning that there was anything amiss before the conflagration. Except the pilots nose- burning, I smell burning!!