My thinking here is that if my rigid airship body is, say, 24g, with vacuum, why would it float with helium or hydrogen inside, when they have mass and thus weight? Makes very little sense, unless it has something to do with the density?
I haven’t actually done this yet, and I’m working out ideas for one. Everyone I know tells me I’m wrong for thinking a vacuum (assuming a full one, although they are elusive) would float over helium or hydrogen.
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The problem is that with a vacuum inside, most things will get crushed by the atmosphere. Check out this classic [50 gallon barrel crushing experiment](https://youtu.be/Bi6sDTXE9TE).
All other things equal, a vacuum-filled volume will in fact weigh less than the same volume filled with H2 or He, and yes, it will be more buoyant.
The trouble is, the forces on a zero-pressure container filled with gas are very small, which allows you to make it very light weight.
OTOH, a vacuum filled container must resist huge stresses caused by atmospheric pressure unbalanced by anything on the inside. So your rigid container has to be engineered much stronger, and it ends up being much, much heavier than the difference between He and vacuum.
You can’t make a ridig airship with helium without greatly reducing the payload size. It’s too heavy. A blimp has a soft shell to reduce the weight. You can’t fill one with vacuum because the difference in pressure on the outside vs the inside would be so great that anything you build strong enough to withstand that pressure would be too heavy to be buoyant in the air. In order to float, you need to displace more mass in your volume than the fluid you displace. Lighter than air flight literally requires you to be lighter than air.
Just a side note, If you got a hole in the vacume It wouldn’t slowly leak out until the airship landed like with helium, but it would just tear open and implode.
You can’t make a ridig airship with helium without greatly reducing the payload size. It’s too heavy. A blimp has a soft shell to reduce the weight. You can’t fill one with vacuum because the difference in pressure on the outside vs the inside would be so great that anything you build strong enough to withstand that pressure would be too heavy to be buoyant in the air. In order to float, you need to displace more mass in your volume than the fluid you displace. Lighter than air flight literally requires you to be lighter than air.
Because it would get crushed by the pressure differential. A craft large enough to float would crumple like a tin can.
Because it would get crushed by the pressure differential. A craft large enough to float would crumple like a tin can.
As others have said it’s theoretically possible but no material exists that is strong enough, but also it isn’t really that much more effective than helium –
1l of air weighs 1.28g, 1l of vacuum of course weights 0g, but 1l of helium only weighs 0.178g
So vacuum actually only has 14% better lift than helium, with the massive problem of having material strong enough not to get crushed vs just a thin bag to contain helium in.
It would work fine but only if the pressure vessel was light enough.
Good example of this is a steel boat Steel is really heavy but as long as it’s not crazy thick and displaces enough water – it will float just fine.
Water is way denser than air so making a rigid hull to float in air is not very practical.
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