Design and Verification of a Large-Scaled Flapping-Wing Aircraft Named “Cloud Owl”

Round 1

Reviewer 1 Report

This paper describes the analysis, development and flight testing of a large span avian-based flapping wing vehicle capable of efficient autonomous flight. It is a very useful study that can help future vehicle designs. 

Major comments:

1) If there is overlap with some of previous research by same authors, please provide appropriate reference next to the presented results. This will be important to understand the main contributions from the present paper. 

2) More details on control system design 

3) Improvement of general grammar in the article. 

4) Provide discussion on the major reasons for the vehicle achieving an endurance of 154 min, almost twice of that of previous flapping wing vehicles. 

Other comments:

1) Line 26 "high lift efficiency" - due to low Reynolds number situation, micro air vehicles have low aerodynamic efficiency. Please correct the statement.

2) Figure 1 - Can flight performance be defined and units added on y-axis

3) Line 61 - Can authors comment on stall speed of the vehicle

4) Line 123 - Please provide short description of the parameter estimation discussed in [15] and how the numbers in Table 3 were obtained.

5) Line 128 - should be "amplitude" instead of "frequency"

6) Eq 4 - Is this definition by authors or is there a reference used by other researchers for this?

7) Line 163 - Wingspan 1.82m - how did the authors arrive at this number? Were there any dimension constraints?

8) Figure 5 - how is wing deformation calculated

9) Line 198 - how was required lift and thrust determined? was weight of the aircraft iterated within the design loop

10) Figure 8 -can provide a larger image for clarity. If this result was a part of another paper published by the same authors, please indicate reference number.

11) Eq 7 - perhaps replace with small "g"

12) Line 247 - How was motor output torque measured? If the result is part of another paper please cite reference

13) Figure 9 - Please expand x-axis label as Torque to avoid confusion with Thrust

14) Line 251 - Please explain deceleration ratio requirement in this context

15) Line 253 - "deceleration ratio of 1.5" - is this a typo?

16) Line 287 - Did authors mean table 5 instead of Table 7

17) Figure 13 - a larger clear image with labelling of different parts will be good.

18) Line 298 - how did the authors define failure in the context of this study

19) Line 320 - "optimized parts" - please provide brief description on what were the improvements done to improve reliability.

20) Lines 321-322 - after 20H what happens to the failure?

21) Line 341 - was the flight control system commercially available? If so, please provide details of the sensors and controller units

22) Line 363 - can authors briefly describe how take-off is achieved and provide video link of a representative flight of the vehicle

23) How was the controller determined for executing the autonomous flight test?  Can authors provide brief description of how pitch, roll and yaw of the vehicle were achieved using the available actuators.

24) Section 3.2 - Heading is repeated please correct. 

Typos, grammar need to be improved

Author Response

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Reviewer 2 Report

Improve the quality of figures 1 and 12.

The Tables 2, 3, 4 and 6 exceeds the page format.

Make a comparison between simulation and experimental results.

It is ok.

Author Response

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Reviewer 3 Report

COMMENTS OF REVIEWER

General Comment: The manuscript entitled “Design and Verification of a Large-Scaled Flapping-wing Air-2 craft Named “Cloud Owl”” by Meng et al. has been reviewed. In this paper, a new bionic flapping-wing aircraft with large wing-14 span, named “Cloud Owl”, is designed. It weighs 980g and has a wingspan of 1.82 m. Although the reviewer is positive in terms of the topic, layout, academic writing, presentation pattern and content of this paper, there are some remarkable points should be answered and revised for publication in the journal of “Applied Sciences”. The final decision about the manuscript will be given after the examination of the revised paper.

Comment 1. A nomenclature is recommended to introduce all the variables and abbreviations used in the paper. Add a List of Nomenclature/abbreviation and their unit.

Comment 2. The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty). Please clarify that if your study is published, what type of gap will be filled in the literature ?

Comment 3. In my opinion, the pronoun "we" should not be used in articles.

For example, in line 50, the sentence of “we designed a flapping-wing aircraft named "Cloud Owl"” should be changed with “a flapping-wing aircraft named "Cloud Owl" is designed”.

Likewise, in line 373, the sentence of “we also record the flight data” should be changed with “the flight data are also recorded”.

Comment 4. The quality and resolution of Figure 22 (b), Figure 23 (a) and Figure 23 (b) should be enhanced.

Comment 5. The quality and content of the results and discussion section should be improved. If possible, new figures should be added with their explanations.

Comment 6. All assumptions made in the study should be explained.

Comment 7. The following two current articles related to aerodynamics of small and micro-air vehicles will be beneficial for the readers.

The impact of the ground on flow structure and aerodynamic characteristics of a double delta wing

 

Effect of ground on flow characteristics and aerodynamic performance of a non-slender delta wing

Author Response

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Reviewer 4 Report

- In the “Abstract” part, the content should be composed of the philosophy and methodology behind the newly-design rather than the specifications of the designed final aerial vehicle.

- In “Figure 1” there is no need to define any label for the y-axis such as “Flight performance”.

- In Page 2, line 53, where is the picture is defined as “shows a side view of the owls, highlighting the frame structure, electronics, and power system configuration.”

- In Table 1, the term “area” should be used rather than “surface”. (i.e. wing area, tail area)

- In Page 3, line 88, the number of Figure is incorrect since the same number was used before. Moreover, the figure is so small that is unreadable and should be expanded.

- Weight estimation is mentioned but there is no any information or explanation about the position or range limitations of center of gravity of the vehicle.

- In the tail design, the tail airfoil is said to be replaced with the NACA 0006 airfoil but there is no explanation about the idea behind it. In addition, the results of the aerodynamic analysis in XFLR5 are unreadable, in Figure 8. Moreover, the main parameters and conditions of the analyses are not given.

- In Table 6, the term “angle of attack” is used incorrectly as “attack angle”. Similar mistakes should be corrected.

- The “Conclusions” part must present the conclusions rather than a summary of the research.

- The language of the paper is found poor, and should be improved with respect to the scientific literature and terminology.

Author Response

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Round 2

Reviewer 4 Report

The graphs of Figure 8 (b) and Figure 9 are unreadable. In Figure 9, the labels of the axes are not readable.  Also, other graphs that are proposed to be corrected in my suggestions are not corrected properly. Headings of Table 2 include different fonts applied. In Figure 6, the airfoil should be given larger and clearer. 

 

The language of the paper is still poor.

Author Response

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