An air cycle machine system comprising an air cycle machine coupled to a fan inlet diffuser housing, wherein the air cycle machine comprises a fan rotor configured to draw outside air, and said fan inlet diffuser housing being configured to receive an airflow from said fan rotor, said fan inlet diffuser housing, comprising: a housing body formed from a composite material, the housing body comprising a heat exchanger interface portion comprising a heat exchanger interface that is configured to connect to and receive an inlet flow from a heat exchanger, said heat exchanger interface portion being positioned between an ejector housing portion and a bypass housing portion, wherein the housing body further comprises a flange at an air cycle machine interface of the ejector housing portion; a diverter vane configured to divert the inlet flow along an inlet flow path as the air flows towards the fan rotor; and wherein a diffuser cone is disposed within the housing body and aligned with said fan rotor so as to receive said airflow; a first transition region of the housing body between the heat exchanger interface portion and the ejector housing portion comprising an air cycle machine end reinforcement patch proximate to said heat exchanger interface, wherein the air cycle machine end reinforcement patch comprises a first patch thickness and a second patch thickness, and a ratio of the first patch thickness to the second patch thickness is between 2.02 and 3.11; and an ejector formed as a gap having an ejector gap width between a nozzle portion and a diffuser portion within the ejector housing portion of the housing body and disposed between the fan rotor and the diffuser cone, said diffuser portion being at a fan end of said diffuser cone, wherein the diffuser portion has a downstream ejector gap width which is measured from an outer face of the flange to the diffuser portion, and a ratio of the downstream ejector gap width to the ejector gap width is between 4.62 and 5.01, wherein the ejector defines a recirculation flow path configured to provide flow to the fan rotor in the event that the inlet flow is reduced, and the bypass housing portion is disposed downstream of the diffuser cone and configured to route a heat exchanger bypass flow to an exit flow of the air cycle machine system. a housing body formed from a composite material, the housing body comprising a heat exchanger interface portion comprising a heat exchanger interface that is configured to connect to and receive an inlet flow from a heat exchanger, said heat exchanger interface portion being positioned between an ejector housing portion and a bypass housing portion, wherein the housing body further comprises a flange at an air cycle machine interface of the ejector housing portion; a diverter vane configured to divert the inlet flow along an inlet flow path as the air flows towards the fan rotor; and wherein a diffuser cone is disposed within the housing body and aligned with said fan rotor so as to receive said airflow; a first transition region of the housing body between the heat exchanger interface portion and the ejector housing portion comprising an air cycle machine end reinforcement patch proximate to said heat exchanger interface, wherein the air cycle machine end reinforcement patch comprises a first patch thickness and a second patch thickness, and a ratio of the first patch thickness to the second patch thickness is between 2.02 and 3.11; and an ejector formed as a gap having an ejector gap width between a nozzle portion and a diffuser portion within the ejector housing portion of the housing body and disposed between the fan rotor and the diffuser cone, said diffuser portion being at a fan end of said diffuser cone, wherein the diffuser portion has a downstream ejector gap width which is measured from an outer face of the flange to the diffuser portion, and a ratio of the downstream ejector gap width to the ejector gap width is between 4.62 and 5.01, wherein the ejector defines a recirculation flow path configured to provide flow to the fan rotor in the event that the inlet flow is reduced, and the bypass housing portion is disposed downstream of the diffuser cone and configured to route a heat exchanger bypass flow to an exit flow of the air cycle machine system.