# Fast Airfoil Selection Methodology for Small Unmanned Aerial Vehicles
## 5 Results
### Results Export from XFLR5 and Import to Spreadsheet Software  
Unfortunately, XFLR5 does not provide any automated routine for user-defined result exporting. Despite this fact, the user can acquire the precise numerical pairs of any given point on a plot curve. Given this, all of the measurements of interest were transferred manually to spreadsheets. The following Tables 6-9, were constructed in order to be used by the SUAV designer at the airfoil comparison procedure, if needed (all twenty participating airfoil's aerodynamic measurements can be found in.xlsx format under Supplementary Materials Table S2, for methodology repeatability and verification purposes). The measured attributes of the above Tables 6-9 are explained in detail in the following numbered paragraphs, according to [8,21]:  
1. **Minimum drag coefficient \(C_{dmin}\):** Is the minimum \(C_{d}\) value in the \(C_{d}\)-\(C_{l}\) diagram (Units: dimensionless);
2. **bucket width \(C_{bucket\_width}\):** the authors thought that it could be useful to conduct a series of measurements under the \(C_{bucket\_width}\) name. It is observed that regarding the classic airfoils, such as the NACA series, the bucket always has a smaller width compared to the low Reynolds number airfoils, where the bucket is more spread out in the x axis. An example is demonstrated in Figure 6, where the SG6043 low Reynolds number airfoil is simulated at Re = 350,000, contrary to a classic NACA 662-415 at Re = 3,000,000. The low Reynolds number-widened bucket, is an excellent advantage both for the designer and the operator of the SUAV, as the possible suitable airfoils are increased for the designer and the deviation margin in the flight envelope is also bigger for the operator, without a big penalty in the range and the endurance of the vehicle. (Units: dimensionless);  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{10}{c}{**Re = 100,000 (Flap \# 80\% Chord, 30\({}^{\circ}\))**} \\ \hline \hline \multirow{2}{*}{ID} & \multirow{2}{*}{**Airfoil**} & \multirow{2}{*}{\(C_{\text{\emph{Image}}}\)} & \multirow{2}{*}{\(\mathbf{\Delta C_{\text{\emph{If}}}}\)} & \multirow{2}{*}{\(C_{\text{\emph{Image}}}\)} & \multirow{2}{*}{\(\mathbf{a_{\text{\emph{g}}}}\)} & \multirow{2}{*}{\(\mathbf{\Delta a_{\text{\emph{g}}}}\)} & \multirow{2}{*}{\(\mathbf{a_{\text{\emph{g}}}}\)} & \multirow{2}{*}{\(\mathbf{\Delta a_{\text{\emph{g}}}}\)} & \multirow{2}{*}{\(\mathbf{\Delta a_{\text{\emph{g}}}}\)} \\  & & & & & & & & & & \\ \hline  
GU00 & 0.004 & 0.0 (0.31-0.49) & 0.3 & 0.5 & \(-\)0.08 & 87 & 8 & 1.04 & 2 \\3. **Ideal lift coefficient \(C_{li}\):** It corresponds to the minimum drag coefficient. When studying an ideal airfoil with a symmetric bucket, \(C_{li}\) should be in the middle of the bucket. In the real world, \(C_{li}\) can be anywhere close to the curve that we consider as the bucket. (Units: dimensionless);
4. **Ideal angle of attack \(\alpha_{i}\):** Is the angle of attack that corresponds to \(C_{li}\). (Units: degrees);
5. **Pitching moment coefficient \(C_{m}\):** The Variations of Pitching Moment Coefficient versus Angle of Attack. The design objective is to have \(C_{m}\) close to zero as far as possible. (Units: 1/rad);
6. **(\(C_{l}\)/\(C_{d}\))\({}_{max}\):** Is the maximum value of the \(C_{d}\)/\(C_{l}\)-\(\alpha\) diagram. Large values are desirable. (Units: dimensionless);
7. **Stall angle \(\alpha_{s}\):** Is the critical angle of attack beyond which the airfoil will suffer a decrease in lift force. Large values are desirable, especially at lower Reynolds numbers and when using flaps. (Units: degrees);
8. **Airfoil gross maximum lift coefficient \(C_{max}\):** It corresponds to the maximum \(C_{l}\) value on a \(C_{l}\)-\(\alpha\) diagram. (Units: dimensionless);
9. **Stall quality:** It is a prediction of what is going to happen in the uncomfortable situation where the airfoil will enter the stall region. More details on the stall quality judgment procedure can be found in the next Section 5.2.