It is possible to identify few geometrical parameters which should modify sensibly the expected performances represented in figure 3. Table 1 collects the main data which lead to a maximal power coefficient for a rotor of Savonius type. The combination of these results should allow to obtain an optimum Savonius rotor.
In order to verify these hypothesis, a prototype of such a rotor was realized. One can notice that if a double-stepped rotor (each step being staggered from the other with a 90° angle) ensures a sufficient stability of the mechanical torque (figure 4), a higher number of steps is not necessary and should uselessly loads the rotor and raise its inertia. In the same way, a higher number of paddles than 2 no longer raises the efficiency of the rotor, and decreases it in most cases.