Principle
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 or hydrogen. 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.
Read more about this topic: Vacuum Airship
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—Oscar Wilde (1854–1900)
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—Walter Lippmann (1889–1974)
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—Ezra Pound (1885–1972)