An engine, connected with a flywheel, is designed to operate at an average angular speed of $$800$$ rpm. During operation of the engine, the maximum change in kinetic energy in a cycle is found to be $$6240$$ J. In order to keep the fluctuation of the angular speed within $$ \pm 1\% $$ of its average value, the moment of inertia (in kg-m²) of the flywheel should be ____________.