A Bio-Inspired Flapping Wing Rotor of Variant Frequency Driven by Ultrasonic Motor
Round 1
Reviewer 1 Report
This paper studies a bio-inspired flapping wing by combining the motion of flapping and rotation. CFD simulations and experiments are provided to verify the validity of the design. The overall structure of the paper looks good, but some materials should be refined or clarified before being acceptable to publish. In the following list my detail comments:
In Line 117, the sentence starting from "where..." should not be indented, because this is not a whole new sentence. Same errors occur throughout the whole paper. Please correct them. In Line 142, "rotary speed" should be changed to "rotational rate" or "rotational speed". These two are more commonly used. Same errors occur throughout the whole paper. In Line 154, the factor for normalization is defined as 0.5(tu+td) = 0.5(1/fu+1/fd). However, in Eqs. (3) and (4) the factor 0.5 are not employed. Why? In Line 166, "install angle" should be changed to "installation angle". Same errors occur throughout the whole paper. Please correct them. Please add one more figure or description to depict the definition of the installation angle. In Fig. 18, what does the unit (r/s) mean? If it is revolution per second, it is commonly written as "rev/s" to distinguish from "rad/s", where both "rev" and "rad" starts with "r". Although the flapping rotary wing has higher efficiency, I just wonder how it is able to be implemented. How can the moment generated by the rotary motion be balanced when an aerial vehicle flies? Some other relative work for authors' information: "Autopilots for Ultra Lightweight Robotic Birds: Automatic Altitude Control and System Integration of a Sub-10 g Weight Flapping-Wing Micro Air Vehicle" by Hsiao et. al. "The Three-Dimensional Flow Simulation of a Flapping Wing" by Lung-Jieh Yang et. al. "2D quasi-steady flow simulation of an actual flapping wing" by Lung-Jieh Yang et. al.
Author Response
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Reviewer 2 Report
The paper has been well organized and presentation is very clear.
Author Response
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Reviewer 3 Report
Overall, the paper is concise, relatively easy to follow, well
organized. The progress reported in this paper seems to be incremental but enough interesting/important to publish as a research paper.
My major comments and questions are as below:
1) The authors have claimed FWR (with VFF) shows higher efficiency than the other mechanisms. I expect an objective comparison to other actuation mechanisms based on lift-to-power ratio (N/W) will make the paper more persuasive. The authors used Pf for discussion about the efficiency. It is good to consider the aerodynamic performance. However, the lift-to-power become more important from the point of view of actual MAVs, which are driven by limited payload and power. Because they measured the lift force and power, it is easy to calculate it.
2) The reported average lift forces are about 200 mN (~20 gf) but it is smaller than the fabricated actuator's mass (50 g); the current performance is insufficient to take-off. Can you increase the lift by simply increasing the rotational rate? Or, are there any technical challenges?
3) The author concluded one of the merit of the VFF actuation is positive average inertial force. I do not consider the force is available as lift for a robot in the air. I consider that the force resulted positive due to the fixed constraint; it seems to be owing to the reaction force from the floor. In the other words, the up-down motion generates only internal forces so it cannot propel a system floating in the air.
Minor comments:
4) In page 3, line 101-102: "The aerodynamic forces, the rotary angle, twisting angle, .. are plotted in blue arrows"
However, the angles are not plotted in blue in fig.1.
5) Please indicate xyz-coordinate in the figures (fig. 1, 2, 3, 6). It will be helpful to understand the mechanism and motion.
Author Response
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Reviewer 4 Report
The paper presents analysis on the effect of variable flapping frequency to the lift generated by the FW rotor. The followings need to be addressed to improve the quality of the paper:
The total weight of the FW is around 50g, but the flapping frequency is only 1-3 Hz. This is very low. Will it actually able to provide sufficient lift to fly the FW? This makes the results not convincing enough. What is the effect of having an ultrasonic motor instead of any other typical DC motors/servos used for FWs? This is not elaborated in the paper. Fig 12 and 14 are too crowded. It is suggested to split some plots. Line 256-258, it is not clear how to see this in the crowded Fig 12. Fig 18(b), are these meant to be the maximum lifts produced?
Author Response
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Round 2
Reviewer 1 Report
This paper studies a bio-inspired flapping wing rotor of variant 2 frequency driven by ultrasonic motor. The errors in the previous version are corrected, and the questions are clarified. The current version looks fine and I have no further questions. It is recommended to publish in this journal.
