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Mach #'s , Shock Heating, Etc... C'mon You Rocket Scientist

A place to ask general spud cannon related questions.
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Mach #'s , Shock Heating, Etc... C'mon You Rocket Scientist

Unread postAuthor: jeepkahn » Sat Mar 14, 2009 4:23 pm

There's been some discussion here lately about mach numbers, shock heating, and various other phenomena...

How many of you have used or considered using velocity stacks at the chamber/barrel junction??? Has anyone considered a de laval nozzle and how it may pertain to spudguns???

I'm sure D_Hall is quite familiar with these terms and their posibble uses for improving cannon performance...

Velocity stacks or convergent nozzles will increase the speed and temperature of gases being forced through them to speeds in excess of the relative mach #....

So in theory, if you have a convergent nozzle that transitions from your chamber diameter down to your barrel diameter then the gases could exceed the speed of sound, and if you can get the gases moving faster than mach1, then it's even more feasible to break the sound barrier with a projectile...

Now, if anyone has the math skills to calculate the initial pressure needed and the correct geometry of the convergent nozzle to create the proper rate of convergence, we could give those dimensions to our site sponsors or other machine shop and we could have fittings that not only act as barrel/chamber mating fittings, but also act as velocity improvers...


Thoughts?? discussion??
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Re: Mach #'s , Shock Heating, Etc... C'mon You Rocket Scien

Unread postAuthor: Ragnarok » Sat Mar 14, 2009 5:20 pm

jeepkahn wrote:How many of you have used or considered using velocity stacks at the chamber/barrel junction??? Has anyone considered a de laval nozzle and how it may pertain to spudguns???

There is an older topic on De Laval nozzles here:
http://www.spudfiles.com/forums/topic-t16641.html
General conclusion was that they weren't suitable for spudguns.

Velocity stacks on the other hand - some spudguns do use similar methods, with larger piston seats than barrel diameters and a smoother transition. Not quite the same, but another way to the same aim.
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Unread postAuthor: brogdenlaxmiddie » Sat Mar 14, 2009 5:24 pm

All I need to know in terms of Mach Numbers, is that in my location, the speed of sound is about 1116 FPS at around 40% humidity (the average). :D
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Unread postAuthor: jimmy101 » Sat Mar 14, 2009 5:34 pm

Or, just build a combustion gun. All the "MACH" problems go away. (Well, at least all the "MACH" problems behind the ammo.)

MACH in a combustion gun chamber is about 3x MACH at NPT. (GasEq calculates all kinds of handy things.)

In a rifle, there is virtually no affect of MACH limitations behind the ammo. The round never gets moving anywhere near the local MACH number. Though when it exits the barrel is is suddenly going at about MACH 2.
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Unread postAuthor: Gippeto » Sat Mar 14, 2009 7:01 pm

Version 2 of my "airsoft" bb gun mach experiment uses a "simple" (ie. straight angle, not curved) converging nozzle.

I need to run it over the chrony again, this time with a camera running. :)
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Unread postAuthor: btrettel » Sat Mar 14, 2009 7:09 pm

With non-heated air, going supersonic is really difficult. It's possible, but I wouldn't go for it.

I've been considering adapting a vortex tube to get hot air to try to get supersonic velocities with air that starts unheated. I'm guessing combining that with the typical adiabatic heating and thermal insulation I could make an unheated air gun shoot past Mach 1 (of the atmospheric air) without too much difficulty. That's assuming of course that a vortex tube would work here and that I can make an effective vortex tube without effecting flow, pressure, and efficiency too greatly, but I suppose uncertainty is part of the fun. Maybe someone can get a head start on me. :wink:
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Last edited by btrettel on Thu Mar 26, 2009 5:16 pm, edited 1 time in total.
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Unread postAuthor: psycix » Sat Mar 14, 2009 7:48 pm

As stated by wikipedia, the velocity stack just makes sure to make use of the full diameter, instead of ~90%. So as ragnarok said, having a larger piston seat then barrel diameter (where the barrel diameter is no larger then ~90% of the piston seat), no fancy curves needed. But of course they can always help.


btrettel, I think the vortex tube will suck up most of your stored energy. Maybe you are better off with simply heating the air with a electrical discharge, or, combustion.
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Unread postAuthor: btrettel » Sat Mar 14, 2009 8:07 pm

btrettel, I think the vortex tube will suck up most of your stored energy. Maybe you are better off with simply heating the air with a electrical discharge, or, combustion.


That's what I'm thinking, but I actually am going to use one for something else so I'm willing to experiment if I'm going to make one. I'm just throwing the idea out there. It might work and I think it has a lot more merit than some other ideas if you want to stay with an air powered design.

Hybrids and light gases are the way to go if you want supersonic velocities and simplicity.
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Unread postAuthor: jeepkahn » Thu Mar 19, 2009 2:52 pm

btrettel wrote:
btrettel, I think the vortex tube will suck up most of your stored energy. Maybe you are better off with simply heating the air with a electrical discharge, or, combustion.


That's what I'm thinking, but I actually am going to use one for something else so I'm willing to experiment if I'm going to make one. I'm just throwing the idea out there. It might work and I think it has a lot more merit than some other ideas if you want to stay with an air powered design.

Hybrids and light gases are the way to go if you want supersonic velocities and simplicity.


something not terribly complicated would be a "pneumatically sprung springer gun"...

sorry about the crappy paint diagram, but if you're familiar with the post that d-hall referanced you'll get the Idea...

the chamber as I'm figureing will be 3"x24",the green is a 1.5" barrel, the red object would a 4oz perfect seal projectile/compression piston, and the pink would be a reducer to go from 1.5" to 3/4" and the barrel would be sch120 x 3/4" paintball size, there's also a spring to help cushion the impact of the compression piston...

I would imagine that would send a 3.2gm paintball supersonic...
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Unread postAuthor: ramses » Thu Mar 19, 2009 3:44 pm

that is pretty much a light gas gun, but without the light gas. It could work, but it would work better if you filled the green area with light gas (helium and hydrogen would be best, and the most available)
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Unread postAuthor: SEAKING9006 » Thu Mar 19, 2009 4:09 pm

ramses wrote:that is pretty much a light gas gun, but without the light gas. It could work, but it would work better if you filled the green area with light gas (helium and hydrogen would be best, and the most available)
And even better if the surrounding chamber gasses are combustible, bonus points for high-mix.
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Unread postAuthor: jeepkahn » Thu Mar 19, 2009 4:46 pm

I was thinking it was more along the lines of a springer using the coax/pneumatic as the spring...
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Unread postAuthor: POLAND_SPUD » Thu Mar 19, 2009 4:47 pm

@seaking

the easiest way would be to build a combustion for it...
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Unread postAuthor: Technician1002 » Mon Apr 06, 2009 1:32 am

[quote="btrettel"] With non-heated air, going supersonic is really difficult. It's possible, but I wouldn't go for it.

[quote]

I'm working on it. I am getting somewhat close with apples and fairly low pressure. A smaller tank at much higher pressure will see how close I can get. A fast valve with a smooth air flow is essential.

If I triple the chamber pressure, do you think Mach 1 is in reach?

I have an apple clocked at 882 FPS. When it hits a stationary object, the impact is impressive.

[youtube]http://www.youtube.com/watch?v=rLJzwO2DNAg[/youtube]

An orange and expanded metal screen is also nice to watch. This is a little slower, but still quite fast.

[youtube]http://www.youtube.com/watch?v=LOQrXpK5AT4[/youtube]
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