A rocket cart!?

[ImSAMazing]

Hi guys,

I just thought of something. The lvl 2 ability of a Conjuration Wizard is that it can summon a 3 by 3 by 3 feet non-magical item, weighin less than 10 pounds. If we take a normal cart, and we summon a tank made from tungsten(a metal with a high melting temperature and also a lot of pressure resistance) as optimized as possible within these limits, with a small exit hole(and a hole at the top, protected a bit by the tungsten so we can use it to drop oil into the engine), and we then construct a simple device that drops 0.24 kg's of oil(around 0.3 pints) into it each round(shouldn't be too hard), and the Wizard casts Gust(a cantrip from EE) each round, that should give around 0.8 kg's of pure oxygen(I calculated it, since Gust moves a creature back 5', that should mean that you move a 5' by 5' by 5' square of air, which consists of around 0.82 kg's of oxygen), enough to let all the oil oxidize, creating a lot of pressure providing a lot of thrust through the small exit hole. A simple rocket engine! I google'd Lamp Oil, and apparently lamp oil = kerosine = lot's of energy when it oxidizes. Oil is also damn cheap(1 pint = 1 sp), meaning a low-level wizard can easily afford lot's and lot's of oil pints.

With some basic physic approximations, we can easily say that this engine allows a speed of around 250-330 m/s(I approximated, not totally sure on the exact value. I'd need to simulate it, and I don't really have the time for that). That's almost the speed of sound!

Am I missing something or have I just started a revolution?

[M Placeholder]

Hi guys,

I just thought of something. The lvl 2 ability of a Conjuration Wizard is that it can summon a 3 by 3 by 3 feet non-magical item, weighin less than 10 pounds. If we take a normal cart, and we summon a tank as big as possible within these limits, with a small exit hole(and a hole at the top, protected a bit so we can use it to drop oil into the engine), and we then construct a simple device that drops 0.24 kg's of oil(around 0.3 pints) into it, and the Wizard casts Gust(from EE) each round, that should give around 0.8 kg's of pure oxygen, enough to let all the oil oxidize, creating a lot of pressure providing a lot of thrust through the small exit hole. A simple rocket engine! I google'd Lamp Oil, and apparently lamp oil = kerosine = lot's of energy when it oxidizes. Oil is also damn cheap(1 pint = 1 sp), meaning a low-level wizard can easily afford lot's and lot's of oil pints.

With some basic physic approximations, we can easily say that this engine allows a speed of around 250-330 m/s(I approximated, not totally sure on the exact value. I'd need to simulate it, and I don't really have the time for that). That's almost the speed of sound!

Am I missing something or have I just started a revolution?

Air resistance, kinetic friction, static friction and spell slots.

[ImSAMazing]

Air resistance, kinetic friction, static friction and spell slots.

Spell slots: not needed my friend. Gust is a cantrip, and the engine summon ability is the lvl 2 at-will ability from the Conjuration subtype. And seeing how small the cart can be, I don't think that friction and air resistance will be that big of a problem, it might slow it down a bit(to maybe 200 m/s instead of the 320 m/s it could have in a vacuüm, taking a 50% efficiency, by converting chemical energy into kinetic energy), but that is still one hell of a speedy cart.

[Ninja_Prawn]

It'd be fairly simple for a DM to rule that a) the materials science needed to design rocket engines does not exist in the setting; for your wizard to use that knowledge is too metagamey or b) the Gust cantrip does not offer the power or control needed to pressurise air in a small chamber.

But even without those sensible rulings, what have you assumed for the payload? The weight of the cart and contents will significantly reduce the speed of your rocket.

[ImSAMazing]

It'd be fairly simple for a DM to rule that a) the materials science needed to design rocket engines does not exist in the setting; for your wizard to use that knowledge is too metagamey or b) the Gust cantrip does not offer the power or control needed to pressurise air in a small chamber.

But even without those sensible rulings, what have you assumed for the payload? The weight of the cart and contents will significantly reduce the speed of your rocket.

a) and b) are true, but that pressure can create thrust shouldn't be too hard to be discovered. For the payload I assumed 100kg, which is pretty reasonable with a high elf weighing not more than 130 pounds, and a cart that shouldn't weigh more than 40 pounds. That leaves 30 pounds of equipment, quite a lot for a wizard. I think that around 10 to 15 pounds of oil should be more than enough to get to the nearest village most of the time.

With a portable hole, you can carry another 8100 pints, enough for a very long ride.

[Regitnui]

Considering your character would be slapping this together on the fly like McGuyver and a toolbox, I'm perfectly justified in saying the contraption results in a need for diamonds or new character sheets. In other, less subtle words, you go KABOOM!

But, that being said, if a player spoke to me (as DM) about this, made it explicitly a downtime activity, and was willing to let me then have House Orien either buy them out, send assassins, or sabotage their attempts until it stopped being funny, then I'd be open to the idea of "rocket sleds".

[ImSAMazing]

Considering your character would be slapping this together on the fly like McGuyver and a toolbox, I'm perfectly justified in saying the contraption results in a need for diamonds or new character sheets. In other, less subtle words, you go KABOOM!

But, that being said, if a player spoke to me (as DM) about this, made it explicitly a downtime activity, and was willing to let me then have House Orien either buy them out, send assassins, or sabotage their attempts until it stopped being funny, then I'd be open to the idea of "rocket sleds".

But what if, say a mid-level wizard, invented it in a village somewhere in the Greenlands of Faerun? Would you still send assassins? And if so, why would they kill him? Steal his idea? That would mean they already know how it works, why it works and how they could use it. Hell, they might kidnap him, dominate person him and then "hire" him to transport stuff for them.

[JAL_1138]

Oh no. Oh gno. I've been clean for so long gnow. I gneed to refrain—but I can feel myself slippigng back ignto old habits...feeligng a terrible urge to roll up a Rock Gnome Cognjuratiogn Wizard agnd commegnce the ignsagne-cogntraptiogn-buildigng shegnagnigagns. This will egnd badly.

[ImSAMazing]

Oh no. Oh gno. I've been clean for so long gnow. I gneed to refrain—but I can feel myself slippigng back ignto old habits...feeligng a terrible urge to roll up a Rock Gnome Cognjuratiogn Wizard agnd commegnce the ignsagne-cogntraptiogn-buildigng shegnagnigagns. This will egnd badly.

You sir, deserve a cookie! Kudos to you my friend, you made my day. Any opinions if it will work?

[JackPhoenix]

But what if, say a mid-level wizard, invented it in a village somewhere in the Greenlands of Faerun? Would you still send assassins? And if so, why would they kill him? Steal his idea? That would mean they already know how it works, why it works and how they could use it. Hell, they might kidnap him, dominate person him and then "hire" him to transport stuff for them.

House Orien is Eberron-specific mercantile house that bases its business on land-based transportation services. They would send assassins to prevent him from threatening their monopoly. They can already transport stuff effectively enough, what with teleportation and lightning rail, but both of those things require their dragonmark to work, meaning nobody else can compete with them, or worse, replace them. If such simple method (in Eberron, level 2 spellcasters are pretty common, even if they are magewrights and not wizards) showed up, their monopoly would be threatened: even if they started using that method themselves, someone WOULD steal it to see how it works, discovers that it doesn't require dragonmark and copies it, eventually either running Orien out of business or at least diminish their profits (as if Lyrandar's air- and sea- shipping services weren't bad enough). They would want to destroy that thing and make sure it never shows up again. Not being to replicate your stuff at all is better trademark protection than suing someone who can replicate your stuff and hoping the court (that either doesn't exist or doesn't care because it's got its own interests) will decide in your favor and that the other side will abide by its decision.

[MBControl]

Seems fine, providing you don't plan on turning.

[Vogonjeltz]

Am I missing something

Yes.


its form must be of a nonmagical object that you have seen

Emphasis added.

[MrStabby]

If the pressure from gust is enough to force air into the combustion chamber it must produce higher pressure than is within the chamber.

If gust can produce higher pressure than is within a combustion chamber then there is no need for a rocket - use gust instead.

[JackPhoenix]

Also, I doubt lamp oil in D&D is kerosene which was discovered in 19th century, it's more likely whale oil, olive oil or something similar, which doesn't work for rocket fuel.

[Hawkstar]

So many reasons it doesn't work.

But I dropped here for a quick reminder

oh no. Oh gno. I've been clean for so long gnow. I gneed to refrain—but i can feel myself slippigng back ignto old habits...feeligng a terrible urge to roll up a rock gnome cognjuratiogn wizard agnd commegnce the ignsagne-cogntraptiogn-buildigng shegnagnigagns. This will egnd badly.

GNO GNOMES!

[Slipperychicken]

Has your wizard seen such a highly-specialized container made of tungsten? Would your wizard even know what Tungsten is, much less seen it in person? Have people in the campaign setting even started producing it? I didn't think so.


But more seriously, as a GM I'd just tell the player the same thing I'd tell a guy who wants his rogue to invent automatic firearms overnight: No.

[JAL_1138]

You sir, deserve a cookie! Kudos to you my friend, you made my day.

:smallbiggrin: Thank you!


So many reasons it doesn't work.

But I dropped here for a quick reminder


GNO GNOMES!

Yes, yes, I kgnow. *twitch* I'm tryigng to resist the temptatiogn.


Any opinions if it will work?

Aaaagnd I've fallegn off the (rocket-propelled) wagogn agaign. :smalltongue:

As mentioned, it would be vegetable or animal oil rather than kerosene. Olive oil, fish oil, whale oil, or even oils from nuts were common. Petroleum would be more like alchemist's fire. Then there are other design issues with making a rocket this way, but they're beyond me to explain properly. You could make a (really expensive) monopropellant, igniter-less rocket with alchemist's fire, since it degrades exothermically in contact with air, but it's more likely to end in disaster than a useful rocket.

I'm no propulsion expert, so take the following with a grain of salt. Or more like a 20-lb brick of rock-salt. Also, legal disclaimer, do not try this at home.

You might do better off making a pulse jet, and might be able to use high-proof Dwarven liquor instead of petroleum, with some DM leeway--Chris Perkins' Acquisitions Inc. games usually have some form of Dwarven booze as either highly flammable or outright explosive, more so than typical liquor, even 180-190-proof alcohol. It might also take the Fabricate spell and alchemist's fire instead of Conjuration due to the "have seen" restriction, but pulse jets are in some ways simpler than rockets. You need a very specifically shaped pipe (not a pressurized tank) that uses its own shape as a pseudo-valve due to internal air-flow pressures. Once it's ignited, the internal engine temperature could sustain the pulse effect; you don't need to worry about spark timing once it's running. You need Fire Bolt or Prestidigitation instead of Gust for it, to get it started, and a single valve--the only moving part--to regulate fuel flow (with careful design, even this valve can be eliminated, but that's not practical for the tech level here). The valve can be quite simple in construction; look at ones from the hardware store for guidance there.

You might or might not need some way to kickstart it with something even more combustible, like alchemist's fire. The engine can be set up such that it draws liquid fuel from a tank without a fuel pump once it's running, meaning no moving parts (aside from the flow-regulating valve) or pressurized fuel tanks are needed.

You could potentially make it without magic at all, with Smith's Tools proficiency, some sheet metal, and a way to get a spark--you could probably rig up something out of a flint-and-steel mounted internally, with an external control to strike one against the other; something akin to one of those tongs-like strikers used to light acetylene torches.

[Asmotherion]

Depends on your DM. Some DMs interprete that anything that causes damage, no matter if it would be neglectable by the real thing, will destroy the magical replica. Others allow great length of experimentation. Personally I once allowed a Plasma Explosion (at the cost of the players being in the AOE, obviously), under the pretext that they have seen the sun. Depends how much your DM likes improvising really.