pressure transducers and accelerometers. Because bending, shear, and torsion in a structure can be determined by proper measurement and inter~ pretation of strains developed,’ bonded strain gages may be used as the primary sensing element for the measurement of these response functions. Consideration of the factors mentioned in paragraph 2.3 led to the choice | wey id Prom previcus experience it was known that the major problem re- . ee OU wes. atete . Sa oeHere : Ta oe garding strain gage use would be the obtaining and maintaining of a good, atmosphere-tight bond between the gage and the metal. Several methods were tried but because of time limitations field testing was precluded, The method finaliy adopted for strain gage application was the cornventicnal procedure employingArmstrong cement as the bonding agent, a v feee 2.3.2.1 Bending Moment Bending momert measurements were made on the wings of both air craft and the fuselage and horizontal stabilizers of the B-36 aircraft. The vending moment gage comprised four strain gages bonded to the primary structure and connected electrically so as to froduce an output propor tional to the bending induced. A typical bending gage installation em ployed for two-spar structures and a schematic diagram of the electrical circuit are shown in Fig. 2.1. The resulting strain bridge, a four-ac- tive-arm Wheatstone oridge circuit, is relatively unresponsive to loads we & ete NN compensated. s ‘ ete wine L. other than those producing vertical bending. In some instances the bending of individual spars was measured and the bridge outputs combined, in a manner determined by special calibration, to give total Lending moment. The installation was essentially the same as that shown in Fig. 2.1 for the two~spar structure, except. that all four strain gages were placed on the one spar, two at the top and two at the bottom, using the same electrical interconnection. In the 5-36D aircraft, fuselage bending is absorbed by the four main longerons. To determine fuselage bending, one gage was located on the inside of the outer flange of each longeron for a total of four rages. The standard bending gage bridge circuit wea employed to combine strain gage outputs. 2.3.2.2 ° Torsion The torsion bridge, an installation for direct measurement of torsion, was located ‘iin the left outer wing panel of the B26 aircraft, Sixteen strain gages were located on the inside and outside surfaces of the skin tetween the front and rear spar; eight gages on the upper skin, four inside and four outside, and eight gages on the lower skin. A sketch of the installation and schematic circuit diagram is shown in Fig. 2.2. The resulting circuit is essentially a four-active~arm wheatstone bridge circuit somewhat analogous to the cerding gage except that there are four strain gages rer arm. 2.3.2.3 Shear Two types of shear measurements were made: the direct measure~ « of Baldwin EBDF~13D strain gages for all bended strain gage use. These strain gages had a nominal resistance of 350 ohms and were temperature f