lighter than air ship using vacuum instead of gas

[lemur]

Lighter than air ships have been made to float using light gasses such as hydrogen and helium. Hot air balloons reduce the density of air by heating it. I wonder if it would be possible to make an air ship float by emptying the air out of it instead of replacing that air with light gas.

[JillSwift]

Lighter than air ships have been made to float using light gasses such as hydrogen and helium. Hot air balloons reduce the density of air by heating it. I wonder if it would be possible to make an air ship float by emptying the air out of it instead of replacing that air with light gas.

 

This rings a bell. I think it's been tried before...

 

As I recall, a "vacuum balloon" would be significantly more efficient (in the 7-10% range or so) than a helium or hydrogen balloon, except for the weight penalty incurred by the need for a rigid envelope.

 

Oh, right here on these forums:

http://www.scienceforums.net/topic/30004-vacuum-balloon/

[lemur]

This rings a bell. I think it's been tried before...

 

As I recall, a "vacuum balloon" would be significantly more efficient (in the 7-10% range or so) than a helium or hydrogen balloon, except for the weight penalty incurred by the need for a rigid envelope.

 

Oh, right here on these forums:

http://www.sciencefo...vacuum-balloon/

Good memory. That thread was from @2008 on the posts I checked. I wonder if size somehow makes a difference. It has always baffled me that zeppelins like the Hindenburg appear to have had heavy steel frames and a heavy payload. I suppose that's my subjective impression though, so I should go google it. Thanks for posting the link to the old thread.

[JillSwift]

Good memory. That thread was from @2008 on the posts I checked. I wonder if size somehow makes a difference. It has always baffled me that zeppelins like the Hindenburg appear to have had heavy steel frames and a heavy payload. I suppose that's my subjective impression though, so I should go google it. Thanks for posting the link to the old thread.

 

==

[Moontanman]

One of my favorite series of books raises this question in an unusual way, in one of the Books of swords by Saberhagen the protagonist conjures up a technology jinn. He wants to build a craft lighter than air and he instructs the magical creature to build a huge hollow sphere of metal and then commands it to remove the air, of course the balloon collapses as the air is removed. (wild books by the way, technology mixed with swords and sorcery gods demons and all sorts of odd stuff created by the ultimate dooms day weapon in a war between the USA and the Soviets) but the point is that if the hollow sphere is thin and light enough to weigh less than the air inside the sphere would collapse.

 

Another book "Across Real time" by Verner Vinge uses the same concept somewhat more successfully but yes if the sphere is lighter than the air inside it will float if the air is removed and the walls are strong enough to prevent collapse.

[Janus]

Lighter than air ships have been made to float using light gasses such as hydrogen and helium. Hot air balloons reduce the density of air by heating it. I wonder if it would be possible to make an air ship float by emptying the air out of it instead of replacing that air with light gas.

 

Moontanman points out the main difficultly in this. When you use a gas, you are equalizing the pressure on the inside and outside, while still having the gas on the inside being of lower density than the outside air. Thus the material from which your container is made does not have to be rigid.

 

If you try to contain a vacuum, you will have a pressure of ~14psi working to crush your container. So let's say that your "balloon" has a 1 foot radius. This gives a surface area of ~1810 in² for a total force of 25334 lbs. This also works out to a volume of 7238 in³. at 20°C, this much dry air weighs about 0.00004 lbs(0.02g). This is the maximum weight that the material of our "vacuum balloon" can have and have even neutral buoyancy.

 

Diamond, for instance, has a density of 3.5g/cm³. A hunk of diamond with a mass of 0.02g would have a volume of 0.006cc. Spread into a shell with a surface area of 1810 in², you get a thickness of 5 nanometers,. This is about 1/40th the thickness of a typical sheet of aluminum foil. Since diamond is 3.6 times harder than aluminum, this hardly seems enough to withstand the 25334 lbs of crushing force exerted by the atmosphere on our balloon.

[StringJunky]

Moontanman points out the main difficultly in this. When you use a gas, you are equalizing the pressure on the inside and outside, while still having the gas on the inside being of lower density than the outside air. Thus the material from which your container is made does not have to be rigid.

 

If you try to contain a vacuum, you will have a pressure of ~14psi working to crush your container. So let's say that your "balloon" has a 1 foot radius. This gives a surface area of ~1810 in² for a total force of 25334 lbs. This also works out to a volume of 7238 in³. at 20°C, this much dry air weighs about 0.00004 lbs(0.02g). This is the maximum weight that the material of our "vacuum balloon" can have and have even neutral buoyancy.

 

Diamond, for instance, has a density of 3.5g/cm³. A hunk of diamond with a mass of 0.02g would have a volume of 0.006cc. Spread into a shell with a surface area of 1810 in², you get a thickness of 5 nanometers,. This is about 1/40th the thickness of a typical sheet of aluminum foil. Since diamond is 3.6 times harder than aluminum, this hardly seems enough to withstand the 25334 lbs of crushing force exerted by the atmosphere on our balloon.

 

About in the same league as trying to make a perpetual motion machine then?

[lemur]

Moontanman points out the main difficultly in this. When you use a gas, you are equalizing the pressure on the inside and outside, while still having the gas on the inside being of lower density than the outside air. Thus the material from which your container is made does not have to be rigid.

 

If you try to contain a vacuum, you will have a pressure of ~14psi working to crush your container. So let's say that your "balloon" has a 1 foot radius. This gives a surface area of ~1810 in² for a total force of 25334 lbs. This also works out to a volume of 7238 in³. at 20°C, this much dry air weighs about 0.00004 lbs(0.02g). This is the maximum weight that the material of our "vacuum balloon" can have and have even neutral buoyancy.

 

Diamond, for instance, has a density of 3.5g/cm³. A hunk of diamond with a mass of 0.02g would have a volume of 0.006cc. Spread into a shell with a surface area of 1810 in², you get a thickness of 5 nanometers,. This is about 1/40th the thickness of a typical sheet of aluminum foil. Since diamond is 3.6 times harder than aluminum, this hardly seems enough to withstand the 25334 lbs of crushing force exerted by the atmosphere on our balloon.

This may sound naive, but could it be possible to contain and use free neutrons as a lighter than air gas? Of course, I don't know where you can get them except for as a by-product of radioactive decay.

 

 

[ewmon]

What about a substance such as aerogel, but one that's produced in a vacuum or somehow evacuated after manufacture, and hermetically sealed within a skin? Wikipedia says:

 

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.

One m³ would have a buoyancy of 200 g, equaling 40,000 kg for something the size of the Hindenburg.

[Janus]

This may sound naive, but could it be possible to contain and use free neutrons as a lighter than air gas? Of course, I don't know where you can get them except for as a by-product of radioactive decay.

 

Free neutrons decay into a proton, electron and anti-neutrino in a half-life of ~15 min. Besides, a single free neutron actually masses more than a hydrogen atom, so hydrogen gas would be less dense and be more buoyant than a free neutron "gas", not to mention the problems of containing such a "gas".

[swansont]

Free neutrons decay into a proton, electron and anti-neutrino in a half-life of ~15 min. Besides, a single free neutron actually masses more than a hydrogen atom, so hydrogen gas would be less dense and be more buoyant than a free neutron "gas", not to mention the problems of containing such a "gas".

 

I think the latter would be the major problem. A neutron "gas" would not follow the ideal gas law and tend to leak out of any container.

[lemur]

Free neutrons decay into a proton, electron and anti-neutrino in a half-life of ~15 min. Besides, a single free neutron actually masses more than a hydrogen atom, so hydrogen gas would be less dense and be more buoyant than a free neutron "gas", not to mention the problems of containing such a "gas".

 

 

I think the latter would be the major problem. A neutron "gas" would not follow the ideal gas law and tend to leak out of any container.

The only real value I saw in the neutrons was that I assumed they would be non-combustible, unlike hydrogen. I didn't know they decayed. I might have to start a new thread to discuss that. I suppose I'll throw in the discussion about why they don't follow ideal gas laws too. Interesting, thanks for raising these new questions for me.

[padren]

If the skin's interior was appropriately insulated from electrical discharge, could it be filled with a small number of highly like-charged particles to equalize the pressure through the repulsive effect, while only trivially increasing mass?

 

 

Personally, I am pretty sure that even if a solution could be found for the "vacuum balloon" crushing issues, the end result would be a total apparatus that was less efficient than using light air or gasses, just due to the extra weight involved in trying to engineer a viable solution. The mass of the air being displaced only weighs so much, and naturally the mass of hydrogen/helium/hot air is even less - so any solution that adds more mass than the mass of the classically used lighter-than-air gasses is going to be less efficient despite being more mechanically complex.

 

It's not exactly as bad as perpetual motion, but there are some hard limits on maximum lift and minimum outer pressure that make it really difficult (barring new materials) aren't likely to be overcome. If they are, they most likely will be "proof of concept" only solutions but still be less efficient than the traditional methods we already use.

[CaptainPanic]

Personally, I am pretty sure that even if a solution could be found for the "vacuum balloon" crushing issues, the end result would be a total apparatus that was less efficient than using light air or gasses, just due to the extra weight involved in trying to engineer a viable solution. The mass of the air being displaced only weighs so much, and naturally the mass of hydrogen/helium/hot air is even less - so any solution that adds more mass than the mass of the classically used lighter-than-air gasses is going to be less efficient despite being more mechanically complex.

You have to consider whether the weight of your apparatus scales linearly with volume, or with surface area of the displacement volume that you want.

If it scales linearly with the surface area of the volume of the "vacuum balloon", then you only have to make it bigger to reach a point where your balloon can lift the apparatus.

[michel123456]

If you try to contain a vacuum, you will have a pressure of ~14psi working to crush your container. (...)

 

That is at sea level.

What would happen if you build a vacuum sphere in outer space and sink it in the atmosphere? Would it float?*

 

Constructing a vacuum sphere at sea level looks like constructing a boat in the abyss.

 

* if it does I'll keep the Copyright.

Edited April 29, 2011 by michel123456

[lemur]

That is at sea level.

What would happen if you build a vacuum sphere in outer space and sink it in the atmosphere? Would it float?*

 

Constructing a vacuum sphere at sea level looks like constructing a boat in the abyss.

 

* if it does I'll keep the Copyright.

That's a good idea to start from space and work down instead of working from sea-level up. Maybe such vehicles could be used to lower payloads slowly into the atmosphere to avoid re-entry friction and then carry some air up on their way back to space.

[insane_alien]

Maybe such vehicles could be used to lower payloads slowly into the atmosphere to avoid re-entry friction

 

the payload would first have to slow down first match speeds with and dock with the balloon. it would also have to go quite deep into the atmosphere. altitude =/= orbit

 

and then carry some air up on their way back to space.

 

which would have to make most of the journey by rocket.

 

the big problem with launches is the velocity not the altitude

[lemur]

the payload would first have to slow down first match speeds with and dock with the balloon. it would also have to go quite deep into the atmosphere. altitude =/= orbit

Could a vacuous sphere "bounce and roll" into the atmosphere without burning up?

 

which would have to make most of the journey by rocket.

 

the big problem with launches is the velocity not the altitude

Isn't the velocity needed dependent on gravity, which is dependent on altitude? Also, what about air pressure/density? Doesn't that make a different in drag?

 

 

[Janus]

That is at sea level.

What would happen if you build a vacuum sphere in outer space and sink it in the atmosphere? Would it float?*

 

Constructing a vacuum sphere at sea level looks like constructing a boat in the abyss.

 

* if it does I'll keep the Copyright.

 

 

The difference is that water is more or less incompressible, while air is compressible. In other words, one cubic ft of water at the bottom of the abyss masses just about the same as 1 cubic ft at the surface. Air is different. Not only does its pressure go down with altitude but so does its density. 1 cubic ft of air weighs less at 100,000 m than it does at sea level. Since the buoyancy of our "balloon" depends on the balloon material weighing less than the volume of air it displaces, as you go to higher and higher altitudes, you have to lower the weight of the balloon to compensate. Thus the thickness( and strength) of the walls of your balloon must also get thinner meaning that they can withstand less and less pressure without collapsing. Edited April 29, 2011 by Janus

[insane_alien]

Could a vacuous sphere "bounce and roll" into the atmosphere without burning up?

 

there would be some plasma formation, this is inevitable.

 

Isn't the velocity needed dependent on gravity, which is dependent on altitude? Also, what about air pressure/density? Doesn't that make a different in drag?

 

yes, but this won't change significantly in the altitudes the balloon is able to operate at. i'd say at a push you could get to maybe 50km max.

 

far below minimum orbital height (due to atmospheric drag) so you'll still need to accelerate any payload to 7.5 km/s

 

yes, there will be lower drag to start out with but not really that much saving compared to the vast velocity you must attain to maintain an orbit.

[SMF]

A hot air balloon is approximately neutral at 100 degrees C and generates maximum lift at 120 C (250 F). This maximum temperature is constrained by the potential melting point of the envelope. I wonder what kind of performance might be gained from heated hydrogen or helium. I realize that there are some major practical considerations, at least for hydrogen, but where between hot air and vacuum would hot hydrogen or helium be, and how hot? SM

[insane_alien]

that has been done for some of the balloon altitude/endurance records.

 

you typically don't want to use it until you get very high up to save on fuel costs.

[SMF]

Insane_alien. Do you know what the typical practical advantage is, what is the temperature of the gas, and how do they heat it? SM

[insane_alien]

well, the practical advantage is a larger volume with no mass addition so the gas is less dense, not a clue what the temperature would be, hotter than the surrounding air which at those altitudes could mean -30*C

 

and they heat it with gas burners.

[SMF]

I understand the principle and was hoping for some more practical information. For example, running a gas burner into an envelope of hydrogen or helium would be adding hot CO2, so probably some sort of heat exchanger would be required. SM