Air bearing shaft

An air cycle machine assembly comprising:

• a journal bearing;
• and
• an air bearing shaft comprising a seal disk and a shaft body, the shaft body comprising a first shaft body portion positioned within the journal bearing, the first shaft body portion extending from a face of the seal disk to a knife-edge seal, the first shaft body portion comprising:
• a plurality of journal bearing cooling holes positioned axially closer to the knife-edge seal than to the face of the seal disk, the journal bearing cooling holes extending through the first shaft body portion to a hollow interior, and the journal bearing cooling holes having a total cooling area;
• and
• a plurality of start-up holes positioned axially closer to the face of the seal disk than to the knife-edge seal, the start-up holes extending through the first shaft body portion to the hollow interior, the start-up holes having a total start-up area, and a ratio of the total cooling area to the total start-up area is between 2.17 and 4.06.

A method of installing an air bearing shaft in an air cycle machine assembly, comprising:

• inserting the air bearing shaft into a journal bearing, the air bearing shaft comprising a seal disk and a shaft body, the shaft body comprising a first shaft body portion positioned within the journal bearing, the first shaft body portion extending from a face of the seal disk to a knife-edge seal, the first shaft body portion comprising:
• a plurality of journal bearing cooling holes positioned axially closer to the knife-edge seal than to the face of the seal disk, the journal bearing cooling holes extending through the first shaft body portion to a hollow interior, and the journal bearing cooling holes having a total cooling area;
• and
• a plurality of start-up holes positioned axially closer to the face of the seal disk than to the knife-edge seal, the start-up holes extending through the first shaft body portion to the hollow interior, the start-up holes having a total start-up area, and a ratio of the total cooling area to the total start-up area is between 2.17 and 4.06;
• and
• coupling the air bearing shaft to a thrust shaft of the air cycle machine assembly;
• and
• coupling the air bearing shaft to a turbine rotor of the air cycle machine assembly.