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Technology, Travel

Null Ship: a Vacuum Airship Lifts With No Hydrogen or Helium

It is strange but true that “nothing” floats. That is, a vacuum is lighter than air. If you had a material strong enough, you could create a closed shape with it and pump all of the air out of it, creating a lifting body for transportation that would be even lighter than gas filled blimps. We aren’t there yet, but the idea of a null ship is still very interesting.

A vacuum airship, also known as a vacuum balloon, is a hypothetical airship that is evacuated rather than filled with a lighter than air gas such as hydrogen or helium. First proposed by Italian monk Francesco Lana de Terzi in 1670,[1] the vacuum balloon would be the ultimate expression of displacement lift power. …

An airship operates on the principle of buoyancy where air is the fluid in contrast to a ship where water is the fluid. The density of air at standard temperature and pressure is 1.28 g/L and 1 L of displaced air has sufficient buoyant force to lift 1.28 g. Airships use an airbag to displace a large volume of air; the bag is usually filled with a lightweight gas such as helium. The total lift generated by an airship is equal to the weight of the air it displaces, regardless of the materials used in its construction or the gas used to fill the airbag; However for flight it is necessary for the total lift capacity to exceed the ship’s weight, which includes the weight of the gas used to fill the airbag

Using the molar volume, the mass of 1 L of helium (at 1 atmospheres of pressure) is found to be 0.18 g, since every displaced liter provides 1.28 g of lift the effective lift is reduced by 14%.

Vacuum airships would theoretically replace the helium gas with a near-vacuum environment and would theoretically be able to provide the full lift potential of displaced air. The main problem with the concept of vacuum airships however is that with a near-vacuum inside the airbag, the outside pressure would exert enormous forces on the airbag and causing it to collapse if not supported. Though it is possible to reinforce the airbag with an internal structure, it is theorized that any structure strong enough to withstand the forces would invariably weigh the vacuum airship down and exceed the total lift capacity of the airship, preventing flight …
via Vacuum airship – Wikipedia, the free encyclopedia.

Since we can’t make hydrogen non-flammable there is the idea of building a hull that is super light and strong to support a vacuum inside it.

If 1 L of displaced air can lift 1.28 g, my hull will need to contain 708,738 liters of vacuum in order to lift 1 ton (2,000 lbs).

What is the best shape?

Years of submarine design experience gives what seems to be the best answer: A sphere (or tubes with spheres on the end). Pressure hits from all sides so a sphere is the strongest structure against air pressure.

What material?

Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength and elastic modulus respectively. This strength results from the covalent sp2 bonds formed between the individual carbon atoms. In 2000, a multi-walled carbon nanotube was tested to have a tensile strength of 63 gigapascals (GPa).[37] (For illustration, this translates into the ability to endure tension of a weight equivalent to 6422 kg (14,158 lbs) on a cable with cross-section of 1Âmm2.) Further studies, such as one conducted in 2008, revealed that individual CNT shells have strengths of up to ~100 GPa, which is in agreement with quantum/atomistic models.

Under excessive tensile strain, the tubes will undergo plastic deformation, which means the deformation is permanent. This deformation begins at strains of approximately 5% and can increase the maximum strain the tubes undergo before fracture by releasing strain energy.

Although the strength of individual CNT shells is extremely high, weak shear interactions between adjacent shells and tubes leads to significant reductions in the effective strength of multi-walled carbon nanotubes and carbon nanotube bundles down to only a few GP’s.[40] This limitation has been recently addressed by applying high-energy electron irradiation, which crosslinks inner shells and tubes, and effectively increases the strength of these materials to ~60 GPa for multi-walled carbon nanotubes[38] and ~17 GPa for double-walled carbon nanotube bundles.[40]

CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling when placed under compressive, torsional, or bending stress.[41]

via Wikipedia

There are different kinds of strengths of materials. What we want is something that is both strong and rigid. Can CNTs be made into a rigid hollow sphere? Has anyone done this?

One paper I read used Liquified Petroleum Gas (LPG) to provide a cheap carbon source for large scale production of carbon nanotube arrays on a sphere surface. The spheres made were only 1100 to 1200 micro meters, however.


About Xeno

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