Vacuum Airships - would multi-skinning work?

[some bloke]

Vacuum airships are a scifi idea where you evacuate the air out of a chamber to achieve lighter-than-air lift.

I put this in scifi as it's just a curiosity at the moment.

The issue faced with these designs is the chamber buckling with the pressure of the atmosphere around it, which puts pay to it being lighter than air.

I realize that there is a theoretical maximum pressure difference the wall of a chamber can withstand before buckling - this represents the strength of the wall.

I'm wondering it would be feasible to use multiple layers of wall, with steadily increasing pressures inside, to prevent it from buckling under the strain.

Let's say that the wall can take 5psi before buckling. Atmospheric pressure is 15psi, so if it's fully evacuated, the chamber buckles.

now, if I wrap the chamber at 0psi in another chamber at 5psi. The pressure on the internal chamber is now 5psi, and the pressure on the outer is 10psi - so the outer would still collapse.

Add another layer at 10psi and you have 3 walls, each only taking 5psi, but with a vacuum on the inside. I don't know whether this would be any lighter than just making the chamber strong enough to withstand 15psi, but that's beside the point.

My question is - would this work? can you stagger the pressures via sequential containers? or am I missing something?

 

[DrStupid]

I don't know whether this would be any lighter than just making the chamber strong enough to withstand 15psi, but that's beside the point.

No that's the main problem. Of course you can stagger the pressures via sequential containers. That's out of question. However, it doesn't help you. Three containers that withstand 5 psi are as heavy as a single container that withstands 15 psi. All you get is less room inside.

 

[russ_watters]

No that's the main problem. Of course you can stagger the pressures via sequential containers. That's out of question. However, it doesn't help you. Three containers that withstand 5 psi are as heavy as a single container that withstands 15 psi. All you get is less room inside.

It's probably even worse than that,, since structural strength doesn't scale linearly with thickness; it's quadratic.

 

[Vanadium 50]

Vacuum airships are a not-even-a-solution looking for a problem.

There is a market for about two dozen airships in the world. Making them orders of magnitude more expensive to get at most 30% more lift - and we have not accomplished that - is a non-starter.

 

[Baluncore]

I realize that there is a theoretical maximum pressure difference the wall of a chamber can withstand before buckling - this represents the strength of the wall.

The radial pressure gradient is not the biggest problem with a vacuum airship.

If the cross section became dented, or elliptical, it could implode to a flat sheet. Only a structural or high internal wall pressure can keep that from happening.

There is also a lengthwise concertina that must be countered by high pressure in the wall(s). The wall section, multiplied by the wall internal pressure conspires to equal the volume of the vacuum.

See also; https://www.physicsforums.com/posts/5701397

 

[DrStupid]

It's probably even worse than that,, since structural strength doesn't scale linearly with thickness; it's quadratic.

I'm not sure about buckling (that's an even more complex problem) but at least the compressive (or tensile) stress in a spherical or cylindrical hull is inversely proportional to the thickness and proportional to the pressure difference. That means that even in the ideal case of uniform mechanical stress (and therefore no buckling) there is nothing to win.

 

[russ_watters]

I'm not sure about buckling (that's an even more complex problem) but at least the compressive (or tensile) stress in a spherical or cylindrical hull is inversely proportional to the thickness and proportional to the pressure difference. That means that even in the ideal case of uniform mechanical stress (and therefore no buckling) there is nothing to win.

A large, cylindrical chamber is a row of truss bridges, from a structural standpoint. I don't think the hoop stress idea for pressure vessels really applies. The structure needed to hold a vacuum is not fundamentally different (just more substantial) than the structure needed so it doesn't collapse under its own weight:

 

[russ_watters]

There is a market for about two dozen airships in the world. Making them orders of magnitude more expensive to get at most 30% more lift - and we have not accomplished that - is a non-starter.

How are you getting 30%? Google is telling me the density of helium is just under 14% that of air. Even worse.

 

[DrStupid]

The hoop stress idea for pressure vessels doesn't really apply.

It works quite well for submarines.

The structure needed to hold a vacuum is not fundamentally different (just more substantial) than the structure needed so it doesn't collapse under its own weight

It actually is. There are a lot of structures that doesn't collaps under their own weight but would never hold a vacuum. I think you do not mean the the structure needed to hold a vacuum but to withstand the pressure difference between top and bottom. That corresponds to the weight of the structure if it floats.

 

[russ_watters]

It works quite well for submarines.

I think the rules change when the structure gets longer and thinner and the pressure lower. I think that that the flatter the arch, the closer it is to a bridge than a small pressure/vacuum vessel. And I think the difference is the buckling failure you set aside in your earlier post. Avoiding buckling is what a bridge does.

For a pressure vessel, hoop stress is everything. They don't buckle because the pressure opposes the buckle and makes them stable. That's why a mylar balloon can hold pressure even though un-inflated, it is just a pile of mylar on the ground. But if you inflate it, you can poke at it with your finger and it won't buckle/collapse. But for a vacuum, buckling is a key failure mode.

I'm having trouble finding specific reference for what I'm describing, but mathematically: because the hoop stress equation is linear and moment of inertia of a beam quadratic, reducing the thickness as you reduce the pressure should increase the risk of buckling.

It actually is. There are a lot of structures that doesn't collapse under their own weight but would never hold a vacuum.

I'm talking about the shape/structure type and wasn't suggesting supporting its weight was harder than supporting a vacuum -- I said the opposite.

I think you do not mean the the structure needed to hold a vacuum but to withstand the pressure difference between top and bottom. That corresponds to the weight of the structure if it floats.

Is the pressure difference between top and bottom a substantial strength issue for a vacuum vessel/submarine, or is the vacuum itself the larger strength issue? I would have expected that the strength needed to support a vacuum is so much larger than the strength to support its own weight that they would barely even bother with the strength to support its own weight. E.G., ships are flat bottom and can easily be made to be self-supporting against that pressure difference. For a submarine, I would expect that pressure difference to be the least of the worries.

 

[hutchphd]

Just to complete the category, I suggest a look at the Goodyear Inflatable Airplane. Only the engine was not inflatable I believe.
As I recall, the wing spar was internally tied to enable it to be rigid when inflated.

 

[Vanadium 50]

How are you getting 30%?

By mistake. He/N is 30%. He/N2 is half that.

 

[DrStupid]

moment of inertia of a beam quadratic

Is it? According to https://en.wikipedia.org/wiki/Second_moment_of_area it should be cubic. In addition the angular momentum increases with the deformation. That results in a sudden collaps if the deformation exceeds a point of no return. The calculation of this point is not trivial - not even for a flat surface without structual weakness (e.g. windows). That's why I set it aside and just referred to the best case.

 

[Stormer]

Vacuum airships are a not-even-a-solution looking for a problem.

There is a market for about two dozen airships in the world. Making them orders of magnitude more expensive to get at most 30% more lift - and we have not accomplished that - is a non-starter.

I don't think it is about making more lift really. It is more about not wasting helium that is a finite resource here on earth.

Imagine if airships could be made cheap and without finite resources like helium. Then we can replace expensive low Earth orbit satellites with a limited time in orbit with high altitude airships that can stay up there indefinitely and can even be taken down to Earth for service and upgrades and sent back up again.

 

[Baluncore]

Then we can replace expensive low Earth orbit satellites with a limited time in orbit with high altitude airships that can stay up there indefinitely and can even be taken down to Earth for service and upgrades and sent back up again.

There are already many high altitude balloons up there, giving a mobile phone service, from 60,000 feet. https://loon.com/

You can see where some are deployed at anytime. https://flightaware.com/live/fleet/HBAL
Operators drop them after more than 100 days. They are recovered for re-release at a different launch site. I see the tracking as they are landed in NT Australia.
Watch the tracking of HBAL236, this weeks candidate for a landing in NT.au

 

[Stormer]

There are already many high altitude balloons up there, giving a mobile phone service, from 60,000 feet. https://loon.com/

You can see where some are deployed at anytime. https://flightaware.com/live/fleet/HBAL
Operators drop them after more than 100 days. They are recovered for re-release at a different launch site. I see the tracking as they are landed in NT Australia.
Watch the tracking of HBAL236, this weeks candidate for a landing in NT.au

As i said. Wasting helium. And also limited time operation while a vacuum airship can in theory stay up indefinitely with a small PV Powered vacuum pump to pump down again any small leak in the vacuum vessel.

 

[Baluncore]

Helium would cost more if it was so scarce. It is not wasted by Loon HBALs, they compress and expand the same gas to change the buoyancy, altitude, and so select optimum winds for navigation.

I don't think we need dirigible airships up there. But if we did, and they were vacuum balloons, what are the limiting factors?

Communication balloons need to be near 60,000 feet. Below that they would be in the turbulent jet streams and commercial airspace. Above that, the 0.25 bar air is too thin to provide buoyancy.

A double walled envelope with internal gas pressure, sufficient to keep the ends apart, weighs too much. So there must be a rigid two-layer-truss structure to keep the ends apart and prevent an implosion. A slack envelope would rest on the outside of the truss, with inward dimples wherever there are holes in the truss. That would reduce envelope surface tension being added to the truss stress.

A fixed volume balloon/airship would need to start from the ground with about 0.75 bar internal air, that would be pumped down towards zero as altitude increases, maintaining the 0.25 bar difference as it climbs. That procedure reduces the maximum envelope differential pressure to 0.25 bar.

So what is the real challenge?
It is the design of the light-weight truss structure that supports the envelope.

 

[DrStupid]

Wasting helium.

Then use hydrogen instead. It is an infinite resource, less expensive and has only half the density. Yes, it is inflammable, but that is no problem in case of unmanned balloons.

And also limited time operation while a vacuum airship can in theory stay up indefinitely

The longest flight of the Loon system was 187 days. Two restarts every year is not an issue. Staying up indefinitely would require maintenance-free systems. That might even increase the costs.

On top of that are vacuum ballons even less feasible at high altitudes. Using vacuum instead of helium and aluminium instead of Kevlar in the Loon system would result in pretty much the same thickness of 76 µm just to hold the balloon itself. It would need to be even thinner in order to carry the payload.

 

[Vanadium 50]

About 7% of helium production is used for lifting, and this includes a substantial fraction for party balloons. If the problem you are trying to solve is helium use, wouldn't it be better focusing on the other 93%?

 

[Stormer]

Helium would cost more if it was so scarce. It is not wasted by Loon HBALs, they compress and expand the same gas to change the buoyancy, altitude, and so select optimum winds for navigation.

And oil wold cost more if it was a limited resource right? The fact is that helium is not produced in the Earth at nearly the same rate that we use it and it is released out to the atmosphere and eventually to space. And there is many initiatives to preserve the helium resources we have for useful things rather than using it for mylar baloons for kids.

Do they really re compress the helium in these balloons? I wold think that they just packed the supply they needed for the time intended and just release the excess to the atmosphere.

Then use hydrogen instead. It is an infinite resource, less expensive and has only half the density. Yes, it is inflammable, but that is no problem in case of unmanned balloons.

Even unmanned balloons you don't want exploding the whole launch area from the slightest spark. Remember hydrogen leaks trough almost all materials and has a really wide flammable mixing range with air.

 

[Baluncore]

Even unmanned balloons you don't want exploding the whole launch area from the slightest spark. Remember hydrogen leaks trough almost all materials.

Yet we drive around in, and fill our cars with gasoline.

 

[Baluncore]

Do they really re compress the helium in these balloons? I wold think that they just packed the supply they needed for the time intended and just release the excess to the atmosphere.

No. On a long voyage, helium is too valuable to waste.
The helium conservation process now used is described here;
https://loon.com/technology/flight-systems/
“Made from polyethylene, each tennis-court-sized balloon envelope actually consists of a balloon inside of a balloon. A fixed amount of lift gas in the inner balloon keeps the system aloft. Adding or releasing outside air to the outer balloon changes density, allowing the system to ascend or descend when needed.”

It therefore takes about 1/4 of the envelope volume of lift gas per flight. Flights are getting longer.

 

[russ_watters]

Even unmanned balloons you don't want exploding the whole launch area from the slightest spark. Remember hydrogen leaks trough almost all materials and has a really wide flammable mixing range with air.

Someone should tell NASA.

Imagine if airships could be made cheap...

Imagination is not reality. The vacuum balloon idea is just a total non-starter because even if it were *possible* to build one, it is inherently impossible that it could be done cheaply.

The hydrogen danger is not zero, but for unmanned balloons it is vanishing small. Hydrogen is a common industrial gas. At anyone time there are probably thousands of trucks driving around our highways, constantly leaking. When was the last time you heard of one exploding?

For a large scale deployment, you'd build the hydrogen factory next to the launch facility, and have no people near it, which would make the injury risk basically zero.

 

[DrStupid]

Even unmanned balloons you don't want exploding the whole launch area from the slightest spark. Remember hydrogen leaks trough almost all materials and has a really wide flammable mixing range with air.

Exploding the whole launch area from the slightest spark is almost impossible with hydrogen gas. Leaking hydrogen doesn't accumulates on the ground but escapes rapidly upward into the air. It would need a massive release in order to get a large volume of explosive mixture.

Hydrogen is routinely used for a long time, in very large amounts and for a lot of applications - including weather balloons. The safety measures are technically matured in an extend that there are even public hydrogen stations for cars in many countries all over the world.

If you are afraid of hydrogen than you should be even more worried about large vacuum contaiers with razor-thin walls. The volume energy of a vacuum balloon with the scale of the Loon system would be at least 2 kg TNT equivalent (corresponding to 13 HG 85 granades). You don't want to be there when it implodes.

 

[Baluncore]

You don't want to be there when it implodes.

Just like when a catfish opens it's mouth.

 

[russ_watters]

Exploding the whole launch area from the slightest spark is almost impossible with hydrogen gas. Leaking hydrogen doesn't accumulates on the ground but escapes rapidly upward into the air. It would need a massive release in order to get a large volume of explosive mixture.

Yeah; the Hindenburg and Challenger are notable rare examples of large/rapid release. But continuous "leaks" are a normal part of operating liquid hydrogen systems; they are continuously boiling. If you drive behind one on the highway you can sometimes see water vapor condensing in the air by the vent. You wouldn't/can't do that with propane. Any propane leak carries a major explosion risk.

YouTube has examples of all these...

 

[anorlunda]

Someone should tell NASA.

 

[DrStupid]

the Hindenburg and Challenger are notable rare examples of large/rapid release.

Even these rare examples don't really fit to scenario above. The Challenger tank was filled with liquid hydrogen and oxygen (nobody would handle them side by side in order to fill ballons) and the Hindenburg didn't explode (you known the difference if you ever heard an oxyhydrogen explosion).

 

[Stormer]

Well close to where i live there was a explosion at a hydrogen filling station last year.

The investigation concluded that the cause was a leak because of two bolts on a hydrogen bottle that was not tightened enough. So yes small slow leaks of hydrogen can definitely cause explosions. At least in enclosed spaces. And in open places it can cause fires really easy. And even if a human is not harmed the balloon material and the satellite electronics will most likely be damaged.

And even though hydrogen does not accumulate unless it is in an enclosed space like propane does, hydrogen has a really large flammability range as i said. And it leaks a lot easier than propane. In fact it often leaks by design because of boil off that is vented to the air when stored in liquid form, or it just leaks right trough materials (like the balloon skin) in gas form.

 

[Baluncore]

Well close to where i live there was a explosion at a hydrogen filling station last year.

Then they should stop supplying hydrogen to all transport, because it is safer to use it in high altitude balloons.

 

[Stormer]

Then they should stop supplying hydrogen to all transport, because it is safer to use it in high altitude balloons.

A long as there is ground filling stations for them the problem is the same.

 

[Baluncore]

A long as there is ground filling stations for them the problem is the same.

You are imagining it. There is no problem with high altitude hydrogen balloons.

 

[russ_watters]

Even these rare examples don't really fit to scenario above. The Challenger tank was filled with liquid hydrogen and oxygen (nobody would handle them side by side in order to fill ballons)

Good point. I'm not sure how it could have gone with only hydrogen, but it was a catastrophic, large release.

and the Hindenburg didn't explode (you known the difference if you ever heard an oxyhydrogen explosion).

I'm not sure that difference mattered much to the passengers of the Hindenburg, but sure, that difference would matter for other applications. Googling around, I found THIS document on hydrogen fuel for transportation, which includes a case study. The media inaccurately described it as an explosion, but the operator sustained only minor uv radiation burns and the truck was still drivable. The difference definitely mattered there.

 

[russ_watters]

Well close to where i live there was a explosion at a hydrogen filling station last year.
View attachment 270514
The investigation concluded that the cause was a leak because of two bolts on a hydrogen bottle that was not tightened enough. So yes small slow leaks of hydrogen can definitely cause explosions. At least in enclosed spaces. And in open places it can cause fires really easy.

Can you provide a link to a description of that incident? I'm seeing very little damage and evidence that the building was probably designed to survive a minor explosion (with blow-off panels).

Another attribute of hydrogen vs propane is it is very light, so it has something like 1/10 the energy density for a confined space explosion (or 1/3 that of natural gas). So smaller confined space explosions pose less risk.

Let's put that another way; natural gas is much more dangerous than hydrogen for a confined space explosion, yet it is extremely commonly used in confined spaces (buildings). Explosions do happen, but they are rare enough it is considered worth the risk.

And even if a human is not harmed the balloon material and the satellite electronics will most likely be damaged.

That's a pretty straightforward part of cost-benefit analysis. I'm sure high altitude balloons/payloads are regularly damaged/destroyed due to inherent fragility vs the weather, and I highly doubt the risk of hydrogen would add significantly to it.

 

[Stormer]

You are imagining it. There is no problem with high altitude hydrogen balloons.

Am i imagining the exploded hydrogen filling station in the picture above?
Or am i imagining that a hydrogen balloon filling station will be essentially the same as a hydrogen car filling station except the customer filling parts? Look at the picture. The part that exploded is the elektrolyser and hydrogen storage building.

Googling around, I found THIS document on hydrogen fuel for transportation, which includes a case study. The media inaccurately described it as an explosion, but the operator sustained only minor uv radiation burns and the truck was still drivable. The difference definitely mattered there.

I have just showed you a hydrogen station that exploded just a year ago throwing debris everywhere. And this is one of only a few in operation in my country. If there was more of them the explosions wold have happened more often.

And burning off the hydrogen in the air before launch like NASA does with it's rockets will not work either. The rockets aluminium skin can handle the heat for a couple of seconds but i am pretty sure the ultra thin skin of a high altitude balloon can not.

 

[DrStupid]

I'm not sure that difference mattered much to the passengers of the Hindenburg

I think it does. 62 of the 97 persons on board survived. I wouldn't expect that in case of an explosion.

 

[Vanadium 50]

This thread is filled with what Perry Mason would call "assuming facts not in evidence."

First is that balloons (primarily weather balloons) are a major consumer of helium. As I said, the National Academies estimates 7% of helium is lifting. Party balloons make up most of this, so that leaves at most a 3% fraction. If one is concerned about reducing helium use, there is at most 3% to be gained here.

"Helium is a finite resource". So is hydrogen. Where does helium come from? It's a natural gas contaminant and is a by-product of natural gas production. Where does hydrogen come from? It'ss a by-product of natural gas production. What is certainly true is that hydrogen is cheaper.

Suppose weather balloons were replaced with hydrogen. So what? You're not transporting people, you're transporting instruments. And balloons fail and instruments are damaged all the time already. You need to demonstrate a) that switching to hydrogen makes things substantially worse, and b) the cost to switch to a technology that is so expensive it doesn't even exist is lower than living with it.

 

[Stormer]

First is that balloons (primarily weather balloons) are a major consumer of helium. As I said, the National Academies estimates 7% of helium is lifting. Party balloons make up most of this, so that leaves at most a 3% fraction. If one is concerned about reducing helium use, there is at most 3% to be gained here.

That is assuming current use. If LEO satellites are to be replaced by balloons as i suggested, and a lot of companies is going to make global wireless internet networks like starlink using balloons that will massively increase the number of balloons in the air by orders of magnitude compared to today's use.

And this is not some far fetched idea. Google, Facebook, Microsoft, and probably many others has had projects making internet networks via high flying "satellites" either in the form of solar powered drones, or in the form of balloons.

 

[russ_watters]

"Helium is a finite resource". So is hydrogen.

Perry, hydrogen is finite only insofar as all resources are finite by definition. The limitation in the hydrogen resource would probably first come from complaints by owners of formerly beach-front property as their property values decreased. Upside: reduced flood insurance costs.

Yes, I know most hydrogen *today* comes from underground sources as biproduct of natural gas production. But alternatives once that resource is expended are thin, and production itself is limited. But the alternative to steam reforming of natural gas is an effectively limitless source.

 

[akhmeteli]

Vacuum airships are a not-even-a-solution looking for a problem.

I am not sure. There is an obvious problem: altitude control. For example, after an airship unloads a heavy load, it needs to take ballast to avoid having too much buoyancy. Releasing helium after each flight is expensive. There are some solutions to the problem (see, e.g., http://aeroscraft.com/technology-copy/4580412172), but they are not simple. With a vacuum aircraft, one can just admit air to decrease buoyancy.

There is another serious problem: (long-term) storage. One may need large hangars as, again, releasing helium is expensive. There is no such problem with hot-air balloons, but they require energy to heat air. On the other hand, one can disassemble vacuum aircraft for storage (at least theoretically).

Another problem: it is not easy to prevent helium leak through the envelope.

There is a market for about two dozen airships in the world.

So maybe the market is small because current lighter-than-air aircraft have a lot of problems.

Making them orders of magnitude more expensive to get at most 30% more lift - and we have not accomplished that - is a non-starter.

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

 

[Baluncore]

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

Business can ignore vacuum airships until you can build a toy vacuum airship, or a prototype.
To do that you need a low mass truss, or some other structure to oppose the vacuum implosion.
You will have credibility when you can demonstrate a solution to that structural problem.

 

[akhmeteli]

Business can ignore vacuum airships until you can build a toy vacuum airship, or a prototype.
To do that you need a low mass truss, or some other structure to oppose the vacuum implosion.
You will have credibility when you can demonstrate a solution to that structural problem.

My credibility or lack of it does not seem relevant. I just noted that there are indeed problems that vacuum aircraft could solve. If you disagree, I would like to hear your arguments.

Let me also note that some work on vacuum aircraft is being done at Los Alamos, NASA, Air Force Institute of Technology, and other places.

(https://www.lanl.gov/projects/feynm...techsnapshots.php?id=5d0116573be4dbb4f26c7e87)

(Jenett, B. E., Gregg, C. E., Cheung, K. C., Discrete Lattice Material Vacuum Airship, AIAA SciTech Forum, 7-11 January 2019, San Diego, California, May–June 2015, 52, (3), pp 1-12)

(Adorno-Rodriguez, R., Palazotto, A. N., Nonlinear Structural Analysis of an Icosahedron Under an Internal Vacuum, Journal of Aircraft, May–June 2015, 52, (3), pp 878-883.)

 

[Baluncore]

I just noted that there are indeed problems that vacuum aircraft could solve. If you disagree, I would like to hear your arguments.

There are other ways available now to practically solve all your hypothetical problems.
There is no vacuum aircraft available to magically solve those hypothetical problems.

 

[akhmeteli]

There are other ways available now to practically solve all your hypothetical problems.
There is no vacuum aircraft available to magically solve those hypothetical problems.

What is hypothetical about the problems that I mentioned? So yes, there are other ways to solve them, and no, there is no vacuum aircraft. I just insisted that there are indeed problems that vacuum aircraft could help solve.

 

[russ_watters]

Note: per our PM discussion, we are reviewing whether we can discuss your paper and patent application in this thread.

I am not sure. There is an obvious problem: altitude control.

I don't think you heard what @Vanadium 50 said. You're talking about engineering (and maybe environmental) problems, but he's talking about economics problems. I understand that you are an aspiring inventor, but even if you succeed in inventing a functional vacuum airship, you still have to solve someone's economic/environmental problem in order to sell it. There has to be a market for the product. So when the time comes, you'll need to be able to show that your solution costs less than a traditional helium balloon or that the cost premium is worth the environmental savings. Right now, you seem to be completely ignoring the cost/market issue.

I suggest watching the TV show "Shark Tank" to see how inventors fare on it. One important thing to note: they pretty much always have a working prototype and a pending patent before pitching their ideas to investors. But that's not enough: they need to prove they are solving a market problem.

That said, I think you are downplaying the engineering benefits as well, by basically ignoring completely how the existing solutions work. For the sake of your own business model and the potential time/energy/money wasted in pursuing an idea that really isn't likely to go anywhere, you need to take an honest look at both sides of this. On the engineering side, I can't understand why you wouldn't consider pumping the helium back into a pressurized tank to be a solution to the engineering/environmental problem of wasted helium and airship storage. It seems really obvious. On the other side, since that is obvious but isn't apparently common, maybe that's because ballast is cheap and easy? I suppose you can say that a vacuum balloon with a pump and valves for ballast control is "a solution" to this technical problem, but other solutions clearly exist and I don't see a reason to believe the vacuum balloon would be a cheaper solution (back to the economic problem) -- because ultimately that's what matters most here.

It is possible that there will never be a business case for vacuum aircraft, but it is not obvious so far.

It may not be obvious to you, but it seems obvious to several of us. But here's the thing: the burden of proof is entirely on your side whereas the criteria/demands of proof are entirely on ours (or that of prospective investors). We can tell you what we think it will take and you'll have to provide that. Or not -- it seems you've been working on this for a long time and haven't gotten far.

Step 1: Build a functioning prototype to prove it is actually technically possible. And no, your arxiv paper and patent application are not sufficient as such proof. Even if all the math is right in your paper, it isn't enough.

 

[gmax137]

Vacuum airships are a scifi idea where you evacuate the air out of a chamber to achieve lighter-than-air lift.

...

I'm wondering it would be feasible to use multiple layers of wall, with steadily increasing pressures inside, to prevent it from buckling under the strain.

...

Add another layer at 10psi and you have 3 walls, each only taking 5psi, but with a vacuum on the inside. I don't know whether this would be any lighter than just making the chamber strong enough to withstand 15psi, but that's beside the point.

My question is - would this work? can you stagger the pressures via sequential containers? or am I missing something?

... Of course you can stagger the pressures via sequential containers. That's out of question. However, it doesn't help you. Three containers that withstand 5 psi are as heavy as a single container that withstands 15 psi. ...

(emphasis added)

Has anyone challenged @DrStupid 's contention in post #2? If not, I don't know what all the subsequent posts are for. Question asked and answered.

 

[DrStupid]

Has anyone challenged @DrStupid 's contention in post #2?

It has been challenged insofar that it refers to the theoretically best case. The reality is even worse.

 

[jrmichler]

Just for grins and giggles, I did some quick calculations for a vacuum airship. Some simple assumptions to get started include a tube 100 feet diameter with a perfect vacuum. The lift per foot of length at sea level is then the cross sectional area times the density of air: Liftperfoot=π/4∗1002∗0.075=589lbs/footlength.

The circumferential compressive force per foot length is Forceperfoot=14.7∗144∗100/2=106,000lbs/foot.

The longitudinal force per foot circumferential distance: Forceperfoot=π/4∗1002∗14.7∗144/(100∗π)=53,000lbs/foot.

Square feet of structure per foot length: 100∗π=314feet.

Maximum possible weight of structure is the lift per foot divided by the length of structure per foot: Maxweight=589lbs/foot/314feet=1.9lbsperfoot2. The sketch below shows this:

Not shown in the sketch is the vacuum force of 2117 lbs per square foot into the page. The absolute maximum weight of one square foot of the vacuum structure that withstands the above forces is 1.9 lbs. The structure must not buckle. The structure needs attachments for crew, cargo, engines, fuel, control surfaces, mooring, etc.

In practice, the airship structure must weigh about half that much, or about 1 lb per square foot, in order to carry crew, cargo, engines, fuel, control surfaces, mooring, etc. Any person who proposes a vacuum airship needs to do these calculations, and show a solution using commercially available materials

 

[Baluncore]

@jrmichler
Your computations are for sea level. Some things scale sensibly.
I think the idea of using an unmanned vacuum airship at 60,000 feet for mobile phone and internet connectivity is an interesting model. The air pressure at that altitude is only about 1 psi. The airship structure therefore need only counter a 1 psi differential envelope pressure. But the volume must be sufficient to lift the gross weight. At sea level the external pressure is about 14.7 psi, the same volume could have an internal pressure of 13.7 psi and generate the same lift force for the same structure. The differential envelope pressure would still be only 1 psi.

The OP's question, asking about multiple skins, can be dismissed since sea level atmospheric pressure differential will never be present. Any structure that survived with negative 14.7 psi envelope pressure at sea level would be too heavy to rise to an altitude where only one psi difference is available for lift.

 

[russ_watters]

The absolute maximum weight of one square foot of the vacuum structure that withstands the above forces is 1.9 lbs. The structure must not buckle. The structure needs attachments for crew, cargo, engines, fuel, control surfaces, mooring, etc.

In practice, the airship structure must weigh about half that much, or about 1 lb per square foot, in order to carry crew, cargo, engines, fuel, control surfaces, mooring, etc. Any person who proposes a vacuum airship needs to do these calculations, and show a solution using commercially available materials

Great stuff, thanks. By comparison, the Hindenberg class airships were 135ft in diameter, 800 feet long (equivalent 500ft pure cylinder), 7.1 million cubic feet and had a cargo capacity of 22,000 lb. That's a structure weight of 481,000 lb and hydrogen weight of 40,000 lb for a displacement of 543,000 lb of air. Or per square foot, (pure cylinder), that's 0.96 lb of structure. So if they held a vacuum they could carry almost triple the cargo. But...they would have to hold a vacuum. Buoyed by helium they'd need to shed 12,000 lb to get airborne.

Also, they flew at a top speed of 80mph.

By comparison, a 747-8 has a similar empty weight of 485,000 lb and with a full load of fuel can carry 80,000 lb of cargo (or more if you reduce the 422,000 lb of fuel) and cruises around 550 mph.

It also compares quite unfavorably to a modern inflatable/hybrid blimp such as the Zeppelin NT which cruises at about the same speed and has a 4,000 lb cargo capacity at 1/20th the volume.