Calibration for the Sensitivity Matrix of the Collins Strain Gauge ...

Calibration for the Sensitivity Matrix of theCollins Strain Gauge BalanceExecutive SummaryMeasuring the aerodynamic forces and moments on models of airborne bodies is oneof the major functions of the Low Speed Wind Tunnel (LSWT), operated by theDefence Science and Technology Organisation (DSTO). The data acquired by thesemeasurements are needed for the evaluation, design, and research of military aircraft,missiles, and air vehicles in general, and for assessment of their performance.One of the primary tools used to measure these loads is the internal strain gaugebalance. Reliable and accurate wind tunnel measurements require frequent calibrationof these balances. A calibration matrix has been determined previously for the Collinsstrain gauge balance. Since the upgrade of the data acquisition system in the DSTOLSWT, a new set of amplifiers has been installed and new wiring from the balancepatch board to the instrumentation cabinet has also been laid. The new amplifiers andwiring will cause the values of the calibration coefficients for the Collins balance tochange significantly so that a new calibration is necessary. To obtain a new set ofvalues for the calibration coefficients in a short timeframe, only the sensitivity matrixwas redetermined. This was adequate because the particular readout system in useonly affects the sensitivity matrix.Details of the calibration methodology and the equipment used are given in this reporttogether with the new sensitivity matrix. The results have been verified allowing thecontinued use of the tunnel to determine the forces and moments on a model undertest with acceptable accuracy pending a full calibration.