# A UAV Wind Field Perception System Inspired by Biological Perception
## 2 Wind Field Calculation Method and Measurement System Construction
### Wind Tunnel Experiment of Wind Field Measurement System  
The angle of attack and sideslip angle measured by the angle sensor installed on the aircraft may be different from the actual angle of attack and sideslip angle of the aircraft because the local airflow is affected by the flow field of the aircraft body and what it feels is the direction of the local airflow. It is different from the actual airflow angle of the aircraft. Therefore, the relationship between the airflow angle measured by the sensor and the actual airflow angle must be established, which needs to be determined through wind tunnel experiments. The experiment consists of the following parts:  
* Airspeed meter calibration and evaluation experiment  
The measurement accuracy of the airspeed meter is related to the ambient temperature, air pressure, etc. The airspeed meter used in this paper integrates temperature and pressure measurement devices with the flight control. The measured values under the pressure and temperature conditions have been compensated during the delivery stage, but in actual use, under different wind speed conditions and different measurement environments, there is still a certain difference between the air velocity measured by the pitot tube air velocity meter and the actual air velocity. This corrected relationship is important for obtaining the corrected airspeed. This can be achieved by adjusting the wind tunnel output wind speed through the wind tunnel control computer and setting the airspeed meter at 5 m/s, 6 m/s, 7 m/s, 8 m/s, 9 m/s, 10 m/s, 11 m/s, 12 m/s, 13 m/s, 14 m/s, and 15 m/s for full-range wind tunnel wind speed measurement. Waiting for the output wind speed to be stable and then record the airspeed meter measurement data. Measuring for 20 s and continuing to adjust the wind speed setting until the next wind speed is stable, then measuring again, recording the measurement data, and repeating the experiment for all 5 groups. Therefore,  
Figure 7: Estimated lift-to-drag ratio curve. in order to simulate the influence of different environments on the measurement, five sets of experiments were carried out for airspeed calibration at different temperatures and at different time periods, and the above steps were repeated for each experiment. The evaluation standard is the correlation coefficient R2 between the fitted calibration curve and the measured value. The closer the coefficient is to 1, meaning that the higher linearity of the function, and the better the measurement characteristics of the airspeed. * Angle sensor calibration Since the measured value of the angle sensor is actually the magnitude of the voltage, its measurement accuracy is affected by the characteristics of the circuit. The factory-set voltage and angle conversion curve is only a reference curve under the standard state. In actual use, it is related to the power supply voltage of the sensor. Therefore, it is necessary to calibrate the measured value of the angle sensor and evaluate the measurement characteristics of the sensor, that is, the relationship between the measured angle and the actual angle under a certain airflow angle. The experiment is not only for the angle of attack sensor but also for the angle of sideslip sensor. By changing the horizontal rotation angle of the angle deflection mechanism in the wind tunnel system, the simulation experiment of different sideslip angles is realized, and the control operation is realized through the computer control interface. This can be achieved by inputting the expected deflection side slip angle on the computer control interface and confirming it. The angle deflection mechanism will rotate according to the command. Recording the data at this time after the rotation mechanism reaching the designated position and stabilizes. In order to determine the experimental angle range, these steps were carried out several times in the early stages.