Éolienne Bollée: An Unusual Windmill

The design and working principle of a windmill or a wind powered machine haven’t changed much since they first appeared in Persia some 1,200 years ago. All windmills contain vanes or sails exposed to the wind, which causes them to turn. The rotary motion is then used to do work, such as grind grains into flour or pump water.

In 1868, French engineer Ernest Sylvain Bollée came up with a new design that made his windmill look and work radically different from a traditional windmill.

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Most windmills have only one rotating wheel of blades. The Éolienne Bollée had two sets of blades arranged in two rings. The outer ring (facing the wind) was fixed and was called the stator. The inner ring, located behind the stator, rotated and did the actual job. The fixed blades first guide and concentrate the airflow before it reaches the rotating blades. This arrangement is common in water turbines but extremely unusual in wind machines.

In a later version, a large funnel was added in front of the blades to capture wind from a wider area and direct it towards the rotor. The funnel effectively increased the amount and speed of air reaching the turbine. As the wind passed through the stationary blades, the airflow was straightened and given the ideal angle before striking the rotor. This reduced turbulence and improved efficiency.

The inner rotor blades then converted the wind's kinetic energy into rotational motion. Because the air had already been organized by the stator, the rotor could extract energy more effectively than many conventional windmills of the period.

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The rotor turned a shaft running down the tower. Through gears and mechanical linkages, this motion operated a pump that lifted water from a well into a storage tank. From there, the water could be distributed for household use, irrigation, fountains, or livestock.

A small auxiliary vane (similar to the tail of a weather vane) detected wind direction. Through a gear system, it rotated the entire turbine so that the intake always pointed into the wind. When the wind became too strong, a counterweight mechanism gradually turned the machine sideways to the wind, reducing the force on the blades. This acted like an early automatic governor and prevented damage.

Bollée and his three sons continued operating the windmill business until 1898, when the business was sold to Édouard-Émile Lebert. During the three decades when the business was under the Bollée family, some 260 Éoliennes were made and installed across France. The vast majority of purchasers were aristocrats and gentry. After Lebert took over, the pattern of sales changed, with more éoliennes being sold for communal water supply, particularly in Indre-et-Loire and Sarthe. A few éoliennes were sold abroad, including two to a monastery at Cowfold, Sussex, one to a monastery at Tarragona, Spain, one to a hospital in Tunisia, one to a mine in Brazil, and one to Cotonou, Dahomey.

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Several éoliennes have survived till today, with the oldest surviving éolienne at the Bollée bell foundry in Saint-Jean-de-Braye, near Orléans. One is preserved in working order at Épuisay, Loir-et-Cher, and another at the Bollée museum in Orléans. A few have been restored to working order. The grounds of Château Bouvet-Ladubay in Saumur also contain an excellent example.

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