Vacuum Zeppelin

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Zake
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Re: Vacuum Zeppelin

Postby Zake » Sun Nov 11, 2007 10:05 pm UTC

Build it at low altitude but don't seal off the vacuum chamber, so theres no structural strain whatsoever. Then seal it and pump in hydrogen to lift it off, and steadily pump out the hydrogen to lift it higher into the atmosphere.

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Re: Vacuum Zeppelin

Postby Cosmologicon » Mon Nov 12, 2007 1:59 am UTC

Any benefit you get from lower air pressure at high altitudes is more than negated by the penalty for lower air density. If the air isn't dense enough, you don't have any buoyant force! There's no way you could get into orbit with this method.

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Re: Vacuum Zeppelin

Postby eternauta3k » Mon Nov 12, 2007 3:02 am UTC

Zake wrote:Build it at low altitude but don't seal off the vacuum chamber, so theres no structural strain whatsoever. Then seal it and pump in hydrogen to lift it off, and steadily pump out the hydrogen to lift it higher into the atmosphere.

A steampunk space-station!

If there were a way to produce large ammounts of hydrogen (solar power?) and balloons (...) we could make cloud city!
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Re: Vacuum Zeppelin

Postby evilbeanfiend » Mon Nov 12, 2007 1:54 pm UTC

Cosmologicon wrote:Any benefit you get from lower air pressure at high altitudes is more than negated by the penalty for lower air density. If the air isn't dense enough, you don't have any buoyant force! There's no way you could get into orbit with this method.


you might be able to launch a conventional rocket from a floating platform however and reduce you total launch costs
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Re: Vacuum Zeppelin

Postby Cosmologicon » Mon Nov 12, 2007 4:52 pm UTC

Well, yes, but it would be by a tiny fraction. For low Earth orbit, the large majority of the energy you impart to your satellite isn't to escape Earth's gravity: it's to get the stuff up to orbital speed. Weather balloons get up to 40km, and orbital speed is around 8,000 m/s. So the amount of energy you save is less than (g * 40km) / (8000 m/s)^2 = 0.6%.

For comparison, if your launch platform were in geosynchronous orbit 42,000 km above the surface, then you could save 100% of the energy needed.

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Re: Vacuum Zeppelin

Postby evilbeanfiend » Mon Nov 12, 2007 6:09 pm UTC

i wasn't thinking energy so much as money, but yes, its even worse then as getting to 40km isn't free, although you do save the extra height twice(ish) as you don't need fuel to gain that height or to accelerate the mass of that fuel.

clearly space elevator > zeppelin
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Re: Vacuum Zeppelin

Postby Cosmologicon » Mon Nov 12, 2007 8:05 pm UTC

Oh. How does launching from high altitude save you money other than very slightly reduced fuel costs?

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Re: Vacuum Zeppelin

Postby evilbeanfiend » Tue Nov 13, 2007 9:44 am UTC

it doesn't, i was agreeing with you and pointing out its even more pointless from a money perspective rather than energy perspective as helium ain't free.
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Re: Vacuum Zeppelin

Postby grythyttan » Tue Nov 13, 2007 11:31 am UTC

But would it be worth it if it was really, really cool?
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Re: Vacuum Zeppelin

Postby zealo » Tue Nov 13, 2007 3:55 pm UTC

why have 'vacuum spheres' within the main structure? surely a ballast system similar to a submarine's would be used? (fill tank from outside to sink, push air/water out of tank back to outside to rise)
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Re: Vacuum Zeppelin

Postby devizer » Thu Feb 25, 2010 5:09 am UTC

I have read this, now ancient thread and am surprised none of you seem to be acquainted with Bucky Fuller's Tensegrity construction system. My solution to the vacuum dirigible problem is thus.
Stop thinking about Total vacuum. Think instead of 10% vacuum. If you remove 10% of the contained air then the pressure differential is only 1.4psi.Then for a tensegrity sphere of 60ft diameter (18.29m) you have a volume of 2,405M cube, which is an air mass of 2.958 Tonnes. Remove 10% and you have a net lift of 295kg.
Not impressed?
Try 50m dia. vol= 49,602m3, air mass =2,405Tonnes and your net lift is 6.o35 Tonnes.
Still not impressed lets go to the size of the Hindenburg -
245x41m, 200,000m3, air mass about 450T, net lift 45T.

So Hindenburg was built 80 years ago, we can build a same size structure with todays materials for 1/3 or less weight using tensegrity system.
There is no doubt that we could today build a vacuum dirigible to equal or better old Hindenburg's performance. Even a prototype would cost less than an Airbus.

comments?

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ZZamfir
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Re: Vacuum Zeppelin

Postby ZZamfir » Thu Feb 25, 2010 8:26 am UTC

But Deviser, it's still better to fill the Zeppelin with helium or hydrogen. That way, you only have to worry about overpressure (as you get higher and the atmospheric pressure decreases), and a tensile-loaded structure is much easier (and therefore lighter) to design than a structure with compressive elements.


but I have a much better idea: why not make a vaccum-filled zeppelin, and use photonic pressure to keep it inflated? The downside would be that it requires kazillion of energy to produce that much light. The upside is that could use LEDs to make that light.

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Re: Vacuum Zeppelin

Postby PM 2Ring » Thu Feb 25, 2010 4:36 pm UTC

ZZamfir wrote:but I have a much better idea: why not make a vaccum-filled zeppelin, and use photonic pressure to keep it inflated? The downside would be that it requires kazillion of energy to produce that much light. The upside is that could use LEDs to make that light.

I doubt that would work very well, due to the huge energy density required. Photons may have zero rest mass, but they are never at rest, and your LED zeppelin will be too heavy to float. But feel free to ramble on. Far be it for me to tell you what is and what should never be.

:)

http://en.wikipedia.org/wiki/Photon_gas

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Re: Vacuum Zeppelin

Postby Cosmologicon » Thu Feb 25, 2010 4:48 pm UTC

PM 2Ring wrote:
ZZamfir wrote:but I have a much better idea: why not make a vaccum-filled zeppelin, and use photonic pressure to keep it inflated? The downside would be that it requires kazillion of energy to produce that much light. The upside is that could use LEDs to make that light.

I doubt that would work very well, due to the huge energy density required. Photons may have zero rest mass, but they are never at rest, and your LED zeppelin will be too heavy to float. But feel free to ramble on. Far be it for me to tell you what is and what should never be.

:)

http://en.wikipedia.org/wiki/Photon_gas

According to that link, for a given pressure P and volume V, the energy required is 3 P V. So for P = 1atm and V = 200,000 m^3, that comes to about 60.8 GJ, which probably has some other issues, but it's certainly not too heavy: it has a mass of less than 1 milligram.

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Re: Vacuum Zeppelin

Postby PM 2Ring » Thu Feb 25, 2010 4:56 pm UTC

According to that link, for a given pressure P and volume V, the energy required is 3 P V. So for P = 1atm and V = 200,000 m^3, that comes to about 60.8 GJ, which probably has some other issues, but it's certainly not too heavy: it has a mass of less than 1 milligram.

Ok. I wasn't too sure how to apply those formulae.

FWIW, Google calculator says (60.8 * (10^9) joules) / (c^2) = 0.676491234 milligrams.

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Re: Vacuum Zeppelin

Postby sikyon » Thu Feb 25, 2010 5:11 pm UTC

The primary problem with a vaccume zepplin has been ignored here. That is the fact that if you have a zepplin filled with vaccume, a leak will cause loss of vaccume at a very rapid rate, possibly compounding cracks and fractures which expand at an exponential rate. In contrast, if helium balloon springs a leak, helium will leak but at a massivly reduced rate (and force) because internal pressure ~= external pressure... most of the atomic movement will be diffusion, and not molecular transport . And in a large, floating object like that? You WILL get leaks.

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Re: Vacuum Zeppelin

Postby SWGlassPit » Thu Feb 25, 2010 5:20 pm UTC

akhmeteli wrote:You may wish to look at our US patent application 20070001053 (11/517915). We propose an evacuated sandwich spherical shell with two thin face sheets and a light core between them. Finite element analysis confirmed that the structure using commercially available materials (e.g., boron carbide face sheets and aluminum honeycomb core) can be light enough to float in air and strong enough to withstand the atmospheric pressure with decent safety factors for strength, buckling, and intracell buckling. Actual manufacturing, while definitely possible, is not easy.


What constitutive model are you using for your finite element analysis? Are you modeling the actual honeycomb structure, or are you just using some homogenized model? If you are homogenizing, on what basis do you assert that the stress field calculated is valid?
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Re: Vacuum Zeppelin

Postby Korrente » Fri Feb 26, 2010 4:08 am UTC

As far as I know the origin of this idea comes from n Italian named Francesco Lana de Terzi (ca. 1631 – 22). He planned for four large evacuated copper spheres to be masted to a boat-like body. It was never built but he put forth quite a bit of research into it.

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Re: Vacuum Zeppelin

Postby gmalivuk » Fri Feb 26, 2010 4:16 am UTC

ZZamfir wrote:But Deviser, it's still better to fill the Zeppelin with helium or hydrogen.

Or perhaps, after removing 10% of the mass of the air, we could do something to the remainder to equalize internal and external pressure instead of worrying about tensegrity or whatever. Hmm... I guess heating it up might work to do that...

I wonder if anyone's tried doing that before?

(Seriously, what possible advantage does the partial vacuum balloon have over a regular hot air balloon? You can reduce the density by rather more than a mere 10% by heating up the air, with the advantage that you only need a nylon sheet between the inside and the outside of your balloon.)

Though you're also right that helium or hydrogen are both much better, as well. Even a complete vacuum is only 16% more efficient than helium, and only 7% more efficient than hydrogen, in terms of lifting power per given volume. Which makes a mere 10% vacuum just plain silly.
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Re: Vacuum Zeppelin

Postby Tass » Fri Feb 26, 2010 7:41 am UTC

One thing is silly, another thing is awesome. I mean, Mythbusters actually build a lead balloon.

It wouldn't be practical, but would it be possible? We make ships that float in water using compression strength in stead of internal pressure, the air filled hull being a near vacuum compared to the water (albeit at only slightly less pressure, or if you don't think regular ships qualify then subs certainly do). Could the same thing be done in air? Incidentally it will be easier the colder the surrounding air is, and the heavier the air molecules, because you will get more buoyancy from a given pressure drop. If we can't do it on Earth, maybe we can on Titan? In cold SF6 it would probably be straight forward.

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Re: Vacuum Zeppelin

Postby snowyowl » Fri Feb 26, 2010 12:58 pm UTC

Going to Titan in the first place presents a few slight problems. Surviving once you get there, in an environment with no oxygen or water, is also not easy (plenty of methane but no oxygen to burn it in).

Finally, even if you do reach Titan and build a vacuum zeppelin, there are even more awesome ways of flying. Oh, and did I mention that the surface pressure on Titan is actually higher than on Earth, since the atmosphere is thicker? You'd be better of staying on Earth.

This isn't a feasible idea, but it would be awesome in a "soft" SF book, which doesn't actually respect the laws of physics, and is proud of it.
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Re: Vacuum Zeppelin

Postby ZZamfir » Fri Feb 26, 2010 1:56 pm UTC

snowyowl wrote:Oh, and did I mention that the surface pressure on Titan is actually higher than on Earth, since the atmosphere is thicker?


The actual pressure doesn't matter, since (as Tass points out) we can clearly build submarines based on the vaccuum principle. What matters is how much buoyancy you get from a given pressure difference.

If a given difference gives you lots of buoyancy (as in liquid water), you can afford to spend loads of mass on the construction (steel submarine hulls).

If a given pressure difference doesn't give you much buoyancy (air at room temperature), your structure must be lightweight, so you have to fill up the vacuum with .

On Titan, the atmosphere is nitrogen, so very similar to our nitrogen+oxygen atmoshere when it comes to buoyancy. But the absolute temperature is one-third of the earth temperature, so a pressure difference gives you 3 times the buoyancy.

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Re: Vacuum Zeppelin

Postby Minerva » Fri Feb 26, 2010 4:30 pm UTC

I recall that this idea actually features in Neal Stephenson's The Diamond Age, where the skin of the airship is made of nano-unobtainium.
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Re: Vacuum Zeppelin

Postby oxoiron » Fri Feb 26, 2010 6:30 pm UTC

Burroughs used it well before that and he may not have been the first.
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Re: Vacuum Zeppelin

Postby PM 2Ring » Sat Feb 27, 2010 3:26 am UTC

Korrente wrote:As far as I know the origin of this idea comes from n Italian named Francesco Lana de Terzi (ca. 1631 – 22). He planned for four large evacuated copper spheres to be masted to a boat-like body. It was never built but he put forth quite a bit of research into it.

On a side note, this is the first time I've been able to use my major on this forum! \o/

Interesting! I remember seeing a diagram of such a vessel when I was a kid, but it was attributed to Galileo, IIRC. Or maybe he was just promoting de Terzi's idea. He was rather fond of adopting other people's ideas...

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Re: Vacuum Zeppelin

Postby Soralin » Sat Feb 27, 2010 7:57 pm UTC

gmalivuk wrote:
ZZamfir wrote:But Deviser, it's still better to fill the Zeppelin with helium or hydrogen.

Or perhaps, after removing 10% of the mass of the air, we could do something to the remainder to equalize internal and external pressure instead of worrying about tensegrity or whatever. Hmm... I guess heating it up might work to do that...

I wonder if anyone's tried doing that before?

Well, back to tensegrity: http://en.wikipedia.org/wiki/Cloud_nine ... _sphere%29
Cloud nines are airborne habitats first proposed by Buckminster Fuller. Fuller proposed that giant geodesic spheres might be made to levitate by heating the air inside.

Geodesic spheres (structures of triangular components arranged to make a sphere) become stronger as they become bigger, due to how they distribute stress over their surfaces. Because of this, they may be imagined on colossal scales.

As a sphere gets bigger, the volume it encloses grows much faster than the mass of the enclosing structure itself. Fuller suggested that the mass of a mile-wide geodesic sphere would be negligible compared to the mass of the air trapped within it. He suggested that if the air inside such a sphere were heated even by one degree higher than the ambient temperature of its surroundings, the sphere could become airborne. He calculated that such a balloon could lift a considerable mass, and hence that 'mini-cities' or airborne towns of thousands of people could be built in this way. These 'cloud nines' could be tethered, or free-floating, or perhaps maneuverable so that they could 'migrate' in response to climatic and environmental conditions.

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Re: Vacuum Zeppelin

Postby akhmeteli » Sat Mar 27, 2010 12:48 pm UTC

SWGlassPit wrote: "What constitutive model are you using for your finite element analysis? Are you modeling the actual honeycomb structure, or are you just using some homogenized model? If you are homogenizing, on what basis do you assert that the stress field calculated is valid?

We just used a homogenized model. We believe the results are valid because we followed manufacturer's recommendations (http://www.hexcel.com/NR/rdonlyres/8012 ... Design.pdf , p.20), and, according to the manufacturer, this "simplistic approach has proven to give reasonable engineering solutions for practical applications." We also considered the issue of intracell buckling (IB) - the radius should be big enough (on the order of one meter for standard commercial honeycomb) - otherwise IB may be a problem.

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Re: Vacuum Zeppelin

Postby Steax » Sat Mar 27, 2010 1:28 pm UTC

So say we construct a large and hollow and strong chamber in LEO. We let the insides stay a vacuum and shove the orbit so it falls back to earth. Either
A. It bounces back off
B. It descends, but slowly decelerates, until finally rising back up again
C. It descends continuously till impacting the ground, but intact
D. It descends and collapses in the descent

I guess it would have to do a lot with the exact orbit. Say we put it in the same orbit as the shuttle's descent trajectory?
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Re: Vacuum Zeppelin

Postby Zamfir » Sat Mar 27, 2010 2:40 pm UTC

Steax wrote:I guess it would have to do a lot with the exact orbit. Say we put it in the same orbit as the shuttle's descent trajectory?

It would burn up in a hideous fashion

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Re: Vacuum Zeppelin

Postby Antimony-120 » Sat Mar 27, 2010 11:35 pm UTC

Steax wrote:So say we construct a large and hollow and strong chamber in LEO. We let the insides stay a vacuum and shove the orbit so it falls back to earth. Either
A. It bounces back off
B. It descends, but slowly decelerates, until finally rising back up again
C. It descends continuously till impacting the ground, but intact
D. It descends and collapses in the descent

I guess it would have to do a lot with the exact orbit. Say we put it in the same orbit as the shuttle's descent trajectory?


There's about a million possible assumptions to make. For example. we could make it be in a compeltely stable orbit (neglecting air friction) that would STILL burn it up if it was going the opposite way of the rotation of the earth (and hence the atmosphere, which is moving very, very fast). You can't just take a geosynch orbit and slowly make it lower and lower, so your trajectory in is going to mean damn near everything.

However, let's ignore all that orbital mechanics stuff, and just look at dropping an idealized vacuum sphere onto an idealized flat earth. This is very similar to dropping a rubber ball into a bucket. If you drop it very lightly from a few inches above the surface it will simply hit the surface and bob up and down abit. If you drop it from higher up it will plunge beneath the surface before bobbing back up. If you throw it down as hard as you can it will hit the bottom, depending on the depth of the bucket and how hard you throw it of course. You're unlikely to ever hit the bottom of the marinas trench for example, even if you throw really really hard. Of course a bucket of water has a much better defined "surface" than the atmosphere, and the density gradiant across a bucket isn't nearly as large. But it gives you an idea as to what could happen in this idealized scenario.

In reality, it depends entirely on what your aim is. If you want it to touch the ground before bouncing back up, you're in for some detailed calculations. One of the major reasons the space shuttle has such reentry heat is because it is moving at roughly 300km/hr when it touches down on the ground (IIRC. That number is one of those ones that's kicking around in my head with no good source attached, and somewhat dubious). It uses the fact that it's slamming into the atmosphere all the way down as a braking mechanism, which helps slow it's descent. You have the advantage that your desent is slowed by the buoyancy of the sphere, but the disadvantage that you're speed is now dictated by "has to be close to the rotation speed of the atmosphere, which is dependant on distance from the center of the earth".

If however you're just dropping it very lightly into the upper reaches of the atmosphere (and have some magical way of constructing it such that it's buoyant enough to stay there) then it's a relatively simple matter of matching the speed of the upper layers of the atmosphere approximatly, and dropping it in.
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Re: Vacuum Zeppelin

Postby inhahe » Thu May 27, 2010 12:58 pm UTC

oxoiron wrote:From: http://en.wikipedia.org/wiki/Aerogel
The world's lowest-density solid is a silica nanofoam at 1 mg/cm3, which is the evacuated version of the record-aerogel of 1.9 mg/cm3. The density of air is 1.2 mg/cm3.

If it is possible to reintroduce gas into and then reevacuate this substance, then it should be possible to cover a large chunk with foil and hook it up to a vacuum pump to regulate the level of reduced pressure inside the foam. The foil would prevent air from entering the foam and the foam would prevent the foil from collapsing under atmospheric pressure. Hang a gondola off the bottom, and problem solved.

Unfortunately, I suspect that it is not possible to move gas in and out of the foam, or it wouldn't be much of an anti-convective insulator. My guess is that the evacuation takes place during synthesis and is permanent and irreversible.

EDIT: from the same article..."They are good convective inhibitors because air cannot circulate throughout the lattice."

I guess that screws that idea, but it still might be possible to create a nanoporous material that allows air to move through it, is less dense than air when evacuated, and strong enough to not collapse under atmospheric pressure.


I don't know much about it either, but from what i've read (getting the run-around trying to find out if lighter-than-air aerogel has been made and how to do it), apparently when they make evacuated aerogel they give it some coating to protect it from the outside air. Though i'm not sure if that's because air would otherwise fill the aerogel or because it would simply collapse. Either way, though, I think making a craft out of floating aerogel would be pretty useful. If you need to be able to control how light/heavy it is, just do that in a separate component from the aerogel -- like a hot-air-balloon-like thing just big enough to off-balance the aerogel's bouyancy (sp), or maybe a litlte compression chamber.

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Re: Vacuum Zeppelin

Postby Sockmonkey » Fri May 28, 2010 5:21 am UTC

Zake wrote:Its a concept which has interested me for awhile since I saw it in Diamond Age; alas, the math says its unlikely.

...At least near sea level. How about we fly our theoretical vacuum zeppelin really high up in the atmosphere- at this point, there is less atmospheric pressure to worry about, and (if my physics intuition serves me here) the benefit of using vacuum rather than hydrogen becomes that much greater. Near-orbital zeppelins would be around as awesome as normal ones, IMHO.

The thinner air also gives less lift so no.

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Re: Vacuum Zeppelin

Postby NotationToby » Thu Nov 18, 2010 11:45 pm UTC

How about 2 having a cigar shaped zeppelins with air in, connecting them together in parallel, spinning them both in opposite directions, gradually letting the air out while they spin up until the centripetal force of the last bit of air and that of the fabric covering creates a dynamic force to resist air pressure and create a partial vacuum?

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Re: Vacuum Zeppelin

Postby inhahe » Fri Nov 19, 2010 1:35 am UTC

NotationToby wrote:How about 2 having a cigar shaped zeppelins with air in, connecting them together in parallel, spinning them both in opposite directions, gradually letting the air out while they spin up until the centripetal force of the last bit of air and that of the fabric covering creates a dynamic force to resist air pressure and create a partial vacuum?


Sorry, I don't understand your idea...

all i'm thinking so far is, why not just use a helicopter-like propeller, even if it's lighter and wider and turns more slowly.
also, as the blimps lose air, if there is air left only in the tips, they won't be able to maintain their structure..

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Re: Vacuum Zeppelin

Postby NotationToby » Fri Nov 19, 2010 4:48 am UTC

the rotational forces on the fabric and residual air act outwards radially to create a vacuum inside the blimp.

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Re: Vacuum Zeppelin

Postby inhahe » Fri Nov 19, 2010 5:07 am UTC

oh, i get it. i don't think it'll ever work because you'd have to spin it so fast to get a relative vacuum vis a vis the weight of its material to make it buoyant that the air friction would by far defeat the purpose.
i think.

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Re: Vacuum Zeppelin

Postby NotationToby » Sat Nov 20, 2010 1:15 pm UTC

Don't forget we don't necesarrily have to have a total vacuum. If we retain 1/x the density of outside we only have to accelerate the internal air to slightly more than x gs.

TThere is another option that we could go with. Circumferential tube ribs kept inflated by a fast moving circular flow of gas (hydrogen allows subsonic air flow between mach 2 and 3 - think of the radius of curvatures that could provide accelerations greater than 9.81 - that needed to supply counter pressure to the envelope - this could be quite a large structure)

And failing that, there is always space fountain technology!

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Re: Vacuum Zeppelin

Postby Soralin » Sat Nov 20, 2010 6:11 pm UTC

inhahe wrote:oh, i get it. i don't think it'll ever work because you'd have to spin it so fast to get a relative vacuum vis a vis the weight of its material to make it buoyant that the air friction would by far defeat the purpose.
i think.

Instead of cigar shaped, you could make them propeller shaped. :) But then the whole relative vacuum thing might not matter much.

inhahe
Posts: 59
Joined: Sun Feb 22, 2009 11:16 pm UTC

Re: Vacuum Zeppelin

Postby inhahe » Sat Nov 20, 2010 6:20 pm UTC

Soralin wrote:
inhahe wrote:oh, i get it. i don't think it'll ever work because you'd have to spin it so fast to get a relative vacuum vis a vis the weight of its material to make it buoyant that the air friction would by far defeat the purpose.
i think.

Instead of cigar shaped, you could make them propeller shaped. :) But then the whole relative vacuum thing might not matter much.


how about a wing made of lighter-than-air aerogel?

Agent_Irons
Posts: 213
Joined: Wed Sep 10, 2008 3:54 am UTC

Re: Vacuum Zeppelin

Postby Agent_Irons » Fri Nov 26, 2010 7:43 am UTC

inhahe wrote:
Soralin wrote:
inhahe wrote:oh, i get it. i don't think it'll ever work because you'd have to spin it so fast to get a relative vacuum vis a vis the weight of its material to make it buoyant that the air friction would by far defeat the purpose.
i think.

Instead of cigar shaped, you could make them propeller shaped. :) But then the whole relative vacuum thing might not matter much.


how about a wing made of lighter-than-air aerogel?

It would fly upside down to avoid falling up! I like this.


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