Art and science

The aim of this program is to optimise aircraft spraying systems so that the output from the aircraft is as uniform as possible across the span of the spray boom (known as the coefficient of variation) and the droplet spectra, sizes, ‘driftable’ quotients, relative span, swath width and coverage are all measured and, if possible, improved.

The reason for this testing is that almost every aircraft is different in terms of spray boom set-ups, with different equipment such as pumps and flowmeters leading to different aerodynamic impacts on wake and thereby droplet deposition. Add to this additional aerodynamic impacts from propellers, fuselage shapes and even rigging, and it is clear that science can be applied for significant productivity and performance benefits.

Pattern testing for liquids is conducted by passing the aircraft at normal spray height – about 3 metres depending on aircraft – over a measuring array that features cotton string. The aircraft spray output includes water and a fluorescent dye. All aircraft are thoroughly decontaminated before testing. The spray deposit then settles on the cotton string, providing a snapshot of deposition. After each run, the string is wound in and analysed using a black light fluorometer and sophisticated software.

In discussion with the analyst and using the results of the last pass, the pilot can then make a range of adjustments to nozzles and related equipment to improve the performance of that particular set-up.

While it sounds relatively straight forward, there is a certain amount of ‘art’ and experience as well as science involved in getting it right. Too much spray into the vortices and the pattern can be made very uneven or release height increased. Too little into the wing-tip vortice can unnecessarily shorten the swath width and compromise productivity. Creating too many small droplets as a quotient of the total spray volume may actually aid coverage of the target pest or plant, but it can also fuel drift as smaller droplets – especially those less than about 160 micron – take longer to sediment out under gravity.

There is a certain amount of ‘art’ and experience as well as science.

Different set-ups can also be used to target different parts of the crop. Insects on the top of a sorghum plant present a different challenge to targeting the underside of leaves or deep into a closed canopy crop such as cotton.

It can often be a ‘goldilocks’ challenge juggling these different tools – especially when other variables such as weather are considered. But the flexibility aircraft have becomes a real strength in experienced and knowledgeable hands.

A similar approach is used for assessing granular application – such as when most of the Australian rice crop is sown by air or for the tens of thousands of tonnes of fertiliser applied aerially every year – but instead of string and dye, collectors catch the rice or other granule being tested, the contents of each metre-wide collector is weighed and inputted to a database and then analysed for an acceptable Cv – or ‘evenness’ of pattern – swath width and coverage.

In addition to field-testing of aircraft, the industry also has access to modelling through sophisticated predictive software programs and AAAA has also invested in wind tunnel research through the University of Queensland at Gatton. This has allowed the Association to develop nozzle calculators for members that allow us to understand precisely – and under what variables including release height, spray pressure and airspeed – the spray quality a nozzle will produce.

To round out this comprehensive approach to quality assurance, AAAA also runs a range of training, assessment and accreditation programs – such as Spraysafe – that are recognised by every State and Territory government as the national standard for aerial application pilot chemical competency. Our AIMS program takes it a further step into the QA realm.

To ensure all pilots keep up to speed with developments in the industry, AAAA has run the Professional Pilot Program since 2002. This continuing professional development program requires pilots to earn 15 education units over each three year period to renew their Spraysafe accreditation, which in turn is required for their Chemical Distribution licence issued by the States.

Underpinning all of this work is the commitment of our pilots and business owners to continuous improvement and quality assurance – making Australian aerial application one of the most reliable and effective platforms for crop protection.