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 ; 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 ; 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 ; 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 . <EOS>