Propeller Position Effects over the Pressure and Friction Coefficients over the Wing of an UAV with Distributed Electric Propulsion: A Proper Orthogonal Decomposition Analysis
Round 1
Reviewer 1 Report
When I accepted the abstract I had much higher expectations. The topic of distributed propulsion is very important and must have more emphasis in the near future.
As I started to read, the first issue I faced is the definition of 2.5D. The computational domain is not explained properly. Is it 3D with two symmetry boundaries between two successive propellers? If that is the case, how do you explain the effect of the rotation of the propellers? Symmetry will not work in this case.
Second, what is the purpose of POD? There is no simple curve that shows the drag coefficient as a function of the propeller height and angle of attack. That would be more important in my perspective than the complex mathematics that is not used in this paper. POD has other advantages as it can be used for future optimization, which is not addressed. The results on its own are worthy of presenting, and they are not.
Referring to the 2.5 D, the authors say they extracted the results in the plain of the propeller as shown in figure 5. Again. is it 3D? Why did they not extract the drag coefficient for the wing section in the simulation, rather than the sectional information?
While reconstruction of pressure coefficient and sectional drag coefficient using POD is interesting, what engineering value does it add? I would like to see the wing drag coefficient as a function of the two free parameters.
Author Response
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Reviewer 2 Report
I appreciate interesting subject and good quality of this paper. I have two minor comments concerning spelling:
line 207 - there should be probably "..., whereas the eigenvectors ..."
line 215 - projected
I have suggestion for future work or possible modification of the current paper for authors. You have used POD analysis forpressure and friction coefficients. I think that it would be interesting to add also lift and drag coefficients, i.e. how many modes are sufficient for the description of lift and drag based on your decomposition of pressure and friction coefficients.
Author Response
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Reviewer 3 Report
The paper investigates the effects of positioning the propellers of a DEP UAV using POD analysis. The authors investigated these effects on an UAV with MTOM of 25 kgs. The paper is well written and the results are logically presented. Some details can be elaborated with more details, as given bellow. My specific comments are the following:
- In the present case, the propulsion plants are located behind the wing for increased aerodynamic efficiency. However, if they are placed in front of the wing, their control authority is higher due do increased lift generated by the propulsion plant at the washed area of the wing. This can be used for roll control for example, instead/in combination with classical ailerons. I recommend elaborating about this trade-off in the paper.
- It would be interesting to see how the number and size of the propellers influence the results.
- Figure 1 shows 12 propellers, the text states 13 of 80 mm propellers.
- What are the limitations and drawbacks of the applied POD technique?
- The figures are sometimes too big and the colors of the plots are not always intuitive (Figures 8, 9 10, 12, 14, 16 for example).
I recommend accepting the paper once it is revised based on the comments above.
Author Response
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Round 2
Reviewer 1 Report
I leave it up the editor to decide on publishing. Science is correct, however, there is no contribution. You can always apply POD to any data set, the question of what its useful for arises? To me the authors have failed to show the potential use of the data they generated.
Author Response
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