Nonlinear Control of a Single Tail Tilt Servomotor Tri-Rotor Ducted VTOL-UAV

Round 1

Reviewer 1 Report

1) The number of “Introduction” is 0, which is incorrect.

2) You wrote: “As shown in Figure 1, the maximum design cruising speed of SB-1 composite helicopter is 460km / h, and the speed of V-280 tilt-rotor aircraft is more than 519km / h in flight tests.” This is incorrect, there is no such data in Fig. 1.

3) You wrote: “The team of this paper…” Who are they? If you talk about the authors, indicate it clearly.

4) You wrote: “The other two fronts of rotors rotate in opposite directions, which created reaction torque almost zero, as shown in Figure 2.” It is incorrect. Fig.2 does not provide these data.

5) When you provide review of the previous arts, You have not only show the idea, you must explain, why it is not applicable to your project.

6) You wrote: “d1 and d2 are the unknown external bounded disturbances”, but did not explain, which type of disturbance you meant.

7) You wrote: “…is the angle”. Which angle are talking about? You have to explain all parameters carefully. You’d better draw them.

8) You wrote: “…is the angle rate”. The same comment as for angle.

9) You wrote: “…attitude vector transformation matrix”, but did not provide it.

10) You wrote: “…is the total aerodynamic force (excluding gravity)”. You’d better explain, which force it includes.

11) You wrote: “…Ftr generated by the left and right tilting tail rotor”, which does not correspond to the picture. Correct it.

12) You wrote: “…aerodynamic force Ff us acting on the fuselage”. How does it correlate with F (total aerodynamic force)? Explain

13) Denote all characters in (2) and (3).

14) I suggest to change signature in figures from “alpha” to the corresponding character.

15) You’d better show all angles in the 3D figure of the UAV.

16) Are d1 from (1) and (7) similar or not?

17) From your explanation is unclear, what is f1?

18) From your explanation is unclear, what is u?

Author Response

We are very thankful to the Associate Editor and the reviewers for evaluating our manuscript and providing us with detailed and insightful comments and suggestions. In accordance with these comments and suggestions, we have revised the paper carefully and extensively. All the issues raised in the reports have been addressed.

In the attached PDF file, we detail the changes made with respect to the AE' and reviewers' suggestions and concerns.  For convenience, the comments and suggestions of the AE and reviewers are printed in blue, whereas our statements of revision are printed in black.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors presents a hybrid control method combining model prediction control with sliding mode nonlinear dynamic inversion for the three culvert rotor composite VTOL-UAV with tiltable tail rotor. The article is well-written, well-structured, and has consistent simulation and experimental results. However, in order to improve the article, below are some comments about the article.

1. The introductory section is adequate, presenting the conventional types of high speed helicopters, the state of the art of controllers for these types of aircraft and the difference/contribution of the proposed aircraft and proposed controllers. However, in order to contribute to the improvement of this section, I suggest that the authors name all the acronyms used (such as L/D and FTC).

2. In Figure 3 the forces Fvf and Fhv are not properly explained in the text.

3. Please correct the caption of Figure 5

4. The authors quote in lines 128-129: "It is planned to reduce the resistance coefficient and improve the lift drag ratio of the ducted rotor system by optimizing the culvert shape." When exactly is this improvement being scheduled? Should this study not be incorporated into this work? I suggest that the authors further develop this statement in order to explain the reason for the postponement of this study.

5. I suggest the authors improve the layout of Figure 7. There are captions broken into different lines and arrows "invading" control blocks.

6. Authors should rewrite the article in a more formal way, avoiding the use of personal pronouns as in the phrases "we used..."

7. Why was the reference path chosen on an XY plane with constant Z height (equation 28)? To prove the take-off and landing capability, shouldn't height (Z) have a dynamic trajectory? The same comment can be made in relation to flight tests.

8. Why is the disturbance estimate d2 oscillating? Do the authors have any comments for this result?

Author Response

We are very thankful to the Associate Editor and the reviewers for evaluating our manuscript and providing us with detailed and insightful comments and suggestions. In accordance with these comments and suggestions, we have revised the paper carefully and extensively. All the issues raised in the reports have been addressed.

In the attached PDF file, we detail the changes made with respect to the AE' and reviewers' suggestions and concerns.  For convenience, the comments and suggestions of the AE and reviewers are printed in blue, whereas our statements of revision are printed in black.

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for the improvements. However there are still some minor issues.

1) When write reference numbers, use spaces.

2) The acronyms are typically denoted as: Aaaaa Bbbbbb Cccccc (ABC).

3) You wrote: “A novel tri-rotor ducted vertical takeoff and landing composite unmanned aerial vehicle system (Tri-Rotor Ducted VTOL-UAV) is developed by the authors, and it is equipped with a single tail tilt servomotor to delete the inverse torque and enhance controllability of yaw moment.” I

4) Use capital letter: “moment. the”

5) You wrote: “For the tri-rotor ducted VTOL-UAV, the aerodynamic characteristics are more complex than the compound UAV…”. Explain the structure of compound UAV.

6) Improve quality of Fig.6, use vector graphics.

7) Provide better resolution for Fig. 1. It seems that it is below quality required by journals.

Author Response

We are very thankful to the Associate Editor and the reviewers for evaluating our manuscript and providing us with detailed and insightful comments and suggestions. All the issues raised in the reports have been addressed.   Please see the attachment for the specific changes.

Author Response File: Author Response.pdf

Reviewer 2 Report

All my comments have been addressed. Congratulations on the work.

Author Response

Thanks again for the valuable advice and suggestions.