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16 inch gb-barrel

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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16 inch gb-barrel

Unread postAuthor: jean » Sun Oct 21, 2012 5:19 am

hi

what is the best chamber size for a 16 inch golfball barrel?
i know the 0.8 rule and i used hgdt.... but it seems so small with only 29inch^2.
the finished cannon will be as quite as possible but with resonable power.
what chamber size should i choose?
what is the power i can estimate?
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Unread postAuthor: Fnord » Sun Oct 21, 2012 10:57 am

You can go a little higher than .8 for additional power. With a small gun, 1.5:1 might be closer to optimal. This is to try and negate additional heat losses from the larger [chamber surface area]:[chamber volume] ratio.
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Unread postAuthor: jean » Sun Oct 21, 2012 11:36 am

thanks
yes it is a small gun and even a coax with 4 inch chamber diameter.
what is about the noise ?
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 21, 2012 11:42 am

jean wrote:what is about the noise ?


loud.

With this I went smaller and smaller with the chamber, but it still sounded like a bloody shotgun.
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Unread postAuthor: jean » Sun Oct 21, 2012 12:00 pm

nice cannon jack

years ago i had a combustion that was only a 2 inch pipe and a endcap with a bbq igniter. that thing shoot a potato near noiseless.(cant remmber the c:b)
the potato was tight in the barrel.

can i get a reduced noise by a tight fit projectile with a resonable weight or by a burstdisk?

jack i dont read the complete post about you cannon but can you remember the weight of the projectile?

the fuel will be metered butane and 2 ignition points.

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Unread postAuthor: jackssmirkingrevenge » Sun Oct 21, 2012 12:10 pm

projectile weight and tightness doesn't really influence noise. Is making a silencer an option?
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Unread postAuthor: jean » Sun Oct 21, 2012 4:36 pm

mh ok
a mini combustion here makes a "plöpp" with a marble and a loud sharp bäng with wax slug...what happened here?
silencer isnt an option because of a fixed lenght.
ok what do you think how far can shoot this thing?

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Unread postAuthor: jackssmirkingrevenge » Sun Oct 21, 2012 8:15 pm

jean wrote:a mini combustion here makes a "plöpp" with a marble and a loud sharp bäng with wax slug


Could be that the tighter slug allows greater pressure to be generated before the projectile "uncorks".

silencer isnt an option because of a fixed lenght.


A silencer doesn't have to add length, look what I did here

Image

Drill some holes at the end of the barrel and sleeve it with a wider pipe, could be the same material as the chamber if you're using 4" pipe.

Pack the pipe with heavy gauge steel wool and it will absorb the heat and therefore lower the pressure of the gasses.

ok what do you think how far can shoot this thing?


http://www.thehalls-in-bfe.com/HGDT/

Here's a rough simulation assuming you're using propane:
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Unread postAuthor: jean » Mon Oct 22, 2012 9:24 am

thanks for the reply

ähm if i bore holes in the barrel..... isnt it like shorten the barrel?

mh if i perforate the last inch of the barrel and add an head absorber... will it have a noticeable effect?


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Unread postAuthor: jackssmirkingrevenge » Mon Oct 22, 2012 9:42 am

jean wrote:mh if i perforate the last inch of the barrel and add an head absorber... will it have a noticeable effect?


it will have a slight effect on velocity, but nothing you would notice without using a chronograph.
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Unread postAuthor: jean » Mon Oct 22, 2012 9:50 am

meaning the effect on the prouduced noise
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 22, 2012 9:55 am

Yes, especially if you pack the pipe with steel or copper wool to absorb the heat.
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Unread postAuthor: jean » Wed Oct 24, 2012 11:20 pm

ok thanks than i will give it a try with c:b 1:1 and drilled barrel..

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Unread postAuthor: jackssmirkingrevenge » Wed Oct 24, 2012 11:54 pm

I would go for 0.7-0.5:1, and of course, syringe metering ;)

[youtube]http://www.youtube.com/watch?v=EoVDuh3ziNg[/youtube]
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Unread postAuthor: Technician1002 » Wed Oct 24, 2012 11:56 pm

That size ratio is often cited comes from Burnt Lake data. That data looked at various barrel sizes with a fixed chamber size.

I find that data set incomplete as much of it is power vs barrel length which is a function of acceleration distance. A too short of a barrel regardless of chamber size has a short acceleration distance. A fixed barrel length with a variable size chamber is missing from their data set. Take Burnt Lake data for what it really is.

Barrel Length vs fixed chamber size. That data is good, but don't just jump to conclusions of an optimum C:B ratio from that limited data set. To be complete, the effect on barrel length on an infinite chamber needs to be added. Then an optimized barrel length for optimal flow vs acceleration distance needs set against various chamber sizes to find a combination of optimum barrel size with optimum chamber size.

In summary, don't jump to conclusions that .8 is optimal for all barrel lengths. It isn't. Their data only found an optimal barrel length for one size chamber. That ratio will not remain constant for any barrel length.
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