Cyclic Hailstone Impacts: Evaluating Aircraft Canopy Resilience
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have successfully established an experimental procedure for assessing the impact of hailstones on aircraft canopies. While bird strike investigations have long been a mature field of research, supported by both experimental and numerical studies, hailstone impact remains comparatively less explored. Therefore, this study is praiseworthy, as it addresses a relatively under-investigated phenomenon with limited literature.
However, since the present work focuses only on artificial hailstones, it is recommended that future studies complement these experimental findings with numerical simulations. Such efforts would allow broader parametric investigations and set a benchmark for future researchers to develop validated numerical models in this domain.
Finally, the authors should revise the conclusion section to more explicitly highlight the current study's main findings.
Author Response
Manuscript ID: aerospace-3912263
CYCLIC HAILSTONE IMPACTS: EVALUATING AIRCRAFT CANOPY RESILIENCE
The authors highly appreciate the detailed valuable comments of the Reviewers concerning our paper. The suggestions were very helpful for us, and the authors incorporated all of them in the revised version of the manuscript by introducing major improvements.
The answers to the Reviewers’ comments have been submitted as follows. In this regard, the required modifications and added descriptions according to the comments of each Reviewer have been marked up using the “Track Changes” function in the text of the revised manuscript.
Author's Rejoinder to Reviewers' Comments
The authors thank Reviewers for their time and efforts to provide constructive comments and suggestions. All the reviewers’ comments have been incorporated in the revised manuscript as detailed below.
The reviewers’ comments are quoted in bold and italics, followed by the authors' response.
Reviewer#1:
The authors have successfully established an experimental procedure for assessing the impact of hailstones on aircraft canopies. While bird strike investigations have long been a mature field of research, supported by both experimental and numerical studies, hailstone impact remains comparatively less explored. Therefore, this study is praiseworthy, as it addresses a relatively under-investigated phenomenon with limited literature.
However, since the present work focuses only on artificial hailstones, it is recommended that future studies complement these experimental findings with numerical simulations. Such efforts would allow broader parametric investigations and set a benchmark for future researchers to develop validated numerical models in this domain.
The authors thank the reviewer for the positive remarks regarding our experimental procedure. The authors acknowledge the recommendation for future studies to include numerical simulations to supplement our findings. While our current focus is on artificial hailstones, the authors agree that numerical analyses could significantly enhance the understanding of the impact phenomena. The authors will address this point in discussion section of the revised manuscript and suggest that future research should incorporate both experimental and numerical approaches to build a comprehensive understanding of hailstone impacts. Please refer to Lines 12-17 on Page 18 of the revised manuscript.
Finally, the authors should revise the conclusion section to more explicitly highlight the current study's main findings.
The authors appreciate the reviewer’s suggestion. In the revised manuscript, the authors have rewritten the conclusion section to emphasize the key findings more clearly, including a summary of the experimental results and their implications for aircraft safety. Please refer to Lines 7-12 on Page 18 of the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsNote that the submitted manuscript has NOT been formatted on the MDPI template.
Without line numbers and without the cited references in MDPI format, it is difficult to review.
In general, the use of the English language poses no problems. It is largely idiomatic, with only a few concerns.
Throughout the manuscript, it would help if the impact velocities are also given in pilot customary units of knots in addition to m/s. i.e. 120 m/s is ~230 knots.
First paragraph of Section 3 notes a flight speed of 200 KEAS (at what altitude? at sea-level standard day 200 KEAS is 200 knots true whereas at 20,000-ft AGL (FL200) 200 KEAS is ~275 knots true airspeed (~141 m/s). Please clarify the requirements better.
There should be an additional paragraph explaining why the 120 m/s test condition represents a nominal compliance check (or a factor-of-safety type check) based on the design conditions for the given canopy.
Please add a proper reference to document TBTEU-5210-FWS-134, called out in the manuscript p.5. An additional sentence or two summarizing this document would strengthen the paper.
Please add a proper reference to document MIL-PRF-8184, called out in the manuscript. p. 6. An additional sentence or two summarizing this US MIL standard would strengthen the paper. Also explain why the US standard is germane for applications worldwide.
Discussion of dual-use technology to build hail resistant roofing tiles (p. 17) not really germane to the rest of the manuscript - best to delete. What would the requirements be? it would seem to this reviewer that the aerospace application is much more rigorous.
Author Response
Manuscript ID: aerospace-3912263
CYCLIC HAILSTONE IMPACTS: EVALUATING AIRCRAFT CANOPY RESILIENCE
The authors highly appreciate the detailed valuable comments of the Reviewers concerning our paper. The suggestions were very helpful for us, and the authors incorporated all of them in the revised version of the manuscript by introducing major improvements.
The answers to the Reviewers’ comments have been submitted as follows. In this regard, the required modifications and added descriptions according to the comments of each Reviewer have been marked up using the “Track Changes” function in the text of the revised manuscript.
Author's Rejoinder to Reviewers' Comments
The authors thank Reviewers for their time and efforts to provide constructive comments and suggestions. All the reviewers’ comments have been incorporated in the revised manuscript as detailed below.
The reviewers’ comments are quoted in bold and italics, followed by the authors' response.
Reviewer#2:
Note that the submitted manuscript has NOT been formatted on the MDPI template. Without line numbers and without the cited references in MDPI format, it is difficult to review.
The authors sincerely apologize for this oversight. The authors have reformatted the manuscript according to the MDPI template, ensuring that line numbers and references adhere to the required format. This revision should facilitate a more straightforward review process. Please refer to the references and page lines of the revised manuscript.
In general, the use of the English language poses no problems. It is largely idiomatic, with only a few concerns. Throughout the manuscript, it would help if the impact velocities are also given in pilot customary units of knots in addition to m/s. i.e. 120 m/s is ~230 knots.
Thank you for this valuable suggestion. The authors have added the conversion of impact velocities from m/s to knots throughout the manuscript where applicable. Please refer to Lines 4-5 on Page 9 of the revised manuscript.
First paragraph of Section 3 notes a flight speed of 200 KEAS (at what altitude? at sea-level standard day 200 KEAS is 200 knots true whereas at 20,000-ft AGL (FL200) 200 KEAS is ~275 knots true airspeed (~141 m/s). Please clarify the requirements better.
The authors appreciate the reviewer's attention to detail. The authors have revised the paragraph in Section 3 to clearly indicate the altitude context for the flight speed of 200 KEAS, specifying that at standard day conditions. Please refer to Section 3 in Lines 25-31 on Page 5 of the revised manuscript.
There should be an additional paragraph explaining why the 120 m/s test condition represents a nominal compliance check (or a factor-of-safety type check) based on the design conditions for the given canopy.
The authors have included an additional sentence in the methods section explaining the rationale behind selecting the 120 m/s test condition as a factor-of-safety type check requested by Turkish Aerospace Industries, Inc. (TAI) and Volo Composites & Engineering. Please refer to Lines 2-4 on Page 9 of the revised manuscript.
Please add a proper reference to document TBTEU-5210-FWS-134, called out in the manuscript p.5. An additional sentence or two summarizing this document would strengthen the paper.
The authors have added the reference for TBTEU-5210-FWS-134 as requested by the Reviewer 2. Please refer to Lines 20-24 Page 5 of the revised manuscript.
Please add a proper reference to document MIL-PRF-8184, called out in the manuscript. p. 6. An additional sentence or two summarizing this US MIL standard would strengthen the paper. Also explain why the US standard is germane for applications worldwide.
The reference to MIL-PRF-8184 has been included to the revised manuscript. Please refer to Lines 13-16 on Page 6 of the revised manuscript. The authors have added a discussion highlighting the relevance of this standard to global applications, noting that adherence to rigorous US military standards can enhance the reliability and safety of aerospace components worldwide, benefiting international manufacturers and operators by providing a common framework for quality assurance. Please refer to Lines 17-23 on Page 18 in the discussions of the revised manuscript.
Discussion of dual-use technology to build hail resistant roofing tiles (p. 17) not really germane to the rest of the manuscript - best to delete. What would the requirements be? it would seem to this reviewer that the aerospace application is much more rigorous.
The authors appreciate the reviewer’s suggestion regarding the relevance of the dual-use technology discussion. The authors have opted to remove this section from the manuscript to maintain focus on the primary research topic of hailstone impact on aircraft canopies. By concentrating on aerospace applications, the authors ensure that the manuscript remains tightly aligned with the underpinning experimental studies and their implications for flight safety. The related sentence on Page 17 in the original manuscript has been removed for the revised manuscript. Please refer to the conclusion on Page 18 of the revised manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
One of the factors which significantly exerts a negative influence on flight safety apart from bird strikes is a potential hail impact on the aircraft canopy. The consequence of breaking the windshield is likely to cause serious injuries of the pilot, which will prevent him from continuing the flight. Therefore the subject regarding experimental simulations of hailstones impact on the canopy discussed in the article is important in the era of increasing air traffic density. Nowadays, experimental methods are exploited to model various components of aircraft in order to conduct simulated crashworthiness tests. Generally the paper is organized well. It contains all main parts of an original science paper. The abstract is written correctly. Chosen methods for the experimental tests are suitable and efficiency.
Nonetheless, I have got several remarks regarding the paper.
Below the most important ones are specified.
- On page 6, the following inaccuracies were identified:
– the material data for the sample simulating the canopy are missing.
– the reference to Figure 1 is incorrect; Figure 1 is located on page 3 and presents the effects of hail impact.
– the statement that Figure 3 shows the mounting of the sample on the test stand is incorrect. - Page 9: In my opinion, the use of the term “canopy” in Chapter 5, which presents the test results, may be misleading, as it suggests that the experiments were conducted using an actual canopy. In reality, the tests were performed with a flat plate made of PAMMA. This situation may cause misunderstanding among readers.
- In my opinion, the results could be compared with the results obtained by others researchers.
Editing remarks:
Page 5: there is “velocity of 200 KEAS” should be “velocity of 200 kt EAS”
Figure 2 and 9-16 are poor quality and are low readable.
Author Response
Manuscript ID: aerospace-3912263
CYCLIC HAILSTONE IMPACTS: EVALUATING AIRCRAFT CANOPY RESILIENCE
The authors highly appreciate the detailed valuable comments of the Reviewers concerning our paper. The suggestions were very helpful for us, and the authors incorporated all of them in the revised version of the manuscript by introducing major improvements.
The answers to the Reviewers’ comments have been submitted as follows. In this regard, the required modifications and added descriptions according to the comments of each Reviewer have been marked up using the “Track Changes” function in the text of the revised manuscript.
Author's Rejoinder to Reviewers' Comments
The authors thank Reviewers for their time and efforts to provide constructive comments and suggestions. All the reviewers’ comments have been incorporated in the revised manuscript as detailed below.
The reviewers’ comments are quoted in bold and italics, followed by the authors' response.
Reviewer#3:
One of the factors which significantly exerts a negative influence on flight safety apart from bird strikes is a potential hail impact on the aircraft canopy. The consequence of breaking the windshield is likely to cause serious injuries of the pilot, which will prevent him from continuing the flight. Therefore the subject regarding experimental simulations of hailstones impact on the canopy discussed in the article is important in the era of increasing air traffic density. Nowadays, experimental methods are exploited to model various components of aircraft in order to conduct simulated crashworthiness tests. Generally the paper is organized well. It contains all main parts of an original science paper. The abstract is written correctly. Chosen methods for the experimental tests are suitable and efficiency. Nonetheless, I have got several remarks regarding the paper. Below the most important ones are specified.
The authors appreciate the reviewer’s acknowledgment of the topic's relevance. The authors have expanded our introduction to further emphasize the implications of hail impacts on aviation safety and how these issues relate to the growing volume of air traffic. This enhancement aims to underline the urgency of addressing this critical safety concern. The authors appreciate Reviewer’s acknowledgment of our methods, which reflects our effort to ensure the robustness of our experimental design.
On page 6, the following inaccuracies were identified:
– the material data for the sample simulating the canopy are missing.
The authors acknowledge this oversight and have added a detailed section outlining the material data used to simulate the aircraft canopy, any relevant specifications, to enhance the manuscript's completeness and clarity on Lines 11, 13-18, 23 on Page 6 of the revised manuscript. However, the more mechanical data for the sample simulating the canopy is currently unavailable for sharing due to its military purpose and the ongoing nature of the project within the framework of the Turkish Basic and Primary Training Aircraft (TBTEU) project, the more mechanical properties will be provided in subsequent studies focusing on the FE model components after this research is completed.
– the reference to Figure 1 is incorrect; Figure 1 is located on page 3 and presents the effects of hail impact.
The authors would like to thank Reviewer 3 for bringing this error to our attention. The authors have made the necessary corrections regarding the references to Figure 1 in the revised manuscript. Please refer to the caption and reference of Figure 1 in the revised manuscript, as well as the references in Lines 27-28 on Page 2. However, due to page limitations, the placement of Figure 1 will remain on Page 3.
– the statement that Figure 3 shows the mounting of the sample on the test stand is incorrect.
The authors apologize for the confusion. The authors have revised the text to clarify the purpose and content of Figure 3. Please refer to Line 33 on Page 6 and Lines 1 and 9 on Page 7 of the revised manuscript. All figure references throughout the manuscript have been reviewed and verified.
Page 9: In my opinion, the use of the term “canopy” in Chapter 5, which presents the test results, may be misleading, as it suggests that the experiments were conducted using an actual canopy. In reality, the tests were performed with a flat plate made of PAMMA. This situation may cause misunderstanding among readers.
The authors thank the reviewer for bringing this important issue to our attention. To avoid any potential misunderstandings, the authors have added the sentences in Chapter 5 to enhance the manuscript's clarity and better communicate the specifics of our experimental approach. Please refer to the Lines 22-26 on Page 8 and Lines 1-2 on Page 9 of the revised manuscript.
In my opinion, the results could be compared with the results obtained by others researchers.
Yes, the authors agreed with the Reviewer 3 that a comparative analysis would enhance the findings. Due to manuscript length constraints and ongoing research, we will include comparisons with finite element simulations and relevant studies in future publications. Please refer to Lines 12-17 on Page 18 of the revised manuscript.
Editing remarks:
Page 5: there is “velocity of 200 KEAS” should be “velocity of 200 kt EAS”
The authors have corrected the terminology to "velocity of 200 kt EAS" on Page 5 to reflect the proper units accurately. Please refer to the Lines 28-32 on Page 5 and Lines 1-2 on Page 6 of the revised manuscript.
Figure 2 and 9-16 are poor quality and are low readable.
The authors are sorry for the poor quality of Figures 9-16 due to lighting issues caused by AC lighting, which resulted in artifacts in the images. We have taken steps to enhance the clarity and readability of Figures 2 and 9-16. Please refer to Figure 2 of the revised manuscript. However, for Figures 9-16, while contrast and brightness adjustments were made to improve the overall quality, readability was still affected. All figures have been replaced with higher-resolution images (300 dpi). Since the photos were taken at the moment of impact, retaking them is not possible. The resolution has been enhanced; for ongoing studies, these issues will be addressed by using DC lighting for future photos. To facilitate this, a 185-W LED light connected to a converter, which allows the light to operate on DC instead of AC, has been acquired to eliminate flickering detected in video footage captured at high frame rates. This setup ensures sufficient lighting for the use of a high-speed camera.
The authors believe that these changes address the concerns raised and improve the overall quality of the manuscript. Thank you for your thorough review and constructive feedback.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have carefully considered all reviewer feedback and made appropriate revisions.
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors have addressed all concerns from initial review. Good to go.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
Thank you for considering my suggestions. In my opinion, the article can be moved to the next stages of the publishing process.
