# Design and Control of an Ultra-Low-Cost Logistic Delivery Fixed-Wing UAV
## 2 Overall UAV Design
### Design of Main Parameters  
The three most crucial parameters for an aircraft are the wing area, S (m\({}^{2}\)), the takeoff weight of the aircraft, \(m_{0}\) (kg), and the static thrust of the power unit, \(P_{o}\left(dan,1 dan=10^{-5}\text{N}\right)\). The corresponding parameters are  
\[P_{O=}\frac{m_{o}g}{10S}\left(\text{dan/m}^{2}\right) \tag{16}\]  
The above equation is the formula for calculating the load of the starting wing.  
\[v_{\text{max}}=10P/\left(m_{o}g\right) \tag{17}\]  
The above formula is the common formula for calculating the takeoff thrust-to-weight ratio.  
The maximum takeoff weight of the UAV in this article is 2 kg; the thrust of the selected brushless motor is 1.47 kg, and the wing area is 3400 cm\({}^{2}\). From this, it can be calculated that the maximum wing load at takeoff is 65 g/dm\({}^{2}\), and the takeoff thrust-to-weight ratio is 1.5.  
1. Lift-drag ratio (1) Lift and lift coefficient According to [PERSON]'s theorem, the amount of lift generated by an airfoil can be calculated using the following formula:  
\[L=\frac{1}{2}\rho V^{2}SC_{L} \tag{18}\]  
where L is the lift force (N), \(\rho\) is the air density (kg/m\({}^{3}\)), \(V\) is the relative velocity (m/s), \(S\) is the wing area (m\({}^{2}\)), and \(C_{L}\) is the wing's lift coefficient.  
(2) Drag and drag coefficient  
Figure 16: Aerodynamic analysis of the whole UAV.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Overall Length/mm** & \
\begin{tabular}{c} **Maximum** \\ **Height/mm** \\ \end{tabular} & **Width/mm** &
\begin{tabular}{c} **Magazine** \\ **Length/mm** \\ \end{tabular} \\ \hline
655 & 97 & 80 & 182 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Fuselage parameter.  
The resistance formula is  
\[D=\frac{1}{2}\rho V^{2}SC_{D} \tag{19}\]  
where \(D\) is the drag force (N), \(\rho\) represents the air density (kg/m\({}^{3}\)), \(V\) is the relative velocity (m/s), \(S\) is the wing area (m\({}^{2}\)), and \(C_{D}\) is the coefficient of lift for the wing.  
From (3) and (4), it can be seen that the lift-to-drag ratio of the aircraft is \(\frac{C_{L}}{C_{D}}\).  
2. Service ceiling (Hmax)  
The practical ceiling refers to the maximum flight altitude at which an aircraft can maintain a level flight state under human operation, and the magnitude of Hmax can be determined using the relative air density value at this altitude [51]. It can be derived according to the equations \"weight = lift\" and \"thrust = drag\" when the aircraft is in a level flight. Using polar curves, \(C_{x}=C_{x0}+D_{0}C_{y}^{2}\), the following can be obtained: \(K_{\max}=\left(\frac{C_{y}}{C_{x}}\right)_{\max}=\frac{1}{2\sqrt{D_{0}C_{x0}}}\) and the rule \(\Delta_{I}=\frac{1.67\sqrt{D_{0}(C_{x0})}}{\xi F_{D}}\), where \(\Delta_{I}\) is a practical ceiling. It can be seen that the practical ceiling of the aircraft is directly proportional to the thrust-to-weight ratio.  
Through the above calculation formula of the aircraft performance and the basic requirements for designing UAVs, the main design parameters of UAVs are determined, as shown in Table 6.  
Figure 17 shows the top, side, and bottom views of the aircraft design, as well as some dimensional data. The aircraft has a wingspan of 1487 mm, a slender length of 233 mm, an aspect ratio of 6.87, a warp of 1.50 degrees, and a vertical tail main angle of attack of 25 degrees. The main components of the aircraft are made of balsa wood and laminate, and some of the connections are made of carbon fiber materials.