Preprint: Towards a gigantic Magnus balloon with motorized belts

[PierreB]

I wondered if it was possible to have a balloon inflated with nitrogen (inexpensive, common, and non-flammable), knowing that the weak aerostatic thrust would perhaps be sufficient to compensate for the mass of the envelope, and also ensure stability.

On this topic:

https://www.quora.com/Could-we-build-airships-again-using-nitrogen-Its-lighter-than-air-or-is-the-buoyancy-not-enough-because-its-78-air

Could we build airships again using nitrogen? It’s lighter than air, or is the buoyancy not enough because it’s 78% air?

Two representative answers:

Lucas Curtis

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Science teacher (2001–present)5y

The density of nitrogen at 20ºC and 1 atmosphere of pressure is 1.165 grams per liter.

The density of air at 20ºC and 1 atmosphere of pressure is 1.205 grams per liter.

While pure nitrogen is less dense than air, it’s not enough of a difference to allow a nitrogen-filled airship to lift any significant weight.

The Hindenburg held a whopping 200,000 cubic meters (200 million liters) of hydrogen gas. If you had a blimp of the same size, but filled with nitrogen instead of hydrogen, its internal mass would be 233 million grams (233 metric tons). Assuming the skin of the blimp is negligibly thin, it will displace 200 million liters of air, with a mass of 241 million grams (241 metric tons). So the buoyant force acting on this gas-filled bladder would be equivalent to the weight of 8 metric tons.

The Hindenburg’s average gross weight — that is, the weight of the ship without hydrogen — was 215 tons. Ergo, a Hindenburg-sized blimp, filled with nitrogen instead of hydrogen or helium, would be woefully inadequate to lift its own weight, let alone any passengers or cargo.

Yes, nitrogen is slightly lighter than air, all other things being equal. But for an airship, you need a gas that is much lighter than air. Nitrogen just won’t cut it.

Kim Aaron

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Has PhD in fluid dynamics from Caltech

· 5y

Could we build airships again using nitrogen? It’s lighter than air, or is the buoyancy not enough because it’s 78% air?

No. The 78% you are quoting is NOT the ratio of nitrogen density to air density. It is the fraction of air that is nitrogen. The other 22% is mostly oxygen and a few other traces gases. The density ratio - the thing that matters for buoyancy - is more like 97%. Good luck taking advantage of that 3% difference. In principle, this could be made to float. But it’s a rather poor starting point.

For all balloons supposed to work in pumping mode (Wind Fisher, Omnidea, this one and others), the aerostatic thrust should be approximately neutral to facilitate the recovery reel-in phases, and also ensure stability.

There are no passengers, and possibly no aloft motors if the @WindFisher system was applied, just the envelope and the tethers.

Now let us try with several sizes, knowing the square law for the area, and the cube law for the volume leading to the aerostatic thrust, which is noted in kg to simplify, knowing that for 1 m³, it is about 0.035 kg. Below are some rough calculations for cylindrical balloons made of a film of 0.2 kg/m².

50 m span and 10 m in diameter.
Mass: about 350-400 kg.
Volume: 3925 m³.
Aerostatic thrust: 137 kg. It is not enough!

100 m span and 20 m diameter balloon.
Mass: 1400-1500 kg.
Volume: 31400 m³.
Aerostatic thrust: 1100 kg. Just a little more effort!

200 m span and 40 m diameter balloon.
Mass: 6000-6500 kg.
Volume: 251200 m³.
Aerostatic thrust: 8800 kg. We are a little above, but not if we count the tethers, and the discs around the balloon.

And for such dimensions it will not be possible to pressurize the gas contained in order to have a sufficiently rigid shape to avoid overconsumption for the rotation motors, unless the thickness and mass of the envelope film are increased, or/and some light rigid rods should be integrated.

So using nitrogen is therefore a possibility but not a probability. For giant balloons like this, it would perhaps be a better (or a worse) alternative to the heating wire which requires an electric cable from the ground station.

[tallakt]

ChatGPT says

At ground level, air is composed primarily of nitrogen (N₂, ~78%) and oxygen (O₂, ~21%), with an average molar mass of about 29 g/mol.
Gases that are lighter than air will have a lower molar mass than this.
Here’s a list of lighter-than-air gases and their molar masses relative to air:

1. Hydrogen (H₂)

   • Molar mass: 2.02 g/mol
   • Relative to air: ~1/14th the density of air
   • Notes: Hydrogen is the lightest gas and highly flammable.

2. Helium (He)

   • Molar mass: 4.00 g/mol
   • Relative to air: ~1/7th the density of air
   • Notes: Helium is inert and non-flammable, making it ideal for balloons and airships.

3. Ammonia (NH₃)

   • Molar mass: 17.03 g/mol
   • Relative to air: ~0.59 times the density of air
   • Notes: Ammonia is less dense than air but has a strong odor and is toxic.

4. Methane (CH₄)

   • Molar mass: 16.04 g/mol
   • Relative to air: ~0.55 times the density of air
   • Notes: Methane is highly flammable and a major component of natural gas.

5. Neon (Ne)

   • Molar mass: 20.18 g/mol
   • Relative to air: ~0.7 times the density of air
   • Notes: Neon is inert and used in neon signs.

6. Acetylene (C₂H₂)

   • Molar mass: 26.04 g/mol
   • Relative to air: ~0.9 times the density of air
   • Notes: Acetylene is used as a fuel in welding and is highly flammable.

7. Ethylene (C₂H₄)

   • Molar mass: 28.05 g/mol
   • Relative to air: ~0.97 times the density of air
   • Notes: Ethylene is close to the density of air but slightly lighter. It’s used in the production of plastics.

These gases are all less dense than air and will rise or disperse quickly in the atmosphere.
The suitability of these gases for applications (like balloons or airships) depends not only on their buoyancy but also on factors such as safety, reactivity,

And about leakage

When comparing gases in terms of leakage through a membrane, two primary factors come into play: the size (molecular weight) of the gas molecules and the membrane permeability to those molecules.

Key Factors:

1. Molecular Size: Smaller, lighter gases will typically leak faster than heavier, larger ones because they can more easily pass through microscopic pores in the membrane. The lighter the gas, the higher its rate of diffusion.

2. Membrane Permeability: Different membrane materials have varying levels of permeability to different gases. Some membranes may allow certain gases to pass through more easily due to their chemical structure or molecular interaction with the material.

Comparing Leakage of Gases:

1. Hydrogen (H₂):

   • Molar mass: 2.02 g/mol (lightest)
   • Leakage rate: Extremely high due to its small molecular size. Hydrogen diffuses faster through membranes compared to any other gas on this list.
   • Applications: Hydrogen gas can quickly escape through small pores or imperfections in a membrane.

2. Helium (He):

   • Molar mass: 4.00 g/mol
   • Leakage rate: Very high, but slightly slower than hydrogen. Helium atoms are very small and inert, making them highly prone to leakage.
   • Applications: Helium is often used to test for leaks in systems due to its tendency to escape quickly through even the smallest openings.

3. Ammonia (NH₃):

   • Molar mass: 17.03 g/mol
   • Leakage rate: Lower compared to hydrogen and helium, but still relatively high due to its smaller molecular size. Ammonia’s polarity can also affect how it interacts with different membrane materials.

4. Methane (CH₄):

   • Molar mass: 16.04 g/mol
   • Leakage rate: Moderate. Methane molecules are small but not as small as hydrogen or helium, so their leakage rate is slower through most membranes.

5. Neon (Ne):

   • Molar mass: 20.18 g/mol
   • Leakage rate: Moderate. As an inert gas with a relatively low molar mass, it will diffuse through membranes faster than heavier gases, but slower than hydrogen and helium.

6. Acetylene (C₂H₂):

   • Molar mass: 26.04 g/mol
   • Leakage rate: Slower compared to gases like hydrogen and helium due to its larger molecular size.

7. Ethylene (C₂H₄):

   • Molar mass: 28.05 g/mol
   • Leakage rate: Similar to acetylene, with a slower leakage rate due to its relatively larger molecular size compared to hydrogen or helium.

Summary of Leakage Rates (from highest to lowest):

1. Hydrogen (H₂)
2. Helium (He)
3. Ammonia (NH₃)
4. Methane (CH₄)
5. Neon (Ne)
6. Acetylene (C₂H₂)
7. Ethylene (C₂H₄)

In general, lighter gases like hydrogen and helium will leak faster through a membrane than heavier gases due to their smaller molecular size and higher diffusion rates. The specific rate of leakage can also vary depending on the membrane material and its permeability to the particular gas.

And about ammonia as a polar gas it adds

Polar membranes: If the membrane material is also polar or hydrophilic (such as certain polymers), it may interact more strongly with ammonia molecules. This could slow the diffusion of ammonia compared to non-polar gases like methane, as ammonia could adhere to the surface or interact with the membrane through dipole-dipole interactions or hydrogen bonding.

[tallakt]

Ammonia seems interesting because it could serve a dual use of levitation and energy storage. So a plant producing ammonia would have ample amouts of gas to refill their blimps. I guess Hydrogen is the same though. But their retainment qualities may differ, the small H2 molecules may be harder to seal shut in a thin blimp skin compared to ammonia.

I have to say though that any magnus cylinder filled with lighter than air gas seems quite totally in the science fiction realm to me because I would expect it was even harder to seal a blimp that was rotating in high winds over time, compared eg. to a transport zeppelin.

You have established that levitation is not singularily a factor to choose gas. So it seems my shortlist is:

• H2 with very explosive and high permeability, large lift, easy to access
• Ne [edit: I meant Helium here] which is not renewable as of today. High lift and inert
• Ammonia toxic and less permeable (possibly) and much less explosive than H2

[dougselsam]

Once I realized, years ago, that Methane (the “natural gas” we all use) is so highly buoyant, it seems surprising it is not used more for that purpose. Take Hot Air ballons, for example: hot air has 87% of the mass of regular air. Not a huge difference. Methane has a density of only 55% of air, a methane ballon would only need to have less than 1/3 of the volume to lift the same weight. That’s a huge difference. And methane is about half as buoyant as helium, so it would seem to be a reasonable choice for weather balloons, as one example. Not only that, but natural gas is relatively cheap and available everywhere. And yet I do not recall EVER hearing about a methane balloon, airship, or blimp, etc. in production for any purpose - even as a toy or research project. Why? Too simple? “global warming” (That would be a new reason, whereas methane has been around forever.) Methane - “The Rodney Dangerfield of buoyant gases”.

[tallakt]

@dougselsam

And yet I do not recall EVER hearing about a methane balloon, airship, or blimp, etc. in production

Yes it seems strange to me as well why we havent heard of these. I guess Helium is still to available to need to consider alternatives. And releasing methane/ammonium at high altitude is probably a huge global warming contributor… [sarcasm, please dont reply]

[PierreB]

@dougselsam

And yet I do not recall EVER hearing about a methane balloon, airship, or blimp, etc. in production for any purpose - even as a toy or research project. Why? Too simple? “global warming”

Previously, some gas balloons were inflated with city ​​gas (sometimes turned after into natural gas) which contains a lot of methane.

@tallakt

And releasing methane/ammonium at high altitude is probably a huge global warming contributor… [sarcasm, please dont reply]

About global warming or “global warming”, https://en.wikipedia.org/wiki/Permafrost:

Depending on conditions at the time of thaw, decomposition can release either carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback[…]

This could mean that if AWE develops sufficiently and industries can capture the methane escaping from permafrost, said methane would not immediately escape into the atmosphere. In this case AWE balloons would be doubly positive.

[Windy_Skies]

@tallakt

Neon

According to Prices of chemical elements - Wikipedia hydrogen is 1.39 USD/KG, fluorine is 1.84-2.16, helium 24.0, neon 240 USD/KG.

The density of air is about 1.225 kilogram per cubic meter. The density of hydrogen is about 0.08375 kilogram per cubic meter. The difference is 1.14125. To lift a kilogram you’d need 1/1.14124=0.876 cubic meters of hydrogen, which would cost 0.876 * 0.08375 * 1.39 = 0.102 USD

The density of air is, again, about 1.225 kilogram per cubic meter. The density of neon is about 0.8528 kilogram per cubic meter. The difference is 0.3722. To lift a kilogram you’d need 1/0.3722=2.687 cubic meters of neon, which would cost 2.687 * 0.8528 * 240 = 549.9 USD.

So neon would be 549.9/0.102 = 5390 times as expensive as hydrogen.

@PierreB

and industries can capture the methane escaping from permafrost

They can’t.

And using methane is completely insane.

If you want to entertain the idea of lighter than air balloons, hydrogen makes most sense I think, although it is also a greenhouse gas. It is now banned for this use, but you could argue to allow it for unmanned balloons. You could use hydrogen filled ballonets inside the balloon, allowing you to more easily and cheaply integrate the idea. You could also try using higher humidity, perhaps heated, air, as a lifting gas. But then I think you want to insulate the balloon so the water doesn’t condensate so much on the balloon (or ballonet) envelope.

[dougselsam]

@Windy_Skies

And using methane is completely insane.

As usual, a lot of math, mostly about using neon as a buoyant lifting gas, which to me is about as insane as it gets - who in their right mind would ever even consider using neon as a lifting gas? Seems quite irrelevant as a point of discussion, to me anyway. I didn’t see anything to back up the claim that using methane is “completely insane”. Why would it be “completely insane”? Methane is routinely burned (“flared”) at the point of extraction, because it is not even worth the cost of containing and distributing it, in many cases.

[tallakt]

@dougselsam

who in their right mind would ever even consider using neon as a lifting gas

Sorry I was mixing Neon and Helium there. I meant Helium of course.

I think this also brings up an interesting subject; as some of these buoyant gases are also climate gases (methane 28-36x global warming potential compared to CO2 according to ChatGPT, hydrogen and ammonia small potential). So if Methane was selected as a gas, the leaks worldwide would in sum over time contribute to significant global warming. So a renewable energy world would probably not be built predominantly on methane as an energy carrier.

Ammonia still seems borderline usable though it seems issues with smell, toxidity, corrosiveness and flammability make it a non starter for many applications.

I would like, though to compare flammability of ammonia vs hydrogen. Hydrogen is flammable in concentrations 4% to 75% mixed with air, but the same number for ammonia is 15% to 28%, making it easier to deal with. For example, if a cylinder was filled with “100%” ammonia gas, you would have to mix a significant amount of air and also have an ignition, before the cylinder exploded. Such a leak would probably be detectable through pressure drops if the internal pressure was higher than atmospheric pressure.

So while Helium is both cheaper and better in almost all respects, if it can’t be used, the options seem difficult to implement. And if lighter than air AWE is to give a significant power contribution to the earth, vast amounts would be used.

Lets estimate how much gas is necessary. Lets use the Wind Fischer MAG100 as an example. It is 160 m3 volume and lets assume it produces 100 kW [I did not find any stated power on the web page]. In 2023, 1 terrawatt of wind energy was installed over the world. Lets assume we double that by installing MAG100s. That would require 1.630.000.000 m3 of Helium gas just for the initial fill. This represents (according to ChatGPT) 5% or the world’s Helium gas reserves…

[Windy_Skies]

@tallakt

the options seem difficult to implement.

Or we are ignorant of the solutions that are already used. Hydrogen is the best option, if you explore the idea of lighter than air balloons you should look at hydrogen first and make sure that it is difficult to implement, and not just seems to be so. If hydrogen is difficult, any other solution is going to be either more difficult, or plain “impossible”.

@Windy_Skies

Hydrogen is odorless, colorless, and tasteless, so human senses won’t detect a leak. However, given hydrogen’s tendency to rise quickly, a hydrogen leak indoors would briefly collect on the ceiling and eventually move toward the corners. For that and other reasons, industry often uses hydrogen sensors to help detect hydrogen leaks and has maintained a high safety record using them for decades.

Combustion

Hydrogen combustion primarily produces heat and water. Due to the absence of carbon and the presence of heat-absorbing water vapor created when hydrogen burns, a hydrogen fire has significantly less radiant heat compared with a hydrocarbon fire. Because a hydrogen fire emits low levels of heat near the flame (the flame itself is just as hot), the risk of secondary fires is lower.

Like any flammable substance, hydrogen can combust. But hydrogen’s buoyancy, diffusivity, and small molecular size make it difficult to contain and create a combustible situation. In order for a hydrogen fire to occur, an adequate concentration of hydrogen, the presence of an ignition source, and the right amount of oxidizer (like oxygen) must be present at the same time.

Hydrogen has a wide flammability range (4% to 74% in air), and the energy required to ignite hydrogen (0.02 mJ) can be very low. However, at low concentrations (below 10%) the energy required to ignite hydrogen is high — similar to the energy required to ignite natural gas and gasoline in their respective flammability ranges — making hydrogen realistically more difficult to ignite near its lower flammability limit.

Explosion

An explosion cannot occur in a tank or any contained location that contains only hydrogen. An oxidizer such as oxygen must be present in a concentration of at least 10% pure oxygen or 41% air. Hydrogen can be explosive at concentrations of 18.3% to 59%. Although this range is wide, it is important to remember that gasoline can present a greater danger than hydrogen because the potential for explosion occurs with gasoline at much lower concentrations: 1.1% to 3.3%. Furthermore, there is very little likelihood that hydrogen will explode in open air due to its tendency to rise quickly. This is the opposite of what we find for heavier gases such as propane or gasoline fumes, which hover near the ground, creating a greater danger for explosion.

So you add a hydrogen sensor. And IIRC you would always have an ignition source so the flame/explosion would occur as soon as possible, limiting the size of the explosion. That is if you are using hydrogen-filled ballonets inside the balloon leaking hydrogen into the balloon.

One idea might be to fill the balloon with nitrogen instead of or in addition to air, but I think then the risk of asphyxiation might exceed the original risk of explosion. Maybe there is a balance.

@dougselsam

I didn’t see anything to back up the claim that using methane is “completely insane”. Why would it be “completely insane”?

Using methane is your idea. Do the homework yourself. You can compare the cost of the gas, cost of the larger envelope, impact on other aspects of the design from the lower lift, and so on.

[tallakt]

@Windy_Skies

However, at low concentrations (below 10%) the energy required to ignite hydrogen is high — similar to the energy required to ignite

So you could use a magnus cylinder filled with 10% H2 and the rest air and be buoyant enough to be useful and still not too explosive?

[Windy_Skies]

Compared to just using off the shelf hydrogen-filled ballonets that doesn’t make sense I think. You’d needlessly use the more expensive impermeable fabric for the whole balloon, and the more expensive manufacturing and design.

[tallakt]

Also, Hydrogen mixed with nitrogen may be buyant enough but pose little explosion hazard.

I think H2 can be replenished quite easily?

[Windy_Skies]

I’m not a hydrogen airship designer, but maybe you could sense the tension of the ballonet envelope or the gas pressure and include a hydrogen gas cylinder to replenish the hydrogen lost when it gets low. Because of the flammability, permeation, and embrittlement of metals that is going to be more difficult than for helium, I don’t know about other flammable gases.

You could compare the hydrogen lost from the ballonet to that from the balloon, if sensors can measure hydrogen concentrations. Then if the loss from the balloon always exceeds that from the ballonet, hydrogen concentrations shouldn’t be able to build up enough in the balloon to become dangerous.

[tallakt]

@Windy_Skies

You could compare the hydrogen lost from the ballonet to that from the balloon, if sensors can measure hydrogen concentrations

I think we are probably getting a little closer to what such a system could look like. Add the need that the cylinder must rotate at high speed while still maintaining sensing and replenishing gas, as well as making sure there are no leaks and ignition sources (did you say lightning?). This would be pretty ____ hard to build.

Lightning itself could be a showstopper because it would happen now and then, and if that did lead to an explosion, the noise would be quite disturbing, even if no major harm was caused to third person due to the long length of the tether.

[Windy_Skies]

I’m not sure that the ballonets need to rotate, or if they do that the electronics also need to rotate. Or if it is better that they do what the rate of rotation is and what effect that has on the electronics, close to or on the axis of rotation.

Lightning should have a harder time reaching the ballonets I think, or maybe even balloon with lightning rods and landing in thunderstorms. How do zeppelins and blimps manage lightning? Hydrogen concentration should be too low in the balloon and too high in the ballonet for combustion let alone explosion, so the main risk is when the ballonet is ruptured, and then concentrations for combustion are sooner reached than concentrations for explosion.