Sorry if this is the wrong place to post this as it is probably more of an engineering question.

I'm trying to derive the extension of a cylindrical coiled spring in terms of E (YOUNG's modulus, K(bulk modulus), No of turns per metre, spring diameter, (D), spring length (l), wire diameter (d).

Torsional deflection is important but I'm at a loss to how it could be extended to 3-D.

Anyone knows, the derivation or could point me in the right direction - Thanks.