The proliferation of unmanned aerial vehicles (UAVs) has led to important technological and operational advancements in the management of farms.  With drones, what was once tedious and time-consuming field work, often requiring long hours in the hot sun using expensive difficult-to-recruit farm labor, has become a fast, efficient and cost-effective process that makes farming more sustainable than ever.

The new methods available are nothing short of remarkable.  High-performance pilot-less drones equipped with AI-enhanced algorithms can be programmed to seed crops from the air, then spray them with fertilizer and pesticides at recurring intervals to ensure their optimal growth.  Precision drones can also precisely target planting and spraying at areas of the farm most in need, minimizing the waste of valuable farm inputs.

But even these efforts are far from perfect. Weather (especially wind) or the drones’ own mechanical limits can still limit the ability of drones to plant or spray as precisely as intended.   How serious is the problem  of “spray drift”?  In the first study of its kind, researchers in Ohio are studying the movement of spray droplets after they leave drone sprayers to find out.

Sidaard Gunasekaran, an assistant professor of mechanical and aeronautical engineering at the University of Dayton, is coordinating the new study to help chemical and equipment manufacturers better understand the drift potential of drone sprayers.  Gunasekaran has previously conducted drift testing with ground-based spraying equipment at a low-speed wind tunnel located at a research lab on campus.  But the extraordinary growth of the UAV industry in recent years has led to increased demand for new research on drone spray drift.

To accommodate the new testing requirements Gunasekaran and his research team created a special rig that positions a cube-shaped frame holding a spray boom below a series of standard drone propellers. The rig allows them to test and evaluate various nozzle placements, propeller configurations and propeller speeds to determine how and why spray drift occurs, and to estimate its potential effects.

Guansekaran says industry suppliers of chemicals and drone equipment are concerned about any waste that might occur due to spray drift but they’re especially concerned about its impact on pesticide spraying because of the health issues involved.  Pesticide drift from crop-dusting airplanes is already recognized as a major health hazard and is one reason – among many – that precision drone application of pesticides at lower altitudes in designated farm areas is being encouraged.

But until recently, reliable data on drone spray drift has been hard to come by.  “Nobody’s really sure exactly what’s going on underneath a drone and that’s why there’s a need for these studies,” says Kyle Butz, a technical advisor for Spray Analytics.

Butz has been working with Gunasekaran as an industry partner on the drift experiments.  He says these studies are badly needed to head off concerns over spray drift that could undermine confidence in drone technology at a time when the demand for its commercial application to farming is skyrocketing.

“If you do it right, you should be limiting [health] risk at the same time as you’re increasing efficacy,” Butz says. “If you do it wrong, you’re losing on both [counts]”

The Dayton tests are still in their infancy.  An initial set of experiments using laser technology suggested that the larger spray droplets typically emitted by drones with downward facing nozzles were less likely to be sprayed and scattered outside the target zone. However, subsequent tests revealed that finer droplets could be caught up in propeller wake and scattered more widely.  Other tests that factor in wind and other weather conditions remain to be conducted.

Butz and Gunasekaran are planning to share the preliminary results of their research during a free seminar offered at the University of Dayton’s Kettering Labs on May 24. Interested participants can also attend a day-long course on the mechanics of drone spray testing at the lab’s low-speed wind tunnel facility on May 25.

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