Preprint: Towards a gigantic Magnus balloon with motorized belts

[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.