My balloon technology (the LDH honeycomb)

Ok so I don't know how to post a new thread so I'll post my question here:

So I have been developing this balloon technology (the LDH honeycomb) and I've since made changes to it:
First, instead of making compressive structures out of rigid LDH honeycomb, I've decided to use tensegrity structures, out of pressurized liquid sacs, or silicon fluid sac. Silicon fluid won't boil in near vacuum, so it should deform in near vacuum pressures.
This is quite different, as it uses an inflated double skin design. It's shape depends on the way the tethers connect. See the vacuum balloon Memon from ideasbank for a better understanding of this(keep in mind, I'm not making a vacuum).

With that said, the question here is: Is liquid truly incompressible? Can water weigh less than air for the same amount of pressure, if it's tightened enough? And would a vacuum balloon filled with silicon fluid stay in shape without tethered connections? And of course, tell me how I can figure these things out please or show your work.
Again, I don't want to create a vacuum, I just want to know if it will stay in shape under vacuum pressure loads.

PS, I know none of you know how this is relevant because you didn't read the full question. BTW, I don't believe in airships anymore, as I don't believe in using balloons for long distance travel. I instead believe that aerostats should be built into existing vehicles, which will inflate or deflate when the vehicle needs to float or lift itself a short distance. How the vehicle will propel itself or control direction, I haven't figured out yet.

[Moderator's note: spin-off from another thread]

KingoftheChaosEmpire said:

With that said, the question here is: Is liquid truly incompressible?

No. There is some compression. How does that inform your designs though?

KingoftheChaosEmpire said:

Can water weigh less than air for the same amount of pressure, if it's tightened enough?

What??

KingoftheChaosEmpire said:

And would a vacuum balloon filled with silicon fluid stay in shape without tethered connections?

How could it be filled with both vacuum and fluid simultaneously? Is this the double wall design you're talking about? It won't stay rigid, no.

KingoftheChaosEmpire said:

Again, I don't want to create a vacuum, I just want to know if it will stay in shape under vacuum pressure loads.

Just because a fluid won't compress doesn't mean it won't happily change shape under load.

KingoftheChaosEmpire said:

First, instead of making compressive structures out of rigid LDH honeycomb, I've decided to use tensegrity structures, out of pressurized liquid sacs, or silicon fluid sac.

I see where you are going, and the problem you will have.

To counter the low internal pressure, you will use a positive gas pressure in compression parts of the structure. You are going to find that the pressure needed in the structural gas, will result in a density increase in the structural gas, that elegantly cancels the advantage of a low internal pressure balloon.

If you replace the structural compressed gas with a silicone oil, the structure will weigh more than the pressurized gas solution. There is no such thing as a free lunch.

Baluncore said:

I see where you are going, and the problem you will have.

To counter the low internal pressure, you will use a positive gas pressure in compression parts of the structure. You are going to find that the pressure needed in the structural gas, will result in a density increase in the structural gas, that elegantly cancels the advantage of a low internal pressure balloon.

If you replace the structural compressed gas with a silicone oil, the structure will weigh more than the pressurized gas solution. There is no such thing as a free lunch.

Where is the post that you answered this similar question before on? If none, I venerate you, your ability to understand things on such a deep level is a rare talent and a skill sorely desired these decades. Are you a counselor? Anyway, seeing that silicon fluid doesn't work, I guess it would be a waste of time asking about any else liquid but it's worth a try. So I have a couple new questions:
Would air heated to 100°C(or boiling point of water) be less dense than water vapor?

Does anyone know the bond strength of PG5? Does it cost a lot to make a macro structure out of? What state of matter is it at room temperature? Maybe if these can be inserted in during the vacuum process it'll have the strength to resist the vacuum and not be crushed.

And going along with my balloon structure idea, would there be any disadvantages of say a table made of tight silicon fluid filled sacs vs a steel table? I know air is fickle so I want to stick with something that doesn't change much to temperature. The skin would have to be thickened though so it's not easily busted due to impact. Damage to the sac table would be much more destructive but at the same time it would be much easier to repair. Just patch and refill. What do you think?
Sorry I'm on mobile so it's hard for me to make replies quick as you all do.

KingoftheChaosEmpire said:

Sorry I'm on mobile so it's hard for me to make replies quick as you all do.

Your BB-code quotes seem to have become confusingly nested. If you click on the [] "toggle BB codes" button in the reply or an edit window, you might be able to untangle them.

This is not a competition or race. It has taken us quite some time to understand the system. If you do not understand, (or you think we are wrong), ask one clear question at the time, and we will do our best to explain. The quality of our answers will depend on the quality of your questions.

Imagine you had a fabric cylinder or tube containing compressed gas. The force, pushing the ends apart, would provide some structural compressive strength. Now, if you halve the cross-sectional area of the tube, you will need twice the internal pressure to provide the same force between the now half-area ends. Twice the pressure will double the gas density, so the mass of gas will remain constant. The advantage of a small tube is that it can have less wall material, so it will have less mass, but that brings on another problem.

A structural tube, subjected to an internal pressure, will need a wall that is strong enough not to split length-ways due to "hoop stress". Using a thinner tube with higher pressure will have less tube material mass, so will be lighter than a thick tube, but the thinner tube will buckle due to "column stability" failure, before there is any structural advantage gained. If you shape the tube like a spindle to avoid buckling, the volume of high pressure gas would increase, so the structure would weigh more again. You might neck the tube at each end, so it had a greater end contact area, but then the middle portion would need to be a spindle or sphere, containing compressed gas to maintain rigidity. You end up with a heavier-than-air strut opposing your lighter-than-air balloon. At best, it all cancels out.

KingoftheChaosEmpire said:

Would air heated to 100°C(or boiling point of water) be less dense than water vapor?

At what different pressures and temperatures ?
The number of moles of gas in a volume, is decided by temperature and pressure. The weight of the volume is therefore also proportional to the molecular weight of the gas molecules contained.
Air is a mixture, so we must weight average, (≈ 80% nitrogen + 20% oxygen).
M'wt (nitrogen = 14); N₂ gas = 28 g/mole;
Mwt (oxygen = 16); O₂ gas = 32 g/mole;
M'wt average of air ≈ (28*0.8 + 32*0.2) ≈ 28.8 g/mole.
M'wt of water, H₂O = 1+1+16 = 18 g/mole;
Water(gas) 18, is significantly lighter than air 28.8, so steam is a lighter-than-air lifting gas, (so long as you can keep it from condensing). Steam also has the thermal lift advantage of a hot air balloon.
That also explains the two reasons why, without ventilation, the ceiling in a bathroom or kitchen is wet.

KingoftheChaosEmpire said:

Does anyone know the bond strength of PG5? Does it cost a lot to make a macro structure out of? What state of matter is it at room temperature?

Bulk PG5 would form jelly-like soft lumps in water at room temperature. Those lumps would be held together by the water. The bond strength between PG5 molecules would be low. If you heat PG5, or subject it to UV light, it will break down into smaller molecules. If you dry it out, it will become brittle and fragile.

PG5 is more like an open spherical sponge than a strong chain. There are many structural polymers that have a far greater tensile or compressive strength than bulk PG5. PG5 is slow and difficult to make, so it is only a candidate for use in molecular transport of smaller active molecules in water, or in the bloodstream.

Baluncore said:

If you replace the structural compressed gas with a silicone oil, the structure will weigh more than the pressurized gas solution.

Helium gives you 85% of the lift you are ever going to get. That's the key - anything that you add to reduce the weighty of your lifting gas also adds weight. To win, any solid or liquid you add needs to support thousands of times its own weight in gas. (Either keeping it in or keeping it out) And that's hard.