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. 
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. 
FUNCTION OF THE COMPONENTS. 
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 
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 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. 
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. 
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