3156. “”Standard”” SAWE Mass Properties Calculation Software and Algorithms

Paper

Abstract

Although most CAD programs now include routines for calculating the mass properties of the various elements of a system or vehicle, there is still a use for basic mass properties calculation software. If such software were written in JAVA, then it could be easily shared by all members of the SAWE and would run on any type of computer. This software could be used when estimating the mass properties of new designs, or it could be used to make quick simplified mass properties calculations to verify that the results of the CAD programs are reasonable. In addition to describing the software, this paper is a tutorial on the calculation of mass properties (moment of inertia, centerof gravity, product of inertia). We have included a discussion of the coordinate transformation of inertias using tensors and have provided a number of simple mathematical tests that can be used to verify the reasonableness of calculated values. There are numerous textbooks on dynamics that devote a few pages to the theory of these properties. However, these textbooks quickly jump from a very brief description of these quantities to some general mathematical formulas without giving adequate examples or explaining in enough detail how to use these formulas. The purpose of this paper is to provide a detailed procedure for the calculation of mass properties for an engineer who is inexperienced in these calculations. This paper will also provide a convenient reference for those who are already familiar with this subject. This paper contains a number of specific examples with emphasis on units of measurement. The examples used are rockets and re-entry vehicles. The paper then describes the techniques for combining the mass properties of sub-assemblies to yield the composite mass properties of the total vehicle. Errors due to misalignment of the stages of a rocket are evaluated numerically. Methods for calculating mass property corrections are also explained. It was hoped that an outcome of this paper will be the generation of SAWE standard mass properties utility software written in JAVA that is available on the SAWE web site. Tutorial booklets could also be downloaded which would explain the use of the software and describe the process of making mass properties calculations. Unfortunately, due to concerns regarding United States export restrictions, the JAVA software described in this paper is currently only available for distribution and licensing to United States companies and citizens.