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Vortex Cannon

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18 pointsctingom20 comments

... and then the third little big actually put some mortar between his bricks...

So, he's firing vortex rings at 200mph from an acetylene powered cannon, and you complain that he didn't use mortar on the construction to demonstrate the impact?

Interesting ...

he's firing vortex rings at 200mph from an acetylene powered cannon

Which, while sounding impressive, apparently is only powerful enough to knock down things that are equally vulnerable to being bumped into by a toddler.

Perhaps it's just that the reaction of the host in that video seems a bit out of proportion to the actual accomplishment?

Thank you - I've learned something. I honestly hadn't believed that someone in HN could fail to appreciate what's really going on here, but you've convinced me that some people just don't find it impressive. Having built air-bazookas of various sizes as an exercise in hands-on science at kids' roadshows and exhibits, they (the kids) are always impressed by the targeting, impact, effect, and sheer unexpectedness of the vortex effect. Maybe I've become overly infused with enthusiasm for these sorts of things by the naive excitement that children get from this sort of thing. Maybe it's just so much better doing yourself for real, rather than just watching it on a video. I know a lot of experiments and demonstrations that are truly impressive and awe-inspiring in real-life, but cause very little reaction when viewed on video. The video experience immediately removes you from the personal experience.

To better help me understand your mindset I looked at your profile. There wasn't any information about you, just the two links. I was interested to see that the first was about a web monitoring service, and even more interested to see the result of visiting the second:

  There has been an error processing your request.
  SQLSTATE[28000] [1045] Access denied for user 'root'@'localhost'
    (using password: YES)
  Trace:

   ... <snip> ...

I would've sent that to you personally rather than posting it here, but, as I say, your profile has no contact details. Just thought you'd like to know.

The air canon itself is very interesting, and I don't fail to appreciate it. I'd very much enjoy seeing a video or reading in-depth about how one is designed and constructed, or about real-world uses for such a technology.

I do fail to appreciate a video that is entirely focussed on using one to knock things down, when said things are obviously constructed to be as weak and fragile as possible. Thus, the reaction of the presenter seems to me somewhat contrived and incongruous. It appears on the face to be typical over-the-top T.V. production and I, personally, don't find it particularly impressive.

Since you are obviously involved in this stuff, do you have any links to some material that talks about the technology itself? That I would appreciate.

Let me start by apologising. My comments were snarky and I shouldn't've said what I did. It's now too late to edit them, but perhaps it's better to let them stand anyway.

With regards links, no, I don't have any links to pages explaining the technology. The best I have is this one:

http://www.eskimo.com/~billb/amateur/vortgen.html

There's a lot of stuff scattered around, but I've never found a single, coherent treatment.

The reason smoke/air/fluid rings happen, in short, is this. Throw a lump of air forward. The air in front of it gets pushed outwards to let the lump through. As the displaced air streams around the outside, it drags on the lump, causing the front face of the lump to follow the displaced air. That makes the front flow around the outside, and then the back comes forward through the middle to replace the air at the front, and hence you get a toroidal circulation.

(in truth it's more complex, but that's the basic idea)

Here's an animation that shows the idea.

http://www.amasci.com/wing/smring.html

That site has much that's poorly expressed, so don't take it all too seriously.

Making air/fluid rings is pretty easy, just throw a lump at a sensible speed. They turn up everywhere, but there are some surprises. Send a smaller, faster ring after a larger, slower one. The faster one catches up and goes through the larger one. The larger one even gets bigger to let it through, then shinks, catches up and goes through the other. You can get "leap-frogging" smoke rings, which is cool.

http://serve.me.nus.edu.sg/limtt/video/leapfrog.mpeg

All the basic fluid-dynamic ideas are Newtonian in principle and you can treat air as incompressible, near frictionless marbles flowing around.

Until you can't.

ADDED IN EDIT:

Collisions between smoke rings are interesting, both head-on and oblique. Most of the time you get a spray of smaller rings, each made half from one, half from the other. Or so I'm told - I'm still hoping to get the opportunity to explore that situation sometime.

HA! Found video:

http://serve.me.nus.edu.sg/limtt/video/collision.mpeg

http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_fron...

http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_top....

http://serve.me.nus.edu.sg/limtt/#Video_Gallery

Finally, bit puzzled as to why this comment is getting down-modded at the moment since I'm trying to contribute interesting stuff. My guess it's the same person who down-modded the grandparent to this comment, and wants to punish it further. <shrug> I'll live with that - it was more snarky than I intended, and inappropriate for HN. We all make mistakes.

Since I made the original objectionable comment I would just like to say that shpxnvz explained my annoyance very well. The issue is not the technology, it is the way they chose to demonstrate it by riffing off the three little pigs but then cheating the demo to fit their narrative.

I personally detest this kind of "whizz bang gloss over the details" style of science show. I am one of those sad and pathetic individuals who think science and technology are intrinisically exciting without needing to resort to cheap tricks. I also hate being told how to feel - the dude is the science show equivalent of a laugh track and really grated on me.

There is an argument that one has to resort to this kind of presentation in order to engage kids. I find this patronizing and it does not match my own limited experience talking at schools, but I concede I could be wrong.

If I remember the (full) episode correctly, the presenter went into a good level of detail about the working of the cannon, showing a prototype in the lab and explaining what was happening. What is on YouTube is just the conclusion of the experiment. This is clearly a marketing clip; Bang Goes the Theory is a pretty good attempt at a science show, and indeed is an Open University show.

Thanks for the apology, and the links that you did have. Those were much more interesting videos, I thought. And it would particularly cool to see a vortex blimp in action.

Oh, for the record, you got an up-vote from me.

http://en.wikipedia.org/wiki/Three_Little_Pigs

s/big/pig/ ?

Is there a technical term to describe typos that form legitimate words and therefore don't get flagged by a spelling checker?

Type II error? ß-error?

Maybe a "typo II error"? :-)

I don't think there is. I suggest: typhous

tyro ?

Misspelling.

It's some way off from being a weapon, I think. The bricks didn't so much blow off as they fell off (from being blown off balance). Ok, I did not say that very clearly. Still, awesome experiment.

I want one. Much like a Bugatti Veyron, I have no idea when I would have the opportunity to really use it or where I would safely store it but I want one nevertheless.

I think it is to big to mount it on a Bugatti Veyron, but it would be nice (would the resulting Vortex Ring be faster by the speed of the car, or would the car drive into the ring, if it is fast enough?).

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