Abstract: An air cycle machine (10) has a first stage turbine (60) mounted to a central portion of a common shaft (12), a compressor (50) mounted to the central portion of the shaft (12), a second stage turbine (30) mounted to a first end of the shaft (12), and a fan (40) mounted to a second end of the shaft (12), all for rotation therewith about a longitudinal axis (14). The first and second stage turbines (60, 30) are operative to extract energy from a flow of compressed air for driving the shaft (12), and the fan (40) and the compressor (50), in rotation about the axis (14).

Abstract: An air cycle machine (10) has four wheels mounted on a common shaft (20) for rotation therewith about a longitudinal axis (12), including a second stage turbine rotor (30) mounted to a first end (20a) of the shaft, a fan rotor (40) mounted to a second end (20b) of the shaft, a first stage turbine rotor (50) mounted to a central portion (20c) of the shaft, a compressor rotor (60) mounted to the central portion of the shaft in back to back relation to the first stage turbine rotor, the first and second stage turbine rotors being operative to extract energy from a flow of compressed air for driving the shaft (20), and the fan rotor (40) and the compressor rotor (60), in rotation about the axis, and first and second hydrodynamic gas film foil bearings (70, 80) for supporting the shaft for rotation about the longitudinal axis (12).