Modular rotor balancing

A modular method of forming a dynamically balanced a rotor assembly comprising n rotor sub-assemblies, wherein n≥2, the method comprising the steps of:

• forming a rotor unit consisting of one of the rotor sub-assemblies and n−1 simulators each of which corresponds to and substitutes a respective rotor sub-assembly;
• dynamically balancing the rotor unit by applying a respective set of one or more balancing weights to one or more of the rotor sub-assembly and the simulators of the rotor unit so that a set applied to a given rotor sub-assembly or simulator corrects unbalance contributed to the rotor unit by that rotor sub-assembly or simulator only;
• noting the radial and azimuthal positions of any balancing weight applied to any simulator in step (ii) and the simulator to which it is applied;
• repeating steps (i) to (iii) for n−1 other rotor units each comprising a different rotor sub-assembly and in which each of the other n−1 rotor sub-assemblies of the rotor is substituted by a respective simulator
• for each balancing weight applied to a simulator in step (ii), applying a balancing weight to the corresponding rotor sub-assembly, the balancing weight having the same weight and being applied to the corresponding rotor sub-assembly at the same axial, radial and azimuthal positions as the balancing weight applied to the simulator;
• and
• mating the n rotor sub-assemblies to produce the dynamically balanced rotor assembly.