Report KD 439, in which the pendulum safety system with a torsion spring is described, has been reviewed. The chapter in which the moment equations are derived for a steel rotor with blades with a 7.14 % cambered airfoil, is cancelled because such a rotor will be too heavy. A new chapter 6 has been added in which the use of the VIRYA-5.2 rotor and generator is investigated.