As an extension to the short takeoff and landing (STOL) hybrid wing body (HWB) concept, a low-fidelity model is needed to perform the experiment. It was calculated that it is impossible to match the Reynolds number and the range of Mach number of the original design and the test model, so the group redesigned the experiment just to validate the potential flow software used for conceptual design. Because the experiment is self-funded, we shrank the size by half to reduce the cost, which turned into the worst mistake made in this experiment.

The simplified model is then simulated with the planned testing condition. Characteristics of the model were recorded to compare with the results of the planned test. The span-wise load distribution is used to design the test model with the required factor of safety.

To ensure that the experiment is safe for the personnel in the lab, the requirements, also considering the ability of the other groups to perform their test, the professor required a factor of safety greater than 4. The data collected from the simulation is used to calculate the greatest force that the model would experience in the test.

The simplified model is then imported into Dassault Systèmes 3DExperience. To reduce the material and time required for 3D printing, the meshes of the structurally critical parts are generated to perform static simulation and topology optimization. Show in the image carousel, the model for printing is exported from the optimized mesh.

The parts are then 3D printed, reinforced, and polished. The small size of the model became a major source of difficulties. When printing with FDM printers, the sharp trailing edge is omitted during slicing and printing. This behavior of the printer caused unevenly shortened chord lengths that need to be fixed by hand. Polishing the model consumed an extremely long time. The size of the gap on the outer shell needs to be removed, and the size of those steps depends on the slope when printing. It took more than 10 cycles to fill and polish the gaps on the chine of the centerbody, which would cause a large deviation in the shape and dimension if the precision shape is critical.

The test was performed in the small open-loop subsonic wind tunnel in the lab. As expected, the recorded voltage from the pyramidal balance was not usable, and the group had to rely on the flow visualization experiment. The method chosen was to paint a mixture of kaolin clay powder and kerosene onto the surface, and set up the flow before the mixture dries. The shear force experienced by the clay particles causes them to move in the direction of the flow, and the flow pattern on the surface is then visible to human eyes.

The test was conducted at different angles of attack, with the same increment of angle as the simulation completed in the earlier stage. The reduced size caused more issues than expected. The low Reynolds number near the tips was the main concern till the manufacturing issue occurred, and more problems followed in the testing; it became harder to calibrate and paint evenly. With the data recorded not precise enough for the comparison, the experiment was then focused on visualization.

A transparent overlay with a grid and outline of the model is used as a reference to more easily locate the coordinates of a certain pattern. More information can be found in the report attached below.