Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 5, Unbalance
Section 4, Static Unbalance in a Uniform Rotor
It's easiest to start with a "uniform rotor" with its CG as shown.
Visualize the plane of the rotor's CG as the one at which it will balance, if placed on a fulcrum.
The net result of "pure" static unbalance (no couple present) can be assumed to be acting in the plane of the rotor's lateral CG.
A single static unbalance force that is acting through the rotor's CG can be resolved to two separate forces, one in each chosen measurement plane. Each force would be half the magnitude of the original single force, equal to each other and at the same angle relative to each other (0° out-of-phase).
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