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Mile shooting cannon?

A place to ask general spud cannon related questions.
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Unread postAuthor: reedfe » Wed Mar 31, 2010 8:13 pm

wow more info than i'll ever use
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Unread postAuthor: Gun Freak » Fri Apr 02, 2010 11:39 am

Here's a cannon that shoots a quarter of a mile on only 40 psi. Maybe you could look into something like it.
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Unread postAuthor: deathbyDWV » Fri Apr 02, 2010 1:49 pm

That would work but one like mine would be MUCH cheaper... It'll shoot a bouncey ball that far at 60.
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Unread postAuthor: Ragnarok » Fri Apr 02, 2010 6:29 pm

Gun Freak wrote:Here's a cannon that shoots a quarter of a mile on only 40 psi.

Hmm. I wonder how accurate that claim really is.

Obviously, if you scale a projectile up, its ballistic coefficient improves (because the ratio of mass to cross sectional area increases), but I'd actually need to go away and work some numbers to tell how viable that is.
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Unread postAuthor: CpTn_lAw » Sat Apr 03, 2010 4:36 am

Rag, you wouldn't remember the drag coef. of an arrow, would you? All i can find on the internet is the relation that gives the Cd , but, quite honestly, i do enough maths and physics to wanna do it again in my free time. Even if i just have to replaces values.
So, before i go check the formula, maybe you know it, and can just throw it away like that.....



P.S.: and yes i realize it took more time writing this that actualy finding out myself. Lazy too.
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Unread postAuthor: qwerty » Sat Apr 03, 2010 10:02 am

Thinking of a commercial air rifle with a 14" barrel firing a 177 pellet at 1150fps+ would probably go around 500m+ right?. Apparently the peak pressure of a spring air rifle is about 3000psi so if u had a 5 foot unregged HPA coax i think a mile could be possible.

Basicly small diameter and long barrel could achieve it.
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Unread postAuthor: POLAND_SPUD » Sat Apr 03, 2010 12:44 pm

@qwerty
probably 500m and less... at least that's the result I got using chairgunpro

anyway it's not that it is impossible to build a mile shooting cannon... you can build a gun like that and you don't need 3000 psi to achieve that range

the point is that a gun that can achieve it will be a bit expensive and impractical
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Unread postAuthor: Ragnarok » Sat Apr 03, 2010 5:55 pm

CpTn_lAw wrote:Rag, you wouldn't remember the drag coef. of an arrow, would you?

Sorry, it's far too variable to know with any sort of certainty. A wild guess would be that it would be somewhere in the 0.1-0.2 range, but it depends on the shape of the nose, the surface finish, shape of the tail of the arrow.

qwerty wrote:Thinking of a commercial air rifle firing a 177 pellet at 1150fps+ would probably go around 500m+ right?.

Maybe 500 metres, but that's a bit optimistic and would require the right angle.

So if you had a 5 foot unregged HPA coax I think a mile could be possible.

Depends ENTIRELY on the projectile.

Let me demonstrate. I'll be using the concept of a velocity coefficient - the percentage of the velocity retained over each metre of flight.

A decent air rifle pellet has a velocity coefficient of about 99.5% - it loses about 0.5% of its velocity for each metre flown. Bear in mind, that's not its muzzle velocity, but the velocity it started that metre with - so in that way, it's like compound interest.
Bear in mind that while 99.5% sounds impressive, it's pretty average.

A tennis ball is pretty bad aerodynamically - it has a velocity coefficient of about 98.9%. And that's at low velocity. It gets worse the higher the velocity.

How fast does a tennis ball have to go to fly a mile? Well, I once figured that the required muzzle velocity to fire a tennis ball a mile would... wait for it... make the same cannon capable of destroying any modern battle tank at short range. And no, I'm NOT kidding - the energy lost to drag is inconceivable.

The important thing is the projectile, NOT the cannon. With no drag, all you need to shoot a mile is a velocity of a modest 125.6 m/s (412 fps). That kind of velocity doesn't take a powerful cannon.
But when you add in drag, you obviously need more velocity to compensate for the energy lost. The obvious trick is to minimise the energy lost to drag and therefore minimise the energy that needs to be added.

As far as range is concerned, efficiency has a huge edge over raw power. Get a good projectile, and you could shoot a mile on less than 500 fps.

Not a word of a lie, the darts I mentioned before could do a mile at a muzzle velocity of only 450 fps - their velocity coefficient of ~99.99%* speaks for itself.
*And this is good - twice as good as even the best .50 calibre bullets!

If the examples don't make it obvious why the important part is a good projectile, not some kind of super cannon, then I don't know what else I can say.
Of course, there's nothing to stop you combining an uber projectile and a really powerful launcher, but get the projectile right first.
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Unread postAuthor: Technician1002 » Wed Apr 07, 2010 12:43 am

Just a quick note on projectiels. When testing a t shirt cannon, we had some shirts come open on launch. It made the difference between 300 foot shots and 30 foot shots. An unrolled t shirt does not fly far.
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Unread postAuthor: CpTn_lAw » Fri Apr 09, 2010 9:08 am

Ragnarok wrote:
CpTn_lAw wrote:Rag, you wouldn't remember the drag coef. of an arrow, would you?

Sorry, it's far too variable to know with any sort of certainty. A wild guess would be that it would be somewhere in the 0.1-0.2 range, but it depends on the shape of the nose, the surface finish, shape of the tail of the arrow.


That's what i figured running the formula...For a carbon fiber arrow that i have here, i found just over 0.1 (0.109) , and that gives me a maximum range of 1702 meters at 8x.
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Unread postAuthor: Gun Freak » Fri Apr 09, 2010 5:30 pm

I think we can all agree that Larda's hybrid can shoot over a mile... at 3026 feet per second :D
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Unread postAuthor: Ragnarok » Fri Apr 09, 2010 6:11 pm

Gun Freak wrote:I think we can all agree that Larda's hybrid can shoot over a mile... at 3026 feet per second :D

ONCE AGAIN, it entirely depends on the projectile.

Raw velocity and power means precisely bugger all if your projectile isn't aerodynamic enough.
As I explained above, if all that energy is being wasted to drag, it's not going to go a mile, almost regardless of the velocity it's going.

Take a tennis ball. While you can theoretically work out how fast it would need to go to make it possible to fire one a mile, in a practical situation, it's actually physically impossible for any cannon to fire one a mile - the air friction involved would cause it to immolate in flight.

Get any ideas about velocity and power being the secret to long range out of your head now. The secret is a projectile with a high ballistic coefficient (NOT drag coefficient).

I wouldn't back the 700m/s golfballs the HyGaC's ~43mm barrel can put out for any more than 600 metres range. And that's a long way short of the 1609.344 metres that make up a mile.
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Unread postAuthor: qwerty » Sat Apr 10, 2010 1:51 am

Fine then...... Lardas hybrid could shoot a mile with a saboted, low air friction, stainless steel dart. :)
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Unread postAuthor: CpTn_lAw » Sat Apr 10, 2010 3:49 am

I can back up Rag, At 8x I can shoot a plastic cap at more than 640 m/s, (yes...it's awfuly light and 16mm wide) but when i run it through the range calculator in HGDT, maximum range is at 80 meters. A 0.2g airsoft BB will go 100 meters. A marble 830 m, a saboted 8mm ball bearing, 900, an arrow, 1700.....
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Unread postAuthor: qwerty » Sat Apr 10, 2010 4:35 am

A 0.2g airsoft BB will go 100 meters


Only that far?

My coaxail piston could do that at very low pressures(under 50psi)
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