# A UAV Wind Field Perception System Inspired by Biological Perception
## 2 Wind Field Calculation Method and Measurement System Construction
### Wind Field Measurement System Scheme Design  
According to the overall demand analysis of the measurement system, a 3D wind field measurement system scheme based on the wind vane sensor is designed in this paper (Figure 4), and it is integrated on a certain type of UAV platform. The overall system scheme is shown in the figure. In this system, the UAV can be manually controlled by the operator, and can also fly autonomously according to the flight mission uploaded by the ground station. When the data link is lost, the UAV can automatically switch to the return mode according to the preset setting. The real-time transmission to the ground station is also all recorded in the memory card of the flight controller.  
The UAV wind field measurement system is mainly composed of three parts (Figure 5): a fixed-wing UAV system, airflow information measurement system, and ground control and display system. Of these, the airspeed of the UAV is determined by the digital airspeed. The airflow angle is measured by the wind vane sensor. In this paper, a wind vane angle sensor is used to measure the angle of attack (AOA) and the angle of sideslip (AOS). The angle sensor is composed of symmetrical airfoil carbon fiber blades (wind vane), a mechanical shaft, precision micro potentiometer, counterweight, and other parts. In order to obtain the movement speed of the UAV relative to the incoming flow, we use a digital airspeed meter for measurement, which is a small ceramic-based pressure sensor powered by a 3.3 V or 5.0 V power supply. The three-dimensional ground speed is obtained by data fusion of GPS and IMU units, and the processor on the flight controller is used to calculate the attitude angle, airflow angle, and three-dimensional ground speed to obtain the three-dimensional wind speed.  
Figure 4: Schematic diagram of system composition.  
In this paper, a UAV with a large aspect ratio is used as a flight test platform, a 6 s 5300 mAh lithium battery is used as a power source, and a propeller is used to provide forward power. Some parameters are shown in Table 1:  
This paper uses Tornado aerodynamic estimation software to evaluate the UAV's aerodynamic performance. The UAV is modeled in the software in accordance with the relevant UAV parameters and in accordance with the geometric parameters of the actual UAV airfoil (the Boeing16 airfoil in the airfoil library is used for the main wing in this paper). The symmetrical airfoil NACA0011 is used as well, shown in Figure 6, and the vortex grid method is used to estimate the flight performance of the established model. According to the calculation, the stall speed of the UAV is about 6.3 m/s, and the lift-to-drag ratio curve at the cruising speed is shown in Figure 7.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Index** & **Value** & **Index** & **Value** \\ \hline Span & 3000 mm & Power & 22.2 V 5000 mAh Li-Po \\ Fuselage length & 1870 mm & Motor & 4258-KV460 \\ Endurance & 30 min & ESC & 70A \\ Wing loading & 64.5 g/dm\({}^{2}\) & Servo & 23 g \(\times\) 6 \\ Wing square & 36.2 dm\({}^{2}\) & Propeller & 15 \(\times\) 7.5 \\ Max take-off weight & 4900 g & Center of gravity & 9.2 cm (distance from wing leading edge) \\ \hline \hline \end{tabular}
\end{table}
Table 1: The parameters of the UAV.  
Figure 5: Interface relationship of wind speed measurement system.  
Figure 6: Geometric shape of the wing.  
The formula used to calculate the cruise speed is  
\[V_{\text{cruise}}=\sqrt{\frac{2*W*g}{C_{L,0}*S*\rho}} \tag{11}\]  
where \(W\) is the take-off weight, \(g\) is the acceleration of gravity, \(C_{L,0}\) is the lift coefficient at 0 angle of attack, \(S\) is the reference area of the wing, and \(\rho\) is the air density. The cruising speed can be calculated by substituting the parameters into 11 m/s.