Dear Authors, I have reviewed your article and provided my comments below.

General comments

The topic of the article, which focuses on the design and experimental characterization of a scale model of a low specific-rating rotor, is significant for the research community and aligns with the scope of WES. The methodologies outlined in the article are valuable for the design of scale model wind turbines, and the results obtained from the testing campaign enhance the understanding of the operational characteristics of low specific-rating rotors. This study can contribute to their further development and commercial viability.

The research objectives and hypotheses are clearly defined. The discussion of the methodology and results is supported by sufficient detail. The article is generally well-structured.

For these reasons, I believe the article merits publication in the WES journal. Prior to publication, I request the authors address the comments below. Specific suggestions to enhance the effectiveness of the article are included in the "specific comments" section. Technical corrections, including typos and improvement suggestions for presentation quality, are provided in the attached PDF.

Specific comments

Introduction. I recommend that the authors include a discussion on the potential impact of the article, particularly in relation to the development of low-specific-rating rotors and the scale model testing of wind turbines in general.

Scaling methodology of the Hybrid-Lambda rotor. This section is hard to follow as scaling requirements are introduced gradually. I recommend restructuring it into: 1) Scaling constraints, 2) Scale factors, 3) Blade design algorithm, 4) Results of the blade design. Essentially, divide it into inputs, methodology, and outputs.

Figure 1. The diagram is hard to follow due to undefined variables. It should be simplified and the comparison with MoWiTO1.8 might be removed.

11: “both rotors”. It's not clear if the two rotors mentioned here are the two scale models (Hybrid-Lambda and conventional) or the scale model of the Hybrid-Lambda and its full scale version.

62: “the large geometric scaling factor”. Can you recall its value here?

71-76: this paragraph is a bit disconnected from the rest of the introduction. Consider to remove it and merge its content to the rest of the text.

140-141: This sentence should clearly connect with Eq. 1-4, as it forms the basis of the methodology described in the article.

161: “fulfil the constraints … number”. Can you recall the constrains, i.e. the minimum allowed chord and Re?

169-171: “Second, … in the wind tunnel”. Please clarify with examples or explain in more detail.

192: “first tower eigenfrequency”. Report the value.

210-211. Can you briefly explain how the control strategy works?

215-216. This statement is unclear. There is only one time scale. It can be stated that the maximum rotor speed is not scaled in relation to the maximum rotor speed of the full-scale turbine.

226-228. To provide clear guidance, it is recommended to avoid asking open-ended questions and instead offer definitive answers.

Figure 6. Can you add the constrains to the plots with horizontal lines?

288: “Here”. In this study or a cited one?

394-395: “as we aimed … blade design”. How does this goal influence the tuning of viscous diffusion in OLAF? Please explain.

409: “only a small portion of the results”. How did you choose which results to plot and which to discard?

415: “with a considerable offset”. Could this offset be due to thrust being estimated from the tower base bending moment and requiring corrections for nacelle and tower drag, making it less certain than the torque (power) measurement?

Eq 14: “My”. Could you please clarify what "My" refers to? Is it the bending moment of individual blades that have been measured using strain gauges?

420: “the measured flapwise RBM are in good agreement with the simulations”. Have you estimated rotor thrust from blade-root bending moment? It might compare better with simulations than the tower base moment estimate.

436-465. This discussion should precede the LDA measurement results. Condense the FVW simulation results (e.g., using Fig. 11) to show that the BEM model's 2D flow assumption is invalid in the blending region, explaining the poor agreement between BEM and measurements there.

485. You should clarify that the shear layer is between the wind tunnel jet and the still air around the nozzle.

489-490: “A major advantage … operating modes”. Can you relate this discussion to the control schedule shown in Fig. 4?

496: “leads to an outer annulus with reduced wake deficits”. Could you please highlight it in the figure by delineating the edges of the annulus?

504-505: “to a second shear layer at the boarder to the inner wake core with lower wind speeds” Can you highlight it in the figure?

504-517. Are two shear layers expected in the Hybrid-Lambda rotor based on prior numerical studies? If so, how do the measurements align with the numerical results?

Figure 13. The text in this figure is very small. Please, increase it.

542. Please add a sentence explaining how the assumptions of the FVW model relate to the experimental conditions. If I understood the text properly, clarify that the results from the FVW model are useful for indicating the location of vorticity but that the strength estimated by the FVW model should not be directly compared to the strength observed in the experiment.

Figure 15. Please add titles to the subplots to indicate if they refer to Convention or Hybrid Lambda rotors.

589: “must be considered critically”. Not clear what you mean.

598: “are very similar”. Could you please clarify the parameters? Are we discussing velocity, radial extension, or another aspect?

624-629: I think this paragraph belongs to the conclusions.

Data availability. Can you provide any measurements or numerical models? This is encouraged by the journal.

Technical corrections

See attached pdf file.

Please see the attachment.