It's been a long night OT Air cane again

peter nap

peter nap

Joined
Nov 27, 1999
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It's about 5:00 AM and I've been working on pointy things for about 3 hours.
I still haven't found a source for the alloy Mete told me about but I settled for some scrap Ti.
I found out several things tonight. One very startling fact is that it's difficult to push a bladed object faster than 1100 FPS using air. Almost impossible because of the atmospheric pressure,Etc.

Nitrogen creates a thinner atmosphere within the barrel and Helium thinner yet and will drive it faster but will still not break 1200 FPS with the projectiles I made.

So after a disappointing series of tests, I'm back to square 3.

Square 3 is increasing the energy of the blades from the air cane rather than the velocity. The answer is in fluid reaction blades Rather than pure gas.

The next step for tonight will be to try to use carbonated water as liquid wadding behind the Titanium blade, in the hope that the energy from the initial CO2 charge...in essence shakes it up during the trip down the barrel and gives it a secondary boost.
 
Peter, any chance of a picture of this contraption so I can get my head round it? :D
 
It wouldn't mean much yet Temper. The cane is a piece of hydraulic tubing and right now, I have about a dozen different breeches with valves for different things. The real work is being done with the blades.

If the fluid drive works out I'll post a picture. It works on paper but many times my paper calculations fall flat on their face in the real world.

The thing works like this. A hollowed out blade is filled half way with carbonated water. Inside the blade is a thin, pointed rod. A co2 cartridge with an O ring plugs it up. It goes in the cane. The breech for the cane is a hammer with a valve that is long enough to push the co2 powerlett forward.

When you fire it, the hammer strikes the firing pin/valve stem. This drives the co2 forward and punctures the seal. The valve snaps shut.

The co2 pressurizes the blade interior while overcoming the outside seal friction. The blade starts moving forward with the barrel pressure still holding the liquid in.

When the barrel pressure drops below the internal pressure of the blade it starts forcing the liquid out. Since the liquid is carbonated, the action is raising the pressure further.

The liquid is more dense than the co2 inside the barrel and gives more boost than just gas alone. By the time it exits the barrel the liquid is gone and the energy of the blade takes over.

It's a little like a 2 stage rocket.
 
I'm sorry I asked lol :eek:

Could you sabot the blade to get the FPS you wanted? Or would that defeat the whole point?
 
Nope, I tried that and after a lot of reading, found out why. Compressed air pressure is different than gunpowder. With the GP, you start the thing with a primer and the nitrates produce O2 as it burns. That's common knowledge and the pressure will continue to be produced even though the pressure curve decreases due to the increased space between the bullet and the powder charge.

With the sabot-ed blade using compressed gas, the pressure is a given and decreases at a greater rate because it is not being produced, just released.
The problem is further amplified because the speed cannot exceed the difference between the internal atmosphere density and the outside. This can be overcome to a certain extent by using thinner gas like nitrogen or helium, but your still stuck with the power of that container of gas. In the case of co2...about 850 PSI.
 
I've seen a similar....aahh.... project. Friend of mine made a butane powered shooter. Had the velocity but sorely lacked in the accuracy department. Just couldn't hit those turkeys out the shop window:-) bruce
 
Well....I'm glad I'm not the only nut out here Bruce.......This is really the prelude to phase 2 though. After I get the power up on the thing, I am going to make a Taser like unit. I've already made the head for it. It is just the circuitry for a stun gun with barbed contactors, powered with lithium batteries for weight reduction and encased in epoxy.

Where the Taser fires barbs attached to wire (and there is a ton of loss in the wires) this fires the entire unit. The longer barbs penetrate deeper and it has more range (like 20 feet as opposed to the Taser's 12 or so)

The thing still weighs over 700 grains though and I need the power to move it along.
 
Ah, I was only the innocent bystander:-) I did add some refinements to my buddies' "invention"
This was from the same fella who, when overrun with his mother-in-laws cats, wired up garbage can lids with 110v, baited them with tuna and called "Here kittykitty" (BOG)
What an inventive mind! bruce
 
If you could use liquid Hydrogen instead of Helium and supply a little spark, you could get a great two-stage effect. The H2 sould also give a greater expandability than the He in the liquid/gas transformation.

It might be a little risky carrying around the H2, it is not easily contained except in glass or ceramics.
 
back in university chemistry class.... we had a couple of exam questions that deal with finding out the volume and pressure of gas created with the "car air bag" contraption..... it's actually an explosive that is used in cars...

if you could get ahold of this material.... i'm sure it's precisely measured ... and set off with lectricity too..

just be careful....and do the math .... maybe too much psi in a small bore barrel.. but it would be clean and predictable

Greg
 
The explosive in airbags are an easy home brew project as well as the igniter's. The problem is when you use burning gas instead of compressed gas, it becomes a firearm and all the stupid restrictions that go with it.

For instance, the original Tasers used a small powder charge to propel the darts. To keep it legal they had to put rifling in the barrel (all 1/4" of it) and sell them as a pistol.

Pneumatics are Sarah Brady free zones.
 
On the installation I work at, there was an automobile airbag charge manufacturing company there, also. The powder they used was referred to as lead azite, the same material used in cartridge primers. Seriously BAD STUFF, one of the two most dangerous materials to handle there. It is said to become unstable if left in the bulk form and allowed to vary in humidity and temperature. We have had a few very serious bad episodes with the said material there, with people blown to smithereens, connected with anti personell mines manufactured there during the 'Nam war. The mines were a small canvas pouch containing the lead azite. They easily would blow off a foot. I would in no way mess with that stuff. Just a bit under your fingernail will blow off that first section of your finger. The installation used the stuff for many years, manufacturing munitions for the military. I am around high explosives with my job and have handled explosives for years, and know what is safe to handle. A small charge of it in the weapon you are building would do the job, but the stuff too unsafe to handle.
 
thanks John

that was my bad ! :(
I've no experience with the material physically....only the theory on paper !
- and now that I think bout it the chemical reaction was a decomposition of sodium azide

anyhow.. still too dangerous

sounds like an interesting project so far....

Greg
 
How about this (caution possiblly stupid question ahead), could you use a electric spark to vaporize a liquid and use that as a propellent? Something as simple as water to steam. Just a thought that I have had in the past but have no idea if it would work. Thanks.
 
I wasn't going to name it John. I was trying to keep the experimenters healthy for a while. Yes it would work and so would a number of others. The others aren't as sensitive but would still have to be detonated with Mercury Fulminate or Potassium iodide and Alcohol or something of the such.

They would still make it a firearm and I need to stay away from that to make this thing do what I want and still be cost feasible.

Good thinking Mark but sadly, detonating gas is still a firearm. There are some exceptions like potato guns that use hair spray and you could slip in under that loophole however, the market for this is Va. Residents that don't want to get CCW's and for that, it has to be pneumatic.
 
From what little I remember from my college days, you will have a problem getting an object past 1100 fps. Your 1100 fps is about what the speedof sound is and to get air to flow through an oriface at super sonice speeds requires more than just a hole. You need nozzle shapes and all that jazz.

In my sub-sonic aerodynamics class it was called choked flow. Once you hit 1116 fps, you could not push more air through the hole no matter how much pressure was behind it.

Now that is air at ambient conditions and assuming non compressable flow, so if you do change the gas/propellant it will help, but you may be getting "choked" before you get the flow into the cane. There might be a restiction in you valves or connections.

I wish I could remember more, but it is all in a beer haze. But even in jet turbine engines, everything is sub sonic except at the exhaust nozzle area (after burner). But where all the work gets done in the compressor and turbine it is pretty much subsonic even in jet fighters. All those little diamonds in the blue exhaust from the afterburners are called mach diamonds, but all that exhaust has shape like rocket nozzels to alloow for super/trans sonic flow.

OK, enough of that that, I need a beer. ;)
 
Your exactly right although I've never heard the term choked flow. But since that's not my field, I guess it's understandable.

Changing the gas to one with a smaller molecular makeup changes that some and the restriction at the valve, is the reason for having the propellant bottle inside the barrel itself. the only thing the valve does is bump the powrlett into the piercing rod. From there on, it's mothers best.

Now when I was in college, I didn't drink at all
lightening.jpg


Well.......not much anyway :footinmou
 
Hey Peter If the gaget is long enough couldn't you use a arrow like in the picture of the Arrow Gun you showed us a while back.
That would easily take out some old lady that is assaulting you with a heavy purse. :D
 
Sure could Pete. I built one like that years ago, I just didn't have access to high pressure tanks then. I expect I'll have to build another one.
Right after I finish the AF on the new Lancaster. :D
 
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