Dear Friends
I am afraid that I must correct the source for the second illustration of the Herkules wind turbine in my previous comment:
The illustration is taken from:
"Windkraft gestern und heute - Geschichte der Windenergienutzung in Baden-Wurttemberg" by Karl Handschuh - Germany 1991
And not from the book by Matthias Heymann as previously mentioned.
Greetings - JF