One of the main questions we get asked is “what is the swath width on my drone?”
The simple answer is “we don’t know!”
This article aims to explore and explain some of the many factors that affect spray swath and how we can maintain effective coverage.

Introduction

The agricultural sector is continually evolving, with technological advancements driving increased efficiency and precision in various practices. One such innovation is the use of aerial drones for chemical application. Drones offer a range of benefits including reduced labour costs, increased application speed, and the ability to access hard-to-reach areas. They enable farmers to apply pesticides, herbicides, and fertilisers with unprecedented precision, ensuring that crops receive the necessary treatments while minimising waste and environmental impact.

There is a legal obligation for all unmanned aerial operators involved in the application of chemicals to adhere to industry best management practices about minimising spray drift.

A crucial aspect of effective aerial drone chemical application is the maintenance of the spray swath. The spray swath refers to the width of the area covered by the drone’s nozzles during application. Ensuring a consistent and accurate spray swath is essential for several reasons:

Proper swath maintenance guarantees that the chemicals are evenly distributed across the entire field, preventing under- or over-application in certain areas. This uniformity is vital for effective pest and weed control, as well as for the optimal growth of crops.

A well-maintained spray swath reduces the likelihood of chemical drift, where chemicals are carried by the wind to non-target areas. Drift can lead to environmental contamination and harm to surrounding ecosystems, including unintended crops, waterways and wildlife.

Accurate swath maintenance ensures that chemicals are used efficiently, reducing waste and lowering costs. This efficiency is particularly important given the high cost of agricultural chemicals and the increasing emphasis on sustainable farming practices.

All Australian states have strict regulations regarding chemical application in agriculture. Maintaining a precise spray swath helps farmers adhere to these regulations, avoiding potential fines and ensuring the safety of their operations.

There are two primary systems used for maintaining the spray swath in aerial drone applications: the TeeJet nozzle system and the Controlled Droplet Application (CDA) system.

This system uses a variety of nozzle types to produce specific spray patterns and droplet sizes. It offers flexibility and can be adjusted to suit different application needs, making it a popular choice among farmers.

The Controlled Droplet Application (CDA) system employs rotary atomisers to produce uniform droplet sizes. This system is highly effective in reducing drift and ensuring precise application, particularly in variable weather conditions.

Both systems have their advantages and are chosen based on specific application requirements, but the core principle remains the same: maintaining a consistent and accurate spray swath is essential for effective, efficient, and environmentally responsible chemical application in agriculture.

Parameters for Maintaining Spray Swath Integrity

Maintaining the integrity of the spray swath in RPA (Remotely Piloted Aircraft) chemical applications is critical for achieving uniform coverage, minimising drift, and ensuring resource efficiency. Here are the key parameters to consider:

  • Nozzle Selection: Choose the appropriate type of nozzle (e.g., TeeJet, CDA) based on the desired droplet size and spray pattern.
  • Nozzle Calibration: Regularly calibrate nozzles to ensure consistent droplet size and distribution.

  • Effective Spray Width: Account for the nozzle’s nominal spray width and any overlap required to achieve uniform coverage.
  • Overlap Management: Typically, a 25% overlap is recommended to prevent gaps and ensure even application.

  • Flight Speed: Maintain a consistent speed (e.g., 3.5 m/s) to ensure even chemical distribution.
  • Flight Height: Adjust the RPA’s altitude (e.g., 4.5 meters) according to the nozzle’s specifications and wind conditions to minimise drift and maintain coverage.

  • Wind Speed and Direction: Monitor and adjust for wind conditions to prevent drift and ensure chemicals reach the target area.
  • Temperature and Humidity: Consider these factors as they can affect droplet evaporation and drift.

  • Stability: Ensure the RPA is stable during flight to maintain a consistent spray pattern.
  • GPS and Path Planning: Utilise accurate GPS systems and pre-planned flight paths to ensure the RPA follows the designated spray route precisely.

  • Regular Inspections: Perform routine checks and maintenance on the RPA and spray system to ensure they are functioning correctly.
  • Cleaning: Keep nozzles and tanks clean to prevent blockages and maintain optimal performance.

By meticulously managing these parameters, operators can ensure the integrity of the spray swath, leading to effective and efficient chemical application in agricultural practices.

Factors Affecting Spray Swath Integrity and Poor Performance Indicators

Maintaining spray swath integrity is essential for achieving precise and efficient chemical application using RPAs. Several factors can influence the integrity of the spray swath, and recognising poor performance indicators is crucial for timely adjustments and maintenance. Here’s an outline of the factors and indicators:

Factors Affecting Spray Swath Integrity

  • Wear and Tear: Over time, nozzles can wear out, leading to inconsistent spray patterns.
  • Blockages: Debris or residue can clog nozzles, causing irregular spray distribution.
  • Pump Errors: Irregular pump pressure or liquid flow rate will result in inconsistent nozzle performance where the swath integrity will be compromised especially in swath width. This inconsistency can produce results such as ‘striping’ or inconsistent coverage within the spray pattern.

  • Inconsistent Speed: Variations in the RPA’s flight speed can lead to uneven application rates.
  • Altitude Variations: Deviations in flight height can affect droplet size and spray pattern, leading to either excessive drift or insufficient coverage.

  • Wind Speed and Direction: High winds or gusts can cause drift, dispersing chemicals away from the target area.
  • Temperature and Humidity: High temperatures and low humidity can increase evaporation rates, reducing the effectiveness of the application.

  • Pressure Variations: Inconsistent pressure in the spray system can result in uneven droplet size and distribution.
  • Improper Calibration: Incorrect calibration of the spray system can lead to inaccurate application rates and patterns.

  • Turbulence: Flight instability caused by turbulence can disrupt the spray pattern.
  • GPS Accuracy: Inaccurate GPS data can lead to deviations from the planned flight path, resulting in missed areas or overlapping applications.

Poor Performance Indicators

  • Stripes or Gaps: Observable stripes or gaps in the treated area indicate uneven coverage.
  • Pooled Chemicals: Excessive pooling or runoff in certain areas suggests over-application.

  • Pest or Weed Persistence: Areas with persistent pests or weeds may indicate under-application.
  • Crop Damage: Signs of chemical burn or damage to crops can point to over-application.

  • Chemical Presence in Non-Target Areas: Detection of chemicals in adjacent fields or water sources suggests drift.
  • Complaints from Neighbours: Reports of chemical presence in neighbouring properties indicate drift issues.

  • Pressure Warnings: Alerts or fluctuations in spray system pressure can signal potential issues.
  • Nozzle Performance Data: Data indicating nozzle blockages or wear can affect spray integrity.

  • Deviation from Planned Path: GPS data showing deviations from the intended flight path can lead to coverage issues.
  • Inconsistent Speed and Altitude: Flight logs indicating speed or altitude inconsistencies suggest potential problems with spray distribution.

By closely monitoring these factors and indicators, RPA operators can maintain the integrity of the spray swath, ensuring effective and precise chemical application in agricultural operations.

Aircraft Spray System Design and its Impact on Spray Swath Performance

The design of an aircraft spray system is crucial for achieving efficient spray swath performance. Inefficiencies and poor performance in the spray system are often attributed to the placement of nozzles in relation to the rotor head system and the resulting downforce.

Importance of Nozzle Placement

The positioning of nozzles relative to the rotor head system plays a significant role in the effectiveness of the spray swath. Proper placement ensures that the spray is evenly distributed and reaches the target area without significant drift or loss.

Impact of Rotor Head System and Downforce

The downforce generated by the rotor head system influences the behaviour of the sprayed droplets. Optimal nozzle placement considers the downforce to maintain a consistent and accurate spray pattern.

Terrain Following/Collision Avoidance Functionality

Most automated/manual flight systems are equipped with active radar/laser guided terrain following and collision avoidance systems for all terrain types. Sudden attitudinal shifts in the aircraft flight path, altitude and direction change of the flight path will impact the spray system distribution.

Example of Poor System Design

Poor boom design on a homemade drone

Nozzles outside the rotor head system

When nozzles are positioned outside of the rotor head system, the spray is likely to be drawn into the vortices produced by the blade tips. These vortices can cause the spray to become turbulent, leading to uneven distribution and potential drift away from the target area.

By understanding and addressing these design considerations, the efficiency and effectiveness of the aircraft spray system can be significantly improved, ensuring better performance and more accurate chemical application.

Explanation of Flight Systems and Their Impact on Spray System Distribution

Most automated and manual flight systems are equipped with active radar or laser-guided terrain-following and collision-avoidance systems, designed to handle various terrain types. However, sudden changes in the aircraft’s attitude, altitude, and flight path direction can significantly impact the distribution of the spray system performance.

Key considerations:

  • Attitude: Sudden changes in the aircraft’s pitch, roll, or yaw can disrupt the even distribution of the spray, causing it to be applied unevenly. This can also induce spray swath introduction into the rotor head and blade system.
  • Altitude: Variations in altitude can alter the spray pattern, affecting droplet size and coverage area.
  • Direction Change: Sharp turns or changes in the flight path can lead to gaps or overlaps in the spray coverage.

  • Reducing Ground Speed: Slowing down the aircraft’s speed can help stabilise the spray pattern and ensure more consistent application.
  • Increasing Flight Height Above Ground Level (AGL): Flying at a higher altitude allows more time for the spray to settle evenly, reducing the impact of turbulence and downwash.
  • Adjusting Target Height: Maintaining an appropriate height above the target ensures that the spray reaches the intended area without significant drift or loss.

“Dragon’s Tail” effect due to ground speeds in excess of 6m/s

By considering these factors and making necessary adjustments, the performance of the spray system can be optimised, resulting in more precise and effective chemical application.

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