# Technicalities of Airships



## Gryphos (Oct 28, 2014)

Very early on in the world-building process of my story I decided that airships would be a very prominent aspect of my world. The 'Aerial Revolution', well, revolutionised how the world worked, with fast and reliable transportation across any terrain and a new dimension in which to wage war.

When I originally decided to have airships I also decided that they were going to be very different from real life zeppelins. I wanted them to be smaller and have the gondola be suspended beneath the balloon, and the ship be propelled and steered by propellers.

Basically, I wanted my airships to be like this:







Only recently have I been forced to really come up with the details of how airships operate, and consider all kinds of crazy things.

So, with the balloon so small in proportion to the hull compared to real life, I decided that I wasn't going to use any real world gas as the lifting agent. So I made up a gas which for the time being I'm calling _aerithium_. Aerithium is a non-combustible gas with tremendous amounts of lift, allowing the balloons to be a lot smaller. The balloons would also be compartmented so if there's a hole the entire ship won't go down.

So that's how the ship stays up, sounds good. But how does it come back down again? Well, I thought that, so long as the lift of the gas and the weight of the ship's load are in equilibrium, the ship could be made to rise and fall through use of vertical mounted propellers on the sides of the ship. Meanwhile horizontal mounted propellers on the stern move the ship horizontally. (Yes, I know how zeppelins corrected altitude in real life, with air intake and whatnot, but because of the reduced size of my airship balloons, that won't work here)

But then I realised, for that to work the ship's load weight must be kept constant, but with passengers boarding and leaving and cargo being loaded and unloaded, the weight's going to be changing a lot. So perhaps then it's possible for the crew to alter the amount of gas in the balloon. Letting gas loose to account for loss of weight would be simple enough, but what about when you're gaining weight? There would definitely be pumping stations at docks, but when not docked I'm not entirely sure what they'd do. One option is to just jettison stuff of equal weight to what you've gained, but that might not always be possible.

So I had another idea, something I'm calling aerithium bricks. On ships they would have stores of aerithium bricks which, when burned inside a special compartment, will break down into aerithium and fill the balloon. The brick doesn't need to be pure solid aerithium or anything like that, probably just some kind of compound. But even so, I don't know a huge amount about physics, so it's possible that might not be a sound idea.

So what have I missed? What have I failed to consider? Also, how equal must the lift and weight be in order for the propellers to be able to control altitude? Will it need to come down to a single kilogram or is there a bit of leeway?


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## CupofJoe (Oct 28, 2014)

There is a thing called the hybrid airship. Roughly it is a huge aerofoil and the airship is flown up and down with the usual aircraft controls. From what I remember, they are very slightly negatively buoyant, so if left to their own will sink gently to the ground, but if you drive them forward the aerofoil generates lift and the thing takes off and you don't have to be going too fast.
You would still have to be somewhat careful about the weight but it wouldn't supercritical unless you were at the extremes of what the aerofoil could cope with.
Here is a company SkyCat that is trying to sell the idea.


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## Devor (Oct 28, 2014)

Physics is by far my worst subject, so I hope someone will correct me if I'm wrong.  But it's my impression that a stable weight, and a stable amount of gas, would result in a specific altitude where the two equalize with the atmospheric pressure.  So to go up ten feet, you need to add a little gas.  To go down ten feet, add a little weight or remove a little gas.  There's no level where it hovers, and you can just pull it up or down and have it hover at that altitude.

That said, simply having the balloon, and using your gas bricks as fuel, should be fine.  And there's absolutely no reason small balloons means you can't release gases and have it work just like a zeppelin - especially as, realistically, it could be several small balloons _inside_ a larger one, so that if the outer one popped, you still have the inner ones.  The outer balloon might even be mostly a protective frame, but it might still have mechanisms for releasing the gases.  Also, the lift might be dependent on the heat of the gas, giving pilots yet another mechanisms for adjusting the ship's movements.

If you're looking at any kind of combat or fast maneuvering, I think propellers could still be pretty cool.  You need to get out of the way, or ram another ship, then turn on the propellers for that quick boost to one side.  I don't think I would use propellers for regular movements, though.  Too many propellers and you might question the need for a balloon.

Come to think of it, you could also consider the use of a sail, especially if it was attached to that outer frame of the balloons I mentioned or to the sides and underbelly of the ship.  Sails don't get you up, but they do look cool and move you forward.  I have no idea how the speed of a sail might compare to the air release mechanisms of a zeppelin.  But if they're not faster, they could work as a backup if those fuel bricks are scarce or expensive.


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## Penpilot (Oct 28, 2014)

I think your basic idea is sound. I have a background in science. It's computer science, but I had to take a lot of chemistry, and physics etc, and it doesn't ring false to me. I'm no expert, but I think that's the point. Unless, an expert picks your idea apart, I don't think the average reader is going to pause during reading and say to themselves, "Hey that doesn't make sense at all."

I think you've thought out the idea well enough and taken it to a point to where the rest can be handwaved away.


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## BronzeOracle (Oct 28, 2014)

Haha brings back memories of Castle in the Sky Laputa - gotta love those big flying ships!  Wow, sails on an airship what a great idea Devor.  Devor's description sounds right - its about the buoyancy you have that determines your altitude (think of the smoke of forest fires that plateaus/mushrooms out at a certain altitude) and you can control that solely with the amount of gas, its similar to a hot air balloon or to scuba diving, in each case you have set weights. 

Another thing you could consider Gryphos would be exotic/magical hull materials that are light weight, and the use of jet propulsion for fast manoeuvres - depending on how far you want to extend your technology.


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## Gryphos (Oct 29, 2014)

Alright, so to be clear, my idea of there being a lift/weight equilibrium and the ship being made to rise or fall by propellers will not work, and you can only change altitude by changing gas levels?


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## BronzeOracle (Oct 29, 2014)

Well you can get propellers generating lift if they spin on a vertical axis (like a helicopter's) so yes it could work with a lift/weight equilibrium and using propellers to rise/fall - but you'd need to still control the gas to keep the buoyancy equal to the air density as you go up or down by a substantial distance and the air density changes - ie you need to add more 'light' gas the higher you go up - otherwise the propellers would need to work much harder to keep the airship up.  It would be like being weighed down with stacks of weights while you are scuba diving - yes you can stay at your position by paddling down with your flippers but its harder work, you're using mechanical power rather than bouyancy to remain at your elevation.  Modern helium blimps do use propellers that can rotate so they can point upwards to give lift, but I understand they also use gas/weights so that the propellers are used mostly for manoeuvring rather than a major lift force.


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## Gryphos (Oct 29, 2014)

Devor said:
			
		

> Come to think of it, you could also consider the use of a sail, especially if it was attached to that outer frame of the balloons I mentioned or to the sides and underbelly of the ship. Sails don't get you up, but they do look cool and move you forward. I have no idea how the speed of a sail might compare to the air release mechanisms of a zeppelin. But if they're not faster, they could work as a backup if those fuel bricks are scarce or expensive.



Sail-powered airships do sound pretty call, and in a way I could make that work as a kind of emergency protocol. Say an airships runs out of fuel mid-flight, if they had sail mechanisms stored in their ship somehow they could set some sails up and fly back to civilisation using the wind.



			
				BronzeOracle said:
			
		

> Another thing you could consider Gryphos would be exotic/magical hull materials that are light weight, and the use of jet propulsion for fast manoeuvres - depending on how far you want to extend your technology.



I was thinking the ships' hulls would mainly be made out of wood with some kind of structural metal skeleton, at least for civilian ships. For military ones they'd probably be made out of a fairly lightweight metal and maybe even have an armour-plated balloon. As for the jets, I can't really see that working in the kind of steampunkesque setting I've created.



			
				BronzeOracle said:
			
		

> Well you can get propellers generating lift if they spin on a vertical axis (like a helicopter's) so yes it could work with a lift/weight equilibrium and using propellers to rise/fall - but you'd need to still control the gas to keep the buoyancy equal to the air density as you go up or down by a substantial distance and the air density changes - ie you need to add more 'light' gas the higher you go up - otherwise the propellers would need to work much harder to keep the airship up.  It would be like being weighed down with stacks of weights while you are scuba diving - yes you can stay at your position by paddling down with your flippers but its harder work, you're using mechanical power rather than bouyancy to remain at your elevation.  Modern helium blimps do use propellers that can rotate so they can point upwards to give lift, but I understand they also use gas/weights so that the propellers are used mostly for manoeuvring rather than a major lift force.



Ah, I see, that does make sense. So basically my airships could operate altitude using only the propellers, but upon rising or falling a great enough distance for there to be a considerable change in air density, they would need to be permanently spinning to maintain that altitude. That's where the aeronithium (I'm now calling it aeronithium) bricks and letting loose of gas comes in, finding that equilibrium again so that the vertical propellers don't have to stay on.

So I'm imagining the propellers could still be entirely relied upon up until there's a noticeable difference in air density. What kind of bounds are we talking about here? And I'm still keen on knowing how precise the equilibrium would have to be. For example, would a new passenger on board mean having to adjust the gas levels?


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## BronzeOracle (Oct 29, 2014)

These are tempting questions for the engineer in me, I'm fighting the impulse to make a spreadsheet!  

Yes, the propellers would primarily be for horizontal movement and some vertical manoeuvring, with the gas/weights used for vertical elevation changes.  The use of the propellers for vertical movement outside of the buoyancy equilibrium elevation (ugh I'm not sure that's even a correct terminology... my old lecturer could be turning in his grave here) would increase depending on how high or low you went from the equilibrium elevation.  Basically if you go above it there's a force pulling you down, if you go below it there's a force pushing you up.  It would get more noticeable the further you go.  In terms of how noticeable, how fast the propellers would need to go, I really don't have an idea without doing calculations - probably using Stokes law see Stokes' law - Wikipedia, the free encyclopedia 

The buoyancy of the airship will change for any change in weight - including a new passenger.  So a new passenger would make the airship start to drop, but its just the velocity of the drop would be slight - depending of course on the proportion of the passenger's weight to the total weight of the airship. I'm guessing the weight of your ship but with wood and steel it would be many tonnes, so a person at 70 kg is what only 1% of that?  So it wouldn't drop fast (you could again estimate the drop speed using Stokes law) but yes you'd need something to compensate, either more gas or using the propellers pointed upward.  Or accept the drop in altitude.  I'm guessing that using a dash of aeronithium brick would be the way to go and a skilled airship pilot would know roughly how much to burn for an average passenger??

BTW helium airships typically don't go that far up in altitude partly because it requires more helium, which is expensive as it ultimately needs to be vented in order to drop back down again.


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## Gryphos (Oct 29, 2014)

BronzeOracle said:
			
		

> I'm guessing that using a dash of aeronithium brick would be the way to go and a skilled airship pilot would know roughly how much to burn for an average passenger??



Yeah, that's exactly what I was thinking. I'm imagining little dialogues happening when a new passenger comes aboard.
"How much do you weigh?"
"Like 70 kilograms."
"Alright, so that's, what, half a brick?"
"Sounds about right."



> BTW helium airships typically don't go that far up in altitude partly because it requires more helium, which is expensive as it ultimately needs to be vented in order to drop back down again.



I imagine my airships probably won't go particularly high either. They'll probably still need to go around mountain ranges rather than over, unless of course the captain's particularly daring and/or insane.


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## BronzeOracle (Oct 29, 2014)

Gryphos said:


> I imagine my airships probably won't go particularly high either. They'll probably still need to go around mountain ranges rather than over, unless of course the captain's particularly daring and/or insane.



Yeah I can imagine a captain whingeing when requested to ascend to a height to get to some hero's destination "That's not going to be cheap... these bricks don't grow on trees!!"  unless of course they do grow on trees? ;o)


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## psychotick (Oct 30, 2014)

Hi,

I'm actually writing a steampunk at the moment which has an airship, but it's actually a hot air balloon with a propellor and tail assembly. 

However there is a way you can decrease altitude in a helium airship without venting gas. In essence it's about density. So if you have a compressor in your balloon that you can turn on and off, you can decrease your boyancy simply by sucking up a little of the gas into cylinders. Sucking the gas out of the balloon decreases the volume of the balloon. The total weight of the airship remains the same, therefore the overall density of the airship increases a little, and the airship sinks.

Sails on an airship sound cool, but practically speaking they would be useless. The airship sails along at the speed and direction of whatever wind current it's in. Sails can't increase this speed. Nor can the help the ship move at an angle to the wind, because an airship has no keel. In a yacht the sails take the wind pressure which tries to push it in one direction. The hull and the keel of the boat are held by the water, which assuming no current, acts as resistence. And the boat moves in a direction determined by the product of these two forces. In an airship there is no resistence. So there is only one force acting on the ship and that's the air current. The way a balloon changes direction or speeds up or slows down is by changing alititude so that it finds a more suitable air current. If you added sails to an airship what you'd see was nothing save the sails hanging flat. The ships moving at speed x in direction y and so is the wind.

Sorry to be a kill joy.

Cheers, Greg.


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## Gryphos (Oct 30, 2014)

psychotick said:
			
		

> However there is a way you can decrease altitude in a helium airship without venting gas. In essence it's about density. So if you have a compressor in your balloon that you can turn on and off, you can decrease your boyancy simply by sucking up a little of the gas into cylinders. Sucking the gas out of the balloon decreases the volume of the balloon. The total weight of the airship remains the same, therefore the overall density of the airship increases a little, and the airship sinks.



That is pretty nifty, but thinking about it, I'm really liking the idea of balancing venting gas and burning bricks, and all the interesting situations and stuff it can lead to.



> Sails on an airship sound cool, but practically speaking they would be useless. The airship sails along at the speed and direction of whatever wind current it's in. Sails can't increase this speed. Nor can the help the ship move at an angle to the wind, because an airship has no keel. In a yacht the sails take the wind pressure which tries to push it in one direction. The hull and the keel of the boat are held by the water, which assuming no current, acts as resistence. And the boat moves in a direction determined by the product of these two forces. In an airship there is no resistence. So there is only one force acting on the ship and that's the air current. The way a balloon changes direction or speeds up or slows down is by changing alititude so that it finds a more suitable air current. If you added sails to an airship what you'd see was nothing save the sails hanging flat. The ships moving at speed x in direction y and so is the wind.



Huh, learn something new every day. Ah well, I was never particularly set on the idea of sails anyway. I was always thinking in terms of engine-powered propellers.


One thing that there is to also consider is the docking of these airships. The way I have it now they dock at massive mooring towers. The way I'm picturing these mooring towers is kind of like a more cylindrical Eiffel Tower, each one being abel to hold a varied amount of airships, but usually about a dozen or so I'm imagining (keep in mind my airships are much smaller than real-world zeppelins). Each docking point on the tower would have a pier for the airship to dock alongside and support struts for it to rest on. Upon docking the airship would be attached to the pier via docking cables that hook onto the ship's railing. The tower might even have a kind of crane built into it to help with the loading of goods onto ships.

Of course there are exceptions. One city that features prominently in my story is situated on the top of a plateau. There they don't bother with mooring towers and instead just put the piers and support struts on the edge of the cliff.

And of course some ships I imagine would be specially designed to be able to land on the ground, built to have flat bellies and retractable stands or something like that. Explorer ships would definitely be made like this, as they'll be having to stop in uncharted territory and be able to be loaded with exotic animals and whatnot.

As to ships having to make long journeys that last several days. Some may choose to fly through the night, but when they really need to stop what would they do? One option is for them to stop at a random port they come across and wait there for the night, which would probably be what most would do. But what about military ships on campaign, who perhaps have to wait at a rendevouz point or something like that? Military ship designs, which would likely have a gun or two sticking out from the bottom, wouldn't be able to land on the ground. So I'm thinking they would bring the ship down low and attach it to a set of stakes or a tree or something, just to stop it blowing away. Then the crew could either sleep on the ship over night or perhaps set up a rope ladder and sleep on the ground.


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## BronzeOracle (Oct 30, 2014)

Gryphos have you read 'Songs of Dying Earth'?  There's a short story in it titled 'The Guiding Nose of UlfÃ¤nt Banderōz' by Dan Simmons, which is a great yarn and it includes an old airship with description of the docking yard, embarkation and travel, and attack by aerial foes.  Haha and it also features sails even though these don't work!!  See this link: High Homage: The Guiding Nose of UlfÃƒÂ¤nt BanderÃ…Âz by Dan Simmons | Tor.com


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## Cerberus (Oct 30, 2014)

psychotick said:


> Hi,
> 
> I'm actually writing a steampunk at the moment which has an airship, but it's actually a hot air balloon with a propellor and tail assembly.
> 
> ...



In my fantasy story I also use lifting gas canisters to pump gas in and out of the balloons as the main means of ascent and descent. I also have the ship built out of extremely light materials so it's somewhat flimsy but doesn't require as much to keep in the air, and has double the balloons necessary to keep it aloft in case of malfunction or so they can bring on extra cargo.

This is a good subject since IMO the most important questions for an airship are weight and propulsion. For propulsion my airship uses a massive engine to turn two propellers on the sides of the ship. Its maneuverability comes from lessening or even reversing the speed of the propellers in relation to each other, as well as limited ability to rotate the direction the propellers are pointing to also give it some vertical maneuverability without increasing or decreasing the lifting gas in the balloons.


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## Terry Greer (Nov 3, 2014)

I have airships in my novels. I've stuck with hydrogen as I want the combustability and it's a gas that can be produced by a living creature from water (which is what my airships are).
The buoyancy is increased however by my having the world one with a higher atmospheric pressure - so I get a lot more lift per unit volume.

In theory the best 'realistic' lift would be from a vacuum airship with no gas in it at all i.e. a vacuum - the problem is however making that strong enough to not crumple - so I guess that won't ever happen. Your fantasy gas sounds like it beats a vacuum by several orders of magnitude - nothing wrong with that in a fantasy setting.


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## CupofJoe (Nov 3, 2014)

Terry Greer said:


> In theory the best 'realistic' lift would be from a vacuum airship with no gas in it at all i.e. a vacuum - the problem is however making that strong enough to not crumple - so I guess that won't ever happen. Your fantasy gas sounds like it beats a vacuum by several orders of magnitude - nothing wrong with that in a fantasy setting.


Oh... Vacuum ships.... I like the sound of that... [reaches for Quill and Ink...]


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## Svrtnsse (Nov 3, 2014)

I too have airships in my setting. One of my characters is working as import manager at a small company that specializes in selling small luxury vessels to the very rich.

I have admittedly not spent very much time thinking about the technicalities of how the ships actually work - they just do. It's a big balloon thingy with some kind of gondola beneath. For my story, the important part isn't how the airships stay flying or how they're piloted, but how they fill a role as a means of transportation within the society. 

Basically, they function in much the same way as passenger ferries do in the real world. They're not very fast, but they are (or can be) quite comfortable and can carry a lot of passengers etc.


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## Gryphos (Nov 3, 2014)

Svrtnsse said:
			
		

> Basically, they function in much the same way as passenger ferries do in the real world. They're not very fast, but they are (or can be) quite comfortable and can carry a lot of passengers etc.



That's one of the ways my airships are used too. Airships have basically become the go-to method of transportation, at least between cities and major towns. Horse-drawn carriages are still obviously used within cities and travelling between towns without mooring towers, but any long-distance travel is done via airship. This leads to a variety of specially designed airships for certain needs, whether they be passenger ships with a below-deck area to sit in comfort, or huge cargo ships with deep hulls in which to store things.


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## wordwalker (Nov 4, 2014)

psychotick said:


> However there is a way you can decrease altitude in a helium airship without venting gas. In essence it's about density. So if you have a compressor in your balloon that you can turn on and off, you can decrease your boyancy simply by sucking up a little of the gas into cylinders. Sucking the gas out of the balloon decreases the volume of the balloon. The total weight of the airship remains the same, therefore the overall density of the airship increases a little, and the airship sinks.



A great option, if they have the machinery to suck the gas back in that way; lower-tech ships might not.

In a lot of ways it comes down to weight, and cost. Is the fuel (and compressors and tanks) to recycle 1 "brick" of gas lighter than just dumping the gas and having another brick ready for later? Or is the heavier way still cheaper, so only the more expensive ships take the really weight-efficient option to stretch out their long runs?



Terry Greer said:


> In theory the best 'realistic' lift would be from a vacuum airship with no gas in it at all i.e. a vacuum - the problem is however making that strong enough to not crumple - so I guess that won't ever happen. Your fantasy gas sounds like it beats a vacuum by several orders of magnitude - nothing wrong with that in a fantasy setting.



This would be a fun twist on things, if you have reinforcing spells that can make a ship with a partial or even total vacuum in the gas envelope. (They'd have to be a highly specialized magic or superscience, or else you'd have a *lot* of supermetal available and better airships would be the least of your world's quirks to keep up with.) I guess the difference between these and other airships would be that they might be smaller (thus more maneuverable?), and they might have more (or less?) endurance because the material or the reinforcing power adds a different amount of weight than the usual amount of ordinary fuel. Or if the ship was _really_ tough you might finally have an airship that didn't "pop like a balloon" in a fight-- until someone cancelled the reinforcing spells.


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## Gryphos (Nov 4, 2014)

Wordwalker said:
			
		

> In a lot of ways it comes down to weight, and cost. Is the fuel (and compressors and tanks) to recycle 1 "brick" of gas lighter than just dumping the gas and having another brick ready for later? Or is the heavier way still cheaper, so only the more expensive ships take the really weight-efficient option to stretch out their long runs?



The way I'm picturing it, aeronithium bricks would be mass-produced and dirt cheap, so it probably would be cheaper in almost every case, to the point that people don't even bother with gas compressor systems, the weight of which would make the ship less fuel efficient. As to long stretches out of port, I think any ship would be more likely to run out of fuel than bricks, as the bricks only ever need to be used sparingly.


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## scientia (Dec 28, 2014)

When Burroughs wrote Buck Rogers back in 1928, he resorted to using a magic metal that was repelled by gravity. It was so common for authors to make up a mysterious substance X to have whatever properties they wanted that it became cliche. You can find it in most early science fiction like E.E. Smith's Skylark series (also from 1928). I guess anyone can resort to this if they don't feel that their readers would care. Clearly though, any substance that was repelled by gravity would not be safe or practical.

Lighter than air craft were the first that could fly. These predated both gliders and powered flight. But, let's look at ships first.

It took Columbus 5 weeks to cross from the Canary Islands sailing with the trade winds. About the fastest you can expect to sail from London to New York against the prevailing wind in the north Atlantic is 42 days or six weeks. The very first steam ship that had enough capacity to cross the Atlantic was the Great Western, built in 1838. It steamed at about 9 mph and typically crossed the Atlantic in 16 days. By 1858, the much larger Great Eastern could maintain 15 mph and make the crossing in 10 days. Hindenburg could maintain 60 mph and make the flight in 3 days.

Could you build a craft like Hindenburg in a steampunk novel? Not really because the frame was made of aluminum and this was not available in the 1800s. Could you use steam engines? Not very easily because the boilers and pistons are quite heavy. You would also have to have some kind of condensing system to prevent loss of water. The craft would not be very practical. Hindenburg actually used four, 1100 HP diesel engines. These engines weighed over 2 tons apiece. That might sound like a lot of weight but consider this. It would have taken 7 of these engines to equal the horsepower of a Union Pacific Big Boy steam locomotive. That would be 28,000 lbs of engine weight. In contrast, a Big Boy locomotive weighed 760,000 lbs. Sure, about 1/3rd of that is linkages, frame, articulation and wheels. But, you are still going to be 28,000 lbs versus 500,000 lbs. The water alone for a Big Boy weighed 200,000 lbs.

Hindenburg was 800 feet long and contained about 7 million cubic feet. The total lifting force was about 511,000 lbs. However, by the time you subtract the weight of the frame, gas envelope, engines, and fuel, you don't have a lot left since most of the weight goes for fuel. Hindenburg was designed to use helium but using hydrogen gave it an extra capacity of 37,000 lbs. This is pretty remarkable considering that the total design payload was only 22,000 lbs. However, there is no indication that Hindenburg ever used much of the extra capacity. There was no material available at that time could have kept the envelope from slowly losing hydrogen. However, hydrogen loss wasn't the problem. The engines ran at 850 HP making 3,400 HP total. They would have burned 0.35 lbs/HP/hour. So, on a 78 hour flight, they would have burned 100,000 lbs of diesel. So, Hindenburg had no choice but to release hydrogen to keep from gaining too much buoyancy. In fact, Hindenburg could burn as much as 119,000 lbs of fuel and have to release a whopping 1.7 million cubic feet of hydrogen. There is a compromise you can do where you have an engine that burns hydrogen gas. That way you can reduce your diesel consumption and also get some use from the hydrogen rather than just venting it. However, hydrogen doesn't have a very good power density. So, it would be better to fill some bags with methane. Methane is lighter than air so it would add some buoyancy but it is good for about 3x as much power per cubic foot as hydrogen. For example, if Hindenburg had burned off 1.7 million cubic feet of methane, it would have made the craft about 55,000 lbs heavier which you could compensate by burning 55,000 lbs of diesel.

The hard part about managing a craft like this is that everything effects buoyancy and pressure. As you gain altitude, the lower air pressure would cause the bags to expand and rupture. The idea that they can handle pressure is somewhat comical. They were made of two layers of cotton with a sealer in between. Even a small amount of pressure would exceed the tensile strength. Instead, you have bags inside the bags which are just filled with air. As you gain altitude and the hydrogen expands, you allow the internal bag to collapse by venting air. When you descend, you maintain the volume of the bags by pumping air into the internal bags. If you are moving, you can do this with an ordinary wind scoop. If you were stationary, you would need a fan to blow air in. Another problem is temperature. At night, the gas will contract as it gets colder so you'll lose some buoyancy. A small amount can just be compensated by the lift produced by moving forward with the envelope at a slight upward angle. In the morning, when the sun rises and heats up the envelope, the hydrogen will expand and increase buoyancy again. So, you would trim the nose down to reduce lift. You can either trim the craft with horizontal surfaces like short wings and tail or you can do it statically by moving hydrogen between the front and the back. Obviously, more in the front would trim the nose up. How do you move the hydrogen? Well, you open up a duct that connects the bags together and then you blow air into the internal bags which forces hydrogen out. You simultaneously vent the bags where you want more hydrogen in.

So, let's look at cargo capacity. A clipper ship from the 1800s could have carried 1,000 tons of cargo. Great Western carried a bit less because of the coal. However, Great Eastern could easily carry 10,000 tons. Compare this with the trivial 11 ton capacity of Hindenburg. As you can see, dirigibles were not built to carry cargo. I've already shown that a steam engine is ridiculous on a craft like this. However, since the earliest internal combustion engine was 1856, you wouldn't really have to stick with steam.

I'm not sure what exactly you would do with a dirigible. Hindenburg carried about 90 people. However, Hindenburg wasn't really the best design. Graf Zeppelin's envelope was only half the size of Hindenburg's yet it's payload was 50% greater at 33,000 lbs. This was because it used blau gas for both fuel and buoyancy compensation (similar to what I mentioned about methane). Graf Zeppelin traveled a million miles during its career. A Goodyear blimp from 1969 with a length of 192 feet and a width of 50 feet, only carried 7 people.

The easiest way to add ballast is to pump water on board when it docks. This can be easily dumped as needed. The Goodyear blimps only have a single main wheel. When they are docked, the nose attaches to a pole and the blimp pivots around it like a wind vane.


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## evanator66 (Dec 28, 2014)

Do these airships have pirates? I am guessing they do. A few tactics would be to fly above the enemy ship, and harpoon structural areas of the enemy, while at the same time puncturing the balloon. That way they would be at your mercy. Also, these pirates might fly underneath the enemy ship with a camouflaged balloon, and boarding parties could cut a hole in the hull of the other ship, climb aboard, and steal everything not bolted down, then escape through the hatch undetected. The only problem with this is that the ballast is probably positioned right above them, forcing them to attach the ship to their own and pump the ballast into special tanks, pumping it back when the heist is complete.


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## Terry Greer (Dec 29, 2014)

I love airships

I use airships in my novel series Jangada.
Jangada

But I cheat - the world has a higher air pressure - so I get more lift per volume.
The airships are based on  a living creature from that world.
There is no other way to traverse between the islands of that world - (Its a void) - so only peopel, expensive items and luxuries are transported.
The renaissance-like technology uses reinforced resin a lot for the actual gondola - strength and lightness.
There are engines - based on ceramics - and they are used on gimbals to vector thrust during take off/landing and provide forward/backward thrust where needed.

Some technology is a remnant (or technique) from a much earlier time - now long-forgotten by most apart from the inhabitants of one particular island who more or less monopolize airship travel between the islands (and are therefore very rich).

BTW - sails on an airship are pretty useless - you might get a little bit of tacking ability by using them - but you won't be able to sail against the wind, although you might get some forward propulsion if going across the wind the amount of drag the main airship body has largely negates any advantage. And if you want to sail with the wind then the airship itself will drift with it quite nicely. 
The best use for sails would be for orientating the airship - not propulsive power - and they could then be quite small.


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## stephenspower (Dec 29, 2014)

The book you want to read is John McPhee's _The Deltoid Pumpkin Seed_, which about trying to create a new form of rigid aircraft and includes tons of science. You might also read Ken Liu's wonderful story in the November _Clarkesworld_, "The Long Haul, From the ANNALS OF TRANSPORTATION, The Pacific Monthly, May 2009," which takes McPhee's _Common Carriers _and replaces 18-wheelers with zeppelins.

Basically, though, everyone should read everything by McPhee. Inspired by the Liu story, I want to adapt his piece in _The Control of Nature_ called "Cooling the Lava," about Iceland's Heimaey volcano, into a story about an eruption of some strange eldritch matter that threatens a town, their unflappable approach to the semi-regular occurrence held in contrast to the weirdness that the eldritch lava causes.


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## Surad (Dec 29, 2014)

This is a subject that's important to me, too. In the Dieselpunk themed world I'm creating, airships do have their place and are very important despite the fact that lots and lots of heavier-than-air aircraft available. The whole point in my world is that it is 5 times larger than our planet, and lots of unexplored territory. Plus the technology is much more advanced, with airships being able to carry a lot more than any other aircraft, and being faster than ships, they're useful for transporting priority cargo and other valuables... which make them prey for air pirates that also use them as mobile bases and a means of a quick getaway.

Their endurance makes them perfect for exploration, since they can spend weeks or months away (like I said, more technically advanced) without having to refuel, and their ability to fly low and slow makes mapping new territory easier, as well as providing a nicer mobile base for explorers when they touch down. On top of that, their sight makes quite an impression on any natives they meet, regardless of their technological level.

Your idea of using a fictional gas is pretty much what I came up with myself, since I'm not a fan of hydrogen and helium really won't cut it (it's heavier than hydrogen and doesn't provide as much lift). My main problem was just how to design and make such large ships functional. The civil/exploration aspect is quite easy, since it has been done. The first round-the-world flight was done in a Zeppelin in the 1920s, and the transportation would work. Albeit it would cost more than a trip by boat or train, which is why those methods of transport still exist in my world. The biggest question is the military designs I have in mind. In the 1930s, there was some experimentation in the US to make flying aircraft carriers a reality. The two helium airships at the time actually worked to both launch and retrieve fighter planes and in a military exercise, they were able to successfully defend themselves against air attack. The death of the flying aircraft carrier came when both airships were lost to accidents, and the biggest proponents of flying aircraft carriers also died in those accidents, and the idea died with them.

My main question is to justify, at least from a military perspective, the existence of both aircraft carriers, and flying aircraft carriers together. What advantages does one have over the other? Flying aircraft carriers are more mobile, faster, and can provide forward support… but how many planes do they carry? A WW2 era aircraft carrier, from the United States, could carry 90 to 100 aircraft. How much would an airborne aircraft carrier pack? 30? 40? That’s still a hell of a lot of planes when you realize that in RL, the USS Akron and Macon carried 3 or 4 aircraft at the most. I figure that some major disadvantages of flying aircraft carriers would be their visibility. They can be seen from far greater distances than any regular aircraft and carrier, and they’re easier to take down. Also their vulnerability to anti-aircraft guns, especially hidden guns, would limit their overland capability, especially if they don’t know what the enemy has in stock. While I know that in RL, Zeppelins were not that easy to take down, but they were only used militarily in WW1, when anti-aircraft guns were quite primitive and aircraft sent against them were packing only rifle caliber machine guns, with maybe incendiary bullets. By the time WW2 rolled around, aircraft were much better armed, and while I did hear that they would still be durable since the bullets would pass through the frame without causing much damage, and even rockets fired might not do that much since they too will pass through like giant bullets. With the tech of WW2, they might even have a variant of self-sealing gas bags (like those used in fuel tanks on most WW2 aircraft).

Working out the technicalities will actually be the real fun of the whole thing. There’s definitely a place for them in any fantasy/scifi world. Heck, there’s still some room for them today, though the chances of being used as passenger/cargo aircraft are slim to none, I’m pretty sure the tourist sector would love them, being able to fly low and slow over major landmarks with a minimum of noise is something definitely useful.


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## K.S. Crooks (Dec 29, 2014)

For any gas used when it is heated it becomes less dense than the surrounding air, thus the ship will rise. When the gas is allowed to cool the gas become denser and the ship will lower. You can keep it this simple. You can also have the ship shoot out anchors from harpoons attached to a pulleys and wind the ship back down. Hope this helps.


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## stephenspower (Dec 30, 2014)

Actually in terms of defense from anti-aircraft guns, a zeppelin could fly well above the range of the guns, then drop its airplanes likes bombs, the planes picking up speed as a result and generating lift, much like firing them off an aircraft carrier with a catapult. Scary moment their for the pilots, but no more than being catapulted. Of course they'd still be sitting ducks in the air unless protected by a swarm of fighters.

Another story prompt: The reason the Hindenberg was using hydrogen was because helium is only found in quantities in Kansas and Texas, and the US wasn't about to sell any to Germany at the time. How would such an embargo or regional scarcity affect your worlds?


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## Gryphos (Jan 1, 2015)

Alright, so here's something I've also been trying to work out. How would aerial warfare play out in this world? At the time of the story aeroplanes have been invented, but it's an extremely recent and unreliable invention. What I'm talking about is how fleets of airships would do battle.

One immediate thing I've considered is that airships wouldn't be able to mount super-heavy artillery on them, as the force of the gun firing would have disastrous consequences on the ship. Perhaps there would be a class of massive ships able to mount such weaponry, but for the most part ships would have to stick to relatively minor artillery. Also, because of the three-dimensional nature of air warfare, you couldn't mount an airship's guns like cannons along the broadside, as that would always require the ships to be at the same altitude. So for airships what I'm imagining is free-aiming turrets mounted at strategic points on the ship, each manned by a single crew member. These turrets wold also come in many kinds. There could be a gatling gun designed for targeting the other ship's crew, flak cannons for explosive damage, maybe even harpoon guns for pulling the other ship in for boarding.

But one thing I'm having difficulty with is the balloon. I want battles to be hectic and action-packed, so I don't want ships going down with one shot to their balloon. In fact I want the emphasis to be away from the balloon. So how can I do this? Aeronithium gas isn't flammable, so the balloons won't explode. But that doesn't deal with the fact that ships will go down when the balloon is punctured. One idea I've had is for the balloons to have armour plating on them, strong enough to make shooting them be less of a priority than shooting the actual hull. I've already established that aeronithium gas has extreme lift capability, so the weight of the armour wouldn't be an issue. All it means is that military ships would have to have larger balloons than civilian ones.


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## stephenspower (Jan 1, 2015)

Nothing, when it comes to zeppelins, is hectic.

To figure how battle will go, work out the evolution of zeppelin defenses based on the changing strategies of attackers. Similarly, work out the evolution of zeppelin attack strategies by figuring out how defenses frustrated them. As a bonus, you'll have a lot of interesting background to work with, which could lead to character living in the past, others worried about new and untested techniques, and ironies around what people think will still work, but won't.


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## Gryphos (Jan 1, 2015)

> Nothing, when it comes to zeppelins, is hectic.



Maybe not in the real world, where airships were massive, delicate, sluggish behemoths, but in my world airships are small and manoeuvrable. In the development of my world I had to discover early on that equivalencies to real world airships would be difficult.


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## Gryphos (Feb 1, 2015)

All right, this I'm having trouble with. In an aerial fleet, how would the ships communicate and coordinate? In the real world around the age of sail I know that they would use those flag symbol things, which worked, I imagine, because of the two-dimensional field. However, with airships operating in three dimensions and three dimensional fleet formations, not all ships would be able to see because of the hull or balloon blocking the view. So what are some possible ways of ship-to-ship communication?

As I'm working with a late 19th / early 20th century aesthetic, my options are somewhat limited. I've looked into radio communication as a likely candidate, some kind of Marconi-esque technology, which would definitely be ideal, each ship being fitted with a radio communicator and each crew containing a communications operator to coordinate with the other ships. But are there things that would hold this back? Power sources? Physics stuff? Are there any other options I haven't considered?


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## Queshire (Feb 1, 2015)

You could use an array of mirrors to get around the line of sight problems, though I think it would work better with flashes of light than semaphore flags.


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## psychotick (Feb 1, 2015)

Hi,

To get around the popping balloon, plummeting to death from one shot scenario, I'd chamber the balloons. That way you shoot out one balloon, you don't lose everything, and you sink rather than dive bomb. But I'd also remember that this is always going to be a major weakness of inflatables over planes.

For communications I'd go with light boxes and a Morse code type thing. Remember the bags would be in the way if one balloon was more or less directly above another but if you simply have a rule about flying in widely spaced formations - perhaps so that they don't crash into one another in heavy wind storms - you don't have this problem. Also it prevents one balloon from rising into another above it which it can't see.

Cheers, Greg.


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## ThinkerX (Feb 1, 2015)

Your world has radio, presumably it has the light bulb as well.  Colored lights at intervals along the hull, used to send coded messages back and forth.


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