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Following on from my previous question about airship engines, I was planning to limit the development of the internal combustion engine and much modern technology in my world by greatly restricting the availability of metals. Iron and all heavy metals like nickel and copper are known but are very rare or are widely dispersed so technological development has not proceeded as on Earth. Electricity has not been discovered because of the lack of metals so there is no aluminum either (although it is present). Otherwise technology is as “modern” as it can be without much metal. Iron is more expensive than silver but less expensive than gold is in our world. They still mostly use stone tools, but might use iron-based tools for very specialist work.

I’m interested in building an airship in this world. The engines can be an exception (built at great cost) but other than engines, is it realistic to build an airship here? For example could natural fibre and resin composite formed parts replace the light metal alloy used in airships in our world? Would this limit airship size and durability?

The background is a world that supports human life but is not the Earth. There is roughly 1g gravity and plenty of water but relatively little land. The atmosphere is very thick and the only populated areas are large plateau islands raised high up where the atmosphere is more bearable. The story will revolve around the development of airships in this world.

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Trees and wood in the past has been a strategic resource. If you look at ship building, forests and trees like oak were protected by the King. The shipwrights would look at the branches and forks, and curves in trees and understood how to use the different shapes in different parts of the ship.

Bamboo has a higher tensile strength than steel, is light and has long fibers. There is interest in using it as a low cost alternative to carbon fibers in composites. While your world may not have epoxy, it probably could have natural resins that could could be used to make some kind of laminates that could be very strong. Bamboo has been used as a structural material in southeast Asia for housing. I think modern architects are looking at a variety of ways of using it in buildings. It grows fast.

Balsa wood is also light and can be relatively strong and shaped may be useful for the airship cabin a replacement where we would use sheet metal or plastics, rather than a few millimeters of sheet metal it might be thicker but still lighter.

Textiles could be important, silk, or natural fibers, and the types of weave used in parachutes are very dense. Perhaps natural latex as a rubber could be used to help keep the lifting gas inside.

As an alternative to obtaining hydrogen by electrolysis, perhaps steam reforming of methane or natural gas gas could be used, but you still have storage problems since Hydrogen is such a small molecule. Of course that transfers your problem to getting methane, but a lot of industrial hydrogen is obtained by steam reforming usually in a two stage process, the first at very high temp between 700 and 1100 C producing carbon monoxide and hydrogen and the second stage around 400C producing CO2 and water.

If you already have a methane, it could be used as a lifting gas (not as good as hydrogen), and it has a bigger molecule so would stay in the balloon textiles better.

As a side note: I think with out the enough availability of metals for conductors for long wires, you could still have small amounts for critical applications and it might drive the application of wireless, Or still be used in chemistry applications. Carbon can be a pretty good conductor in some ways and depending on what is around there may be other conductors. Before electrical distribution lines, I think by the 1820's there was street lighting using coal-fueled gas lights in major cities.

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    $\begingroup$ +1, great answer. If you allow me to nitpick on a little detail, the major problem with large low-tech balloons aren't with the textiles, they lie in the seams. These are the major points of failure and leakage, unless the waxed canvas is pierced. $\endgroup$
    – Mindwin
    Aug 23 at 19:01
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    $\begingroup$ @Mindwin good point, it sent me down the hot air ballon making rabbit hole. $\endgroup$
    – UVphoton
    Aug 23 at 19:54
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    $\begingroup$ You don't wax the canvas, you glue the bladders of larger animals together. To punchtures allowed. Read about the R101 to see how they did it back then. $\endgroup$
    – boatcoder
    Aug 24 at 14:20
  • $\begingroup$ @boatcode Interesting, the R101 is a good example. Lots of wood used and very large. $\endgroup$
    – UVphoton
    Aug 24 at 18:59
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Composites with strength-to-weight comparable to light metals like aluminum or magnesium are possible with bronze age, if not neolithic levels of technology. What is needed is a combination of long, straight fibers (linen, hemp, or bamboo are likely sources, with sugar cane a potential fourth) and an adhesive or resin that cures hard and is waterproof after curing -- one potential candidate is pine pitch (given a suitable catalyst to accelerate the curing process that takes centuries to produce amber), there may be others.

Water resistance in the fiber binder may be optional if there are coatings that can make the airship envelope weathertight; if that's the case, protein glues (like the classic rabbit skin glue in a small pot in a double boiler) are easy to apply and allow easier rework in case of errors or damage. One candidate for such an exterior coating is linseed oil (from the seeds of the same linen that might supply the fiber for the frames) -- it can make paper or light fabric virtually airtight, never mind waterproof, though it takes a long time to fully cure.

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    $\begingroup$ It is such a coincidence - my airship is named the "Sugar Cane Potential" and our team shirts say "CURES HARD!". Upvote! $\endgroup$
    – Willk
    Aug 23 at 12:56
  • $\begingroup$ Hot air ballons have very little metal in them and they are able to fly. The only place you need metals is for the storage of the burnable gas (under pressure) and the nozzle where it burns. The rest could easily be built out of wood like material. $\endgroup$
    – boatcoder
    Aug 24 at 14:22
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    $\begingroup$ @boatcoder Early hot air balloons carried charcoal or wood for fuel. Propane is used today because it's easier to regulate the fire, it can be much hotter without require huge volumes of wood, and the fuel is already available. Alcohol in a bladder with external spring pressure might work nearly as well, and require almost no metal (not even to drill for petroleum). $\endgroup$
    – Zeiss Ikon
    Aug 24 at 14:30
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The Schütte-Lanz airships had their frames built from plywood and other wood-based composites. At small scales, wood's superior compressive strength beats aluminum's superior tensile strength, and a small wood-framed airship is lighter than a metal-framed one. (Keeping the wood dry is critical).

But airships benefit strongly from scale: a large airship can carry a proportionately larger payload than a small one, while not requiring a larger crew. On a metal-poor world, a wooden airship is more practical than a wooden airplane, but it also needs to compete with other forms of transportation, such as wooden ships. Where the balance ends up depends on how rare metal is: an airship is faster than a sailing ship, but the sailing ship does not require any metal at all.

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  • $\begingroup$ This sounds very promising for structural components. If in our world these plywood airframes were used and could lift 30-60 tonnes then in a world with no metals they would have be the go to choice and could easily have beaten the metal element airships on price even if their performance was more problematic. $\endgroup$
    – Slarty
    Aug 23 at 23:19
  • $\begingroup$ plywood requires high end metal tools, if metal is so rare they can't use it for engines they certainly are not using it to make giant metal lathes to peel logs for plywood. $\endgroup$
    – John
    Aug 24 at 2:10
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    $\begingroup$ Are you certain that you can't use a ceramic blade to peel logs for plywood? I'm pretty sure we don't, just because steel is easier. Although that's a long way past "mostly stone tools" into "advanced non-metallic technology". $\endgroup$
    – nigel222
    Aug 24 at 9:47
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    $\begingroup$ "sailing ship does not require any metal at all." I would disagree with this clause -- even in the Bronze Age, ships (both galleys and sailing ships) were critically dependent on small bronze parts. shafts for sheaves, for instance. They could be built without metal, but metal parts made critical components last much longer and less prone to failure under way. And then there was the "beak" on a war galley... $\endgroup$
    – Zeiss Ikon
    Aug 24 at 11:09
  • $\begingroup$ @ZeissIkon, there are a lot of places where metal is really nice to have on a sailing ship, but you can get by without it. That's not the case for an airship, where any practical propulsion system needs metal. $\endgroup$
    – Mark
    Aug 24 at 22:46
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Very Unlikely. While there should be no scarcity of lift gasses (Hydrogen is damn near everywhere and assuming that it's a fundamental building block of life for your world, it should be quite easily found in any water), there's a problem with extracting it that you encounter.

Electricity has not been discovered because of the lack of metals so there is no aluminum either (although it is present).

So first of all, the word electricity was first used in 1646, though the phenomena was known 2750 BC, when Egyptians described electric fish native to the Nile as "Thunderers of the Nile" (although the relationship between Lightning, Thunder, and Electricity wasn't proven until the experiments of Benjamin "I'll fly a kite in a thunderstorm and see what happens and then help found a nation" Franklin made the discovery. By comparison, Aluminum wasn't discovered until 1825 although you are right about the scarcity, as it was extremely expensive. Napoleon III (not the short but not really Emperor of France, but a couple successors later) had a full dinner set made of Aluminum that was used only for the fanciest of dinners... when the golden dinner sets just wouldn't impress enough. And the United States capped the Washington Monument with a single Ingot of Aluminum to symbolize the wealth of the new nation. A method to synthesize aluminum in such a quantity that we can drink soda from cans made of the stuff for less than a dollar wouldn't be invented until 1886... and by this point Thomas Edison had already invented the lightbulb, was illuminating cities with DC Power in the U.S. and Europe, and had this uppity Hungarian immigrant named Tesla quit because he couldn't take a joke and invent AC power to compete... 1885 was the start of The War of the Currents!

All of this is a problem because the best way to make a lighter than atmosphere gas, hydrogen, would be to take some water, run electric current through the water, and separate the hydrogen gas from the oxygen gas in such a way that the highly reactive O2 gas, doesn't meet with the highly flammable H2 gas and... well, when I ask you what the first thing that comes to mind when I say the name "Hindenburg," I'm going to go out on a limb and say your answer will not mention the German President from 1925 to 1934 Paul von Hindenburg beyond the passing mention that the more famous one was named in his honor.

The only other lift gas available is Helium. Which while it's cheap enough to fill children's party balloons, or was... prices have doubled in the past decade. Unlike Hydrogen, Helium cannot be synthesized... well... not without nuclear physics involved or a particle accelerator and that's not happening if we're stuck on a possible internal combustion engine on a non-metal airship... as it is lighter than air, it has a tendency to wander away from earth... but unlike Hydrogen, Helium is a noble gas... which means you can only have it in a pure state. Almost all of the world's supply is mined from natural gas found in mines under the United States (90%) to be exact. The remaining 10% is produced by Canada, Russia, and Poland (It's at this point if your still asking "Why didn't the Swastika-emblazoned Hindenburg use non-reactive Helium instead of the explosively reactive Hydrogen, don't the Germans understand Chemistry?" I must question the validity of any passing grade you received in world history.). Hydrogen would be more likely your lifting gas because it's far more plentiful and renewable. Hydrogen provides more bang for your buck (Don't you dare tell me it's "Too Soon" for that joke, I stand by it.).

That said, arguably the World's First Aircraft Carrier was fielded by the Union forces in the Civil War, a converted river barge that could launch and recover a single hot air balloon teathered to it's deck with a telegram wire to provide battle field intel. Hot air rises, no matter the gaseous mixture. There was even a hypothesis that the Nazca Lines were drawn by pre-Columbian natives in Peru using hot air balloons, although this theory seems to be debunked by a dedicate team of archeologist who were able to produce similar designs in mere days with some planning and coordination. Still, it's not the most ludicrous theory out there regarding the Nazca structures. Looking at you, Giorgio "I'm not saying its aliens... but aliens" Tsoukalos!

All this is to say that a society that never had a bronze age would likely not have the capability to develop an internal combustion engine, which would require metals, nor electricity to extract hydrogen, which also requires metals, or gas mining for Helium (which requires metals). I don't think this idea passes a smell test. Unless your world is... nope... nope... not going to say it... I've already made a reference to Ancient Aliens and because of course someone who is a meme for trying to say every human achievement ever done was because of aliens has to have a name I cannot spell... Of course he does...

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  • $\begingroup$ Hydrogen generation by dropping zinc into acid was known in the days of alchemy, and extraction of zinc is Bronze Age tech. Hydrogen can also be made by passing steam over red hot iron -- too bad about that metal rarity... $\endgroup$
    – Zeiss Ikon
    Aug 23 at 12:34
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    $\begingroup$ @ZeissIkon I feel like the entire problem here is shaping up to that Simpson's gag educational film where the guy wished he lived in a world without Zinc. $\endgroup$
    – hszmv
    Aug 23 at 12:57
  • $\begingroup$ Hydrogen can be extracted from natural gas using steam reformation and the water gas shift reaction at relatively low pressure - that's were 90% of the commercial hydrogen comes from today very little comes from electrolysis. And what does is mostly a biproduct from the extraction of chlorine. It can also be produced from ethanol. $\endgroup$
    – Slarty
    Aug 23 at 16:28
  • $\begingroup$ One of the most enjoyable answers I have read in a while! +1 $\endgroup$ Aug 25 at 19:36
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I would say don't let yourself get stuck into thinking about your world's resources as strictly "earth minus metals". If this is not Earth then there may be some very un-Earth-like resources available, especially plants and fungi.

The subject of hydrogen keeps coming up, as well as the difficulty in containing it. Both could be supplied by a plant that keeps a bladder of hydrogen around for its own needs. Add some selective breeding and the plant could be farmed in quantity. (Additional processing and assembly required.) Amusingly, a whole farm of such plants would be a massive hazard and potential plot point.

The low-altitude, high-pressure zones of your world might harbor extraordinary resources that can only be harvested by specially-adapted humans. The existence of such people is ready-made for social commentary on a variety of fronts (racism, class, colonialism, interdependence, etc..)

Technologically, your people might have a good command of chemistry and thermodynamics. For example, their understanding of ceramics could be superb. They might not know how to extract aluminum from bauxite, but that doesn't prevent them from knowing how to use minerals in many other ways.

There's more than one kind of engine to consider for your airships. Pistons and propellers are one option, but so is steam, the sterling engine, and maybe (my favorite) some kind of low-temperature turbofan using fins made of treated wood coated in ceramic.

The performance requirements of an engine for lighter-than-air craft are quite a bit lower compared to heavier-than-air craft. An engine doesn't have to be very good by today's Earth standard.

Liquid high-density fuels can be distilled from the charcoal-producing process, of course. No petroleum required.

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  • $\begingroup$ I would look into heavier-than-air airships. These have many advantages: there's no reason to vent lifting gas outside of abnormal situations to land, they require less liftinggas to function and still dont need the performance of Heavier Than Air aircraft. $\endgroup$
    – Demigan
    Aug 24 at 16:53
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If the airships you mentioned are close in design to constructs like zeppelins or blimps, then there could be a chance of completely replacing the aluminium with some sort of natural fibre like carbon-based fibre, for example; and research shows that carbon fibre is in many cases stronger and lighter than aluminium, which makes it seem a rather reasonable replacement. However, many natural fibres are very brittle compared to metals like aluminium, and would not handle the rather strong conflicting forces acting on an airship very well, likely causing the entire skeleton holding up the airship to break or even collapse entirely if it were to actually fly. There hasn't really been much research into natural fibre-resin composites though, so perhaps there may be some merit there in terms of making the material more malleable and hence adaptable to conditions on an airship.

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Depends on the goal of your air ship.

Hot air balloons don't have a lot of metal. They usually have a cloth balloon, wicker basket, and a small amount of metal to hold them together and take the heat of the flame. Also metal fuel tanks, but they are hollow.

Blimps don't necessarily need a lot of metal either.

Similar to hot air balloons you could have 1 flame to keep it a float and a second/third to propel it forward.

It would probably be best to have metal tanks to hold the fuel(probably gas) your going to burn.

If you can harness some helium and/or hydrogen you can have permanent lift without as much fuel. You could pump some of the hydrogen/helium back into a pressurized tank when you want to go down. Although it sound like your going to have to use hydrogen as helium maybe too complex.

You might be have to fly at lower heights, or have shorter ranges than modern airplanes but it can be done for limited use cases.

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Hot Air Baloons

You could make hot air balloons pretty easily. The main pieces of metal needed are for the burners, which is relatively small compared to the balloon as a whole.

Hot air balloons can be used to travel to specific destinations as long as you have good instruments for measuring the wind. From this article:

A hot air balloon has no built-in mechanism for steering. It uses the direction in which the wind travels to steer itself. However, that does not mean that pilots let the balloon amble anywhere. At different altitudes, the wind direction is different, so pilots use this to steer their hovering crafts.

If you want a true airship, add a propeller and you get a Thermal Airship.

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If they can't develop an iron- then steel- based technology, they might develop some very advanced ceramics over time. First glass, then the sort of ceramics you can make excellent woodworking tools out of (although brittle, so loss of tools caused by unexpected contact with stone or other ceramics would be painful).

Thence plywood. Several successful WW2-era fighters were wood, plywood and fabric airframes. And Howard Hughes built the "Spruce Goose" which for decades was the largest airframe ever to have flown. So I don't see any reason they can't get to a non-metallic airship, apart from the engines.

You might cheat a bit and have hydrogen-emitting microbes rather than the methane-emitting microbes we have here on Earth. So the lift gas is easy to make in a fermenter.

Another cheat might be spider-grade silk in large quantities. "Insects" like silkworms omnipresent, rather than just one species? Larger than on Earth, because they evolved lungs of some sort?

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Consider ditching the engines if you really want a low metal world

Others have described the difficulties of acquiring a lifting gas, but that's certainly not unsurmountable for purposes of a story. If you've got an airship with lift, you could have it rely entirely on sails and man powered propellers. Strong headwinds may require anchoring the ship as tacking won't work anywhere as well without being at the interface of two different mediums (water and air for boats).

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    $\begingroup$ In theory you can have the "keel" and "sails" on long masts/booms to put them into two different wind systems. If you're close to the ground the keel should try to fly inside the boundary layer so as to be able to extract energy from the difference between two different fluid flows (they don't necessarily need to be different mediums). The amount of energy you can extract from wind moving at different speeds is quite significant. The fastest radio controlled planes are not rocket or jet powered but do what's called dynamic soaring - alternatively dipping from fast to slow moving wind $\endgroup$
    – slebetman
    Aug 24 at 9:02
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If you are actually basing this on the real periodic table, I think a few moments studying it will start to reveal some problems with this scenario. Iron is crucial to oxygen transport, so sentient mobile life that is not rooted to the ground becomes much harder in its absence. A significant number of solids above the weight of iron (i.e. massive enough to form a planet with 1g gravity, that won't lose its atmosphere are transition metals, so the premise leaves little to work with that could produce solid geographic features; it's going to require a bit of finessing to even have solid ground without metals.

And of course, there's the issue that a planet with solid ground and large enough to do these things related to gravity, will produce sufficient pressure at its core to turn many materials molten, and so whatever you imagine is the preponderant material will probably be exploding up into the atmosphere. Many of these would be very toxic.

Finally, a non-magnetic planet would not be able to generate the fields that make navigation possible for one thing; but also gain the protection of those same fields from rays that would shred the DNA of most living things...

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  • $\begingroup$ We don't know what's possible with life elsewhere. Oxygen transport might be fluorocarbon based (it works here on Earth an an emergency blood substitute). There might be lots of Iron in the core of the planet, bur it never got stirred up by merging with another planet so the crust is aluminosilicates with other metals rare. Since they don't have electrical technology they can't produce aluminium. Back to biology, toxicity is stuff you haven't evolved a metabolism to cope with, and dangerous levels of radiation likewise. Even here, for some reason, cockroaches are very radiation resistant $\endgroup$
    – nigel222
    Aug 24 at 10:09
  • $\begingroup$ Not the point of the question. Assume you have a low-metal world with sentient humanoid life, would an airship be practical? Questioning the premise needs to be productive. You dont question magic in a story for not being realistic because its integral for the story, and for this story the low metal planet is integral. $\endgroup$
    – Demigan
    Aug 24 at 17:15
  • $\begingroup$ Nigel's points are reasonable, but the underlying assumption, that with radically different conditions, somehow things would otherwise be relatably similar is what makes fantasy dull. Demigan and his amusingly peremptory tone, dictating the point of the question assumes that your reader is less intelligent and inquisitive than you are. You may as well start the story with, "Ever since the magic foxes came and stole away all the metal that rainy night, Jimmy's airship plans had been on hold"; small children will love it. Others, maybe not. Worldbuilding is not putting googly eyes on the world $\endgroup$ Aug 25 at 7:07

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