SPRAY TECHNOLOGY


and coarse nozzles,” says Dan. It also emphasis- es how nozzle selection is hugely important as a way to reduce driftable fines, which he ob- served are pushed down and outwards by the rotors on UAVs. “I measured a windspeed of 15.5m/s (35mph) under the rotors of my spray drone hovering at 3m. While this will effect drift, one benefit we are now researching is how this may assist crop penetration: helping droplets to move into the canopy and under the leaves.” Many drones are coming equipped with 80 005 nozzles, which create huge amounts of drift. “HSE-UAV, which supplied its drones for our experiments fitted with Lechler 80 005s, has already changed to offering a choice of Lechler IDK 110 01, 015 or O2 as standard fol- lowing the tests,” adds Dan. “The 015s work well as do even an 02 in areas where drift could be a problem.”


Swath width variation Whether nozzles are mounted beneath the rotors or on a boom, the research found that their position doesn’t necessary set the swath width on a UAV. Switching from fine to medi- um nozzles, however, will narrow the swath. “We haven’t been able to test the effect of nozzle location on drift yet. Our best guess is that it will not affect drift nearly as much as nozzle selection,” Dan adds. Swath width was measured by applying the


Specifications of tested drones Model


Operating weight (kg) Tank capacity (l)


HSE V6A* n/a 5


Measured swath width (m) 3.0-4.5m


Rotors 6 6 Nozzle (standard)


HSE M6E** DJI Agras MG-1 HSE M6A Pro HSE M8A Pro 24 10


22.5 10


9.0


34.5 15


7.6-9.0


48 20


8 6 8


TR 80 005*** 015, 01 or 02*** XR 110 01 TR 80-0067*** TR 80-0067*** 6.0


9.0 * no longer available ** specifications for latest M6E-X2 model *** Lechler **** coarser nozzles will reduce swath width


product over a cotton string and then analys- ing this in the lab to determine the quantities deposited along its length. All the flights were carried out at 3m, which the researchers had already determined to be the optimum application height. “We found this to be the ‘sweet spot’ that allows the pattern to fully develop. UAVs need to be operated in Visual Line of Sight (VLOS) and at 3m it’s possible to keep them in view, even over undulating land, without them disappearing into dips. This is also above head height and helps avoid any obstacles.”


Reduce the risk of drift “At a height of 3m we discovered that this provides the optimum swath width and cover age with the selected nozzles. The spray has plenty of time under the rotors and this helps to reduce the risk of drift,” explains Dan. The 20-litre M8A PRO drone, which has its


nozzles fitted to a boom, initially produced a noticeable ‘spike’ in the pattern in the middle. This was overcome simply by adjusting the spacing between the in-board nozzles. Meas- ured swath widths varied between models from 3.6 to 9 m and, with fine nozzles, this ranged from 7.5 to 9.0 m. Operating speed is an important consideration when calibrating for flow rate and this can also influence the application rate and coverage. Speed and height actually had little effect on an effective swath. The most important param- eters were the nozzle and the size of the air- craft (its power). Although 7m/s did provide the largest effective swath for the V6A, it is not statistically different from the other speeds. While 3m/s was the best speed for the MG-1, again it is not statistically different from the other speeds. Higher speeds deliver increased productivity, but the application rates on the label must be met.


Droplets were collected on water-sensitive paper across the working width, to assess droplet size, the number and coverage in order to characterise the droplet spectrum.


56 ▶ FUTURE FARMING | 20 November 2020


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