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Old 02-07-2014, 03:41 AM   #21
Pomphis
 
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Default Re: Steam Bomb

Sorry for sidetracking, but it is somewhat related, especially to the Boil Water spell. Fantasy Tech 1 has steam cannons on page 9. Has anybody an idea how many Boil Water spells of what size would be needed for them ?
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Old 02-07-2014, 04:33 AM   #22
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Default Re: Steam Bomb

iirc, there was an explanation in the Guardians of the Flame series where the mages guild created guns in a very similiar way. It was a rather convoluted setup where, similiar to the ideas here, water got superheated in a metal casing, and the casing held together with magic. Somehow they ended up with a highly pressurized bullet, which somehow released this energy upon contact with water (which had been defined as breaking the enchantment holding everything together).

As I said, it was a bit convoluted. Also, the mages guild in the books never was able to mass produce these wizard guns. Still, the description in the books might be of interest.
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Old 02-07-2014, 10:10 AM   #23
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Default Re: Steam Bomb

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Originally Posted by Pomphis View Post
Sorry for sidetracking, but it is somewhat related, especially to the Boil Water spell. Fantasy Tech 1 has steam cannons on page 9. Has anybody an idea how many Boil Water spells of what size would be needed for them ?
Not me. I tend to think that many things in Fantasy Tech only work on a ^ basis.

However, if we compare the size/cost relationship of the examples in the Boil Water text t quantities of black powder I have seen used the basic "fist-sized" for 2 energy would do any small cannon such as a swivel gun up to maybe a 6-pounder.

For 4 energy it does a cubic foot of water which should handle most Age of Sail guns. With the next size up from that you're giant siege gun size.
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Old 02-07-2014, 10:23 AM   #24
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Default Re: Steam Bomb

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Originally Posted by Gedrin View Post
After a bit of looking, that's what I figured. Given a proper shape, the integrity of the vessel would be sufficient for launch, but fail on impact.
I think you've got a big mismatch in magnitude of the forces in question.

If the water which was displacing an equivalent volume of air at 15 psi expands by a factor of 1600 that appears to me to be having your steam bomb pressurized at 1600 atmospheres or 24,000 psi. That's at the high end of black powder gun barrel pressures and you're trying to contain it for a much longer time i.e multiple seconds instead of thousandths of a second.

I won't say you can't make a sphere out of simple iron with Shape Metal that can do it but it's going to be much thicker than a gun barrel and _heavy_. It would probably be very unlikely to hold the steam but then rupture upon hitting the ground or even a stone wall.

You could make a Steam Bomb with Boil Water and Delay and make your metal walls no thicker than you want for fragmentation purposes. That would be about 1/2 the whole projectile weight if using the rule of thumb that applies to aircraft bombs and mortar rounds.
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Old 02-07-2014, 10:26 AM   #25
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Default Re: Steam Bomb

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Originally Posted by Pomphis View Post
Sorry for sidetracking, but it is somewhat related, especially to the Boil Water spell. Fantasy Tech 1 has steam cannons on page 9. Has anybody an idea how many Boil Water spells of what size would be needed for them ?
Problem is that boil water doesn't specify what pressure of steam it produces, and given that it doesn't cause explosive damage, it may simply not produce enough pressure to power a useful gun. Other than that, figure 1 hex of steam is about equivalent to 1 ounce of gunpowder.
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Old 02-07-2014, 10:35 AM   #26
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Default Re: Steam Bomb

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Originally Posted by Fred Brackin View Post
I tend to think that many things in Fantasy Tech only work on a ^ basis.
Most of them do. That said, the steam cannon has been demonstrated to work. An operational model was constructed a few years back (I think it was a bunch of MIT students) and successfully fired. That's what provided the performance from which FT's steam cannon stats are derived.
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Old 02-07-2014, 11:10 AM   #27
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Most of them do. That said, the steam cannon has been demonstrated to work.
High pressure steam is a perfectly viable working substance for a gun, it's just that you need it at ridiculous temperatures (exceeding the triple point of water) to actually produce cannon-level force.
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Old 02-07-2014, 11:55 AM   #28
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Default Re: Steam Bomb

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Thing is, I don't need to heat the bomb all the way to critical via magic. I can heat it to volatile but stable via plain old fire. The only reason Heat is needed (or it's new brother), is to push it over the edge after launch. There's probably a lot of "margin of safety" research in the R&D effort.

I'll be sure to check out the steam cannon. However, I want to avoid "teams of mages". They're beyond the resources of this idea. A large coal fire pit to pre-heat bombs is a better deal.

The shrapnel point is a good one, but I'm imagining projectiles of significant size, 300-400 pounds at the big end. RL trebuchet's could manage that without the fantastic materials available IMC. However, the point about shrapnel is well taken. I think this could be overcome by properly shaping the sphere to fragment. That would be a later innovation to the same weapon, but likely a significant one.

Is your materials science/metalurgy, dimensional tolerancing, temperature measurement and magical control of heat flux advanced enough that your operators can reliably predict when the casing will fail? If not it seems like you are asking them to risk messy death or ineffectiveness with every launch.

If all of those problems are solved then pre-grooving for shrapnel is trivial.
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Old 02-07-2014, 12:09 PM   #29
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Default Re: Steam Bomb

Just make it two enchantment/spells.

The first dramatically increases the pressure the vessel can contain.

The second makes the steam.

When the first one ends or fails, the pressure is already so far past the vessels ability to contain it just explodes into (pre-grooved?) shrapnel. With linking spells, you could have it reliably air burst, or make it like a landmine that goes of only when people get close.

Another option is that instead of making steam, you summon essential steam from where the elemental planes of fire and water meet.
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Old 02-07-2014, 12:10 PM   #30
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Default Re: Steam Bomb

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High pressure steam is a perfectly viable working substance for a gun, it's just that you need it at ridiculous temperatures (exceeding the triple point of water) to actually produce cannon-level force.
Potato launchers using just pressure (instead of steam pressure via heated water) are a bit of a hobby sport are pretty easy to build if you have a way of generating and delivering that pressure. You can get surprisingly powerful launchers.

Having said that, I'm guessing that's you're working very hard to duplicate what a fire mage can do with just Create and Shape Fire across enemy lines... Or perhaps even what a small conjured elemental would do.
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