tomtom wrote: ↑
Wed Nov 28, 2018 12:19 am
It cannot be so simple
Rigidity is thickness cubed ,skin modul linear and then long long nothing and them core properties. Pressure is infact core
Just had a look at one of the links nixmatters posted:
Air-Inflated Fabric Structures, Naval Undersea Warfare Center Division, Newport, Rhode Island, 2006
It seems page 7 concurs with my suggestion that rigidity is a simple function of Pressure * Radius cubed.
BUT this got me thinking.... and much more interesting is it seems that smaller diameter, higher pressure air-beams are actually heavier for the same rigidity.
Calculations taking into account:
1) Smaller diameter = smaller volume (square law) but increased pressure gives increased air mass (cube law): overall air mass is greater.
2) Smaller diameter = smaller surface area so less Dacron (linear relationship) but increased pressure results in more stress in Dacron, even though the diameter is reduced, so Dacron (or whatever) needs to be thicker: overall material mass is increased.
Rather surprisingly the overall outcome of this is, for same rigidity and material stress, the overall mass ratio is the simple ratio of the diameters.
ie an 8cm tube will be 1.5 times heavier than a 12cm tube.