Vacuum Balloons.

[Blood Legend]

I was thinking about typical fantasy airship designs; something that doesn't require a lot of fuel or flammable substances when it came to me that perhaps a vacuum (which is neither expensive or very flammable!) could lift a hollow metal ball into the air if the ball was made out of a light enough and strong enough material not to collapse in on itself.

I was thinking perhaps some dark alchemy would use preserved or golemized dragon lungs as airship ballasts but then decided I'd google this concept first, and wouldn't you know it, some old crusty dude from the 17th century already came up with the idea. Using science of all things. How am I supposed to compete with science?

I was wondering if anyone here had any knowledge on the subject. Is it possible with modern materials to make a vacuum balloon (even on a parlor trick level)?

[Anthony]

No; the structure is heavier than the lift.

[Ulzgoroth]

Turns out pressure from low molecular weight gas is the most weight-effective way to support your lifting cavity against outside air pressure.

[Fred Brackin]

Also, even without the containment weight issue, vacuum is only 10% lighter than hydrogen so it wouldn't really be revolutionary even if you could do it.

[alimantando]

http://en.wikipedia.org/wiki/Cloud_n...rity_sphere%29

[whswhs]

Originally Posted by Fred Brackin

Also, even without the containment weight issue, vacuum is only 10% lighter than hydrogen so it wouldn't really be revolutionary even if you could do it.

I seem to recall doing those calculations for GURPS Steampunk. The key is that the lifting force doesn't come from the inside of the balloon; it comes from the air outside the balloon.

Bill Stoddard

[Bruno]

Originally Posted by Blood Legend

I was wondering if anyone here had any knowledge on the subject. Is it possible with modern materials to make a vacuum balloon (even on a parlor trick level)?

As mentioned, not with realistic modern materials. Fantasy materials on the other hand might be so ridiculously strong for their weight that it's possible to make lifting vacuum canisters out of them. We're talking corrugated orichalcum foil probably - it needs to be absolutely air tight, to be able to stand up to one atmosphere of pressure difference in the exact worst shape possible, and then to survive hanging things off of it, buffeting, bird strike, etc.

You'll probably need internal reinforcements too.

[Michael Cule]

If we're talking about fantasy with magic, an Utter Dome could create a perfect vacuum. Whether the cost to enchant a large enough, self powered Utter Dome projector to lift an airship would be cheap enough to justify the effort I leave as an exercise for the technomantic gearheads hereabouts....

But as someone points out you just need to make the right assumptions about your handwavium and narrativium settings.

[Anaraxes]

Originally Posted by Bruno

stand up to one atmosphere of pressure difference in the exact worst shape possible

What do you mean? The typical spherical hot air balloon should be a good shape for resisting external pressure. See all the submarines that use it.

Fred's pointed out the biggest limitation -- there's just not a lot extra to be gained, compared to using hydrogen or helium. With a magically strong material, you wouldn't have the problem that causes real lighter-than-air craft to use internal pressure for support, so you're left with the fact that there's just not a large percentage increase there. But, in fantasy, it may be easier to Destroy Air than to Create Helium.

As long as we're talking fantasy, you could handwave a super aerogel (with vacuoles of vacuum, if you like). Not much advantage if you've already got magical material that could support itself just as the skin of a sphere, but it gets extra levitation power from the Rule of Cool. And perhaps you can get an adventure out of retrieving some trunks of the sky-tree, or finding the mage that knows the formula for hardening the spit of the elvenwasps, or whatever.

[Fred Brackin]

Originally Posted by Michael Cule

If we're talking about fantasy with magic, an Utter Dome could create a perfect vacuum. Whether the cost to enchant a large enough, self powered Utter Dome projector to lift an airship would be cheap enough to justify the effort I leave as an exercise for the technomantic gearheads hereabouts....

You don't want Utter Dome because that blocks magic so you can't cast Destroy Air inside it.

You could cast that spell inside a Force Dome but there's a clause in the spell text where Force Domes are always filled with breathable air. So it fills upo agan as fast as you emuty it. There's also no syandard Item or permanent version of Force Dome.

What you can do it cast the permanent version of Force Wall for 200 per yard of length (and automatically getting 4 yards of heght) and use Small Vision to make sure you cast them at edge to edge on a molecilar level.

You can form a Force Rectanlge that way which will stay empty after you Destroy Air iinside it. You have to build a ship of some kind first to anchor rte Forece Walls on. If you don't do this the Walls/Rectangle will stay wherever you cast them no matter how light they are.

So there is still significant and unavoidable structural weight invollved and no this really isn't going to be an efficient way to create a flying ship.

If it were just me I'd make an Amntigravity Paint with Alchemy or possibley develop a Create Aether Spell. I''d expect Aether (as the Celestial Element) to have much more bouyancy than hydrogen.