High Pressure kite by Bruno Legaignoux

[tilmann]

could be interesting to make an experiment: If you reduce the diameter of a hose from 12 to 8 cm. How much PSI do you need to get the same amount of stiffness ?

[nixmatters]

could be interesting to make an experiment: If you reduce the diameter of a hose from 12 to 8 cm. How much PSI do you need to get the same amount of stiffness ?

Some food for thought here (files size over max limit):

Air-Inflated Fabric Structures, Naval Undersea Warfare Center Division, Newport, Rhode Island, 2006
https://apps.dtic.mil/sti/citations/ADA458590

Technology and Mechanics Overview of Air-Inflated Fabric Structures, Naval Undersea Warfare Center Division, Newport, Rhode Island, 2006
https://apps.dtic.mil/sti/citations/ADA462232

The second paper seems to be a shorter version of the first one

P.S. above links have been updated

[grigorib]

moment of inertia of object cut shape defines rigidity

mmmh, can you explain this ?

Some basic definition is here https://en.m.wikipedia.org/wiki/Flexural_rigidity

But in basic words - if you make a perpendicular cut of an object and calculate moment of inertia of shape you get then the higher the number will be the more rigidity it will have for the same area of the cut.
So if you imagine an I-beam and a rod with identical area of the perpendicular cut the I-beam will be much more rigid for bending and twisting but of course will have identical lengthwise pull strength.
In this case the strut is a thin wall object, there are special approaches for those, but overall same result - a tiny pipe inflated to huge pressure will be easy to bend compared to larger tube inflated proportionally to diameter change (same force on the walls)

[kitexpert]

Bigger diameter structure (tube) has a benefit for rigidity for two reasons: 1) material of it is further from where forces affect 2) there is more material there (larger diameter=larger circumference=larger area).

So if beam diameter is reduced from 12cm to 8cm (33%) there will be about 70% loss of rigidity (for same weight). Perhaps increasing pressure 3x as high would give about original rigidity. If strut is too thin it is almost impossible to get similar rigidity by adding pressure.

[nixmatters]

fully agree with kitexpert that decreasing diameter and (dramatically) increasing pressure will only work to a point.
Then flying with scuba tanks and having 100psi explosions at a busy beach won't help much our sport grow.

Someone mentioned dropstitch above. I wonder if this could be an option, especially with 3D dropstitch that is already available, but for much larger inflatable structures. Here is an example I spotted at a trade fair earlier this year:

[grigorib]

All that said, a proper support bridle might compensate for loss of rigidity so it’d be nice to see something new evolve be it more or less practical eventually

[faklord]

For what it’s worth, by my calculations, the ‘rigidity’ will be a function of: Pressure * radius (or diameter) cubed.
Thus an 8cm tube will require 3.375 * the pressure of a 12cm tube. (12cubed/8cubed).

[tomtom]

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

[Lokihel]

fully agree with kitexpert that decreasing diameter and (dramatically) increasing pressure will only work to a point.
Then flying with scuba tanks and having 100psi explosions at a busy beach won't help much our sport grow.

Someone mentioned dropstitch above. I wonder if this could be an option, especially with 3D dropstitch that is already available, but for much larger inflatable structures. Here is an example I spotted at a trade fair earlier this year:

The dropstitch is what we have in inflatable SUP's.
It goes against the original intent of the high pressure industrial tubing to keep the costs low.

[GregK]

Thank you mixmatters for the links to the papers on Air Inflated Fabric Structures.

They do an excellent job of explaining how a pressurized fabric tube works, very enlightening.