# Design, Manufacturing, and Flight Testing of an Experimental Flying Wing UAV
## 4 Aircraft Aerodynamic and Stability Design
### Design of Experimental Flying Wing UAV  
The matching plot is used to obtain the appropriate wing loading and power loading, and the maximum take-off weight is formulated and estimated in the weight estimation approach. Then,the energy consumption and wing reference area of the aircraft are obtained. The estimated total weight of the electric-powered UAV is 6.5 kg (63.7 Nt), and the maximum energy consumption calculated from a power loading of 0.5887 Nt/W is 102 W. Based on the motor specifications [19], the AXi 4130/20 kv305 electric brushless motor (Figure 3a) is sufficient to provide the required power.  
Aircraft aerodynamics and stability design starts with the given wing reference area. Then, the aircraft's shape and configuration are determined. Considering aerodynamic and static stability requirements, a Selig S5010 low-Reynolds-number airfoil is selected. Aerodynamic design consists of selecting the appropriate wing planform, aspect ratio, sweep angle, twist angle, and dihedral angle to meet the aircraft's requirements. The induced drag factor and zero lift drag coefficient are fed back for performance calculation and weight estimation. Stability design provides an appropriate center of mass to meet the static stability requirements.  
For a wing load of 59.53 Nt/m\({}^{2}\) and total weight of 63.7 Nt (total mass of 6.5 kg), the wing area is calculated to be 1.07 m\({}^{2}\); aerodynamic design and static stability design are based on this wing area. Figure 3b shows the s5010 airfoil profile. The aerodynamic characteristics are estimated using XFLR5 [17] and DATCOM software. The cruise speed is 17.6 m/s, root chord is 0.54 m, tip chord is 0.22 m, wingspan is 2.83 m, aspect ratio is 7.48, sweep angle is 30\({}^{\circ}\), twist angle is \(-4^{\circ}\), dihedral angle is \(2^{\circ}\), and flight angle of attack is \(4^{\circ}\).  
XFLR5 and DATCOM software can be used to easily build a 3D model and estimate the aircraft's zero-lift drag coefficient and induced drag factor. When these parameters are obtained, we can check their variations to ensure that the empirical value obtained from the first calculation is appropriate. If the variations are smaller than desired, the design is considered complete. If the variations are larger than desired, the new zero-lift drag coefficient and induced drag factor of the aircraft are substituted into the next process. Figure 4a shows the 3D wing planform of the flying wing UAV. Figure 4b shows the drag polar and that the induced drag coefficient \(K=0.0516\) and zero-lift drag coefficient = 0.009.  
Figure 4: (**a**) 3D wing planform of flying wing UAV and (**b**) drag polar.  
Figure 3: (**a**) AXi 4130/20 kv305 brushless electric motor and (**b**) s5010 airfoil profile.  
To obtain proper stability, the center of mass of the whole machine is set at 0.439 m from the head and the static stability margin is 8.6%. Figure 5 shows the relationship between the lift coefficient and the angle of attack and the relationship between the pitching moment coefficient and the angle of attack. At an angle of attack of 4\({}^{\circ}\), the pitching moment coefficient is 0 and lift coefficient is 0.325. Table 2 lists the main aerodynamic characteristics.