vr ee PT Tg Point Load System The National Advisory Committee for Aeronautics (NACA) has developed and presented in NACA Report TN 2993, a method for measuring shear, bending moment, and torsion in the principal lifting or control surfaces of an airborne aircraft. This method, as utilized in this investigation, is hereafter referred to as the Point Load Method. The point load method differs from other methods of strain gaze instrumen- tation primarily in the manner in which the three principal terms perti~ nent to load investigations, i.e., shear, bending moment, and torque, are separated, In the past, strain bridge installations for the measurement of loads on aircraft have been made using many schemes for reducing the effects of cross coupling and interaction. Most of these schemes are still qutte valuable in the field of less complex structures, but as the structures beeome more complex, errors increase and the principles of these methods become more and more difficult to apply. The point load method is based on the premise that, in general, the strain along all lines through any point in a structure is a function of shear, bending moment, and torque. The point load system consists essentially of a method of separating these principal functions. This FREEOL ORS Bete Ne TO PIT 203e7ed is accomplished by a method of calibration and mathematical analysis of the calicration data, Point loads were applied on 13 points of each semi-span of the norizontal tail surface for four different conditions. Combined gage equations were then derived from these data. The equations express the relationship between the response of the selected bridges and the de~ sired function. A detailed presentation of how the point load method of instrumentation was calibrated and employed to measure blast loading FIELD TESTING PROCEDURE After the aircraft were instrumented, as described in paragraph 2.3, they were flown to check out the instrumentation and then readied for overseas flight for participation in IVY. The IVY tests, conducted at the Facific Proving Grounds in the Fall of 1952, comprised two shots, Mike and King, Both the 3-36D and the B47 aircraft were flown in the two IVY shots, In the Spring of 1953, the 5-36 aircraft was exposed during Snot 9 of UFSHOT-KNOTHCLE tests held at the Nevada Proving Grounds. The field testing procedure consisted cf two essential parts: positioning the aircraft for the desired inputs and operation of the instrumentation equipment for measuremert and recording of the resvonse data. The position selected was a point in space where, from predicted data, the maximum allowable input would te realized if the weapon yield reached its upper limit. To position the aircraft at the point selected with a maximum of accuracy and a minimum of danger required precision tiring ard flawless navigation. The procedures emplcyed for exposing the two aircraft are given below, + 2.4 RM eet! is given in NACA Report TN 2993. CMH tee. wren pe rvviee yet RT eywoe ~ ee or a ww ee enn ey mere ue 6 OE RT P * MMAR be be