A radial-bearing apparatus, comprising: an inner bearing assembly comprising: an inner support ring circumferentially surrounding an inner ring axis; a first plurality of superhard bearing elements coupled to the inner support ring, each of the first plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface comprising a partial-ellipsoidal surface shape; an outer bearing assembly comprising: an outer support ring circumferentially surrounding an outer ring axis; a second plurality of superhard bearing elements coupled to the outer support ring, each of the second plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface of each of the second plurality of superhard bearing elements contacting a superhard bearing surface of at least an opposing one of the first plurality of superhard bearing elements, wherein the superhard bearing surface of each of the second plurality of superhard bearing elements comprises a substantially planar surface facing toward the inner bearing assembly. an inner bearing assembly comprising: an inner support ring circumferentially surrounding an inner ring axis; a first plurality of superhard bearing elements coupled to the inner support ring, each of the first plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface comprising a partial-ellipsoidal surface shape; an inner support ring circumferentially surrounding an inner ring axis; a first plurality of superhard bearing elements coupled to the inner support ring, each of the first plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface comprising a partial-ellipsoidal surface shape; an outer bearing assembly comprising: an outer support ring circumferentially surrounding an outer ring axis; a second plurality of superhard bearing elements coupled to the outer support ring, each of the second plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface of each of the second plurality of superhard bearing elements contacting a superhard bearing surface of at least an opposing one of the first plurality of superhard bearing elements, wherein the superhard bearing surface of each of the second plurality of superhard bearing elements comprises a substantially planar surface facing toward the inner bearing assembly. an outer support ring circumferentially surrounding an outer ring axis; a second plurality of superhard bearing elements coupled to the outer support ring, each of the second plurality of superhard bearing elements having an element side surface extending between a base and a superhard bearing surface, the superhard bearing surface of each of the second plurality of superhard bearing elements contacting a superhard bearing surface of at least an opposing one of the first plurality of superhard bearing elements, wherein the superhard bearing surface of each of the second plurality of superhard bearing elements comprises a substantially planar surface facing toward the inner bearing assembly.