Balancing simulation mass, apparatus and associated methods

A rotary disc balancing simulation mass 412 for balancing a rotary disc 402 configured to support a set of rotary components is described. The rotary disc balancing simulation mass 412 is configured to be attached to the rotary disc 402 and simulate the mass of two or more of the rotary components. The rotary disc 402 may have a plurality of attachment features 406 corresponding to the set of rotary components. The set of rotary components may be circumferentially spaced around the rotary disc 402. The rotary disc balancing simulation mass 412 may have one or more radially extending feet 414 configured to be attached to the rotary disc 402. Also disclosed is a balancing simulation apparatus 400 and a method of balancing a rotary disc. The rotary disc 402 may be a rotor of a gas turbine engine such as a fan disc, compressor disc, or turbine disc configured to support a set of blades.