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 . <EOS>