Statically equivalent vector distribution
Correction-Unbalance Decomposition
Distribute one supplied add-mass correction-unbalance vector at the CG between two planes while conserving the resultant vector and its axial first moment.
Equivalent plane corrections
The first two equations conserve the correction-unbalance resultant and the axial first moment about the CG. Dividing g·mm by mm gives correction mass in grams. The angle is normalized to [0°,360°).
These equilibrium equations are general mechanics, not a formula claimed from ISO. ISO 21940-11:2016 con Amd 1:2022 addresses procedures/tolerances for rotors with rigid behaviour, including correction-plane requirements and tolerance allocation; flexible rotors are excluded. ISO 21940-13:2012 addresses criteria/safeguards for in-situ balancing and explicitly does not provide methods for calculating correction masses from vibration data.
Do not substitute this split for influence-coefficient balancing: measured bearing response, cross-effect, rotor flexibility and couple unbalance require the appropriate one-/two-plane balancing procedure and safe trial-weight practice.
