The Aerodynamic Research on Windmill Sails of Poul la Cour, 1896–1900 - Wind Power for the World: The Rise of Modern Wind Energy - page 98

of course he had no need for the interior machinery used for flour
production.

Figure 4.4 La Cour's windmill in Askov.

Instead he built a slim wooden tower, sufficient to carry the
turbine and a vertical spindle down to the DC dynamo in the building.
To begin with it was used with canvas sails, but very soon these were
changed to wooden shutters, which were a well-known technology.
But la Cour is known for the improvement of the automatic regulating
system of the shutters.

Figure 4.5 Details of the sails.