From Herborg Blacksmith to Vestas - Wind Power for the World: The Rise of Modern Wind Energy - page 268

9.1 Theory Is Not Enough

In early 1977 we visited Tvind several times. And there I found
various literature on wind power. The most inspiring topic
was

1

Sol og vind by Claus Nybroe and Carl Herforth, a classic

manifestation of grassroots energy and still worth reading

because of the technology as well as the gusto.
The theoretical aspect of the wind turbine technology appealed
to me from the very beginning. My mathematics-physics A level
made subjects such as aerodynamics, electric technology and
calculations of loads accessible at a simple level; these issues
were challenging, at the same time by being about something to
be used here and now, of a suitable complexity, but not sufficiently
difficult to discourage me.
Of course, theory is not enough, and we soon carried out some
practical exercises. The first experiments were about making
a 2-bladed rotor out of a thick piece of laminated wood. The
diameter was just over a metre, the width of the blades about
10 cm, and we used a bit of 3/8-inch water pipe as shaft. We ran
the rotor simply by holding the shaft with our hands, using our
palms as the

, and the hand in front served as a thrust
bearing. After a bit of fine honing and balancing the little rotor ran
quite well, and it turned out to have many of the characteristics
that we came later to know in real wind turbines.
When the rotor was set moving by means of a brisk grasp
around the shaft it began to accelerate slowly until it reached a
certain speed—then it began to accelerate madly, running like
blazes, making sounds like a helicopter in strong wind. It was a
great experience to feel so directly how the rotor's behaviours
changed radically as soon as it gained speed. The wind pressure
rose dramatically, and we felt distinctly how the rotor reacted
to all small turbulence eddies. To stop the rotor at low wind, we
just pressed the shaft harder and braked it. But this did not work
with strong winds, as the momentum was too high, and then we
had to yaw by turning the rotor so that the shaft was 90 degrees
out of the wind.
Even at moderate winds the small rotor ran so fast that it
was impossible to follow the blades with your eyes, and at stronger
1

bearing

Herforth, C., Nybroe, C. (1976) Sol og Vind (Sun and Wind), Informations Forlag,

Copenhagen.