I'm building my first pneumatic launcher after several combustion launchers. I have two questions:
What is the recommended chamber to barrel ratio for a pneumatic launcher? I have a 10ft x 3" barrel what should the length of the chamber be if it is 4" PVC?
Second, I'm going to be making a "Barrel Sealing Tee Valve":
http://forums.spudtech.com/topic.asp?TO ... hichpage=1
but I'm unsure what to use as a piston. Any ideas? I'd like something fairly common and not too exotic. It will be made inside a 4" tee.
Any tips or advice would be greatly appreciated.
Christopher
Piston cannon
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Pete Zaria
- Corporal 5
- Posts: 954
- Joined: Fri Mar 31, 2006 6:04 pm
- Location: Near Seattle, WA
@piperchris
Welcome to the forums.
Aim for at least a 1:1 ratio (by volume), 1.5:1 is better, 2:1 is best. Anything much over that is approaching the point of diminishing returns. I know at 4:1 you're wasting performance, because the barrel isn't long enough to harness the energy being released.
Handy volume calculator: http://www.online-calculators.co.uk/vol ... volume.php
As to piston materials, search around this forum and spudtech and see what other people have used in large cannons. Many people make a piston from hotglue (using a mold...), or PVC/lightweight wood with sheet rubber on the front for a sealing face. If you have access to a lathe, your work is quite cut out for you. Also check this out: http://www.spudfiles.com/forums/viewtop ... sc&start=0&
Hope that helps.
Peace,
Pete Zaria.
Welcome to the forums.
Aim for at least a 1:1 ratio (by volume), 1.5:1 is better, 2:1 is best. Anything much over that is approaching the point of diminishing returns. I know at 4:1 you're wasting performance, because the barrel isn't long enough to harness the energy being released.
Handy volume calculator: http://www.online-calculators.co.uk/vol ... volume.php
As to piston materials, search around this forum and spudtech and see what other people have used in large cannons. Many people make a piston from hotglue (using a mold...), or PVC/lightweight wood with sheet rubber on the front for a sealing face. If you have access to a lathe, your work is quite cut out for you. Also check this out: http://www.spudfiles.com/forums/viewtop ... sc&start=0&
Hope that helps.
Peace,
Pete Zaria.
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piperchris
- Recruit
- Posts: 2
- Joined: Tue Mar 06, 2007 10:30 pm
Wow, those were some quick replies!!
rmich732:
I was thinking of using a 4" tee but is there any reason I shouldn't? It's bigger so it should be less of a bottle neck (I would think) and it should require less fittings/adapters than a 3" tee.
Pete Zaria:
I have a 10ft x 4" inch piece of pipe I'm going to use for the chamber. According to my rough calculations the chamber should be about 10 ft long for a ~ 2:1 ratio. Is that correct?
Thanks again!
I'll make sure to keep everyone updated on my project.
rmich732:
I was thinking of using a 4" tee but is there any reason I shouldn't? It's bigger so it should be less of a bottle neck (I would think) and it should require less fittings/adapters than a 3" tee.
Pete Zaria:
I have a 10ft x 4" inch piece of pipe I'm going to use for the chamber. According to my rough calculations the chamber should be about 10 ft long for a ~ 2:1 ratio. Is that correct?
Thanks again!
I'll make sure to keep everyone updated on my project.
-
Pete Zaria
- Corporal 5
- Posts: 954
- Joined: Fri Mar 31, 2006 6:04 pm
- Location: Near Seattle, WA
@Piperchris:
No. It should be 1.5-2x the VOLUME of the chamber size.
10ft x 4" chamber = ~1508 cubic inches.
You want your chamber to be 1.5-2x of the volume of your barrel.
If you wanted to use 2" pipe for the barrel, you'd need a 2" x 20ft (754ci) barrel for a 2:1 ratio, or a 2" x 26ft (1005ci) barrel for a 1.5:1 ratio.
If you wanted to use a 3" pipe, a 2:1 ratio would require a 3" x 106" (8.8ft) barrel. A 1.5:1 ratio would require a 3" x 143" (11.9ft) barrel.
Getting the idea? The ratios are by volume, not by feet. A 10 ft x 4" chamber is 1508 cubic feet. For a 1.5:1 ratio you want a ~1000ci barrel, for a 2:1 ratio you want a ~750ci barrel. You can achieve this with different lengths of different sizes of pipe, as I showed above.
Volume calculator: http://www.online-calculators.co.uk/vol ... volume.php
Peace,
Pete Zaria.
PS: Use the GGDT (Gas Gun Design Tool) and plug in the numbers. Run simulations and see what provides the best results. Get it here: http://www.thehalls-in-bfe.com/GGDT/
No. It should be 1.5-2x the VOLUME of the chamber size.
10ft x 4" chamber = ~1508 cubic inches.
You want your chamber to be 1.5-2x of the volume of your barrel.
If you wanted to use 2" pipe for the barrel, you'd need a 2" x 20ft (754ci) barrel for a 2:1 ratio, or a 2" x 26ft (1005ci) barrel for a 1.5:1 ratio.
If you wanted to use a 3" pipe, a 2:1 ratio would require a 3" x 106" (8.8ft) barrel. A 1.5:1 ratio would require a 3" x 143" (11.9ft) barrel.
Getting the idea? The ratios are by volume, not by feet. A 10 ft x 4" chamber is 1508 cubic feet. For a 1.5:1 ratio you want a ~1000ci barrel, for a 2:1 ratio you want a ~750ci barrel. You can achieve this with different lengths of different sizes of pipe, as I showed above.
Volume calculator: http://www.online-calculators.co.uk/vol ... volume.php
Peace,
Pete Zaria.
PS: Use the GGDT (Gas Gun Design Tool) and plug in the numbers. Run simulations and see what provides the best results. Get it here: http://www.thehalls-in-bfe.com/GGDT/