tension member in this exemplary embodiment only one biasing means 10 is shown the angled broad end of the biasing means 10 serving as its base is disposed in an opening 20 in the body of the fan blade 6 2 the other end of the spoke shaped biasing means 10 is held in an abutment 12 secured to the fan blade 6 2 by means of a nut 14 adjacent to the abutment 12 there is shown an adjustment means 13 which may for example be a nipple by means of which the tension of the spoke shaped biasing means 10 can be changed in this embodiment an adjustment means 13 is installed only on one side of the fan segment 6 a tightening of the adjustment means 13 causes movement of the fan blade end 9 parallel to the axis of rotation and towards the blade side to which the biasing means 10 is mounted a loosening of the adjustment means 13 causes movement away from the blade side to which the biasing means 10 is mounted by utilizing the inherent tension of the fan blade material by way of such loosening or tightening the tip of each fan blade may be trued with precision to its appropriate position in coordination with the alignment device on frame 1 as shown in fig1 the distance of each fan blade end 9 from the opening 3 of the alignment device can be set accurately by.