Tuesday, August 20, 2024

Drone defense

Some of the video from Ukraine suggests that drones are getting to be quite effective weapons. If they were quieter, I suspect the criminal cartels would be using them for assassinations already--loiter and attack the witness/judge/competitor.

Some of the videos show them capable of entering shelters through windows or passages. And, of course, they're good at watching for things, whether they have offensive capacity or not.

OK, how do you stop them? You're with your buddies in a truck and hear/spot something headed your way. Shooting won't do much unless you're super-super-accurate. Net guns... they look nice, but I wonder how practical those are in the field. Hide behind trees...

Pros and amateurs try their hands at downing drones in this video (which has a very annoying long commercial in the middle). Some of the methods are more amusing than useful.

One of the methods tried is the vortex ring cannon, which can pack more of a punch than you might expect. For sufficiently large vortex cannons, of course. Of course, you could also try using guns adapted (with blanks) for the purpose. The article cited talks about "knock-down effect" on humans (mediocre), but it might be suitable for trying to knock down lighter flying objects.

Copter-type drones are somewhat at risk for vortex ring state, where instead of pushing the air down the propellers push air down and around and up and back through the blades again, in a "circle" that doesn't provide lift. The article explains how designers have been mitigating this. However, if a strong vortex ring hits a quadcopter, it should provide some impact, some twisting, and maybe cause one or more of the propellers to get into VortexRingState.

If the equipment is just an adapter on the end of your rifle (and maybe blank rounds, maybe not), it might be easy to carry, cheap(*), and relatively quick to field. The vortex ring is a lot bigger than a rifle bullet, so your chances of hitting are better.

There are obvious possible issues--would it destabilize the drone enough with an average hit? would the ring move fast enough to reliably hit a moving target (80 m/sec??? with my sloppy estimates for vorticity)? and can soldiers/civilians aim well enough, especially at night? Oh, and is the effective range good enough?


(*) "Cheap" would probably be the kiss of death, unfortunately.

UPDATE: I found an Army report. The Wikipedia image of the vortex ring was out of a 40mm barrel, and they developed 100kpsi in their chamber, using a "rupture disk" to get the cleanest possible flow. They did not design the test system for rapid fire. So this probably wouldn't be a snap-on, but a separate (hopefully light) blunderbuss. They found that C4 wasn't great--the ring momentum was low--so they converged on "exotic" explosives like Red Dot and Bulls Eye (up to 30g). They were getting about 160'/sec.

Their aim, so to speak, was attacking humans, who are typically less fragile than drones in flight. The idea might work. I assume that with lower pressures the final velocity would be proportionately lower, but fluid dynamics is messy.

5 comments:

Thomas Doubting said...

The vortex cannon is interesting. Jamming is possible. I also think light might be useful. Most of these are FPV, so there's an operator out there using the drone's camera to fly it. Temporarily blinding or disorienting the operator could give you time.

If you have the means, it's possible to track the beam back to the operator and counter-attack or send a team to capture him. However, that means there's someone on your side monitoring for drones and so I can't imagine this would be useful for individuals unless the target knew in advance a drone attack was likely and also had the ability to prepare for it.

Grim said...

The best method is a kill vehicle, somewhat like the Iron Dome for drones but with other drones instead of other missiles. The upside is that the kill vehicle can be survivable.

Vortex cannons are good versions of C-RAM gunnery.

Israel is having a lot of trouble countering drones, but Ukraine is getting about 2/3rds of them. All the best lessons about how to do this drone stuff are coming out of the Ukraine war right now.

Thomas Doubting said...

Wouldn't the best means of defense depend on the situation? The methods for the Israelis to defend Israel against drone attacks are probably different from the judge worried about a cartel hitman using a drone. For that matter, the infantryman in a combat zone probably can't marshal an Iron Dome type defense for his squad. That said, maybe a backpack radar and 6-pack of mini killer drones are the answer in the individual's case as well.

Douglas2 said...

Hezbollah's drones to Israel use GPS -- once addressed and sent they are autonomous and not emitting any RF Energy. For these drones, I'd think that detection is the biggest issue, they are small, largely plastic and flying close to the terrain, so the radar reflection is tiny and often not in the field-of-detection.

For FPV drones such as in Ukraine, it has puzzled me that they're not more amenable to electronic detection, as by definition they are emitting to send the video data back to the pilot. In most locales you're not likely to have any other unknown sources of such RF above the horizon.

Grim said...

It's also possible to generate quasi-EMPs using directed high powered microwaves. The US is testing a device called Leonidas at CENTCOM; it's in prototype. The Chinese already have one in production.