The manuscript presents a high-quality experimental study on a 1:6.5 scale LEI kite using stereoscopic PIV, providing a benchmark dataset for validating CFD and Vortex-Step Method models. The work is scientifically significant, as it elucidates local 3D aerodynamic phenomena, including strut-induced flow effects, and directly confirms stall onset at high angles of attack. Methodology and analysis are rigorous, and results are clearly presented. Minor technical revisions are suggested to improve clarity, including sentence refinements, explicit description of pseudo-2D assumptions in force calculations, and clarification of some PIV limitations. Overall, the manuscript represents a valuable contribution to the field of kite aerodynamics and is recommended for acceptance after technical corrections.

Technical correction  :

Split long sentences in Discussion and Conclusion for readability for example : “Characterizing the aerodynamics of LEI kites with numerical prediction and experimental measurement poses several challenges, owing to the highly flexible nature, pronounced anhedral and sweep, and unconventional airfoil geometries.”;  “The combination of increased downward, sideways, and upstream flow near the strut suggests the presence of a tilted or angled vortex structure.” ; “Measurement quality could be further improved by employing a narrower laser light sheet to concentrate laser power, potentially reducing reflection intensity.”

General comments:

The paper “Flow Field Analysis of a Leading-Edge Inflatable Kite Rigid Scale Model Using Stereoscopic Particle Image Velocimetry” describes an experimental study of a rigid, downscaled model of a flexible kite with an inflatable leading edge. A large amount of stereoscopic PIV measurements are conducted at various locations around the kite model and for two different inflow angles in a wind tunnel. The authors performed a flow field analysis and claim to have provided comprehensive validation data for CFD simulation results.

The paper is well-written and clearly structured. However, while there is certainly a demand for experimental reference data for validation purposes of CFD simulations, especially considering the complex geometries that are relevant in the field of airborne wind energy, it is my assessment that the data provided and the analysis performed will be of no particular use for such efforts outside of the immediate circle of the authors. As the authors discuss themselves, the measurement data is seriously flawed and the insights generated from the analysis of the experimental data are very limited. A short, interesting analysis of CFD results at the strut location is provided in the paper but there is a limited connection with the experimental work that the paper is centred around.

Therefore, it is my conclusion that I cannot recommend this paper for publication unless additional, higher quality experimental data is provided and the analysis is extended and improved.

Specific comments:

Line 62: It is not clear what the claimed novelty of the applied stereoscopic PIV measurements is. The technique has been developed more than 25 years ago. While the specific application to highly flexible LEI kites would be novel, this is mitigated by the fact that the authors chose to investigate a rigid model instead.

Figure 2a: The model appears to be relatively large compared to the diameter of the open jet wind tunnel, which could result in undesirable effects. The discussion mentions that the model has been rotated and moved during the measurements. Has it been verified that the aerodynamics, in particular the tip flow, is not affected by the turbulent mixing layer that originates at the wind tunnel nozzle edges?

Line 119: Aiming the laser directly at the curved surface is likely to create strong reflections in the PIV images that cannot be mitigated by black paint. A different measurement setup orientation should be selected to produce reliable measurements.

Line 148: It appears that the measurement campaign was not finished, with important data points missing.

Line 160: The transitions between measurement regions were smoothed out but they are still clearly visible in Figure 6. Please report the difference in flow velocity at the same location for different overlapping measurements as indication of the measurement error.

Line 179: There are no arguments provided why the formulation of Noca was used for the application of the conservation of momentum in integral form. On the contrary, the formulation of Noca was adapted to suit the particular test case. The classical formulation of the Navier-Stokes equations would be an obvious alternative here, which the authors do not consider. This formulation is often rejected in the literature when unsteady flows are analysed (due to the required volume integration and pressure computation), which is however not the case here. A significant drawback of Noca’s method is the required computation of multiple velocity gradients, which are prone to amplify measurement errors. I sincerely doubt that Noca’s method is superior to the classical formulation in this case.

Line 214: The performed PIV uncertainty analysis is too simple to understand the complex sources of error in the presented measurement data. Irrespective of that, Table 3 present uncertainties that go beyond commonly acceptable limits, particularly for measurement data that is intended to validate numerical simulations.

Line 231: Despite already filtering the experimental data considerably for unreliable measurements in large regions, the discrepancies with the CFD results are still significant and lack physical explanations. This suggests that the PIV measurements should be repeated.

Line 268: The idea of comparing circulation directly between experiment and CFD is good because it circumvents the lift calculation. However, the selected approach of showing the results with 90% confidence intervals is misleading at least. One would expect the confidence intervals to capture the variable choice of integration contour shape (ellipse vs. rectangle). See also the following comment.

Figure 8: The measurement point “PIV ellipse” near y = 0.4m is presented with a very small error bar and confidence interval, while it is clearly an erroneous data point (relative error on the order of -40% compared to CFD reference data). Representing incorrect data with low uncertainty indicated is a problematic decision, casting doubt on the entire data analysis performed.

Table 4: Negative drag values are not only reported for measurement data but also for CFD results based on Noca’s method. This is in an indication related to my discussion point for Line 179 that the selected method is not well-suited for the analysis performed in this paper.

Line 343: The discussion on the strut effects is interesting but only loosely connected to the rest of the paper. Only CFD results are discussed because the experimental data is of insufficient quality.

Line 402: The basis of the conclusions are questionable. The fact stall occurs at alpha = 17 deg has been shown experimentally before and can be considered trivial with basis knowledge of airfoil aerodynamics. The stall onset angle and details on its development could be of interest but have not been investigated.

Line 408: “good agreement with CFD” is a statement that I would tend to disagree with considering the data presented in the paper.

Technical comments:

Figure 2b: this figure is not discussed in the text. If the figure is not contributing to the discussion in the paper, it should be removed.

Figure 8: Data for Y7 is missing without explanation.