Thanks Doug. I am not a specialist in wind energy. I only try to deduce the divergences and convergences in the evaluation methods of current wind turbines and AWES. For now it is difficult to me to reply to your questions. However I think we should distinguish the load from the generator and the aerodynamic drag. Peter Jamieson clearly explains the secondary rotor concept in his book page 128. Otherwise it has to do with Induction factor. The secondary rotors lead to an additional aerodynamic drag in the whole system compared to a wind turbine. But for a flygen AWES (and also for a wind turbine as Peter Jamieson indicates) it can be a solution as the device scales.
By changing the pitch? By changing the trajectory? By changing the orientation of the secondary rotors?
I think the small generator inboard (per each turbine) produces the load. But it is not enough to prevent overspeed.
I am not sure, because 4/27 can be a huge value for an AWES. Makani wing could reach the theoretical 16/27 (slightly less because of the secondary rotors) but it should be far below 4/27 because it harnesses a tiny part of the annulus and nothing inside. In the other hand if reaching Betz limit (16/27) becomes possible within a huge area, that could make a difference. AWES undergo their own weight in addition to efficiency requirement. The space use is another major requirement (imho). However Loyd’s analysis takes into account of the wing area, not the swept area, and states an equivalent efficiency for both drag and lift devices, which does not contradict the 16/27 and 4/27 mentioned above.