Chapter 23. -GAS TURBINE 



The starting and ignition circuits receive 

 power from storage batteries. The warning and 

 safety circuits receive power from the ship's 

 power supply panel. Power for the indicating 

 circuits is self generated by thermocouples 

 and other units in the circuits. 



Ehgine Starters 



Of the various methods used for starting gas 

 turbine engines, the three most common devices 

 are the air turbine, the hydraulic starting de- 

 vice, and the electric starter-generator. 



The air turbinestarter is a turbine-air motor 

 with a radial inward-flow turbine wheel assem- 

 bly and an engaging and disengaging mechanism. 

 Compressed air is supplied to the air turbine 

 from an external source. 



The hydraulic motor starter consists of a 

 motor-driven hydraulic pump mounted sepa- 

 rately. It supplies high pressure hydraulic oil 

 to the hydraulic motor starter, which is mounted 

 on the accessory pad along with its engaging 

 and disengaging mechanism. The hydraulic 

 motor starter is quite similar to the air turbine 

 starter; however, the hydraulic motor starter 

 is usually used for larger and higher horsepower 

 gas turbine engines. 



The electric starter- generator is a shunt- 

 wound d-c generator with compensating windings 

 and a series winding, using a 24-volt battery 

 power source. The generator is usually mounted 

 on the accessory drive pad. The generator is so 

 designed and controlled that it can be used as an 

 engine starter. When the designed engine speed 

 is reached, the starter- generator is automati- 

 cally switched from a starter to a generator. 



TRANSMISSION OF ENGINE POWER 



The two main types of gas turbine engine 

 installations used for ship propulsion are (1) 

 the geared drive, and (2) the turboelectric 

 drive. 



The fundamental characteristics of the gas 

 turbine engine make it necessary for the drive 

 mechanism to change both the speed and the 

 direction of shaft rotation in the driven mechan- 

 ism. The process of transmitting engine power 

 to a point where it can be used in performing 

 useful work involves a number of factors, two 

 of which are torque and speed. The gas turbine 

 engine does not produce high torque, but it does 

 produce high speed. Therefore, a gear train is 

 used with most gas turbine engines to lower 



speed and increase torque. This is true in 



both types of installations. In the case of the 

 geared drive installation, the gears are used 

 between the gas turbine engine and the propel- 

 ler shaft. In the case of the turboelectric drive, 

 the gears are usually used between the gas 

 turbine engine and the generator shaft, to reduce 

 the rpm of the generator to a practicable oper- 

 ating value. 



The propelling equipment of a boat or ship 

 must be capable of providing reversing power 

 as well as forward power. In a few ships and 

 boats, reversing is accomplished by the use of 

 controllable pitch propellers.^ In mostvessels, 

 however, reversing is accomplished by the use 

 of reversing gears. 



Reducing the speed of rotation and reversing 

 the direction of shaft rotation are not the only 

 requirements of the drive mechanism of a ship 

 or boat. It is also necessary to make some pro- 

 vision for the fact that the engine must be able 

 to operate at times without transmitting power 

 to the propeller shaft. In the electric drive, 

 this is no problem because the transmission 

 of power is controlled electrically. With the 

 gear type of drive, however, it is necessary to 

 include a means of disconnecting the engine 

 from the propeller shaft. Devices used for this 

 purpose are called clutches . 



The arrangement of components in a gear- 

 type drive varies, depending upon the type and 

 size of the installation. In some of the small 

 installations, the clutch, the reversing gear, 

 and the reduction gear may be combined in a 

 single unit. This type of arrangement is shown 

 in figure 23-20. In other installations, the clutch 

 and the reversing gear may be in one housing and 

 the reduction gear in a separate housing attached 

 to the reversing gear housing. Drive mechan- 

 isms arranged in either manner are called 

 transmissions . 



GAS TURBINE ENGINES AND 

 JET PROPULSION 



Thus far, we have considered the gas turbine 

 engine as a prime mover which delivers power 

 in the form of torque on an output shaft. In con- 

 cluding this chapter, it should be noted that 

 the gas turbine engine also serves as the prime 



Controllable pitch propellers are discussed in chap- 

 ter 5 of this text. 



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