Archive

Principle of Operation of an MOI Instrument

Other Industries - Golf Clubs
August 12, 2020

The moment of inertia of any object can be measured through its CG by hanging the object from a wire, twisting it slightly to initiate oscillation, and timing the period of oscillation. However, anyone who has ever tried this finds that the object swings from side to side and bounces up and down rather than […]

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Torsion Pendulum Theory

Consider the torsion pendulum of Figure 1 consisting of a disk of mass moment of inertia I lb-in-sec2, restrained in rotation by a wire of torsional stiffness K in-lb/radian. If the disk is turned an initial angle and sharply released, it will oscillate with damped harmonic motion as shown in Figure 2. The period of […]

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How to Find MOI Through CG Without Knowing the CG Location

Why measure Moment of Inertia (MOI) through the Center of Gravity (CG)? When an object is free to rotate, it will rotate around an axis passing through its center of gravity. Therefore it is essential to know moment of inertia through center of gravity to assess the flight characteristics of a payload. The MOI about […]

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How to Calculate Product of Inertia From Moment of Inertia Measurements

Product of inertia (POI) is the characteristic of an object that causes dynamic unbalance. Knowing the POI of an object is essential to determine some of its flight characteristics, such as its tendancy to wobble. Knowing POI in all planes allows determining the principal axes of a payload. How to measure product of inertia? Product […]

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A New Spin Balance Machine

This page describes a new low speed vertical axis aerospace¬† balance machine that takes advantage of recent advances in technology. This machine measures moment of inertia (MOI) in addition to product of inertia (POI) and center of gravity (CG) offset. Spin speeds as low as 15 RPM yield useful results. This machine has a number […]

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Using the “Moment of Inertia Method” to Determine Product of Inertia

Product of inertia is generally measured using a spin balance machine. In this type of machine, the object is rotated at a speed of about 100 RPM, and the reaction forces against the upper and lower spindle bearings are measured. Product of inertia is then calculated automatically by the machine’s on line computer, using formulas […]

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Pan Weighing vs Moment Weighing

The terms used in turbine blade balancing can be confusing. The two main terms used are pan weighing and moment weighing. What is Pan Weighing? Pan weighing simply means measuring the mass of the blades. This could be called weighing the blade. We call it pan weighing to avoid the confusion with moment weighing. Pan […]

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Improve Your Sensor Image With Balance

This paper reviews the properties which inherently limit the image quality of a gimbal mounted optical imaging system. It further describes how image quality is degraded by external influences, particularly vibration, in the supporting vehicle. The primary emphasis is to quantify, through physical principals, and verify, through experimental demonstration, the degree of static balance required […]

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