Modeling of the Flight Performance of a Plasma-Propelled Drone: Limitations and Prospects

Round 1

Reviewer 1 Report

Thanks to the authors for a fantastic paper. This work clearly lays out the challenges facing use of EAD propulsors for mid- and large-size UAVs in particular. It contributes a clear and concise background and related work section, a rigorous modeling approach and benchmarking with existing designs, and a strong discussion about future prospects. The figures are of a uniformly high quality. 

-Can you be more precise about use of "quiescent conditions" (e.g., in line 123)? I assume you mean near-zero freestream velocity. In the case of (6) in particular, it is derived for one-dimensional ion flows (hence the simple "d" instead of one relying on a true ion path), and the freestream velocity is captured by there being no convective term.

-I am not sure how the assumption in line 267 is possible for freestream velocities 5, 10, and 15m/s. For example, ion drift speed (from muE) at only 0.1MV/m is 20m/s, and the thrust at that field strength will be negligible. Am I misunderstanding something? How does this assumption change the results quantitatively?

-New approaches (Gomez-Vega et al, Drew et al, Nelson et al) focused on multi-stage ducted thrusters should be mentioned as a way to improve propulsive efficiency. The additional duct mass would be interesting to push through your model.

-In general I dislike reliance on spanwise thrust measurements, especially when scaling them to arbitrary high values, because I have trouble relating them to simple models for achievable thrust density. Can you comment on how some of your scaled spanwise thrusts convert to thrust densities (N/m^2, as in lines 246-251), and how those relate to space-charge limited thrust density estimates (via F=9/8 eps0 A E^2)? If, as I expect, these values are beyond theoretical maximums, perhaps that connects to my prior comment about recent work focused on many-stage ducted devices.

-I think that even the 20 mN/W highlighted as achievable is, in reality, very very challenging to achieve with current technology at useful thrust levels. I appreciate that being optimistic in this regard strengthens the paper in some ways. 

Overall, I am eager to see how your approach extends into the MAV space. I think it also quite clearly shows that emulating VTOL/static hover platform configurations is currently impossible. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Please find the review attached.

Comments for author File: Comments.pdf

The authors are requested to check the grammar and style of writing. Quite often, the sentence structure was incorrect.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is much in the form of a project report, including three appendixes. The editors should pronounce is this design and size of the manuscript appropriate for the journal.

Some unification of the notations is needed. For example in Eq.16 the authors define Thrust per meter of span, but in fig.3 and 5 they refer to it just as Thrust.

In most other respects the material is well presented and explained. The manuscript is a good feasibility study on the EAD propulsion. The conclusions drawn, may serve as a basis for further research in the area of EAD propelled UAV.

Lines 31-32: 'If Although this drone...,it is a proof of concept...'

Line 64: ' both the an EAD'

other similar errors possible

Author Response

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Author Response File: Author Response.pdf