Test

$f\left({\frac {a}{W}}\right)={\frac {2+{\frac {a}{W}}}{\left(1-{\frac {a}{W}}\right)^{\frac {3}{2}}}}\cdot \left(0,76+4,8\left({\frac {a}{W}}\right)-11,58\left({\frac {a}{W}}\right)^{2}+12,43\left({\frac {a}{W}}\right)^{3}-4,08\left({\frac {a}{W}}\right)^{4}\right)$