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Jul 25, 2004, 09:55 AM
K4UAV
dalbert02's Avatar

lipo fire on maiden flight


Today, after what seemed like eternity for weather to co-operate, my maiden flight finally happened. Sadly, it ended in a li-po fire. The CG was just a little off resulting in a tip-stall on take off. I believe the small amount the motor mounting screws went past the blind nuts punctured the li-pos when the plane stalled at 5-6 feet altitude. The plane was not damaged in the slightest by the crash, but the resulting fire took out a Phoenix 25 ESC and the 3s kokam 1500 lipos. I think the servos and Berg Rx are salvageable. Whaaa!
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Jul 25, 2004, 11:42 AM
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brianb10's Avatar
man that stinks. is the plane ok? looks a little toasty
Jul 25, 2004, 01:17 PM
Registered User
sorry to see a nice bird get damaged this way.

looks fixable, though.

send me the receiver and i'll chek it out for you.

peter berg
Jul 25, 2004, 01:43 PM
K4UAV
dalbert02's Avatar
Wow Thank you Peter!
That is very kind of you!
Please send me the address to which I should send. I really appreciate your help. Thankx
-dave
Jul 25, 2004, 04:00 PM
Registered User
Dave, Li-poly fires after crashes are pretty rare, so luck was definitely not on your side. Just wondering if you had seen any of the messages warning about mounting Li-polys with consideration for avoiding damage in a crash, such as applying padding, etc.?
Jul 25, 2004, 06:14 PM
Aerobatic Extremist
SharksTooth's Avatar
Oh man, I hate to see that happened. You may want to look that battery over real good for evidence that the screws did damage. There have been alot of 1500's that have vented and have been reported on here. It may have not been a result of the slight impact at all. It takes a pretty good wallop to dent these things or break the seal on them. I'd be willing to bet the two are unrelated.
Jul 25, 2004, 07:23 PM
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Andy W's Avatar
I like the idea of wrapping my LiPo in foam, or having it up against a foam block inside the fuselage. This prevents damage in an abrubt stop..
..a
Jul 25, 2004, 08:58 PM
K4UAV
dalbert02's Avatar
I have not read about lipos blowing up after a crash, the incidents I have read about concerned high charge or discharge rates, and that it would be prudent to monitor crashed packs closely. I guess next time I will put foam around the lipo packs. I put the burnt lipos in a bucket of water after the crash, I can't see any evidence of the motor mounting screws hitting them, but they are pretty crispy (black) and it is hard to see anything. The screws are only about 1/16" to 1/32" (maybe a 1mm max ?) past the blind nuts, but I can't think of any logical explanation why the packs would blow up on such a small impact. I built the packs myself but the solder joints were perfect, no cold joint and very smooth. I hold the iron to the tab until it makes a small puddle and dip the pre-tinned wire in, holding the iron unitl it becomes one with the puddle. Each cell was insulated with three wraps of kapton tape so there were six layers between each cell.

Whenever I read about lipo fires, I usually said to myself, "Gee, I wonder what this idiot did that he isn't telling us?" I just could not see how a lipo could blow when one follows all the safety advice out there. Now that I am on the other side of the coin, I still don't know. What did I do wrong? Now I am the idiot!

If this were that pack in my mini-IFO, I would almost expect it. My IFO has crashed at least 50 times. But this pack was brand new, I had just made it. I charged each cell individually, then soldered the 3 cells together, then charged again as a serial pack. The final charge only took 10ma before the charger stopped.

Any thoughts?
Jul 25, 2004, 09:00 PM
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Andy W's Avatar
Take a look at some of the coverage from SEFF.. nice pics and video of large LiPo packs smoking away after a crash..
..a
Jul 26, 2004, 05:27 AM
Registered User
In one of the threads on RC Universe and also in one of the recent magazines there was an incedent where a gentleman crashed a lipo powered airplane. Put it in the trunk of the car and a period of time later lost the car and airplane to a fire.

It is recommended to remove the lipo batteries from a plane in such a case and let them stand for a while. When they vent off it is spectacular, from the pictures I have seen.
Fortunately I haven't had that happen yet.
Key word "YET".
George
RAGBAG
Last edited by RAGBAG; Jul 26, 2004 at 05:30 AM.
Jul 26, 2004, 05:33 AM
Registered User
Quote:
Originally Posted by dalbert02
... What did I do wrong? ... Any thoughts?
As Andy said, you didn't cushion the front of your pack (Quite fragile) against the usual crushing force (Many Gs!) LiPos are subjected to in Eflight: A nose-in crash.

- RD
Last edited by RD Blakeslee; Jul 26, 2004 at 05:36 AM.
Jul 26, 2004, 06:23 AM
It flies? I like it!
I damaged a brand new TP2100 Gen2 3S1P in a racer on the first flight. I forgot to put some foam in front of the pack, the person doing the handlaunch had a sweaty grip which resulted in too high an angle followed by the classic stall/spin. The pack drove itself into the back of the motor creating a perfect impression of the motor in the cells. I removed the pack immediately and placed it on the gravel in the parking lot. Whithin 10 minutes the pack vented and burned. It was a valuable (costly!) lesson to lose that $80 pack for lack of $0.05 worth of foam.
Jul 26, 2004, 06:57 AM
Registered User
Quote:
Originally Posted by dalbert02
I have not read about lipos blowing up after a crash, the incidents I have read about concerned high charge or discharge rates, and that it would be prudent to monitor crashed packs closely. I guess next time I will put foam around the lipo packs.
The reason that Li-poly packs are supposed to be monitored after a crash is that some have caught fire immediately on impact and some have had catastrophic failures after a delay of several minutes. The latter has resulted in at least one SUV burning to the ground after a crashed aircraft was put in the back seat.

Crash descriptions vary widely. Some li-polys have been known to survive high-speed impacts intact, while others have failed after minor, low-speed impacts. In the absence of slow-motion video of each pack during the crash, most of the discussion about what happened in each case has been pure speculation. Reading about these incidents has caused many people to take measures to cushion Li-poly packs from impacts, such as making sure there are no sharp objects near their mounting location in the aicraft and putting foam in front of them to protect them if they slip forward on impact.

Most of this is anecdotal and not scientific. So I don't believe there is a definitive strategy for totally avoiding the possibility of catastrophic Li-poly cell failure, only some things that people believe should reduce the possibilities.
Jul 26, 2004, 07:09 AM
Registered User
Dave, That last paragraph sounds a little like one of DNA's might.

It's more than a matter of "belief", I think. It stands to reason that cushioning a fragile object from a G force applied on a known vector is going to help avoid damage, e.g., cushioned dashboards in automobiles.

Nobody that I know of who uses cushioning expects total avoidance.

- RD
Jul 26, 2004, 07:48 AM
Registered User
Just a thought ... was the throttle still wide open when the aircraft went in? If so, could that cause an electrical overload when the prop is stalled on hitting the ground?


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