SpudFiles

I am designing an artillery type cannon that will be aimed by a sophisticated electronics system. The cannon itself will be made of metal. The projectile will be between 3-5 lbs and will be stabilized. A) I would like to know which platform (Pneumatic, Combustion, or Hybrid) offers the greatest repeatable accuracy (consistency). B) which platform offers the greatest range and if so any examples/figures C) is there an optimal bore diameter for range or accuracy. Thanks.

A properly designed cannon will always offer you the consistency you desire.
In my opinion, a hybrid is a temperamental pain-in-the-ass and wouldn't offer the consistency you want.

Pneumatic?... for a 3-5 lb. projectile? You're going to need a large reservoir and a large source of compressed gas.

A simple metered-propane combustion, offers the greatest ease of operation, when launching large and/or heavy projectiles.

All of the platforms can be made fairly repeatable. It's just based on the precision you use to measure the fuels/oxidizers/pressures involved.

A 3-5 pound projectile is one heaping big projectile (relative to handheld cannons anyway) and your artillery mounts should be able to account for the fairly large recoil.

A hybrid is ultimately going to offer you the best range possibility. However, before attempting this project, if you haven't already built a basic combustion and pneumatic cannon, you should endeavor to do so first. Working at this level will allow you to answer this sort of question for yourself....

Sounds like quite an ambitious project, what sort of range did you have in mind? If it's anything substantial then the cannon will have to be correspondingly big in terms of dimensions and construction.

I'd say for such a heavy projectile, you'd need a hybrid to get any significant range, or a massive air chamber (like those the mythbusters used in their attempts to tenderize steak and rip apart a baseball), but such a size would be very unwieldy.

If you can, hybrid I say.

Reeyah wrote:A) I would like to know which platform (Pneumatic, Combustion, or Hybrid) offers the greatest repeatable accuracy (consistency).

Answer: The one with the highest quality of build (with particular emphasis on pressure gages, regulators, etc.).

B) which platform offers the greatest range and if so any examples/figures

Answer: The one that can deliver the most energy.

C) is there an optimal bore diameter for range or accuracy. Thanks.

No.


You'll notice that the first two answers don't tell you too much. There's a reason for that: Your first two questions are too open ended. ANY gun design can be made very consistent if you're willing to build it to tight tolerances and such. Are you?

Similarly, which option is best for you (with regards to "greatest range") is primarily dependent upon other variables. Is there a particular range you have in mind? Does the gun have to be portable? What are the local laws like? Do you have a portable air compressor? If so, how big is it? And on and on and on....

Basically, you've asked some questions that don't have a single answer.

there are a few more factors that we would need to know before giving advice:
1) Is there a specific range you would like to achieve?
2) Does it need to be portable?
3) What is your budget for this project?
4) What is your goal for this project?

as for your other questions:
1)IMO pneumatic offers the greatest repeatable accuracy, if you have a valve that isn't affected by human inconsistency(ball valve etc.)

2)No one has fired a full sized hybrid so i couldn't tell you, i know with sweet potatoes i can get around 500 yards out of my 3" porting pneumatic, I'm not sure about winged projectiles.

3)As for combustions, I'll let someone with more experience with large models answer that one.

spudtyrrant wrote:2)No one has built a full sized hybrid

They haven't?

Wow... You make me wonder WTF "full sized" means.



(Admittedly, Vera has yet to be fired.... but she has been built!)

D_Hall wrote:

spudtyrrant wrote:2)No one has built a full sized hybrid

They haven't?

Wow... You make me wonder WTF "full sized" means.



(Admittedly, Vera has yet to be fired.... but she has been built!)

touche, no one has fired a full sized hybrid(full sized meaning 3" + barrel)

I forgot to mention that this will be a breach loading design similar to but scaled up in terms of power source. In the way of range I was hoping to achieve .5 to 1 mile and yes I am willing to build withing tight tolerances (would not bother adding an electronic aiming system if it wasn't)

In spudgun standards, pneumatics are the most consistent, provided that you can feed it with a consistent pressure (regulator?).

Hybrids are commonly regarded as the most powerful and I would say that because of that these have the largest range.

Half mile to one mile range? Sounds like you're building a 75mm howitzer here. I support this wholeheartedly. You're going to need a large chamber (1:1 C/B ratio still applies at this scale) and a very fast valve. If you have access to the tools, a large, lightweight aluminum piston with a large porting valve will be the most desireable. Pneumatic will definately serve this purpose well. Get with someone that is skilled with using GGDT and model your valve and cannon in it, to try and find the optimum dimensions. Quality of build and guage accuracy is going to be paramount. You may wish to spend more money than you usually would on the gauges. Cheaper guages are sometimes quite inaccurate. The biggest killer in terms of accuracy and repeatability is the fit of the ammo in the barrel. If you can get a tight seal between the ammo and barrel (and I don't mean with wadding, wadding would make accuracy unacceptible at the ranges he's describing. A sabot would be way more appropriate givin that the projectile will be fin stabilized), you will have much better accuracy.

Good luck, can't wait to see what you come up with!

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I am starting to think that Pneumatic is the way to go because of the ability to control the pressure. What is the optimal chamber to barrel ratio or is there one? Like if I have a much larger chamber than the barrel? The barrel will be about 3 inch (76.2mm).

What is the optimal chamber to barrel ratio or is there one

not really... rag has posted some nice graphs comparing ratios to muzzle energies you can achieve with them... to cut a long story short you don't get much power gain above 1:1... the law of diminishing returns is at work in this case


IMO the biggest challange with this project is to build a piston valve with large enough porting (and one that can handle high pressures). If I were you I'd look for large verions of this -> http://www.spudfiles.com/forums/viewtop ... tml#279478
...and mod it into a piston valve... the rest seems fairly simple... get some large bore steel pipes for the barrel and the chamber...

though if you want to get decent range you have to use high pressures so you have to design a gun that can use 400 psi or so... and this in turn is pretty darn difficult with large bore parts...

it seems that you can save yourself a lot of troubles if you switch to lighter ammo... (~1kg and less... )

I suggest using ggdt first... you'll see what I mean