What Happens When a Drone Hits an Airplane Wing? [video] | Hacker News Reader

What Happens When a Drone Hits an Airplane Wing? [video]

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102 pointsprotomyth94 comments

The sheer amount of airplanes in the sky at anytime is incredible. Also designated no fly zones can change and users may be unaware. So to avoid this issue I think we need to do more than just depend on users knowing where they can fly and not.

Drone collides with helicopter in a temporary flight restrictions (TFR) zone: https://arstechnica.com/tech-policy/2017/12/drone-collides-w...

Map of all airplanes currently flying: https://www.flightradar24.com/40.21,-88.24/6

That's really an ADS-B map, which is not actually all planes flying, at least not yet. It's especially sparse for small private planes, which are probably the most likely to find themselves tangling with a drone.

Prediction: There will never be a time when all air traffic is ADS-B out equipped. It's certainly not a current mandate, and is only mandated for aircraft desiring access to some select airspace after Jan 1, 2020. I will equip, because I own a hangar inside the mode C veil of Boston, but if I were 6 miles farther out, I may very well choose to avoid class B/C airports and not equip. Lots and lots of traffic will certainly make that choice.

There is a lot of air up there. I fly drones in Australia (https://serio.com.au/) and it's easy to stay well out of the way of large aircraft (don't launch anywhere near airports, and restrict your maximum altitude) and helicopters (you can hear them from a long way away).

DJI's software enforces a survey with local regulations before you can fly. The default settings are all very restrictive too.

The authority here provides an app that quickly indicates the flight rules in a particular location - airports and approach paths, non-controlled aerodromes, etc. It's quick enough that it's easy to check as part of your setup procedure.

The riskier situations I think are cropdusters (fly very low and launch from rarely used airfields) or sightseeing planes/choppers (operating close to the ground despite launching from a fair distance away). I often fly at this location (https://serio.com.au/media/20180171.jpg) and on weekends there can be vintage sightseeing planes coming down the beach in that bay, definitely below the 120m (400') drone limit.

There are hundreds of bird strikes every year around the world and so far no drone strikes. Admittedly birds are a lot more numerous but I think drone fliers are also a lot more intelligent with where they place themselves to avoid damage.

There is obviously very real potential for danger but so far drones haven't been an actual danger to aviation.

Less than 3 seconds on google says otherwise. Ignoring the hundreds of near-misses, here's a handful of actual collisions.

https://www.bbc.com/news/uk-36067591

https://www.newswire.ca/news-releases/investigation-report-i... international-airport-quebec-674056663.html

https://www.bloomberg.com/news/articles/2017-12-14/drone-ope...

https://petapixel.com/2018/02/16/drone-causes-aircraft-crash...

I enjoyed that the expert's recommendation was not "regulation", but to change drone design so they more easily break apart on impact. More likely to be implemented and does not need enforcement on the consumer level.

Well, there go my plans to build an adamantium drone! :-p

(I know, i know, adamantium is not real...)

Even if it were real, you'd get a ~3 minute flight time, so eeeeeh.

I would also support drone manufacturers self regulating via GPS deadzones in designated no fly areas.

Nearly all drones of a meaningful size are GPS enabled and could be disabled in range of a no fly zone. Yes it could be spoofed, yes it would require some effort from manufactures, but self inflicted regulation as an industry here could pay dividends if the alternative is ham fisted regulation following a drone/airplane catastrophe.

That's exactly what all major drones do. DJI has a market share of about 75% [1] and you cannot take off any of their success in a restricted flight zone. Flight zone updates are also mandatory and forced to the users. Same for Yuneec, which has another 5% market share.

1. http://thedronegirl.com/2018/09/18/dji-market-share/

Ah interesting, I didn't know!

I feel like that's kinda the wrong route to go; because manufactures shouldn't be encouraged to design things for planned obsolescence.

There has to be a balance, to where the drone is of the same quality, but has safety components that collapse like the engine compartment of a car.

>More likely to be implemented

In the big guys, sure. "My first drone" bought from some low-end chinese reseller over ebay probably isn't going to do anything which raises costs unless it has to, which is why regulation exists.

Not suggesting regulation at this point is fair - but I suspect this will take the path these things always take. A problem is identified and the industry creating it is given a chance to solve the problem itself. It doesn't, and so a harder tool is needed to enforce it for the safety of everyone. Sometimes it does get solved itself, and that's wonderful, but this particular area isn't good at that.

It made a hole and caused internal damage. But would not have taken down the plane.

Recommendation to make drones "frangible", so they break on impact and do not penetrate into the wing.

In comparison a bird crushed the wing surface but did not cause internal damage.

Wings also hold fuel, so it can catch on fire.

We're looking at a collision between a big kerosene-tank and a fist-sized Li-Po battery.

Sounds like a fun time.

Yeah... the fuel in many GA aircraft is usually inside of a relatively thin rubber bladder inside the wing. It does not self seal. If it leaks, it’s going to run down the back of the aircraft and may drain into the cabin. In some aircraft with engines mounted on the rear of the aircraft it can run towards or into the engine.

Now, on top of dealing with an emergency that has disabled control surfaces like ailerons and flaps that pass through the inside of the wing, damaged the leading edge which is critical for generating lift, and potentially having a wing come off if you hit a rough patch of air with a damaged spar, the pilot may have to deal with a fuel leak that would endanger the people in the cabin or cause a midair fire.

Not good.

Most piston aircraft run on gasoline, which is far more flammable than Jet-A/kerosene.

Now also imagine the drone hit the windscreen, and not the wing. Or went into the prop / engine. Or hit the tail and damaged the rudder.

The leading edge of the wing is likely the best case scenario. All others probably result in far more serious consequences.

The drone penetrated the wing and broke spars. It is very easy for such an impact to also destroy control surface cabling, wiring, or hydraulics which certainly can cause a plane crash.

Dented the front spar and some compression members. It probably reduced the wing's margin for maneuvering, but should still have been manageable to get down safely. Not to downplay the danger, but let's not exaggerate it either.

What if the drone was heavier or impacted somewhere else more critical? Drone is pretty much a mini aircraft so it has to be regulated somehow.. which i believe is being done already!

I am not exaggerating. Several years ago, a bird strike in Alaska resulted in a fatal crash of a 172. Does it happen often? Probably not, but a large heavy drone can easily take down a small civilian aircraft.

I'm just pointing out your exaggeration of the result of this test, not the danger in real life, which I believe you assess accurately.

That was enough to take down a plane easily. Wings don't just sit there on the ground like in the video, they support the fuselage of the plane against serious aerodynamic forces.

They are under load, it's like taking out a bunch of columns at the ground floor of a building. Not to mention that wings are full of fuel, as well as the cables or hydraulic lines connected to the control surfaces.

The engineer that conducted the test concluded that the plane would have been able to survive the impact. However, he said that if the test were conducted on a faster aircraft like a business jet, the results could be worse.

Realizing I should go watch the video, did he say at what height it would be recoverable?

For example, there's been at least one high-profile plane crash in the past (Lauda Flight 004) where a thrust reverser (diverts the jet output forward instead of backwards, used to slow you down quick during landing) deployed mid-flight. That should have been recoverable, but turns out Boeing only projected outcome at low speeds and altitudes. The outcome at cruising speeds/altitudes turned out to be far different and the plane went down.

While cruise wouldn't be an issue (don't think they get up that high!) I'd expect the outcome of a drone hitting a flight control surface might vary between takeoff, landing, and lowish-altitude holding.

You’d be shocked how little of the wing is actually supporting the entire structure. Typically there is one main spar that holds up the entire wing and the skin and ribs only hold a fraction of the load which is distributed to the spar. As you might imagine the spar is going to be a pretty heavy duty piece of aluminum and not easily damaged by something like this. A wing can sustain a fairly large hole as long as the spar isn’t damaged.

Control cables would be a concern but hydraulics and fuel aren’t typically going to be a concern. Fuel isn’t as combustible as everyone likes to think. There are also additional tanks. Hydraulics offer redundancy on aircraft that use hydraulic control surfaces.

I’ve seen a Cirrus SR20 hit a deer at takeoff speed and leave a 2.5 ft hole in the skin of the wing the went as deep as the reinforced fuel tank. The aircraft continued flight and came back around and landed just fine. Even flew to the repair airport after cleaning up some loose fiberglass.

Personally what worries me more is what would happen if they fired this thing at the plexiglass windscreen. In a GA airplane that would likely be fatal.

I think 230mph is unrealistic for such tests. A quick google search shows something between 70mph - 100mph on approach [1]. I doubt drones are found at altitudes of aircraft at cruising speed.

I'm not saying that this isn't a concern but can somebody with actual aviation knowledge (I have none) chime in and explain the 230mph figure?

1: http://www.mooneyland.com/how-to-land-a-mooney-properly/

Landing speed for a loaded 737 can be up to 203 mph [0]. Among general aviation, a Gulfstream 450 landing speed can be up to 186 mph at full weight and high altitude. The drone itself can have some speed opposite to the airplane. 230 mph is only a little conservative.

[0] http://www.b737.org.uk/vspeeds.htm Note that numbers are in knots.

[1] http://www.code7700.com/g450_vref.htm

But surely a 737 wing is completely different to the one tested here?

I'd be very interested to see a 737 wing being tested like this.

Completely different? No. Still mostly aluminum sheets riveted to spars with a big ol' gas tank in them. Biggest difference is the control cables would be mostly replaced with hydrolic lines.

Your referenced speeds for the 737 are for an overweight landing at the lowest allowable flap setting. 186 mph for the G450 would also occur at a weight above max landing weight. An incredibly low likelihood.

But we should consider the worst case scenario, not an average one. Thus 230 mph is conservative. They didn't even consider fast gliders, which alone can reach 460 mph.

14 CFR 91.117 restricts aircraft to 250 knots indicated under 10K feet.

Yet you can go on YouTube and see people fly them.

Do you have a reference for fast gliders? I’ve never heard of anything like that.

I don’t think the FAA plans everything for the worst possible scenario. The odds of a classic 737 landing at max take off weight and thus high speed are infinitesimally small. I don’t have a landing distance chart but at the max over weight landing it likely can’t even land on 99.99% of runways in the US in that configuration.

If the FAA planned and approved everything at worst case scenario then we wouldn’t fly anywhere.

The 230mph is combined speed and they don't mention approach as the time of impact. Single engine prop planes can do between 140mph to 200+mph for some of the fast ones. Some of the business jets have higher landing speeds also. You would be surprised how low a lot of these planes fly over rural areas, they are well within range of some of these camera drones doing crop pictures.

It's very unlikely that a drone would hit an aircraft wing at combined speed that high - but certainly possible. I'd be more concerned about one going through a windshield at a slower speed and damaging the pilot.

In US airspace, there's a speed limit of 250 knots (around 290mph) below 10,000 feet. Most light aircraft cruise significantly slower (~140 mph for a Cessna 172) and closer to the ground, whether on approach, takeoff, or other, most aircraft are likely to be going slower than that - so this test is at the high end of that range, even if you add the maximum speed of a DJI Phantom (~40mph) and assume it's flying directly at the aircraft.

Your point that speeds are restricted to be lower at lower altitudes is really salient to the discussion because it's an intentional procedural mitigation for collision hazards in the more densely-populated and less-controlled airspace down low. Drones were but a glimmer in anyone's eye at the time the regulation was emplaced, but the same theories are still relevant.

Bear in mind though that the under-10,000 ft limit is knots of "indicated airspeed", which is a constant-dynamic-pressure pseudospeed uncorrected for density. 250 KIAS at 10,000 ft is about 290 knots/330 mph relative to the airmass, and sometimes up to 10 kt faster on a hot day.

I agree. 230 mph seems high. Most commercial airliners and business jets make their approach at no greater than 150 knots which rounding up is 175 mph. I think the latest DJI drones do about 40 mph.

A drone striking a Mooney at 230 mph seems pretty unlikely. One has to ask what the GA pilot is doing if he’s flying 200 mph at 400 ft or less. It’s not necessarily an unsafe operation but it would definitely be an abnormal operation.

Edit: As pointed out elsewhere the latest DJI Phantom does 40 mph. Updated post to reflect that.

Sadly, there are quite a lot of imbeciles flying drones well beyond the legal limits.

https://www.youtube.com/watch?v=I5izg2cueP4

https://www.youtube.com/watch?v=GPpEnojFTwU

what about takeoff?

My brother actually hit a deer on takeoff a few years ago in Charlotte. It was all over the news that day. It did not do as much damage as this drone did. Mostly just dented in the face of the wing which caused fuel to leak out. It was a little closer to the fuselage. That prompted an emergency landing.

Delta v for the deer was likely significantly lower. The video says impact increases with square of velocity.

How does a deer hit the wing? Aren't they rather high? A small plane that's much slower on takeoff/landing than a commercial airliner?

>It did not do as much damage as this drone did.

probably wasn't shot out of air cannon at 230mph

This is not all that much more than the damage done by a Canadian goose. I guess makes sense. The drone has to fly so it can't be built like a tank.

I'm just glad they used gelatin to simulate a bird. As soon as I heard the guy say he wanted to compare the impact of a drone vs the impact of a bird, I was mentally gasping. XD

I wonder if the results would have been different if they moulded the gelatin into a bird shape (it's moulded as a cylinder in the video, if I'm not mistaken) because then the pressure would have been different. Of course it would probably have been harder to fire from the air pressure cannon.

The block of gelatin also didn't seem to have any hard bits embedded inside. Real birds have bones. While small birds' bones aren't particularly tough, I'm pretty sure the beaks of raptors and some nut-eating birds are tough stuff.

Initially plane parts (engines, wings, cockpits) were tested against dead birds but nowadays we have so many live strikes every year that in practice we know what the proxy based on gelatin is for a variety of birds.

Gelatin is harder than flesh but softer than bone and the overall effect is that on average it has the same effect as birds because it is more like an average representation. While parts of birds are relatively tough they aren't in sufficient volume or weight to penetrate any more.

That isn't to say a bird strike isn't pretty dangerous because they can be. Jet cockpits get severely damaged by them as do engines and you can see in the video the effect on a wing.

Supposed they have used a pneumatic cannon with bird carcasses for testing purposes and Mythbusters tried it with a frozen and non frozen IIRC, though this says clay works just as well. https://www.snopes.com/fact-check/catapoultry/

I guess it would depend on if it is this sort of drone:

https://defensesystems.com/articles/2017/05/02/~/media/GIG/D...

or this sort

https://api.ning.com/files/LxgTrYw8IckDE2ljSVm61iv7MVev4tELr...

It's similar to the question asked here before: "Can a dog kill a man with a cane?". I personally accepted the answer:"Depends on the dog, depends on the man, and depends on the cane".

“How is the dog holding the cane?”

I'm concerned that the test uses a static wing. If you drop a fishing float directly in front of an obstacle in a river, it will be moved with the water around the obstacle, not hitting it.

Air is a lot less dense than water, but my instinct is that unless the drone hit a very narrow sweet spot it would simply be swept around the wing. And even in that sweet spot, there will be a buffer of compressed air that would substantially slow the impact.

Could someone with more knowledge of fluid dynamics comment on the applicability of static tests like this to actual aircraft damage?

I do not have a fluid dynamics background, but my hunch is that at the speeds involved, and the fact that there is a column of air from the cannon already surrounding the projectile, that this makes this simulation close enough.

Ah, good point about the air column.

Does a baseball move out of the way of the swinging bat? There might be some small effect, but it's not the dominant one. In this scenario the wing is just a slightly bigger bat, and the drone is a slightly bigger ball. It would of course take a very (un)lucky strike to collide dead on like this, but not that unreasonable. I do hope they test indirect strikes too though.

I think you're probably right, but note that even for a powerful hitter, bat speed is ~80 mph. This is significantly less than 238 mph used in the video as a typical airplane speed.

Air movement is a rounding error in this test.

Suppose the curvature of the wing's airflow could in fact push the drone 15cm up or down in the time it takes the wing to advance 30cm forward (a tiny fraction of a second). That would require such a high G load exerted on the drone, it would disintegrate even if it didn't hit the airplane.

But of course, the air density and curvature is not nearly enough to affect a drone so dramatically. Mooney M20's wing generates only about 15 pounds of lift (down force) per square foot of the wing at cruise speed.

If instead of the drone we had a feather (small low density item) and the speed was 5 knots then yes, that might have worked.

Keep mind water is much more dense than air. Also air is easily compressed compared to liquids.

So the higher density of water means it can transfer more inertia onto objects. Moreover, it has higher drag than air.

A year ago I saw someone flying a drone from the top of the Shard building in London. The person was promptly told to land his drone immediately by the security. However the scary thing for me is that the smaller business planes and commercial plane that fly into London city go really close to the Shard on their approach.

So definitely a collision is now a real risk

Interesting experiment. Looks like a lot of fun to use that air cannon to blast things at things.

That aircraft doesn't have any de-icing equipment so it is basically just sheet metal where it hit. I'd be curious to see what would happen if it ran into a wing with than just a thin skin.

I don't know that much about air dynamics. How likely is it that a drone would strike exactly on the leading edge of a wing, as opposed to passing just over or just under the wing?

Also (along the lines of air dynamics) I am wondering about whether an airplane has a force in the direction it is traveling in and if that force does push anything small out of the way.

As a small example if I have a pot in my hand and I move it in the direction of a tissue the tissue will move. So we have a very large airplane wing moving in the direction of a much smaller drone and the test does not simulate that at all.

Two things:

1. Airplane wings are designed not to "push" forward on the air in front of them. That's drag and airplanes are designed to minimize it.

2. What little air is pushed forward is only going to be affected by the oncoming wing a few inches in front of the wing, and at 230 mph closing speed that doesn't provide nearly enough time for the force of the oncoming air to move the drone out of the way.

Thanks. But one question. What is the chance that a drone in the path of an airplane will not be impacted by the force of some other object on, or design of, the plane that is not the wing? For example the engine or the landing gear (small plane) or the fuselage? So we hover a drone in front of a small plane and will the small plane hit the drone? And if a larger jet will the drone remain in place or move out of the way by some force (not the wing).

And remenber that the drone has to exactly strike in a particular way.

As an example (of 'in a particular way') think of a nail on the road. The nail needs to be in exactly the right position to puncture a modern tire. That only happens in a very small amount of cases (or with a screw). Normally if it doesn't randomly happen the nail or screw gets pushed aside and does not puncture the tire. [1]

This is not a statement based on expertise I am just offering another point to consider and am curious.

[1] This I think is what happens with a paper cut sharp edge and precise angle.

At high closing speed, the determiner is whether the drone is in front of some part of the plane as the plane approaches. It's not going to be "pushed out of the way" because there just isn't time.

Think about moths hitting the windshield of your car. They weigh thousands of times less than your car, yet they still routinely splat on your windshield as you're going down the highway. Why? Why doesn't the air flowing around your car push them out of the way?

If the drone somehow misses the wing, no problem. But the question was: what happens if it doesn't miss?

Safety engineering is about what will happen when that thing that's pretty improbable absolutely happens or at a minimum, trying to plan for things that no one really planned for (like low delta-V deer mentioned above).

I'm honestly surprised we haven't seen anyone try to take down a plane by flying a drone into an engine on takeoff.

It turns out, the risk of terrorist attacks are much lower than some agencies want us to believe.

I was discussing this with someone a few weeks ago, and swarms of drones (flying in formation) are a concern, and the only thing really stopping it is that no one has tried (as neuralRiot says).

Unfortunately, I don't really know how you would prevent it.

I’m sure it could be done, but I’m also willing to bet there are even easier ways to threaten airplanes that don’t involve relatively new consumer products.

We need to set about reinforcing the leading edges of airplane surfaces. :-)

I wonder how easy it would be to make drones have a stronger radar signal? It's probably not nice to clutter up the displays of ATC, but it would be I think a more direct solution for controlled airspace

It's fairly straight forward to implement this. Some modern USAF missiles are built to mimic various planes' radar signatures to suss out any ground-to-air missile defenses before actual planes move in. [0]

[0] https://foxtrotalpha.jalopnik.com/the-pentagons-flying-decoy...

Radar reflectors are common on certain aircraft or even boats:

https://www.gaelforcemarine.co.uk/en/GB/Trem-IOR-Radar-Refle...

They used to equip some stealth aircraft during training with them so they could be more easily tracked.

Stealth aircraft deploy them whenever they’re operating in civilian airspace so they can integrate into the existing radar-based ATC infrastructure.

They’re called Luneburg Lenses: https://en.m.wikipedia.org/wiki/Luneburg_lens

This type of incident seems unlikely to happen by accident.

Against a commercial airliner you'd pretty much have to be flying right near the runway of the airport, but for a GA Cessna those can be flying pretty much anywhere.

I can easily see how a small plane could accidentally hit a drone.

yeah and on 9/11 they had to fly right near the twin towers.

That's a good point - you don't even have to kill anyone to effect a pretty significant scare. How much would it cost to buy enough drones to shut down an airport by having them hover in front of the runways? And how quickly could they be taken down?

Unless the drones have onboard AI, all you'd need is to jam the signal.

It can't be that hard to shut down drone frequencies seeing as how they have gear to shut down cell phones (to prevent them being used to set off IEDs).

In my particular movie theater plot, I'm assuming they've been loaded with firmware to just keep station at a particular location in space.

Plus, how long would it take to get signal jamming equipment to the runway? Can it be used safely around an airport? Etc, etc. Novel-research stuff.

They'll run out of battery before someone gets equipment in place to jam the signal.

As the technology stands right now, the "fun" will be limited with the battery life.

If you had reasonable battery life, and on-board independent flight capabilities, then you can probably play tag with the staff all day all night.

Shotguns. 12 gauge, shooting at a stationary target. Easy.

If you're talking about the Cessna planes I think you're talking about, this test doesn't apply because those don't travel at 238 mph. Actually I think that speed is typically subject to altitude requirements that would exclude most drones?

But also we're talking about tiny objects traveling through a giant 3-D space. If they meet, it was on purpose.

4D. Space + time. The odds of a collision are astronomically low outside of an airport's restricted zone. There are 1.5 billion cubic miles of atmosphere between the Earth and the maximum altitude of a commercial jet (7.8 miles).

In 4D the drone is not "travelling through", it's instead a static and enormously long curve that has to avoid touching any other aircraft curve at any point.

It would even be really difficult to do on purpose.

If you use more then one drone, you create something similar to a mine field, you don't have to hit the tip of the wing, a hit in the engine or cockpit can also cause damage.

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