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the ratio between the length and width of the sails compared to
the space between them. However, it was not until 1919 that a
new formula was presented by Albert Betz. He showed that the
power of a mill depends on the proportion of the circle area
covered by the rotor—not the frontal area of the sails. Betz also
calculated that the theoretical and practical limit would be 59%
of the wind power available.
The contribution of Poul la Cour was an important step on
the road to understand the force of vacuum lift on mill sails. This
force was discovered on windmill sails 5-6 years before the
Wright brothers started flying, although it is the same force that
keeps an aeroplane in the air. As far as we know, the “mussel”
diagram was constructed by Poul la Cour and thereby introduced
the new concept of the tip velocity ratio, which is commonly used
in descriptions of modern wind turbines.
Poul la Cour died from a lung infection on 24 April 1908. His
contribution to knowledge in many fields was outstanding. He
covered every step from fundamental theoretical to practical
research, making inventions and implementing his ideas for the
good of society. In addition he was the author of several textbooks
such as
. Besides
being a scientist, he was also a very religious man and felt no
contradiction in that. His epitaph, carved in a memorial stone a
few kilometres south of Askov, expresses that:
Historical Mathematics
and
Historical Physics
As Light from Heaven gives Light to our Eye.
Thoughts are inspired by Light from on High
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