Report KD 333: “The Gö 711 airfoil modified as the Gö 711-12% and the Gö 711-10% airfoil —– is reviewed. The Gö 795, the Gö 796 and the Gö 797 airfoils are used for the modification procedure.The airfoil characteristics of these three airfoils were already given but a new table 2 is added which gives also the geometry of these three airfoils.

A new chapter 8 has been added to report KD 409: “Development of an ecliptic safety system with a torsion spring”. In chapter 8 an alternative is described for which the spring moment is constant. This results in lower maximum values for the rotational speed, the thrust, the torque and the power than for the original option for which the spring moment increases by a factor 1.5 at the maximum angle of rotation of the vane arm. I think that a constant or only little increase of the spring moment gives the best result but to realise this might be technically more difficult.

Report KD 409 describes the ecliptic safety system with a torsion spring. The spring stiffness has been reduced such that the spring moment for 100 degrees rotation of the vane arm is now a factor 1.5 higher and not a factor 2 higher than at the beginning position. The rated wind speed is increased from 7 m/s up to 8 m/s. These modifications make that the delta-V curve is lying closer to the ideal curve.