Soap Film Visualization of a 10 cm-Span Flapping Wing

Round 1

Reviewer 1 Report

This manuscript reports the use of soap film visualisation to study the fluid mechanics of a small flapping wing apparatus. Whilst the study of flapping wing fluid dynamics is instructive for the design of small air vehicles, the current manuscript has a number of shortcomings which the authors should address. Most notably, a number of instances of vague or poorly defined analysis and discussion of the results and a lack of detailed quantitative data. More specific comments are given below.

1. The manuscript needs to be thoroughly edited to correct grammar, syntax and spelling. There are too many instances of this to identify individually.
2. Page 1 lines 23-25 “Flapping wing MAVs . . . and forward flight [9-11].” This statement does not make sense and needs to be reworded.
3. Page 2 lines 70-71 “The volume of . . . of Equation (1).” What do you mean by “volume time-changing of the small element”? This needs to be clarified in the manuscript.
4. Figure 1. All parameters should be defined in the figure legend.
5. Page 5 lines 132-134 “Furthermore, the magnitude . . . 3D flow field.” These statements have not been adequately supported by the data presented or any reference to existing literature. It should be clear to all readers why you consider the thrust to be smaller than the lift and why you would cut and analyse a 2D slice from the 3D flow field.
6. Page 5 line 162 “. . . sustainable time for the soap-film.” You need to define what you mean by “sustainable time” in this context.
7. Page 5 lines 167-170 “The soap-film solution . . . the solution polarity.” The composition of this soap film solution needs to be properly defined so that the work is repeatable.
8. Page 5 line 172-173 “So, the soap-film . . . certain moment.” This statement is vague. Can you define the time length involved here rather than making a generalised statement?
9. Table 2. The figures for the lift in the wind tunnel test and the soap-film experiment are clearly very different. These differences have been explained in terms of significantly different travelling speeds but if the travelling speeds are having such an impact on the lift then there appears to be little value in comparing lift between two very different testing scenarios. This could have been addressed by using multiple different travelling speeds encompassing that used in the previous references. This also highlights a lack of depth to the quantitative data.
10. Page 14 lines 353-355 “After filtering the . . . wind tunnel data.” It is unclear which data this statement refers to in this paper. The connection between this discussion and the presented data needs to be clearer.
11. Page 14 lines 373-375 “Subject to the . . . in a normal manner.” This statement doesn’t make sense and needs to be rewritten.
12. Page 14 line 382 “ . . . PIV.” This abbreviation should be defined at this point in the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

You can also check it in the attachment.

In this work, the authors showed an interesting and low-cost method to visualize a 10 cm-span flapping wing. The topic is consistent with the journal of “fluids”. I believe this work can be published on “fluids”.

However, several questions need to be answered by the authors before it can be published.  

 

Main:

• Line 46-47: the authors aim to investigate the 2D flow field around a 10cm wingspan FWMAV by interact it with the soap-films along the longitudinal and lateral directions. Compared to the past works, what is the innovation point of this work? Please specific in the introduction part?
• Line 178: The authors mentioned that the sedimentation downward speed has been evaluated as about 0.25 cm/s. Could the authors specifically explain the methods to measure in this work.

 

• Line 277: The authors mentioned about a given standard color template. How to get the standard color template? Please describe it here. 

 

• Line 280: The authors mentioned that the standard color template is composed of 512 different colors with thickness from 0nm to 1000 nm. What if the film thickness is higher than 1000 nm? Can the authors detect that if the film thickness is higher than 1000 nm?

 

• Table 2: What are the possible reasons that the difference of lift force between wind tunnel test and soap-film experiment ae super large. 

 

• What are the reasons that the frequency of lift force and thrust force test are different (7.58Hz and 20.8Hz)?

 

Minor:

• Line 42: please add a “.” at the end of the sentence.

Comments for author File: Comments.docx

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Whilst the data presented is quite preliminary in nature and the force measurement results, particularly of the lift, need better comparison to another reference technique under similar experimental conditions, I feel that the manuscript has been improved to the extent that the approach is publishable.