Building a better airship engine (catgirl killers wanted)

[Hirax]

I've seen riverine+permanent wall of fire+decanter of endless water mentioned as a good ways to create an engine, but let's see if we can refine this design so that it's cheaper.

First, as an alternative to permanent wall of fire we have Darrson's fiery furnace (Shining South), a second level spell that lasts for hours/level, and can even be made permanent with permanency if you don't want to fiddle with recasting. However, it only gets things up to extreme heat. It references the DMG, which has extreme heat as the highest heat band, with the relevant crunch being: "air temperature over 140° F, fire, boiling water, lava." The problem is Sandstorm comes along and adds 2 bands above that, capping extreme heat at 180. What cheap ways are there to make this hotter? At the very least, I believe wall of magma to be a superior option to wall of fire, because it's hotter (basing this on magma's hirer damage for proximity), has smaller minimum dimensions, can be shaped in useful ways (like a 5' long tube), and can also be made permanent.

Second, what's the cheapest source of infinite water? Traps are of course cheaper than decanters, but is there something out there free?

Third, what's the cheapest way to containerize all this into something with dimensions of around a 5' cube? Wall of stone and stoneshape can get us something to containerize our Darrson's fiery furnace or wall of magma. Darrson's isn't hot enough to melt stone, and the description of wall of magma indicates that it is actually plays nicely with wall of stone (or any existing stone) oddly enough, so we really only need to be sure that the resulting engine will not explode due to the pressure. What's the cheapest method to do this? Or is this even a concern? I have no idea what the optimal architecture for this would be, if it's something other than just a straight tube then pressure is probably a concern.

If it strikes any inspiration, Shining South also has Darrson's chilling chamber, which is just the opposite of fiery furnace, and puts an area into the extreme cold band (-20 to -50 F per Frostburn). I know jet engines somehow involve hot and cold, so you could have a fiery furnace and chilling chamber in the same device if necessary.

[2xMachina]

Thermoelectric effect (http://en.wikipedia.org/wiki/Thermoelectric_effect)

Link the Darrson's fiery furnace and Darrson's chilling chamber. Generate unlimited electricity. Use to run propellers.

[Hirax]

Propellers aren't ideal because they're large. I'd like for the engine to be small enough to mount to a ship's rudder, so you could actually steer it left and right with the steering wheel.

[ericgrau]

A practical engine needs 2000-4000 degrees. A 300 degree boiler is a novelty item that doesn't push very hard. Typically this uses a coal furnace with fast air blowing in to get such temps but I assume we need something lighter to power an airship that can actually float rather than a train. That leaves either magical propulsion or extremely hot magical heat. Magma is about 2000 degrees IIRC so we probably want some sort of repeated or permanent magma spell that fills only a small space yet repeatedly replenishes itself.

The best thing for hovering are wide fans rather than small jets: You'd have to essentially cover the top or bottom entirely with helicopter blades. A 300 m/s downdraft (about 670 mph) should ideally provide enough lift to hold 4 tons per square meter (about 10 square feet), though 1 ton or less is more realistic. The power required for this is about 10 million watts which is about 14,000 horsepower. The heat required assuming a high temp efficient engine is at least 30 million watts and more likely 50-100 million watts which is about 170-340 million btu per hour. You might pull up to 200 watt hours out of a kilogram of magma so you'd need 125 tons of magma per hour which is about 2 tons of magma per round. To lift 1 ton. Dam. We need a lighter weight yet extremely high temperature high flow heat source.

Oh I know. Cutting the downdraft speed in half reduces the weight carried to 1/4 but cuts the power required by 1/8. Reducing it to 1/4 reduces the weight carried to 1/16 but the power required by 64. Now with a mere super tornado force 170 mph down draft we can lift about 125 pounds per 10 square feet and only 30 pounds of that is devoted to magma flow. The ship still needs to be relatively light and empty but if made large enough it could hold a decent amount of cargo.

Shorter version: Find a spell that delivers 30+ pounds of magma per round for every 10 square feet and make it permanent. That leaves about 90 pounds for the steam engine, structural wood and cargo per 10 square feet. The engine and cargo aren't actually that far spread out, just anywhere on the ship. I'd suggest darkwood and mithril to save weight. Propellers must cover the entire top of the ship Final Fantasy I style.

[2xMachina]

How about just hot hellium balloon? Less energy needed.

[ericgrau]

Ya that's the easy way. But where's the fun in that :smalltongue:. Also a slow takeoff, while helicopter style zips off of the ground.

And if we want to get medieval then most of the helium is in the New World. We're left with hydrogen hindenburg style.

[Hirax]

Getting off the ground is the easy part, I'll simply be casting suspension (Shining South) on multiple objects and using them as lifts. The engine only needs to provide thrust and be steerable in some way. I probably should have mentioned that originally. How suspension would interact with the engine is unclear, I plan to have 3 lifts in the front and 3 in the back, so perhaps a generous DM might let allow raising and lowering the front lifts combined with the thrust from the engine to allow for ascending and descending. If the engine could be mounted to the rudder, that would allow for left and right movement. This will be done on Mordenkainen's capable caravel.

[rmg22893]

Get a bunch of items of phantom steed 14th CL 2/day. Attach them to airship. Profit.

[ericgrau]

You'd probably want something to activate/deactivate a portion of the suspension lifts to go up and down.

In that case it's a matter of acceleration. The same fans pointed sideways provide 1 G of acceleration at the stated weight. Half as much, half a G, etc. When the ship reaches half the fan speed the acceleration likewise drops in half. When it matches the fan speed the acceleration is zero, but long before that point drag will slow you down. Slow acceleration is about 0.1 G. A car is about 0.3 G. I imagine you'd want 0.1 G or less for a relatively gentle ride unless you want this thing to do loops. It could still reach high speeds after a minute or so of acceleration. Assuming 170 mph fans I'll make a wild guess (since drag limited top speed is complicated) that a 30-40 mph top speed isn't unreasonable. That's about 300-400 feet per round.

So the above post designed for a 10 square foot (about 3.5 foot diameter) propeller could gently accelerate about 1000 pounds of ship weight using a tornado force blast.

Alternatively, use control winds and sails. Even at 85 mph you simply use 4 times the area (in sails rather than propellers) to get the same push as 170 mph. Either way use strong sails.

[Mando Knight]

...You just made me cringe. In pain.

First: 300 m/s? For a fan? You realize that's close to Mach 1 at room temperature, right? Propellers don't like that.

Second: units. The units! Degrees what? Centigrade (in which case you'd be dead wrong)? Fahrenheit (THE HORROR)? Energy in Watt-hours? Btu? Horsepower? Metric tons or customary/English/whatever-you-call-it? Eeeeewww... :smallyuk:

Third: I don't know how you're getting your thrust values for magma at all.


...The endless water engine is a rocket without the fuel problem, pure and simple. It's limited to 18.9 kg/s mass flow per decanter, and its thrust depends on the heating value of the wall of fire and nozzle shape, but it's a simple rocket.

Your other main choice is an air-breathing propulsion system. Probably a turbofan. Then you need to have someone to build your turbomachinery, but you could then skip the decanter. Unfortunately, since really good materials are needed to build the turbine, you'll be spending more on the mithral or adamantine than you would on the decanter.

Also, a pressure vessel should not be made out of stone. Way too heavy and requires a thicker vessel to compensate for its low tensile strength.

[ericgrau]

Even a decanter of endless water doesn't blow that fast. Rockets are less efficient, so you'd need even more heat. Again if you only go a little above boiling it's a weak novelty item not a very useful rocket. In short you need an even greater source of magma you just don't have to worry about propeller mechanics anymore. Otherwise roughly the same considerations apply for a water rocket. You likewise need a large outlet rather than a narrow nozzle or it will consume an order of magnitude more power and probably have worse issues with the sound barrier because of the high speed needed.

I did calcs in metric but converted to both so that more people could understand. In the end 75 m/s seemed more practical than 300 m/s, besides being farther from the speed of sound. The thrust comes from a typical engine operating at 10-30% efficiency (heat to work not work to work, so 40-60% is the ideal not 100%). A steam engine for example.

A decanter of endless water and a massive heat source could provide an endless supply of super heated steam to propel the thing with less complication and fewer moving parts, but like I said we're talking huge amounts of heat hence something very hot and high flow like some sort of decanter of endless magma. And the output "nozzle" is likely to be very wide for more thrust without breaking the sound barrier 10 times over.

[Hirax]

The stone is free, so making it thicker isn't a problem, unless you're saying the amount of thickness required would become cumbersome. Hardening could be used on it to get additional hardness, easily surpassing adamantine's default hardness. Would this be sufficient as a vessel for a turbofan? If not, sufficient for a rocket engine? Is either practical to mount to a rudder to propel a 100~ ton ship?

edit: hardening for the character I have in mind would get stone to hardness of 32, compared to adamantine's default of 20. That's probably enough? I don't think there's really a good way to be sure.

[Gavinfoxx]

You've responded to my Airship post here: http://www.giantitp.com/forums/showthread.php?t=233352 noting that you don't actually, you know, NEED to do a rocket engine to get decent speed...

Also note that there are lots of great D&D supermaterials to make things out of...

[Radar]

The stone is free, so making it thicker isn't a problem, unless you're saying the amount of thickness required would become cumbersome. Hardening could be used on it to get additional hardness, easily surpassing adamantine's default hardness. Would this be sufficient as a vessel for a turbofan? If not, sufficient for a rocket engine? Is either practical to mount to a rudder to propel a 100~ ton ship?

edit: hardening for the character I have in mind would get stone to hardness of 32, compared to adamantine's default of 20. That's probably enough? I don't think there's really a good way to be sure.
For a big vessel it would by highly impractical to attach your engines to a rudder. Either go for a bit more sophisticated machinery like multiple azimuth thrusters or make a single rocket/jet engine with valves to direct the thrust to the sides (thrust vectoring wouldn't hurt as well, but requires more moving parts).

[Gavinfoxx]

I use Invisible Spell Wall of Iron for parts of the hull... then get the various hardening spells and powers and such on it...

[agahii]

Id just use stronghold builders and make a flying stronghold that looks like an airship.

[Gavinfoxx]

Id just use stronghold builders and make a flying stronghold that looks like an airship.

Problem is, you might have to actually use the COSTS in SBG... which is pretty bad... I mentioned the issues with that in my post!

[Hirax]

You've responded to my Airship post here: http://www.giantitp.com/forums/showthread.php?t=233352 noting that you don't actually, you know, NEED to do a rocket engine to get decent speed...

Also note that there are lots of great D&D supermaterials to make things out of...

As I recall I was only speaking in terms of suspension, which only generates lift, not speed.


For a big vessel it would by highly impractical to attach your engines to a rudder. Either go for a bit more sophisticated machinery like multiple azimuth thrusters or make a single rocket/jet engine with valves to direct the thrust to the sides (thrust vectoring wouldn't hurt as well, but requires more moving parts).

I'm not looking for a high level of maneuverability, I'm fine with being able to turn around 180 degrees over the course of, say, 200 feet. Mostly I need to know how practical the rocket and turbofan designs are, and the finer points of making them work.

[Tvtyrant]

Couldn't you also combine Gust of Wind with the contraption to increase the pressure of the water as it goes through the maximized wall of fire?

[Godskook]

What kind of airship are you designing this for? A dogfighter or a freighter? If a dogfighter, are you shooting for a versatile bruiser(X-Wing), Heavy bomber(Y-Wing) or highly mobile skirmisher(A-Wing)? If a freighter, are we shooting for a small barricade runner(Millenium Falcon) or something bigger?

[Hirax]

Mordenkainen's capable caravel (Stormwrack). You can come up with the deckplan, so that grants some leeway in summoning the ship in a fashion that makes it engine ready, like there being an opening in the rudder to mount it to. Ideally I'd like to eliminate the need for masts. As far as function, just a mobile and replaceable base.

[DeAnno]

There's the nuke rocket approach for the particularly demanding applications (space travel mostly).

Set up a Wall of Force or similar on the back of your spaceship (and preferably all around it too). Stock a supply of correctly sized U-235 solid and hollow spheres, such that the solid sphere fits into the hollow and creates a critical mass when it does. Teleport a hollow sphere to directly behind your ship, then teleport a solid sphere inside of it. Upon placement, the spheres will explode with nuclear force and the momentum of the material that hits your spaceship will push it forward.

Of course that's pretty vague, and there are various things you might want to add or work out including but not limited to:
-Life Support
-Working out the targeting for your teleports, if you need LoS for some reason you may want to a drill small peekhole in each hollow sphere.
-Inertial Dampening, probably utilizing an extradimensional space of some kind
-Using magic (probably more traps) to create the spheres of Uranium while in transit
-Ability to place your nukes at further distances for weapons purposes
-The exact means of teleportation may be tricky, as teleporting objects without creatures is finicky at times
-You will probably want to either have means to turn your ship's blast surface around or just use any part of your ship for this so you can slow down or turn

[Radar]

I'm not looking for a high level of maneuverability, I'm fine with being able to turn around 180 degrees over the course of, say, 200 feet. Mostly I need to know how practical the rocket and turbofan designs are, and the finer points of making them work.
Well, I don't have engineering experiance, but both engines will be way too big and heavy to attach to a rudder. I would probably go with a rigid steamjet engine and put the rudder (frankly, something more akin to shutters) behind the engine to vector the thrust. This can give you solid horizontal steering.

[Hirax]

Well, I don't have engineering experiance, but both engines will be way too big and heavy to attach to a rudder. I would probably go with a rigid steamjet engine and put the rudder (frankly, something more akin to shutters at the end of the thruster) behind the engine to vector the thrust. This can give you solid horizontal steering.

A turbofan or rocket engine as I've described wouldn't need to be all that big, actually. The rocket could fit in a 5' cube, and the turbofan could would probably be 5' tall and 10' long, because you'd need one section for the chilling chamber and one for the fiery furnace, and 5' spaces are probably as small as you could go. They'd stick out, sure, but hardening would easily give the rudder the strength to support it. If that's practical, I also lack any engineering experience.

[Radar]

Heh, forgot about that part. :smalltongue:
There is another problem, if you put that much thrust on a movable rudder it will most likely be quite unstable: always trying to go left or right for pretty much the same reasons it's difficult to balance a pencil verticaly on your finger. You will have two forces applied so to say toward each other, so any deviation from a straight position will push it even further away.
You could fix that by inverting the rudder - put that big flap with engines in front of the axis (it will stabilise itself then). At any rate keep in mind, that the axis will have to be very strudy, since the whole thrust goes to ship through it.

edit:
Forgot about one thing: make sure you secure your engines with some solid spells and whatnot - otherwise they will be an easy target.

[Feralventas]

There's a much simpler method of putting an engine together that requires much less direct engineering. Take a look at the bound elementals from Eberron's setting; I've got a high level artifacer in one of my games that's using them as a main-stay method of powering complex machinery in combination with golem-based mechanics.

Set up an interior and exterior set of air-foils, bind half a dozen air-elementals to each, and have them channel the air over the airfoils so as to generate lift. Some bound fire-elementals should be able to generate some forward propulsion, though it might not be as fast as the Phantom Steed option noted earlier.

[Hirax]

Binding elementals is not cheap, and you're also tying them to one ship. Also, Eberron airships don't use elementals for lift, they only use them for propulsion. The soarwood gets the ship into the air all on its own, but without any steering or propulsion that's like releasing a balloon into the air.

[Demonic_Spoon]

I recall there being some sort of super starship engine somewhere in this (http://community.wizards.com/go/thread/view/75882/19872670/Broken_Super_Symmetry_in_an_Advanced_Theoretic_Gen eral_Relativistic_Interpretation_of?pg=1) thread.