Historical Development of the Windmill - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 9

Figure 1-3. An existing windmill of the Persian type in Neh. (a) The millstones are now
below the rotor and the sails are bundles of reeds [Wulff 1966]. (b) a general view of the
downwind (south) wall of the mill. (c) Close-up view of the reed sails. (Reprinted by
permission of MIT Press; ©1966, MIT Press)
steel thrust pin that rests on a wooden thrust block in a cavity lined with a tallow-soaked
lubrication pad of many layers of cloth. The upper millstone is attached to this steel pin,
and the lower stone rests on a brick structure. These stones are about 2 m in diameter.
The rotor shaft supports ive tiers of spokes, with eight spokes in each tier. Each sail
is composed of several long bundles of reeds pressed against the end of the spokes by tie
bars and is about 56 cm wide and 15 cm thick. The tie bars are secured to the spokes by
pegs and ropes, and there are several sets of stay ropes to tie the whole rotor assembly
together. The system is certainly elastic, as we see in Figures 1-3(b) and (c), and it seems
as if it might need frequent adjustment so the millstones can operate with proper clearance.
The thrust block with its “tallow-soaked lubrication pad” also does not seem to make a
precise bearing.