inductance for spiral air core..


                <-Radius->
          ___________
         / __________ \
        / / ________ \ \
     __/ / / ______ \ \ \
        / / /      \ \ | |
     ___|-|-|-     | | | | Number
        | | | \____| | | |
         \ \ \______/ / /
          \ \________/ /
           \__________/

                    <---> Width

L_uH =  (Number*Radius_in)^2/(8*Radius_in +11*Height_in);