Chapter 23. -GAS TURBINE 



mover in the power plants of many military 

 aircraft. When so adapted, the gas turbine 

 engine develops power by converting thermal 

 energy into mechanical kinetic energy in a high 

 velocity gas stream. The highly accelerated gas 

 stream creates thrust which propels the air- 

 craft. This methodof creating thrust is called the 

 direct reaction or jet propulsion method. 



The concept of thrust is basic to an under- 

 standing of jet propulsion. The concept of thrust 

 is based on Newton's third law of motion, which 

 may be stated as follows: For every acting force 

 there is an equal and opposite reacting force . 

 In the case of aircraft in flight, the acting force 

 is the force the engine exerts on the air mass 

 as it flows through the engine. The reacting force 

 (thrust) is the force which the air mass exerts 

 on the components of the engine as the heated 

 air mass is discharged from the jet nozzle at 

 the rear of the airplane. In other words, thrust 

 is not produced by the ejected air mass reacting 

 against the atmosphere; rather, thrust is cre- 

 ated within the engine as the air mass flowing 

 through the engine is accelerated and dis- 

 charged. 



Engines which include the gas turbine and 

 which create thrust by the direct reaction 

 method are commonly identified as turbojet 

 engines. Except for a diffuser and a different 

 type exhaust system in engines of the turbojet 

 type, the basic components of the turbojet engine 

 are similar in design and function to the com- 

 ponents of any open-cycle gas turbine engine. 

 The function of the diffuser is to decrease the 

 velocity of the inlet air and to increase its 

 pressure before the air enters the compressor. 

 The exhaust system of aturbojet engine consists 

 basically of a cone and a convergent nozzle. 

 The exhaust cone is designed to exhaust to the 



nozzle the accelerated air mass which the other 

 components of the engine deliver to the cone. 

 As the accelerated air mass flows through the 

 convergent nozzle, its velocity is greatly in- 

 creased and thrust is created within the engine. 



MAINTENANCE 



The maintenance of gas turbines is the 

 normal function of operating activities. Cleanli- 

 ness is one of the most important basic essen- 

 tials in operation and maintenance of gas tur- 

 bines. Particular care should be exercised in 

 keeping fuel, air, coolants, lubricants, rotating 

 elements, and combustion chambers clean. Peri- 

 odic inspection procedures should be followed 

 in order to detect maladjustments, possible 

 failures, and excessive clearances of moving 

 parts. All inspection and maintenance require- 

 ments should be accomplished in accordance 

 with the 3-M System (PMS Subsystem). 



CAUTION : Never use lead pencils for mark- 

 ing gas turbine hot parts, because the carbon 

 content of the pencil lead will cause stainless 

 steel to become brittle, causing a possible fail- 

 ure of the parts that were marked. A grease 

 pencil should be used in marking gas turbine 

 parts. Do not use steel wool to clean gas tur- 

 bine parts, unless the wool is stainless steel. 



Overhaul periods and procedures are set 

 up by the Naval Ship Systems Command. These 

 periods and procedures are reported to the 

 Fleet through NavShips Technical Manuals and/ 

 or direct correspondence. Accurate operating 

 logs should be kept on each engine so the number 

 of hours and operational history on each engine 

 is readily known. These records aid in devel- 

 oping measures which improve engine reli- 

 ability . 



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