Flat spiral vs Solenoid Wire Length/Inductance Observations

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Original poster: "Jolyon Vater Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>


Is it not true that the inductance and length of wire in a flat spiral can be
deduced by considering it a solenoid with same average diameter/number of turns
as the flat spiral? 

In the course of winding my spiderweb TC primary I used formula wl =2*pi*r*n to
calculate the total wire needed to complete the winding where wl is the average
radius of the spiral, r the average radius and n the number of turns; 

And if the wire needed for flat spiral with maximum Q ie. with width to radius
ratio of 8:11 were calculated with the method above would this be the same as a
solenoid with maximum Q i.e. height to radius ratio of 9:10?

The wire on my spiderweb primary is wound spirally on a flat board of minimal
thickness -is there any reason why the inductance should not be equal to L=
r^2*n^2/[8*r+11*w] -the same as for a flat spiral?