Aerodynamics from Cursorial Running to Aerial Gliding for Avian Flight Evolution
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors:
The manuscript is an aerodynamic investigation from cursorial running to aerial gliding to describe the avian flight evolution. This subject is particularly important due to the innovation and the promising results. The paper is of interest for the potential readers of Applied Sciences Journal.
The manuscript has been considerably improved since the previous submission. Now the scientific content is adequate for journal publication.
The abstract is extensive enough and well written.
INTRODUCTION: The introduction is well written and structured. However,
Split Figure 2 into two different figures, Fig 2a and Fig 2b. I would suggest a legend of color or something similar to explain better the figures.
Section 6: conclusions
The conclusions are not clearly described. Please, explain in more detail all the conclusions and findings of the current study. The first paragraph is too long. The conclusions have to be based on the current results and acutely described and compared.
Please, check the whole manuscript, there are some typos and misprints. Please be consistent in your writing and format style and apply the manuscript correctly to the journal template.
Please revise the Reference style along the paper. Also the list of references and apply the MDPI ref style
Author Response
Please see the attached PDF file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please see the comments below.
1) Length of the manuscript can be reduced by removing the explanation for trivial things like
Eq. 10, 11, 12, 14 are well known standard equations and need not be given in such details.
2) Lines 399-402 explaining the stability of flight is not clear. Please elaborate
Author Response
Please see the attached PDF file.
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper sets forth a new hypothesis to explain how flight developed in the ancestors of modern-day birds. Based on an analysis of flight trajectories reconstructed using fossil-derived body parameters for the Anchiornis Huxleyi, they hypothesize that paravians could exploit the strong winds along mountain sides to lift off the ground and glide, allowing them for instance to glide to tall trees further downhill. Gliding down from steep slopes, in time paravians would have adapted their feathers to improve their aerodynamic performance, and learned to steer in flight by changing the orientation of their wings.
The authors present an interesting theory to explain the origins of avian flight and support it with simple but plausible calculations. The content may potentially be of use also to the bio-inspired MAV community. I have some minor remarks:
- Please revise the language and grammar. Although the article is fairly readable, there are numerous small errors that detract from the overall clarity. Also note that “plain” should be spelt “plane”.
1. Introduction: please emphasize the scope of the paper more clearly. It would also be helpful to add a short overview of the structure of the rest of the paper.
2. The final paragraph of the introduction seems misplaced and not strictly necessary. Consider integrating it in sec. 2, if needed, or removing it.
3. The initial velocity is sometimes called v_t and sometimes v_1.
4. Some of the equations are unnecessary:
(a) Eqs 9-12. Least squares regression is common knowledge, it is enough to mention the approach and show eqs. 8 and 13
(b) Eq. 14: Runge Kutta integration is likewise well-known. Sec 4.3 can be reduced to one sentence included in the previous sections.
(c) Eq 16. These equations introduce new variables at the end of the paper, and are not central to the content of the article. Even without showing the equation, it is clear that flexible body parts can be used to control orientation.
4. Figures
(a) Should be in vectorised format, to avoid resolution issues
(b) In all legends, v2 has no units
(c) It is not immediately obvious how some of the figures differ from each other and the captions are not helpful. E.g. figures 3, 4 and 5 are for different slope angles, but this is not mentioned in the captions, which are identical for all three figures.
(d) Brown lines on brown background are almost invisible (e.g. fig 5b, line for v2=12)
(e) Caption fig. 6. “45m/s”à this velocity never occurs in the figure
(f) Fig 6: the caption is far too long and leads to poor readability. I recommend to mention the key parameters for each plot in the subcaption: e.g. subfig (b) Anhiornis trajectories for mountain slope = 30deg, v1 = 8m/s. Furthermore, add a legend to each figure showing the velocity ranges for cases 1-3.
5. Table 2. The numbers under case 1-case 3 should have units and be labelled in the column heading (v_2?), not just described in the table caption. Does the range refer to the difference in wind between bottom and top of the slope?
6. Conclusions: please add a sentence describing how the hypothesis is supported. Lines 412-414: I suggest moving the generalisation to MAVs to the end, as it currently interrupts the discussion of the hypothesis, which continues in lines 415-418. An example of how the findings could benefit MAVs would also be helpful.
7. Consider showing fig. S11 in the main text, perhaps with added arrows clarifying the wind flow.
Author Response
Please see the attached PDF file.Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Review of: Aerodynamics from Cursorial Running to Aerial Gliding for Avian Flight
This article presents an analysis of avian lift off, dependent on ground conditions such that flight trajectories may be established. These results are then used to “validate” competing models for the origination of flight.
To this reviewer, the article lacks technical rigor required for an archival journal. It is poorly organized and tedious to read. The grammar is rather poor; it needs careful proof reading by a suitable native English speaker.
The analysis is also simplistic; it’s essentially 2D, finite effects are not accounted for; neither is ground effect.
Fig. 2, which is central to the formulation is poorly defined, and likely contains errors. The authors need to differentiate between the velocity of the animal, and the velocity it experiences due to its motion. Despite, these issues, I believe Eq. 2 is correct.
The analysis is missing significant amounts of information; mass, reference area, calculated CL, CD, etc values. Are the values reasonable?
Because of these short comings, I do not think this article is suitable for publication. It needs a lot more effort.
Reviewer 2 Report
Dear Author, please find attached my comments
Regards
Comments for author File: Comments.pdf
Reviewer 3 Report
The manuscript provides interesting insight into the gliding flight of feathered paravians. The key element in the trajectory prediction is the accurate estimate of Lift, drag, and wind conditions.
A few typos need to be corrected, for example, the spacing is not proper in line 151, page 5.
The below-mentioned comments need to be addressed by the authors.
1) How good is the 3D drag estimate?
2) In supplementary material, it is mentioned that the reduction in lift happens after 40 degrees of angle of attack. What could be the reason for such high stall angle of attack?
3) What is the role of Aspect Ratio in the trajectory prediction?
4) There is no mention of longitudinal and lateral stability. So is it an assumption that the stability is maintained? If so then need to mention that explicitly in the manuscript.
