Technical Guide to the UTAD-2 Wind Tunnel

5. Instrumentation

5.1 Three Component Strain Balance

UTAD-2 wind tunnel is equipped with external three-component rider balance ABMK(t), located above the test section. The cinematic scheme is shown on Fig. 5.1. Lateral support base is constant and equal to 450 mm, longitudinal base can be continuously varied in 300...450 mm range. Balance provides measuring of three components P1, P2, and Q of full loading on the model in vertical plane and model weight compensation. Built-in mechanism for angle-of-attack alteration permits 60 deg variations with angle reading by dial. Drag, lift, and pitch moment coefficient dependences vs. angle-of-attack can be obtained in wind axes. Measuring range:

P1 - 0...50 N, P2 - 0...50 N, Q - 0...50 N.

Both manual balancing and automatic data acquisition are possible. In the last case industrial strain gauge transducers ("Veda" company, Kiev) are connected to loading transfer path and remotely controlled electric drive is used for angle-of-attach change.
Calibration is performed using special loading device and reference weights. Measuring errors are: 0.03 N for P1 and P2 components, and 0.014 N for Q component at 90% confidential probability.

Figure 5.1 Cinematic Scheme of ABMK(t) Balance

5.2 Dynamic Pressure Transducer

The dynamic pressure in the test section is measured using pressure measuring complex IKD-6TDf-0.016, which is inductive differential pressure transducer with built-in electronic modulator-demodulator. It is powered with stabilized DC source and output signal is a high-level DC voltage, functionally dependent of applied pressure difference. Output voltage in data acquisition and processing system is converted to digital form and further processed.
The pressure side of transducer is connected to a pipeline, in which the pressure from plenum chamber is supplied. Vacuum side is vented to atmosphere. The dynamic pressure is calculated using the so-called "dynamic pressure field coefficient", which is determined during test section flow calibration.
The transducer is calibrated every six month using standard liquid pressure gauge MKB-250 with an accuracy of +0.1 Pa. Polynomial is used to approximate calibration function that ensures measuring error less then 0.5 Pa within 600 Pa full range.