PHOTOS: DAN MARTIN
SPRAY TECHNOLOGY ▶▶▶
How to avoid drift during drone spraying
BY MICK ROBERTS D
rone spraying is still in its infancy. However, there are mounting con- cerns about high levels of drift and the quality of the application.
Dr Dan Martin from the US Department of Agri culture’s Aerial Application Technology Research Unit in Texas, a specialist researcher in manned aerial applications, realised that there still is a fair amount of uncertainty over the efficiency of UAVs in terms of the uniform- ity of sprayer deposition and application effi- cacy. The objectives of the research were to de- termine the ‘effect of application height and ground speed on the swath width (actual working width), spray pattern uniformity and droplet spectrum from different unmanned aerial application systems (UAAS)’. The study looked closely at standard equipment on drones, calibration, nozzle choice, operating height, operating speed and swath width. The team collected an array of commonly used drones with six to eight rotors, with capacities from 10 litres to 20 litres and four to six nozzles –
Independent, in-depth research in the USA shows that spraying from drones can be safe and effective, provided operators pay close attention to the correct set-up and operation.
either fixed to booms or mounted beneath the rotors. “When it comes to spray equipment they are fairly basic – and not one of them is fitted with a pressure gauge. Also nearly all of them came equipped with 005 to 0067-sized nozzles, which create fine droplets,” explains Dan.
Calibration is crucial Dan started off by calibrating the sprayers. Not an easy task when none are fitted with pres- sure gauges. So he made an adaptor and quick coupler to fit into the drone’s plumbing sys- tem. “The set pressure varied from 33 psi (2.27 bar) to 72 psi (5 bar). While it’s important to reduce weight on a drone, it’s also crucial that it’s calibrated correctly. To do that you need to know the pressure and forward speed of the sprayer and, without a gauge, you are missing a vital part of the equation. What it needs is a small transducer that displays
pressure on the operator terminal (or ground station),” he suggests. Dan and the team set the appropriate pressure and measured the flow rate by collecting the output from each nozzle in cups over a set time. With manned aerial applications, which are common in the US, there are a wide range of approved products, which have to be applied according to the label recommendations. For most this is an application rate of 2 gal/acre, equivalent to about 20 litre/ha, which was also used for the experiments. It’s important to know the drone pumps’ outputs. “We found that this varied among the different models with the smallest, V6A, unable to deliver 20 litre/ha even at the lowest speed with the 005 nozzle.” Forward speed is also an im- portant calibration factor. The team tested at four ground speeds: 1m/s, 3m/s, 5m/s and 7m/s.
Dr Dan Martin carried out the test of standard, ‘off-the- shelf drones’.
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During the static calibration procedure the researchers also assessed the set-up and level of equipment that comes with a standard ‘off the shelf’ spraying drone.
▶ FUTURE FARMING | 20 November 2020
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