Historical Development of the Windmill - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 34

in Wisconsin and was named the Eclipse (second from left in Figure 1-17). A hinged tail
vane on the rear framework of the system could turn from being perpendicular to the wheel
to a parallel position for shutting it down. A much smaller ixed side vane was mounted
on an arm parallel to the wheel, with its tip projecting just beyond the circumference. The
drag force on this small vane was such that it tended to turn the wheel out of the wind, thus
reducing the effectiveness of the blades in high winds and hence controlling the speed. The
restoring force was supplied by a weighted lever or spring. This form of control remained
the most common throughout the era of the American windmill to the present day, but there
was considerable variety in the form and use of the side vane. Instead of a side vane, the
wheel was mounted somewhat off the tower pivot centerline in a number of designs, its
thrust providing the spoiling effect as the wind speed increased.
The number of manufacturers of windmills multiplied rapidly after these beginnings.
Steel blades were introduced in the late 1870s, but there was considerable skepticism about
them at irst. There is a reasonable explanation for this, in that wood construction usually
means more rapid repairs in case of breakage and does not require much machinery, and
straightforward carpentry can be applied. Metalworking is more dificult, and repairs
sometimes require that replacement parts be ordered, with a consequent increase in machine
downtime.
All-Steel Windmills: The Aermotor
A third major step in the development of the American windmill occurred in 1888
when two men, LaVerne Noyes, and inventor and manufacturer, and Thomas Perry, an
engineer with a scientiic bent, joined in organizing The Aermotor Company in Chicago.
By 1900, the Aermotor windmill had captured more than half the market; by the middle of
this century, the company claimed to have 800,000 mills in service, more than half of them
operating for more than 40 years [Baker 1985]. The Noyes and Perry combination appeared
to be a symbiosis of entrepreneur and engineer akin to that of Matthew Boulton and James
Watt (albeit in a minor key), achieving both economic and technical success. Perry might
also be likened to Smeaton. Not only did he test an enormous number of existing technical
artifacts to instruct himself, and then design and test his own constructions, he also devised
a steam-powered whirling arm for testing model wheels, together with instrumentation to
measure speeds, temperatures, and pressures.
The Aermotor did not have any major new operating features, but it did have thin,
curved, sheet-metal blades, properly angled and supported by steel members offering
minimum drag resistance. This resulted in a much lighter wheel with improved
aerodynamic performance, capable of useful work at both lower and higher wind speeds
than wooden wheels. However, its rotational speed was too fast for a reciprocating pump.
This necessitated a reduction gear, effected by means of a small pinion on the wheelshaft
and a larger gear on a separate crankshaft. This was called a back gear , and it had several
advantages, including a high starting torque , a longer pump stroke , and a division of the
bearing load between the wheel and the pump. The Aermotor was not the irst all-steel
mill, but it performed very effectively in terms of eficiency, structural design, and economy
of manufacture.
Automatic Lubrication
One notable technical problem must be related, however — a problem that surfaces
in all engineering designs that include dynamic action — namely, bearings and their
lubrication. Two mainstays were the poured babbitt bearing and (perhaps strangely) wood,
particularly maple. The latter was used especially to support the pitman , or connecting rod,