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Technicalities of Airships

Discussion in 'World Building' started by Gryphos, Oct 28, 2014.

  1. Gryphos

    Gryphos Auror

    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.
  2. scientia

    scientia New Member

    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.
    Last edited: Dec 28, 2014
    wordwalker and BronzeOracle like this.
  3. evanator66

    evanator66 Minstrel

    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.
  4. Terry Greer

    Terry Greer Sage

    I love airships

    I use airships in my novel series 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.
  5. stephenspower

    stephenspower Inkling

    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.
  6. Surad

    Surad Minstrel

    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.
  7. K.S. Crooks

    K.S. Crooks Inkling

    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.
  8. stephenspower

    stephenspower Inkling

    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?
  9. Gryphos

    Gryphos Auror

    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.
  10. stephenspower

    stephenspower Inkling

    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.
  11. Gryphos

    Gryphos Auror

    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.
  12. Gryphos

    Gryphos Auror

    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?
  13. Queshire

    Queshire Auror

    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.
  14. psychotick

    psychotick Auror


    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.
  15. ThinkerX

    ThinkerX Myth Weaver

    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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