Introduction to Aerospace Structures and Materials: Monocoque Structures

[@HowtosayaBadEnglish-ms4fg]

Good explanation

[@kentgladden4316]

The water in the sandwich structure can be eliminated by shaping & kiln-drying the sandwich matrix before being bonded to the surface material. Then place in a vacuum chamber (pressurized to 1,140 torr of Helium), where it is pressure-sealed, & dried again. Then, it has the surface material bonded to it. The sandwich material is now filled w/ millions of lighter-than-air pockets, that are pressurized to 1.5 atmospheres (at 14.7 psi/atmosphere). Sea-level atmospheric Air has a molecular weight =29. Helium = 4.02. So... 4.02 (x 1.5 atmospheres) = 6.03. Which is almost 5x lighter than Air. Helium is also inert & abundant. Making it an excellent choice for producing metal foams weighing a fraction of solid metals. Protected against internal degradation & pressure-reinforced by inert Helium.

[@appa609]

the mass of the air in most sandwich panels is an insignificant fraction of the total. Helium as a lightweughting measure is silly.