When it’s all up in the air: rotary or conventional nozzles

What would farmers think about turning half the nozzles on their ground sprayer upside down so they point straight up rather than down toward the crop?

Researchers have established that when mounting nozzles on spray planes, it’s important to locate them as far down and aft of the wing as possible. This gets the product further away from unstable turbulent air.

Rotary atomizers sling half the chemical down toward the target area and the other half up into turbulent, unstable air from the wing.

I recently spent three hours with a dealer who sells atomizers in Canada, comparing side-by-side data. We agreed there was no difference in the amount of fines or in the amount of large droplets.

Neither of us had droplet data that showed superior performance from atomizers or conventional hydraulic nozzles.

I find it troubling when a pilot’s goal is only to increase aircraft efficiency by applying less water. Our goal as agricultural pilots is first and foremost to do the best job we can. Efficiency is necessary to any business, but quality needs to come first.

Operators pushing rotary atomizers at low water volumes do not achieve a better pattern or better coverage than properly set up conventional nozzles at the same water volume.

Our target droplet size under most circumstances is a 280 to 320 micron volume mean diameter (VMD), which is droplet size.

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The bottom line is rotary atomizers do a great job, but so do conventional hydraulic nozzles. So the question becomes, is two gallons of water enough?

It might be under perfect weather conditions with high humidity, low temperatures, low average winds and systemic products, but here are a few questions I will let farmers answer for themselves:

  • How often is the weather perfect when spraying by ground or air?
  • Is it right to use just enough water for an adequate job when we have the capability to do a superior job with more water?
  • Atomizers are not a superior method of application in agricultural application if the operator is properly using hydraulic nozzles. There are two reasons why some operators have found an improvement in their droplet spectrum when moving to rotary nozzles:
  • Their conventional nozzles were set up incorrectly and not adjusted properly for varying weather conditions.
  • Rotary atomizers might create smaller than target VMD. This translates to better coverage on a water sensitive card, but under marginal conditions there’s a higher percentage of evaporation and off target spray movement that doesn’t register on the cards on the ground.

Water sensitive cards can look amazing with the rotary atomizer, but a downwind drift test will also show that off-target application is taking place.

To avoid this, operators need to increase water volume while keeping the same VMD.

Our goal as product applicators is to create as small a droplet as possible while limiting the risk for drift, off target application and evaporation. Whether we spray with rotary atomizers or hydraulic nozzles, our target VMD is the same.

Some people claim hydraulic nozzles produce a high percentage of large undesirable droplets and more undesirable, fine, driftable droplets. I haven’t experienced this.

A pilot should consider weather and atmospheric conditions and consider calibrating and changing nozzle settings every hour if necessary. This is true for hydraulic nozzles and atomizers.

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Increasing aircraft speed with a rotary nozzle drastically increases cage speed, which decreases the size of the VMD and increases driftable fines.

Changing relative humidity, temperature, wind speed, wind direction, aircraft spraying speed, crop canopy, geographical location, field obstacles, neighbouring susceptible crops, product being applied and water rate all influence how a plane is setup.

Many of the largest aerial spray businesses in Canada use a higher, more appropriate water volume for fungicides. No type of nozzle is a substitute for water volume. Some products may work well at lower volumes, while others need the coverage created by volume and correct calibration.

As a farmer, look for an applicator willing to put the extra water on for fungicides. Ask if the applicator has the aircraft calibrated every 12 to 18 months.

There are many good folks in the region who do this.

Editor’s note: Our new aerial application columnist is Clayton Rempel, owner of Clayton Air Services at Leask., Sask., which operates a pair of 500-gallon Air Tractor 502s. He is a licensed spray pattern analyst and contractor for the Canadian Aerial Applicators Association and certified by the National Aerial Applicators Research and Education Foundation.

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