In the winter of 2012 I have given a wind energy course in the district Woensel-West of the Dutch town Eindhoven to seven people. This course was meant to transfer the basic knowledge of windmill rotors, safety systems, generators and electronics of small windmills because people of the group have the intention to build their own windmill. The first three course evenings were spent on rotor design and matching. Report KD 35 (ref. 1) was used for this course part.