They can. From what I've read the real problem is much like birds. If they get sucked into the jet engine then they can do a huge amount of damage. More than a bird even because of the fact that you've usually got a good bit of metal and a lithium battery or two. That's enough to take out the engine just like a bird but with the lithium battery that's going to get splattered around there's an increased chance of fire starting that could make even losing one engine a really bad prospect. Combine that with the fact that the plane is likely to be at a low altitude and it's unlikely that the plane will be able to glide somewhere it can safely crash land at either an airport or long stretch of road.

> More than a bird even

A lithium battery is going to get chopped up and spit out the rear of the engine - if it manages to get in the intake to begin with, which is a huge if. There's ZERO chance any of that lithium would stick around long enough to cause a 'fire', whatever that means. It's not called a 'jet' engine for nothing.

Given that a big part of a jet engine is that there's a large series of rotors to perform the compression of the air intake as it streams in[1], and then constricts the space to get even higher compression before the combustion chamber there's a good chance of things getting stuck once the primary rotor has been damaged by something going into it. That's the primary way that birds and other debris disable a single engine. They don't usually cause a fire because they're not likely to combust/explode on being punctured or torn[2].

[1] https://upload.wikimedia.org/wikipedia/commons/4/4c/Jet_engi... [2] https://www.youtube.com/watch?v=hhJf9pJ6gOk ; many more just look for lipo explode

How much experience do you have with the lithium polymer batteries commonly used on hobbyist drones?

I've been flying for a little over a year now and personally seen some pretty gnarly LiPo failures in that time.

I would _not_ want to be flying on a plane with one of those hitting the turbines. Would you?

Howdy! I've been flying all sorts of R/C for 25 years, so quite a bit of experience. Had them splode/catch on fire occasionally. Jet engines are quite a bit bigger than said batteries and the flows through them are sufficient to exhaust most, if not all, of the battery out the ass end before the lithium could experience thermal runaway (which is what li-ion fires are).

I think the worst thing is not the fire, but what happens if the wiring gets gummed up on some blades and unbalances the engine. These things turn at a crazy number of RPM, so even a small amount of weight off-balance could cause them to vibrate and self-destruct catastrophically if it hit the right harmonic.

Given the speeds I'm not even sure it'd take that. The debris being sucked in I think would be enough to break/bend a blade or two which would unbalance it just as easily. Making even more debris for the rest of the engine.

Those blades are crazy tough and the battery is the least of your worries when ingesting a drone. I'd be more concerned about the motors doing the damage to the blades.

If a bird strike can do this [1], I don't see why a drone could be any "better" for an aircraft to hit.

[1] https://en.wikipedia.org/wiki/US_Airways_Flight_1549

That's a whole flock of birds though.

It only really takes one to whack an engine. The "flock" bit was particularly interesting there because it got both engines at once. A single drone would presumably only take out a single engine. The airplane would likely survive the encounter, since they're built to survive an engine failure. But it would still do a hefty amount of damage (I bet the drone owner doesn't want to be on the hook for the cost of a new engine!) and survival, while likely, is far from guaranteed in the event of a single engine failure.

The fact that people need to be convinced to keep drones away from planes is a little disconcerting. People just aren't going to be convinced until there's an accident. I wrote the apology a couple days ago. Bookmark it:

https://h4labs.wordpress.com/2015/07/19/dangerous-drones-dai...

We're discussing it again 2 days later as the #1 HN story. Has everyone seen Groundhog Day?

A whole "flock" of drones is not hard to imagine.

Yes. Here are some examples:

1. they distract the pilot during the most critical phase of flight

2. In an airport environment, planes are closer to each other than elsewhere in space, so if a pilot has to suddenly deviate to miss a drone, he might hit another plane

3. If a drone gets in the way of one side of a LOC or a GS signal, it might mess up the plane's ILS approach, possibly causing it to crash. Birds (being radio-transparent) do not.

Yes, compared with what a bird can do. This is what a single bird (vulture) did in to a a small airplane in Brazil recently: https://www.youtube.com/watch?v=ICbWN3XTcig (strong images). This was what another bird did to a large airplane a few years ago also in Brazil: http://g1.globo.com/rio-de-janeiro/noticia/2013/08/aviao-da-... (article in pt-br).

It is a criminal offence to operate any flying device in a controlled airspace in Europe without prior authorization from the appropriate air space control (EASA regulations). It does not really matter whether it is a Cessna, a paraglide, a Chinese lantern, or a UAV drone. I bet a similar law is in effect in the US.

The responsible guy will probably avoid jail, but will surely be convicted.

Bird strikes have taken down commercial aircraft, so I would guess that yes drones are a threat

Yes. https://en.wikipedia.org/wiki/Bird_strike

Wonder if we should create an FAQ for drone questions? It's only been two days since the last HN discussion:

https://h4labs.wordpress.com/2015/07/19/dangerous-drones-dai...

Try birds, for starters.