This thesis deals with an experimental evaluation of an interesting wing tip geometry. This is the second version of the thesis as the first one did not pass.

The thesis starts with the research part, where wing tip vortices, induced drag, types of tip devices, etc. are presented. The research part lacks a bit in explaining what exactly is the goal of the geometry, which is then shown a bit out of the blue without reasoning for why the respective choices were made.

Data analysis for the measurements is improved from the before version of the thesis. The meassurement itself has been done first for lift and drag of a baseline and a test geometry. Some of the graphs are very jaggy and wavy, no confidence intervals are shown either. The results are thus maybe not as accurate as could have been achieved. They show that the induced drag was decreased, but the parasite and viscous drags were also increased. Next a wake measurement was done using wake pressure deficit mapping. A clear difference in wake structures was shown. There are some small errors in the description of the results but overall the evaluation is correct. At last a tuft measurement is shown with a very detailed textual analysis. The tufts themselves unfortunately can not accurately show flow on static pictures in the thesis.

The thesis has been improved and the main deficiencies were ammended. Unfortunately some smaller issues still remain. As such I recommend the thesis for defence.

The submitted Master’s thesis deals with the experimental assessment of the aerodynamic performance of a toroidal wingtip. The topic is interesting and relevant, focusing on the potential reduction of induced drag while considering the additional parasitic drag associated with the increased wetted area.

The theoretical part provides the necessary background in finite-wing aerodynamics, induced drag and wingtip devices. The literature review has been sufficiently developed and the relevant statements are supported by references. Nevertheless, some analogies, particularly between toroidal propellers and static wingtip devices, could have been discussed more critically.

The main contribution of the thesis is its experimental part. The author designed and manufactured the test models and carried out an extensive wind-tunnel campaign, including aerodynamic force measurements, wake measurements and flow visualization. The amount of experimental work and subsequent data processing is appropriate for a Master’s thesis and provides an interesting comparison between the conventional and toroidal configurations.

My main reservation concerns the interpretation of some experimental results. Conclusions regarding vortex suppression, redistribution of circulation or reduction of downwash are occasionally formulated more strongly than can be directly demonstrated by the applied experimental methods. More detailed velocity-field measurements or numerical analysis would be necessary to confirm some of these explanations quantitatively. The thesis also contains several minor language and stylistic deficiencies, which, however, do not significantly affect its readability.

The objectives of the thesis have been fulfilled. The author demonstrated the ability to independently design and perform an aerodynamic experiment, process the measured data and formulate conclusions. Despite the above comments, I consider the thesis to meet the requirements for a Master’s thesis and recommend it for defence. Topics for thesis defence:

1. The changes observed in the wake are interpreted as a redistribution of circulation and reduction of wingtip vortex intensity. Which additional quantities or flow-field characteristics would have to be measured to verify this conclusion quantitatively?
2. The toroidal configuration has a larger wetted area than the baseline wing. How could the increase in parasitic drag caused by the additional wetted area be experimentally distinguished from changes in induced drag caused by the modified wingtip flow?