Thanks, not sure why mine wouldn't work...

So at first the coaxial design did not work.

I removed the "spike" at the end of the barrel-seal, and it improved.

I further refined the barrel-seal with gasket material, rather than a machined rubber stopper, and it began producing vortex rings just as well as the "T-Valve" cannon did.

However ...

Especially in the case of a "spring-piston" pellet gun, and other such devices (such as a light-gas gun), you also need to account for the rapid heating (a factor which greatly impacts the speed of sound) due to compression of the propellant gas (air) which occurs during firing.

The speed of sound is a very relative thing, and varies greatly depending on the gas you are using, the heat and pressure of that gas, etc.

It holds that a projectile cannot be propelled faster than the speed of sound in the propellant gas.

The "weird physics" that accounts for an air-powered gun ...

That looks like the design I was thinking about!

I shot the new coax cannon this morning, I'm fairly sure the spike is too large a constriction.

Going to remove it at first, then maybe try a smaller one.

I know, I may change the design to a more "aerospike" like design.

SO.

Where I left off, I belive I was complaining about the shape of my cannon, the speed of the valve, and the size of the air tank.

And I've decided to upgrade to a 4" coaxial piston valve cannon design.

This will give a more uniform flow into the barrel from all directions, provide the smaller ...

I would, in hindsight, have used a coaxial tank of a smaller volume...

I have, in hindsight, actually just built this!

Post comming soon.

Feel free!

My intention was simply to share what I've learned, as I had such a difficult time finding any projects like this, there must be others out there having the same trouble.

Lets fill this thread with experimental results!

I've actually been looking at those ARL papers for a while.

However, they are diffusing high-mach flow with their rig, I'm fairly certain my cannon doesn't create supersonic flow yet .

The military did try this :)

The project was canceled after a year, because there was just not enough progress to justify spending more on what was already a kindof silly project.

The problem is twofold:

The army was trying to dispense powdered agents with the gun they designed.

These powders ...

In an ideal gas, the speed of sound would depend on the gas, and temperature.

However, air is not an ideal gas.

The increase in density at high pressures leads to increasingly prominent deviations from its behavior as an ideal gas.

At ~3000 PSI, such as in some of the PCP guns, this effect could ...

The speed of a projectile is limited to the speed of sound in the propellant gas. In an air cannon, this would be at or around the speed of sound.

In a combustion gun this can be significantly higher than the speed of sound, depending on the temperature of the combusted gasses (the speed of sound ...

Video of the more sucessfull tests at 100 PSI with the shorter tank:

[youtube][/youtube]

I see exactly what you mean, almost like those conical "aerospike" rocket nozzles that have cropped up in recent years.

That may be on the list, but for now with the smaller tank volume, its making great, accurate, and repeatable vortecies at 100-110 PSI.

Counting frames, and with a 65 foot shot ...