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Cargo airships could be big

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Re: Cargo airships could be big

#221

Post by mike-the-mikado »

TylerE wrote: post #74
rootusrootus wrote: post #42

Earlier quoted context omitted.

There is a large dichotomy between the value of goods sent by plane vs ship, almost certainly due to the trade-off on speed. The intent with the airship idea seems to be to make something roughly similar in price and speed to trucking on land, but over the ocean. There is arguably a big chunk of cargo that would like to be in that middle area.

Why airships, a known failed technology, rather, than, say, a large hydrofoil/catamaran, tech that has been proving quite successful on long distance ferries for decades. The Hindenberg-class Zeppelins had the theoretical lift capacity of approximately... 8 40ft containers.

Electric cars were failed technology for about a hundred years. But with better battery technology, combined with a need to reduce carbon dioxide emissions, they are the future.

If something can only work effectively at huge scale, there are likely to be a number of enabling technologies needed to get there.

Re: Cargo airships could be big

#222

Post by dbrueck »

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air)

A vacuum (or near vacuum) would provide more lifting force per liter, would not have the scarcity problem of helium nor the safety problem of hydrogen, and assuming the thing that generates the vacuum is transportable, it'd eliminate the need for separate ballast.

Edit: the wikipedia article cited by slibhb has all sorts of good info - thank you for sharing that!

Re: Cargo airships could be big

#223

Post by lucideer »

dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

Wild wild speculation: I'd imagine "rigidity" is a trade-off between weight and ability to withstand the given pressure differential for any two gases (outside & inside). A vacuum would undoubtedly give extra buoyancy but the additional weight required to achieve rigidity might not make the trade off worthwhile.

Re: Cargo airships could be big

#224

Post by vel0city »

dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

I'd imagine its because its one thing to make a basic rigid shell (able to hold its own weight without collapsing) and another thing to make a giant pressure vessel able to withstand immense pressures. Imagine a storage tank made out of glued together popsicle sticks with a plastic bag around it versus a CO2 cylinder. One is going to weigh quite a bit more than the other, all because one is trying to fight some massive pressure differentials while the other can accept near ambient pressures on both sides.

Re: Cargo airships could be big

#225

Post by oliveshell »

dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

I looked into this a while back, and there's simply no feasible way to construct an airship from known materials that could sustain a vacuum of the necessary volume without being crushed by atmospheric pressure.

You can keep reinforcing the vacuum chamber, but by the time it's strong enough, it'll be too heavy for the buoyant forces to lift it.

Re: Cargo airships could be big

#226

Post by impossiblefork »

criddell wrote: post #167
worik wrote: post #148

Earlier quoted context omitted.

> But even with helium, airships are still very fragile and dangerous. True. But with high speed landing and takeoff aeroplanes are extremely dangerous too. Thousands of gallons of high octane fuell in the tanks on board does not help

> high octane fuel Doesn’t jet fuel have a relatively low octane rating compared to most liquid fuels?

Yes, but this octane-fire mixing is a bunch of confusion to begin with.

Gasoline is less ready to ignite than diesel~=jet fuel, but has fumes.

Diesel~=jet fuel has little fumes, but is easier to ignite by heat, i.e. in an engine, but it will almost never be ignited outside of an engine. Meanwhile, gasoline is hard to ignite with heat and pressure in an engine, but easier to ignite in air than diesel.

Octane also has a higher boiling point than for example heptane, so higher octane fuel is probably not related to easy of ignition due to the fumes either.

Re: Cargo airships could be big

#227

Post by cdot2 »

dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

I suspect that the materials and engineering required to maintain a vaccum would be so much heavier than the engineering required to hold hydrogen that it would literally outweight the benefit.

Re: Cargo airships could be big

#228

Post by slibhb »

dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

That's a fascinating idea. I googled it and came upon https://en.wikipedia.org/wiki/Vacuum_airship and https://scholarsbank.uoregon.edu/xmlui/handle/1794/22370#:~:....

Sounds like it's feasible but a materials/engineering challenge.

Re: Cargo airships could be big

#229

Post by einpoklum »

elihu wrote: post #108
andbberger wrote: post #45

Earlier quoted context omitted.

what are we going to do from mars

Tourism, mining high value minerals for Earth, mining low value minerals for construction on Mars, manufacturing rocket fuel so that Mars can be the gas station for ships headed for the asteroid belt (enabling more high value mineral mining), low-gravity retirement communities for people with mobility issues who would be wheelchair-bound on Earth, real estate speculation, movies, sports, manufacturing space infrastru…

If I were living on Mars, I would absolutely not be willing to let the rare minerals get sent up into space then down to Earth. Learn to recycle, damn lazy Earthers.

Re: Cargo airships could be big

#230

Post by xg15 »

echelon wrote: post #33
splitrocket wrote: post #12

This, my friends, is why we should colonize the upper atmosphere of Venus, where you could chill outside with only a respirator, rather than the inhospitable, irradiated, mangnetosphere free mars. https://en.wikipedia.org/wiki/High_Altitude_Venus_Operationa... https://spectrum.ieee.org/nasa-study-proposes-airships-cloud...

I've always felt people with these ideas are doing pie in the sky thinking and missing the other trends that would beat this concept out. Humans aren't suited for these environments. We evolved to fit this planet. These gasses, radiation levels, terrestrial foods, etc. The economics of going to Mars, Venus, etc. are iffy, and humans probably won't enjoy being there. It's McMurdo times about 1000. Getting back is hard…

Still having a soft spot for some cyber/biopunk future where we'll just eventually become the machines - or be able to bioengineer bodies which will be capable of overcoming those limitations :)
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