Testing and Validation of the Dynamic Inertia Measurement Method

Abstract

The Dynamic Inertia Measurement (DIM) method uses a ground vibration test setup to determine the mass properties of an object using information from frequency response functions. Most conventional mass properties testing involves using spin tables or pendulum-based swing tests, which for large aerospace vehicles becomes increasingly difficult and time-consuming, and therefore expensive, to perform. The DIM method has been validated on small test articles but has not been successfully proven on large aerospace vehicles. In response, the National Aeronautics and Space Administration Armstrong Flight Research Center (Edwards, California) conducted mass properties testing on an "iron bird" test article that is comparable in mass and scale to a fighter-type aircraft. The simple two-I-beam design of the "iron bird" was selected to ensure accurate analytical mass properties. Traditional swing testing was also performed to compare the level of effort, amount of resources, and quality of data with the DIM method. The DIM test showed favorable results for the center of gravity and moments of inertia; however, the products of inertia showed disagreement with analytical predictions. KEYWORDS: dynamic inertia measurement frequency response function ground vibration test mass properties moment of inertia Nomenclature AFRC = Armstrong Flight Research Center CAD = computer-aided design CG = center of gravity CRV = Crew Return Vehicle DFRC = Dryden Flight Research Center diff = difference DIM = dynamic inertia measurement DOF = degree of freedom ETA = engineering test article F = force FRF = frequency response function

Inertia property determination by spectrum analysis of damped oscillation detection signal

“…Together with mass, centre of mass, product of inertia etc., it constitutes mass characteristics (properties) [1,2]. All machines with rotational behaviour, such as aircraft, satellites, automobiles and robots, need to be tested for inertia properties to verify their rotational performance [3][4][5][6][7][8][9][10]. Precision measurement of inertia properties is of significance for air vehicles, which need precise attitude and orbit control, such as missile, high supersonic aircraft, interceptor and satellite [11,12].…”