The Bolkow Bo.46, three experimental prototypes of which were built for the German Ministry of Defense, served as a flying test-bed for the Derschmidt semi-rigid rotor. The first model, built jointly with SIAT, began test flights in January 1964. The Derschmidt rotor underwent a long series of wind tunnel tests, for each blade had a hinge about half-way along its radius, enabling the outer section of the blade to rotate 40° backwards or forwards in relation to the inner section connected to the hub. This enabled the movement of the advancing blade to be "delayed," thereby considerably reducing the tip speed. Conversely, by "accelerating" the movement of the outer portions, quite high rotational speeds could be achieved. However the complexity of this system prevented the Bo.46 from passing the experimental stage.