7 ms·

But they're so cool. Maybe with advances in materials science this kind of design could be viable again. Probably not likely with the looming helium shortage,

But they're so cool. Maybe with advances in materials science this kind of design could be viable again. Probably not likely with the looming helium shortage, lack of replacement gasses (?), etc. But I want my sweet 1920s art deco retrofuturist reality :(

jakear 5y ago
Could some combination of a partial vacuum and hot air substitute for helium? Of course you'd need some ultra light superstructure to maintain the giant vacuum, but that's "just" engineering.
- masklinn 5y ago
  > hot air Air at 175C has about 40% the lifting power as the same volume of helium (or hydrogen). That is very hot, and requires a lot of energy to sustain. Lower temperatures will reduce the lifting power. That's why thermal airships (https://en.wikipedia.org/wiki/Thermal_airship https://en.wikipedia.org/wiki/Thermal_airship) are very uncommon, the lift inefficiency means the structural weight doesn't scale, and the cross-section makes them very hard drive and control.
  - jandrese 5y ago
    I guess because airships were already out of fashion by the time the atomic age came, but a thermal airship where the heater is just a radioactive pile seems like a super simple design. The enormous bulk of the airship is an advantage in this case, you can reduce the amount of shielding you need by keeping the radioactive stuff way off on one side of the vehicle and the people on the other. Of course it would still be a nasty cleanup effort if your airship crashes, and you have to deal with radioactive materials when landed or when doing maintenance. From a practical standpoint there are issues, but in theory the concept works.
    - robonerd 5y ago
      A reactor powered thermal airship is a fascinating idea! I'm skeptical that it could work though. Some quick web searching suggests that 3 MW burners for hot air balloons is fairly typical. I'm not sure how light and powerful a reactor could be made, but wikipedia says the Convair NB-36H had a 1 MW air-cooled reactor weighing 16,000kg. That reactor definitely wouldn't work then, too heavy by far and not enough power output. But that was a prototype reactor in the 50s. Also, shielding seems like a big concern even if the reactor can be built light. To stop neutron radiation you need light nuclei like hydrogen, making water or concrete (containing water) popular choices. These are heavy and bulky though, not conducive to airships.
      - jandrese 5y ago
        That's why my consideration for shielding was mostly just distance. Certainly a concept for a time when people were more cavalier about radiation safety.
      - deleted 5y ago
        [deleted]
  - jakear 5y ago
    That’s where the vacuum comes in. Extract half of that hot air, seal the container, and you have 70% of the helium lifting force. (Math may be wrong there but you get the idea) Really you don’t need hot air at all. If you have a massive vacuum contained by a rigid shell of some super light super strong material you’d be set. Density of air at sea level is around 1 kg/m^3, so 100 m^2 of material lifts 3 tons. Assuming one ton for material, one for propulsion, one for cargo, you end up needing a shell material that can weigh up to 1 kg/m^2 and can hold a near vacuum. Like I said earlier, “just” and engineering problem. The good news is economies of scale are on your side: 10000 m^2 of shell can lift 3 thousand tons. At that scale your shell can be up to 300 kg/m^2. A bit more reasonable.
bombcar 5y ago
The revival will truly come when we accept running them on hydrogen for lifting gas. It can likely be done quite safely, as the gasbag of the Hindenburg was very flammable and could have burned even if full of helium. And hydrogen is basically free.
- masklinn 5y ago
  The reality is that airships are kinda crap: 1. they get "free lift" but you need a lot of gas to lift a lot of mass, which quickly makes them extremely unwieldy as it leads to gigantic cross sections (and sheer stuff to move, positioning a lift bag the size of a sports stadium is not exactly great, and requires humongous engines) 2. they're so damn slow 3. even ignoring the tendency to get on fire, hydrogen is a pain in the ass, it absolutely refuses staying put and embrittles structural metals leading to accelerated fatigue
  - bombcar 5y ago
    Yeah, they'd likely be best used as "cruise ships in the sky" where they can take advantage of large swaths of empty space (you could have ballrooms in a zeppelin pretty easily as they wouldn't weigh much) and the speed wouldn't be a huge issue. And you'd likely have to make them out of something other than metal, and it would vent hydrogen most of time.
    - WalterBright 5y ago
      I'd love to take a low and slow tour.
  - outworlder 5y ago
    For passengers sure, they are slow. They could instead transport cargo. I think the biggest problem with them is mooring. It's a complex process, much more so than landing a plane, and requires lots of ground crew. It would have to be automated first.
    - masklinn 5y ago
samizdis 5y ago
Not sure how the company is doing atm, but the Airlander project by Hybrid Air Vehicles seemed quite promising: https://www.hybridairvehicles.com/ https://www.hybridairvehicles.com/

jakear 5y ago

Could some combination of a partial vacuum and hot air substitute for helium? Of course you'd need some ultra light superstructure to maintain the giant vacuum, but that's "just" engineering.

masklinn 5y ago
> hot air Air at 175C has about 40% the lifting power as the same volume of helium (or hydrogen). That is very hot, and requires a lot of energy to sustain. Lower temperatures will reduce the lifting power. That's why thermal airships (https://en.wikipedia.org/wiki/Thermal_airship https://en.wikipedia.org/wiki/Thermal_airship) are very uncommon, the lift inefficiency means the structural weight doesn't scale, and the cross-section makes them very hard drive and control.
- jandrese 5y ago
  I guess because airships were already out of fashion by the time the atomic age came, but a thermal airship where the heater is just a radioactive pile seems like a super simple design. The enormous bulk of the airship is an advantage in this case, you can reduce the amount of shielding you need by keeping the radioactive stuff way off on one side of the vehicle and the people on the other. Of course it would still be a nasty cleanup effort if your airship crashes, and you have to deal with radioactive materials when landed or when doing maintenance. From a practical standpoint there are issues, but in theory the concept works.
  - robonerd 5y ago
    A reactor powered thermal airship is a fascinating idea! I'm skeptical that it could work though. Some quick web searching suggests that 3 MW burners for hot air balloons is fairly typical. I'm not sure how light and powerful a reactor could be made, but wikipedia says the Convair NB-36H had a 1 MW air-cooled reactor weighing 16,000kg. That reactor definitely wouldn't work then, too heavy by far and not enough power output. But that was a prototype reactor in the 50s. Also, shielding seems like a big concern even if the reactor can be built light. To stop neutron radiation you need light nuclei like hydrogen, making water or concrete (containing water) popular choices. These are heavy and bulky though, not conducive to airships.
    - jandrese 5y ago
      That's why my consideration for shielding was mostly just distance. Certainly a concept for a time when people were more cavalier about radiation safety.
    - deleted 5y ago
      [deleted]
- jakear 5y ago
  That’s where the vacuum comes in. Extract half of that hot air, seal the container, and you have 70% of the helium lifting force. (Math may be wrong there but you get the idea) Really you don’t need hot air at all. If you have a massive vacuum contained by a rigid shell of some super light super strong material you’d be set. Density of air at sea level is around 1 kg/m^3, so 100 m^2 of material lifts 3 tons. Assuming one ton for material, one for propulsion, one for cargo, you end up needing a shell material that can weigh up to 1 kg/m^2 and can hold a near vacuum. Like I said earlier, “just” and engineering problem. The good news is economies of scale are on your side: 10000 m^2 of shell can lift 3 thousand tons. At that scale your shell can be up to 300 kg/m^2. A bit more reasonable.

bombcar 5y ago

The revival will truly come when we accept running them on hydrogen for lifting gas. It can likely be done quite safely, as the gasbag of the Hindenburg was very flammable and could have burned even if full of helium. And hydrogen is basically free.

masklinn 5y ago
The reality is that airships are kinda crap: 1. they get "free lift" but you need a lot of gas to lift a lot of mass, which quickly makes them extremely unwieldy as it leads to gigantic cross sections (and sheer stuff to move, positioning a lift bag the size of a sports stadium is not exactly great, and requires humongous engines) 2. they're so damn slow 3. even ignoring the tendency to get on fire, hydrogen is a pain in the ass, it absolutely refuses staying put and embrittles structural metals leading to accelerated fatigue
- bombcar 5y ago
  Yeah, they'd likely be best used as "cruise ships in the sky" where they can take advantage of large swaths of empty space (you could have ballrooms in a zeppelin pretty easily as they wouldn't weigh much) and the speed wouldn't be a huge issue. And you'd likely have to make them out of something other than metal, and it would vent hydrogen most of time.
  - WalterBright 5y ago
    I'd love to take a low and slow tour.
- outworlder 5y ago
  For passengers sure, they are slow. They could instead transport cargo. I think the biggest problem with them is mooring. It's a complex process, much more so than landing a plane, and requires lots of ground crew. It would have to be automated first.
  - masklinn 5y ago

samizdis 5y ago

Not sure how the company is doing atm, but the Airlander project by Hybrid Air Vehicles seemed quite promising: https://www.hybridairvehicles.com/ https://www.hybridairvehicles.com/