5
$\begingroup$

I have a post-apocalyptic scenario, set in the ruins of an American metropolis with flooded streets. Boats are used most of the time, but aircrafts have advantages, for battle or if you have to get on top of some skyscraper ruin.

With the apocalypse some decades ago, I tend to compare the post apocalyptic world to the situation in present-day developing world countries:
The rich can afford advanced weapons and lifestyle while the poor live as farmers or fishers under primitive circumstances (mixing in some exceptions that are necessary and easily available).
The only difference: While a nowadays those things are ordered from industrialized countries, there is no industrialized country left (or at least known) in the post apocalyptic world. Instead scavenged technology is filling that gap, if it can be reconditioned and run.

For one-person flights I discovered a really badass and simple aircraft that actually works: the Paravelo (and here is another clip of the takeoff).

 


I need big aircrafts for transportation, travel and battle, that can land on water and on dry land.

More specific:
One impressive looking flagship (kind of a flying siege tower) and
some transporters for soldiers and goods.

I thought about going with airships but if you have completely different ideas for a physically working badass aircrafts that are not too technologically advanced just post them below.


 

1. Materials:

Scavenged materials are an obvious choice, living in the remains of a metropolis. Empty gasoline barrels (metal or plastic) or plastic tubes as floating bodies for the catamaran. Aluminum traffic signs (big highway lane/direction signs) as floor or walls. Some plastic sheets maybe somehow for the actual balloon.
On the other hand there are natural resources: Bamboo is very light but bending and strong, it could be used for some scaffolding constructions (cf. Chinese skyscraper scaffoldings; there actually was an airship with a bamboo frame) and maybe rattan mattes/basket constructions.
Do you have any more ideas for materials/constructions that could be used (either natural or scavenged materials)?

2. Buoyancy:

A lifting gas should be easy and cheap to produce with primitive means (cf. retrieving helium while most of the earth is under water?) and safe enough not to burst into flames by one burning arrow (cf. hydrogen).
(Not saying it may not be flammable at all - storywise nothing is more boring than an invincible weapon. It only shouldn't be too easy to shoot them down.)
I thought about using hot air or steam for the lift, ideally by burning wood or straw (one of the first experimental airships in France burned straw and fabric) or another resource that is easy to produce in a pre-industrial society. Is that efficient enough to keep an airship flying for some hours with 7 to 15 people aboard and some transported goods and weapons, given the materials used in point 1? (On the other hand I don’t have an aluminum frame or a luxurious, hotel-like lounge as provided in the Hindenburg). Especially carrying wood (to provide heat) seems to be way overweight for an airship. How could a steam-balloon work with limited technical possibilities?

3. Drive:

I guess the use of scavenged material and technology can be compared to non-renewable resources in our time: As long as there is enough of them it's more self-evident to use them instead of inventing/producing own stuff that is more costly, takes more time to build and works less effective.

Gasoline is not very durable but electricity is quite easy to produce and there are other things to burn (like alcohol or even coconut oil) to keep old, modified motors running.
Otherwise a hot air turbine or a steam engine could be built into the oven heating the balloon.
(Sails don’t work for airships because there is not enough water/air resistance to choose a direction willingly, the whole ship would just be gone with the wind all the time.)
Especially the drive by manpower is interesting: People are quite inefficient as power source but there are (special lightweight, one-person) pedal-powered blimps. So - could one make that work and even be agile and quick? An air galley (a modified version of the normal airships with pedals for the propellers) would make an interesting aircraft for slave traders...

4. Shape:

How important is streamline for an airship? The airship doesn't have to win races but should be able to keep up with sailing ships on the water. Would a catamaran boat with a cabin on top as gondola be a big disatvantage, compared to the classical fantasy monohull airship-ship-gondolas?

5. Floating body:

Do airships need a floating body (monohull or catamaran or a raft made of plastic cans) to land on water?


I know that is more than one question, but they are linked somehow (like using an oven for a thermal airship could be combined with a hot air turbine for propellers)

$\endgroup$
  • 5
    $\begingroup$ It took decades of engineering, materials science, and failed efforts to make a dirigible that didn't promptly crash on it's third-or-fourth flight, killing much of the crew. Scavenged materials are likely to be much too weak and much too heavy. Without lightweight, powerful engines, your leader is essentially ballooning, at the mercy of the strongest breeze. Oh, and fuel burned causes the airship to rise, so be ready to valve some of that precious helium. And the threats of common weather. $\endgroup$ – user535733 Aug 16 at 0:02
  • 5
    $\begingroup$ You keep using the word "balloon". An airship is not a balloon, and the nice rounded shape is just an envelope, basically a fairing. (Yes, there are non-rigid airships where the envelope is pressurized to provide strength. It still is not a balloon.) Hot-air airships have been made, but they require advanced 20th century technology, and have very much less carrying capacity than a hydrogen or helium-filled airship of the same size. $\endgroup$ – AlexP Aug 16 at 0:17
  • 1
    $\begingroup$ @AlexP My bad. I'm neither a native speaker nor an airship expert. "Balloon" was meant to name the envelope of a (non-rigid) blimp. What do you mean by requiring 20th century technology? Motors, light, gas-tight fabric for the envelope or lightweight materials for the airship frame? The Montgolfière relied on heat (but was not dirigible of course and didn't have to carry much weight), Stanley Spencer even created an airship frame of bamboo (but that was also a lightweight one-person-only scaffolding). $\endgroup$ – Cee Mon Aug 16 at 3:22
  • $\begingroup$ @user535733 It has been decades since the fall of the old world but the times are chaotic. And it is easier to employ a da Vinci to puzzlle everything out (more or less) than to construct a helium plant and keep it running or built the factory to melt aluminum to gigantic frame parts if you are at war with your neighbors and struggle to feed your people. $\endgroup$ – Cee Mon Aug 16 at 3:58
  • 1
    $\begingroup$ why not make crude helium, if you have access to crude oil or natural gas you can make crude helium. it has a lot of argon, co2, and hydrogen in it but its safe and provides most of the same lifting power. also there are other hydrocarbon fuels besides gasoline,.kerosene and diesel come to mind. $\endgroup$ – John Sep 13 at 13:10
14
$\begingroup$

hydrogen is too weak – one flaming arrow and the approaching flying battle-platform turns into (cinematographically appealing) fireworks.

Only if your engineers are idiots. The cinematic flames from the Hindenburg crash are not burning hydrogen--they are from the combusting envelope, which was basically painted with jet fuel. The hydrogen didn't help, and in fairness there were good reasons for the envelope being constructed as it was, being originally designed to be filled with helium, but hydrogen is not as dangerous in airships as people commonly believe.

If your ship is well-designed, especially knowing that it will be going into battle, there will be no way for a flaming arrow to get anywhere close to the hydrogen, short of catastrophic damage to the point that you've already lost the battle anyway. The outer hull of a rigid airship does not contain the lifting gas directly--rather, it is a protective and aerodynamic structure surrounding a series of more-nearly-spherical internal ballonets. Make the external hull sheathing out of something non-flammable, and you'll be fine. Make it out of something that will burn when hit with an arrow, and fill it with lifting gas directly rather than using partitioned ballonets, and it won't matter what lifting gas you use--your ship is going down anyway.

Ideally, you'd fill the interstitial space with some other inert buffer gas, like nitrogen, but that might be difficult for your recovering civilization to source.

Steam-lifted airships are technically possible, but extremely tricky. It's a decent lifting gas, and makes it very easy to control bouyancy by allowing some to recondense into water, but the ballonets must be extremely well insulated, and it takes a lot of energy to boil all that water and keep it hot even with good insulation. And if one of the ballonets is damaged in flight, maintenance s just about impossible--rather than a lazy diffusion of hydrogen into the hull, which you can slap a patch over at leisure, you'll have a jet of superheated steam waiting to scald your crew to death.

A decent compromise might be to use syngas. The CO content makes leaks somewhat toxic, but in-flight maintenance is still possible if done quickly, and if the hull is kept well-ventilated. It can be produced with a wood gassifier, but unlike a steam balloon or a straight hot air balloon, you don't need to carry enough fuel to keep the lifting gas hot for the whole flight--just enough to generate the lifting gas in the first place, and maybe heat/cool it for fine bouyancy control.

Syngas also has the advantage of being useful fuel for engines. There have been cars designed to run on wood gassifiers, so if you can build or recover some decent lightweight internal combustion engines, you don't necessarily need to find or carry gasoline or diesel fuel; you can run them off the same gas generator that supplies your ballonets.

If you want it to go reasonably fast, streamlining is important. That's why rigid airships are cigar-shaped, rather than spherical. But a catamaran arrangement, with two lifting hulls encasing parallel series of ballonets, is perfectly fine for an airship, just as it is for a ship-ship. The problem with putting a cabin on top is roll instability; an airship is suspended within its medium, not on top of it like a watercraft, so roll is not counteracted by differential bouyant forces as it is for a regular catamaran. You can have a small cabin sticking out the top, but you will need to ensure that most of the weight of the airship is concentrated at the bottom, or it will just flip over shortly after you leave the water.

As for materials, lacquered cloth is traditional for making balloons to hold lifting gas. You could use that ballonets, but I would stick to plastic sheeting, or just plain canvas, for the exterior envelope, for fire safety.

$\endgroup$
  • 1
    $\begingroup$ @CeeMon Buoyancy depends on the precise composition of any particular batch, which may make it kind of a crapshoot. As long as you can keep the CO2 fraction low, though--which is really just a matter of controlling the flow of air to the gassifier--it should be fine. And there are fairly low-tech ways of pulling the CO2 out of the gas stream, if that turns out to be necessary. $\endgroup$ – Logan R. Kearsley Aug 16 at 17:49
  • 1
    $\begingroup$ I like this answer so will tack on my idea here: scavenged graphene sheets for your envelope. Graphene is nonreactive, non biodegradable and super tough - ideal for your hydrogen filled airship. $\endgroup$ – Willk Aug 18 at 0:33
  • 1
    $\begingroup$ @Cee Mon: read up on graphene explainthatstuff.com/graphene.html One thought - to replace window glass. It would be easy to make multi-ply graphene windows which let thru more light than glass, was much lighter than glass, and was unbreakable. $\endgroup$ – Willk Aug 19 at 21:52
  • 1
    $\begingroup$ @Cee Mon - I imagined enormous windows, as might be in an airport or reception hall. Huge windows made of a single unbroken stretch of graphene. $\endgroup$ – Willk Aug 21 at 0:40
  • 2
    $\begingroup$ @CeeMon - youtube up some graphene. The premise here is that you can make a thin flexible graphene film that looks like plastic and is stronger than steel. The problem with current tech is making a single sheet that is big enough. In your world, use the salvaged windows as panes in a blimp made up of multiple polygons like a soccer ball or geodesic dome. $\endgroup$ – Willk Aug 21 at 2:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.