Turbine Engine Bearings and Seals

The main bearings have the critical function of supporting the main engine rotor. The number of bearings necessary for proper engine support is, for the most part, determined by the length and weight of the engine rotor. The length and weight are directly affected by the type of compressor used in the engine. Naturally, a two-spool compressor requires more bearing support. The minimum number of bearings required to support one shaft is one deep groove ball bearing (thrust and radial loads) and one straight roller bearing (radial load only). Sometimes, it is necessary to use more than one roller bearing if the shaft is subject to vibration or its length is excessive. The gas turbine rotors are supported by ball and roller bearings,  which are antifriction bearings. [Figure 1-75J Many newer engines use hydraulic bearings, in which the outside race is surrounded by a thin film of oil. This reduces vibrations transmitted to the engine.

In general, antifriction bearings are preferred largely because they:

• Offer little rotational resistance,
• Facilitate precision alignment of rotating elements,
• Are relatively inexpensive,
• Are easily replaced,
• Withstand high momentary overloads,
• Are simple to cool, lubricate, and maintain,
• Accommodate both radial and axial loads, and
• Are relatively resistant to elevated temperatures.

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