Function File: [ac, pn, ref] = loadwing (filename)

Loads the basic wing geometry from file filename. The geometry should be described in the file as follows:

     mchord <reference mean aerodynamic chord>
     area <reference wing area>
     mcenter <reference mean aerodynamic center>
     
     centers
     <z1>  <x1>  <y1>  <c1>  <tw1>
                  :
     <zN>  <xN>  <yN>  <cN>  <twN>
     
     polars
     <polar file name 1>
     <polar file name 2>
     

xK, yK, zK are coordinates of the K-th point on the mean center line, cK is the corresponding chord length and twK the twist.