The 1/3 speed reduction is well known. I already used these small propellers in different conditions, by car with a good efficiency in spite of they are propellers, or to power the leds of a FlygenKite by night, or on tips of a bar I rotated.The small propellers are fixed to a motor with a shaft adapter.
I think the problem I just related comes from the physics, not the propellers as such since they worked in other and different arrangements comprising the FlygenKite module. These propellers were oversized (0.23 m diameter) compared to the main propeller (0.57 m diameter) in such a way (less than 1/3 instead of the usual 1/10) that they cannot produce anything, being not able to take the front wind.
Sure, but they were not available in small dimensions with their suitable generators at the time of the tests. So I used propellers with DC motors for model planes, as wind turbines. It may be unorthodox but it worked pretty well (see measurements).
Yes, but I think that here the physical problem (too large secondary rotors) prevails. I also believe that the propellers at the end of the main rotor destroy the aerodynamics of said main rotor if it is not designed to carry them.
I tried with smaller secondary rotors (0.15 and 0.18 m, see below) for the same primary rotor (0.57 m) and it was not better. Unless the design is specially studied, the secondary rotors destroy the aerodynamic of the primary rotor where the tips of blades were more efficient.
