Fall Testing of the Personal Airborne Equipment Backpack: Ground and Flight Testing
Round 1
Reviewer 1 Report
The article „The fall test of the personal airborne equipment backpack – ground and flight testing” has described partially an extraordinary experimental investigation under free fall conditions. Although there are some parts in the manuscript which might be corrected for better understanding.
One of my concerns is the chosen rope type. The authors dealing with rope type which corresponds to the EN 564 standard type. There is two other standard which may be used for similar purpose: static rope with safety quotient 1.0 (EN 1891) and dynamic rope with safety quotient 1,77 (EN 892). The dynamic rope could be more suitable for the purposes described in the manuscript. It would be nice to mention in the manuscript the reason of using EN 564 type of rope.
My second remark is regarding the rope length during calculations. The mentioned formulas are correct, but they are applicable for center of mass. In the manuscript, on the other hand, authors using the length of rope, when calculating the free fall time or the maximum force during impact. It would be more correct if authors during calculations take into account the shift of center of mass as a length. That may cause the difference between calculated and measured values mentioned in line 262 of the manuscript: “This way measured values can be considered as correct”. The discrepancy is almost 10% between measured and calculated values.
Third remark: it is not clear what authors trying to say in the manuscript 299 line: “…the force impact values will achieve lower figures in this case.” Does it mean, that the peak values in the figure 12. do not reach the adjacent value?
Fourth remark: the line 329 in the text: “it is difficult to define ropes exact operation life”. The manufacture standards for the rope safety regulation says 5 year of storing plus 5 years of using.
Author Response
Dear Reviewer 1:
Thank you for your review. We revised the article „The fall test of the personal airborne equipment backpack – ground and flight testing” according to your review.
- Your remark: One of my concerns is the chosen rope type. The authors dealing with rope type which corresponds to the EN 564 standard type. There is two other standard which may be used for similar purpose: static rope with safety quotient 1.0 (EN 1891) and dynamic rope with safety quotient 1,77 (EN 892). The dynamic rope could be more suitable for the purposes described in the manuscript. It would be nice to mention in the manuscript the reason of using EN 564 type of rope.
Our Answer: The following refinement has been inserted in the article to select the rope:
The type of rope for testing was designed by the backpack manufacturer, taking into account two basic rope requirements. The first was sufficient strength and the second the smallest possible rope diameter to take up as little volume as possible after being placed in the backpack. Therefore, a rope according to EN 564 standard with a diameter of 6 mm was used in the tests. For example, dynamic ropes according to EN 892, which would be more advantageous for the absorption of impact forces, are only produced with a larger diameter.
- Your remark: My second remark is regarding the rope length during calculations. The mentioned formulas are correct, but they are applicable for center of mass. In the manuscript, on the other hand, authors using the length of rope, when calculating the free fall time or the maximum force during impact. It would be more correct if authors during calculations take into account the shift of center of mass as a length. That may cause the difference between calculated and measured values mentioned in line 262 of the manuscript: “This way measured values can be considered as correct”. The discrepancy is almost 10% between measured and calculated values.
Our Answer: The following refinement has been inserted in the article:
The values measured in this way can be considered correct with the accepted simplification that the length of the rope and its calculated elongation were used in the calculations. It would be more accurate to use a center of gravity shift in the calculations. But measuring the center of gravity shift in drop tests (especially flight tests) is difficult to implement. Therefore, the calculations are performed with the accepted simplification.
- Your remark: It is not clear what authors trying to say in the manuscript 299 line: “…the force impact values will achieve lower figures in this case.” Does it mean, that the peak values in the figure 12. do not reach the adjacent value?
Our Answer: The peak values in the figure 12. reach real measured values. Modified sentence in the article:
These tests confirmed a prediction that absorption of the fall energy by the rope anchored into the elastic system of the parachute gear on a human body (compared to fixing to a fixed inelastic point) can be more effective, and the force impact values will achieve lower figures in this case.
- Your remark: The line 329 in the text: “it is difficult to define ropes exact operation life”. The manufacture standards for the rope safety regulation says 5 years of storing plus 5 years of using.
Our Answer: Added sentence to the article:
Ropes with a lifetime of 10 years are also currently available. However, in the case of free fall capture with a higher value of the fall factor, manufacturers generally do not recommend further use. The value of this fall factor varies from manufacturer to manufacturer and ranges from approximately 0.5 to 1.5. Of course, it is also important whether the rope was stressed over the sharp edge or not.
We hope that our corrections met your expectations. If the article will be approved for publication, we will use MDPI service for English revisions. Thank you for your consideration.
Sincerely,
Ing. Alica Tobisová, PhD., Ing. Paed-IGIP
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper verifies the functionality and reliability of a personal airborne equipment backpack TL-98 rope through ground and flight tests, it is interesting, but there are some problems that need to be improved.
- The abstract needs to be improved, it does not describe clearly the methods used and the experimental findings.
- "Another objective of this research has been a collection of knowledge in order to define TL-98 rope lifetime", the contribution of this sentence in the abstract is not obvious in the paper and is only mentioned in the conclusions, which is recommended to add relevant content in the paper.
- If I understand correctly, it is actually a verification of the functionality and reliability of TL-98 ropes, right, so does the article title need to be adjusted?
- There are few studies related to the functionality and reliability of TL-98 ropes described in the introduction, so are there any other similar studies in the field? If so, it is recommended to add descriptions of relevant studies.
- It is suggested to add the organization of the paper at the end of the introduction.
- Section 2 Materials and Methods should have additional secondary headings to make the structure of the article clearer.
- In the paper, 5 m of rope was used for the experiment, and one meter of the rope was used for tying the knot, which should also be given at line 86.
- Line 124, the unit of memory is dates?
- There are three types of backpack weights in the paper, 50kg, 60kg and 28kg, why did the authors choose the 28kg backpack for the experiment?
- Why did the authors do 3 ground tests and only one flight test, and what was the difference between the 3 ground tests?
- The data obtained from the experiments declared in the introduction are added to the manual, so is the number of experiments in the paper sufficient as a description in the manual?
- There are italicized and non-italicized units "N" in the paper, please unify them.
- Line 275 “cumulative number of falls has been documented in [10], [11] and [12]” should be “cumulative number of falls has been documented in [10-12]”. Line 327 “The tasks included in [13] and [14,15] became basics…”should be “The tasks included in [13-15] became basics…”.
Author Response
Dear Reviewer 2:
Thank you for your review. We revised the article „The fall test of the personal airborne equipment backpack – ground and flight testing” according to your review.
- Your remark: The abstract needs to be improved, it does not describe clearly the methods used and the experimental findings.
Our Answer: We modified the abstract:
This article has been dedicated to representing a functionality and reliability of a personal airborne equipment backpack TL-98 before its launching in military parachute operations. An objective of this project has been a verification of TL-98 characteristics which could be important in terms of safety of parachute operation – i.e., the functionality and reliability during flight and fall tests. A major effort within this research has been focused on the fall tests of TL-98 in standard parachute operational conditions. By the flight tests was verified the strength of the backpack's anchorage points (by which the backpack is attached to the parachute harness) when dropping from the aircraft at the maximum operating speed and at the maximum operating weight of the backpack increased by a safety factor of 1.2. During the fall tests of the backpack after its disconnection from the parachute harness (ground tests and test during the test jump), the strength of the backpack's anchoring eye and the strength of the rope with which the backpack is connected to the parachute harness were verified. Another objective of this research has been a collection of knowledge in order to define TL-98 rope lifetime which serves for throwing off TL-98. For this purpose, there have been compiled methods applicable for ground verifications and the project has been competed upon flight tests. To fulfil this goal, the impact forces in the rope during the backpack's fall were measured using a force sensor. The values of the impact forces were then calculated and compared with the values from the experiment. Using experimentally obtained results and their comparison with the calculated results, the lifetime of the TL-98 rope for parachuting operation was determined on the basis of predetermined rules.
- Your remark: "Another objective of this research has been a collection of knowledge in order to define TL-98 rope lifetime", the contribution of this sentence in the abstract is not obvious in the paper and is only mentioned in the conclusions, which is recommended to add relevant content in the paper.
Our Answer: We modified the abstract plus in the conclusions we highlighted in a separate paragraph the result regarding the determination of the life of the rope.
- Your remark: If I understand correctly, it is actually a verification of the functionality and reliability of TL-98 ropes, right, so does the article title need to be adjusted?
Our Answer: Due to the modified abstract and other chapters, we suggest not to change the title of the article.
- Your remark: There are few studies related to the functionality and reliability of TL-98 ropes described in the introduction, so are there any other similar studies in the field? If so, it is recommended to add descriptions of relevant studies.
Our Answer: Paragraph added (lines 70-77):
Several studies [1-7] are devoted to the issue of rope testing, but they are applied for mountaineering or for work at heights using rope procedures. These studies provide procedures for testing ropes and the results of their testing. However, testing in this area is strictly regulated by standards, and in the European area these are, for example, the standards for static ropes EN 1891 [8], for dynamic ropes EN 892 [9] or for auxiliary ropes EN 564 [10]. Testing according to these standards can only be performed in laboratory conditions and cannot be applied during flight or parachuting operations.
- Your remark: It is suggested to add the organization of the paper at the end of the introduction.
Our Answer: Paragraph added (lines 78-84):
Chapter 2 identifies the materials used in the experiment and describes the experimental methodologies. Chapter 3 presents the results of the fall tests from ground testing and from the test jump. The theoretical calculation of the impact force during the fall tests is given in Chapter 4, including a comparison of the calculated values with the values measured during the experiment. In the conclusions, there are predetermined rules for determining the lifetime of the rope and the result about it.
- Your remark: Section 2 Materials and Methods should have additional secondary headings to make the structure of the article clearer.
Our Answer: Chapter 2 was divided into 3 parts.
- Your remark: In the paper, 5 m of rope was used for the experiment, and one meter of the rope was used for tying the knot, which should also be given at line 86.
Our Answer: We modified the sentence:
For the purpose of the fall tests there was used a 5 meters long rope (of which one meter was used to tie the knots) with a 6 millimeters diameter and meeting EN 564 standards.
- Your remark: Line 124, the unit of memory is dates?
Our Answer: Corrected for data.
- Your remark: There are three types of backpack weights in the paper, 50kg, 60kg and 28kg, why did the authors choose the 28kg backpack for the experiment?
Our Answer: During the flight tests with the test dummy, a weight of 60 kg was used – modified paragraph:
There were performed 6 flight tests for this project (delivery of a test dummy) without the measurement of the force impact values. The backpack weight was 60 kg (maximum operational backpack weight 50 kg was multiplied by a safety coefficient of 1.2). By the flight tests was verified the strength of the backpack's anchorage points (by which the backpack is attached to the parachute harness) when droping from the aircraft at the maximum operating speed and at the maximum operating weight of the backpack increased by a safety factor of 1.2. The tests of the backpack and rope functionality and reliability were performed in the frame of the definition of the controlled characteristics which have been presented in the foreword of the point 2 (applicable for all tests in this project).
Paragraph added:
During ground fall tests and test jump, a weight of 28 kg was used, which was limited by the maximum operating weight of the OVP-80 parachute for the jump, which is 140 kg (test parachutist 91 kg, main and reserve parachute 19 kg, backpack 28 kg, force sensor 2 kg - total 140 kg). Therefore, due to the possibility of comparing the results between the ground fall tests and the test jump, a backpack weight of 28 kg was chosen for all these tests. And this weight could not be exceeded.
- Your remark: Why did the authors do 3 ground tests and only one flight test, and what was the difference between the 3 ground tests?
Our Answer: Due to the complexity of performing a test jump from the point of view of safety, it was decided that one test jump was sufficient.
The difference between the 3 ground tests was that the same rope was used all the time and this caused an increase in the maximum impact force with increasing number of falls.
Lines 271-275:
Upon comparison of the fall tests number 1, 2 and 3 that have been performed from the fixed spot and the same rope used, it has been verified following. By increasing number of falls, the rope is losing its capacity to absorb the fall power and the force impact values gradually increasing. Above mentioned reduction of rope´s dynamic effects by a cumulative number of falls has been documented in [3-5] too.
- Your remark: The data obtained from the experiments declared in the introduction are added to the manual, so is the number of experiments in the paper sufficient as a description in the manual?
Our Answer: Yes, the methodology for determining the lifetime of the rope based on flight tests was approved in advance by the user (Armed Forces of the Slovak Republic) and the lifetime of the rope was intended for 60 parachute applications. This value is given in the operation manual for use of the TL-98 backpack.
- Your remark: There are italicized and non-italicized units "N" in the paper, please unify them.
Our Answer: We corrected this units in the article.
- Your remark: Line 275 “cumulative number of falls has been documented in [10], [11] and [12]” should be “cumulative number of falls has been documented in [10-12]”. Line 327 “The tasks included in [13] and [14,15] became basics… ”should be “The tasks included in [13-15] became basics…”.
Our Answer: We corrected this citation in the article.
We hope that our corrections met your expectations. If the article will be approved for publication, we will use MDPI service for English revisions. Thank you for your consideration.
Sincerely,
Ing. Alica Tobisová, PhD., Ing. Paed-IGIP
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I appreciate the careful work of the authors to answer all comments to the previous revision. I only have a few minor comments discussed below.
- The new paragraph (lines 81-87) does not have a natural transition to the following. Suggest adding transitions such as "What experiments were conducted because of the shortcomings of the current study…"
- Line 157, shouldn't the units of memory be KB, MB, GB, TB, etc., or is there some special meaning here?
- In Figure 11 and Figure 12, the decimal point in the horizontal coordinate is suggested to be changed to ".", instead of ",". In addition, the picture quality can be better, if this is an excel drawing, the picture can be directly pasted into the word.
Author Response
Dear Reviewer 2:
Thank you for your second review. We revised the article „The fall test of the personal airborne equipment backpack – ground and flight testing” according to your review.
- Your remark: The new paragraph (lines 81-87) does not have a natural transition to the following. Suggest adding transitions such as "What experiments were conducted because of the shortcomings of the current study…".
Our Answer:
For these reasons, a procedure was developed for testing the rope in parachute operation during parachute flight, and this procedure was also applied in ground fall tests. This made it possible to compare the results from the fall tests obtained during the parachute flight with the results from the ground tests. The developed methodology used during the experiment is described in Chapter 2.
- Your remark: Line 157, shouldn't the units of memory be KB, MB, GB, TB, etc., or is there some special meaning here?
Our Answer: In this way, the manufacturer of the TSG-073 device defined the capacity of the memory unit. This means that the memory unit is able to archive a maximum of 25,000 measured force values.
Edited / added text:
maximum 25 000 data (25 000 measured force values).
- Your remark: In Figure 11 and Figure 12, the decimal point in the horizontal coordinate is suggested to be changed to ".", instead of ",". In addition, the picture quality can be better, if this is an excel drawing, the picture can be directly pasted into the word.
Our Answer: For decimal point purposes, the commas were replaced by a dot and the original graphs were inserted.
We hope that our corrections met your expectations. If the article will be approved for publication, we will use MDPI service for English revisions. Thank you for your consideration.
Sincerely,
Ing. Alica Tobisová, PhD., Ing. Paed-IGIP
Author Response File: Author Response.pdf
