SpudFiles

Alright yall, get ready to read

One project that has been in the back of my mind is a cannon called OverKill. And that is the only name that would fit this animal.

Although I would love to have a 30 - 40' barrel, storing it and moving it around would just be ridiculous. So 20' would be the biggest I can reasonably go. I will have two barrels: 2.5" and 3". I know, GGDT says it will choke performance

Imagine 4 4"x5' chambers running parallel to the barrel and arranged radially around the barrel. Valving would consist of 4 piston valves (3" piston, 2" or 2.5" porting) exhausted by 4 1" sprinkler vavles all piloted by another 1" sprinkler vavle. And possibly that valve piloted by a ball valve with a string I could holler and yank, reminiscent of large scale artillery.

I was playing on GGDT, and entering these numbers using the 2.4" barrel and a 56g tennis ball. At 120psi, I was getting 720mph! I know the variables of dead space and pilot volume will affect performance, but this is looking possible. Also with the 3" barrel, sooting coke bottles full of concrete, muzzle energy is rougly 9000 ft lbs! I was shooting for energy close to a .50 cal, but getting 11,000 ft lbs would need a pretty hefty projectile so we'll see.

I know this is a little ridiculous, thats why I was wondering if the program became less accurate as the scale increased to something this size. (not to insult d_hall by any means) This project would take quite a few 4" tees and a cross or two from mcmaster. This has started getting pretty pricey, but as I have always been fascinated by the punkin chunkin cannons, this would be my own small scale one! And with ranges over 1/4 mile, this would be one to tell stories about.

Being realistic, what do yall think?

wow, that is quite an endeavor

i say go for it, there is no reason why it can't be done, sure it will be a little pricy, but when its completed i have no doubt you will be happy you made it.

just be careful where you shoot it!

might have to think of another name for it, overkill is taken

Ahhh it is? Damn. Shoulda searched first. Alrighty then... hmmm

Dude figure out a way to have a barrel add on, because you could get so much more performance for a few dollars and a little ingenuity more.

biggsauce wrote: I know this is a little ridiculous, thats why I was wondering if the program became less accurate as the scale increased to something this size. (not to insult d_hall by any means)

Although I haven't seen any test data for large scale launchers, I have seen no reason to suspect that GGDT gets less accurate with larger launchers. It is less accurate if you are exceeding the speed of sound in the model, but if you are dealing with velocities below that (such as the coke bottles filled with concrete) then it should still be fairly accurate.

Go for it. My hybrid rifle breaks the sound barrier and biohazard(my huge hybrid) should break it twice according to hgdt does anyone know if anyone has hit mach 2 yet?

I would reccomend a lighter, smaller projectile so you can get it going alot faster.

Hmmm I think you can do it, but if you really want to be sure, you should use Helium or Hydrogen.
OK scratch that hydrogen, its not safe on that scale.

Good luck!

If your only intent is to break the sound barrier, you don't need to go so large. Just use a lighter projectile.

Although, if you still have your mind set on this project http://www.sprinkler.com has pretty good prices on 4" fittings.

I had imagined a pvc cannon that would send a concrete projectile through an old car. This was my initial goal, and still is important, but breaking the sound barrier with a pneumatic would be very intense and could be acheived with a smaller diameter barrel. In all reality, this is going to be quite a build, more for the "because I can" factor than anything else. Besides, paint it olive drab and mount it to an old boat trailer, it would be on hell of a sight to see!

Alright yall I appreciate the feed back, (and thanks to clide for the clarification on ggdt), but there is another concern that has come to mind.

A 20 - 30' barrel has a considerable amount of air in front of the projectile, right? As it travels down the barrel, will there be a significant pressure buildup in front of the projectile? I say signifcant in that will it hurt performance?

I would think that if the air in front of the projectile was already moving toward the muzzle, performance would increase. Maybe injecting air through check valves at certain points along the barrel?(however impractile and unrealistic that may be)

Or possibly injecting another gas in the barrel. Maybe I can have helium flowing through a check vavle and since its less dense than air, the back pressure would be less.

Or is the back pressure of the air in the barrel negligible?

sounds very very powerful
I hope you will build it or something like it
and I can't think of a name either for this
but when the sound barrier is broken
do you have the big kaboom like when an aeroplane does ?

And thanks for the link daberno123, this says sch 40, although there are no pressure ratings listed. Safe?
http://www.sprinkler.com/buy/item/sch40_tees_slip/1953

edit: just found the pressure ratings. great site!

GGDT is somewhat generous around or above the sound barrier, and will even predict impossible velocities under extreme conditions - but the size of the cannon is unlikely to be a problem.

It was previously considered near impossible to break the sound barrier with a pneumatic, but the current theory is that breaching the sound barrier is possible with enough pressure (and a little dead space) - rather than just the rather "American" approach of bigger is better.

The pressure threshold for breaching the sound barrier will depend on the launcher, but I've used 300 psi behind light projectiles without going supersonic - it takes really serious forces to overcome the sound barrier.

Although I admire your objective, I somehow doubt that this cannon, regardless of it's size will be able to break the sound barrier without significantly more pressure than you're planning, or evacuation of the barrel.

@pat123: It's not really correct to think of Mach 2 as breaking the sound barrier twice - as the act of breaking the sound barrier is the projectile passing Mach 1, to break the sound barrier twice, you'd need to decelerate below Mach 1, then re-accelerate past it again.
That's not actually impossible, but to say the least, it is tricky.

@Carlman: Ah, but think of the ridiculous number of launchers called "Anti-materiel cannon/rifle" or AMC/AMR.

I would assume that he plans on using helium or hydrogen to attempt to break the sound barrier, as it's common knowledge that air at such low pressure definately won't cut it.

Also, how do you plan on getting the helium to that pressure? Helium regulators for over 60 psi output are rather expensive. You could try to fill directly from the tank output, with extremely restricted flow to prevent the unregged helium from blasting apart the launcher's pressure chamber.

DYI wrote:... as it's common knowledge that air at such low pressure definitely won't cut it.

If only - most people, even pretty experienced ones will trust GGDT to worrying levels, even if the numbers are high enough that it would actually be impossible to achieve such velocities.

GGDT is good subsonic, but transonic or supersonic - I would be very wary.