Improvement of Take-Off Performance for an Electric Commuter Aircraft Due to Distributed Electric Propulsion

Round 1

Reviewer 1 Report

The paper in general gives a good analysis of the impact of DEP effects on take-off aerodynamics. However, a few comments in the following to further improve the quality of the paper:

# line 55: "due to FAR23 constraints" - it should be briefly explained what specific constraints prevent landing with DEP. And why FAr23 over/in addition to CS23? Is there any constraint in FAR23 which would not show up in the EASA regulations??

# line 93: "that an induced drag up to 15%" - that a reduction of induced drag ...

# line 122f: "which involves in possible of 6% block fuel" - in a possible reduction of 6% ...

# Figures 4-6: scales illegible

# Table 5: the data in Table 5 DEP (a) and TIP (b) are identical. Looks like a copy&past error

# Table 6:
   - should be (a) and (b) rather than (c) and (d)
   - the data in Table 6 (a) M114 airfoil and (b) SDA1075 are identical.
     Looks once more like a copy&past error

# Figure 8: font sizes way too small; what is the small black component at the trailing edge - notation missing

# line 296: "and W is the result." - W is the resulting velocity

# equations (2)-(4): equaiton (1) missing; "n" not listed in the Abbreviations

# line 303f: "was the indications of defined during the preliminary design phase" - language remains incomprehensible

Table 8: "Wing/Flap cord ratio" - no, the value relates to the Flap/Wing cord ratio

# Figures 11,12: the textual description to a large extent uses different parameters compared to the figures (e.g. k1-k5 could be P1-P5. Or something else?). Furthermore, the content from line 321 to line 341 including the two Figures does not add any value to the overall topic of the paper. It is there proposed to delete this section as it is absolutely obsolete.

# Table 9: "c_l_a" not defined - could be c_l_alfa?

# line 414: Error! Reference source not found

# Figures 22, 23: ideally, the scales of (a) and (b) would be identical to enable a direct comparison

# line 583f: "the increment of pitching moment due to propulsion could lead to structural issues related to tailplane balancing loads" - this is a far stretched argument given the way higher load requirements for manoeuvres and gusts ...

# References:

   - 5, 18: year of publication missing

   - 10, 15, 18, 29: journal/publication missing

   - 41: author missing

   - 7: "Commission, E." should stay European Commission

   - 8: "FAA Part 23 No Title Available online:"; it is also questionable why FAR23 should be required over and beyond CS23 (67)

   - 67: While it could be acceptable to reference to the full text of Amendment 4 over the reduced content of Amendment 5, Amendment 3 is definitely outdated.

# General: a multitude of minor English language and style issues would justify a thorough language review.

Author Response

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Reviewer 2 Report

The work presented is very extensive, and involves several areas. There is no adequate introduction of the link between the different numerical solutions obtained. There is no hierarchical tree of the results obtained, it is not clear how they interact with each other.

From the point of view of the software used, there are several levels of accuracy, which affect the overall results, but is not highlighted as.

The configuration taken as a reference is not clearly identified (in terms of propeller profile, flaps, gap, and other characteristics analyzed in the work).

It is not clear where the increased CL effect of the take-off speed reduction comes from.

I suggest we review the structure of the work, to make it clearer.

Author Response

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Reviewer 3 Report

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Comments for author File: Comments.pdf

Author Response

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Reviewer 4 Report

This works presents an aerodynamic analysis of a full-electric commuter aircraft, using high-fidelity tools such as 2D/3D CFD  solvers. Emphasis is put on the determination of propulsive effects in terms of lift capabilities at take-off, to quantify the changes in take-off field length. Moreover, significant effort is put into the design of the propellers and the wing flaps.

It is an interesting scientific work, of high quality and relevant for the scientific audience of Aerospace journal, in my opinion.

First, I’d like to thank the authors for providing this informative work in a clear and careful manner. Second, I believe that this article could be somewhat improved after some minor modifications and clarifications/better explanations before it is made publicly available. The suggested comments are the following:

- Line 93: Perhaps you would like to say ‘an induced drag reduction up to 15%’.

- Line 158: Is the laminar airfoil used in this assessment? It could be misleading at this point.

- Line 196: Is the metric appropriate here? Are you referring to a cell height? I'd expect 'mm' to capture the y+ referenced later on.

- Line 355: I do not think this sentence adds any value since no such results are presented here, and the flap analysis is done in 2D.

- Page 13, section 3.1: Is any optimization study done at this point? This is what is also mentioned in line 568 but I wasn’t able to find any optimization description. Please comment/clarify in the text.

- Page 15 onwards: A ‘cosmetic’ comment is that you consider presenting the results of the take-off condition first, instead of landing, since the paper emphasizes at the ‘improvement of take-off performance…’.

- Lines 428-429: This is not very clear in Section 2.2, in my opinion. Some better clarification/explanation would be appreciated. The use of DEP propellers vs using the term DEP, in general, to refer to the overall configuration can be misleading. In the end, all propellers contribute to the DEP but if I understand correctly, you make the differentiation here to specifically describe the steps taken for the Tip propellers. Overall, the use of Patterson’s method over MIL and the method used for each propeller (DEP/TIP) should be clear.

- Lines 447-449: A description of the results shown in Figures 22-24 would be appreciated.

- Lines 523-524: Is Piaggio’s greener aircraft used as the reference aircraft throughout the whole paper? Even for example in the ‘Clean’ configuration mentioned in Line 388?

- Overall comment: A final point that in my opinion deserves some more discussion is the validity of the results presented since this is a purely numerical simulation-based article. The question is raised at several points while reading the whole article. For example, on page 14 (line 368), it is commented that a filleting effort was made to avoid undesired flow separations generated by wing-fuselage intersection and magnified by the flow perturbation due to flap deflection. In the same critical point of the aircraft, I see the relevant skewness angle map (Page 7) but the acceptable skewness angle limits are not described. Also, on Page 16 (Lines 396-398) a discrepancy between the CL_max calculated from VLM methods and CFDs is shown. As far as I understand, the main underlying reason is in the optimized (?) flap and not the fidelity of the tools used. Please clarify and discuss in some point about the position of the paper to enhance validity (i.e. y+, grid independence, comparison with other studies/prior experience, others).

- I suggest doing a final text editing for typos/grammatical errors.

Author Response

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Round 2

Reviewer 2 Report

The work was improved in term of readability, but there are still some misunderstanding.

In the flap design, it is not clear the choose of the gap/overlap final values. The fillet presence shows a huge effect on the separation zone, but not all the gap/overlap conditions were investigated with/without fillet (figure 18).

Figure 19 shows an increase of the stall angle in take-off and landing conditions, usually there is a decrease of this value, why this behaviour?

Same performance in the power off/on tests, increase of the angle of stall, any explanation?

Trimmed values were computed using an empirical method, but since you made a lot of 3D full aircraft simulations, it was not possible to do just 1 simulation to confirm the trimmed results?

Author Response

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Reviewer 3 Report

Table 2: Caption and title should be changed, as it includes also solver settings (turbulence, flow model etc)

Section 2.3: more than a flap design, it is a flap setting design. Please update title and subsequent sentences on flap <<settings>> design.

Fiure 18: Please specify in the legend if the first two dataset refer to the geometry with or without fillet.

Author Response

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Round 3

Reviewer 2 Report

Nothing to add