Vacuum Dirigibles a Stupid Idea ?

[Michel Van]

Wat is lighter than Air ?

Nothing !

better say a Vacuum
in 1670 Francesco Lana de Terzi had that Idea for a Balloons with Vacuum inside 4 big copper sphere.

of course the Technology of 17 century was not ready for this.
and with 21 century Technology ?

or is this still a stupid Idea?

source
http://airshipworld.blogspot.com/2007_09_01_archive.html
picture
http://www.rusring.net/~levin/levin3d/dz.htm

 

[Orionblamblam]

or is this still a stupid Idea?

Pretty much, yes. Structures used to contain light lift gasses, hydrogena nd helium, are in *very* slight tension, sinc ehte gas pressure within is pretty much the same as the surrounding atmosphere. But a vaccuum chamber has a fairly high delta-P... and in the *wrong* direction. The structural weight required to hold the thing together would be massive.

Think of it this way: You can put fairly high pressures into a plastic 2-liter bottle. Several atmospheres worth, I believe. But if you simply try to suck the air out with your lungs, it will collapse. The internal or external structure required to keep the bottle from collapsing would weight a lot more than the bottle itself. That's because when pressurized the plastic is in tension... a stress that causes the plastic to want to straighten out. But when depressurized the plastic is now in compression, which works agaisnt straightening out the plastic.

 

[Simon666]

Think of it this way: moving from helium to hydrogen:

Weight of air per liter at STP = 1.20 gr/l
Weight of helium per liter at STP = 0.18 gr/l
Net lift per liter of helium at STP = 1.03 gr/l

Weight of air per liter at STP = 1.20 gr/l
Weight of hydrogen per liter at STP = 0.09 gr/l
Net lift per liter of hydrogen at STP = 1.11 gr/l

So only a measily 8% increase by moving to a gas that is twice as light but a lot more flammable. Moving from hydrogen to vacuum gives:

Weight of air per liter at STP = 1.20 gr/l
Weight of vacuum per liter at STP = 0.00 gr/l
Net lift per liter of vacuum at STP = 1.20 gr/l

Or just another measily 8 8% increase by moving to something flammable to something that needs a pressure vessule that is *very* difficult to make very light.