RING-VORTEX (smoke ring)
1997 W. Beaty

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Many years ago WHAM-O sold a plastic air-puff gun. The puffs of air could fly across a room and knock over cardboard targets.

It turns out that this gun used ring-vortices, or "invisible smoke rings" as its ammunition. Also turns out that smoke-ring guns are extremely easy to make. Take a soup can, cut out the top and bottom, tape a piece of cardboard over one end, and cut a 1" hole in the center of the cardboard. Tape a disk of thin card stock or heavy paper over the other end (or better yet, snip a balloon in half and stretch it across the other end.)

When you gently whack the covered end of your vortex launcher, a transparent ring of spinning air will shoot out of the hole. Aim the device at your face or arm, and you'll feel the puff of air when it hits your skin.

             /                         /\
            |                         |  |
           |    SOUP CAN             |    |
           |                         |    |
          |                         |      |
          |                         |  __  |
RUBBER    |                         | (  ) |
SHEET __\ |                         | (__) |      
        / |                         |      | /__ WITH
          |                         |      | \   HOLE
           |                         |    |
           |                         |    |
            |                         |  |
The vortex rings can be made visible with a bit of smoke. I use stick incense, and just shove the end of the stick into the hole for awhile (don't set the cardboard on fire!!)

Tap the bottom gently, and slowly spinning smoke rings will be launched. Tap it hard, and the smoke rings will zoom so fast that you'll only see a grey blur. Tap it too hard and you generate air turbulence but no smoke rings.

To see the details of the smoke rings it helps to have bright lights and a dark background. Work in a darkened room while placing your device between you and a bright table lamp. The light should shine towards you, through the smoke, but position things so you observe the smoke against a darkened wall. Smoke rings are similar to tornadoes, but the ends of the tornado is curved around so its ends are joined into a circle.

Try shooting slow rings then immediately shoot faster ones. The faster ones will catch up to the slower ones and move through them (the slower ones open wider to allow the fast ones to pass.)

Rather than using smoke, you could instead use scent. Any fumes in the can will end up inside the air in the smoke ring. Try putting perfume in the can. When you launch your ring vortices, they will be invisible. But if you target a distant nose, your victim will know when they've been hit.

Or even easier than building the soup-can launcher, K. Larsen suggests using a 1-gallon polyethelene milk jug. Whack the bottom and a vortex ring is launched from the spout. Aim it at your face and you can feel the rings of air hitting you, even if you don't use smoke.

Fig. 2 Vortex-ring animation

Other similar sites:


The vortex cannon is a cool physics demonstration. How can we convert it into an experiment? Easy. Ask a question, change your question into a statement, then perform an experiment to prove or disprove your statement.

For example, ask this question: how far can a 4-inch vortex cannon send a ring vortex? Change this into: "A 4-inch vortex cannon can project a smoke ring across xx centimeters." Then do the experiment, and find out what xx is. (PLEASE DON'T USE THIS EXAMPLE AS YOUR EXPERIMENT. THAT'S BORING. BE DIFFERENT. THINK UP A WEIRD AND INTERESTING QUESTION, ONE THAT YOU DON'T KNOW THE ANSWER FOR.)


It's not hard to make a giant vortex cannon. Instead of a soup can, get an old plastic garbage can. Cut a six inch circular hole in the center of the bottom. Put the plastic can cover on the can and whack on the cover to launch vortices. Or better, use duct-tape and a plastic garbage bag to form a sort of "drum head" over the open top of the garbage can.
             /                          /\
            |                          |  |
           |  PLASTIC TRASH CAN       |    |
           |                          |    |
          |                          |      |
          |                          |  __  |
 PLASTIC  |                          | (  ) |
  BAG__\  |                          | (__) |    6" HOLE
       /  |                          |      |  /__IN THE
          |                          |      |  \  BOTTOM
           |                          |    |
           |                          |    |
            |                          |  |
             \            ______________\/


Suppose we replace the drumhead with a large bass loudspeaker, hook the speaker to a power amp, and drive the power amp with the output of a soundblaster card? This would give us total control of the impulse waveform applied to the vortex generator. Instead of a garbage can, use a wastebasket for the body of the device, and maybe mount it on a tilt/pan tripod.

I haven't completed one of these devices. I went as far as building the body, then using an audio power amp and a square wave generator to run the device. Even this was pretty cool, since the amplifier level would control the speed of vortex launch, the duty cycle controlled launch speed and spin rate (I think!), and the repetition rate of the square wave generator allowed me to create streams of vortices.

As far as sound cards go, in theory there should be some shapes of pulse waveform which give very robust smoke rings. I would try creating various shapes with a waveform editor, then see how far and fast the resulting smoke ring would travel. It might be possible to vastly extend the maximum range of vortex travel by designing the perfect waveform.

Here are some waveforms to try. The waveform is a single pulse. The steep leading edge of the pulse creates the vortex. The edge of the pulse would last maybe 1/5 second or 1/10 second or so depending on the size of the hole and the loudspeaker. Also you'll want to try pulses of different shapes. The loudspeaker cone should move forward quickly, then suddenly stop, then slowly return to its original position. The signal pulse would look like this:

      /    ----____
     /             ----____
    /                      ----____
___/                               ----____

The steep part of the pulse should last about 1/10 second, and the slow part afterwards should last maybe 1/2 second. Feed this signal to an amplifier and a loudspeaker (turn the volume way down at the start, just in case the pulse is so big that it might damage the loudspeaker.)

To create smoke rings which fly fast, change the start of the pulse so it looks like this:

       |    ----____
       |            ----____
     _/                     ----____
___--                               ----_____

It starts rising gradually, then rises very fast, then it stops at the peak. That should make the core of the smoke ring spin slowly, while the outer regions spin fast, and the whole smoke ring will travel quickly forwards. (The outer region of the smoke ring touches the outside air, so if the outer region is rotating fast, it will drive the smoke ring forward at high speed. )

To make smoke rings where the core spins fast, change the pulse so it looks like this:

      _--   ----____
     /              ----____
    |                       ----____
____|                                ----_____
It starts off very fast, then rises more slowly to the peak. That makes the core of the smoke ring spin fast, but the outer regions move more slowly, so the whole smoke ring drifts along slowly.

Also, fast-spinning vortices can act as "time bombs", they drift along for awhile and then suddenly shatter into turbulent smoke. Perhaps a particular waveform will make this effect programmable. The resulting smoke rings would move for a particular distance, then shatter into a smoke cloud. A stream of these rings would fly out and shatter, which would allow me to pump smoke out to a distant cloud which just sits there in the air. Suggested experiments w/ programmable vortex generator


While discussing a friend's small prop-driven helium blimp, I had an interesting insight:

Could we build a blimp which flew like a ring-vortex does?

Suppose we made a big stack of disk-shaped helium balloons and threaded them onto a big thin steel rod, then bent the rod to form a ring. It would look like a sliced donut. When this "donut" of balloons was forcibly flung broadside through the air, all of the helium balloons would rotate, and the air friction would be very low, just like a ring vortex. If such a device could be motorized, so that the disk-balloons would be forced to rotate on axis, then the whole affair would travel forwards. (And if selected sectors of the balloon-stack were run backwards, then the entire device would turn, sort of like steering an army tank.)

Rather than a circular stack of disks, perhaps it could take the form of several large football-shaped blimps, where the tips of the blimps are connected together. Six blimps? Or even four or two. Like this:

            /        \ 
           /          \
           \          /
       / \  \________/  / \
     /     \          /     \     "SQUARE DONUT" 
    |       |        |       |   AIRCRAFT MADE FROM
    |       |        |       |     ROTATING BLIMPS
    |       |        |       |
    |       |        |       |
     \     / _______  \     /
       \ /  /        \  \ /
           /          \
           \          /

The above "square smoke-ring" craft could go tearing horizontally across the sky like some sort of big silver water-weenie! If the blimps were rigid, turbulence wouldn't tear them apart. To steer, spin one of the blimp-motors a bit faster than the others.

Heyyyyyyy! Maybe they wouldn't need helium! If the "smoke ring" was oriented horizontally like a donut on the ground, and if the gasbags were spinning, maybe it would act like a helicopter and drive itself upwards. It would be VERY quiet since the air flow would be almost laminar. It would look like a flying saucer. With the large surface area it would need, it may as well have some helium fill for a bit of extra lift. But with enough power, maybe helium wouldn't be necessary for flight.

How would it behave? If it was hovering, and if the blimp-motors were suddenly cranked up fast, it would eject a "starting vortex" and be strongly accelerated. Being neutrally bouyant, it would only experience parasitic drag and not "induced drag," and because the surfaces are rotating WITH the air and perhaps maintaining laminar-flow conditions, the parasitic drag would be minimal too. The craft would coast along like a big flywheel, just as smoke-rings do. If the spinning of the blimps was suddenly halted (use electromagnetic braking and recover their energy!), maybe it would create another starting-vortex in the air, and would stop on a dime? Maybe not.

Hmmmm. EM braking. What if the whole thing was powered by electric motors, so that the kinetic energy of the spinning blimps could be quickly removed and stored in big internal capacitors? This might give a high-G acceleration capability.

The whole idea is SO STUPID!! Just think of a 50ft silver donut hovering erect above the airforce runway. Turn the balloons one way and it moves forwards. Turn them a different way, and the whole thing rotates. Everyone laughs really hard. But then the pilot kicks in the ultracapacitors... and the whole aircraft blinks out of sight. Huh? It accelerates at 30G and unexpectedly goes tearing across the sky, but because it is a laminar-flow propulsion system, it is SILENT. Just don't aim the "exhaust" side of the blimp at a building when you punch the accelerator, because it launches a huge "starting vortex" which has enough overpressure to do some serious damage.

Imagine getting into a military dogfight with such a beast. It might not need weapons. During sudden accelerations it would launch "clear air turbulences" which would have enough wind-shear to shread conventional craft into confettii. It would be like battling a UFO that's equipped with a titanic "Wham-O" air-puff gun!

Hmmm. Can smoke rings move faster than the speed of sound?


In messing with the square-wave generator mentioned above, it looks like the "stink gun" is feasible. The vortex launcher emitted a beam of fast smoke rings which went all the way across the room. Lots of smoke drifted out of the generator though, so if I were to put a nasty odor in the device, the operator (me) would suffer as much as the distant victims.

If the vortex launcher emits a stream of vortices, does this drive the launcher backwards? Is there a reaction force? If so, then hang the whole device from a helium blimp and use it to drive the blimp forward. A loudspeaker inside a bucket is a very strange aircraft engine! It's the Feynman Sprinkler problem, AC version instead of DC. Or use it underwater. A ship with no propellor, just a big piston, and the intake and outlet orifices are the same. Maybe even get rid of the piston and instead use a large bubble. Expand and contract the bubble using a steam boiler? What if this technology had been invented long before "ships' screws?" Today we live in an age of propellors where the Wham-O air blaster is just a toy, but things could just as well have been the opposite!

Suppose the computer-based launcher created a string of smoke rings with varying speeds. If the string was made of fast-slow-fast-slow rings, then pairs of rings would pass through each other periodically, as if they were square dancing. Or, what if you shot a string of slow-fast-faster-faster rings? In this case the later rings would overtake the first, and the whole string might squash down to the length of a single ring. The string of smoke rings would momentarily become a disk of concentric smoke rings! If the vortex generator was fairly powerful, maybe this "vortex disk" would be able to knock over larger objects. The vortex generator sends out energy in a long stream of rings, but then the varying speeds make it concentrate into a brief burst. Remember, a stick of dynamite will burn for hours as fuel, or it will "burn" all at once in a fraction of a second.

Pure argon gas allows you to create very long electric sparks. When a stream of argon is sprayed at a tesla coil, long sparks jump up through the stream. So, what would happen if a string of pure argon smoke-rings was sent towards a very large tesla coil? Would the arcs jump from ring to ring, so the "lightning" would reach out and strike the smoke ring generator? What would happen if a battery-powered smoke ring device (and an argon tank) was installed inside the oblate terminal of a really large tesla coil? Hobbyists' directed energy weapon?

A VandeGraaff electrostatic generator with a wire connected to its sphere is a source of charged air. Electrified air flows out from the wire tip. If a VDG was used to supply electrified air to a vortex launcher, the result would be a "static electricity gun". Victims would suddenly feel 'lethal' levels of clothes-dryer cling, and they'd get zapped by anyone they might bump against. If the string of charged vortices was sent to a pop-bottle electrostatic motor, the motor should spin without needing any wire connections. Can you say "perpetual motion hoax?" And if the vortex generator was supplied with pure argon, maybe you'd see a blue flash whenever a charged argon smoke ring touched a grounded object or person. (Note: the body of the vortex launcher might need to be metal, or at least cover the interior with grounded aluminum foil.)

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