h a l f b a k e r yAssume a hemispherical cow.
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The idea's simple, really. You basically build a structure frame (say a dodecahedron) out of something that can withstand the compression from the atmosphere, then cover the thing with something that can withstand the compression when it's applied as a tensile problem.
As an example (I'm using silk
only as an example, I'm not claiming that it has the strength): construct a metal frame, and then cover it in silk and suck out all the air. You'll (hopefully!) end up with a structure resembling a golf ball, with the silk being pushed inwards but resisting the pressure.
(Incidently, I came up with this idea after reading a halfbakery idea for an inflated vacuum blimp).
World is running out of helium
http://blogs.discov...ning-out-of-helium/
[sqeaketh the wheel, Jan 04 2011]
_22Prayer_20Wheel_22_20Vacuum_20Blimp
[FlyingToaster, Jan 06 2011]
[link]
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Of course. A _structure_ to support pressure. Here I was just using the silK. |
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//something that can withstand the compression when it's applied as a tensile problem.// |
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Wrong, or at least you've worded it wrong. I think what you meant to say is "something that is better suited to withstand the compressive forces". You can't turn this issue into a purely tensile stress problem, I guarantee it. Just like you can't build a rigid structure solely using members under tension. It just doesn't work that way. You will find that your buckeyball like structure will feature most, if not all of the members under compression. |
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That said, I like your thinking. You may be able to avoid the thin shell buckling issue by making a more robust substructure. I personally don't think we have suitable materials to make this work either, but kudos for the lateral thinking. |
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This is a great HB idea. I think so partly because a few days ago I independently invented it myself, then found it here before posting my own version, which goes like this (no credit for the idea, but I did introduce a couple of new thoughts, which someone might enjoy): |
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Dirigibles Filled with Nothing: |
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ALICE: Hey, Bob. Did you know the world is running out of helium, making it prohibitively expensive to fill dirigibles, not to mention party balloons? You don't want to use hydrogen for dirigibles, for obvious reasons. What can we do? Nothing is more buoyant than helium and hydrogen. |
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BOB: Exactly! Nothing is perfect! |
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ALICE: What do you mean? What are you going to fill the dirigibles with? |
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ALICE: Come on, give me a hint. |
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ALICE: Don't be so modest. Tell me. |
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BOB: OK. We pump all the air out of a dirigible, thereby filling it with a vacuum. No other thing is lighter than vacuum, so the dirigible will float upward in the atmosphere. |
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ALICE: So what keeps the dirigible from collapsing under the 14 psi (100,000 Pa) pressure of the outside air? |
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BOB: Of course, we need a structure to support the balloon wall material, which should be made of the strongest material known, that probably being a monolayer of graphene. To maximize the ratio of volume to surface area, the support structure should be a spherical geodesic dome. |
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ALICE: Can such a balloon displace an amount of air whose mass is greater than the mass of the balloon plus its support structure, as needed to make it buoyant? |
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BOB: That is left as a homework exercise for you. It's only a materials problem, not a physics showstopper. |
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ALICE: Here's my homework. It's just a stack of references to the many other places where this idea has been beaten to death. The summary is that a complete vacuum isn't much lighter than hydrogen or helium, and any structure that could support a vacuum is gonna be too heavy to be practical, and any vacuum container is just waiting to fail catastrophically. Kinda like your brain, Bob. |
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I can't be bothered to find the exact amounts, but
helium is about 10% the weight of air, making a
vacuum only 10% more efficient. However, the
structure clearly needs to be more than 10% stronger. |
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[baconmark] The point is that helium is running out (really, as documented in many scientific articles) and can never be replaced. And hydrogen explodes. In the future (remember we are supposed to be visionaries), the materials problems might be solved, making the vacuum blimp practical and best. I apologize for beating a supposedly dead horse, but I was excited to reinvent this hair-brained idea, not knowing of the earlier death beating. As I like to say, I might not be the smartest, but I am gaining on 'em. |
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Where is the helium going? And can it not be
replaced by Hydrogen fusion? |
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And fusion would at best create minute amounts of helium (even if that is feasible, which I don't know) |
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//And hydrogen explodes.// Well, yes it does, in a
thermonuclear bomb. But I think what you mean is "a
stoichiometric mixture of hydrogen and oxygen explodes."
The
Hindenberg did not contain such a mixture, and most of the
people abord survived. |
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Hydrogen is the answer. We can produce it from seawater, it's lighter than helium, and it's safe.
As Mouse points out, the Hindenberg fire was mostly not a hydrogen fire. When the envelope ruptured, the hydrogen escaped upward. Some of it burnt, where it was mixed with air, but the oxygen in the air was soon exhausted and most of the hydrogen didn't burn. It must be among the safest fuels when leaked. I never slipped over in a puddle of hydrogen. |
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//I never slipped over in a puddle of hydrogen.// |
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And I never slipped over in a puddle of vacuum. |
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You can't really have been trying, then. |
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As always, this assumes that a vacuum is significantly better than hydrogen or helium, but it isn't. Helium has 14% less lifting power and hydrogen has 7% less. Not worth the effort. |
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//Not worth the effort// until you figure out that vacuum is much cheaper and readily available than either H2 or He. No storage costs, either. |
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A hundred foot diameter vacuum balloon would have a lifting power of 18 tons. A hydrogen balloon of the same size would have a lifting power of just one ton less. The small force on the skin of the hydrogen balloon would allow you to use no internal supports and a lightweight membrane, while the force on one hemisphere of the vacuum balloon would be 8,000 tons at sea level, and you would have to use far more than your 18 ton capacity to support it against collapse. It would never leave the ground. |
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Working (HB) Vacuum Blimp <link> |
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Unlike your critics condemned to live out their miserable petty negative existence knocking suggestions, you have vision but search the wrong direction.
A possible answer exists employing the Roman lock stone method coupled with a lightweight material.
Suitably sized Styrofoam lock stones formed into a sphere will gain strength when collapsing inward under even compression. |
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There is another reason vacuum is better: if you attach a vacuum pump to the blimp, then you can pump air in and out as ballast. With other gasses, if you vent any you can only replace it from tanks carried onboard which add extra weight. |
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Now - is this just a weird deja-vu monent or have I seen this idea on HB several times, and elsewhere? |
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Sorry. I am not bi lingual. |
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//Not worth the effort.//
In most cases, a 14% gain is considered well worth the effort. Even a 7% gain is usually considered worth some effort. |
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A good intermediate step might be a buoyancy tank strong enough to resist 50.5 kPa (7.35 psi). Then fill it with half the amount of helium you normally would. As materials get stronger, use less helium, until eventually you have your vacuum airship. |
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