Fishing/Bait launcher Pneumatic cannon

[Gun Freak]

Oh, hah well I'm not used to fishing at piers. Spoiled with a 23 Mako, for salt, and a huge lake a minute's walk away

I don't think all of the hassle, if it even ends up working, would be worthwhile. Not to mention how silly you'd look trying to get your homemade casting contraption to work properly :tongue3:

I like the way you think though

[hash]

Wish I could have a boat. I usually do a 3/4 day trip down to mexico once a month but idk if that's gonna keep happening. Mexico wants us to purchase a visitor visa for a damn near additional 30 dollars for one day.

[Crna Legija]

i dont see it working out very well, you'll just birds nest the reel.

save you cash and get a boat that's what i did, you already have the advantage of being in USA they are much cheaper there.

[Pbbraun]

Hash or anyone else. Hash referred to sabots that are biodegradable or remain on the line. I would like info on the company that sells these sabots. I am struggling with how to design a sabot for my air cannon that I can retrieve. Attaching a line from the sabot to the cannon doesn't work if the line goes down the barrel before the sabot as the line tangles and breaks. I thought about attaching the sabot to the cannon with the line going into the cannon after the sabot but I am concerned that the sabot, when arrested by the line, would significantly change the direction of the bait flight.

[jackssmirkingrevenge]

Ideally the sabot never leaves the barrel, here's some theory when it comes to historical uses of captive sabots. In practice you need a way to machine as light a sabot as possible out of an impact resistant material (for example UHMWPE) an also a strong metal barrel to which you can securely attach an arresting mechanism that has to halt a sabot that is after all traveling at the same velocity of your projectile.

[Pbbraun]

Thank you for the suggestions. My bait launcher currently has a schedule 40 pvc 2" barrel. I should be able to cut out the center of a 2" Pvc cap the correct dimensions to stop the sabot. I am making a sabot out of 2" od aluminum tubing that just fits inside the 2" pvc. I plan on welding a 2" circle onto one end of the aluminum tube to make the sabot.

I believe your solution is better but I hope this will work.

[jackssmirkingrevenge]

My bait launcher currently has a schedule 40 pvc 2" barrel. I should be able to cut out the center of a 2" Pvc cap the correct dimensions to stop the sabot. I am making a sabot out of 2" od aluminum tubing that just fits inside the 2" pvc. I plan on welding a 2" circle onto one end of the aluminum tube to make the sabot.

I'm afraid an aluminum sabot will just blow through a PVC catcher...

One way to greatly reduce the stress on the sabot catcher is to have a very large barrel volume proportional to your chamber volume. Here is an example using a combustion launcher but the same principle would apply to pneumatics:

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Basically when the expanded volume of gas in the chamber ( chamber pressure/15 * chamber volume ) is less than the barrel volume, the sabot is naturally going to start to decelerate. In practice, the sabot would decelerate but the bait inside would continue moving forward at its maximum velocity.

If done right you might not even need a sabot catcher. The disadvantage though is that you would need a rather long barrel for practical velocity.

Here's an example modeled in GGDT with a 9 foot x 2 inch barrel and 1 foot x 2 inch chamber running at 150 psi:

As you can see, the theoretical barrel pressure drops below zero before the sabot leaves the muzzle, meaning it would have started to decelerate. Assuming your bait is a sphere, you would still range several hundred feet.

Here's what you would need to stop the sabot in the barrel without a catcher:

I kept the same specifications bur reduced the chamber volume from 12 inch length to 4 inch length. As you can see, the sabot never exits the muzzle, but within the barrel itself it reaches a peak velocity of about 200 feet per second, and this would be the velocity imparted to the bait.

edit: a way to apply the concept without having an excessively long barrel is to port the barrel half way through and fit a sleeve over it - this will greatly increase the barrel volume, and therefore gas expansion and sabot deceleration, without needing a ridiculously long barrel.

baitlaunchersleevedbarrel.jpg (35.94 KiB) Viewed 6586 times

[Pbbraun]

Thank you for the info. I will experiment starting with reduced pressures and let you know how it goes. Hope to finish the sabot and try this in the next two weeks. How would I replace my 2" ID PVC with a 2" ID aluminum tube? I would attach pictures but don't see an easy way to do that. :drunken:

[Pbbraun]

I really like the idea of adding the 4" pvc as a sleeve over the 2" barrel. How large should the ports be? How many ports. Is the sleeve sealed at both ends?

What would happen if I only drilled ports in the 2" pvc and didn't use the sleeve?

I plan on taking this in checked baggage and I have made it so I can disassemble it. Therefore the barrel is made up of two 2' sections of 2" pvc, jointed by a hub that is not glued.

If I add the sleeve I believe I can do the same thing, gluing the 2" x 4" adapter to the lower end, gluing the first section of 4" sleeve to the adapter, connecting the 2nd section of 4" pvc with a hub (no glue) and gluing the top end 2"x4" adapter to both the 2" PVC and the 4" PVC sleeve. The weak point will be the midline barrel/sleeve hubs that are not glued.

Thank you so very much for your help.

Bill

[jackssmirkingrevenge]

How would I replace my 2" ID PVC with a 2" ID aluminum tube?

If you don't have machining facilities, epoxy casting would be my recommended route - in this case epoxying the pipe into a threaded fitting, perhaps a union to make it replaceable.

I would attach pictures but don't see an easy way to do that.

1) Click on the "Upload attachment" link below the post text box

2) Click on "Browse..." and select the image you want to upload

3) Click on "Add the file"

I really like the idea of adding the 4" pvc as a sleeve over the 2" barrel. How large should the ports be? How many ports.

As many and as large as possible, but not exceeding the length of the sabot. For this concept to function, it is essential that the air in the barrel remains as contained as possible in the sleeve:

Is the sleeve sealed at both ends?

For the same reasons articulated above, you need the air not to escape the sleeve.

What would happen if I only drilled ports in the 2" pvc and didn't use the sleeve?

The air would exit the barrel and stop accelerating the sabot, but since you haven't created a "suction" effect, it would not be trying to brake the sabot.

The best way to illustrate the idea is to press your finger against the nozzle of a syringe and pull the plunger. You'll note that there is a force trying to push the plunger back in, because atmospheric pressure is greater than the pressure inside the syringe chamber - this is the effect we are after. Otherwise if you only rely on barrel friction, you're going to end up with a ridiculously long barrel that is completely impractical.

If I add the sleeve I believe I can do the same thing, gluing the 2" x 4" adapter to the lower end, gluing the first section of 4" sleeve to the adapter, connecting the 2nd section of 4" pvc with a hub (no glue) and gluing the top end 2"x4" adapter to both the 2" PVC and the 4" PVC sleeve. The weak point will be the midline barrel/sleeve hubs that are not glued.

Since the integrity of the sleeve is paramount, I don't think you can really separate it.

That being said, all you want is the spare volume. You could for example epoxy a couple of bottle caps into the sleeve and when you arrive at your destination, screw in 3L bottle et voila, tons of spare volume that you don't have to pack in your bags:

edit:

Screw having a sleeve at all, why not fabricate a central hub that you screw several 3L bottles into?

Looks a bit silly but pretty is as pretty does, you have your expansion chamber cheap at destination without eating into your baggage.

Another point worth making, this system will work much better with a combustion as opposed to a pneumatic launcher. Unlike pneumatics, in combustions the heat generated is an important contributor to the pressure, and as the gasses expand into your sleeve, they lose temperature and therefore pressure more rapidly. Of course it depends where you are, I would imagine combustions are a no-no in most areas.

[Pbbraun]

Would a 5 gallon collapsible water bladder work?

Attached with a short section of garden hose.

[jackssmirkingrevenge]

Would a 5 gallon collapsible water bladder work?

No, and come to think of it, the soda bottles wouldn't really work for the same reason - once the air in the barrel expands beyond the chamber volume at atmospheric pressure, a soft container (one that would not withstand holding vacuum) will collapse and not effectively contribute to sabot deceleration.

[Pbbraun]

I am going the sleeve route. How long should the 4" sleeve be? My 4" air pressure
reservoir is about 14" long.

[jackssmirkingrevenge]

The sleeve should be as long as the barrel, you really want maximum volume for the best effectiveness.

My 4" air pressure reservoir is about 14" long.

This sounds far too big for this concept to work within a reasonably barrel length, unless you use very low pressure which in turn will give you poor performance.

[Pbbraun]

Currently I have a 40" barrel. How far from the base should I drill the holes to vent the barrel into the sleeve? Once I get it together I will experiment to see if I need to extend the barrel and the sleeve.

Thank you,

Bill