Product Design Aspects for Design of Accurate Mass Properties Measurement System for Aerospace Vehicles

Abstract

Mass properties of aerospace vehicle viz Weight, Center of Gravity (Xcg, Ycg, Zcg) & Mass Moment of Inertia (Ixx, Iyy & Izz) are critical inertial parameters which are vital to meet the intended mission objectives. Accurate mass properties measurement is needed for fast maneuvering aerospace vehicles to meet the Control and Guidance requirements within the tolerable limits generated by the System Designer. Mass properties estimation is vital during the configuration design phase of an aerospace vehicle. Assumptions and Constraints during the configuration design, limits the accuracy of estimations making the mass properties measurement mandatory. The mass properties of the aerospace vehicle can be measured by numerous methods, but for achieving high accuracies within the tolerable limits, the measurement system should have advanced technologies and measurement methodologies. Based on the experience, mass properties measurement systems were designed using Load Cells and Cross-Flexural Pivots in two different systems (Weight and CG in System-1, MOI in System-2), which have limited accuracy and also involves tedious external measurements. Adopting Air-Bearing (T / H / Spherical shape) supported with accurate sensors using Inverted Torsion Pendulum method, Multiple Point Weighing method and a proper measurement methodology, enhances the accuracy of the measurement system. Usage of spherical bearing yields a better accurate system but has the difficulty in realization of the system indigenously, whereas use of T or H-shape bearing is a feasible solution for achieving the desired accurate mass properties specifications. This paper gives an insight into to the product design aspects to be considered for realization of accurate mass properties measurement system.