Wind energy doesn’t contribute to greenhouse gases or release pollutants into the air, but the growing popularity of turbine farms could be hazardous for small aircraft.
That’s the conclusion of a study done by the University of Kansas for the Kansas Department of Transportation.
“These turbines can set up a circular vortex that can roll a plane if it gets in there,” said Tom Mulinazzi, a KU professor of civil, environmental and architectural engineering.
A second problem, Mulinazzi said, is that “they can increase crosswind speeds above what’s expected, which can be a real danger to small aircraft, which don’t typically take off and land with crosswinds stronger than about 12 miles per hour.”
The study was commissioned about two years ago after the Transportation Department’s aviation division started hearing more pilots complain that they had experienced unusual turbulence as they flew near wind farms.
Kansas is one of the leading states for wind farm developments, a booming industry across the country.
With 140 public-use airports in the state, those complaints got regional aviation officials thinking there might be something to the notion that wind turbines pose a potential safety hazard. Sixteen wind farms now operate in Kansas, but proposals have been made for 58 more, including some near airports.
“It is an issue nationwide,” said Jesse Romo, director of the aviation division.
The study, he said, is the first of its kind and a first step in what is expected to be a long process toward getting additional regulations on the construction of wind farms and their proximity to airports.
“The Federal Aviation Administration reviews the potential hazard that the height and location of any structure might have on aircraft, but there is no consideration given to any of the emissions from such a structure,” Romo said. “This study makes it clear that wind turbines create some level of turbulence.”
More study is needed to determine just how much turbulence and how big a hazard it is for aircraft, he said.
The KU research team used advance computational aerodynamics modeling to study the effect of winds from 10 to 40 mph. They found that the higher the wind speed, the farther the turbulence reached — stretching as far as nearly 3 miles from a single turbine — before dissipating.
Even before the study, a coalition of pilots who use the public airport in Pratt, Kan., petitioned against plans for a wind farm to be built within 3 miles of the Pratt airport runway. Part of their objection, in addition to the more than 400-foot height of the proposed 68 turbines obstructing takeoff and landing, was the possibility they would create winds causing dangerous turbulence.
KU’s research team looked at the pilots’ objection to the proposed location at Pratt and another airport 5 miles south of Stockton, Kan. Researchers concluded that at both airports, pilots could potentially encounter a crosswind or “roll upset” generated from a wind turbine.
Subsequently, “the Pratt wind farm project has been relocated farther away from the airport,” said Reid Bell, airport manager at Pratt.
Also, city officials approved an ordinance protecting airspace around the airport from any future wind farm hazard.