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The inhabitants of my Earth similar world have a preindustrial society, but have managed to create airships. These use plywood, hot air and relatively thick material for the envelope. But these inefficient craft are fully practical thanks to the recent discovery of Heavenium which can reduce the weight of these airships by up to 90%.

How can the inhabitants of my world use Heavenium to propel these airships forward? And are there any obvious inconsistencies with Heavenium?

Heavenium is a light weight red colored substance found in some rare mineral veins. It is inert and has defied all analysis. When it absorbs heat it reduces the effect of gravity in its vicinity. After sufficient heating a large quantity of Heavenium can reduce the effect of gravity in its vicinity by up to 90%.

The effect rapidly decays with distance (inverse square law) so that things more than around 10m away from it feel little effect. The gravity reduction effect lasts for many days after which the Heavenium needs to be strongly heated again.

If used to transfer potential energy into objects by moving them higher the Heavenium become discharged. The amount of discharge is directly related to the amount potential energy transferred (energy is conserved).

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    $\begingroup$ If increasing the potential energy of a Heavenium-affected object creates a discharge, is Heavenium recharged / overcharged if the affected object decreases in potential energy (ie descends)? Is the practical upshot that the airships must maintain a constant or decreasing altitude over the length of their journey? $\endgroup$ – KerrAvon2055 Dec 12 '20 at 13:19
  • $\begingroup$ I don't really get what you want from us. There isn't enough information for us to find inconsistencies. Of course it's impossible and the color red is rather unlikely and I don't get from your post how it works (give us more quantitative numbers and if it's reducing up to 90% and that's it, your world has super strange physics), but since you're basically doing magic, do anything you like with it. $\endgroup$ – Raditz_35 Dec 12 '20 at 13:32
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    $\begingroup$ @Raditz_35 -- It's pretty straightforward: he wants an answer to his questions! This is pretty much meat-n-potatoes worldbuilding: a fantastic substance that counters the effect of gravity. It's not our job to just say "it's impossible". It's not our job to cry "magic! Figure it out yourself!" It's our job to exercise creativity in considering the problem posed by the OP. ... $\endgroup$ – elemtilas Dec 12 '20 at 13:48
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    $\begingroup$ @Raditz_35 -- (cont). ...In this case, the problem is fairly simple: how can the fantastic antigravity substance be used for lateral motion. As decribed, I don't think it can; but someone else might come up with a different answer, and that would be most excellent. $\endgroup$ – elemtilas Dec 12 '20 at 13:49
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    $\begingroup$ @KerrAvon I don't think that there would be a discharge. If the affected object descends the potential energy is lost as heat as per normal. So there is no penalty for going down only going up doing work against gravity and the Heavenium might well allow a fair amount of going up and down rinse and repeat before becoming totally discharged depending on the details. $\endgroup$ – Slarty Dec 12 '20 at 18:04

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Heavenium engine

Take an ordinary water wheel. No water. Put a piece of heavenium under one side of the wheel. The side above the heavenium will become lighter, and the wheel will rotate. Use this heavenium engine to power propellers. Problem solved.

Note that the same principle can be used to power lathes, mills, mechanican looms, spinning jennies, and so on. Heavenium engines will power a fervent industrial revolution.

After the discovery of heavenium, your society won't remain preindustrial for long.

This    This
half    half
is      is
heavy   light
   _____
  /     \
 /       \
|    <>   |
 \       /
  \_____/

       ^^^^^
       heavenium
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If you lower the heavenium underneath your gondola after you reach altitude you will start to sink and can then glide your airship if it has wings. Then raise the heavenium again to gain bouyancy and you will rise again. You can change your wings such that you glide as you rise and glide as you fall. Keep doing this and you will move forward till the heat energy is converted into kinetic energy in the atmosphere and you will have travelled.

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    $\begingroup$ Tacking, but vertically. $\endgroup$ – Joe Bloggs Dec 13 '20 at 22:55
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    $\begingroup$ The heavenium doesn't even need to be moved up and down it could just be moved away from your cargo. If there were two cargo sections in your gondola, forward and aft, separated by some empty space, i.e. a reasonable distance apart, then two masses of heavenium could be put together in the middle of the empty centre section and repeatedly wheeled away from each other towards the front and back of the empty section then back together in the middle again. $\endgroup$ – Tobe Dec 14 '20 at 13:51
  • $\begingroup$ Hi @Tobe, your answer interests me greatly because it may be relevant to a similar case in a worldbuilding project of my own. I was wondering (since you seem to have expertise/interest in aviation?) if there's a precedent for this kind of gliding? Is there way to get a back-of-the-envelope (lol) calculation for the glide ratio and/or velocity-relative-to-the-wind of a rising/falling airship? $\endgroup$ – Qami Dec 15 '20 at 1:08
  • $\begingroup$ @Qami There is an answer below from Brian Drummond that gives a a link to a underwater glider concept. His answer also gives lift to drag estimates for the Airlander Hybrid Airship of 3/4 and another plane of 8/10. Might be worth asking on the aviation SE as I haven't got the background, unfortunately. $\endgroup$ – Tobe Dec 15 '20 at 17:58
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Heavenium negates a force (the effects of gravity) but doesn't generate any thrust itself and so cannot be used for propulsion.

The 10m radius of effect might be difficult to work with depending on the dimensions and mass distribution of your airship and the amount needed to have the effect. For example, something the size of the Graf Zeppelin would be 236m and 33m high and would need chunks of Heavenium distributed in a 10m grid across the airframe. These chunks would vary in size depending on the mass distribution; lighter parts of the airship would only need smaller chunks. One would need to explain how these chunks in various awkward places in the airframe are accessed so they can be heated. (Looping back to propulsion briefly, it's actually a good thing that Heavenium does not generate thrust or the locations in the airframe would need to be load-bearing too.)

As for conservation of energy, it would be worth doing a quick calculation using the formula for potential energy stored by gravity and the mass of your airship to see how much energy needs to be stored. This will determine how much heat and how much time it would take to charge up the Heavenium; might take a couple of days or even a week in a kiln or something. Also, you say "If used to transfer potential energy into objects by moving them higher the Heavenium become discharged." but does the energy come back when going back down? If not, either the energy is being emitted somewhere or conservation of energy isn't true.

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  • $\begingroup$ You make some good points. But I'm not convinced that Heavenium can't be used to generate thrust by some devious means. However it would need to be distributed. I would assume the places where it was needed would be easy to access by design. Concerning the discharge - no I imagine it is lost as heat to the environment in the same way that any other falling object loses energy. Re the calculations yes good point. $\endgroup$ – Slarty Dec 12 '20 at 18:27
  • $\begingroup$ @Slarty - Heavenium is charged by heat so if you say that energy of descent is released as heat, you would want to explain how that dumped heat is not recharging the Heavenium. Moreover, if the heat isn't recharging the Heavenium, then you're faced with the possible problem of dissipating it so that it doesn't set fire to the airship; a sudden drop in altitude causing a spike of heat to be released would be disastrous. $\endgroup$ – GrumpyYoungMan Dec 12 '20 at 19:53
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    $\begingroup$ The concentrated heat energy of the Heavenium is dispersed as the distributed potential energy of the raised airship. On descent that potential energy is lost as very diffuse heat energy. Think of how much heat is involved when any ordinary airship descends loosing PE it is hard to measure it. Only really an issue for things like spacecraft re-entry. I suppose to the extent that the airship is heated as a whole the Heavenium might get a little energy back but it would be miniscule. A battery may get hot if you discharge it, but you can't charge it by making it hot.. $\endgroup$ – Slarty Dec 12 '20 at 20:51
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There are autonomous underwater craft which move forward by simply making themselves denser or less dense than water (by compressing or expanding an airbag). This allows them to glide, under either weight or buoyancy, with "lift" converted to forward motion by the airfoil shape of their body.

If you're willing to abandon the traditional cigar shaped envelope, you can certainly do the same in the sky with an airship, using Heavenium, by moving it forward or aft to adjust the centre of buoyancy, and angle the nose up to climb, or down to dive.

It might look a bit like a huge flying butt the Airlander, by Hybrid Air Vehicles. (image : Conde Nast Traveler)

enter image description here

An alternative might copy the blended wing/body concept of the AirbusZeroE, but perhaps without the redundant wingtips.

Here the point of the wing isn't to provide lift : there's no need; but to provide forward motion. You may get a lift/drag of 3 or 4 for the flying buttAirlander giving 1 km forward per 250m climbed; the blended wing may be closer to 8 or 10, giving 1km for 100 or 125m climbed.

enter image description here

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Quick reality check:

The Gravitational potential energy is locally

U = mgh

This is for example valid for a stationary object in a stable gravity field. m is the mass, g is the local gravity, h is the height. (Height is relative to an arbitrary point, so that this is mostly useful for measuring differences in potential energy)

When you apply heat to your heavenium, g decreases for objects around it.

This decreases the value of U, resulting in a loss of potential energy.

The energy must be conserved, as you mentioned.

Where does the potential energy go?

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  • $\begingroup$ That is a good point. I think that energy must be held within the heated Heavenium itself. If you try to remove the Heavenium the energy must transfer back into the airship. Would that work or does that lead to other problems? $\endgroup$ – Slarty Dec 13 '20 at 16:29
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    $\begingroup$ @Slarty This means that dropping a ball of heated Heavenium with a dense, perforated shell from a height would function as an incredibly powerful grenade. An asteroid with a Heavenium core would lose a lot less kinetic energy to the atmosphere, smash on impact with the ground, then level cities, even if it was a relatively small one. (Where does Heavenium come from?) $\endgroup$ – wizzwizz4 Dec 13 '20 at 16:51
  • $\begingroup$ Yes I suppose it would. Fortunately this is a pre-industrial society so would not have access to space. On this basis they might still use it as a weapon, but given it's rarity it might be too costly. Probably easier to drop large barrels of burning pitch and oil from an airship. $\endgroup$ – Slarty Dec 13 '20 at 18:30
  • $\begingroup$ the energy needs to go somewhere. Pick a form: en.wikipedia.org/wiki/Energy#Forms . If stored in the heavenium, one option would be that the heavenium heats up, requiring cooling, rather than heat, to get it work (transferring back that energy however requires being able to restore the energy from the heavenium somehow, or ending up with objects with permanently altered gravity) $\endgroup$ – njzk2 Dec 13 '20 at 21:05
  • $\begingroup$ One way to reduce a gravity field is to generate negative gravity. I think one way this could work is if somehow the heavenium had negative mass and if adding energy could increase its mass, resulting in it creating a larger negative gravitational field $\endgroup$ – njzk2 Dec 13 '20 at 21:20
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Heavenium Jet Engine

The theory of this engine is based in the Archemidean principles, and while it would first be used by civil engineers for fountains and other waterworks) and shipwrights (of seas) it could eventually be adapted for airships.

The principle behind it is simple - a still fluid stays still because every other bit of fluid above and to the sides of it presses it down with the same force of gravity. But what would happen if we put a vertical pipe of heavenium into that fluid?

The fluid inside the pipe would get much lighter and the surrounding fluid would force it upwards, just like a piece of cork under water. And it would draw with it a new amount of fluid, which would get lighter and be forced upwards in a constant stream.

This upwards motion of fluid alone would be godsend for civil engineering - a pump with no moving parts! But that is not all - the fluid that has started flowing still has some momentum to it that can be redirected. Just put a bend in a pipe and it will now flow out sideways propelling the engine and anything that is attached to it sideways.

Heavenium Jet Engine

Air is just a form of fluid - and as boat can float on a water - so can balloon on the air. And in the same way the heavier water would force lighter water upwards - so would air.

Of course there are differences. For one - air is about thousand times less dense than water which means that it will propel the ship with much less force. On the plus side, that means that heavenium will need to be recharged less. Also air unlike water can compress, which means that to get a good flow you instead of a simple pipe you would need a much wider funnel in the intake.

Pros:

  • No moving parts
  • Simple construction
  • Easily controlled (rudder + lid or just mount the whole thing on a swivel)
  • Useful in other applications (lower cost and quicker R&D)

Cons:

  • Very low thrust in the air
  • Difficult to recharge

Possible improvements (possibly incompatible):

  • Replace the Heveanium funnel with ordinary funnel + Heveanium mesh on the intake for better pressure profile and efficiency
  • Place re-loadable heaveanium bunker above the funnel for easier refuelling
  • Add access and fittings for in-place recharging - e.g. burning a breazier of coal right below the funnel
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  1. I don't see any obvious logical inconsistencies with the concept of heavenium itself. It's like hydrogen only better at lifting: if it's a solid, it can easily be attached to the airship, or anything else people wish to lift up.
  2. Given your description of heavenium as a countergravitational substance, I don't see how it can be used for lateral movement. I think your aerogators will still need some kind of motive force, a fan of some kind, or sails, to actually propel their ships forward.
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    $\begingroup$ How is this a useful answer? It's just an opinion $\endgroup$ – Raditz_35 Dec 12 '20 at 13:28
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    $\begingroup$ @Raditz_35: Very simple! Because the OP asks two questions. 1. Are there any obvious inconsistencies with Heavenium? and 2. How can the inhabitants of my world use Heavenium to propel these airships forward? And I gave answers to each. $\endgroup$ – elemtilas Dec 12 '20 at 13:37
  • $\begingroup$ That's just a very literal interpretation and doesn't seem very helpful $\endgroup$ – Raditz_35 Dec 12 '20 at 23:29
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    $\begingroup$ @Raditz_35 I can't speak for the OP but I do think this answer is helpful. They are pointing at the need of a guiding force so that the vessel can actually move in a deliberate way, instead of just up. $\endgroup$ – A. Kvåle Dec 13 '20 at 11:00
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Heavenium violates the Second Law of Thermodynamics. You don't need fuel.

What?

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. Isolated systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy.

[…] In all processes that occur, including spontaneous processes, the total entropy of the system and its surroundings increases and the process is irreversible in the thermodynamic sense. The increase in entropy accounts for the irreversibility of natural processes, and the asymmetry between future and past. […]

[…] Its first formulation is credited to the French scientist Sadi Carnot, who in 1824 showed that there is an upper limit to the efficiency of conversion of heat to work in a heat engine. This aspect of the second law is often named after Carnot. — Wikipedia, used under CC BY-SA 3.0

Why?

All processes that require heat are either entropic in nature (e.g. cooking), or actually require a temperature difference (e.g. Sterling engines, solar panels). All natural processes that extract useful energy (aka do work) from a temperature difference also reduce that temperature difference. In short: without access to sunlight and the vacuum of space, you'll run out of usable energy sooner or later.

Heavenium, however, works on absolute temperature, like entropic processes, but provides useful work, which you can normally only get from a temperature gradient. It's a negentropy source. This stuff's worth more than the Sun.

How?

There are countless ways of making use of this, but I'll start with the simplest to explain.

Heat pump in a box

Make a pulley. One end of the pulley should be a box containing some fancy technology and some Heavenium (I'll get to that in a sec); the other should be weighted so that it goes up when the Heavenium is “off” and down when the Heavenium is “on”. Attach the pulley to a really tall tower.

In the box, wind up some clockwork, and attach it to a heat pump. Set the heat pump so that it'll warm up a compartment containing Heavenium and cool down a compartment containing hot water, then start it going and shut the box. The Heavenium box will go up. Use some of this energy to do work (e.g. winding up some more clockwork). Eventually your clockwork will run out, or your heat pump won't be powerful enough to heat the Heavenium to the critical threshold any more, and the Heavenium will run out of magical lifting ability; you know when this will happen in advance, thanks to your calculations, so you can switch to generating energy from the pulley going the other way.

If you use a Sterling engine to recover the energy from the temperature gradient the heat pump made, you will have:

  • Cold water, and a cold box in general; and
  • More energy stored in clockwork / used to do useful work than you started with.

With a sufficiently-powerful heat pump, you could start with regular old ambient-temperature water, cool it down, and generate energy for useful work. Of course, eventually, this energy would run out; friction and other losses would see it slowly lost to heat. But you can extract work from heat.

Your airship does not need fuel.

Heavenium engine

Okay, so maybe building a massive tower in the middle of your airship isn't actually all that practical. You need something more engine-like. Take a heavy flywheel, and put it vertically over a well-insulated Heavenium-containing oven (so that the rising side is lighter); insulation reduces the maximum power your heat pump system needs to have to get the Heavenium hot enough. (Frictional losses aren't all that important because a Heavenium engine uses heat as fuel – I still can't get over how overpowered this is!) Fuel this oven with a powerful heat pump (or chain of heat pumps) powered by the Heavenium engine. The energy will eventually get back to the heat pump no matter what you do, but you can speed it along by sticking the “cool” end(s) of the heat pump on whatever's generating most of the frictional losses.

Now simply heat up the oven to the critical temperature, spin the engine a bit to get it started, stick a fan on the end and you're away!

When?

Heat engines have been known since antiquity. The first refrigerator (requiring pretty good heat pumps) predates the industrial revolution by over 75 years. While this technology might not be immediately apparent, since the Second Law of Thermodynamics hadn't been invented yet, anyone who understood fridges and had heard of Heavenium would probably be able to figure it out, and it wouldn't take much longer to develop heat pumps good enough that this would be viable.

Unless, of course, you need to get the Heavenium really hot. Then this is right out.

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  • $\begingroup$ Well that has certainly given me some food for thought! I had tried to ensure that the system would not allow perpetual motion, but I’m not sure that I have succeeded. Perhaps the devil is in the details here and might be corrected by some clarifications or adjustments? I think you are correct at least with the flywheel in the insulated box +1. Can you see any way to fix this? For example if the Heavenium had to be heated to charge it and then to cool before showing any gravitational effects from the energy stored within it? $\endgroup$ – Slarty Dec 14 '20 at 18:39
  • $\begingroup$ @Slarty Even then, you'd still have Conversation of Momentum violation, which would, in theory, make it possible for a millennia-spanning cult to crash the Earth into the Moon (though they'd need a mountain of Heavenium to do so in a reasonably-short time period). Also in theory (though in a much more dubious theory, relying on quantum physics – something that presumably doesn't exist in your world), it'd make it possible to retroactively change the probabilities of events. $\endgroup$ – wizzwizz4 Dec 14 '20 at 18:55
  • $\begingroup$ If you really want to prevent this, then go ahead – but I don't think it's necessary for your story. You're not going to get this to be completely compatible with current physics without a lot of reworking, and that might take the magic out of it. Instead, I'd go for the “nuclear fusion” route: theoretically possible, and people have managed it, but they've never been able to get out more energy than they put in. Maybe in 50 years, somebody might manage it, but it's sci-fi right now. $\endgroup$ – wizzwizz4 Dec 14 '20 at 19:00
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I can see a problem with Heavenium - at best it only reduces mass to 90% of normal. What this means is a 20 ton airship will plummet out of the sky just as quickly as a 2 ton brick. To overcome this, you suggested hot air to provide lift. So your airship will need to carry a source of heat aloft, which will also require its own fuel. BUT ... all this adds even more weight to your airship.

At first, one would imagine having a crew shovelling wood or coal into a fire which heats the Heavenium with the waste heat being used to lift the now lighter airship. You could have a turbine in your chimney, turning a propeller through a gear mechanism to provide forward thrust. So while the Heavenium itself is not providing thrust, the thrust is generated as a byproduct of the means to lift the airship and heat the Heavenium. Later developments could have more efficient heat sources - gasoline, electricity, nuclear power; jet engines to provide thrust and drive turbines; helium to provide lift (not hydrogen, as it doesn't behave well with flames!); lightweight metals replacing plywood; and so on.

As your airships get larger, you could pump liquified Heavenium around your airship (if the stuff ever melts?), or just pump the heat around your airship heating lumps of Heavenium strategically placed around the structure.

However, there is going to be some tricky balancing between the weight of your airship (structure, fuel, cargo, passengers, etc), the weight reduction properties of Heavenium, the amount of lift provided by hot air/helium, and the air density as it varies with altitude/weather.

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    $\begingroup$ It reduces (effective) gravitational mass, but not inertial mass. This means that everything falls 10% slower. $\endgroup$ – wizzwizz4 Dec 14 '20 at 19:05
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Heavenium heat engine

Take a Bhāskara's wheel filled with half Heavenium, half water. Put heat in one rotating side, left other side to lose heat to air. You will have rotacional force generated in place. A little coal could make you very far.

See Renewable Energy from Evaporating Water for inspiration.

Bonus: You can use the residual heat to keep the lifting Heavenium warm.

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  • $\begingroup$ More efficient: let the Heavenium lose heat to spinning the wheel round. $\endgroup$ – wizzwizz4 Dec 13 '20 at 16:51
  • $\begingroup$ That's the idea above. Only one side is continually warmed, so the heat is lost when the heated side rotates away from the heat source. $\endgroup$ – André LFS Bacci Dec 13 '20 at 17:21
  • $\begingroup$ No, I mean: the OP wrote “If used to transfer potential energy into objects by moving them higher the Heavenium become discharged.” This means that you could have an engine that lost virtually no energy as heat, if you insulated well; instead of losing it, you can use it. $\endgroup$ – wizzwizz4 Dec 13 '20 at 19:07
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There are several subtle implications in your "Heavenium":

  • how efficient is the heat conversion in potential energy (i.e.: how fast will it discharge when "pushing up")? If efficiency is comparable with steam engines then it's mostly useless as "engine", while retaining it's full power as "keep height" device.
  • "perpetual motion spinning engines" as described in other need to be heavy to generate a sizable amount of energy and thus are a bit useless for aircraft motion.
  • It's unclear how do you plan to regulate ascent/descent of your aircraft and I assume it is "normal" Archimedes law (corrected with gravity, and thus weight, reduction).
  • If the above it's true then "airships" need to be huge to leverage on a certain amount of air weight. This, incidentally, means they will have a large cross-surface winds will act on.
  • What happens, exactly, when Heavenium is "discharged"? I will assume it gradually looses it's "power" and thus the nominal "90% reduction" will steadily and gradually decrease as the airship rises up.
  • If you want to be "creative" you can make your airship large and flattish and "power" it with two (or more) Heavenium capsules: one near "forward end" and the other near "aft end".
    • start with airship at equilibrium with 80% Heavenium charge (~70% gravity reduction).
    • heat up forward capsule and ship will start raising "nose first". This will cause a forward drag because of ship geometry.
    • heat aft capsule "just enough" to maintain it's power as ship raises.
    • stop heating forward capsule; this will cause a brief "overshoot" (mass is not affected, so airship has a rather large inertia) and then it will start falling, again "nose first" (if aft crew did their job right) and thus, again, producing a forward drag.
    • rinse and repeat: you ll'have a big flat "whale" moving slowly and steadily (in calm air).
  • Heavenium (as described) cannot be used directly to produce horizontal (orthogonal to gravity force) drag.
  • You can't either use any kind of "sails" because those rely on keel drag, which you don't have.
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  • $\begingroup$ I think Heavenium can be used to produce horizontal force. See the reply from AelxP. $\endgroup$ – Slarty Dec 20 '20 at 1:02

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