History of Danish Wind Power - Wind Power for the World: The Rise of Modern Wind Energy - page 65

From August 1974 until November 1976, there was an intensive
correspondence between the NASA team and Claudi Westh. The
design of NASA's 100 kW “Mod-0” was in many ways inspired
by German Ulrich Hütter's 100 kW turbine from 1957 and had
a 2-blade downwind rotor. Claudi Westh tried in vain to convince
Divone and Savino that the Danish 3-blade upwind solution
should be preferred in order to avoid vibration problems due to the
blades passing behind the tower [18]. He referred to the experience
with these problems on the Aeromotors in spite of its less critical
upwind solution.

Jean Fischer's model of a Darrieus-type wind turbine with six
rotors and a concrete tower on the cover of “Science” in July
1975.

Figure 3.27

The discussion on the best choice of configuration continued
across the Atlantic during 1977, when NASA had experienced
heavy vibrations and blade stresses during the first tests of “Mod 0”
[18]. The vibration problems also stopped discussions about using
FLS-type concrete towers on future US downwind turbines.
Nevertheless, for the next NASA turbine, the 2 MW “Mod 1”, the