Chapter 23. -GAS TURBINE 



147.144 

 Figure 23-10.— Stator element of turbine 

 assembly. 



or multiple-rotor turbines may be used with 

 either centrifugal or axial-flow compressors. 

 In the single-rotor type of turbine, the power 

 is developed by one rotor and all engine-driven 

 parts are driven by this single wheel. In the 

 multiple-rotor type, the power is developed by 

 two or more rotors. It is possible for one or 

 more rotors to drive the compressor and the 

 accessories, while one or more other rotors 

 are used for the power output. 



Main Bearings 



The main bearings in a gas turbine engine 

 serve the critical function of supporting the 



147.145 

 Figure 23-11.— Rotor element of turbine 

 assembly. 



compressor, the turbine, and the engine shaft. 

 The number and position of main bearings re- 

 quired for proper support vary according to 

 the length and stiffness of the shaft, with both 

 length and stiffness being affected by the type 

 of compressor used in the engine. In general, 

 a gas turbine engine requires at least three 

 main bearings and may require six or even 

 more. 



Several types of main bearings are used 

 in gas turbine engines. Ball and roller bearings 

 have been quite commonly used in the past, and 

 they are still used in many aircraft gas turbine 

 engines. Sleeve bearings, split-sleeve bearings, 

 floating-sleeve bearings, and slipper bearings 

 are commonly used in gas turbine engines de- 

 signed for marine propulsion. 



The slipper or pivoted-shoe type of bearing 

 has recently attracted considerable attention and 

 is being used increasingly for main bearings on 

 gas turbine engines and other high speed en- 

 gines. This type of bearing is designed with 

 relatively large radial clearances. Since a 

 rotating object tends to rotate about its true 

 balance center when it is not restrained by 

 bearings or supports, the large radial clear- 

 ances in the slipper bearings allow a kind of 

 self-balancing action or automatic compensation 



603 



