Report KD 551 has been extended by a chapter 6 in which the aerodynamic characteristics of rectangular flat plates with aspect ratios of 2 : 1 and 1 : 2 are corrected for wind tunnel blockage. Report KD 485 has been extended by a chapter 4 in which the effect of using an auxiliary vane with an aspect ratio of 2 : 1 in stead of an eccentrically placed rotor is researched.