Aetherist: "My ELECTON ELECTICITY will not necessarily change any present model (alltho i notice that transmission line design models presently wrongly dont account for whether a transmission line etc is insulated)(underground transmission lines are insulated)(but if there is even a microscopic air gap in some parts between plastic & Cu then its much the same as being non-insulated in air)."
Have you ever seen RG-62/U coaxial cable? The original type, with a hollow tube inside the shield braid and the center conductor spaced coaxially inside the tube with an air gap?
https://www.teslacables.com/media/documents/en/rg-62-a-u-coaxial-cable-93-ohm.pdf
(Note: in recent use, this is often superseded with a foam-dielectric insulation to achieve the same characteristic impedance.)
I suppose that the speed of electricity, or i should say the speed of ELECTICITY, in coax depends on the plastic or air touching the surfaces of the metals on the inside, plus on the outside (of the braid).
Foam would be complicated – it has air – but the main thing is whether air touches any of the surfaces (the speed of light in air is faster than in plastic).
Coaxial cable with air, solid, half-air, or foam insulation is a
mature technology, roughly a century old.
Heaviside came up with the clever notion of adding series inductances spaced along telegraph wires, and the American Telephone and Telegraph Co. exploited this invention while the British telegraph authorities ignored it, and this led to coaxial-cable transmission lines, patented by AT&T in 1931
https://www.wired.com/2009/12/1208coaxial-cable-patent/In fact, at frequencies low enough that the diameter of the coaxial cable is much, much less than the wavelength, the speed of propagation along the cable depends
only on the effective dielectric constant of the insulation (assuming no magnetic material or helical center conductor). That effective constant can be calculated by comparing the measured capacitance to the coaxial dimensions (inner and outer diameters).
This falls out from the mathematics of the inductance and capacitance per unit length of concentric cylinders. Introducing dielectric (solid or layers) into the region between center conductor and coaxial outer conductor increases the capacitance in an easily-calculatable manner. That, and the geometry allows the interested student to calculate the velocity
v = (
L' x
C')
-1/2, where
L' and
C' are the inductance and capacitance per unit length (choosing the unit length gives the length in the resulting velocity: feet, meters, etc.).
It does not matter at all whether there be a metal-to-air surface interface internally to the cable for this velocity to be accurately true, as is found everywhere in RF technology.
In the original RG-62/U, there is an annular layer of air outside the center conductor, and an annular layer of solid plastic between that and the coaxial shield. As can be computed by elementary electrostatics, that decreases the capacitance between center and shield (compared with the same dimensions and solid plastic), which increases the propagation speed. One could achieve the same result by an appropriate layer of air between two plastic layers, each contacting the closer metal layer.
For more complete algebra, see any of many engineering textbooks.