Historical Development of the Windmill - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 8

About A.D. 1300, we have the report of al-Dimashq¯ (A.D. 1256-1326), a Syrian
cosmographer who provided a detailed description and a drawing, shown as Figure 1-2.
The two-storied, walled structure had millstones at the top and a rotor at the bottom, the
latter consisting of a spoked reel with 6 to 12 upright ribs, each covered with cloth to form
separate sails like longitudinal ins on a heat-exchanger tube. The sketch shows the bellying
of the cloth coverings as they catch the wind and push the reel around. Each wall had an
offset opening the height of the rotor, with its perimeter beveled to decrease the free area
through the thickness of the wall and hence accelerate the wind from any direction.
The Windmills of Neh
Windmills of this basic type were still in use in S¯st¯n in 1963, when Wulff saw 50 of
them operating in the town of Neh; they might still be used today. They throw much light
on what al-Dimashq¯ saw, so we will skip a few centuries in this generally chronological
presentation and condense Wulff 's description of the mills in Neh.
The construction is shown in Figure l-3(a). The rotor is about 5.5 m high and 4.3 m
in diameter, enclosed in side walls about 6.5 m high and a half-wall that leaves a 2.2-m-
wide opening facing north, the main wind direction. The central wooden shaft is about 43
cm in diameter. Its bottom end, which extends downward into the mill room, contains a
Figure 1-2. A Persian vertical-axis windmill in S¯st¯n, according to al-Dimashq¯, c.
A.D. 1300 [Wulff 1966]. The earliest windmill design on record. Grinding stones are
above the rotor with its bellying cloth sails. The walls have openings to let the wind in and
out. (Reprinted by permission of MIT Press; ©1966, MIT Press)