During the flurry of wind technology development from the 1970s through the 1980s, one novel—some would say “innovative”—design were those using only one blade.
Of course, you only need one blade to perform the function of sweeping the entire wind stream, but we often use two or three blades for mechanical reasons.
That the idea is not so crazy as it first sounds is indicated by NASA’s experiment with one 15-meter long blade on its test turbine at Plum Brook, Ohio in 1985.
Two firms tried to commercialize this concept: Messerschmitt-Bölkow-Blohm (MBB), and Riva-Calzoni. The German firm, MBB, was the direct corporate descendant of the famed aircraft manufacturer of the Third Reich.
While never commercially successful, optimal material economy has for decades been a siren’s song luring designers onto the rocks of flimsy, one-blade designs. German engineers have been particularly susceptible because of Ulrich Hütter’s 1940s’ doctoral thesis on the design of inexpensive, high-performance wind turbines.
Hütter taught for many years at the University of Stuttgart’s Institute of Aircraft Design, alongside Professor Franz Wortman, himself well known for airfoil sections at the Institute of Aerodynamics. Wortman and his students pursued Hütter’s minimalist design philosophy to its logical conclusion: the one-blade FLAIR or Flexible Autonomous 1-Bladed Rotor.
In the mid-1980s, Wortman installed a FLAIR prototype 8 meters (26 ft) in diameter at the university’s test field near Schnittlingen, in southern Germany’s Swabian Alps. The novel downwind rotor drove a 5.1 kW, four-pole induction generator—it, too, out of the ordinary. The generator on the grid-connected version incorporated high slip (14 percent), enabling the turbine to regulate rotor speed within a vary narrow range by using its Watt or “fly-ball” governor.
Originally developed for the German washing machine company Böwe, FLAIR was subsequently sold to aerospace giant MBB. From it, MBB developed the Monopteros 15 series: turbines with rotors from 12.5 to 17 meters (40 to 55 ft) in diameter, driving generators from 15 to 30 kW (see figure 6-sb1, Monopteros 20). MBB also introduced a greatly scaled-up version of Wortman’s FLAIR: the Monopteros 50 series, with rotor diameters from 47 to 56 meters (150 to 180 ft), rated from 550 kW to 1 megawatt. MBB’s work on the turbine ceased in 1986 after Wortman’s death.
Independently of Wortman’s group, Riva Calzoni developed its own one-blade design. An Italian heavy-engineering company, Riva Calzoni built 25 of its MP5 and another 25 of its MP7 models by 1992, when it abandoned the small turbine market . In the mid-1990s, one MP5 could be found in Milan’s Technical Museum.
Both MBB and Riva Calzoni found that it was more profitable to build larger turbines for commercial wind farms than small turbines for rural residences. At one time MBB envisioned building monstrous 5 MW versions, dubbed GROWIAN II (Grosse Wind Energie Anlage) along the German coast. But MBB completed only three 640 kW Monopteros 50 models near Wilhelmshaven before abandoning the program. Of the two firms, Riva Calzoni was the more successful.
Riva-Calzoni built its 350 kW, M33 model in Bologna and eventually installed more than 100 in Italy before discarding the one-blade approach entirely.
The Central Appenine town of Tocco da Casauria (Pescara) installed two of Riva-Calzoni’s wind turbines 1992. The town prides itself on its firsts—the first oil oil well drilled in Italy (1863) and the first community wind turbines.
The town commemorated installation of the wind turbines with a mural depicting the wind turbines on the rural landscape.
Riva-Calzoni’s turbines were replaced in 2006 with two Enercon E48 turbinesand expanded the project in 2009 with two more E48s. The four turbines comprise a wind plant of 3.2 MW capable of generating more than 7 million kWh annually.
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