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A GE90 jet engine like those used in a Boeing 777 can have a power output up to 75 MW. Let's take a fairly beefy phone battery -- 2500 mAh at 3.7 volts. Convert

by jsolson 10y ago

A GE90 jet engine like those used in a Boeing 777 can have a power output up to 75 MW. Let's take a fairly beefy phone battery -- 2500 mAh at 3.7 volts. Converting those units into something more useful we get 9.25 Wh. If we assume the entire chemical energy of the battery is converted into heat instantaneously, that's 33.3 KJ or .04% of the energy output of the engine per second. It's possible that such a release could cause a catastrophic failure, but I have a hard time convincing myself that the battery poses a real risk.

seanp2k2 10y ago
I think the concern is more about the resultant chemical reaction of lithium: https://m.youtube.com/watch?v=gisdMQbtJqk https://m.youtube.com/watch?v=gisdMQbtJqk than the total power of the pack. Also, larger hobby aircraft (e.g. A 700-size heli) will be using battery packs on the order of 2x packs of 6 cells ("6s" aka 6 3.7v cells in series @4000-5000+ mah), so it's more like ~200-300Wh. Again though, doesn't matter, because even something like a 3s pack @2200mah can make quite a scary fire. This is why there are barrels of salt water at RC flying fields. An overheating lipo goes in the tank before it melts everything with hell fire. Lipo fires are also why you can't take "hoverboards" on airplanes and why Amazon recalled them all: http://fusion.net/story/250086/airplane-hoverboard-ban-list/ http://fusion.net/story/250086/airplane-hoverboard-ban-list/ http://www.theverge.com/2016/1/21/10806816/amazon-hoverboards-refunds http://www.theverge.com/2016/1/21/10806816/amazon-hoverboard... Not sure how this is affected by being struck with a blade rotating at tens of thousands of RPMs at hundreds of miles per hour, but my point is that lipos are nasty beyond just their specific energy density :)
- tim333 10y ago
  The fire in the video looks kind of wimpy against a jet engine that burns a litre a second or so of jet fuel. The heat from the fuel is probably 1000x that from the battery
  - SideburnsOfDoom 10y ago
    The problem though is that the violently combusting battery is also a chunk of metal that, after being struck by the blades, is going to be moving at high speed roughly at right angles to the expected airflow through the jet engine. Damage could ensue, that is not equivalent to bits of bird flesh and bone.
  - Piskvorrr 10y ago
    The heat and flow in a jet engine is also carefully engineered and directed so that the flame front stays beyond a certain point in the combustion chamber. You don't want any of that in the compression stage, for example.
SideburnsOfDoom 10y ago
Maybe there is no real risk, but I did want to point out that it would be a mistake to assume that drone strike to a jet engine would be roughly equivalent to bird strike of the same weight. A drone is unlike a bird, a bird does not have lithium batteries, bird strike will not spray fragments of burning or exploding shrapnel through the jet engine.

by jsolson 10y ago

seanp2k2 10y ago

I think the concern is more about the resultant chemical reaction of lithium: https://m.youtube.com/watch?v=gisdMQbtJqk https://m.youtube.com/watch?v=gisdMQbtJqk than the total power of the pack. Also, larger hobby aircraft (e.g. A 700-size heli) will be using battery packs on the order of 2x packs of 6 cells ("6s" aka 6 3.7v cells in series @4000-5000+ mah), so it's more like ~200-300Wh. Again though, doesn't matter, because even something like a 3s pack @2200mah can make quite a scary fire. This is why there are barrels of salt water at RC flying fields. An overheating lipo goes in the tank before it melts everything with hell fire. Lipo fires are also why you can't take "hoverboards" on airplanes and why Amazon recalled them all: http://fusion.net/story/250086/airplane-hoverboard-ban-list/ http://fusion.net/story/250086/airplane-hoverboard-ban-list/ http://www.theverge.com/2016/1/21/10806816/amazon-hoverboards-refunds http://www.theverge.com/2016/1/21/10806816/amazon-hoverboard... Not sure how this is affected by being struck with a blade rotating at tens of thousands of RPMs at hundreds of miles per hour, but my point is that lipos are nasty beyond just their specific energy density :)

tim333 10y ago
The fire in the video looks kind of wimpy against a jet engine that burns a litre a second or so of jet fuel. The heat from the fuel is probably 1000x that from the battery
- SideburnsOfDoom 10y ago
  The problem though is that the violently combusting battery is also a chunk of metal that, after being struck by the blades, is going to be moving at high speed roughly at right angles to the expected airflow through the jet engine. Damage could ensue, that is not equivalent to bits of bird flesh and bone.
- Piskvorrr 10y ago
  The heat and flow in a jet engine is also carefully engineered and directed so that the flame front stays beyond a certain point in the combustion chamber. You don't want any of that in the compression stage, for example.

SideburnsOfDoom 10y ago

Maybe there is no real risk, but I did want to point out that it would be a mistake to assume that drone strike to a jet engine would be roughly equivalent to bird strike of the same weight. A drone is unlike a bird, a bird does not have lithium batteries, bird strike will not spray fragments of burning or exploding shrapnel through the jet engine.