Different kinds of sprayers used in agricultural UAVs

I notice that there are two kinds of sprayers used in agricultural pesticide spraying system. Yamaha uses jet sprayer (figure1). Besides that, centrifugal sprayers are also used (widely?) in some agriculture UAVs (figure2 and 3) spraying systems.


I’m wondering what are the comparisons between these two kinds of sprayers.


Jetting sprayer v.s. Centrifugal sprayer. Advantages and disadvantages?


centrifugal sprayer1.png

centrifugal sprayer2.png

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    • Yeah, don't doubt that.
      I'm not saying that no one has ever been out there with a few passes left when the wind hit 11 or 12 and they finished those few passes when out in the middle of nowhere, just so they didn't have to haul it back and pump it off the plane, only to have to reload and fly back out there the next day.
      I have landed with many loads over my career due to the wind coming up one or three passes into a 450 gallon load with 20 minutes needed to get it off the plane.
      The state ag department enforcement investigators are always out looking for you. The fine in my state is $10,000 minimum and an additional $1,000 per mile an hour over ten. Thus, if you are found to be applying at 14 miles an hour, you will pay $14,000 per occurrence. You need to take it seriously.

      Look at page 26 and notice that it is only 5 mph. Other variables affect drift such as humidity, and type of carrier.

      Also notice that some labels have a minimum wind requirement of 1 to 3 mph. This is to minimize application during temperature inversions which can cause drift of fines into the MILES. Very dangerous with herbicides.

      This is one of the aspects of UAV spraying that the UAV world has yet to understand about spraying and why the equipment has gotten bigger, not smaller. There is a fine window of operational potential that has to be taken to perform a certain amount of work. The ability to capture that window and perform x amount of work is your profit potential. If you only get a two hour window in a three day period where the wind is less than 10, or in the right direction for a specific application with a sensitive area adjacent, then you have to be able to cover the acres, period. If your equipment can do 10 acres an hour, then you'll do 20 acres. If your equipment can do 160 acres an hour, then you'll do 320 acres. Agriculture is not Monday through Friday, 8 am to 5 pm, 365 days a year. You might have a 150 day season and out of that you'll have about 110 days with flyable weather, and maybe 20 of those will be partial days of 1 to 4 hours of production time. That's what you get to produce and pay your bills.
    • How do the permanent markers typically look like? Any picture of that? How do people make them?

    • I have never seen such a thing Pierre.
      The old school guys would "freehand", that is putting a certain number of passes between power poles or counting fence posts, and knowing how far each are apart.
      Then there were human flaggers, using a pole that they would rotate around so many times for a given swath width. This has it's problems when working on an angled edge. As well as worker protection issues with chemical exposure.
      Then there were paper flags. Basically a 10 foot piece of tissue paper glued to a five inch by five inch piece of cardboard. They are stacked up in a dispenser on the wing and the pilot deploys one at the beginning and end of each pass.
      Last but not least, since about 1994 we have all gravitated toward differentially corrected GPS. Most accurate, keeps flaggers out of the field, and has many features that we use to perform a better job.
      I assume permanent would be setting some type of markers along the field edge at known spacing a.
  • Pierre,
    What country are you located? I am an aerial applicator in the U.S. and if you are here there are going to be chemical label restrictions on certain products that dictate droplet spectrum to be applied. You will want to take those parameters into account when selecting the proper nozzle for your particular application and label compliance needs.
    The usual label requirement is for a coarse droplet of between 250-350 microns average. Some labels call for even larger than that.
    The bottom line is that in the US the chemical label is considered law, and an off-label application is a fineable and/or suspendable offense in the state ag departments eyes. If it says coarse, you've got to go coarse.
    Average droplet spectrum chosen for products that don't have micron specs is between 200-300 micron average. That provides the best compromise between maximum coverage and minimum drift.
    Some special public health ULV mosquito abatement (non-agriculture) applications might go down to 30-50 microns.

    As a side note, one of the other label requirements is minimum volume per acre applied. I am interested to see how the manufacturers approach the EPA about getting that modified so that the smaller equipment could be productive enough to be worthy of actual working. Some of the current fungicides have minimum volumes of five gallons per acre. There are a handful of products that have a ten gallon per acre minimum as well. There are, however, a handful of products that have two gallon minimums. That would mean that the new Yamaha Fazer could do a three acre load.
  • It comes down to the particle size ans consistency of the droplets that you want to apply. This also has a direct effect on drift and the thus the control of where your chemical ends up. Current thinking is towards larger droplets for better control and less fine particles which in turn means less drift. However some applications still us rotary atomisers to produce a finer mist that will drift more but also better coat the targets. this may be more suitable for some applications. What are you planning to spray?

    Atomisers are also generally used for Low volume or Ultra low volume applications since a few large droplets will often not provide a decent coverage. Insecticides are often applied in ULV formulation which means volumes can be reduced from 20-50 lt /ha down to 1-3 l/ha. This has a considerable cost benefit for aerial application. 

    feel free to contact me if you need any further reading links.

    Cheers Ed

    • Thank you very much, Ed Taunton.

      I'm planning to spray different kinds of plants (e.g. vegetable, rice...), but know few about relations between atomisers kind and droplet size. I'd like to have a thorough reading about their relations. Could you please provide me further reading links on this?

    • Here is a UAV rotary atomizer field test.

      You'll notice that the 112 micron average produced by this nozzle would not meet most of the modern chemical label requirements for a coarse sized droplet in the US, and would thus be an off-label or illegal application.
    • Pierre,
      Here is a link to an aerial nozzle manufacturer. They have a spray droplet calculator on their website. Put in the parameters for your set up and it tells you an anticipated droplet size.
    • I can forward you a copy of a local research document if you pm me an email address.

      Do pay attention to  what George is saying as you are entering one of the most legislated areas of aviation and as a current licensed applicator I can confirm it is a minefield for the unwary.

      cheers Ed

    • Here is a Power Point that goes a little bit into the science of droplet spectrum control.
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