Historical Development of the Windmill - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 29

The third major advance was the invention of the fantail , a device that automatically
carried out the operation of winding or yawing the mill. Before this time, post mills and
the caps of tower mills were turned manually to follow the wind. As the size of windmills
increased, the effort to lift up the tail pole and turn the structure became considerable, so
a winch was added to do the job. The large handwheel of the winch on the Dutch tower
mill shown in Figure 1-12 is seen on the right just above the stage. The invention of the
fantail in 1745 by Edmund Lee allowed the wind itself to do the work.
Lee's device consisted of a small windmill with some half-dozen vanes turning on
a horizontal axis set parallel to the plane of rotation of the main sail assembly. With the
wind blowing squarely on the latter, the fantail was edge on and did no work. When the
wind direction changed and blew at an angle to the main sails, it did the same to the fantail,
which then developed power. Through gearing, the small fantail turned the mill bodily until
the sails were again athwart the wind the fantail action stopped. On the post mill, the fan
was mounted on a frame ixed to the ladder near the ground, but on the tower mill it was
up high on the cap, with a short ladder for access from the cap.
Thus, by the middle of the nineteenth century, these three devices — patent sails,
aerodynamic brakes, and fantail — led to a substantial increase in productivity, as we would
now say. Note too that the risk of ire and accident was correspondingly reduced, because
the sail shutters and brakes permitted faster shutdown and greatly lessened the danger of
ire from the friction brake.
It seems remarkable that these inventions did not spread from England to the rest of
Europe for many decades, and even then they were very sparsely adopted. This seems
particularly true for The Netherlands, which had led so much development in the previous
centuries. The Dutch people have a high reputation in the world of commerce and industry;
their resistance to these control devices might possibly have been based on a judgment that
they were not cost-effective. On the other hand, the Dutch have also produced much great
art and architecture, and they continue to do so. So perhaps their aesthetic sense was
affronted by the replacement of the cloth sail by the wooden shutter and the addition of an
odd-looking contraption perched on the cap, which would have spoiled the clean, sparse
lines of so many of the Dutch tower mills. Although the main emphasis in Stokhuyzen's
excellent small volume on the Dutch windmill [1965] is on history and technology,
there is more than a hint of the aesthetic quality of such mills.
Technical Analysis of Windmills: Stevin, Leeghwater, and Smeaton
Up to this point, this story of the windmill has been one of relating the development
from records that consist largely of pictures, drawings, descriptions, and, from later years,
remaining structures in whole or in part. That is to say, this has been an account based on
empiricism in design and on practice in working. Beginning at the end of the sixteenth
century, however, Simon Stevin and Jan Adriaanzoon Leeghwater 2 made some attempts
to analyze the performance and construction of windmills. These were largely given to the
calculation of loads on the internal components and to the hydraulics of the pumping
process, particularly of the scoop wheel, so important for drainage uses. Around the mid-
dle of the eighteenth century (that is, 150 years later), John Smeaton made a major con-
2 His name is handled in different ways. Some authors simply use Leeghwater; others,
Jan Adriaanzoon. L. E. Harris tells us that Leeghwater was an adopted addition in later life
[1957]. Drees states that the name Leeghwater was given to Adriaanzoon because he
emptied 27 lakes with windmills in his lifetime, and that the name literally means “empty
water” [1977, 1984].