Thinking about building a vortex cannon
Got interested in vortex cannons recently and I'm going to try and build one.
Unfortunately there's a surprising lack of technical information on the internet about making a gas-fired vortex cannon. Except this [ame="http://www.youtube.com/watch?v=IyAyd4WnvhU"]glue-tube[/ame]
I'm trying to figure out why the original ww2 German vortex cannons were more or less a tear-drop cannon shape with a small aperture, whereas the BBC guy went for a 'blunderbuss' cone-shape arrangement.
Any thoughts?
Last edited by Onefella; 01-09-09 at 12:06 AM. Reason: tidy-up
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If I had to guess I'd suggest you look towards wave propagation, maybe start at wave equation.
The differences in design could be related to stability, accuracy / performance, noise / vibration, turbulence even? I'm not sure, I have absolutely no idea how these things work but I'm currently quite intrigued.
With what little I have managed to find out about toroidal vortex theory, It seems to me that a tuned-length cylinder would be the best at generating a vortex 'pulse' from a pre-combustion chamber. The vortex gets formed as the high-pressure 'ball' leaves the barrel. Why is it necessary for a cone-shaped barrel?
Guesses-> Maybe cone-shaped barrels are more able to assist in transmitting an impulse (vibration) from fluid to fluid e.g brass instrument? Maybe it is related to the decay of the compressed vortex structure? Like I said, I have no idea how these babies work, or the calculations behind building one.
If i was the local building inspector i think i would have condemned those structures as they would have blown over in a moderate wind before the vortex gun was fired
There is a fine line between "Hobby" and "Madness"
That is a fascinating project to dig up OneFella. The concussion effect to humans would be deadly!
Mm. There's quite a few comments along those lines on the original youtube page. But I still think the concept is interesting. The vortex sort of 'pulls' itself along. Obviously it's not THAT powerful, but still worth a couple of experiments.Originally Posted by allover
If i was the local building inspector i think i would have condemned those structures as they would have blown over in a moderate wind before the vortex gun was fired
Not sure about 'deadly' mate. But if the cannon was sending out multiple pulses like the one in the clip, it might be a bit distracting. Maybe it could be a non-lethal crowd control device similar to a water cannon? I should be starting early experiments soon. I'll post back here with my results.
WTF, nice more info needed !
check out ytube. Onefella I've got a "Zon" carbide [acetylene] bird scarer & if you want I can measure the gas jet & air holes to get the mixture right. It looks like his cannon has a short staight section at the mouth may be this is needed to generate the vortex, the bird scarer has got a cone barrel & and I don't reckon it generated vortexs other wise it would have knocked the apricot trees around & could have given some one a wack as well as a sore ear when in front of it. The lpg gas guns use a reverse cone at the muzzle & they aren't as loud as the carbide ones where. The appox dimensions of the scare gun is combustion chamber 120mmx200mm & 45mm hole into a 400mm long barrel that tapers from 75mm to 120mm at the muzzle.
Onefella (03-09-09)
Nice info there blackpete. I did think of bird-scare cannons as a reference.
The vortex is created by a 'ball' of high pressure moving air, coming into contact with lower pressure non-moving air and it quickly forms a doughnut shape that 'rolls' itself along.
The Germans had huge ones in WW2 that were supposed to be able to knock down low-flying aircraft. It turns out they coudn't really do that, but there is a decent amount of propaganda footage that makes the claim. The Germans also used to put charcoal dust in the barrel to make an even bigger flash and send out a burning vortex.
Lightning balls are believed to be an ionised vortex of air that can last up to few minutes. I would eventually like to do some experiments with high voltage charges just as the vortex is formed at the mouth of the cannon, to try and replicate a lightning ball.
You do realise that you can buy one of these in toy shops ?
ok, not the big explosive gas powered cannons, but rather a simple hand held cannon.
You can build one yourself, they've very simple.
I'm thinking small to start with, so you want a container... something like pringles can would work, but I'm thinking of something with a larger diameter.
If you can find a plastic container with a diameter of about 15cm is a good place to start.
Lets say a 20 litre cyclinderical ice cream barrel. The kind you see in ice cream shops like Baskin Robins. The barrel has two ends. The open end and the sealed bottom end. While we could cut out the whole bottom, all we want to do is cut a hole about half the diameter of the barrel itself.
Now ... take a balloon or some other form of rubber to use as a diaphragm on the open end of the barrel. Make sure it's tight, and you're done.
Now you have a votrex cannon !
Point the barrel at a target, pull back on the diaphragm and let it fire.
A blast of air will come out of the hole forming a vortex and even a small one will travel for several metres.
I made a big one out of an old plastic garbage bin many years ago and it could shoot a ring of air across a basket ball court.
To demonstrate it, there isn't enough power in a hand held version to cause an ectoplasmic ring like in the video, so take a few sticks of incense and fill the chamber with smoke. Then fire the cannon and the smoke will be held in the ring as it flies off across the room.
The reason for the funnel shaped tube in the video is that a vortex is actually a kind of wave. A traveling wave of air in this case. The momentum of the air in the vortex is what carries the energy. It's actually a form of sound.
Microwaves and sound waves have very similar wavelengths. You can imagine how well that horn antenna would work for a microwave signal.
He could have even used a dish for the experiment, but energy would have been lost in reflecting such a large mass of air.
As the shock wave travels down the funnel it's focus into a more unidirectional wave, in exactly the same way as a horn antenna works for mircowaves.
I'm not so sure they're using acetylene. If the muzzle velocity is too high, it will not form a laminar wave, it will be turbulent supersonic air and it will literally tear itself apart. The blast MUST be subsonic.
Acetylene burns at supersonic speed, which is why you get a sonic boom from it's combustion. I'd be looking at something slower. Petrol vapour I know will work, but it is probably too slow for good results.
I'm thinking LPG is the gas of choice. I'd certainly try hydrogen, It makes a pop, so it burns fast but I'm not sure how fast. I've used it as an explosive before.
Godzilla (03-09-09)
Kind of like this but spuds not a vortex
[ame=http://www.youtube.com/watch?v=L9Af5cvjCtk]YouTube - Jeremy Clarkson: Inventions That Changed the World - Make a Gun[/ame]
One word of warning a couple of people here in Victoria were having a great time firing spuds into the river when the police turned up and charged them for using and having an unregisterd firearm and not having a firearms license. Not sure how they faired in court but the cops did not see the fun in it.
Last edited by SystemRat; 03-09-09 at 03:37 PM.
Godzilla (03-09-09)
Trash, yep made a couple of little elastic-band-powered ones out of plastic take-away noodle dishes for junior Onefella. They worked surprisingly well with a bit of smoke puffed into them to make killer smoke-rings.
The BBC guy reckons he used oxy-acetelyne, so I'll certainly try that first, as it's nice and easy to get the right mixture by adjusting a cutting tip to a neutral flame then knocking the flame out, and using the unlit gas to charge the combustion chamber.
At this stage I will be using an old 9kg lpg gas bottle as the combustion chamber (don't worry I've cut and welded them before quite safely) and about 1m cut off the top of an old tapered light-pole for the barrel.
Ignition will be a piezo stove lighter hooked to a regular spark plug screwed into a specially tapped hole in the end of the bottle.
The section of steel I'm using for the barrel doesn't flare very much. It starts at 67mm and goes to 85mm at the 'business' end. But it's all I've got in the way of conical strong steel, so it'll have to do for a prototype.
Today's Adelaide Advertiser (newspaper) had an article about a bloke who was in court for posession of a 'spud cannon'....the Judge-dude ruled the 'spud cannon' a toy firearm and therefore not covered by the Firearms Act - the bloke walked, no offence recorded.
Now every kid will want one....watch your eyes, ears, fingers etc. !
And if you are gonna experiment with one of these wrap the chamber in heaps of duct tape. Especially in the colder months PVC can crack and break/blow apart. The tape might bot necessarily stop this but at least it will hold it together.
I take it a spud cannon is similar to a tennis-ball cannon/orange cannon?
I saw a kid cop a freakishly bad ricochet by an orange fired by a drunk tool from an orange cannon a couple of years ago. Lucky the judge didn't see it.
I like to experiment with stuff I probably shouldn't. But I always try to be careful.
on ytube there is one using a subwoofer & another of a bloke being hit by a vortex but it didn't show the gun. With oxy acetylene mix it goes of better if it's a leaner mix than neutral flame.
Mythbusters built a "chicken" cannon that fired frozen and fresh chickens using (I think) LPG as the propellant.
Cant remember why they did it but I do remember they managed to get a fair amount of damage with the frozen one.
They fired it at an old cockpit window to see if it could penetrate the cabin.
i think you will find that they used compressed air to fire the chickens
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