Assessment of Effect of Circular Cutout of front spar on Accuracy of Strain Gauge Bridge Data to Obtain Shear Load

In order to measure the strain due to the shear force applied on a wing's spar, it is necessary to install a strain gauge on the neutral axis. In cases such as a circular hole on the neutral axis, it is impossible to install a strain gauge. Therefore, by installing strain gauges outside the cutting area of the hole, it will be useful to measure the shear load. Therefore, the main objective of this study is to investigate the effect of circular slices on the accuracy of strain gauge data acquired for calculating shear load. In this regard, the front spar structure of a lightweight aircraft with two sections are considered as strain gauge bridges. In the laboratory for each measurement section, a bridge is installed on the neutral axis and another two bridges with certain distances from the neutral axis are installed. Concentrated load at specific points has been applied by linear electromotor actuators equipped with S-type load cells. Using the calibration method of ground loads, the load equations are written and finally by using of strain gauge signals which extracted from the test, the concentrated loads are calculated. The forces are calculated in non-creep conditions and in spite of the cuts in the sections, and the differences between them are evaluated. Accordingly, the effect of circular slices on the accuracy of the output of the strain gauge bridges was determined. The results show the correctness of the tests and the accuracy of the load equations.