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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.
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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
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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
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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
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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
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| HANDS ON
SESSION Participants will be grouped by interest and
technical background. There will be a maximum of 5 people per group. 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
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| 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
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Registration Form for Mass Properties Seminar
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