F.X Wortmann airfoil naming convention
FX stands for Franz Xaver, Professor Wortmann's given names.

The next two digits stand for the year this airfoil has been designed. Add '19' in front and you have the full year.

Then may follow one or two optional letters which specify a dedicated use, but they can be missing for general purpose airfoils. For example, the 'L' in FX 71-L-150/30 stands for "Leitwerk" which in German is the name for the combination of the horizontal and vertical tail surfaces.

The next three digits denote the relative thickness times one thousand. So the "150" in FX 71-L-150/30 tells us that this airfoil is 15% thick.

The last digits are again optional and denote the relative flap chord in cases of control surfaces, this times in percent. The FX 71-L-150/30 is optimized for a 30% chord control surface.

Reference: Stuttgarter Profilkatalog ISBN 3-528-08464-2, 1981.