4 ms·

I think the key is in the wikipedia article: You only gain 14% lift with a vacuum vs helium. The tradeoff is either: - Build a pressure vessel to withstand the

I think the key is in the wikipedia article: You only gain 14% lift with a vacuum vs helium. The tradeoff is either: - Build a pressure vessel to withstand the differential to the atmosphere - Let the helium do the pushing from the inside but make the thing 14% bigger I don't see how the vacuum ever wins.

Asooka 4y ago
I wonder if there is a sweet spot between the two. Have a rigid structure with an internal pressure less than one, but more than zero atmospheres.
- Tuna-Fish 4y ago
  There is not. The costs of dealing with pressure differentials are extreme, and there are a lot of small thorny issues. For one, if you have a pressure differential, you need to care very much about even the tiniest leaks. A surprising fact about airships is that they don't actually have to be very gas-tight to work just fine. As people found to their surprise in both world wars, you can shoot an airship full of small holes and it only very slowly degrades in performance.
  - hutzlibu 4y ago
    Yes, if you just shoot a hydrogen airship, not much happened, only after they introduced incendiary rounds, strong damage was done.
    - hutzlibu 4y ago
      No idea why this was downvoted, but in case anyone believed it was imaginary: https://en.wikipedia.org/wiki/Pomeroy_bullet https://en.wikipedia.org/wiki/Pomeroy_bullet
- taneq 4y ago
  At the halfway point you get 7% more lift but still need to withstand ~50kPa of external pressure. I can't see how you'll ever build a rigid structure that can withstand 5 tonnes per square meter and only weighs 7% more than a gas bag which operates only under a tiny fraction of that force and only under tension.
wolverine876 4y ago
What was that based on?
cogman10 4y ago
> I don't see how the vacuum ever wins. 3 ways. - Vacuums aren't combustible. - Vacuums can be created without sourcing a gas. - Vacuums allow you adjust buoyancy without requiring you to carry extra gases. The major downside of a vacuum is finding something ridged enough, light enough, and cheap enough to maintain a vacuum.
- dlgeek 4y ago
  Helium isn't combustible either.
  - cogman10 4y ago
    It's also finite and much more expensive.
- o_1 4y ago
  "vacuums aren't combustible" oh I love it idk what you did here, but the assumption of hydrogen still being used is awesome. reminds me of a great Archer episode.
- TheRealNGenius 4y ago
  [dead]
- Brusco_RF 4y ago
  Its a little disingenuous to imply that a vacuum is safer than Hydrogen just because it doesn't combust. Have it spring a leak near the passenger cabin and watch what happens: https://www.youtube.com/watch?v=cPoVuFtWs_Y&t=7s https://www.youtube.com/watch?v=cPoVuFtWs_Y&t=7s

Asooka 4y ago

I wonder if there is a sweet spot between the two. Have a rigid structure with an internal pressure less than one, but more than zero atmospheres.

Tuna-Fish 4y ago
There is not. The costs of dealing with pressure differentials are extreme, and there are a lot of small thorny issues. For one, if you have a pressure differential, you need to care very much about even the tiniest leaks. A surprising fact about airships is that they don't actually have to be very gas-tight to work just fine. As people found to their surprise in both world wars, you can shoot an airship full of small holes and it only very slowly degrades in performance.
- hutzlibu 4y ago
  Yes, if you just shoot a hydrogen airship, not much happened, only after they introduced incendiary rounds, strong damage was done.
  - hutzlibu 4y ago
    No idea why this was downvoted, but in case anyone believed it was imaginary: https://en.wikipedia.org/wiki/Pomeroy_bullet https://en.wikipedia.org/wiki/Pomeroy_bullet
taneq 4y ago
At the halfway point you get 7% more lift but still need to withstand ~50kPa of external pressure. I can't see how you'll ever build a rigid structure that can withstand 5 tonnes per square meter and only weighs 7% more than a gas bag which operates only under a tiny fraction of that force and only under tension.

wolverine876 4y ago

What was that based on?

cogman10 4y ago

> I don't see how the vacuum ever wins. 3 ways. - Vacuums aren't combustible. - Vacuums can be created without sourcing a gas. - Vacuums allow you adjust buoyancy without requiring you to carry extra gases. The major downside of a vacuum is finding something ridged enough, light enough, and cheap enough to maintain a vacuum.

dlgeek 4y ago
Helium isn't combustible either.
- cogman10 4y ago
  It's also finite and much more expensive.
o_1 4y ago
"vacuums aren't combustible" oh I love it idk what you did here, but the assumption of hydrogen still being used is awesome. reminds me of a great Archer episode.
TheRealNGenius 4y ago
[dead]
Brusco_RF 4y ago
Its a little disingenuous to imply that a vacuum is safer than Hydrogen just because it doesn't combust. Have it spring a leak near the passenger cabin and watch what happens: https://www.youtube.com/watch?v=cPoVuFtWs_Y&t=7s https://www.youtube.com/watch?v=cPoVuFtWs_Y&t=7s