93. The Effect of Input Details Upon the Accuracy of Weight and Inertia Calculations

Paper

Abstract

The Northrop Weight Engineering Department, like many other Weight Engineering
Departments, employs the use of International Business Machines in recording weight data. Since the procedures vary among companies, depending upon the type of data desired, a brief explanation of the method used in compiling the data which forms a basis for this discussion, is in order. In general, the system consists of listing the bills of materials of the individual drawings on I.B.M. work cards, accounting for all dash numbers and attaching parts. Opposite each listed item other pertinent data are noted, such as weight, ‘x’, ‘y’ and ‘z’ arms, AN codes, zone codes and where required, the Io’s or the moments of inertia of the items about its own center of gravity. The latter two items, the zone code and the Io’s are for the purpose of determining weight and moment of inertia distributions of the airplane by prescribed zonal breakdowns of the wing, fuselage and tail surfaces. When a sing item extends beyond one zone, it is broken down and listed according to the zone distribution. For example, a spar weight could be coded to several zones along the span of the wing. The work cards are then key punched and stored by IBM personnel. When a tape run is required these punch cards can be processed in such a manner that the several tapes received by the weight list not only the usual items required for weight and balance control, but also furinish data which allows the computation of weight, center of gravity, and moment of inertia of each separate zone. The records are revised were necessary as the design progresses, thus proving current and accurate information which is used by the Dynamics, Loads and Aerodynamics Department as well as by the Weights Department. The calculated weight data and the moment arms are carried to one decimal place in the records. Io’s are listed for items exceeding one pound in weight or whose shape is such as to extend outside a twelve-inch cube
From the above discussion it can be seen that the control records, compiled
under this system of operation, embody are relatively large number of entries. It was believed that this amount of detail was necessary in order to provide the type and amount of data require d by the Dynamics and Loads Department. The question subsequently arose as to whether or not these details are required, an if eliminated what should be the effect on the accuracy of the weight and inertial data. It was with this purpose in mind that a review of completed records was inaugurated.