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Smallest barrel you can go from a 3" chamber ?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Smallest barrel you can go from a 3" chamber ?

Unread postAuthor: tatfree » Fri Apr 30, 2010 7:34 pm

How small ID barrel can you go safely using a 3" chamber ( ABS material ) .

Can I go as small as 1/2" ID or even smaller ?

Using a spray and pray propane battle.


Right now I'm using a 2" chamber and going down to a 1/2 " with no issues using propane.


Thanks
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Unread postAuthor: jackssmirkingrevenge » Sat May 01, 2010 12:17 am

You could probably plug the barrel without getting yourself an improvised grenade, though really for such a small barrel such a huge chamber sounds a bit overkill.
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Unread postAuthor: Gaderelguitarist » Sat May 01, 2010 12:27 am

What design could you possibly be working off of to think that a 3" chamber would look good and be needed with and for a 1/2" barrel. I agree with JSR. It would be overkill

Using a spray and pray propane battle.


What for exactly? Fueling? As the Chamber itself? As a very small bench?
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Unread postAuthor: squishie » Tue May 04, 2010 11:57 am

jackssmirkingrevenge wrote:for such a small barrel such a huge chamber sounds a bit overkill.


no such thing as overkill in the quest to launch various random objects in to space
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Unread postAuthor: metalmeltr » Tue May 04, 2010 2:03 pm

You could go as small as you want-3/16 brake line even-but the barrel would have to be longer for optimal chamber to barrel ratio
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Unread postAuthor: Ragnarok » Tue May 04, 2010 2:14 pm

squishie wrote:no such thing as overkill in the quest to launch various random objects in to space

While this attitude may be amusing at times, there is an important equation to consider:

Amusing ≠ True

Yes, sometimes overkill from the sense of "more than needed to do the job" is a good thing - but overkill also covers "so much more than needed that it's pointless and horribly wasteful".
And in this case, Jack has made a perfectly valid point - in this case, it's the latter variety. Bit like killing an ant with a hydrogen bomb, really.

Also, "launching random objects" strikes me as a good justification to build a cannon that fires dice.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jackssmirkingrevenge » Wed May 05, 2010 12:53 am

Ragnarok wrote:Also, "launching random objects" strikes me as a good justification to build a cannon that fires dice.


Touché :)
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Unread postAuthor: squishie » Wed May 05, 2010 10:26 am

Ragnarok wrote:
squishie wrote:no such thing as overkill in the quest to launch various random objects in to space

Also, "launching random objects" strikes me as a good justification to build a cannon that fires dice.


fuzzie dice or casino dice, if there fluffy mabe you could make them like the kind of pirate ship cannon ball where 2 projectiles were connected by a chain or some thing it would be quite epic
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Unread postAuthor: Gaderelguitarist » Wed May 05, 2010 4:27 pm

squishie wrote:
Ragnarok wrote:
squishie wrote:no such thing as overkill in the quest to launch various random objects in to space

Also, "launching random objects" strikes me as a good justification to build a cannon that fires dice.


fuzzie dice or casino dice, if there fluffy mabe you could make them like the kind of pirate ship cannon ball where 2 projectiles were connected by a chain or some thing it would be quite epic



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Unread postAuthor: Technician1002 » Wed May 05, 2010 9:54 pm

On a more serious side, if you have an infinate size chamber (huge) there is a simple limit to the maximum flow a barrel will provide based on diameter and length. Somewhere between medium size and infinate size, the increase in size will provide very little improvement. Keep this in mind when trying to shoot the moon with overkill.

Use GGDT and HGDT to model your creations to prevent building something impractical. For a given chamber pressure, there are practical maximum limits to chamber size where going larger does not improve things any measurable amount.

For an example showing this, here is an air cannon with too large of a chamber where a chamber less than 1/2 that size will perform almost in an identical fashion. This cannon either needs a much larger valve and barrel or smaller chamber. I have a 3 gallon launcher that will outperform this launcher with a 2 inch barrel. Chronograph measurements prove it. A better valve outperforms the huge chamber. I've launched spuds in excess of 800 FPS. The larger cannon is much slower due to the valve used. His measured spud speed is under 400 FPS. He was measuring launches at 118 Meters/Second which is only 387 FPS.
http://www.crazybuilders.com/item.php?id=000004&type=project_section

Edit; Added a screen shot of his video to show his performance is much less than predicted.
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Large cannon with 2 inch barrel. 118 Meters/Second Actual
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