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indi wrote

I love the idea, but hydrogen is dangerous and helium is non-renewable. Thermal (hot-air) airships may be the way to go, but they're slow and hard to handle, can't really fly in high winds, and can't carry much.

I'd say before we can seriously think about a large-scale airship infrastructure, we'd need:

  • Better materials, not so much for the bag itself, but for all the attached hardware that will hold the cargo and passengers. The materials have to be fairly strong, very light, and - this is probably the most important hurdle - extremely cheap.
  • Better (lighter, more energy-dense) energy storage (for the power for the propellers and other stuff - likely heaters are going to be a huge draw if it's a thermal airship). But that's already being heavily researched because it's just generally badly wanted.
  • Ideas on how to load/unload cargo/people cheaply and safely. Once you've got your airship loaded (and assuming winds won't be a problem), you're golden... it's a practically free, usually smooth, fairly safe trip (albeit a somewhat slow one, but one assumes that's acceptable if you've chosen to go airship). The tricky part is getting stuff on and off the airship. Airship landings are not easy, and even once you manage that, mooring can be tricky if there are winds.

I'm no futurist, but if I had to make a bet, I wouldn't bet on airships. I would bet on propeller lifters (basically helicopters or quadcopters, likely with quite a few rotors) that use clean power.

Regarding that von Kármán calculation in the Scientific American article: I don't put much stock in any calculation of the "price" of a mode of transportation that doesn't include the entire cost... meaning a full lifetime assessment including all environmental costs (such as pollution clean-up), from well to wheel as they say. A freight train may need (relatively) little energy to move... but by the time you factor in the cost of laying all the rail - not to mention maintaining it - I don't believe it would look as good.


edmund_the_destroyer wrote

I think your criticism of the von Kármán calculation is fair.

On the other hand, I suspect even if you calculate the cost of laying rail for trains, freight trains are still the most energy efficient cargo system we have this side of sailing ships.

This article states that a modern airship uses 80% less fuel than a modern cargo plane. I tried to find stats for cargo planes and got this: on page 7 the most energy efficient cargo carrier had payload fuel energy efficiency of 146 in units of kgkm/MJ. So our hypothetical airship might reach 730 kgkm/MJ.

Another measurement I've heard, in US units, is that friction on rail is so low that one gallon of diesel fuel will transport one US ton of freight 400 miles. So that's 2000 pounds/2.2 pounds per kg * 400 miles * 1.6093 miles/km / 136 MJ in a gallon of diesel fuel =~ 4300 kg*km/MJ.

I could have my numbers wrong, please check. But if I'm right, rail is so far ahead of airships that if you spread out the cost of building the rail over the life of the railroad then rail still comes head. And that's true even if you consider that rail is inherently at a disadvantage because it can't travel directly from origin to destination as the crow flies. A 30% or 50% efficiency loss due to circuitous routes still puts it ahead of airships.


indi wrote

There are other costs that rail has that air doesn't, such as the environmental impact of running rail through long stretches of green space (something inevitable in Canada, for example).

But I generally think you're correct. For overland transport, yes, rail is probably the best way to go.


edmund_the_destroyer wrote

As far as running rail through green space, I think that brings up discussions of making infrastructure as environmentally friendly as is practical vs advocating primitivism or something along those lines.

Maybe if I had a more abstract perspective on the situation I would advocate the latter view. But I have an enormous extended family that I love dearly, and I can't see any policy that calls for mass dismantling of infrastructure objectively. I imagine it would require the death of huge portions of the population - which may well happen anyway with what humanity is doing, but I can't bring myself to advocate fixing the problem by proactive mass murder.