Warning for agriculture pilots - crash caused fire - Discussions

So, I was test flying a newly built Skyhunter today before putting cameras in it, the Ruby autopilot appears to have freaked out, rolled the plane inverted, full throttle into the ground. Last data point was 111km/h.

This resulted in my first lipo fire on a crash ever. I've destroyed 40+ aircraft in developing and testing FPV/RC/UAV components for my job, it was a huge impact, the motor was 15 metres away from the fuselage in an almost straight down dive - it flew there after bouncing off the ground.

Now, it was a bad crash, but what made it worse is it hasn't rained here for over 4 months. I was extremely lucky that we had a firetruck within 100m of the crash coming back from priming a pump on a windmill, and that we had no wind (since this was a test flight). The fire truck was with me when I arrived at the plane, and its first cell was just starting to vent at that point, we were stamping out flames jetting waist high within 30 seconds, and didnt have time to start the pump on the truck until the fire died down and this was only a 4s5800mah. I lost the hair on my legs and some on my hands removing the second battery (also destroyed) and airframe from the fire as they were all attached.

If there was any wind, the 3 firetrucks (pictured is their smallest) on the farm would never have had a chance, the district could have been fighting this for days without any question.

If this had crashed more than 100 metres from where we were flying from and able to go stamp out the ground, it would have been a massive disaster costing millions of dollars. This is a 300 acre field, and we could easily have crashed 2 km away if this was an AP flight - there would have been nothing we could do if this happened 2km away.

Therefore, I ask any pilots flying over farm land that is dry, please consider switching away from LiPo. I'm not into the LiPo scare mongering that others are, and as I said, i've had far far more crashes than the average pilot so this is my first fire in over 8 years of flying lipo planes into the ground at high speed. If you can't risk destroying the farm you're flying over... please don't.

I'm looking at using LiFe cells. The prismatic packs (plastic bagged like lipos) worry me a bit, so i'm looking at the cylindrical metal cells for UAV applications.

That being said, here is an excerpt from the A123 whitepaper:

Conversely, Nanophosphate releases only a small amount of heat and oxygen under similar abusive conditions and cells made using Nanophosphate chemistry do not exhibit the energetic thermal runaway that metal oxide lithium ion cells experience (Roth, 2007). This greatly reduces the likelihood of cascading failure—where an incident in one cell spreads to adjacent cells—within a battery pack designed with Nanophosphate chemistry. Even if all of a pack’s safety systems fail, the increased safety inherent to Nanophosphate chemistry provides an additional layer of protection that reduces the incidence, severity and probability of energetic failures.

The failure mode I experienced, and have always experienced when disposing of damaged lipo's (with a high power rifle hehe) has been the cascading failure that is mentioned above - one cell fails, it heats up and vents. This heat then transfers to the adjacent cell which causes it to go into exothermic run away, and the heat builds up higher and higher until on the 3rd or 4th cell it catches fire.

Replies

Luke Moulton March 3, 2014 at 1:55am

Always a concern, particularly here in Aus after a long hot summer. Danger duly noted.
John Butkus March 2, 2014 at 12:48pm

I understand your concern in an arid climate, but what do you suggest that we use that has a similar weight to power ratio to lipo?

A fire extinguisher is part of my flying equipment. I have no delusions that it will put out a lipo fire. It won't. I don't have the cash for a class D extinguisher. The extinguisher is to prevent things around the lipo from catching fire, if I am lucky enough to be close to the fire.
- Mark Harris > John Butkus March 2, 2014 at 7:25pm
  
  I'm looking at using LiFe cells. The prismatic packs (plastic bagged like lipos) worry me a bit, so i'm looking at the cylindrical metal cells for UAV applications.
  
  That being said, here is an excerpt from the A123 whitepaper:
  
  Conversely, Nanophosphate releases only a small amount of heat and oxygen under similar abusive conditions and cells made using Nanophosphate chemistry do not exhibit the energetic thermal runaway that metal oxide lithium ion cells experience (Roth, 2007). This greatly reduces the likelihood of cascading failure—where an incident in one cell spreads to adjacent cells—within a battery pack designed with Nanophosphate chemistry. Even if all of a pack’s safety systems fail, the increased safety inherent to Nanophosphate chemistry provides an additional layer of protection that reduces the incidence, severity and probability of energetic failures.
  
  The failure mode I experienced, and have always experienced when disposing of damaged lipo's (with a high power rifle hehe) has been the cascading failure that is mentioned above - one cell fails, it heats up and vents. This heat then transfers to the adjacent cell which causes it to go into exothermic run away, and the heat builds up higher and higher until on the 3rd or 4th cell it catches fire.

This reply was deleted.