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I stumbled across this video by the University of Dayton, showcasing the amount of damage a certain type of drone can do to a wing, and they wrote a whole article about it. While most of said article sounds like marketing for their research institute with very little actual information about the video they just released, the key thing to take away seems to be that:

researchers in UDRI’s Impact Physics group launched a 2.1-pound DJI Phantom 2 quadcopter at the wing of a Mooney M20 aircraft. The drone did not shatter on impact, but tore open the leading edge of the wing as it bore into the structure, damaging its main spar.

[...]

The researchers then fired a similarly weighted gel “bird” into a different part of the wing to compare results. “The bird did more apparent damage to the leading edge of the wing, but the Phantom penetrated deeper into the wing and damaged the main spar, which the bird did not do.”

If we trust that the researchers accounted for the fact that a damaged wing's structure is obviously compromised in places and that they also accounted for bones making an actual bird slightly more rigid than pure gel, as well as repeating the experiments often enough to make above statement with a reasonable degree of confidence -- none of which the article mentions explicitly -- then what conclusions can we draw from this?

It looks dramatic. Sounds dramatic, too, if you know nothing about aviation at all, which I guess was the intention when they wrote the article.

But how significant is the damage really?

The article doesn't say.

One YouTube comment by one "Stephen Mann", appearing to claim piloting experience states:

You can throw, at 200 MPH, anything weighing 2 pounds at a sheet of 2024-O .04" aluminum, typical of aircraft wings, and get this damage. I've seen worse hail damage.

and notes that:

the Mooney wing uses a thinner aluminum (0.038") than an airliner (0.04 to 0.05"). This made the Mooney lighter and faster, which was a marketing design.

I've had more than a few bird strikes during landing (none during takeoff that I was aware of). Some were Canadian geese that weigh 10-15 pounds. There was never any damage to the aircraft beyond cleaning up the bird guts from the wing.

while generally playing down the significance of the test:

Typically, no aircraft below 400 ft., where most drones operate, will be flying that fast. On final approach most airliners are flying between 130 to 160 knots, and by the time a landing aircraft is below 500 ft. the flaps and slats are deployed and the A/C is probably going 120 knots. General aviation aircraft, like the Mooney in this video, are typically flying between 70-110 knots on final approach. Even slower on takeoff.

I'm reluctant to accept information from YouTube comments at face value -- especially since it may be biased. But if true, this may just reduce the usefulness of the test significantly. And although I guess that's quite possible, I'd like to think they put some thoughts into these experiments before conducting them.

So where does that leave us?

Can "a drone" bring down "a plane" by crashing into it? Most likely, if we're talking about these big US military type drones like the RQ-4.

But can a "hobby drone" (for lack of a better word) like the one shown in the video by the University of Dayton seriously threaten the fly-ability of "the average plane" (if such a thing exists)?

Or let's say we start at the Mooney and scale the damage up for larger planes. Would a plane with that kind of damage get into trouble whatsoever or would it just require a probably costly repair?

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    $\begingroup$ What happens if the hobby drone hits a windshield at 70 mph? $\endgroup$ – Dan Pichelman Oct 10 '18 at 22:03
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    $\begingroup$ The drone opened the wing up in exactly the location where Pipers and Beech products store fuel (anywhere from 20-40gal on a single). The combination of air, fuel, and spark from either the drone's electronics or broken wires in the plane itself could start a fire or create an explosion. In practice, the pilot will likely attempt an evasive maneuver upping the stresses on the skin and structure. The pressure change in the wing and added stress from maneuvering could pop lines of rivets that cause a structural failure. Just spit-balling, but both of these seem realistic to me. $\endgroup$ – acpilot Oct 10 '18 at 22:40
  • $\begingroup$ Wow, the drone just disappeared right into the wing. That could interfere with aileron cables, flap cables, perhaps even the wet wings (sealed rib/skin areas on Mooneys and Cardinals) and who know what to wiring that goes out to the wingtip strobe lights, navigation lights, wing mounted landing lights, and electric flap motor wiring. And if the drone batteries got damaged, who knows what the results could be. $\endgroup$ – CrossRoads Oct 11 '18 at 1:43
  • $\begingroup$ This is what it looks like when a bird hits the window, that guy was lucky the bird didn't hit him in the face, a drone however would have turned into shrapnel... $\endgroup$ – Ron Beyer Oct 11 '18 at 2:09
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Mr Mann doesn't have a clue what he's talking about.

Wings aren't made from 2024-O aluminum, which is fully annealed and very soft. The usual heat treat state is T3 through T6.

A Mooney would NOT have .040" wing skins. The skins will be .016, .020, .025 and maybe .032 in high stress areas around the wing roots. Leading edges would be .025 or maybe .032 inboard, and likely .020 or .016 near the tips and on the control surfaces. Skin sizes are for structural efficiency and rigidity for minimum weight, not "marketing"... geez.

His approach speed comments are more or less correct, but a Canada Goose will do significant damage to any aircraft it hits in flight and has a good chance of bringing down a Mooney at any contact point. A Mooney running into a goose at the wing will, at minimum, completely crunch the leading edge in back to the main spar. A goose will do significant damage to the slat or leading edge of any airliner. There was a CRJ900 that hit a goose size bird just below the windshield on the takeoff roll near V1, and it came back into the pilot's instrument panel, distributing guts and feathers all over the place.

Geese are bad news and are a vexing problem in the spring in central North America. The terrain is all browns and if you are descending with a flock below and in front they are nearly invisible until you are passing through their level.

A goose hitting the windshield in front of the pilot or horizontal tail of a Mooney or similar light aircraft will probably bring it down. On the wing, maybe.

A 2lb drone will do obvious damage as the test showed but would not bring down a Mooney unless it hit the windshield, incapacitating the pilot. It would certainly go though a windshield. 1/8" plexiglass has roughly the same tensile strength as .020" 2024T3. You wouldn't want to hit anything heavier than a few ounces with 1/8" of acrylic in front of your face as the only barrier.

So from that standpoint, drones of any size can be considered a hazard to aircraft.

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  • $\begingroup$ According to wildlife.faa.gov/databaseSearch.aspx bird strikes in NY and NJ in March 2018 caused minor damage to one aircraft and no damage to ten others. Perhaps the risk is not as high as you are suggesting. $\endgroup$ – Paul Smith Oct 11 '18 at 11:05
  • $\begingroup$ @ Paul Smith the vast majority of bird strikes are small birds hitting leading edges and going through engines of transport aircraft. They do little damage. If you were paying attention, most of the strikes are small birds and a couple of ducks hitting transport/corporate airplanes. I was talking about geese in the case of airliners, and on light aircraft, just about anything bigger than a chickadee hitting the windshield in front of your face will become unpleasant. That being said, bird strikes on light aircraft are quite rare, mainly because birds make an effort to get out of the way. $\endgroup$ – John K Oct 11 '18 at 13:37
  • $\begingroup$ I certainly thought I had paid attention when I gave a verifiable reference for all bird strikes, small and large. What makes you think otherwise? $\endgroup$ – Paul Smith Oct 11 '18 at 13:53
  • $\begingroup$ It's the size of the birds. When I look it up I see robin, robin, robin, gull, gull, kestrel, yadda yadda yadda. Couple of ducks. No geese. A robin hitting an airliner leading edge is like a large bug to a light aircraft. As I mentioned, birds generally get out of the way of slow moving GA aircraft and strikes are quite rare. Drones don't get out of the way and are a bigger potential hazard to light aircraft in my opinion. A 2lb drone coming through the windshield of a C-152 will ruin someone's day. $\endgroup$ – John K Oct 11 '18 at 14:48
  • $\begingroup$ What is your fascination with geese? Of the 13 reported bird strikes in NJ in March 2018, none were geese. 7 were birds that are typically over 2lbs (the size of the drone in question) and the damage reported by these strikes was none. Zero, zilch, nada. Is there a risk, yes. Is it significant? On the evidence, no. $\endgroup$ – Paul Smith Oct 11 '18 at 15:16
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Like anything in aviation it depends.

A drone could easily severely damage any fabric covered wing this is everything from ultralights up through piper cubs and lots of high powered back country fliers. Losing your wing covering can be a big issue at speed but weather or not the damage brings the plane down depends on where and how it hits as well as the pilots response to the incident.

Metal covered wings are a bit of a different story and it really depends on the airframe. In some cases you can shear a whole wing off and be fine or even lose a huge chunk of your fuselage while with others airframes small damage can cause serious handling issues and potentially lead to an incident. Spoiled airflow would be the ultimate issue with leading edge damage like that from the video but this does not mean a crash necessarily. There are even instances where deliberately spoiling the airflow is called for.

If you watch the video closely you can also see that the drone impacts directly next to a wing rib which is a weaker area than if the drone impacted a rib its self. I would be curious to see a test impact on a rib collision as well.

Ultimately it may be more of an issue of where then if (similar to this question). As noted in the comments by various people you run the risk of puncturing a fuel tank, damaging or otherwise jamming control cables, and even damaging the spar all conditions that can potentially led to an accident but its highly situationally dependent.

Its also worth noting that GA planes generally have fairly week leading edges (as you can see in the video). Larger transport aircraft may have things like leading edge slats or de-ice systems that make the wing leading edge a bit stronger by design.

Just to nit-pick the semantics a bit, they list the fact they used a Mooney M20 aircraft, strictly speaking the M20 spans from the wood wing A variant all the way up through the current TN/S variant the wings vary heavily in design even within that family of aircraft. They are clearly using a metal wing, likely off a newer airframe but you can see how even that could change the outcome of the collision.

or would it just require a probably costly repair?

All aviation repairs are costly...

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