h a l f b a k e r y
A riddle wrapped in a mystery inside a rich, flaky crust

meta:

account: browse anonymously, or get an account and write.

 user: pass:
register,

 ... 'Phantom' x-ray weapon Photon Torpedo Plug a thug Ponytail Nun-chucks pressure cannon Prion Poisoning Rangefinder-Adjusted Electric Crossbow Raptor warcry + easy listening seed bullet ...

product:weapon
 ... electromagnetic ... food ... gun ... ice and snow ... landmine ... light sabre ... missile ... projectile ... ray

# pressure cannon

open up a gas well
 (+3, -4) [vote for, against]

here's my idea..... and yes it's my first time

i work in the oil and gas industry and i've been thinking of making a cannon out of a gas well... basically you have a 3km. long 3" barrel and some wells have a pressure of 10,000 psi or even 15,000 psi. i've been searching the internet for a while now for a formula involving pressure differential acceleration over a givin distance ie. barrel length.... but no luck, maybe some one has one laying around they could post for me.....i did find one site that listed the needed cannon velocity at ground level to reach orbit at 24-34 times the speed of sound depending on wind resistance.

i've also read some of the postings on this site regarding space cannons that claim that gas can't go faster than the speed of sound...how can that be when an explosion is the creation and release of high pressure gasses, and rifles can send projectiles faster than sound?

some rifle sites claimed instantanious pressure in a rifle to be between 50,000 to 110,000 psi over just 3 feet of barrel, and they break the sound barrier.

so if some one can help me out with the math.... i do have everything i need to make this happen at work, except maybe the owner of the well's permission, i just want to know how fast i could get a 20 pound steel bullet over 3km with 10-15,000 psi pushing it... and yes i know the friction would be murder on the whole system on the way out.... but it sure would be cool to see...

thanks for the help later

 — whitecowboy, Jan 07 2007

 Lets see, you have no direct access to the bottom of the well, so basically you are creating a 3km long muzzle loader that fires straight up.

 Some problems I see.

 First, I think muzzle velocity is more closely related to amount of propellent than to barrel length. So long as the barrel is long enough to contain the compressed gas from the explosion. Probably on the order of meters, or maybe tens of meters, not kilometers. Look at mortars. Short thick barrel, but lots of range.

 Second, loading is going to be a nightmare. You need a 3km ramrod! Also I doubt that the sides of the bore are going to be completly dry, so the charge is going to have to be protected in some way.

 Third, how are you going to fire the charge? If you run a wire down the borehole it will interfere with the charge.

Fourth, your barrel cannot be aimed, so the shot is going to go straight up. Which of course means that it is coming straight back down.
 — Galbinus_Caeli, Jan 08 2007

[21 Quest] Not really. The surface of the earth is moving at a constant speed, and the projectile is going to move in a straight line relative to that position. In actuality it will be a somewhat complex curve, but from the point of vew of the person standing next to the borehole it will appear to go straight up, then fall straight back ... OH MY GOD IT IS GOING TO HIT US!! RUN!!!
 — Galbinus_Caeli, Jan 08 2007

 I think what has to be determined in this scenario is the rate of expansion of the volume of gas The greater the rate of expansion the greater the ultimate velocity. Over the distance you are describing this is really not a function of projective acceleration as it is a expansion velocity.(essentially you want to calculate the icrease of volume of propellant per unit time, when you compare this to the volume of your barrell you will determine the length of the barrel that will be filled per unit time. For overall accuracy you will need to evaluate the fluid dynamics of the gas flowing through the pipe if the distance is long enough your entire calculation may come down to the maximum flowrate for a gas of Density X in a pipe of Size Y which is effectively a question of cross sectional area of the pipe.)

Bottom line I suspect that there is an ultimate limit for the velocity that can be achieved by a gas propelled projectile. I dont suspect the speed of sound really comes into play in this scenario at is variable based on the density of the medium in which it is being measured.
 — jhomrighaus, Jan 08 2007

I have pondered such imponderables many a time. Suppose things work well and the bullet comes rocketing out of the barrel. There would be no good way to watch it go. There needs to be incorporation of a locator device in the projectile to find the thing when it comes to earth, and also an altimeter that records how high it gets.
 — bungston, Jan 08 2007

 To answer the bit about the speed of sound versus projectile speed:

 Quite simply, the speed of sound increases with pressure. (Also possibly with temperature ie hot gasses, but I’m a bit fuzzy on the exact mechanisms). You’ll find that the speed of sound in the propellant gasses in a gun barrel is quite high, like a couple thousand metres per second. Purely gas guns are severely limited by speed of sound in the propellant medium, but can overcome (or more practically, bypass) the problem by ensuring pressure is above atmospheric at the muzzle (this is ignoring the above reference to temperature effects, so ok, to be pedantic, ensure the speed of sound in the propellant gas is above atmospheric at the muzzle). You can get pellet guns now that beat 334m/s, if only just.

This is a bit of an arsed-backwards way of looking at things; as the really critical factors are the kinetics of the propellant particles, which is more about fluid dynamics, temperature, etc.
 — Custardguts, Jan 09 2007

 // W=Area*Press*Length=1/2 (mass)*(Vnoz)^2//

 Area for a 3 inch circle is pi * (3/2)^2 or about 7 square inches. Force with this and 10,000 psi pressure is 70,000 pounds. Acceleration is 70,000/20 gravities, or 3,500 Gs. Switching to metric, about 35,000 metres/s/s

 35,000 m/s/s * 3,000 m = 1/2 Vnoz^2 210 million m m/s/s = Vnoz^2

 This ignores the Bernoulli pressure reduction for high speed gas and the drag pressure drop for high speed gas in the tube.

The Bernoulli pressure drop is probably the same issue as speed of sound, and can be improved with hotter gas. Another way of looking at it is, can the mass of the gas you're accelerating be ignored or is it significant compared to the bullet mass.
 — caspian, Jan 10 2007

Would igniting the gas be an option?
 — BunsenHoneydew, Jan 12 2007

You would need to pump down oxygen first.
 — Galbinus_Caeli, Jan 12 2007

yeah.. i was wondering the same thing about o2. if it could be pumped into the barrel at a rate proportional to the fuel, the device may end up being more like a rocket engine with a very long pipe attached. not sure what kind of pressure a rocket engine generates. also, you may want to pump out all the air before firing, as blasting into a vacuum is a good way to avoid nasty mach 30 friction burns (until ya hit our soup of an atmosphere that is). + coz i want to see this thing in action. oh, and better to just do it than ask permission - forgiveness is much easier to come by.
 — TIB, Jan 13 2007

Straight up is straight down until you get to a point definitely beyond geosyncronous orbit which is a much greater speed requirement than anything else that has ever gone into orbit. I also think this is farther still beyond geosyncronous the farther north you go from the equator. for almost anything less the projectile would fall in between where the muzzle was when it went up and where it is when it went down(at the equator given everything is symetrical except the motion of the earth). That mach number is probably the high one or doesn't even apply in this case. Two things come to mind for you to research, up to the civil war I believe cannon length was based on the fact that Black powder was limited in it's ability to constantly expand and continuously add velocity over a longer barrel, until "Mammoth powder" by DuPont 1862. I think the advantage is in continuous burn. Also the HARP project got a projectile to 180 km. Which if I am thinking right is about the end of the atmosphere. An orbit would probably be more speed still though. Part of the projectile would have to burn as has been stated but there would be something left of it. The metiorite equivalancy is valad but their speed is probably always higher than the minimum orbital speed since none of them came from earth orbit. Their density and wear resistance is probably nothing compared to an aerodynamic steel caseing. Density, wear resistance, and melting point are all different and I am guessing heat conductivity is as well. A better comparison is to the expectations behind satellite dropped Iron rods for purposes similar to artillery that I heard about in passing once and can't seem to find a reference to.
 — MercuryNotMars, Jan 16 2007

nope no oxygen in the pipe..... that is whats called a blow out an they aren't too cool..... end up with a crater.
 — whitecowboy, Feb 22 2007

Shouldn't someone be telling you that you will never get away with this? Where's superman?
 — GutPunchLullabies, Feb 22 2007

 This satisfied my railgun jones. Bread for all!

 [whitecowboy], do workers have access to the ends of these pipes? I would think that the ends are stuck in tanks or somewhere to capture all the gas.

Also, does it come out of the pipe pressurized and is it stored like that? Or is it cooled and liquified? I would think with the pressure change that the gas would be phenomenally cold as it emerged from the pipe.
 — bungston, Feb 23 2007

Put it near the equator. Tilt the projectile towards the earth's spin. Tunnel a mountain to get the outlet tunnel 500 meters above sea level. Make a second big hole connecting to the barrel. Drop an enormous shaped rock into it to create the pressure for launch. Rinse, repeat.
 — Voice, Feb 23 2007

yes we can get at the ends of these pipes and you can build pretty much whatever you want on the end of them.... and yes the gas is super chilly when it drops from 10k psi to atmosphere
 — whitecowboy, Mar 10 2007

impractical to liquify and store natural gas..... that's why we have pipelines.
 — whitecowboy, Mar 10 2007

 [annotate]

back: main index