Spot spraying by drone has issues
YOU’D THINK THAT USING A LARGE DRONE TO HIT PROBLEM weeds in a forest with a targeted spray would be an ideal and costeffective solution but it’s not that simple, according to Scion.
Whilst trials using a real-life helicopter holding a spray unit on a long tether have proved successful, the same could not be said for modelling applied to drones, Scion scientist Tara Strand told the NZIF annual conference in Nelson last month.
It seems that when a spray unit is slung right underneath the drone, the wash from its multiple rotors does not act in the same way as the bigger helicopter.
The single large rotor on the helicopter drives the spray down onto the targeted weed or tree and covers both sides of the leaves with droplets, but the numerous rotors on the drone produce confused vortices that blow the spray away from its intended target.
Even though drones are already being manufactured with payloads up to 20kg to carry small spraying units to be deployed for such tasks, the Scion team says they “lack a robust design that considers wakespray interactions”.
The scientists say more work is needed to develop technology that overcomes this drawback.
In other research, Dr Strand and her colleagues are also working on the development of models to predict how forest fires react in extreme conditions, as reported by NZ Logger last year.
The work is considered vital because New Zealand is likely to experience the sort of extreme wildfires being witnessed in the US, Canada and Australia.
Working with researchers from those countries, Dr Strand and her team are working on a new fire spread model based on a groundbreaking theory that these conflagrations move via convection that pulses the flames forward rather than raising the heat of vegetation through radiation to a point where it combusts. That makes extreme fire events more deadly.
Last year, they carried out a live experiment by setting fire to a field of corn stubble in the South Island, using sensors and video to test the theory, which it seemed to prove. Dr Strand told the conference that two further live fire trials are planned, one using gorse in the Rakaia Gorge this coming summer and a year later in wilding pines on the Pukaki Downs Station.
A fire experiment in a South Island corn field proves fire spreads by convection, not radiation.