Quieter Launchers

[PeteS]

I have been tinkering with a silencer on one of my combustion launchers and it has been somewhat successful. The silencer volume is about the same as the barrel volume and it is stuffed with steel wool. Silencer length is about 2/3 of barrel length. It is still fairly loud, but the noise is much reduced.

I'd like to build a launcher that would be fairly quiet, but want to maximize how fun it will be to use. So I'd like it to be fairly large bore and fairly high velocity. I am thinking 1.5" bore and I assume it has to be slower than the speed of sound if I am to be successful at quieting it down much.

I have read most of what has been written here about silencers, but wonder about other launcher design factors that will affect the effectiveness of the silencer. What other design parameters should I be striving for in an effort to meet those goals

[Brian the brain]

If you simply use a longer barrel noise will go down while velocity goes up.

It should be possible to match your chamber volume to your barrelvolume and have the ammo leave the muzzle with ( almost) no sound.

After ignition there comes a point when the expanding gasses cool and even cause a vacuum.
This principle is what powers simple jetengines.
after the burn, fresh fuel and air are sucked in by the vaccume..no wait..vacume...ehm...vacccume...Oh hell...Where is Spellcheck when I need it??

[PeteS]

I have observed that, but velocity seemed to go down drastically at close to that point. I guess it is a matter of hitting just the right balance.

[noname]

Vacuum!

As for the OP, I can't say much more than Brian already did. If you're using a 1.5" barrel, your silencer is probably going to be 3" or 4" I'm assuming. The only real tip I can give is to make your silencer out of ABS to make it more lightweight, along with the barrel if possible. Cell core or thin wall pipe will help keep the cannon from being too front-heavy.

[Brian the brain]

but velocity seemed to go down drastically at close to that point

Sounds like you past that point.

[PeteS]

but velocity seemed to go down drastically at close to that point

Sounds like you past that point.

Yeah I guess so.

[jackssmirkingrevenge]

You might want to have a look here: http://www.spudfiles.com/pneumatic-cann ... 25170.html

Stopping a sabot with a buffer is a technical challenge.

Stopping it due to barrel suction is another thing.

Have a look at the HGDT model attached. As you can see, a peak velocity of 145 fps is reached, but the projectile then slows down and stops in the barrel. If the projectile consisted of fullbore sabot and sub-caliber projectile, then the sabot would stop but the projectile would carry on.

You can see the effect of having a large barrel and small chamber clearly here:

[youtube][/youtube]

Of course, the example I showed has a 20 foot long barrel, hardly practical - but you can create the equivalent space with a sleeve around the barrel. Putting a 10 inch diameter sleeve on it would mean that you could get away with a two foot barrel.

[PeteS]

Interesting...

[SpudBlaster15]

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[jackssmirkingrevenge]

With metered propane/butane/propylene, you typically have to use something like 0.6:1 or 0.7:1 to keep the noise to a minimum.

Not in my experience, namely with this cannon: http://www.spudfiles.com/combustion-can ... 16467.html

Still sounded like a bloody shotgun going off even cut down to 0.45:1

[PeteS]

What are you using for fuel? In my experience, a C:B ratio of 0.9:1 - 1:1 with a 1.5 or 2" bore makes for a pretty quiet, relatively well performing spray 'n' pray. With metered propane/butane/propylene, you typically have to use something like 0.6:1 or 0.7:1 to keep the noise to a minimum.

Propane. I have been using oversize chambers by that standard.