An axial fan rotor for a ram air fan, the axial fan rotor comprising: a hub that comprises: an inner hub portion; a disk portion connected to a radially outer surface of the inner hub portion and including cooling holes (90, 92); and an outer hub portion connected to a radially outer surface of the disk portion, the outer hub portion having an upstream arm extending axially upstream from a center of the axial fan rotor and a downstream arm opposite of the upstream arm and extending axially downstream from the center of the axial fan rotor, wherein the upstream arm has a radially inner surface, a radially outer surface opposite of the radially inner surface, and a compound contoured surface connecting the radially inner surface to the radially outer surface, characterised in that the compound contoured surface comprises: a first arcuate segment extending from the radially inner surface of the upstream arm and having a first radius R 1; a second arcuate segment extending from the first arcuate segment and having a second radius R 2; a chamfered segment extending from the second arcuate segment and having an angle A 1; and a third arcuate segment extending from the chamfered segment to the radially outer surface and having a third radius R 3; and blades extending radially outwards from the hub. a hub that comprises: an inner hub portion; a disk portion connected to a radially outer surface of the inner hub portion and including cooling holes (90, 92); and an outer hub portion connected to a radially outer surface of the disk portion, the outer hub portion having an upstream arm extending axially upstream from a center of the axial fan rotor and a downstream arm opposite of the upstream arm and extending axially downstream from the center of the axial fan rotor, wherein the upstream arm has a radially inner surface, a radially outer surface opposite of the radially inner surface, and a compound contoured surface connecting the radially inner surface to the radially outer surface, characterised in that an inner hub portion; a disk portion connected to a radially outer surface of the inner hub portion and including cooling holes (90, 92); and an outer hub portion connected to a radially outer surface of the disk portion, the outer hub portion having an upstream arm extending axially upstream from a center of the axial fan rotor and a downstream arm opposite of the upstream arm and extending axially downstream from the center of the axial fan rotor, wherein the upstream arm has a radially inner surface, a radially outer surface opposite of the radially inner surface, and a compound contoured surface connecting the radially inner surface to the radially outer surface, characterised in that the compound contoured surface comprises: a first arcuate segment extending from the radially inner surface of the upstream arm and having a first radius R 1; a second arcuate segment extending from the first arcuate segment and having a second radius R 2; a chamfered segment extending from the second arcuate segment and having an angle A 1; and a third arcuate segment extending from the chamfered segment to the radially outer surface and having a third radius R 3; and a first arcuate segment extending from the radially inner surface of the upstream arm and having a first radius R 1; a second arcuate segment extending from the first arcuate segment and having a second radius R 2; a chamfered segment extending from the second arcuate segment and having an angle A 1; and a third arcuate segment extending from the chamfered segment to the radially outer surface and having a third radius R 3; and blades extending radially outwards from the hub.