# Study of Airfoil Deflections for Unsteady Aerodynamics Optimization in Pitching Airfoils +
## 2 Materials and Methods
### Wing Experimental Design  
With the deflection parameters selected as described in the previous section, the airfoil experimental design was undertaken. Details regarding the wing designs, methodology, and manufacturing are discussed. In line with the deflection testing approach, a model was made for each of the designs, and they were fabricated with internal structure to achieve a light-weight and robust wing that could withstand aerodynamic forces and pitching. The four wings developed with the static deflected airfoil shape parameters are summarized in Table 2 with the location of the deflection and their degree of deflection. Figure 5 provides side-by-side CAD drawings along with photography of the static models manufactured. The chord length is 4 inches in all cases. The internal structure was constructed with an upper portion and a lower portion. The first model, the baseline, was designed with a snap lock feature. When pushed together, the top and the bottom halves snapped together with interlocking parts. This system worked well; however, the locking mechanism was able to be disengaged by flexing the upper and lower surfaces. This would be counterproductive for the project objectives. The second and third models were prepared with the upper and lower portions. However, this system made use of two rods slid into holes located in the airfoil. The holes were formed by the combination of the upper and lower surface geometries. The rod would then not allow the removal of the upper portion from the lower without the removal of the rod, as can be seen in Figure 6. This would in turn allow for the deflection of the upper and lower system \begin{table}
\begin{tabular}{c c} \hline
**Range of \(\alpha\)** & **Optimal Deflection** \\ \hline \multicolumn{2}{c}{Upstroke} \\ \hline \(-2\) to \(4^{\circ}\) & TE2.5 \\ \hline
4 to \(5.5^{\circ}\) & LE6 TE2.5 \\ \hline
5.5 to \(14^{\circ}\) & LE6 \\ \hline \multicolumn{2}{c}{Downstroke} \\ \hline
14 to \(11^{\circ}\) & LE6 \\ \hline
11 to \(7^{\circ}\) & LE6 TE2.5 \\ \hline
7 to \(-2^{\circ}\) & TE2.5 \\ \hline \end{tabular}
\end{table} 
Table 1: Optimal shape deflection for \(\alpha=-2\) to \(14^{\circ}\). \begin{table}
\begin{tabular}{c c c} \hline
**Description** &
\begin{tabular}{c} **Deflection Along the** \\ **Chord (\% of Chord)** \\ \end{tabular} & **Angle of Deflection** \\ \hline Baseline & NA & \(0^{\circ}\) \\ \hline Trailing Edge & 85\% & \(4^{\circ}\) \\ \hline Leading Edge & 25\% & \(6^{\circ}\) \\ \hline Combined LE and TE & 25\% \& 85\% & \(6^{\circ}\) \& \(4^{\circ}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Model parameters. while still allowing them to remain together. The manufacturing process models, with these internal cavities included, while preserving structural robustness, are discussed next. Each of the four models was fabricated out of 6061-T6 aluminum; this was performed by means of a wire electrical discharge machine (WEDM). This methodology was chosen over traditional machining due to the complex features needed inside the airfoil. The thin side walls and complex curves would have proven to be difficult and time-consuming to machine conventionally. Due to the length and simple profile when viewed from a 2D perspective, the WEDM seemed the best solution. Each upper and lower portion of the model was cut out of a 152.4 mm tall block of aluminum. The baseline model and the trailing edge model were made by combining these two 152.4 mm lengths to achieve the full 304.8 mm span. To minimize disturbance during testing with PIV, the surface was thinly and smoothly painted over. To solve this, the LE deflection and the combination deflected models were made by taking one of the 152.4 mm sections and cutting it in half. These remaining 152.4 mm sections were then affixed with a short section on both sides, thereby allowing for a continuous surface. Figure 5: Static model drawings and photography of the VR-12 baseline (**a**) and the airfoils with TE (**b**), LE (**c**), and LE and TE (**d**) deflections.