SpudFiles

Hi All! Long time lurker here.

I've been interested in potato cannons (mostly pneumatic) for some time now.
I'm also interested in lightning.

I'll spare you any other long-winded introductions and cut to the chase.

I've been working on a project for some time now ( ~2 years), attempting to somewhat duplicate the lightning triggering methods that they use at the University of Florida. I created a spooling rocket and a remote launching platform, but soon ran out of extra side money to spend.

I now have the time and some money to start working on it again. I got an interesting idea of possibly using an air cannon to pull a wire up to the heavens (like an antenna launcher) instead of a rocket, as it would be much less expensive per shot.

Here's my main question:

Do you think it would be possible to make an air cannon (or any other type of cannon) that would fire a projectile trailing a thin copper wire up to about 200m?

It's definitely an interesting physics problem...Projectile weight increases linearly with height!

Thanks in advance!

I'm sure with the right projectile and proper spooling/de-spooling method you can get it done. Have a particular projectile design in mind? Right off the top of my head I'm thinking the spool of wire being the projectile...

Of course you will need to remote trigger, just incase you do attract lightning.

Weight of wire/ feet or meters may be a helpful thing to give, also weight of projectile because it could be a simple equation
(distance in meter) X [(wire weight per meter)+(projectile weight)]=weight at distance
also if the projectile has almost no density then your wire's not going up, in other words you can only have 0 newtons of force at 200 m otherwise your projectile will not reach it height.

Rockets seem like a better idea and AFAIK that's what's used for this purpose in real life

dart guy wrote:(distance in meter) X [(wire weight per meter)+(projectile weight)]=weight at distance

A good place to start: http://www.antennalaunchers.com/antlaunching.html

How High will these Launchers reach?
130 to 200 feet of height is easily attained with a Pneumatic Tennis Ball Antenna Launcher while towing a 50 pound test fishing line. It is possible to go much higher with the more efficient or larger launchers, but we have not found suitable antenna trees much over 130 feet tall. So we consider 150 feet to be about optimal.

Remember that the beauty of rockets is that they have a relatively gentle acceleration, while a projectile from a cannon is going as fast as its going to go the instant it leaves the muzzle.

This means that your design priority should be making a projectile that isn't necessarily very fast, but that retains velocity as much as possible. A streamlined dart made of dense metal is the way to go. It would have to be pretty big to sustain the weight and drag of 200 metres of even the thinnest wire, but I think it could be feasible.

200 feet with a slightly weighted tennis ball pulling fishing line is apparently possible according to the above. I have no doubt that a big enough sectionally dense and streamlined dart from a large pneumatic cannon could exceed 500 feet with thin wire in tow.

Some discussion of ideal projectiles here: http://www.spudfiles.com/spud-cannon-re ... 22491.html

long thread but worth reading through as while it concerns a different problem, the ideal projectile is the same.

Large pneumatics are expensive, you might have to consider a combustion cannon.

For the projectile, machining facilities would be an asset but not strictly necessary.

Note that such a projectile fired straight up would be immediately lethal if it struck anyone on the way down, so a clear range is of vital importance. On the other hand, since you're basically taunting Zeus, not sure if safety concerns you much

jackssmirkingrevenge wrote:On the other hand, since you're basically taunting Zeus, not sure if safety concerns you much

Exactly Jack. Taunting me is a big safety concern.


On topic, bear in mind the thinner the wire is, the more fragile it is. I built a casting gun for fishing, and shooting a 1oz bomb(type of sinker), I'd snap everything up to 20lb mono. Even that snaps occasionally.

Zeus wrote:Exactly Jack. Taunting me is a big safety concern.

I thought you'd pick up on that one

On topic, bear in mind the thinner the wire is, the more fragile it is. I built a casting gun for fishing, and shooting a 1oz bomb(type of sinker), I'd snap everything up to 20lb mono. Even that snaps occasionally.

This is why I suggested a relatively low velocity but dense projectile.

Based on the responses here, I think I'll probably use something like a steel arrow, with the line consisting of my kevlar wound copper wire from the rocket part of the project that I've already done. I'm headed out to buy some hardware tonight!

to attach your string you may want to have a spring attached to your projectile so that the initial stress does not break the wire. also look at some stun guns that shoot barbs, they have a figure 8 wrap for the best unraveling .Also @Zeus heavy 50lbs fishing line would make a good shock leader and the spring idea may also be helpful.

dart guy wrote:to attach your string you may want to have a spring attached to your projectile so that the initial stress does not break the wire.

Pure Brilliance. You all really know your stuff, and I don't think I ever would have thought off that! That will probably save me a headache and a half.

Now, the question comes down to spring selection. I''m thinking something pretty long with a relatively low spring constant for a maximum buffer. I'll have to test a variety though!

Again, thanks to all that have responded so far! I think this is getting more plausible with each new insight.

Wow, dart guy... first bit of useful and relevant advice! keep it up

Now, the question comes down to spring selection. I''m thinking something pretty long with a relatively low spring constant for a maximum buffer. I'll have to test a variety though!

Make it a stiff one, otherwise it will deform on the first shot...

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Sacred copulating excrement!

I wonder if this would work? I remembered the whole story with Benjamin Franklin...

You could use a hydrogen balloon for moar awesome!