12 ms·

> Vacuum airship Wow what a fascinating idea! Just thinking out loud here, but the compressive force is proprtional to area, while the boyancy is proportional

by im3w1l 4y ago

> Vacuum airship Wow what a fascinating idea! Just thinking out loud here, but the compressive force is proprtional to area, while the boyancy is proportional to volume. So I wonder if making it big enough would allow using some fairly standard materials. What about a cube made of 6 big (huge) sheets of some strong yet light material supported by a sort of skeleton inside? Or maybe we can use electro-static repulsion to keep it from imploding? Like how a normal balloon compresses the air inside because the rubber tries to shrink but if you had a balloon that tried to expand instead, because of say electric repulsion, or maybe something else, then it would put the air inside at lower than atmospheric pressure.

dvdkhlng 4y ago
Last time I read about that, the problem seemed to be buckling [1]. E.g. if you look at Euler's critical load [2] then the pressure that a slender column can withstand just depends on the aspect ratio of the column (imagine a vacuum airship that uses internal columns to withstand the air pressure). So scaling things up means, that the column's weight has to scale proportionally with total airship volume (and the (air) pressure is a constant anyways). See also these discussions here [3]. Disclaimer: I don't claim to understand any of this. [1] https://en.wikipedia.org/wiki/Buckling https://en.wikipedia.org/wiki/Buckling [2] https://en.wikipedia.org/wiki/Euler%27s_critical_load https://en.wikipedia.org/wiki/Euler%27s_critical_load [3] https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship
- im3w1l 4y ago
  I did check the wiki article on Vacuum airships before writing my initial comment, and they are talking about the buckling of a hollow sphere, not of a column - hence why Akhmeteli and Gavrilin suggest considering alternative structures. But regarding your point that the columns would have to scale with volume you might be right about that. I was thinking that it should scale with the total force, but the bigger your structure the longer distance the force has to be transmitted. So yeah I think I got that one wrong.

by im3w1l 4y ago

dvdkhlng 4y ago

Last time I read about that, the problem seemed to be buckling [1]. E.g. if you look at Euler's critical load [2] then the pressure that a slender column can withstand just depends on the aspect ratio of the column (imagine a vacuum airship that uses internal columns to withstand the air pressure). So scaling things up means, that the column's weight has to scale proportionally with total airship volume (and the (air) pressure is a constant anyways). See also these discussions here [3]. Disclaimer: I don't claim to understand any of this. [1] https://en.wikipedia.org/wiki/Buckling https://en.wikipedia.org/wiki/Buckling [2] https://en.wikipedia.org/wiki/Euler%27s_critical_load https://en.wikipedia.org/wiki/Euler%27s_critical_load [3] https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship

im3w1l 4y ago
I did check the wiki article on Vacuum airships before writing my initial comment, and they are talking about the buckling of a hollow sphere, not of a column - hence why Akhmeteli and Gavrilin suggest considering alternative structures. But regarding your point that the columns would have to scale with volume you might be right about that. I was thinking that it should scale with the total force, but the bigger your structure the longer distance the force has to be transmitted. So yeah I think I got that one wrong.