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Large Wind Turbines

March 14, 2016
Paul Gipe

Was Anderson’s Miller First with Pitchable Blade Tips for Wind Turbines?

Charles E Miller was an Anderson, Indiana industrialist who made a name for himself vulcanizing rubber tires and tubes in the early days of the automotive industry. He also built wind turbines.

Yet Miller is practically unknown among historians for his contribution to wind energy technology. He could be an unsung Hoosier hero for his invention of the pitchable blade tip.

One of the most fundamental requirements of any wind turbine is to survive high winds. Wind turbine designers have struggled with this demand for generations. Controlling a wind turbine in high winds or during emergencies can be done in a number of ways—some more reliable than others, and it becomes ever more problematic as the wind turbines increase in size.

The development of movable or pitchable tips for wind turbine blades by a small Danish blade manufacturer in the late 1970s not only saved the company from failure, but went on to revolutionize the wind industry.

The success of Danish wind turbines during California’s wind rush of the early 1980s is widely credited with rescuing wind energy from failure. It was the ruggedness of Danish turbines and, importantly, their use of pitchable blade tips that proved wind turbines could be relied upon to generate commercial quantifies of electricity day-in day-out.

During the research for my forthcoming book, Wind Energy for the Rest of Us, I delved into the history of Danish wind turbines with the aid of my Danish colleagues. Here’s a passage from my book, describing what happened to Økær Vind Energi, the Danish blade company founded by wind energy pioneer Erik Gove-Nielsen.

In the fall of 1978, two wind turbines with Økær blades destroyed themselves when the rotors went into overspeed. This was devastating to Økær. Grove-Nielsen stopped production while he sought a fail-safe air brake.

One of the turbines destroyed was a 22 kW prototype built by machinist Karl Erik Jørgensen with the aid of promising wind turbine designer Henrik Stiesdal. Jørgensen operated a machine shop in Herborg, Denmark.

Fortunately, Jørgensen, Stiesdal, and Grove-Nielsen didn’t have far to look for a way to protect the rotor in overspeed. [Johannes] Juul had used pitchable blade tips on his Gedser mill and it was still standing. While Juul had used hydraulics to pitch the blades on his much larger turbine, the more practical choice on the smaller turbines was a spring-loaded system that was activated centrifugally. In normal operation the spring retained the blade tip in its operating position. When rotor speed increased beyond a certain threshold, centrifugal force threw the blade tip out along a grooved shaft that turned the tip 90 degrees to the direction of motion. They quickly adopted this design.

Grove-Nielsen and Økær then began building blades with the automatic-acting blade tip. By the winter of 1978, he was supplying replacement blades with the new pitchable blade tip, including a set to Jørgensen and Stiesdal at Herborg Vindkraft.”

Herborg Vindraft was later absorbed by Vestas Wind Systems. It was Grove-Nielsen’s pitchable blade tips that allowed Vestas and other Danish manufacturers to survive while other companies failed. Vestas is today the world’s largest manufacturer of wind turbines.

The passage above refers to Johannes Juuls’ wind turbine installed in 1957 at Gedser, Denmark. The 200-kW turbine operated commercially for a decade. It was the most successful wind turbine of the era and served as a model for all Danish wind turbine designers who followed. One of the Gedser turbine’s key features was the use of pitchable blade tips.

Juul filed a patent on his system of regulation using pitchable blade tips in 1949. Subsequently, he installed an early prototype in 1951 with two of four blades using pitchable blade tips.

Miller had filed a patent on his pitchable blade tip in 1934. The patent was granted in 1936, 13 years before Juul filed for his patent.

By the late 1950s, the use pitchable blade tips to control wind turbines was widely known in Europe. In the spring of 1957 a French engineering journal published an article on wind turbine design by Louis Vadot that included a drawing of a pitchable blade tip. Moreover, the article contained an English translation by the famous British engineer E. W. Golding, the author of The Generation of Electricity by Wind Power.

Historians will have to determine if Juul knew of Miller’s work in Indiana. It’s unlikely. Communications were much more difficult then than now. There were obvious language differences as well. In the history of technology, there are many cases of simultaneous development of similar concepts in widely disparate locations. This could be another example.

Though Miller’s patent is cited by 19 others, including Boeing, Grumman, Lockheed, and Fayette Manufacturing, his wind turbines were not a commercial success. He and his company faded into obscurity.

From 1977 to 1979, Juul’s Gedser turbine was restored to operation with funds from the US Department of Energy (DOE). Research on the Gedser mill was intended to provide information for the development of large experimental wind turbines in the US program. Subsequently, Boeing filed for a patent on pitchable blade tips in 1981 and installed four of its Mod-2 turbines in 1982.

Another question for historians to pursue is whether there was a direct link between the Gedser mill and Boeing’s choice of pitchable blade tips or if Miller’s earlier patent had some influence on Boeing’s design. If Boeing owed some credit to Miller’s patent, how much influence did it have?

More significantly, Fayette Manufacturing filed its own patent on pitchable blade tips in 1981. They were using it on their first turbines when I photographed one of their prototypes in Dubois, Pennsylvania in the early 1980s. This was before Fayette moved manufacturing to California to take part in the great wind rush. Fayette eventually installed some 1,500 wind turbines in the Altamont Pass using their version of pitchable blade tips. Unfortunately for Fayette, their turbine and especially their blades were not as rugged and reliable as their Danish competitors. Worse, the company made a disastrous strategic error that led to its demise. Nearly all the Fayette turbines were eventually removed and sold for scrap. In contrast, many of the early Danish machines are still operating in California or have been relocated to new sites elsewhere and continue to operate.

Pitchable blade tips became obsolete on large wind turbines in the late 1990s. However, for two decades they defined wind turbine blade design. The wind industry exists today because of the success of pitchable blade tips in protecting wind turbines from destruction.

Charles Miller was clearly ahead of his time. Historians will have to determine if an otherwise obscure Hoosier inventor contributed measurably to the eventual commercial success of wind energy.

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