Cargo Airships Are Happening

One challenge I've heard of is: If you carry 100 tons of cargo from point A to point B in an airship, for the airship to return to point A, it needs to take on another 100 tons of new cargo (or ballast), or it needs to vent (or compress) lifting gas, in order to maintain the correct buoyancy. I wonder what the best approach is here, & how it affects the economics? Is water ballast safe & cheap enough, or is there a better way?

Yeah although typically they used water ballast, which is cheap and easy to find.

One thing worth considering is going back to hydrogen as a lifting gas. Not only is it a better lifting gas than helium and much cheaper, it could be used as fuel.

An airship that burned its own lifting gas would have the curious property of getting heavier the further it traveled. This could be countered by dual-fueling it and also have engines that burned heavier-than-air fuel like kerosene or propane. The hydrogen engines could burn the lifting gas at the same rate as the kerosene engines burn the ballast-fuel.

The Graf Zeppelin burnt Blaugas[1] because it's about the same density as air, so as the fuel tanks emptied the buoyancy didn't change. See [2] for other things the Zeppelins did, which says "The LZ 127 Graf Zeppelin had bi-fuel engines, and could use gasoline and Blau gas as a propellant. Twelve of the vessel's gas cells were filled with a propellant gas instead of lifting gas with a total volume of 30,000 cubic metres, enough for approximately 100 flight hours. The fuel tank had a gasoline volume of 67 flight hours. Using both gasoline and Blau gas, one could achieve 118 hours of cruise time."

That article mentions that the Zeppelins experimented with burning Hydrogen lift gas as fuel "without much success" but doesn't add detail.

[1] https://en.wikipedia.org/wiki/Blau_gas

[2] https://en.wikipedia.org/wiki/Buoyancy_compensator_(aviation...

My understanding was blau-gass was unpressurized propane, which is a little more dense than air. But I guess according to that article it's slightly less.

I'd expect that, like a lot of problems zeppelins had in the 1920s, burning hydrogen would be more feasible with modern technology.

I'd also point out that the thing that made hydrogen dangerous in those airships was that the skin was two layers. The inner skin was the gas bags, which were very fragile, and then the rigid structure and the outer skin to protect the fragile bags. This was a problem because hydrogen could accumulate and mix with air between the inner and outer skins. The outer skin also was quite flammable. Nowadays, we can make materials that are both strong enough to serve as an outer skin and impervious enough to serve as a gas bag for lifting gas, so modern airships have only one skin and nowhere for the lifting gas to mix with air inside the structure.

> it needs to take on another 100 tons of new cargo (or ballast) ... in order to maintain the correct buoyancy.

Sounds perfect for a cargo situation. Add new cargo as old cargo is removed.

Rather than taking a huge shipment, delivering it, and having to deal with an empty airship, maybe it's better to think of it as a slowly drifting warehouse. Drones can handle delivery and restock across short distances, and the airship doesn't land at all. This would let you maintain a more or less consistent mass.

To move in the opposite direction you could use photovoltaics to electrolyze lifting/fuel hydrogen from water. Up there above the clouds you'd have pretty good conditions for solar if you could make the panels light enough.

As I understand it, it's common for a cargo ship to unload full containers and take on empties for the return voyage. Are cargo vessels holds always partially full vs. empty containers, bouncing between ports?

Would this issue even be a problem for fixed routes? If you're always taking full containers between two points, that is.

The way the cutaway images on their site look, the bouyant members would be nestled in the actual structure in large tanks.

https://www.shipbyairship.com/

Uncompressed propane would have simply been called Propangas I think. That term had been established well enough in the second half of the century and while the Zeppelin-era was before that, I doubt that the term changed much.

But if you aim for a buoyancy-neutral fuel, you can just add hydrogen to the mix, as little or much as you need. That custom blend then would be precisely the thing you don't invent a creative name for but just use a color code ("the blue one").

That’s cool, but also a quite different business and operating model where storage and delivery multiplexing are much more of a thing than with air freight.

The other problem is the drones. For this to work you’d be shipping either regular TEU containers or the air freight equivalent (not sure what they’re called but there’s a standard shape I believe), however no drone available today can move either of those. That means new drones, new shipping form factors, or both, and those are both hard problems that you probably don’t want to face when already trying to launch a new freight modality.

Awesome idea, but as you say, seems more like a sort of "last mile delivery vehicle" than cargo transport.

You could imagine some sort of futuristic flying Amazon warehouse/drone carrier: It would be pre-stocked at a distribution center, with packets already arranged in a way that they can be picked up by drones individually. Then it floats over a neighborhood while the drones deliver the individual packets to the homes below.

This actually makes me think these people are unserious. This is an obsolescent airship design. ZeppelinNT, Airlander 10, and Lockheed P-719 all use the semi-rigid design with integral gas bags.

I was thinking of these as an alternative to having a distribution center. They're just always traveling on a few routes determined mostly by prevailing winds, making big circles around the planet. If you live on one of those routes, you can last mile delivery directly from the warehouse as it passes overhead. If not, the drones are loading/unloading a train or some such.