It wasn’t so long ago you could buy any spray drone you wanted – provided it came from China. But in the past few years, as rules regulating aerial applications are being introduced in more countries, that dominance is dwindling and domestic manufacturers are introducing locally designed and built drones. That is why Future Farming has put together the world’s first application drone catalogue.
Relatively cheap effective drones have, undoubtedly, revolutionised agriculture’s ability to gather, analyse and act on huge amounts of data. In recent years this has prompted progressive farmers and suppliers to move to the next logical step – using drones for applications of sprays, seeds and nutrients.
At the same time many countries, particularly China, USA and Brazil, have moved relatively swiftly to introduce remote operation pilot licencing as well as rules and regulations to permit spray applications from drones. It’s here where we find some of latest developments and specialist application technology – some at work now and other exciting advances on their way.
Regulations restrict capacity
Regulations, particularly in the China and the USA, apply to drones weighing less than 25 kg – with operators of heavier models having to comply with far more onerous rules. Consequently, the weight restriction limits the size of the sprayer and its carrying capacity. This constrains the size of the spray drone and its tank capacity, usually to about 16 litres, with a few obvious exceptions.
This is why we concentrate on this category, which is also the most popular. These smaller drones are easier to handle and transport. Total weight is also influenced by the number of batteries, their size and capacity. The unit that measures power over time is a milliamp hour (mAh) – which basically shows how long it lasts on one charge. In our survey the power rating varies from 16,000mAh to 22,000mAh, with some drones using one battery and others two.
This alone, however, does not determine how long each drone will fly before recharging, because that’s also influenced by the efficiency of the electrical drives – rotors, spray pump etc. And it will depend on the load and flying conditions. This is worth bearing in mind when comparing the individual entries and, it’s important to note, all manufacturers replying to our survey pointed out that flight times can vary.
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Tests carried out by the USDA show the optimum operating height is 3 m. Fine nozzles will produce a narrower swath width than coarser sizes. - Photo: Dan Martin
Bear in mind that batteries will often take longer to charge than a typical flight time – so you will need more than double the time needed for a typical flight. It’s worth looking carefully at battery details – are spares included, how long do they take to charge and what is the replacement cost? Do not rely on the ‘fast charge’ facility, because this causes batteries to deteriorate more rapidly.
Effective swath width
The application ‘swath’ width will influence the work rate. While on a boom sprayer it’s easy to work out the swath width, on a drone it is harder to determine the actual ‘effective working width’. This is because as well as the nozzle position and mounting, you need to also account for the working height. USDA tests reveal that 3 m is a good practical height for working in visual line of sight with a practical swath width.
Tests show that the position of the nozzles, whether they are mounted beneath the rotors or on a boom, doesn’t necessarily set the swath width on a UAV. But nozzle selection has a big influence. Coarser nozzles, making larger droplets, not only produce a wider swath width, they also cut drift compared with finer nozzles. Many manufacturers now offer a choice with larger 015 and even 02 nozzles, and it’s worth selecting these.
You will need to calibrate your sprayer, but only a few makers offer a gauge or transducer to check the pump’s pressure. It’s difficult to check the flow rate accurately without knowing the actual pressure.
Buy the best back-up
Don’t buy a spray drone off the internet. After investing substantial amounts of time and money in a pilot’s licence and application training and certification, it is a massive false economy not to invest in operator training and support. This is a deal breaker – walk away from any supplier that does not provide this – even if it is an extra cost, it’s an essential part of the purchase, particularly for first-time operators.
What about wings and hybrids?
That’s a good question but, as yet, one we can’t answer. While there are winged and hybrid application drones, we were unable to find enough details to include these.