361–370 of 385 posts
Great essay. How he failed to mention Hybrid Air Vehicles Airlander is beyond me, though. https://www.hybridairvehicles.com/
"It’s a very different vehicle than I am considering. Hybrid blimp instead of non-hybrid rigid. I think even with a blimp 10 tons will be too small to be price competitive in the market I’m talking about."
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The primary emphasis of the analysis is transoceanic.
The capacity of airships is miniscule compared to transatlantic shipping. The article suggests a 450m long airship carrying approximately 800 tons. For contrast, a single container ship is about the same size as that airship, but can carry 230,000 tons. Why would you replace your current system with a new system having 300 times less capacity? A brief estimate suggests that the container ship only uses 100 times as m…
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I don't understand this. LH2/LOX typically burns on the rich side to increase exhaust velocity. This means more momentum for less mass, which is what you want from a rocket. This is the opposite.
John Clark goes into detail in his book Ignition! about why smaller, lighter exhaust molecules are much better than larger and heavier ones.
The airship renaissance is the fusion of transportation world. It's always ten years away. Seriously, I've been hearing about the great promise of modern airships for twenty years. Where are they? Are there any airships operating commercially now outside of niche applications?
I know some of the Canadian provincial governments were looking at using airships to provide a means of supplying some of the more remote northern towns - because of weather/terrain conditions, you can't build a rail head that far north, and the roads aren't reliable, so light cargo planes are the only reliable means of getting goods around. Airships, even of the good year variety, would be far cheaper for the weight…
Can't or it costs too much for the benefit? Norway (with extreme weather and horrible terrain) has an extensive rail network, including in the Arctic, so i doubt there's anything in Canada making railways impossible. Too expensive to service 0.02 people per km2 maybe.
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I mean if the alternative transports also don't work in bad weather I'm not sure you can use some failures to disqualify airships. So long as they work "more" days of the year it's a better solution. Weather doesn't really sneak up on us anymore.
> I mean if the alternative transports also don't work in bad weather But they do. Imagine the kind of storm that can stop a freight train. Or the kind that would give the captain of a large container ship pause. Now imagine airships facing the same storm.
Let me know what freight train can run without rails ... All I have to find is 1 day the airship can travel and its better than your trail.
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> but it would surprise me if you could scale them up to a kilometer in size. It's like the intuitive argument that heavier objects fall at the same rate as lighter objects: throw two shoes off the roof, if you tie their shoelaces together will they fall faster? You start with N kites and connect them, each kite retains its airworthiness and connecting them doesn't change that. > nearly [constant] The ratio falls off…
> You start with N kites and connect them, each kite retains its airworthiness and connecting them doesn't change that. If you do that, you have N wires between the kites and the ground. Keeping them untangled may be a problem. Your best bet probably is tying them together and having only one thicker wire towards the ground. Making sure each of those wires takes 1/Nth of the load from the wind definitely will be a pr…
In terms of keeping the load balanced, I figure the individual kites can modulate their surface area somehow. Maybe they fold like butterfly wings, or dilate, or have accordion pleats, whatever. Some of them would have motors and propellers for active control.
You would also want to allow for flexibility at large scales, by making the connectors elastic or even having motorized spindles.
Last but not least, the failure mode of the large structure is to break up into smaller structures. If you allow this to happen in a controlled fashion at the connectors, then the large structure breaks up into functional autonomous substructures. They can eject any damaged parts and reform.
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When I say "kite" I mean the form of the airfoil (as contrasted with planes or blimps, etc.), not that they are tethered to the ground.
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I don't think the "plank over a ditch" is similar. If anything it's more like a suspension bridge?
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You're exactly right, but perhaps missed that the trade route you're describing is China to Los Angeles, which alone accounts for $132 billion in trade every year, and perhaps that cargo vessels allegedly account for 20-25% of anthropomorphic carbon emissions. Also probably worth pointing out that airships going against the jetstream are still faster than cargo ships which are also going against sea currents. I'll re…
I also find the idea of "they have to land at a airport" pretty murderous for autonomous vehicles. Like no they do not. They can deliver cargo to autonomous barges, which then deliver the cargo slow and steady and reliable to cargo terminals. No autonomous vehicle ever has to touch land..
And that's not even counting the possibilities for water landings
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> 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…
Even once in the lifetime of the airship will be millions of dollars though.
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Or a single tracer bullet, if it's filled with hydrogen.
Apparently that's not actually the case. The Brits and French had a hell of a time shooting down German Zeppelins in WWI with standard tracer ammo.
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I too am not an aerospace engineer, but venting hydrogen after touch down seems easy enough. After all if you open the cells the gas just goes away. By contrast a broken fuel tank leads to liquids spilling on the ground, which seems like fun. That all said, liquids don't explode, gasses do. So if you were unlucky and the hydrogen exploded then life would get very exciting very quickly.
> That all said, liquids don't explode, gasses do There may be a technical definition of explosion that says an exploding tank of fuel is not "exploding". Do you care? A ball of fire is an horrific thing
They can burn of course, and a fireball is a fireball, but an explosion creates shock waves, and all kinds of ancillary damage. Recall the Beirut explosion recently - the fire was relatively contained, but the damage from the explosion is vast.
So yeah, talking about gasoline here - the liquid doesn't explode, it burns. However the gas (as in gas, not liquid) can explode, rupturing the tank and spraying burning liquid everywhere. The worst case is a tank mostly empty - the fumes explode, spraying the rest of the liquid. The best case is a full tank. Liquids can absorb a lot of heat, without expanding or creating pressure. Once they boil though (which requires that the liquid doesn't already "fill the tank", pressure builds leading ultimately to the rapid disassembly of the container.
Incidentally this is why throwing an _empty_ aerasol can on a fire is very dangerous, possibly more dangerous than a completely full one (depending on the contents).
But to your point, and explosion and a fire are very different animals, with very different outcomes.