Evaluation of Spray Drift of Plant Protection Drone Nozzles Based on Wind Tunnel Test

Round 1

Reviewer 1 Report

The manuscript requires minor editorial corrections. It concerns in particular the adaptation to the requirements of the mdpi. You can expand the discussion. Other than that, I have no other significant comments.

Author Response

Dear reviewer,

Thank you for your support and valuable comments. We have modified and adjusted the paper accordingly as follow.

Firstly, we have included evaluations of other people's research on spray nozzles for crop protection drones in the wind tunnel. (Line 350-360)

Secondly, we added a detailed discussion on the drift data of crop protection drones by the field test. (Line 371-392)

Thirdly, we added a discussion on the relationship between downwash airflow and drift. (Line 393-408)

We hope our modifications meet your requirements.

Thanks again for your insightful suggestions.

 

Best,

Guobin Wang

 

 

Reviewer 2 Report

Generally, the paper was very well-written and the conclusions support the data presented. It is also very timely and important since country regulators around the world are searching for these type of data. Overall, I recommend publication for the manuscript but prior to this, some concerns need to be solved. Please see below:

1. We know that field experiments are necessary for drift assessment, whether to carry out further field experiments to compare different nozzles.

2. In your view, which are the most important factors affecting the drift of plant protection drones? Do you think that the use of UAV spraying is more limited than the other spraying types regarding spraying nozzles?

3. Please explain the origin of equ 4.

Author Response

Generally, The paper was very well-written and the conclusions support the data presented. It is also very timely and important since country regulators around the world are searching for these type of data. Overall, I recommend publication for the manuscript but prior to this, some concerns need to be solved. Please see below:

Question 1、 We know that field experiments are necessary for drift assessment, whether to carry out further field experiments to compare different nozzles.

Response: Thank you for this comment. Some field trials on drift distance have been conducted and published[1], but comparing of the two nozzles in the field were not conducted. Based on the current wind tunnel tests, further field drift tests are necessary.

 

[1] Guobin Wang, Yuxing Han, Xuan Li, et al, Field evaluation of spray drift and environmental impact using an agricultural unmanned aerial vehicle (UAV) sprayer[J]. Science of The Total Environment, 2020, 737:139793.

 

2、 In you view, which are the most important factors affecting the drift of plant protection drones? Do you think that the use of UAV spraying is more limited than the other spraying types regarding spraying nozzles?

Response: Pesticide spray drift is a important environmental problem for aerial application. Compared with the manned agricultural aircraft, the droplet drift of UAV is effectively reduced with the lower flight height and the downwash wind. According to the published papers, the 90% drift droplets will be within 20 m when the wind speed is below 3.3m/s. When it comes to the most influential factors, I think it is spray droplet size, wind speed and operating height. Plant protection drones may be more limited in nozzle selection than other spraying equipment. This is mainly due to the fact that the plant protection UAV still has the influence of the rotor wind field, and its spraying height is also higher than that of the ground equipment. The coupling of multiple factors may lead to higher requirements on the nozzle. However, this needs further experimental verification.

 

3、Please explain the origin of equ 4.

 

Response: Equ 4 was the fitting equation between the amount of downwind drift and the drift distance for each treatment. The fitting equation came from the least square method using origin 8.0 (OriginLab Co., LTD, Northampton, MA, USA). By plotting of the decay curve, a regression analysis in different steps was performed on the data to come to a final statistical drift prediction regression with the amount of downwind ground drift as the dependent variable and the downwind distance as independent variable. Using equ 4, the coefficient of determination (R2) was beyond 0.61 for each treatment.

 

Reference:

1）Wang, J.; Lan, Y.; Zhang, H.; Zhang, Y.; Wen, S.; Yao, W.; Deng, J. Drift and deposition of pesticide applied by UAV on pineapple plants under different meteorological conditions.Int.J.Agric.Biol.Eng. 2018, 11, 5-12, doi:10.25165/j.ijabe.20181106.4038.

2）Wang G, Han Y, Li X, et al. Field evaluation of spray drift and environmental impact using an agricultural unmanned aerial vehicle (UAV) sprayer[J]. Science of the Total Environment, 2020, 737: 139793

Author Response File: Author Response.docx

Reviewer 3 Report

This paper describes the authors’ experiments in evaluating the spray drift of drone nozzles using wind tunnel tests, to investigate the potential drift risk, and therefore the environmental risk of drone spraying in agriculture. The authors focused on two types of nozzles, namely the hydraulic nozzles and the centrifugal nozzle. The droplet size was measured using a laser diffraction instrument, and spray drift was measured using sampling lines at the aft section of the wind tunnel test chamber. The results indicated that the centrifugal nozzle had a higher spray drift than the hydraulic nozzles.

 

Overall comments:

As I am not an expert in nozzle design and agricultural chemical spraying, my comments will focus on the experimental design and the analysis. Overall, the authors explained the aim of the project very well and introduced to the readers the problem of spray drift with enough references to the literature. The description of the materials and methods is clear and adequate. The results are also meaningful with detailed analysis.

 

One thing I want to comment on is the authors did not mention the assumed type of drones on which these nozzles would be installed. The experiments would be accurate if the authors assume the nozzles would be installed on fixed-wing type drones, as there would only be a forward air velocity. However, most unmanned spraying drones are of the multirotor type. The spray would experience downwash from the drone’s propellers, which the authors did not consider in their experiments. The authors should state this very clearly in the methodology and perhaps in the title as well.

 

Detailed comments:

Line 156

What is the typical spray altitude? 0.8 m above the wind tunnel floor seems a bit arbitrary. It would be great to include a reference on the typical spray altitude.

 

Line 168

Using different sampling line arrangements for different nozzle types doesn’t sound very consistent. Would the different vertical sampling line densities affect the droplets that would otherwise deposit on the ground sampling lines?

 

Line 199

The authors should include an explanation of what the calibration factor Fcal is.

 

Line 231

It is not clear to me why lowering the spray pressure would give a larger test range.

 

Line 318

Most of the discussion seems to belong to the introduction section. The discussion should focus on discussing the significance of the results.

Author Response

Dear reviewer,

Thank you for your support and valuable comments. We have modified and adjusted the paper accordingly. Please refer to the attachment for detail.

Thanks again for your insightful suggestions.

Best,

Guobin Wang

Author Response File: Author Response.docx

Reviewer 4 Report

Dear Authors,

 

 

 

Thank you for the opportunity to review your manuscript submitted for consideration in the Agriculture journal.

 

 

 

The manuscript is a research article titled “Evaluation of spray drift of plant protection drone nozzles based on wind tunnel test”. The author’s proposal is that the results of this experiment provide a reference for the selection of nozzles and the addition of spray adjuvants. Further clarifying the spray drift characteristics of drones until a drift prediction model is available is still the focus of research.

 

 

 

I carefully and attentively read the entire manuscript and noted that the study is should be improved. Overall, the study neither provides solid results nor sufficient discussion/conclusion to support the methods applied. Conversely, numerous studies with similar proposals already exist, which makes the following study proposal non-exclusive.

 

https://doi.org/10.3390/app11167258

 

https://doi.org/10.3390/drones6080204

 

https://doi.org/10.3390/drones6110329

 

Furthermore, the manuscript does not provide enough information to justify the importance of the approach. Recent studies on the topic should be discussed and the gap should be clearly presented. Therefore, I do not recommend the study for publication.

Best regards.

Author Response

Dear reviewer,

Thanks for your valuable comments. Unlike other studies, the main innovation of our research focuses on the evaluation of centrifugal nozzles of Drones, which is not found in other papers. Thank you very much for providing the three references, which we have added and discussed in our paper.

We have reorganized the discussion section, compared our results with others, and made extensive revisions. The main additions to the discussion include: 1) other’s results of the field drift and wind tunnel tests for drones (L350- L360); 2) the impact of downwash airflow on drift (L393- L408).

Thanks again for your insightful suggestions.

Best,

Guobin Wang

Round 2

Reviewer 3 Report

I am satisfied with the response from the authors to my comments.

Reviewer 4 Report

The authors have improved the manuscript and I can now recommend it for publication.