NAVWEPS OO-ROT-RO  AtRPlANE PERFORMANCE  boundary layer along the fuselage surface. At  supersonic  flight speeds,  the diffuser must slow  the air to subsonic with the least waste of  energy in the inlet air and accomplish the  process  with a minimum of aerodynamic drag.  In addition, the inlet must be efIicient and  stable in operation throughout the range of  angles of attack and Mach numbers of which  the airplane is capable.  The partial expansion of the gases through  the turbine will provide the power to operate  the engine. As. the gases are discharged from  the turbine at point F, expansion will continue  through the tailpipe nozzle. until atmospheric  pressure is achieved in the exhaust. Thus,  continued expansion in the jet nozzle will re-  duce the pressure and increase the volume of  the unit weight of air to point G on the pressure  volume diagram. As a result, the final jet  velocity is greater than the inlet velocity and  the momentum change necessary for the .de-  velopment of thrust ha~s ’ been created. The  area YFGA represents  the work remaining to  provide the expansion to jet velocity after the  turbine has extracted the work requited to  operate the compressor.  The operation of the compressor  can be af-  fected greatly by the uniformity of flow at the  compressor face. When large variations in  flow velocity and direction exist at the face of  the axial compressor, the efficiency and stall-  surge limits are lowered. Thus, the flight  conditions which involve high angle of attack  and high sideslip can cause deterioration of  inlet performance.  Of course, the combustion chamber discharge  could be more completely expanded through a  larger turbine section and the net power could  be used to operate a propeller rather than pro-  vide high exhaust gas velocity.  For certain  applications, the gas turbine-propeller combi-  nation could utilize the high power capability  of the gas turbine with  greater propulsive  efficiency.  The compreJ.ror  s&on is one of the most im-  portant components of the turbojet engine.  The compressor  must furnish the combustion  chamber with large quantities of high pressure  air in a most efficient manner. Since the com-  pressor of a jet engine has no direct cooling,  the compression process takes place with a  minimum of heat Ioss of the compressed  air.  Any friction loss or inefficiency of the com-  pression process  is manifested as an undesirable  additional increase in the temperature of the  compressor  discharge air.  Hence, compressor  efficiency will determine the compressor  power  necessary  to create the pressure  rise of a given  airflow and will affect the temperature change  which can take place in the combustion  chamber.  Each of the engine components previously de-  scribed will contribute some function affecting  the efficiency  and output of the turbojet engine.  For this reason, each of these components  should be analyzed to determine the requite-  ments for satisfactory operating characteristics.  The i&t or &@er must be matched to the  powerplant to provide the compressor entry  with  the required airflow.  Generally, the  compressor  inlet must receive the required air-  flow at subsonic velocity with uniform dis-  tribution  of velocity and direction at the  compressor face. The diffuser must capture  high energy air and deliver it at low Mach  number uniformly to the compressor.  When  the inlet is along the sides of the fuselage, the  edges of the inlet must be located such that  the inlet receives only high energy air and  provision must be made to dispose of the  The compressor  section of a jet engine may  be an axial flow or centrifugal flow compressor.  The centrifugal flow compressor  has great util-  ity, simplicity, and flexibility of operation.  The operation of the centrifugal compressor  requires relatively low inlet velocities and a  plenum chamber or expansion space must be  provided for the inlet.  The impeller rotating  at high speed receives the inlet air and pto-  vides high acceleration by virtue of centrifugal  force. As a result, the air leaves the impeller  FUNCTION  OF  THE  COMPONENTS.  109 