3 ms·
Great analysis. A few random thoughts 1. The dreaded helium leakage. It might not be a problem at all. Think of a party balloon of the foil type. It stays afl
by credit_guy 4y ago
Great analysis.
A few random thoughts
1. The dreaded helium leakage. It might not be a problem at all. Think of a party balloon of the foil type. It stays afloat for weeks. And it has positive pressure. A neutral pressure one would leak much less. But maybe not to zero. Ok, now use a double layer. Just like there are double hull submarines, this would be a double foil balloon. The distance between the outer foil and the inner foil would be only 1cm or so, so 99.9999% of the helium would be inside the inner foil. The gas between the two foils would in time become mixed with air, but the amount of double leakage would be negligible. The weight of the double foil would also be negligible compared to the overall weight of the structure.
2. Going up and down. Hindenburg had a cruising altitude of 200m. Up to 2000 meters or so, the air density goes down by about 1% every 100 meters. So, lowering a balloon from 200m to 0m does not mean you need to fully deflate it, only that you need to reduce its buoyancy by 2%, or add 2% ballast. For a 1100 ton airship, you need to add 22 tons of ballast. Pumping 22 tons of water 200 meters high is not easy feat. But there's a cute shortcut: you could send only 2.5 tons of hydrogen with a hose (hydrogen is more than happy to flow up), and you burn it there. The resulting water vapor needs to be condensed, but you can probably arrange that with a small refrigeration unit that you power with the electricity from a generator powered by the said hydrogen. The current cost of hydrogen is about $5 per kilogram, so this whole affair would cost you less than $15k. It's a rounding error when you ship 500 tons of cargo.
3. Fuel. Yes, it would be cool to have neutrally buoyant fuel, like a mix of methane and propane. But do you think the FAA would like that? How is that different from just having some hydrogen gas onboard, like, you know, Hindenburg? I think the most conservative design choice would be to just use plain old jet fuel.
- SuoDuanDao 4y agowould batteries work for fuel in an airship? I know the battery bank is a structural element in Tesla cars, seems like that could be done with airships as well (it'd increase the price precipitously of course)
- rimunroe 4y ago> 1. The dreaded helium leakage. It might not be a problem at all. Think of a party balloon of the foil type. It stays afloat for weeks. And it has positive pressure. A neutral pressure one would leak much less. But maybe not to zero. Ok, now use a double layer. Just like there are double hull submarines, this would be a double foil balloon. The distance between the outer foil and the inner foil would be only 1cm or so, so 99.9999% of the helium would be inside the inner foil. The gas between the two foils would in time become mixed with air, but the amount of double leakage would be negligible. The weight of the double foil would also be negligible compared to the overall weight of the structure. I assume someone else can address this better, but given how expensive and limited helium is, I don't think we can just write off losses by comparing airships to party balloons. Foil party balloons look noticeably less inflated after a week or two. I have no idea how much gas is being lost, but that seems much more than a trivial amount to the point where I don't think a second envelope is going to help you much. It will have the same outgassing problems as the inner envelope, but will add additional weight and air resistance, both of which will reduce the maximum payload. Relatedly: is it cheap to extract the helium trapped in the outer envelope? Given the quantity of helium needed for an airship fleet, is topping them up regularly even an option? I'd assume it would need dramatically more helium than is currently being produced, and there's only so much helium available to us without using something like hydrogen fusion. In college I briefly worked at Brookhaven National Laboratory on an experiment with the Relativistic Heavy Ion collider. That collider has a set of giant collection tanks next to it so that (at least as it was explained to me) in the event of a superconductor quench event, they can try to shunt all the remaining liquid helium coolant into storage in order to limit how much of the valuable resource they lose. I imagine the amount of helium they're using would be peanuts compared to the amount required for a cargo fleet.
- credit_guy 4y ago> It will have the same outgassing problems. It will not. The outgassing is proportional with the difference in partial pressure. On the outer foil the difference in partial pressure is 1 atmosphere (only helium inside, no helium outside). In time helium will leak out. Air will probably not leak in, by you can add it, to maintain equal pressure. The point is that you won't add a lot. Let's say that in one year 5% of the helium gets replaced. That means the difference in partial pressure on the inner foil is at most 0.05 atmospheres. The leakage will be much lower. Most likely you would not need to refill the helium inside the inner foil more than once during the lifetime of the airship.