An axial-flow fan (10; 110; 210; 310) comprising: a hub (14; 114; 214; 314) including an open end (22; 122; 222; 322) and a substantially closed end (18; 118; 218; 318), the hub defining a central axis (30; 130; 230; 330); a plurality of blades (42; 142; 242; 342) coupled to the hub and extending radially outwardly from the hub, each blade having a root (46; 146; 246; 346) coupled to the hub, a tip (50; 150; 250; 350) spaced from the hub, a first edge (54; 154; 254; 354) proximate the open end of the hub and interconnecting the root and the tip, the first edge defining one of a leading edge and a trailing edge with respect to a rotational direction (62; 162; 262; 362) of the hub about the central axis, and a second edge (66; 166; 266; 366) proximate the substantially closed end of the hub and interconnecting the root and the tip, the second edge defining the other of the leading edge and the trailing edge; and a plurality of ribs (70; 170; 270; 370) coupled to the hub, including a first rib (70a; 170a; 270a; 370a) substantially aligned with a first plane intersecting the central axis and an intersection of the first edge of a first of the plurality of blades with the hub, at the root of the first blade, wherein an angular spacing between the first plane and a reference plane intersecting the central axis and an intersection of the first edge of a second of the plurality of blades with the hub, at the root of the second blade, defines one sector, and a second rib (70b; 170b; 270b; 370b) substantially aligned with a second plane angularly positioned between the first plane and the reference plane, at a location less than or equal to about (1/nR-0,05) sectors from the first plane in which nR equals the number of ribs divided by the number of blades; wherein the entire root of the first blade is positioned on a first side of the second plane, and wherein the entire root of the second blade is positioned on a second side of the second plane opposite the first side. a hub (14; 114; 214; 314) including an open end (22; 122; 222; 322) and a substantially closed end (18; 118; 218; 318), the hub defining a central axis (30; 130; 230; 330); a plurality of blades (42; 142; 242; 342) coupled to the hub and extending radially outwardly from the hub, each blade having a root (46; 146; 246; 346) coupled to the hub, a tip (50; 150; 250; 350) spaced from the hub, a first edge (54; 154; 254; 354) proximate the open end of the hub and interconnecting the root and the tip, the first edge defining one of a leading edge and a trailing edge with respect to a rotational direction (62; 162; 262; 362) of the hub about the central axis, and a second edge (66; 166; 266; 366) proximate the substantially closed end of the hub and interconnecting the root and the tip, the second edge defining the other of the leading edge and the trailing edge; and a plurality of ribs (70; 170; 270; 370) coupled to the hub, including a first rib (70a; 170a; 270a; 370a) substantially aligned with a first plane intersecting the central axis and an intersection of the first edge of a first of the plurality of blades with the hub, at the root of the first blade, wherein an angular spacing between the first plane and a reference plane intersecting the central axis and an intersection of the first edge of a second of the plurality of blades with the hub, at the root of the second blade, defines one sector, and a second rib (70b; 170b; 270b; 370b) substantially aligned with a second plane angularly positioned between the first plane and the reference plane, at a location less than or equal to about (1/nR-0,05) sectors from the first plane in which nR equals the number of ribs divided by the number of blades; wherein the entire root of the first blade is positioned on a first side of the second plane, and wherein the entire root of the second blade is positioned on a second side of the second plane opposite the first side.