how do these giant floating creatures get around? they must certainly have a way to achieve vertical motion.
our most basic flying machines are still modeled after avian structure and body mechanics, would your fictional flying folk not mimic the carnivorous flying creatures of their world?
edit:
i guess what i mean to say is, why would they have galleons at all when their more obvious solution to flight is right over their heads?
edit edit:
man, i didnt mean to sound like a dick there, or anything... my bad. i really like the idea of galleons coursing the tradewinds, but to me something doesnt click about it.
Edit: Since it's an enclosed world, I haven't quite figured out (ie, it just occured to me) how the people navigate without stars or planets or a moon to guide them. Perhaps they have evolved an innate sense of direction?
Almost missed this. Navigation requires knowing where you are and where that is in relation to where you want to be. You don't need stars for this; they're convenient, but other references (say landmarks) exist. You're limited in your desert or ocean travel unless you have decent clocks, some way of gauging speed, and a good way of orienting yourself (a compass might do if you've got a planetary magnetic field handy)...because either you know where you are, or you know where you've been and can estimate where you are by knowing which way you're going, for how long, and how fast. Hopefully your errors don't compound to the point where the spot you're headed for might be beyond the horizon once you get there.
Appropriate abundance of land with distinguishable landmarks would kind of get you around the problem altogether.
Also, I'm assuming that you have some kind of pseudo-sun on the enclosure, or the enclosed world will be boring indeed.
Sky navigation's only necessary in featureless terrain, as said - there's no significant open water, and it's fine to assume any desert is pretty much a deathtrap.
Even without stars (I was assuming the dome would be transparent, with a natural sky behind it, which would allow star navigation), the dome itself provides a sky to travel by, provided it's not entirely featureless. Damage, assembly seams, equipment if the dome somehow maintains the environment within. Even if the inhabitants don't fully understand the dome, plenty of things about it could provide fixed points of reference - since they don't move in relation to the ground, you can write off the need for accurate timekeeping, since the big scratch or the air vent of doom will always be seven miles east of the village or something to that effect.
Sky navigation's only necessary in featureless terrain, as said - there's no significant open water, and it's fine to assume any desert is pretty much a deathtrap.
Even without stars (I was assuming the dome would be transparent, with a natural sky behind it, which would allow star navigation), the dome itself provides a sky to travel by, provided it's not entirely featureless. Damage, assembly seams, equipment if the dome somehow maintains the environment within. Even if the inhabitants don't fully understand the dome, plenty of things about it could provide fixed points of reference - since they don't move in relation to the ground, you can write off the need for accurate timekeeping, since the big scratch or the air vent of doom will always be seven miles east of the village or something to that effect.
I wouldn't expect the dome to be visible or necessarily fixed with regard to the ground. There might not even be viscous coupling from the atmosphere if the dome is big enough.
OP must describe the dome for us now. I'm intrigued.
OP must describe the dome for us now. I'm intrigued.
I haven't been clear with my descriptions of this world. Spoilered for WOT. Ok. Not quite WOT... but spoilered anyway.
The setting is the future, at a time when the creation and cultivation of designer worlds filled with near-microscopic, intelligent, biological lifeforms has become a hobby akin to trainsets and aquariums. The worlds exist in hermetically sealed environments where everything, from life support, gravity and rainfall to night and day, is a value set by the owner and then controlled by a computer. Those outside these artificial worlds can watch what's going on inside via hidden cameras and through artificially intelligent nanobots disguised as the world's creatures. The nanobots also assist in fixing problems within the world, such as unintentional viral outbreaks and junk. The owners can also decide how advanced he wants any civilizations to become by restricting the availability of certain resources. Due to safety issues, the world government has enacted laws setting restrictions on what resources can be allowed in these artificial worlds. There are also rights groups lobbying to make the possession of these artificial worlds illegal and to bestow basic rights on those already existing. Of course, none of that is important to the story.
So, this entire story will take place in a world within a world. This particular world consists of a tree with continents and islands clinging to the branches. So, it's not spherical, the world is more or less vertical. There's an artificial sun and moon, and the "sky" is blue during the day and black at night... so the inhabitants are completely unaware of their situation.
Well, difficulties of having complex, intelligent microscopic life aside, you could fudge a lot of the problematic stuff with sufficiently low gravity and thick air.
I really do like the image I get of the canvas oars with the closing heads. An array of those on articulated arms, moving in a wave like motion give me nice images of some kind of swimming centipede or something.
I don't want to get too far off topic (please post more about this in Writer's Block!) but couldn't navigation be solved by assuming the owner of this world-in-a-jar has thought of this and provided an artifical starscape?
Gabriel_Pitt(effective against Russian warships)Registered Userregular
edited December 2008
If they're navigating an immense tree, landmarks would be much more useful than a starscape frequently occluded by intervening tree.
Anyways, as in most things, KISS will probably help you in this. If the skywhale's flotation bladder is neutrally buoyant, then the simplest and most efficient and rapid means of moving up, down, or any other direction quickly would directed jets of air (like the squid mentioned above). Since it'd be likely the airship designers would've tried taking a page from the airwhales to solve the ascent/descent problem, one of the simplest solutions (that incidentally invovles slave labor) would be large, possible pressurized bellows that would serve the same function.
I wouldn't say simplest, in implementation or effectiveness, but it does raise a point. If the airwhales are the only flying species (or if other flying species in the world-dome-thing operate on the same principle), it may be all the people know. Our flying machines mostly work on principles similar to birds because birds are what we know. We don't have neutrally boyant killer sky squid farting around in our atmosphere.
Well if you assume that these bladders are set up so that thier point of neutral bouyancy would be very high then they could simply use ballast to go up, and sails to go down(or maybe bellows to compress air?). Control surfaces to go up are impractical as the control surface has to provide lift for the whole ship. This could even be interesting from a combat perspective as a ship that runs out of ballast (probably sand) can now no longer go down very easily and could runaway like a submarine that goes to deep in reverse, instead of crush depth you'd have freeze depth or something. In fact the more i think about it I'd treat these things as submarines more than ships only everythings reversed.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
Well if you assume that these bladders are set up so that thier point of neutral bouyancy would be very high then they could simply use ballast to go up, and sails to go down(or maybe bellows to compress air?). Control surfaces to go up are impractical as the control surface has to provide lift for the whole ship. This could even be interesting from a combat perspective as a ship that runs out of ballast (probably sand) can now no longer go down very easily and could runaway like a submarine that goes to deep in reverse, instead of crush depth you'd have freeze depth or something. In fact the more i think about it I'd treat these things as submarines more than ships only everythings reversed.
Control surfaces work exactly the same both ways. Just because you slap one on doesn't mean the gas bag isn't generating lift anymore. Draw the free body diagram.
You don't need ballast, either, and especially not to go up. The ballast is the airship; it's full of slaves, for Christ's sake. It's heavy, just not quite as heavy as an equivalent volume of air. You can always vent the gas bag if you want to go down and recharge it with whatever low-density stuff you can procure (e.g. hot air) if you need to go up.
You're half-right about the submarine bit, but submarines use control surfaces just the same as airships, and tactically things about airship combat are quite different because, well, you can actually see each other. By OP's descriptions I doubt anything more than arrows are in common usage, and...well, I'm having trouble imagining what airships raining arrows upon each other would be like. I'm guessing the highest one would generally win.
Well if you assume that these bladders are set up so that thier point of neutral bouyancy would be very high then they could simply use ballast to go up, and sails to go down(or maybe bellows to compress air?). Control surfaces to go up are impractical as the control surface has to provide lift for the whole ship. This could even be interesting from a combat perspective as a ship that runs out of ballast (probably sand) can now no longer go down very easily and could runaway like a submarine that goes to deep in reverse, instead of crush depth you'd have freeze depth or something. In fact the more i think about it I'd treat these things as submarines more than ships only everythings reversed.
Control surfaces work exactly the same both ways. Just because you slap one on doesn't mean the gas bag isn't generating lift anymore. Draw the free body diagram.
You don't need ballast, either, and especially not to go up. The ballast is the airship; it's full of slaves, for Christ's sake. It's heavy, just not quite as heavy as an equivalent volume of air. You can always vent the gas bag if you want to go down and recharge it with whatever low-density stuff you can procure (e.g. hot air) if you need to go up.
You're half-right about the submarine bit, but submarines use control surfaces just the same as airships, and tactically things about airship combat are quite different because, well, you can actually see each other. By OP's descriptions I doubt anything more than arrows are in common usage, and...well, I'm having trouble imagining what airships raining arrows upon each other would be like. I'm guessing the highest one would generally win.
Sorry i didn't articulate very well what I was saying. A lifting body wouldn't be very effective without some pretty major forward motion, you won't be able to get it with people just pedaling/rowing you could depend on the wind to provide lift but boy is that going to be a rough ride on something that big. sure you have the lift of the gas bag but as soon as you stop moving forward your going to go back to your neutral buoyancy point. From what it sounds like you want to be able to perform radical shifts in altitude to get to higher branches, but not have to significantly increase your airspeed to do so(i.e. tire out your slaves) Ballast at least lets you set your neutral buoyancy altitude point, kind of like a trim tab. A submarine does use control surfaces, but radical shifts in altitude are done via ballast control.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
But I guess I see what you're saying. Make the ship depart with the biggest specific volume possible and then you can drop to your destination by venting.
And yeah, the altitude differential you'll get from a lifting surface is limited. I'm honestly not sure how limited, though; thousands of feet is probably on the outside and hundreds more believable. Now I need to go look and see if Hindenberg was pressurized (don't think so) and what altitude it cruised at.
This would be the best rpg setting, and this thread is all kinds of intresting. A make fictional stuff realistic thread would be pretty fun.
Also, to actually add to the discussion, are the squid the only flying life forms? Do regular birds exist? And what kind if gas are we talking about? If it's flammable I imagine flaming arrows would be the order of the day for combat. And are there smaller vessel? For some reason I have this vision of guys in davinci style flying machines gliding around flinging arrows like some bizzare medieval fighter plane.
Nah, there are birds and also smaller animals that have the same flight mechanisms as the giant squid. The areas surrounding each continent and island are in a sense the ocean; it's a major source of food and it's home to a large assortment of creatures. I haden't thought of it, but there actually could be smaller boats and skiffs and junk.
The gas isn't flammable, but it is toxic in large doses. Since the squid (still haven't thought of a name) have neared extinction, ship to ship warfare is generally a game of boarding and capturing. Only in dire circumstances or special situations do captains opt to destroy a ship and it's gas bag.
I'm thinking grappling hooks and extendable bridges for boarding ships. But, hell, there could be marines with gas bag backpacks and canvas flippers too, I suppose.
Ballast at least lets you set your neutral buoyancy altitude point, kind of like a trim tab. A submarine does use control surfaces, but radical shifts in altitude are done via ballast control.
I can't quite picture how this ballast would function. I keep imagining the accordian style thing my dad had by the fireplace.
Ballast is just dead weight to keep a ship trim in the water, or a submarine submerged. Most large commercial ships and submarines use water as ballast.
In the case of commercial ships, they take it on to compensate when they don't have cargo to act as ballast to stop them sitting to high in the water and expel it when they do have large amounts of cargo to stop them sitting too low.
Submarines take on water to submerge (and usually to adjust trim at the front and rear of the submarine to keep it level). They expel it using compressed air to resurface.
Airships would also use ballast to equalise their buoyancy. Hot air balloons traditionally have sandbags strapped to the basket, which dapper chaps ditch in rather of a panic when they run out of hot air and are in terrible danger of clipping the church spire what what.
I can't remember what those accordion things for fires are called, but I don't think they are called ballasts. Either way, not the same thing.
The problem with dropping ballast to adjust altitude in air travel is that it's a once-per-flight deal. Once you drop it, you can't get it back. A submarine or ship can take on more water, but airships don't have many ways of picking up mass mid-flight. So, in a pinch you might regret not having it, but using it for any altitude change that could easily be done more slowly by normal means might prove short-sighted.
Since the Hindenburg's been mentioned a lot in this thread, it had troughs for collecting rainwater which it used as ballast, but it does have the disadvantage that you have to be in rain to refill your tanks, and even non-flammable airships generally don't like bad weather, as it takes a very small amount of damage to bring them down.
The problem with dropping ballast to adjust altitude in air travel is that it's a once-per-flight deal. Once you drop it, you can't get it back. A submarine or ship can take on more water, but airships don't have many ways of picking up mass mid-flight. So, in a pinch you might regret not having it, but using it for any altitude change that could easily be done more slowly by normal means might prove short-sighted.
Since the Hindenburg's been mentioned a lot in this thread, it had troughs for collecting rainwater which it used as ballast, but it does have the disadvantage that you have to be in rain to refill your tanks, and even non-flammable airships generally don't like bad weather, as it takes a very small amount of damage to bring them down.
Right which is why I was thinking Ballast would almost be your fuel. Raid another ship take it's ballast, leave those bastards floating up into the atmosphere until they freeze or asphyxiate. I mean is someones trying to board you drop some ballast and get above them. but it's a game how much ballast can I drop Before I can'y use sails and such to drop back down to my landing altitude.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
Right which is why I was thinking Ballast would almost be your fuel. Raid another ship take it's ballast, leave those bastards floating up into the atmosphere until they freeze or asphyxiate. I mean is someones trying to board you drop some ballast and get above them. but it's a game how much ballast can I drop Before I can'y use sails and such to drop back down to my landing altitude.
This is an airship, not a weather balloon. It is way too heavy to go that high. It is far easier to increase your density by venting gas instead of adding weight. Which you can always do.
This is me being an asshole, but in any place with gravity, you can ALWAYS GO DOWN. Your visions of aerial combat where people are exiled to the heavens to die are ridiculous. So much so that I ridicule them. Right now. Ridicule ridicule. See?
@OP: non-flammable but toxic gas? Dubious. We fly airships on either hydrogen or helium for good reasons.
Right which is why I was thinking Ballast would almost be your fuel. Raid another ship take it's ballast, leave those bastards floating up into the atmosphere until they freeze or asphyxiate. I mean is someones trying to board you drop some ballast and get above them. but it's a game how much ballast can I drop Before I can'y use sails and such to drop back down to my landing altitude.
This is an airship, not a weather balloon. It is way too heavy to go that high. It is far easier to increase your density by venting gas instead of adding weight. Which you can always do.
This is me being an asshole, but in any place with gravity, you can ALWAYS GO DOWN. Your visions of aerial combat where people are exiled to the heavens to die are ridiculous. So much so that I ridicule them. Right now. Ridicule ridicule. See?
@OP: non-flammable but toxic gas? Dubious. We fly airships on either hydrogen or helium for good reasons.
You missed the part where he said they couldn't make more of the lighter than air gas and the creatures they got them from went extinct, and if you think it's impossible for a Dirigable to go above the altitude of Hypoxia Then I will return the redicule.
Edit:: Actually I stand corrected, while being unable to vent the max altitude is about 8,000 ft
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
You missed the part where he said they couldn't make more of the lighter than air gas and the creatures they got them from went extinct, and if you think it's impossible for a Dirigable to go above the altitude of Hypoxia Then I will return the redicule.
I don't care if they can't make more of it. Buoyancy follows pretty strict guidelines and you don't want to use heavy compounds as a lifting gas. Hell, helium has twice the atomic weight of molecular hydrogen.
Here's another interesting thing: on one of the Hindenberg's transatlantic journeys, they lost a couple engines and started to look for favorable winds at altitude. They thought there might be some at 5000 feet, but they couldn't get that high. If you get hypoxia below 5,000 feet you have serious problems.
I mean, just think about it. Can you get a gas bag up to high altitudes? Sure. But why bother? You'd need a gigantic envelope and people freeze to death and suffocate up there! Instead, why don't you chuff around at low altitudes, where the air is nice and dense, nobody's dying...
See where I'm going with this? Going up is the hard part. No one in OP's universe need fear rapid ascent and demise unless they're tied to the airship envelope while the whole rest of the airship fall off.
You missed the part where he said they couldn't make more of the lighter than air gas and the creatures they got them from went extinct, and if you think it's impossible for a Dirigable to go above the altitude of Hypoxia Then I will return the redicule.
I don't care if they can't make more of it. Buoyancy follows pretty strict guidelines and you don't want to use heavy compounds as a lifting gas. Hell, helium has twice the atomic weight of molecular hydrogen.
Here's another interesting thing: on one of the Hindenberg's transatlantic journeys, they lost a couple engines and started to look for favorable winds at altitude. They thought there might be some at 5000 feet, but they couldn't get that high. If you get hypoxia below 5,000 feet you have serious problems.
I mean, just think about it. Can you get a gas bag up to high altitudes? Sure. But why bother? You'd need a gigantic envelope and people freeze to death and suffocate up there! Instead, why don't you chuff around at low altitudes, where the air is nice and dense, nobody's dying...
See where I'm going with this? Going up is the hard part. No one in OP's universe need fear rapid ascent and demise unless they're tied to the airship envelope while the whole rest of the airship fall off.
Yes but Hindenberg could vent gas to increase bouyancy. If I've understood correctly the bouyancy of the gas bag in this world is fixed, you cannot increase it. If this is the case then I would design my ship to naturally sit at a higher altitude for maximum manuverability in the vertical direction, but that's just me. And I agree the ships that I've read about going above 15K ft altitudes were able to bled off air from thier gas bags. So in these cases Hypopxia will not set in.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
You vent gas to decrease buoyancy. Increase density, decrease buoyancy.
There's just not a lot of reason to want to airship your way up into the hypoxia levels. It gets cold. The air gets thin. Most importantly, it's harder to drag mass that high, and that's really what OP wants to do.
What about mechanical compression of the gas bag? I have no idea if this is at all reasonable, but what if they had like, a netting around it on winches that they cranked to squeeze it, increasing it's density? The squid could accomplish the same thing with muscles.
Also I love how we just keep saying gasbag.
edit: On second thought that idea just seems silly and like it wouldn't work. One of you more physicsy folk confirm?
Tofystedeth on
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Blake TDo you have enemies then?Good. That means you’ve stood up for something, sometime in your life.Registered Userregular
edited December 2008
If you are trying to make the bags somewhat biological, make the bags surrounded by rigid "arms" that can move so the bag can stretch so it is bigger or smaller. While you can change the size the mass you will be changing to overall density of the volume which will account for vertical displacement.
If they are whales just stick huge arse tails on them to provide thrust.
You vent gas to decrease buoyancy. Increase density, decrease buoyancy.
There's just not a lot of reason to want to airship your way up into the hypoxia levels. It gets cold. The air gets thin. Most importantly, it's harder to drag mass that high, and that's really what OP wants to do.
Ummm no actually. When you get to a high enough altitude you start venting Air out of your gas bladder to let the helium expand more, then eventually you actually have to vent helium, as the weight of the helium starts keeping you down. My first project ever was working on High Altitude Airships, they can be pretty counter intuitive. Your right though you would never want to design an airship to go that high, if however there is enough buoyancy in your unventable gas bladder you don't have much of a choice. As I admitted however you can't get as high as I thought without a venting mechanism rendering the discussion pointless.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
Oh, I think I see why you're venting gas like that at high altitude--your envelope can stay expanded without as much gas, so venting allows you to rise.
I'm not going to run the numbers or anything but I bet the benefit of doing that for OP is lesser just because you're not going as high, so the pressure is still relatively high and you can't vent as much mass.
Oh, I think I see why you're venting gas like that at high altitude--your envelope can stay expanded without as much gas, so venting allows you to rise.
I'm not going to run the numbers or anything but I bet the benefit of doing that for OP is lesser just because you're not going as high, so the pressure is still relatively high and you can't vent as much mass.
It actually becomes critical in any blimp/semi-rigid airship. Since the entire structure of your Airship depends on the Volume of your bag holding constant at low altitudes you must be able to pump air in to hold the bag rigid. The whole point of a semi rigid airship is to increase the payload capacity by making the bag a crucial part of the structure. If the bag deflates the ship falls apart, for extremely high altitude airships though you have to design them this way because you cannot afford the structural weight a rigid airship requires. I had my number mixed up though, a rigid airship will get you up to about 8000 ft on the high end wheras a semi-rigid can get you up to 24,000 ft (at least thats the current record) Airships are actually pretty cool I was amazed at the increadibly high technology involved in building one, and how dangerous they are to operate.
Mishra on
"Give a man a fire, he's warm for the night. Set a man on fire he's warm for the rest of his life."
-Terry Pratchett
i guess what i mean to say is, why would they have galleons at all when their more obvious solution to flight is right over their heads?
If there are no major bodies of water in the world, then where did the galleon-esque design of these airships' passenger & crew spaces come from? That's important to SOD. Were they left over from days of yore when there were oceans, and someone took 'the last ship' out of a museum, cut the masts off, and tied it to an air bladder (where'd they get that idea)? Don't forget to explain the origin of the galleon component if there haven't been major waterways in years.
Also, another propulsion and control option that hasn't come up yet:
Some ships could do away completely with the galleon hull below, have platform/walkways and rope ladders all around the air bladder (maybe a small enclosed compartment or two, like the Goodyear blimp), and the crew/slaves use these to climb around and operate sails. Sails that open on all four sides of the ship (top, bottom, left, right). They could open and close like an antique hand fan, and/or pivot in different directions, to take full advantage of wind and create differences in top/bottom/left/right thrust that would be used to change headings.
What about mechanical compression of the gas bag? I have no idea if this is at all reasonable, but what if they had like, a netting around it on winches that they cranked to squeeze it, increasing it's density? The squid could accomplish the same thing with muscles.
Also I love how we just keep saying gasbag.
edit: On second thought that idea just seems silly and like it wouldn't work. One of you more physicsy folk confirm?
By squeezing the bag together you would increase the density of the gas, but decrease the volume of the bag, meaning the overall density wouldn't change.
i guess what i mean to say is, why would they have galleons at all when their more obvious solution to flight is right over their heads?
If there are no major bodies of water in the world, then where did the galleon-esque design of these airships' passenger & crew spaces come from? That's important to SOD. Were they left over from days of yore when there were oceans, and someone took 'the last ship' out of a museum, cut the masts off, and tied it to an air bladder (where'd they get that idea)? Don't forget to explain the origin of the galleon component if there haven't been major waterways in years.
Also, another propulsion and control option that hasn't come up yet:
Some ships could do away completely with the galleon hull below, have platform/walkways and rope ladders all around the air bladder (maybe a small enclosed compartment or two, like the Goodyear blimp), and the crew/slaves use these to climb around and operate sails. Sails that open on all four sides of the ship (top, bottom, left, right). They could open and close like an antique hand fan, and/or pivot in different directions, to take full advantage of wind and create differences in top/bottom/left/right thrust that would be used to change headings.
There's a reason why in blimps the gondola is always at the very bottom. The further below your center of buoyancy you center of mass is, the more stable the ship is. If the center of mass is very close to or at the center of buoyancy, you're going to the rolling/tilting the blimp at the slightest wind.
Yeah, I didn't mean the gondola would work on the sides or top - just that the gondola doesn't need to consist of the Santa Maria dangling below; it could be something less.. nautical.
What about mechanical compression of the gas bag? I have no idea if this is at all reasonable, but what if they had like, a netting around it on winches that they cranked to squeeze it, increasing it's density? The squid could accomplish the same thing with muscles.
Also I love how we just keep saying gasbag.
edit: On second thought that idea just seems silly and like it wouldn't work. One of you more physicsy folk confirm?
By squeezing the bag together you would increase the density of the gas, but decrease the volume of the bag, meaning the overall density wouldn't change.
??? You've got the same amount of gas in a smaller space. Density's gone up. That's the definition of compression.
Posts
our most basic flying machines are still modeled after avian structure and body mechanics, would your fictional flying folk not mimic the carnivorous flying creatures of their world?
edit:
i guess what i mean to say is, why would they have galleons at all when their more obvious solution to flight is right over their heads?
edit edit:
man, i didnt mean to sound like a dick there, or anything... my bad. i really like the idea of galleons coursing the tradewinds, but to me something doesnt click about it.
Almost missed this. Navigation requires knowing where you are and where that is in relation to where you want to be. You don't need stars for this; they're convenient, but other references (say landmarks) exist. You're limited in your desert or ocean travel unless you have decent clocks, some way of gauging speed, and a good way of orienting yourself (a compass might do if you've got a planetary magnetic field handy)...because either you know where you are, or you know where you've been and can estimate where you are by knowing which way you're going, for how long, and how fast. Hopefully your errors don't compound to the point where the spot you're headed for might be beyond the horizon once you get there.
Appropriate abundance of land with distinguishable landmarks would kind of get you around the problem altogether.
Also, I'm assuming that you have some kind of pseudo-sun on the enclosure, or the enclosed world will be boring indeed.
Even without stars (I was assuming the dome would be transparent, with a natural sky behind it, which would allow star navigation), the dome itself provides a sky to travel by, provided it's not entirely featureless. Damage, assembly seams, equipment if the dome somehow maintains the environment within. Even if the inhabitants don't fully understand the dome, plenty of things about it could provide fixed points of reference - since they don't move in relation to the ground, you can write off the need for accurate timekeeping, since the big scratch or the air vent of doom will always be seven miles east of the village or something to that effect.
I wouldn't expect the dome to be visible or necessarily fixed with regard to the ground. There might not even be viscous coupling from the atmosphere if the dome is big enough.
OP must describe the dome for us now. I'm intrigued.
I haven't been clear with my descriptions of this world. Spoilered for WOT. Ok. Not quite WOT... but spoilered anyway.
So, this entire story will take place in a world within a world. This particular world consists of a tree with continents and islands clinging to the branches. So, it's not spherical, the world is more or less vertical. There's an artificial sun and moon, and the "sky" is blue during the day and black at night... so the inhabitants are completely unaware of their situation.
I really do like the image I get of the canvas oars with the closing heads. An array of those on articulated arms, moving in a wave like motion give me nice images of some kind of swimming centipede or something.
Anyways, as in most things, KISS will probably help you in this. If the skywhale's flotation bladder is neutrally buoyant, then the simplest and most efficient and rapid means of moving up, down, or any other direction quickly would directed jets of air (like the squid mentioned above). Since it'd be likely the airship designers would've tried taking a page from the airwhales to solve the ascent/descent problem, one of the simplest solutions (that incidentally invovles slave labor) would be large, possible pressurized bellows that would serve the same function.
-Terry Pratchett
Control surfaces work exactly the same both ways. Just because you slap one on doesn't mean the gas bag isn't generating lift anymore. Draw the free body diagram.
You don't need ballast, either, and especially not to go up. The ballast is the airship; it's full of slaves, for Christ's sake. It's heavy, just not quite as heavy as an equivalent volume of air. You can always vent the gas bag if you want to go down and recharge it with whatever low-density stuff you can procure (e.g. hot air) if you need to go up.
You're half-right about the submarine bit, but submarines use control surfaces just the same as airships, and tactically things about airship combat are quite different because, well, you can actually see each other. By OP's descriptions I doubt anything more than arrows are in common usage, and...well, I'm having trouble imagining what airships raining arrows upon each other would be like. I'm guessing the highest one would generally win.
Sorry i didn't articulate very well what I was saying. A lifting body wouldn't be very effective without some pretty major forward motion, you won't be able to get it with people just pedaling/rowing you could depend on the wind to provide lift but boy is that going to be a rough ride on something that big. sure you have the lift of the gas bag but as soon as you stop moving forward your going to go back to your neutral buoyancy point. From what it sounds like you want to be able to perform radical shifts in altitude to get to higher branches, but not have to significantly increase your airspeed to do so(i.e. tire out your slaves) Ballast at least lets you set your neutral buoyancy altitude point, kind of like a trim tab. A submarine does use control surfaces, but radical shifts in altitude are done via ballast control.
-Terry Pratchett
But I guess I see what you're saying. Make the ship depart with the biggest specific volume possible and then you can drop to your destination by venting.
And yeah, the altitude differential you'll get from a lifting surface is limited. I'm honestly not sure how limited, though; thousands of feet is probably on the outside and hundreds more believable. Now I need to go look and see if Hindenberg was pressurized (don't think so) and what altitude it cruised at.
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Also, to actually add to the discussion, are the squid the only flying life forms? Do regular birds exist? And what kind if gas are we talking about? If it's flammable I imagine flaming arrows would be the order of the day for combat. And are there smaller vessel? For some reason I have this vision of guys in davinci style flying machines gliding around flinging arrows like some bizzare medieval fighter plane.
The gas isn't flammable, but it is toxic in large doses. Since the squid (still haven't thought of a name) have neared extinction, ship to ship warfare is generally a game of boarding and capturing. Only in dire circumstances or special situations do captains opt to destroy a ship and it's gas bag.
I'm thinking grappling hooks and extendable bridges for boarding ships. But, hell, there could be marines with gas bag backpacks and canvas flippers too, I suppose.
I can't quite picture how this ballast would function. I keep imagining the accordian style thing my dad had by the fireplace.
In the case of commercial ships, they take it on to compensate when they don't have cargo to act as ballast to stop them sitting to high in the water and expel it when they do have large amounts of cargo to stop them sitting too low.
Submarines take on water to submerge (and usually to adjust trim at the front and rear of the submarine to keep it level). They expel it using compressed air to resurface.
Airships would also use ballast to equalise their buoyancy. Hot air balloons traditionally have sandbags strapped to the basket, which dapper chaps ditch in rather of a panic when they run out of hot air and are in terrible danger of clipping the church spire what what.
I can't remember what those accordion things for fires are called, but I don't think they are called ballasts. Either way, not the same thing.
The problem with dropping ballast to adjust altitude in air travel is that it's a once-per-flight deal. Once you drop it, you can't get it back. A submarine or ship can take on more water, but airships don't have many ways of picking up mass mid-flight. So, in a pinch you might regret not having it, but using it for any altitude change that could easily be done more slowly by normal means might prove short-sighted.
Since the Hindenburg's been mentioned a lot in this thread, it had troughs for collecting rainwater which it used as ballast, but it does have the disadvantage that you have to be in rain to refill your tanks, and even non-flammable airships generally don't like bad weather, as it takes a very small amount of damage to bring them down.
Right which is why I was thinking Ballast would almost be your fuel. Raid another ship take it's ballast, leave those bastards floating up into the atmosphere until they freeze or asphyxiate. I mean is someones trying to board you drop some ballast and get above them. but it's a game how much ballast can I drop Before I can'y use sails and such to drop back down to my landing altitude.
-Terry Pratchett
This is an airship, not a weather balloon. It is way too heavy to go that high. It is far easier to increase your density by venting gas instead of adding weight. Which you can always do.
This is me being an asshole, but in any place with gravity, you can ALWAYS GO DOWN. Your visions of aerial combat where people are exiled to the heavens to die are ridiculous. So much so that I ridicule them. Right now. Ridicule ridicule. See?
@OP: non-flammable but toxic gas? Dubious. We fly airships on either hydrogen or helium for good reasons.
You missed the part where he said they couldn't make more of the lighter than air gas and the creatures they got them from went extinct, and if you think it's impossible for a Dirigable to go above the altitude of Hypoxia Then I will return the redicule.
Edit:: Actually I stand corrected, while being unable to vent the max altitude is about 8,000 ft
-Terry Pratchett
I don't care if they can't make more of it. Buoyancy follows pretty strict guidelines and you don't want to use heavy compounds as a lifting gas. Hell, helium has twice the atomic weight of molecular hydrogen.
Here's another interesting thing: on one of the Hindenberg's transatlantic journeys, they lost a couple engines and started to look for favorable winds at altitude. They thought there might be some at 5000 feet, but they couldn't get that high. If you get hypoxia below 5,000 feet you have serious problems.
I mean, just think about it. Can you get a gas bag up to high altitudes? Sure. But why bother? You'd need a gigantic envelope and people freeze to death and suffocate up there! Instead, why don't you chuff around at low altitudes, where the air is nice and dense, nobody's dying...
See where I'm going with this? Going up is the hard part. No one in OP's universe need fear rapid ascent and demise unless they're tied to the airship envelope while the whole rest of the airship fall off.
Yes but Hindenberg could vent gas to increase bouyancy. If I've understood correctly the bouyancy of the gas bag in this world is fixed, you cannot increase it. If this is the case then I would design my ship to naturally sit at a higher altitude for maximum manuverability in the vertical direction, but that's just me. And I agree the ships that I've read about going above 15K ft altitudes were able to bled off air from thier gas bags. So in these cases Hypopxia will not set in.
-Terry Pratchett
There's just not a lot of reason to want to airship your way up into the hypoxia levels. It gets cold. The air gets thin. Most importantly, it's harder to drag mass that high, and that's really what OP wants to do.
Also I love how we just keep saying gasbag.
edit: On second thought that idea just seems silly and like it wouldn't work. One of you more physicsy folk confirm?
If they are whales just stick huge arse tails on them to provide thrust.
Satans..... hints.....
Ummm no actually. When you get to a high enough altitude you start venting Air out of your gas bladder to let the helium expand more, then eventually you actually have to vent helium, as the weight of the helium starts keeping you down. My first project ever was working on High Altitude Airships, they can be pretty counter intuitive. Your right though you would never want to design an airship to go that high, if however there is enough buoyancy in your unventable gas bladder you don't have much of a choice. As I admitted however you can't get as high as I thought without a venting mechanism rendering the discussion pointless.
-Terry Pratchett
I'm not going to run the numbers or anything but I bet the benefit of doing that for OP is lesser just because you're not going as high, so the pressure is still relatively high and you can't vent as much mass.
It actually becomes critical in any blimp/semi-rigid airship. Since the entire structure of your Airship depends on the Volume of your bag holding constant at low altitudes you must be able to pump air in to hold the bag rigid. The whole point of a semi rigid airship is to increase the payload capacity by making the bag a crucial part of the structure. If the bag deflates the ship falls apart, for extremely high altitude airships though you have to design them this way because you cannot afford the structural weight a rigid airship requires. I had my number mixed up though, a rigid airship will get you up to about 8000 ft on the high end wheras a semi-rigid can get you up to 24,000 ft (at least thats the current record) Airships are actually pretty cool I was amazed at the increadibly high technology involved in building one, and how dangerous they are to operate.
-Terry Pratchett
If there are no major bodies of water in the world, then where did the galleon-esque design of these airships' passenger & crew spaces come from? That's important to SOD. Were they left over from days of yore when there were oceans, and someone took 'the last ship' out of a museum, cut the masts off, and tied it to an air bladder (where'd they get that idea)? Don't forget to explain the origin of the galleon component if there haven't been major waterways in years.
Also, another propulsion and control option that hasn't come up yet:
Some ships could do away completely with the galleon hull below, have platform/walkways and rope ladders all around the air bladder (maybe a small enclosed compartment or two, like the Goodyear blimp), and the crew/slaves use these to climb around and operate sails. Sails that open on all four sides of the ship (top, bottom, left, right). They could open and close like an antique hand fan, and/or pivot in different directions, to take full advantage of wind and create differences in top/bottom/left/right thrust that would be used to change headings.
By squeezing the bag together you would increase the density of the gas, but decrease the volume of the bag, meaning the overall density wouldn't change.
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There's a reason why in blimps the gondola is always at the very bottom. The further below your center of buoyancy you center of mass is, the more stable the ship is. If the center of mass is very close to or at the center of buoyancy, you're going to the rolling/tilting the blimp at the slightest wind.
PSN/XBL: dragoniemx
??? You've got the same amount of gas in a smaller space. Density's gone up. That's the definition of compression.