h a l f b a k e r yNo, not that kind of baked.
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I'm sure every one who reads this is familiar with a soccer ball. 12 black pentagons 20 white hexagons.
Now take this Buckyball engineering concept. and try to imagine a 5 foot diameter sphere, made of 32 pent-hex interlocking carbon fiber plates(all the plates have a vacuum tight seals on their
edges and undersides, and are purposely bowed slightly like a dome). On each left side of the five and six outer sides, is a protruding (for lack of a better term) "Arm". When these interlocking plates are arranged to form a sphere, each "arm" lies on top of a corresponding plate. Since there are five and six "arms" respective to each type of plate. All the plates are covered by other plates, and are simultaneously covering others. The "arms" allow the pressure of the vacuum to be displaced evenly around the sphere. (Try to draw it if its hard conceptualize). The arms are meant to resist the internal pulling pressure of the vacuum when the air is pumped out.
The thickness of the plates for a 5 foot diameter sphere would be 4-5 inches. The whole sphere would be light as heck compared to using metals. And could be easily lifted by one strong person or a few regular Joes and when sealed and evacuated of air, would easily resist gravity's pull.
Carbon fiber is the only realistic material in modern times that is light/strong enough to resist the "buckling" effect that comes with vacuums. Something Francesco Lana de Terzi never had the pleasure of knowing about in 1670.
Even though vacuums are 7% better than Hydrogen it is STILL BETTER in every other conceivable way than gasses. And would be greener, cheaper and way more fun to cruise the skies than quickly flying on cramped airplanes having to push past people just to use the toilet. Vacuum's can be created on the fly, beat that.
I am a true believer in the potential of vacuum airships its only a mater of time and investment.
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Strangely enough, when I searched "Vacuum Balloon" on
Google I found a page that linked to the Halfbakery for
"further reading." |
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that's actually quite normal. |
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[A] might want to check your math (though I am impressed that you mentioned the 7% difference) |
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I've been meaning to read that book for at least a year now. |
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You're stating three things: |
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1) This structure would be light enough for someone to lift |
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2) Carbon fibre is the only material with which to do this |
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3) The structure would actually be light enough to float
(last two paras). |
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1) How much will it weigh?
Well, the surface area of a 5ft sphere will be 78 square
feet. If it's thickness (as you suggest) is 4 inches, then this
is 26 cubic feet of carbon fibre composite. Now, the
density of carbon fibre composite comes mostly from the
resin, but a typical value is something like 1.5g/cm3, or
about an ounce per cubic inch, or about a hundred pounds
per cubic foot. So, your sphere is going to weigh about
2,600 pounds. Of course, when filled with vacuum it will
be, effectively, lighter than this by the mass of air it
displaces - about 2 grams or a tenth of an ounce lighter. |
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I do not know many men who can lift 2,600 pounds. |
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2) Is carbon-fibre the only suitable material?
No. If the shell is 4 inches thick, then you are making no
significant use of the only truly remarkable property of
carbon fibre - it's high stiffness-to-weight ratio. All the
forces in your shell will be compressive. Carbon fibre
composites are not particularly great in compression - you
would be as well making it out of glass or plexiglass. If you
doubt that a 5ft sphere of 4-inch thick glass can support a
vacuum, just look at submersibles which use these
materials in hemispheres to support far greater differential
pressures. |
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3) It'll float.
Well, yes, it will float on water. In fact, it will float a
couple of millimetres higher on the water due to its
internal vacuum, than it would if filled with regular air. It
will not float in air, if my understanding of gravity is
correct, due its net effective weight of 2,600 pounds. |
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So, is it that you really can't do basic maths or reasoning,
or did you just decide not to? |
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//just look at submersibles which use these materials in hemispheres to support far greater differential pressures.//
Perhaps you could use double-glazing, with an intermediate pressure inbetween the two panes. |
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Structurally, I think it amounts to the same thing (two
spheres, each half-thickness, each supporting half-
pressure). |
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But no - wait!! It will be worse, because the stiffness of a
shell increases as the ??4th?? power of its thickness. |
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So, if each shell is half as thick, it will only be ???1/2^4 =
1/16th as stiff, but will have to support 1/2 the load.
(Stiffness should not be too important if the sphere is
perfect and is not hit or dented; but if it is imperfect or is
knocked on one side, stiffness is the only factor which
prevents catastrophic failure.) |
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//I do not know many men who can lift 2,600 pounds.// |
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All at one time? Or in 20-30lb iterations? |
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I posted something very similar years ago and got shot down |
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Buckminster Fuller himself crunched some numbers back in the 60s, and found that you could in fact make a working vacuum balloon out of ordinary materials, like steel tri-truss girders and sheeting. |
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The catch was that in order for it to work, you had to build it stupungously huge, like the size of a city. As volume increases to the third power of linear scale, and surface area (and thus structural weight) only increases to the second power, while the pressure differential remains constant, the larger the enclosed space the better. |
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This idea gets posted every six months, and the problem is always the same. A hydrogen airship is as efficient as you're going to get. A hydrogen balloon of 102 feet has the same lifting capacity as a vacuum balloon of 100 feet, IF you could contain a vacuum with a thin membrane. But you can't, and even with the strongest materials, the vacuum balloon will never even lift itself, much less compete with hydrogen or helium. |
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// A hydrogen airship is as efficient as you're going to get.//
But a hot hydrogen balloon would be better.
Until you get to Hindenberg, or R101 sort of temperatures. |
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Yes, airship or balloon, doesn't matter, hydrogen weighs 7% as much as air, so the little bit you gain by going to a vacuum is vastly outweighed by the containment. |
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// Hindenberg, or R101 sort of temperatures. // |
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Tend to fail the Design Review on the sustainability criteria (less than 60 seconds). |
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IIRC, [BunsenHoneydew], what Bucky invented was not a vacuum balloon, just a passively heated hot air balloon. The stupendously huge balloon was supposed to contain a small city, and the heat generated by its inhabitants would be enough to make the whole thing float through normal reduction of air pressure due to temperature increase (only a few degrees above external ambient, in this example). |
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Thus, not a vacuum balloon. But definitely one of his cooler ideas that might actually work. |
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Still the principle, of increased volume vs. increased surface are does hold true. Perhaps the issues with vacuum balloons could be partially solved through scaling. |
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//Perhaps the issues with vacuum balloons could be partially solved through scaling.// |
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There's a limit to how big you can go, due to decreasing air density. At 3.5 miles in diameter, for instance, you've already lost half your buoyancy at the top. |
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