499. A Rapid Inertia Estimating Method

Paper

Abstract

During the advanced design phase and in project work also, it often becomes necessary to rapidly but accurately estimate booster vehicle mass moment of inertia. This paper presents the derivation of equations and a method by which this may be done. The rapid inertia calculating equations are not limited to booster vehicles, but apply to any system for calculating inertia. Since the mass moment of inertia of any system can be derived from I= ∑▒I_(o ) +∑▒〖wd〗^2 , the transfer equation (〖wd〗^2) is simplified without sacrificing any accuracy, and Io term is obtained from graphs. It has been proven that in most cases the Io term contributes much less to the total inertia than does the transfer term, so that small errors in estimating Io can be accepted. However, errors in calculating the transfer cannot be tolerated.
In using the rapid inertia estimating method, more time can be saved when estimating inertia for mass systems with more than four masses if the equations in Table 1 can be combined.
In any inertia calculating or estimating method the center of gravity is usually the first item to be calculated. Only now, with the rapid inertia calculating method, it can be determined last or not at all! Nevertheless, when the center of gravity has to be determined, it absorbs the same amount of time independent of inertia calculating method.