"Based on experimental data an empirical formula was produced for

calculating the axial drag coefficient at an angle of attach $\alpha$

from the zero-angle drag coefficient. The scaling function is a

two-part polynomial function that starts from 1 at $\alpha=0^\circ$,

increases to 1.3 at $\alpha=17^\circ$ and then decreases to zero at

$\alpha=90^\circ$; the derivative is also zero at these points."

I can't seem to find the function or the paper it's referencing. Does anyone have any ideas?