Calculating Spray Timing

Introduction

As an operator, being able to quickly analyse a project and make an accurate prediction of the time involved in completing the treatment is fundamental to successful operations. Not only will it allow you to provide accurate quotes, but it will also help to manage client expectations and plan operations to make best use of favourable weather conditions.

Whilst the use of modern flight planning software has negated the need for a lot of complex field planning, the ability to manually perform these calculations is still a valuable tool for a competent operator.

Example Calculation

Let’s calculate the time required to treat a 100-hectare area with an agricultural drone using a CDA nozzle system.

First, break down the job given some basic known parameters:

• Spray Width: 7.5 meters
• Overlap: 25%
• Area to Cover: 100 hectares (1 hectare = 10,000 square meters, so 100 hectares = 1,000,000 square meters)
• Flight Speed: 5 meters per second
• Flight Height: 4.5 meters (not directly relevant for time calculations)

Calculations

Effective Spray Width:

The effective spray width must be calculated as it becomes reduced due to the 25% overlap.

Effective Spray Width = 7.5m x (1 – 0.25) = 7.5m x 0.75 = 5.625m

Number of Passes Required:

To cover the entire area we need to calculate how many passes the drone will need to make.

Number of Passes = Total Area / (Effective Spray Width x Length of Each Pass)

However, to simplify the calculation, we can determine the total distance the drone needs to fly.

Total Distance = Total Area / Effective Spray Width = 1,000,000 sqm / 5.625m = 177,778m

Time Required:

Now, using the flight speed of the drone, we can calculate the total time needed to cover the area.

Time Required = Total Distance / Flight Speed = 177,778m / 5m/s = 35,555 seconds

Converting to Hours:

Finally we can make this a usable figure by converting the result into hours.

Time in Hours = 35,555 seconds / 3600 seconds per hour = 9.87 hours

Conclusion

The drone will require approximately 9.87 hours to cover an area of 100 hectares with a CDA nozzle system spraying at a width of 7.5 meters with a 25% overlap, flying at a speed of 5 meters per second.

Other Considerations

The above calculations are based on an open, flat flight area with no obstacles. These calculations do not take into consideration:

• Equipment setup time, pre-flight checks, or post-operation cleaning and pack-up.
• The distance or time taken to turn around at the end of each row/pass.
• Refuelling/reloading time.
• Ferry time/distance at the start and end of each flight.
• The time taken to navigate around obstacles.
• Buffer zone or boundary flights.

For areas with undulating terrain, obstacles, no-spray zones such as waterways and native vegetation, flight efficiency, and in certain instances spray system performance (swath integrity) could affect operational efficiency.