NAAA developed useful information to refute proposed setback distances from wind turbines and other tower-like obstructions this week. The information may be used by operators and state associations when dealing with wind farm and tower companies making claims that their obstructions do not hamper aerial application activities to crops. The basis for needing the information was a request from a public utilities commission to provide proof that agricultural aircraft need 1 mile or more to turn around safely at the end of a treated field. A wind farm sponsor in South Dakota had proposed a setback of a mere 500 feet, which is far too short a distance for making safe aerial applications with a fixed-wing aircraft in a field adjacent to a wind turbine or tower location site.
NAAA provided the information using two different methods. The first was a calculation using aircraft speed and average turn time to estimate the total distance required to make a turn. An AT-802A with a working speed of 145 mph was used as the example aircraft. The working speed was taken from the midpoint between 130 and 160 mph as denoted on Air Tractor’s specifications page for the AT-802A. An agricultural turn time of 45 seconds was used; this information was gleaned from operators’ experience and used in comments made to the EPA on several pesticide reregistrations. A speed of 145 mph is equal to 213 feet per second; 45 seconds to turn multiplied by 213 feet per second is equal to 9,585 feet or 1.82 miles needed to make the turn.
The second method NAAA used to provide evidence on the distance required to make a turn while conducting an aerial application was via GPS as-applied aerial application maps and Google Earth. Google Earth was used to measure the distance into the field that two turns required. The first was one of the shorter turns from the application from when the aircraft was lighter. This turn pushed 2,273 feet or 0.43 miles into the adjacent field. The second was from a longer turn made when the aircraft was fully loaded. This turn penetrated 9,147 feet or 1.73 miles into the adjacent field.
A Google Earth map showing an application made by an AT-802A. Green represents the flight path with spray on, while red represent the flight path with spray off. The yellow line is the ruler tool used to measure the total length into the field a longer turn required: 9,147 feet (1.73 miles).
You may find the above information helpful if you find yourself countering claims about the dangers wind turbines and other obstacles represent to the safety of agricultural aviators. For more public outreach tools on wind farms from NAAA, click here.