Spot spray­ing by drone has is­sues

New Zealand Logger - - Nzif 2018 -

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.

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