Conceptual Design and Optimization of Distributed Electric Propulsion General Aviation Aircraft
Round 1
Reviewer 1 Report
The article analysed the crucial problem regarding designing and optimising aircraft with distributed electric propulsion. However, the scientific analysis soundness of this issue is average. It means the current description of the analysis needs to be revised to gain scientific character. The mathematical and technical analysis should be presented more precisely using a mathematical description of the presented aspects. Moreover, the Authors should add the scientific discussion chapter to more widely and precisely analyse the presented outcomes and adequately rephrase the conclusion part.
In conclusion, the article requires major revision before publication.
Author Response
Point 1: The article analysed the crucial problem regarding designing and optimising aircraft with distributed electric propulsion. However, the scientific analysis soundness of this issue is average. It means the current description of the analysis needs to be revised to gain scientific character. The mathematical and technical analysis should be presented more precisely using a mathematical description of the presented aspects.
Response 1: Considering the scientific nature of the study in this work, section 2 is introduced to demonstrate the interaction between the slipstreams created by the tractor propeller and the wing. To further demonstrate the significance of the optimization, formula 3–10 is also provided. The addition of the new figure 17 and figure 18 demonstrates the fundamental rationale for the DEP aircraft's enhanced lift coefficient.
Point 2: Moreover, the Authors should add the scientific discussion chapter to more widely and precisely analyse the presented outcomes and adequately rephrase the conclusion part.
Response 2: The conclusion is revised, and the discussion is added to the article at the end.
Point 3: In conclusion, the article requires major revision before publication.
Response 3: In the amended version, almost all of the English has been rewritten.
For the total response ,Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper presents the aerodynamic analysis of distributed electric propulsion on a general aviatin aircraft, including wing tip propellers. It could profit from a thorough review of both quality of presentation as well as English language. Here some recommendations for a revised version, adressing also the sections that remain unclear to the reader:
- Title & line11 & line 129: there are no "Distributed Electric Propulsion General Aircraft". It could either be "Generic Distributed Electric Propulsion Aircraft" or "Distributed Electric Propulsion General Aviation Aircraft". I assume the latter is what is meant, but to be clarified by the authors.
- line 18f: "objective of smallest velocity at angle of attack of 8°" --> unclear: why this objective?
- Line 32 f: "More and more aircrafts powered with electricity some or all have been developed ..." --> meaning unclear
- Line 38: "carrying capacity" -->"payload",
- Figure 1: font size too small
- Figures 1, 2: for readibility of the small text, it is recommended to use a sans serif font
- Figure 2: exit condition of the step "One logical design scheme" unclear
- line 195: "BEM method" not commonly known, acronym introduced without explanation.
- Tables 1, 2 & related text: it seems as if "CFD" is used for VSPAero as well as for STARCCM+. This creates confusion. It is therefore recommended to be more specific wherever CFD is written.
- Line 198: "... the data from the wind tunnel" --> it remains unclear where suddenly the wind tunnel comes from. Is this a reference to the work in [10]?
- Figures 5 (b), 7: no "surface grid" visible, should say "model" instead
- Line 241f: "... with consideration of the requirement in structural strength." --> unclear: what is this requirement and what is its effect on wing area?
- Figure 7: "optical wing" --> optimal wing
- Line 255f: it remains unclear why this chord position is selected out of an infinity of options
- Table 5: "Advance ratio of propeller"
- Equation (2): "G" is a German notation, correct English notation would be "W"
- Conclusions: in the text only L/D and efficiency have been reported, now suddenly range is introduced in the summary. Should be provided in the text sections.
- General: please review carefully the English language: many articles ("the", ...) are missing; acronyms are often misspelled (sloppy proof-reading).
Author Response
Point 1: Title & line11 & line 129: there are no "Distributed Electric Propulsion General Aircraft". It could either be "Generic Distributed Electric Propulsion Aircraft" or "Distributed Electric Propulsion General Aviation Aircraft". I assume the latter is what is meant, but to be clarified by the authors.
Response 1: In this paper, the term "Distributed Electric Propulsion General Aviation Aircraft" has been used in place of "Distributed Electric Propulsion General Aircraft."
Point 2: line 18f: "objective of smallest velocity at angle of attack of 8°" --> unclear: why this objective?
Response 2: Instead of "objective of smallest velocity at angle of attack of 8°," "objective of smallest velocity at an angle near the tail down angle" has been used in the abstract. Due to the DEP aircraft's tail down angle, which is approximately 10 °, the attack angle during takeoff and landing should be a little less than that. It is set to 8 degrees in the initial form. Additionally, minimizing the run distance during takeoff and landing for DEP airplanes is the objective for the lowest velocity. The explanation for the goal is stated in line 344.
Point 3: Line 32 f: "More and more aircrafts powered with electricity some or all have been developed ..." --> meaning unclear
Response 3:In lines 35 and 36 of the revised paper, the words "a great deal of aircrafts have been built that use electricity for either all or part of their propulsion" have been used in place of the phrase "More and more aircrafts powered with electricity some or all have been developed..." in line 32.
Point 4: Line 38: "carrying capacity" -->"payload"
Response 4: The term "payload" has been added to line 42 of the revised version in place of "carrying capacity" in line 38.
Point 5: Figure 1: font size too small
Response 5: The modified version has replaced the manuscript's figures 1 and 2 with figures 3 and 4.
Point 6: Figures 1, 2: for readibility of the small text, it is recommended to use a sans serif font
Response 6: The modified version has replaced the manuscript's figures 1 and 2 with figures 3 and 4.
Point 7: Figure 2: exit condition of the step "One logical design scheme" unclear
Response 7: In the updated paper's figure 4, the exit criterion for the step "One logical design plan" has been changed.
Point 8: line 195: "BEM method" not commonly known, acronym introduced without explanation.
Response 8: The phrase "BEM method" in line 195 has been changed to "BEM (Blade Element Momentum)" in line 228 of the updated version.
Point 9: Tables 1, 2 & related text: it seems as if "CFD" is used for VSPAero as well as for STARCCM+. This creates confusion. It is therefore recommended to be more specific wherever CFD is written.
Response 9: The modified version has "VSPAERO" in place of "CFD" in table 1.
Point 10: Line 198:"... the data from the wind tunnel" --> it remains unclear where suddenly the wind tunnel comes from. Is this a reference to the work in [10]?
Response 10: In the original document, line 198 refers to "... the data from the wind tunnel," which is the information from reference 10. To clarify, "Moreover, the information from the wind tunnel test in [10] is also displayed in the tables below to evaluate the outcomes of the simulations." is added on line 221,222,223 of the corrected version.
Point 11: Figures 5 (b), 7: no "surface grid" visible, should say "model" instead.
Response 11: The surface grid in figure 5(b) of the original document is not very clear, thus in figure 7(b) of the amended version, a "model of wing and virtual disk of propeller in STAR CCM+" is used to represent it.
Point 12: Line 241f: "... with consideration of the requirement in structural strength." --> unclear: what is this requirement and what is its effect on wing area?
Response 12: The sentence “Given the need for structural strength “is maintained in line 278 of the revised paper. Because the force per unit area will grow as the wing area decreases, the force per unit area on the wing should be kept as low as possible according to identical manufacturing processes for wings made of composite materials.
Point 13: Figure 7: "optical wing" --> optimal wing
Response 13: Figure 7 of the original manuscript's figure uses the word "optical wing" which has been changed to "optimal wing" in figure 10 of the amended version.
Point 14: Line 255f: it remains unclear why this chord position is selected out of an infinity of options
Response 14: According to the findings in reference 10, the chord position is determined, and lines 59–61 and lines 168–171in the modified version are appended with the corresponding introduction.
Point 15: Table 5: "Advance ratio of propeller"
Response 15: In the updated version, "Advance ratio of propeller" has been substituted for "advance of propeller" in table 5 of the original document.
Point 16: Equation (2): "G" is a German notation, correct English notation would be "W"
Response 16: The "W" symbol has been used to replace the "G" in formula 2.
Point 17: Conclusions: in the text only L/D and efficiency have been reported, now suddenly range is introduced in the summary. Should be provided in the text sections.
Response 17: Range has been removed from the original document's conclusions, and lines 304–306 add the relationship between range and the lift–drag ratio and propeller efficiency in cruise.
Point 18: General: please review carefully the English language: many articles ("the", ...) are missing; acronyms are often misspelled (sloppy proof-reading).
Response 18: In the amended version, almost all of the English has been rewritten.
For the total response, please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
In this article, the authors discuss a design and optimization method for aircraft based on distributed electric propulsion. This is an interesting exploratory study, but the manuscript needs some improvement in terms of clarity and presentation. Please see specific comments below. I recommend that the authors be asked to complete a major revision before further review and consideration for publication in Aerospace.
1. The English presentation is readable and mostly clear, but some additional polishing and language improvement is needed before the manuscript would be ready for publication. The quality of language and structure also varies significantly throughout the paper, which needs to be addressed. At a minimum, one author needs to polish the paper so that it is in a consistent style and is clear to readers.
2. There are several areas where there are 1-sentance paragraphs; this is distracting and annoying when reading the paper. These should be combined so that all the paragraphs throughout the paper are approximately the same size or presented as bullet points.
3. The novelty of this method and the presented results is not clear. The authors themselves admit that there is already an extensive body of literature on this question. The method is also based on existing modeling and computational tools. While this could be good for a tutorial, it is not enough for a research article. Please provide an argument for why this paper adds to the engineering literature and is appropriate for archiving in a journal.
4. One of the stated main objectives from this paper was to study the interaction between the air flow from the propeller and the wing. However, I do not think this was discussed in enough detail in either the model or the case study. It is never clearly stated what this interaction is and how it should be accounted for during either propeller and/or wing design.
5. All of the work here was done using a rather simple simulation with only a few variables. There are a lot of assumptions and simplifications made. While the final results make sense, there needs to be an extensive analysis of the assumptions and how they add uncertainty into the model/design method.
6. The physical meaning of the results (from the perspective of a pilot or other use) needs to be discussed in more detail.
7. The manuscript vaguely mentions wind tunnel tests completed on a real aircraft to get input information for the modeling. However, very little detail about these tests and their impact on the modeling is given. The RX4E shown in the paper is a completely different type of aircraft and is not representative of the models presented. This needs to be discussed and addressed in any revised paper.
8. Conclusions section is not acceptable as written and needs to be redone.
9. The authors (particularly corresponding author) need to use institutional email addresses for professional articles. It should also be made more clear for readers who are not familiar with the authors' institutions if they are university-based research labs, for-profit companies, or affiliated with a government department or agency.
Author Response
Point 1: The English presentation is readable and mostly clear, but some additional polishing and language improvement is needed before the manuscript would be ready for publication. The quality of language and structure also varies significantly throughout the paper, which needs to be addressed. At a minimum, one author needs to polish the paper so that it is in a consistent style and is clear to readers.
Response 1: In the amended version, almost all of the English has been rewritten.
Point 2: There are several areas where there are 1-sentance paragraphs; this is distracting and annoying when reading the paper. These should be combined so that all the paragraphs throughout the paper are approximately the same size or presented as bullet points.
Response 2: The amended document combines the single-sentence paragraphs from the original manuscript.
Point 3: The novelty of this method and the presented results is not clear. The authors themselves admit that there is already an extensive body of literature on this question. The method is also based on existing modeling and computational tools. While this could be good for a tutorial, it is not enough for a research article. Please provide an argument for why this paper adds to the engineering literature and is appropriate for archiving in a journal.
Response 3: Two examples of the innovation in this study are the use of force balancing and the construction of an optimum design technique that can accurately capture the high-performance regions of distributed electric propulsion aircraft. Despite the availability of low-order and high-order tools, little study has been done to assess design schemes based on script development for OpenVSP. The application of force balance limitations is another essential element in correctly analyzing the cruise performance of an aircraft's distributed electric propulsion system. For distributed electric propulsion aircraft, there is currently little study on cruising performance, which mostly focuses on lift. New insights from this study include the difficulties of optimizing the cruise lift-drag ratio. The updated conclusion gives a synopsis of the earlier information.
Point 4: One of the stated main objectives from this paper was to study the interaction between the air flow from the propeller and the wing. However, I do not think this was discussed in enough detail in either the model or the case study. It is never clearly stated what this interaction is and how it should be accounted for during either propeller and/or wing design.
Response 4: Section 2 is introduced to demonstrate the interaction between the slipstreams created by the tractor propeller and the wing.
Point 5: All of the work here was done using a rather simple simulation with only a few variables. There are a lot of assumptions and simplifications made. While the final results make sense, there needs to be an extensive analysis of the assumptions and how they add uncertainty into the model/design method.
Response 5: Towards the conclusion of the updated version, a discussion of the impact of large assumptions on uncertainty has been added.
Point 6: The physical meaning of the results (from the perspective of a pilot or other use) needs to be discussed in more detail.
Response 6: The conclusions' primary physical significance is that DEP aircraft use less power in cruise. Also, this is covered in the new conclusions and discussions. It appears in the lines 454-457 as terms “The method described in this study may be utilized to enhance the cruise performance of DEP aircraft in contrast to an aircraft with a conventional configuration. There could be an electric aircraft type with reduced cruise power consumption in the general aviation industry soon”.
Point 7: The manuscript vaguely mentions wind tunnel tests completed on a real aircraft to get input information for the modeling. However, very little detail about these tests and their impact on the modeling is given. The RX4E shown in the paper is a completely different type of aircraft and is not representative of the models presented. This needs to be discussed and addressed in any revised paper.
Response 7: The new document no longer includes the aircraft's tunnel test, therefore all analysis is now based only on simulation. The DEP aircraft are designed using the RX4E as a model. In other words, the DEP aircraft's fuselage is identical to the RX4E, and the DEP's performance is evaluated in relation to the RX4E. The new section 4.1 introduces this.
Point 8: Conclusions section is not acceptable as written and needs to be redone.
Response 8: The conclusion has been revised, and a discussion has been included.
Point 9: The authors (particularly corresponding author) need to use institutional email addresses for professional articles. It should also be made more clear for readers who are not familiar with the authors' institutions if they are university-based research labs, for-profit companies, or affiliated with a government department or agency.
Response 9: The corresponding author's email address is kept on file for communication with the editor and may be changed before the submission is approved.
For the total response, please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
1. Please add something about “aerodynamic” to the title of this manuscript, as most studied carried out in this manuscript is related to aerodynamic not the electric part.
2. Literature review is written very well. I suggest the two following papers be added to the Introduction section, as they discuss the optimization for electric aircraft.
https://doi.org/10.1088/1361-6668/acbb34
https://doi.org/10.3390/aerospace9120753
3. Flowchart of the figures 1 and 2 are very blurred. Please replace them with higher resolution figures.
4. More information regarding meshes in figure 5 is needed.
5. Have you considered the weight of added propellers and system into this model?
Author Response
Point 1: Please add something about “aerodynamic” to the title of this manuscript, as most studied carried out in this manuscript is related to aerodynamic not the electric part.
Response 1: The title is not changed here because the aerodynamic layout and other aspects of aircraft conceptual design are still the major focus. Aerodynamics has been impliedly shown in a way.
Point 2: Literature review is written very well. I suggest the two following papers be added to the Introduction section, as they discuss the optimization for electric aircraft.
https://doi.org/10.1088/1361-6668/acbb34
https://doi.org/10.3390/aerospace9120753
Response 2: The reviewer's suggested literature has a very insightful examination of optimization for electric aircraft. Yet, the conceptual design of electric aircraft, not the optimization approach, is the focus of the article. As a result, they are not cited here. They might serve as resources for additional research.
Point 3: Flowchart of the figures 1 and 2 are very blurred. Please replace them with higher resolution figures.
Response 3: The modified version has replaced the manuscript's figures 1 and 2 with figures 3 and 4.
Point 4: More information regarding meshes in figure 5 is needed.
Response 4: Further details on the meshes in figure 5 of the original manuscript are introduced in lines 237–241 of the revised paper.
Point 5: Have you considered the weight of added propellers and system into this model?
Response 5: Section 5.2 of the revised paper now includes a weight analysis of the DEP system.
For the total response, please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The article's authors introduced corrections that significantly improved the presented information's quality, readability and scientific soundness.
The bibliography linked to the analysed scientific problem is relevant and sufficient. Symbols (constants, variables) and functions are appropriately described and explained. Correcting the graphs, scientific discussion, and conclusions improved the paper's quality, and the article will be better understood. English language and style are fine.
To sum up, the revised article may be published in its current form.
Author Response
Thank you so much for your kind comments and valuable advice; it really means a lot to me.
Reviewer 2 Report
Dear authors,
the changes made in this revision have definitely improved the quality of the paper. However, given the amount of changes, the "track change" mode does not really help for the readibility of the new revision.
some minor changes:
line 258: "trailing vortex system"
lines 442 & 531: "optimal solution"
line 469: "surface grid"
Author Response
- I regret if reading the latest revision puzzled you. Please read the manuscript's pdf file to see the updated revisions.
- The revise to the minor changes:
- In the updated pdf version, the phrase "trailing vortex system" in line 258 has been changed to "tail vortex system" in line 149.
- In the updated pdf version, the "optimal solution" in line 442 and 531 has been changed in line 268 and 322.
- In the updated pdf version, line 283 has been changed to reflect the "surface grid" in line 469.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors have addressed my comments adequately. I recommend publication of the revised manuscript.
Author Response
Thank you so much for your suggestions on the manuscript; they were really helpful to me as I revised the paper. Change your mind in open review if the revision is accepted. Thank you once more.
Reviewer 4 Report
according to the authors' response, optimization is not the focus of this manuscript, so, please remove it from the title.
Author Response
Perhaps I did not communicate my meaning clearly. Building and enhancing an optimization method is not the main goal of this research. Yet, optimizing the DEP design is still crucial for this research.
