MASS PROPERTIES MEASUREMENT SEMINARS
FOR ENGINEERS AND TECHNICIANS

Registration Form

Our MASS PROPERTIES seminar is a 3-1/2 day concentrated course in the calculation and measurement of mass properties. Engineers or Technicians are invited to attend. The needs of engineers will be addressed with presentations on theory and analysis of Mass Properties Calculations, combining mass properties of components to make up assemblies, calibration methods, and measurement accuracy. The technicians will be more concerned with emphasis on the practical aspects of measurement techniques, hands on exercises, measurement pitfalls, and methods for cross checking the accuracy of measurements. Selected topics will allow technicians and engineers to confer in small, homogeneous groups to discuss problems and topics that are particularly pertinent to their individual needs.

Since group size is limited, there will be time for discussion of specific questions the participants may have. The outline below may be adjusted at any time to better meet the needs of the participants. Participants are encouraged to bring drawings or data for discussion.

Course Outline

ASSESSMENT OF STUDENT NEEDS

At the start of the seminar, participants will be asked to present problems they have encountered in their work to the Seminar Director. These problems will assist him in directing the seminar to the most pertinent topics.

DEFINITION OF MASS PROPERTIES

Physical description, units of measurement, and interrelationship of these quantities are discussed.

Weight and mass
Center of Gravity
Mass moment of inertia
Axis translation & tilt formulas
Product of inertia
Units
Relationship between CG and MOI
Relationship between POI and MOI
Importance of axis definition when submitting data to others
Common misunderstandings that result in disaster
Case histories of flight failure due to misunderstanding of data

INTRODUCTION TO MASS PROPERTIES INSTRUMENTS

State-of-the-art mass properties measuring systems will be demonstrated. These instruments will provide an opportunity to see the application of principles discussed earlier for the measurement of CG and MOI.

MASS PROPERTIES MEASUREMENT METHODS

Current principles of measurement used in mass properties measurement are discussed along with the inherent advantages and disadvantages of each method. Emphasis will be on tips and techniques to minimize measurement errors. Environmental effects will also be discussed.

MEASUREMENT OF CENTER OF GRAVITY

Gas bearing rotary table CG machine
Mechanical Balance Method
Multiple point weighing method
Spin balance method
Moment of inertia method of measuring CG
Balance restoration transducers vs. load cells
Leveling error
Effect of lean
Importance of fixturing method
Sensitivity vs. Accuracy

MEASUREMENT OF MOMENT OF INERTIA

Torsion pendulum equation of motion
Hanging wire methods (bifilar & trifilar)
Inverted torsion pendulum using gas bearing
Weight sensitivity
Gravity pendulum errors
Effect of damping
Trapped air mass effect (internal & external)
Fixturing errors
Effect of CG offset
Effect of large Product of inertia

MEASURING PRODUCT OF INERTIA

Horizontal vs. vertical spin balance machines
Soft bearing vs. hard bearing machine
Basic equations for a hard bearing machine
Phase shift angle error due to resonance
Spin speed optimization
Rigid vs. flexible rotors
Sensitivity and accuracy
Air turbulence
The moment of inertia method of measuring POI

HANDS ON SESSION

Participants will be grouped by interest and technical background. Participants will measure Weight, CG, and MOI. Exercises developed by Space Electronics staff will permit the participants to develop good measuring habits. They will also see how errors may be introduced by incorrect measuring techniques, and how they may be avoided.

CALCULATING MASS PROPERTIES

Calculations and interrelationship of mass properties are discussed. Examples will be presented to show how mass properties of components may be calculated and combined to yield the mass properties of an assembly. Error sources in measurement will also be analyzed to determine their relative effect on measurement accuracy.

MEASUREMENT VERIFICATION AND TROUBLESHOOTING

In this session, participants will discuss methods for checking the validity of mass properties measurements. Emphasis will be on developing support data to confirm primary measurements and eliminating error sources.

BALANCING INSTRUMENTATION

This discussion will emphasize how mass properties measurements are used to obtain static and dynamic balance of critical components. It will include a discussion of how custom software is used to define a measurement sequence which will minimize time and errors in production measurements.

Static balance applications
Dynamic balance applications

FIXTURING

CG and POI measurements are only as accurate as the fixtures used to support the test item. MOI measurements are sensitive to lean errors. We will review a number of fixture designs and discuss specific case histories where fixturing error rendered the measurements worthless.

Choose the datum - the key to accurate fixturing
Influencing the test item design regarding the datum
Vee block fixtures
Grid plate fixtures
Tilt/translation fixtures
Methods to determine end stop position
Fixture tare variations

Registration Form for Mass Properties Seminar

Back to Main Seminar Page

MASS PROPERTIES MEASUREMENT SEMINARS FOR ENGINEERS AND TECHNICIANS