# Longitudinal Wind Tunnel Tests of the PROSIB 19-Pax Airplane
## 2 Wind Tunnel Setup  
### Experimental Facility and Equipment  
The series of experimental tests have been performed within the primary subsonic wind tunnel facility of the Department of Industrial Engineering. This wind tunnel is a closed-circuit system operating at subsonic speeds and it is equipped with a single return path. Furthermore, the facility is characterized by a closed test section with a tempered rectangular cross-section. The essential components of this wind tunnel are labeled in Figure 2: test section (A-B), the first diffuser (B-C), the second diffuser (D-E), the third diffuser (G-I), the safety screen (C), the first corner (C-D), the second corner (E-F), the third corner (I-L), the fourth corner (L-M), turning vanes within corners, fan ahead the second corner, honeycomb flow straighteners (M), turbulence control screen, stagnation chamber (M), nozzle (M-N). The key features are outlined in Table 1. The measurement equipment includes:  
* Longitudinal strain gauge balance;
* Venturi system;
* Inclinometer sensor;
* Potentiometer;
* Temperature probe.  
An internal strain-gauge balance, made in-house with 2024-T3 aluminum alloy, was used to measure lift, drag, and pitching moment. Table 2 offers an overview of the full-scale readings and maximum errors per axis.  
\begin{table}
\begin{tabular}{l l} \hline
**Characteristic** & **Value** \\ \hline Test section dimensions & 2.0 m \(\times\) 1.4 m \\ Maximum available wind speed & 50 m/s \\ Turbulence level & 0.10\% \\ Maximum power & 150 kW \\ \hline \end{tabular}
\end{table}
Table 1: Main characteristics of the wind tunnel.  
Figure 1: Rendering of the PROSIB 19-pax concept.  
The airflow speed within the test section was determined by assessing the dynamic pressure measured by the Venturi system. This system is furnished with four static pressure probes located on the lateral surfaces of the initial and final sections of the convergent duct. By utilizing a pressure transducer with 2500 Pa full-scale range and 3 Pa accuracy, the static pressure difference between these sections was measured. This pressure variation, in conjunction with the continuity equation, enabled the determination of dynamic pressure just before the test section. By combining the dynamic pressure measurement with air density estimation derived from temperature measurements, the wind speed within the test section was calculated. The temperature probe consists of a flush wall-mounted probe for the measurement of the static temperature in the test section. For the angle of attack measurement, the mono-axial tilt sensor Crossbow CXTLA01 was employed. It offers an accuracy of 0.05\({}^{\circ}\) and a range spanning from \(-75^{\circ}\) to \(75^{\circ}\).  
The longitudinal attitude control was entrusted to an electro-mechanical system led by a PC. This system was placed below the floor of the test section. It incorporates an electric stepper motor providing angular excursions ranging from \(-20^{\circ}\) to \(20^{\circ}\). Digital signals were generated by the data acquisition and control system and transmitted to the stepper motor through an amplifier.