Abstract: The blades (38) of a gas turbine engine fan rotor (32) are uniquely distributed in the rotor hub (48) so that combination tone noise attributable to one or more physical nonuniformities in the blades is mitigated. The invention recognizes that the frequency spectrum of the combination tone noise includes both decay prone harmonics and decay resistant harmonics and that allocation of acoustic energy into the decay prone harmonics and out of the decay resistant harmonics is effective for mitigating combination tone noise. In particular, the blades are distributed so that the spatial or circumferential spectrum of the physical nonuniformity is dominated by circumferential harmonics whose order is no greater than the order of the highest decay prone harmonic of the combination tone noise spectrum.

Abstract: A method disclosed]for balancing the fan rotor (10) of a turbine engine having a hub (12) with blades (16) extending radially therefrom includes the steps of determining (30) a penalty associated with each possible unique blade arrangement in which a limited number of blades is relocated from their initially assigned locations on the hub to new target locations. A subset of these arrangements is selected (34), the subset members being the arrangements having the lowest penalties. For each member of the subset, the penalty determination (36) is made for each possible unique blade arrangement in which a limited number of blades is relocated from their initial locations in each subset member to new target locations. If these latter penalty determinations identify an arrangement having a penalty less than that of any arrangement in the subset, the subset selection (34) and penalty determination steps (36) are repeated until no further reduction in penalty is observed.